PREDICTION OF SRENGTH OF CONCRETE (WITH OPC & OPC REPLACED WITH FLY ASH) MIXES USING ACCELERATED CURING TEST A DISSERTATION Submitted in practical fulfilment of the requirements For the award of the degree of BACHLEOR OF ENGINEERING
IN CIVIL ENGINEERING By
D.MALLIKARJUN(1602-09-732-020) L.MADHU(1602-09-732-019) R.HELA(1602-09-732-012) Under the esteemed guidance of
Dr.T. Srinivas Associate Professor Vasavi College of Engg. Hyderabad
DEPARTMENT OF CIVIL ENGINEERING VASAVI COLLEGE OF ENGINEERING Ibrahimbagh, Hyderabad -500 031, A.P., INDIA
1
VASAVI COLLEGE OF ENGINEERING Ibrahimbagh, Hyderabad -500 031, A.P., INDIA
CERTIFICATE This is to certify that the dissertation work entitled “Prediction of Strength of Concrete (with OPC & OPC Replaced with Fly Ash) mixes using Accelerated curing test” that is being submitted by Mr.D.MALLIKARJUN, L.MADHU, Ms. R. HELA in partial fulfilment for the award of B.E. in “STRUCTURAL ENGINEERERING” to the Department of Civil Engineering, Vasavi College of Engineering, Hyderabad is a record of bonafide work carried out by her under my guidance and supervision. Mr.D.MALLIKARJUN, L.MADHU, Ms.R.HELA has worked on this problem for about one year and the fulfilment for the award of Bachelors’ Degree. The results embodied in this dissertation have not been submitted to any other university or Institute for the award of any degree or diploma. Internal Guide
Head of the Department
Dr.T.Srinivas, Associate Professor, Vasavi College of Engineering, Hyderabad. (Project Guide)
Dr. B.Sridhar, Professor & Head of Civil Engg. Dept., Vasavi College of Engineering, Hyderabad.
2
DECLARATION
I hereby declare that the report of the B.E. Project work entitled “PREDICATION OF STRENGTH OF CONCRETE (WITH OPC & OPC REPLACED WITH FLY ASH) MIXES USING ACCELERATED CURING TEST” which is being submitted to the Vasavi College of Engineering Hyderabad, in partial fulfilment of the requirements for the award of the Degree of BACHLEOR OF ENGINEERING is a bonafide report of the work carried out by me. The material contained in this report has not been submitted any University or Institution for the award of any degree.
D.MALLIKARJUN ( 1602-09-732-020) L.MADHU (1602-09-732-019) R.HELA (1602-09-732-012)
Place : Vasavi College of Engineering, Hyderabad. Date :
3
ACKNOWLEDGEMENT I express deep sense of profound gratitude to my internal guide Dr.T. Srinivas, Associate Professor, Department of Civil Engineering, Vasavi College of Engineering ,Hyderabad for his invaluable guidance and constant co-operation throughout this work. I wish to express my profound gratitude to my external guide Dr.B.Sridhar,Professor& Head of the Civil Engineering Department, for extending all the facilities in Civil Engineering, Department for the Successful completion of my course. I had great pleasure and thanks to my parents, without whose help this project would not have been completed successfully.
D.MALLIKARJUN (1602-09-732-020) L.MADHU (1602-09-732-019) R.HELA (1602-09-732-012)
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ABSTRACT Accelerated strength testing of concrete is being used for quick assessment of 28 day strength of concrete following the procedure laid down by the IS code 9012-1978. This technique is being widely used and its applications include concrete mix design, pre-cast concrete industry and large construction projects etc. By using accelerating curing test we can predict the 28 days strength with in short time using correlation formula given by IS code for normal concrete without admixtures. Now it has become a practice to use fly ash as an admixture to cement in concrete construction to achieve economy as will as certain beneficial properties. When mineral admixtures are added to cement the concrete strength behaviour is somewhat different because it is influenced by the pozzolanic nature of admixture. The formula given by IS code can’t be used directly. Hence it is necessary to modify the codel formula to predict the strength of concrete mixes experienced with mineral admixtures when tested with accelerated curing test. In the present experimental investigation, concrete mixes of four grades M30 , M40 , M50 , M60 and M70 have been tried for OPC & OPC replaced with 20% Fly Ash. The above four grades of concrete are subjected to accelerated curing test, 7 days curing test and 28 days normal curing test. Different correlations are obtained for OPC and OPC replaced with 22% Fly ash cements through analytically based on the experimental results. 5
LIST OF TABLES Table No. 3.1
Description Physical properties of ordinary Portland cement
Page No. 61
3.2 3.3 3.4 3.5
Chemical composition of ordinary Portland cement Sieve Analysis results for fine aggregate. Physical properties of Fine Aggregate Sieve Analysis of coarse aggregate
61 62 65 65
3.6 3.8
Properties of Coarse aggregate Typical oxide composition of Indian fly ash
66 66
3.10
Quantity of materials required per one cubic meter of different grades of concrete. Quantity of materials required per one cubic meter of different grades of Fly Ash replaced concrete
99
3.11 4.1
100
Compressive Strength results for different grades of concrete used with Ordinary Portland Cement Compressive Strength results for different grades of concrete used with OPC replaced with 22% Fly ash
111
4.3
Comparison between Accelerated curing strength for OPC and OPC replaced with 22% fly ash
112
4.4
Comparison between 7 days curing strength of OPC with OPC replaced with 20% fly ash
112
4.5
Comparison between 28 days normal curing strength of OPC with OPC replaced with 22% fly ash.
113
4.6
Comparison between accelerated curing strength and normal 28days curing strength of OPC for different grades of concrete Comparison between accelerated curing strength and normal 28days curing strength of OPC replaced with 22% fly Ash for different grades of concrete
113
4.2
4.7
LIST OF FIGURES 6
111
114
Fig. No.
Description
Page No.
2.1
Typical relation Between Accelerated and 28 days compressive strength of concrete (Warm Water Method)
48
2.2
Typical relation Between Accelerated and 28 days compressive strength of concrete (Boiling Water Method)
49
4.1
Compressive Strength of OPC cement for different grades of concrete
115
4.2
Compressive Strength of OPC replaced with 22% Fly ash for different grades of concrete
116
4.4
Relation Between accelerated curing strength and 28 days of Normal curing of OP Cement
116
4.5
Relation Between accelerated curing strength and 28 days normal curing of OPC replaced by 22% Fly Ash
117
4.4
R2 value for Experimental and Analytical 28 days strength of OPC
116
4.5
R2 value for Experimental and Analytical 28 days strength of OPC- 22% fly ash
117
CONTENTS Page 7
No. 2 3 4 5 6 7
Certificate Declaration Acknowledgement Abstract List of Tables List of Figures CHAPTER I INTRODUCTION
13-33
1.1
13-14
General
1.2 Fly ash 1.2.1 History of Fly ash 1.3 Chemical and Mineral Composition of Fly ash 1.4 Classification of Fly ash 1.4.1 Class C Fly ash 1.4.2 Class F Fly ash 1.5 Physical Properties of Fly ash 1.5.1 Particle shape 1.5.2 Particle Size and Fineness 1.5.3 Specific Gravity 1.5.4 Colour of Fly ash 1.6 Quality of Fly ash 1.6.1 Loss of Ignition 1.6.2 Fineness 1.6.3 Chemical Composition 1.7 Mechanism by Which Fly ash Improves the Properties of Concrete 1.8 Use of Fly ash Concrete 1.8.1 Mass Concrete 1.8.2 Structural Concrete 1.9 Effect of Fly ash on Properties of fresh Concrete 1.9.1 Workability and Water Requirement 1.9.2 Pumpability and Segregation 1.9.3 Bleeding 1.9.4 Setting time 1.9.5 Autogeneous Temperature Rise 1.9.6 Finishability 1.9.7 Air Entrainment 1.10 Effect of Fly ash on Properties of Hardened Concrete 1.10.1 Compressive Strength and Rate of Strength gain 1.10.2 Modulus of Elasticity 1.10.3 Creep of Concrete 8
14 14 14 15 15 16 16 16 16 16-17 17 17 17 17-18 18 18-19 19-20 20 20 20 21 21 21 21 22 22 23 23 23-24 25 25
1.10.4 Bond of Concrete to steel 1.10.5 Impact Resistance 1.10.6 Abrasion Resistance 1.10.7 Temperature Rise 1.10.8 Permeability of Concrete 1.10.9 Sulphate Resistance of Concrete 1.10.10 Drying Shrinkage 1.10.11 Effeoroscence 1.11.1 Fly ash-Structural Concrete 1.12 Application of Fly ash 1.13 Fly ash Soild Bricks 1.11.4 Fly ash-Structural Concrete 1.15 Curing of Concrete 1.16 Concrete Strength Prediction 1.17 Accelerated Curing of Concrete 1.18 Need for Accelerated Concrete Curing 1.19 Necessity of Accelerated Concrete Strength Testing 1.20 Aim of the Present study CHAPTER 2
25 25 25 26 26 26 26 27 27-28 28 27-28 29 29-30 30-31 31-32 32 32 33
REVIEW OF LITERATURE
2.1 Review of Literature on Fly ash Concrete 2.2 Review of Literature on Accelerated Curing of Plain Cement Concrete 2.3 Review of Literature Curing of Pozzolanic Concrete CHAPTER 3 EXPERIMENTAL INVESTIGATION 3.1 Materials Used in the Investigation 3.1.1 Cement 3.1.2 Fine Aggregate 3.1.3 Coarse Aggregate 3.1.4 Fly Ash 3.1.5 Water 3.2 Mix Design of Concrete(M30,M40,M50,M60&M70)
34-42 42-53 53-58 59-67 59 59 59 60 60 60
OPC&OPC+FLYASH a)IS 10262
68-98
b)DOE METHOD 3.3 Preparation of Test Speciments 3.3.1 Mixing 3.3.2 Casting
100 100 102
9
3.3.3 Normal Curing 3.4 Details of Accelerated curing 3.4.1 Description of Accelerated Curing tank 3.4.2 Procedure of Accelerated Curing 3.4.3 Accelerated Strength Prediction by the Codel Procedure 3.4.4 Curing of Test Specimens 3.5 Testing of Specimens 3.5.1 Description of the Compression Testing Machine 3.5.2 Testing Procedure for Compressive Strength 3.5.3 Compressive Strength Results CHAPTER 4
103 104 104 105-106 106-107 107 107 107 108 108
PRESENTATION OF RESULTS
109-117 109 110 110-117
4.1 General 4.2 Details of Tables 4.3 Graphs CHAPTER 5
117-121 117-118
DISCUSSION OF TEST RESULTS
5.1 General 5.2 Predicted strength by Accelerated curing of different types of cements:
118
5.3 Predicted strength by 7 days strength for different types of cements
119
5.4 Predicted strength by 28 days strength for different types of cements:
119
5.5Comparison between accelerated curing strength and 28days normal curing strength of OPC for different grades of concrete
119
5.6Comparison between accelerated curing strength and 28days normal curing strength of OPC replaced with 22% fly Ash for different grades of concrete:
120
5.7 Relation between Accelerated curing strength and normal curing strength of OPC and OPC replaced with 20% fly ash Concrete. CHAPTER 6
120
121-122
CONCLUSIONS
10
CHAPTER 7 REFERENCES
122-126
CHAPTER-I INTRODUCTION 1.1
General: Concrete is the most widely used man made construction material obtained by
mixing cement, water and aggregates in required proportions .Today almost all engineering departments are using design mixes only so that every department require design mix proportions in quick time. Hence it is proposed to have accelerated curing test for the concrete to get earlier reports. 11
Traditionally quality of the concrete in construction work is calculated in terms of 28 days compressive strength. This procedure requires 28 days of moist curing, which is too long period to obtain results for both quality control and corrective measures to concrete. If after 28 days the quality of concrete is found to be doubtful, it would have considerably hardened by that time and also might have been buried by subsequent construction. If the buried concrete strength is found to be not acceptable strength at 28 days, it is not possible for replacement of concrete mass. Even the concrete attains more strength than required value, it would be too late to prevent wasteful use of cement and it leads to uneconomical mix proportionality. Hence standard 28 days cube testing of concrete is not feasible for quality control.
The disadvantage of this quality control check can be offset by other
technique i.e accelerated curing test of concrete. The test results can be obtained within 30 hours. The test results obtained by accelerated curing was reliable and recognized by cement and concrete sectional committee of Indian standard code. This method was formulated by BIS and was illustrated in IS:9013-1978 titled “Method of making, curing and determining compressive strength of accelerated cured concrete test specimens�. This standard lays down the method of making, curing and testing in compressive concrete specimens cured by two accelerated methods namely i) warm water method and ii) boiling water method. The method laid down in this standard may be used for quality control purposes or for the prediction of normal strength of concrete at later ages by the use of an appropriate correlation curve obtained by accelerated cured, 28 days normally cured test results for concrete specimens of mix proportion with materials to be used at site. Accelerated curing of concrete hastens the process of hydration of cement and as a result, a substantial proportion of the strength to be attained in 28 days under normal curing conditions is achieved within a shorter time. The rate and extent of 12
hydration of cement under a particular curing regime depend mainly upon the chemical composition of cement, water cement ratio and mix proportions which are considered to be important parameters in correlation of results from compressive strength results on specimens cured by accelerated curing method and normal curing method. The present investigation is carried out on Potland Pozzolona Cement, Ordinary Portland Cement (OPC) and OPC replaced by 20% fly ash for different mix designs by using boiling water method and an attempt has been made to arrive at a formula by correlating the accelerated compressive strength and 28 days normal curing compressive strength.
Ordinary Portland Cement: This was covered under IS:269 by Indian Standards. This is the cement used in normal concrete construction. This cement is obtained by burning a mixture of i) siliceous materials containing silica ii) argillaceous materials containing alumina and iii) calcareous materials containing lime burnt at a temperature of about 1400 degrees centigrade. The clinker so obtained is cooled and powdered to the required fineness. Cements of different properties are obtained by mixing the above components in different proportions along with small proportions of other chemicals. The Ordinary Portland Cement consists of the following components.
i.
Lime
60-67%
ii.
Silica
17-25%
iii.
Alumina
2-8%
iv.
Iron Oxide
0.50-6%
v.
Magnesia
0.10-4%
vi.
Soda and Potash
0.20-1%
vii.
Sulpher trioxide
1%-2.75%
viii.
Free lime
0-1%
Portland Pozzolona Cement: This was covered under IS:1489 (P-1) 1991 of BIS. This cement is made either intergrading Portland cement clinker and Pozzolona
13
or by uniformly blending Portland cement and fine Pozzolona. Pozzolona content varies from 10% to 25% by weight of cement. Pozzolona does not possess cementing values themselves but have the property of combining with lime to produce a stable lime, a pozzolanic compound which possess cementing property. Since the free lime in cement, which is readily attacked chemically is removed, the pozzolanic concrete have a greater resistance to chemical agencies. They can also resist the attack by sea water better than ordinary Portland cement concrete. The Pozzolona used in the manufacture of cement in India consists of burnt clay of shale or fly ash
1.2
Fly Ash: Fly ash, known also as pulverized-fuel ash, is the ash precipitated
electrostatically or mechanically from the exhaust gases of coal-fired power stations; it is the most common artificial Pozzolona. It is very fine material consisting predominantly of small spheres of glassy material together with crystalline matter and consists of un burnt carbon, silica, alumina, oxides of iron, magnesium, calcium and sulphur trioxide. The fly ash particles are spherical (which is advantageous from the water requirement point of view) and have a very high fineness: the vast majority of particles have a diameter between less than 1 Âľm and 100 Âľm, and the specific surface of fly ash is usually between 250 and 600 m 2/kg, using the Blaine method. The high specific surface of the fly ash means that the material is readily available for reaction with calcium hydroxide. The properties and composition vary widely, not only between different plants but hour to hour in the same plant. Fly ash obtained from cyclone separator is comparatively coarse, where as fly ash obtained from electrostatic precipitator is relatively fine having very high specific surface area about 250-600 m2/kg. i.e., it is finer than the Portland cement. The fly ash once considered as waste-by product, finding difficulty to be disposed off, has now become a material of considerable value, when used in conjunction with Concrete as admixture. Under normal operating conditions modern furnaces do not produce fly ashes containing more than 5 percent carbon (in fact, it is usually less than 2 percent in high calcium fly ashes) larger amounts of carbon in a fly ash that is meant for use as a
14
mineral admixture in concrete are considered harmful because the cellular particulars of carbon tend to increase both the water requirement for a given consistency and the admixture requirement for entrainment of a given volume of air. IS : 3812-1981
(22)
gives the various specifications for fly ash.
1.2.1 History of Fly Ash : Use of fly ash in concrete started in the United States in the early 1930’s. The first comprehensive study was that described in 1937.
By R.E. Davis at the
University of California. The major breakthrough in using fly ash in concrete was the construction of Hungry Horse Dam in 1948, utilizing 1,20,000 metric tones of fly ash. This decision by the U.S. Bureau of Reclamation paved the way for using fly ash in concrete constructions. ASTM specification first allowed the use of fly ash in concrete pipes in 1953. 1.3 Chemical and Mineral Composition of Fly Ash: Fly ashes are complex in their range of chemical phase composition. They consist of heterogeneous combinations at glassy and crystalline phases. Fly ash consists generally of spherical particulars, some of which may be like glass and hollow and of irregularly shaped particulars of un burnt fuel and carbon. The colour varies from light grey, dark grey, or brown. The principal constituents are: silicon dioxide (Sio2) (25 to 69%), Aluminum oxide (Al2O3) (10 to 30%), Iron Oxide (Fe2O3) (5 to 25%), Calcium Oxide (CaO), Magnesium Oxide (MgO) (5%), Sulphur Trioxide (SO3) and Na2O (5 to 10%). Depending on the origin of coal from which a particular fly ash is derived minor elements in fly ash includes Titanium, Iron, Magnesium, Phosphorous, Sulphur, Oxygen, Potassium, Sodium, Carbon and other as traces. Some fly ashes also have trace amounts of organic compounds other than un burnt coal. Most fly ashes (60 to 90%) are glassy phase. Minor amounts of crystalline constituents in fly ash include Mullite, Quartz, Magnetite, and Hematite. Other constituents which may be present in high calcium fly ash include perclase, anhydrate, alkali sulphate, melilite, merwinite, Nepheline, sodalite, C3S, C3A and others.
15
The mineral composition of Indian fly ashes generally consists of Quartz, Mullite with traces of rutile once a while. The glass content in fly ashes is low between 20-30% as compared to fly ashes available in European countries where the glass content goes high as much as 80% in some cases, which makes Indian fly ashes less pozzolanic. 1.4 Classification of Fly Ash Fly ash consists primarily of oxides of Silicon, Aluminum Iron and Calcium. Magnesium, Potassium, Sodium, Titanium, and Sulphur are also present to a lesser degree. When used as a mineral admixture in concrete, fly ash is classified as either Class C or Class F ash based on its chemical composition.
1.4.1 Class C Fly Ash Class-C ashes are generally derived from Sub-bituminous coals and consist primarily of calcium alumino-sulphate glass, as well as quartz, tricalcium aluminate, and free lime (CaO). Class c ash is also referred to as high calcium fly ash because it typically contains more than 20 percent CaO. Concrete made with Type-C fly ash (as opposed to Type-F) has higher early strengths because it contains its own lime. This allows pozzolanic activity to begin earlier. At later ages, Type-C behaves very much like type F-yielding higher strengths than conventional concrete at 56 and 90 days.
1.4.2 Class-F Fly Ash Class-F ashes are typically derived from bituminous and anthracite coals and consist primarily of an alumino-silicate glass, with quartz, mullite, and magnetite also present. Class-F, or low calcium fly ash has lesser than 10 percent CaO. Class-F fly ash provides sulphate resistance equal to or superior to Type-V cement and effectively moderates heat gain during concrete curing. 1.5 PHYSICAL PROPERTIES OF FLY ASH The physical properties of fly ash which influence the properties of concrete in their fresh and hardened state includes the following.
16
1.5.1
Particle Shape Particle shape and size characteristics of fly ash are dependent upon the source
and uniformity of coal, the degree of pulverization prior to burning, the combustion environment (Temperature and Oxygen levels), uniformity of combustion and the type of collection system. The shape of fly ash particulars is also a function of particle size. The majority of fly ash particulars are glassy solid or hollow and spherical in shape. The remaining fly ash particles are transparent to opaque. Slightly to highly porous and vary in shape from rounded to elongate.
1.5.2 Particle Size and Fineness Individual particulars in fly ash ranges from less than 10 um to 45 um greater than 1mm. Fly ash obtained from mechanical separators is comparatively coarse. Whereas fly ash obtained from electrostatic precipitators is relatively fine. The fly ash suitable for use as pozzolana in concrete, the majority of the particles pass the No. 325 (45 um) sieve. Fineness of fly ash has a significant influence on its performance in concrete. The range of Blaine’s fineness of Indian fly ashes is 2300 to 6000 Cm2/gm. The finer the fly ash better is its lime reactivity, which varies between 3.5 to 6.5 N/mm2.
1.5.3 Specific Gravity The specific gravity of soiled fly ash particles range from 1.90 to 3.02 but it is normally in the range of 1.90 to 2.80 and is about two thirds of cement. High specific gravity is often an indication of fine particles, fly ashes high in iron tend to have higher specific gravity. The bulk density of loose dry fly ashes is about 800 Kg/m 3. The dry density of the material compacted at optimum moisture content varies from 1120 to 1490 kg/m3.
1.5.4 Colour of Fly Ash The colour of most fly ashes ranges from cream to dark grey depending on the presence of unburnt carbon and iron content.
1.6 QUALITY OF FLY ASH:
17
Quality requirements for fly ash vary depending on the intended use. Fly ash quality is affected by fuel characteristics (coal), co-firing of fuels (bituminous and sub-bituminous coals), and various aspects of the combustion and flue gas cleaning/collection processes. The four most relevant characteristic of fly ash for use in concrete are loss on ignition (LOI), fineness, chemical composition and uniformity.
1.6.1
Loss on Ignition: It is a measurement of unburned carbon (coal) remaining in the ash and is a
critical characteristic of fly ash, especially for concrete applications. High carbon levels, the type of carbon, the interaction of soluble ions in fly ash, and the variability of carbon content can result in significant air-entrainment problems in fresh concrete and can adversely affect the durability of concrete.
1.6.2. Fineness: The fineness of fly ash is most closely related to the operating condition of the coal crushers and the grindability of the coal itself. Fineness is one of the primary physical characteristics of fly ash that relates to its pozzolanic activity, and is measured by wet sieving over a 45 µm sieve. Particles greater than 45 µm show little or no reactivity under normal conditions, actually the pozzolanic activity of ashes would be directly proportional to the amount of particles less than 10 µm. ASTM and Indian standards limit the proportion of particles retained on a 45 µm sieve to 34 percent. The surface area of fly ash can be measured using the Blaine apparatus. The Blaine and 45 µm values may show similar trends but are not strictly related. For fly ash use in concrete applications, fineness is defined as the percent by weight of the material retained on the 0.044 mm (No.325) sieve. A coarser gradation can result in a less reactive ash and could contain higher carbon contents. Fly ash can be processed by screening of air classification to improve its fineness and reactivity.
1.6.3 CHEMICAL COMPOSITION: The chemical composition of fly ash relates directly to the mineral chemistry of the parent coal and any additional fuels or additives used in the combustion or post combustion processes. The pollution control technology that is used can also affect
18
the chemical composition of the fly ash. Electric generating stations burn large volumes of coal from multiple sources. Coals may be blended to maximize generation efficiency or to improve the station environmental performance.
1.7 MECHANISM BY WHICH FLY ASH IMPROVES THE PROPERTIES OF CONCRETE: A good understanding of the mechanisms by which fly ash improves the archaeological properties of fresh concrete and ultimate strength as well as durability of hardened concrete is helpful to insure the potential benefits expected from highvolume fly ash concrete mixtures are fully realized. These mechanisms are described below. When a concrete mixture to consolidated after placement, along with entrapped air, a part of the mixing-water is also released. As the water has low density, it tends to travel to the surface of concrete. However, not all of this ‘bleed water’ is able to find its way to the surface, some of the water accumulates in the vicinity of the aggregate surfaces. This is due to the wall effect of the coarse aggregate. Thus there is a heterogeneous distribution of water. The interfacial transition zone between the cement paste and aggregate has higher water content and thus there is formation of a highly porous hydration product. Through this transition zone, micro cracks are readily formed as this zone is much weaker. These micro cracks in the inter facial transition zone play an important part in determining not only the mechanical properties but also the permeability and durability of concrete exposed to severe environmental conditions. When finer fly ash particles partially replace Portland cement, the heterogeneities in micro structures of hydrated Portland cement paste are reduced greatly, further, when the pozzolanic reaction proceeds, there is a gradual decrease in both the size of capillary pores and crystalline hydration products, thus eliminating the weak line in the concrete microstructure. Thus the product is highly crack resistant and durable. A very high heat of hydration is produced when ordinary Portland cement is used. The replacement of certain percentage of Portland cement with fly ash reduces this early development of heat and thus thermal cracking chances are reduced.
19
One of the problems with conventional concrete is cracking due to drying shrinkage. The drying shrinkage of concrete is directly influenced by the amount and the quality of the cement paste present. It increase with an increase in the cement paste-to-aggregate ratio in the concrete mixture, and also increase with the water content of the paste. Clearly, the water-reducing property of fly ash can be advantageously used for achieving a considerable reduction in the drying shrinkage of concrete mixtures.
1.8 USE OF FLY ASH IN CONCRETE: Fly ash a waste product from coal burning power plants is used in concrete and mortars primarily because of its pozzolanic and cementitious properties which contribute to strength gain and improved durability when used with ordinary Portland cement. Other principal reasons for using fly ash include economy and beneficial modification of certain properties of fresh and hardened concrete. Fly ash is used extensively in concrete as blended material and ingredient in blended cement. The use of fly ash as an admixture not only extends technical advantages to the properties of concrete but also contributes to the environmental pollution control. One of the important characteristics of fly ash is the spherical from of the particles this shape of particle improves the flowability and reduces the water demand. It should be noted that fly ash may affect the colour of the resulting concrete, the carbon in the ash making it darker. Fly ash because of its lower rate of hydration enabled the production of concrete less prone to thermal cracking. The fly ash may be used in concrete either as an admixture or in part replacement of as an admixture. The fly ash reduces the segregation and bleeding where as when used as a replacement of cement, the silica content combines with the free lime liberated during the hydration of cement. The use of fly ash has no appreciable effect on the drying shrinkage of concrete. It reduces the permeability of concrete improves the resistance to sulphate waters and does not have a much effect on the freezing and thawing resistance of concrete.
1.8.1
Mass Concrete:
20
Fly ash first came in to use in mass concrete applications the smaller temperature rise associated with fly ash lime reaction has led to the wide use of fly ash in massive concrete structures to reduce temperature rise and minimize consequent cracking at early ages. Some of the structures where fly ash has been successfully employed as pozzolanic material, they are Hungry Horse dam, Canyon Ferry dam, the Hartwell dam, and the Wilson dam in U.S.A., the Lednock dam and Portished power house in Britain; and Sudagi dam in Japan. In India fly ash has been used for some portion of Rihand dam in U.P and Sone Bridge in Bihar.
1.8.2
Structural Concrete: Research so far indicated that 20 to 30 percent replacement of cement by fly
ash can be used to produce structural concrete similar in material properties and structural behaviour with that of similar strength of no fly ash concrete. The use of fly ash in structural concrete has not gained popularity because of many factors such as lower early strength, unavailability of scientific approach for its use in mix proportioning , and inadequate knowledge of its mechanical properties. 1.9
EFFECTS OF FLY ASH ON PROPERTIES OF FRESH CONCRETE: Use of right quality fly ash results in reduction of water demand for desired
slump. With the reduction of unit water content, bleeding and drying shrinkage will also be reduced. Since fly ash is not highly reactive the heat of hydration can be reduced through replacement of part of the cement with fly ash.
1.9.1 Workability and Water Requirement The absolute volume of cement plus fly ash normally exceeds that of cement in similar no fly ash concrete mixes. This is because that the mass of fly ash used to replace cement is usually equal to or greater than that replaced and the fly ash normally is of lower density. This increase in paste volume produces a concrete with improved plasticity and better cohesiveness. The smaller size and essentially spherical form of the particles comprising fly ash usually causes a reduction in the amount of water required for a given degree of workability from that required for an equivalent paste without fly ash.
21
The partial replacement of Portland cement by fly ash in concrete reduces the amount of water required to obtain a given consistency or increase the workability and slump for given water content.
1.9.2
Pumpability and Segregation Improved Pumpability of concrete is usually achieved when fly ash is used.
For mixtures deficient in the smaller size of fine aggregates or lean in cements, the addition of extra fly ash as an aggregate supplement will make concrete or mortar more cohesive and less prone to segregation and bleeding. 1.9.3
Bleeding The tendency for water to rise in freshly placed concrete known as bleeding,
results from the setting of the heavier solid particles. The proper proportioning of fly ash will result in concrete of adequate cohesion and plasticity with less water available for bleeding. Factors such as cement content and fines content of the sand also have an effect on the amount of bleeding. 1.9.4
Setting Time The use of fly ash may retard the time of setting of the concrete. With other
factors constant, setting characteristics of concretes are influenced by the amount of fly ash, fineness and chemical composition of fly ash. Pressure on form work may be increased with fly ash concrete due to increased workability, slower slump loss and retarded setting characteristics.
1.9.5
Autogenous Temperature Rise The intense chemical reactions occurring in the first few days of the hydration
of Portland cement result in sufficient temperature rise in concrete. Replacement of cement by fly ash generally reduces the temperature rise in fresh concrete. This reduction however depends upon the percentage of cement replacement by fly ash and also on the Cao content of fly ash. Because of low water content the autogenous temperature rise in high-volume fly ash concrete is low.
1.9.6
Finishability
22
As a result of fineness and improved plastic properties fly ash gives a better finish when used as a replacement of either sand or cement. Using very wet mixtures fly ashes with significant amounts of very light unburned coal particles can cause these particles to migrate upward and collect the surface. 1.9.7
Air Entrainment Frequently by the use of fly ash adversely affects air entrainment in fresh
concrete. Fly ash usually causes an increase in the quantity of air entraining agent requires to produce a given degree of air entrainment. 1.10
Effects of fly ash on properties of Hardened Concrete Fly ash, when used in concrete contributes to the strength of concrete due to
its pozzolanic reactivity. However, since the pozzolanic reaction proceeds slowly, the initial strength of fly ash concrete tends to be lower than that concrete without fly ash due to continued pozzolanic reactivity concrete develops greater strength at later age. Which may exceed that of the concrete without fly ash. 1.10.1
Compressive Strength and Rate of Strength Gain Strength at any given age and rate of strength gain of concrete are affected by
the characteristics of the particular fly ash, the cement with which it is used, and the proportions of each used in the concrete. Compared with no fly ash concrete proportioned for equivalent 28 days compressive strength, concrete containing a typical low calcium fly ash may develop lower strength at 7 days of age or before when tested at room temperature. However if equivalent 3 day or 7 day strength is desired can be product by using accelerators or changing mix proportions. After the strength contribution of cement slows the continued pozzolanic activity or fly ash contributes to increased strength gain at later ages if the concrete is kept moist. Therefore fly ash concrete with equivalent lower strength at early ages may have equivalent or higher strength at later ages then concrete without fly ash.
1.10.2 Modulus of Elasticity The modulus of elasticity of high volume fly ash concrete will be lower at early ages and higher in value later as compared to conventional concrete. The high value later is achieved because a considerable portion of unreacted fly ash consisting
23
of glassy spherical particles acts as a fine aggregate. Also, the low porosity of transition zone between cement mortar and coarse aggregates leads to higher values. 1.10.3 Creep of Concrete The effects of fly ash on creep of concrete are limited primarily to the extent to which it influence the ultimate strength and rate of strength gain. Concrete with a given volume of cement plus fly ash loaded at age of 28 days or less will normally exhibit higher creep strains than concrete having an equal volume of cement only, due to the lower strength of fly ash concretes at the time of loading.
1.10.4 Bond of Concrete to Steel The bond of concrete to steel depends on the surface area of steel in contact with concrete, the depth of reinforcement, and the density of concrete. Fly ash usually increase paste volume and reduce bleeding. Thus the contact at the lower interface where bleed water typically collects may be increased, resulting in improved bond.
1.10.5 Impact Resistance The impact resistance of concrete is governed largely by the compressive strength of mortar and hardness of coarse aggregate. Use of fly ash effects the impact resistance only to the extent that it usually improves the ultimate compressive strength.
1.10.6Abrasion Resistance At equal compressive strength, properly finished and cured concretes with and without fly ash will exhibit essentially equal resistance to abrasion.
1.10.7 Temperature Rise The rate of hydration and heat generation depend on the amount and type of cements, the mass of the structures, the method of placement, the temperature of concrete at the time of placement. The temperature rise can be reduced by using fly ash in the concrete mixture as a portion of the cementitious material. As the amount of cement replaced is increases, the heat of hydration of the concrete is generally decreases. However, some high calcium fly ashes do contribution to early temperature rise in concrete.
24
1.10.8 Permeability of Concrete Concrete is permeable to water to the extent it has interconnecting void spaces. Permeability of concrete is governed by the factors such as amount of cementitious material, water content, calcium hydroxide Ca (OH2) liberated by hydration of cement is water soluble and may leach out of hardened concrete leaving voids for the ingress of water. Through its pozzolanic properties fly ash chemically combines with calcium, potassium and sodium hydroxide to produce C-S-H, thus reducing the risk of leaching calcium hydroxide, as a result permeability is reduced.
1.10.9 Sulphate Resistance of Concrete It was shown that, low calcium fly ashes will be found to improve the sulphate resistance of any mixture in which it is included. The increase in sulphate resistance is believed to be due in part to the continued reaction of fly ash with hydroxides in concrete to continue to form additional calcium silicate hydrate (C-S-H), which fills in capillary pores in the cement paste, reducing permeability and the ingress of sulphate solution. The effect of fly ash on sulphate resistance will dependent upon the types, amount, and the individual chemical and physical characteristics of the fly ash and cement used.
1.10.10 Drying Shrinkage : Drying shrinkage of concrete is a function of the fractional volume of paste, the water content, cement content and type, and the type of aggregates. In those cases where the addition of fly ash increases the paste volume, drying shrinkage may be increased the paste volume, drying shrinkage may be increased slightly if the water content remains constant. If there is a water content reduction, shrinkage should be about the same as concrete without fly ash.
1.10.11 Efflorescence : The use of fly ash in concrete for highway structures can be effective in reducing efflorescence by reducing permeability. However certain high calcium fly ashes of high alkali and sulphate contents may increase efflorescence.
1.11.1 Fly ash-Structural Concrete It is commonly known that fly ash can be substituted for OPC in concrete to the extent of 15 to 20% but now it was established that such replacement can be even
25
upto 50% in structural grade concrete without adversely effecting any one of its important properties. The 90 day strength of concrete made with 50% fly ash is even higher than the ordinary concrete. Concrete with large proportions of fly ash is even higher than the ordinary concrete. Concrete with large proportions of fly ash is less prone to the attack from acids, chemicals etc., thus improving durability. The increase in fly ash content slows the setting process and lowers the heat of hydration. Expensive data is represented by various researchers on the properties of fly ash in the hardened state. Fly ash concrete containing normal weight and light weight aggregates are suitable for structural applications. The mixes are proportioned to have one day strength comparable with concrete without fly ash, possessing adequate cohesiveness and workability to enable them to be compacted into place easily in structural members with reinforcement. It is shown that the curing regime has a significant influence on the strength development. It has been further reported that the tests on reinforced beams and slabs have showed that the fly ash concrete can exhibit structural performance similar to that of conventional concrete with adequate factors. The data presented by many researchers show that with fly ash of controlled quality structural concrete construction can be designed to incorporate fly ash up to 30% by weight of cement. Apart from the reduction in cement there were two major objectives in designing fly ash concrete mixes used for the various studies. i. To obtain one day strength comparable with normal concrete without Fly ash. ii. To produce cohesive and workable mixes that would be easily and satisfactorily vibrated into places in reinforced concrete members with thin sections and bar reinforcement.
Application of Fly Ash :
1.12.
Some of the most important specific areas where fly ash can be utilized are as indicated below: i.
In the manufacture of building materials, such as activated Pozzolona, Portland Pozzolona cement, Pozzolana metallurgical cement, lime
26
pozzolana cement, oil well cement, masonry cement and Fal-G cement etc. ii. To construct structural fills, high way embankment, dams and for filling of mines. iii. As construction material for highways. iv. For land reclamation and soil modification. v. In mortars, grounds and concretes such as mass concrete, structural concrete etc. vi. In fly ash bricks/block, cellular or aerated concrete blocks/slabs. vii.
As filler in fertilizer plants and in recovery of materials like iron, aluminum, titanium, etc.
viii. Cleaning/washing powder, poly propylene, asbestos etc. ix. As light weight aggregate in high strength concretes, in distempers and sanitary products. x. For lining of drains and canals.
1.13 Advantages of Fly Ash Concrete : The use of fly ash as a cement replacement in concrete results in significant enhancement of the basic characteristics of concrete, both in fresh and hardened states. The advantages of fly ash concrete are: a)
Improved long term strength performance and durability.
b)
Reduced heat of hydration.
c)
Reduced water required for equal workability.
d)
Minimized risk of alkali silica reaction.
e)
Reduces heat in mass sections and therefore reduces the possibility of thermal cracking.
f)
Improves resistance to sulphate and other chemicals.
g)
Slightly reduces shrinkage.
h)
Improved workability, reduced segregation and bleeding.
i)
Increased resistance to permeability
j)
Improved pumpability of fly ash concrete.
k)
Resistance to freezing and thawing
l)
Reduced alkali-aggregate expansion
m)
Reduced corrosion of reinforcing steel in concrete. 27
1.14 Limitations in the use of Fly Ash: As described already fly ash in an industrial waste product which is relatively cheaper and can be used in various ways in building construction. Fly ash is pozzolanic in nature and has high silica content. By itself it is an inert material and when combined at certain proportions with free lime present in cement and a cementitious product is produced. Pozzolona take more time for the hardening process to complete and hence the strength gaining is somewhat slowere in the case of Pozzolona mixtures compared to OPC. This aspect is particularly true in case of cement-fly ash mixtures with high fly ash contents. This drawback is to be faced when 40% or greater fly ash content is used with cement. Extended periods of curing up to the extent of 45 to 60 days may be necessary to gain full strength in such cases. This is a serious limitation in the use of high volume fly ash replacement in cement. It is also agreed that more economy and cost effectiveness will be achieved when high fly ash content is used as replacement to OPC. Hence, there is every need to investigate the possibility of gaining adequate strength at 28 days using fly ash concretes. 1.15
Curing of Concrete : Curing is the process or operation which controls the loss of moisture from
concrete after it has been placed in position, or in the manufacture of concrete products, there by providing time for the hydration of the cement to occure. Since the hydration of cement does take time days, and even weeks, rather than hours. Curing must be undertaken for some specified period of time if the concrete is to achieve its potential strength and durability. Curing may also encompass the control of temperature since this affects the rate at which cement hydrates. Curing is one of the critical procedures which determines whether concrete will reach its potential strength and durability. While site conditions may often indicate that curing will be inconvenient (it is at best a messy procedure ). Only very rarely will the cost savings resulting from failure to cure out weight the very real damage which will be done to the long-term strength and durability of the concrete by its neglect. It is always feasible to choose a method of curing which will be both effective and economic.
28
Methods of curing concrete fall broadly into three categories. i. Those which minimize moisture loss from the concrete by covering it with a relatively impermeable membrane. ii.
Those which prevent moisture loss by continuously wetting the
surface of the concrete. iii.
Those which keep the surface moist and at the same time, raise
the temperature of the concrete thereby increasing the rate of strength gain. 1.16
Concrete Strength Prediction: Under the currently quicker pace of construction, there was a great need for
more production of concrete with persisting on the conformability of the quality of the produced concrete with the standards and specifications. The compliance of any produced concrete with these specifications consider to be significant evidence for good concrete. The specifications, generally, include a statement of physical and chemical requirements. Among all, strength tests are prescribed by all specifications, because compressive strength of concrete in the hardened condition is very important and perhaps it is the most obviously required for structural use. Specifications usually specify test method as well as age of test. Strength of concrete, as specified by all the standards, is very important (from 1 to 28 days), because the early development of strength (early gain in strength) is very important. But, as early strength of concrete is important, strength at later ages is more important, because after all, it is this property which is relied upon in structural design of concrete as a construction material. The traditional 28 days standard test has been found to give general index of the overall quality (used in quality control process) and acceptance of concrete and has served well for so many years. Neither waiting for the result of such a test would serve the rapidity of construction, nor, neglecting it would serve the quality control process of the concrete. Moreover, rapid reliable prediction of the results of 28 days strength test as early as possible would be of satisfaction for all parties instead of waiting for the traditional 28 days results.
29
If the hydration process is speeded up it is possible to reduce the waiting period for test results from 28 days to only 1 or 2 days. This is done by using accelerated curing methods that either supply an external source of heat or retain the heat of hydration given off when cement and water react.
1.17 Accelerated curing of Concrete : Accelerated curing of concrete is designed to increase or accelerate the rate at which the concrete gains strength. The rate of development of strength not only depends upon the period of curing but also on the temperatures during the period of curing. It can be seen that the optimum temperature during the curing period is 15 0 C to 380 C. The strength of concrete can be shown to be a function of the summation of the time of curing and temperature of curing. This product is called the ‘maturity of concrete’. The origin for the measurement of temperature is -13 0 C and time is reckoned in hours or days. The strength is found to increase linearly with maturity of concrete. The increase in strength with increased curing temperature is due to speeding up of chemical reaction of hydration. This increase affects only the early strengths without any harmful effects on ultimate strength and cracking of the concrete due to thermal shock. Hence the curing of concrete and its gain of strength can be speeded up by raising the temperature of curing in which curing period is reduced. (50) This type of curing is called as accelerated curing. Accelerated curing has many advantages in the manufacture of pre-cast concrete products since:
a)
The mould can be reused within a shorter time.
b)
The product can be delivered as quickly as possible to the user thus increasing the turn-over and reducing the costs.
c) 1.18
Reducing the storage space required in the factory.
Need for Accelerated Concrete Curing: The consequent rapid strength gain of concrete has many advantages in the
concrete manufacturing industry, such as the increased production and rapid turnover of products in precast plants. There are several ways to cure in the field. One form of
30
curing that has become popular at precast pre stressed concrete plants is accelerated curing. This type of curing is advantageous where early strength gain in concrete is important or where additional heat is required to accomplish hydration, as in cold weather. Accelerated curing reduces costs and curing time in the production of precast members. The use of accelerated curing in the production of precast members has been an industry practice for many years. Early research focused on developing curing cycles to optimize concrete strength while providing economy and efficiency in plant production. With the greater use of high-strength concrete in precast/ prestressed concrete beams, however, some of the traditional practices for accelerated curing need to be reassessed. 1.19
Necessity for Accelerated Strength Testing : The concrete starts attaining strength, immediately after setting is completed
and the strength continues to increase along with time. 90 to 95% of the eventual strength is attained in the first 28 days and hence this 28 day strength is considered as the criterion for design and is called the design strength.
(50)
The purpose of designing
a concrete mix is to produce a concrete having desired strength and workability. The criterion for the assessment of the quality of concrete has commonly been its 28-day compressive strength. However, in many constructions projects, a rapid and reliable prediction of the standard 28-day compressive strength would be advantageous. Early strength prediction can save expenses by avoiding situations where the concrete does not reach the required design strength or by avoiding concrete that is unnecessarily strong. With the assistance of reliable test methods employing accelerated curing techniques, it is now possible to test the compressive strength of concrete with in a short period and thereby to estimate whether it is likely to reach the specified strength at 28-days or not. In this respect, several accelerated curing methods have been developed and standardized in some countries. Bureau of India standard has described two accelerated curing methods in IS code i.e., IS : 9013-1978. 1.20
AIM of the Present Study: As already pointed out, 28 days strength prediction on the basis of accelerated
curing for normal concrete mixes is well established and the procedure given by the IS code (i.e., IS : 9013-1978) is followed for this purpose. When mineral admixtures such as fly ash are employed as replacement to cement and PPC, it is doubtful
31
whether the codel formula predicts the true 28 days strength because these admixtures are pozzolanic in nature. The present experimental investigation attempts to study the variation between the accelerated strength and the normal curing strength at 28 days for PPC, OPC, and OPC replaced with 20% fly ash for M 20, M25, M30 & M35 grades of concrete are considered in this investigation. It is aimed to correlate the accelerated strength with the normal curing strength of PPC, OPC, and OPC replaced with 20% by fly ash for M 20,M25,M30 & M35 grades of concrete to arrive at a formula based on experimental results. The study is useful and important for practical concrete construction where PPC and OPC with fly ash replacement have been increasingly used in concrete to derive various beneficial properties besides economy.
CHAPTER 2 REVIEW OF LITERATURE 2.1 Review of Literature of Fly Ash Concrete : Various number of investigation were carried out on fly ash concrete within and outside of the country. Some of the recent and significant investigations are presented here.
32
Berry et al.,: (3) this paper presents a critical review on properties of fly ash and use of fly ash in concrete in the following manner. Fly ash used as a Pozzolona to replace some of the Portland cement in concrete often achieves energy and cost savings and imparts specific engineering properties to the finished product. To use fly ash effectively and economically it is important to understand the differences between fly ash and Portland cement concretes. The differences in the rate of strength development between the two types and the ways in which this may be influenced by methods of mix proportioning are particular importance. When properly proportioned and placed, fly ash concrete generally shows improved workability, pumpability, cohesiveness, finish, ultimate strength, and durability. It has been found that fly ash is of particular value in highstrength concrete. Its use has often been shown to improve the performance of concretes exposed to sulfate attack or to deterioration caused by alkali-aggregate interactions. Equal strengths at any age to that of control concrete can be obtained in fly ash concrete by correct mix proportioning techniques. The controlling factors are fly ash properties and relative costs; there seems no reason why equal or better durability and permeability properties cannot be attained through similar proportioning methods. If research is applied to the fundamental aspects of the durability of fly ash concretes. The interrelationships between degree of hydration, gel-space ratio, strength, permeability of fly ash concrete should be examined.
Specifications and testing methods should be developed which recognize and utilize the differences between ordinary and fly ash concretes, rather than assuming only that fly ash is a substitute to be tolerated more than valued. For example, there is little to be gained by comparative evaluation of fly ash and Portland cement concretes for sulfate, freeze-thaw, and leaching resistance at stages of curing prior to the time of equal strength or equal degree of hydration.
33
Ozlem Celik et al.,:
(33)
in the structures of different type of fly ash samples
collected from different thermal power plants are used. And based on the experimental work the following conclusions are drawn. It was observed that ash amounts in clinker increased from 15% to 35% causing a decreasing effect on the compressive strength of the mortars. As a result, it is suggested that soma unit IV fly ash samples can be used as cement additives up to 25% (48-49 N/mm2). It was determined that the utilization of fly ash in production of cement is possible by mixing clinker up to 15%. In the follow-up studies, mineral additives ratios are going to use higher ratios in this study. The purpose of this is to utilize a greater volume fly ash and to contribute to economical and environmental aspects and for these purposes, different types of mineral additives and chemical admixtures will be used. When type C and type F fly ash fineness properties are improved, higher compressive strength volumes can be obtained by preparing different mixtures.
Neelamegam et al.,:
(31)
the important conclusions arrived based on their
experimental investigations are reported as follows. The cement replacement materials when used as simple mass replacement will not result in substantial improvement in 28 day strength, especially in case of fly ash. However, it is the transport properties like sorptivity and rapid chloride permeability that show significant improvement. Cement replacement materials result in a considerable increase in the volume of gel pores. And mico capillaries and increase of total porosity. The increase volume of gel pores and decrease of capillary pores improves the transport properties. Triple blend binders are effective in improving the performance of high volume fly ash concretes by reducing the total porosity and increasing the strength.
Haque et al., :
(12)
from extensive laboratory study of air-entrained and non-air
entrained high volume fly ash concrete mixes of medium to low workability, suitable for replacement by slip forming and roller compaction respectively have concluded that Concretes containing fly ash upto 75% by weight of the cementitious material have properties that make them attractive as a sub-base or base coarse in pavement construction. It was concluded that cohesive, non-segregated concretes could be manufactured containing 40 to 75% fly ash in cementitious fraction. When air
34
entrained, these mixes produced, concretes, having freeze-thaw resistance, at least in the richer mixes. Tensile and compressive strength achieved were adequate for the proposed application. With drying shrinkage well within acceptable limits
Patodiya (35) in : this paper titled “Structural Grade concrete with High Volume Fly ash contents� has reported the following conclusions. The replacement of cement by fly ash can be even up to 50% in structural grade concrete without adversely affecting any of its important properties. The 90 day strength of concrete made with 50% fly ash is even higher than the no fly ash concrete. Supperplasticized high volume fly ash concrete with 50% fly ash can provide the advantages such as lower water demand, increased strength, reduced permeability, reduced shrinkage and creep, reduced bleeding, improved workability, greater abrasion resistance and improved durability. High volume fly ash concrete can be used in piers, large columns, black foundations and sea retaining structures. It has superior long term performance than no fly ash concrete. High volume fly ash replacement can be very effectively done where early strength and rapid form stripping is not required.
Swami et al., (36): has studied the use of blocks manufactured by using OPC, 6mm chips, sand and fly ash as replacement of cement to certain percentage. It is reported that after the ingredients were mixed by adding adequate amount of water, this mix was transferred to the moulds. The above specimens were left undisturbed for 24 hours air drying. The curing was done by placing blocks for 21 days followed by 7 days air drying . After conducting various experiments with various mixes replacing the cement by fly ash the following conclusions were drawn. Hollow blocks of mix 1:3:6 with 20% of replacement of fly ash have sufficient strength and can be used for load bearing units. Blocks of leaner mix like 1:5:10 can be used for load bearing units with replacement of fly ash. Non soild blocks made with 1:3:6 even with a maximum of 30% replacement can be used for load bearing construction.
35
When cement is replaced by fly ash there is a reduction of strength between 20 to 40% for a maximum of 50 percent replacement. The period of curing affects the strength of blocks particularly when the fly ash is replaced in the larger percentages. It is recommended that total period of nearly 60 days (28 days wet curing followed by 28 days air drying) give sufficient strength particularly of leaner mixes with fly ash replacement exceeding 20 percent. In general there is 30% increase in strength at the age of 42 days when compared to 28 days strength and this strength increase further by 20% and the total curing period is extended to 2 months. Blocks recommended for load bearing units works to be 20 to 25 percent cheaper than the commercially available blocks. For nor load bearing walls the cost reduction will about 50%.
Sesha sai et al :
(37)
in their investigation titled “Concrete Making Characteristics
of Fly ash from Vijayawada and Ramagundam Thermal Power Station of Andhra Pradesh� have studied the suitability of these fly ash for concrete making with cement replacement (of 10,20,30,40 and 50%) by fly ash. From the test results they have concluded. The normal consistency of cement fly ash paste decrease initially up to 20% fly ash content and increase subsequently as fly ash content increases. Minimum consistency is obtained at 20% replacement of cement by fly ash. This shows that the water requirements of fly ash-cement pastes will be minimal at 20% replacement of cement. This perhaps could be the reason for the maximum strength achieved at about 20 to 30% levels of replacement of cement with fly ash. For the two nominal mixes, M 15 and M 20, there is a fall in the 7 day and 28 day compressive strength of fly ash mixed concretes, the rate of fall being larger at higher percentage of cement replacement. However, the 90 day strengths have increased with a maximum increase of 15-25% at about 30% replacement of cement by fly ash.
36
Swami et al.,:
(38)
have conducted studied on designing fly ash concrete mixes
using the approach of reduction in strength of mortar mixes with fly ash over mortar mixes without fly ash. Through their study it was observed that there is an almost linear reduction in mortar cube strength from 0-40% when the fly ash content in cement increased from 0-50%. Based on this approach reduction factor have been suggested to increase the target strength of concrete appropriately.
Naik et al.,: (47) the authors are carried out a research work to evaluate the effects of source and amount of fly ash on strength and durability properties of concrete. Mechanical properties considered were compressive strength, tensile strength ,flexural strength, and modulus of elasticity. The durability properties considered were: shrinkage, abrasion resistance, air and water permeability, chloride permeability and salt scaling resistance of concrete. A reference concrete was proportioned to attain the 28 day compressive strength of 41 N/mm2. Three sources of Class C fly ash were used in this work. Fly ash from each source was used at three levels of cement replacements(40,50 and 60%) in producing concrete mixtures. The water to cementitious materials ratio was maintained at 0.30 plus or minus 0.02 for all mixtures. In general strength and durability properties for the 40% fly ash mixture were either comparable or better than the no fly ash concrete, except for one source of fly ash at 60% cement replacement level. All the mixture with and without fly ash, tested in this investigation confirmed to the strength and durability requirements for excellent quality structural grade concretes.
Gupta et al.., : (11) has carried out extensive investigations on over 600 specimens of fly ash concrete of normal strength (M 20) proportioned on simple replacement of cement with fly ash, with fly ash content varying between 30% to 60% in steps of 10%. The total cementitious contents were 383 Kg and 354 Kg. per cubic meter for 20mm and 40mm aggregate. The water cementitious material ratios were between 0.46 to 0.57 increasing with the increase in fly ash content. To achieve sufficient workability super plasticizers were added in the range between 1.0% to 2.0%. The results show that proportioning by simple replacement have resulted decrease in 28 day strength.
37
Malhotra et al., :
(25)
the authors of this paper presented their views in this
manner. The challenge for the civil engineering community in the near future will be realize projects in harmony with the concept of sustainable development and this involves the use of high performance materials produced at reasonable cost with the lowest possible environmental impact. Portland cement concrete is a major construction material worldwide. Unfortunately, the production of Portland cement releases large amount of CO 2 into the atmosphere and because this gas is a major contributor to the green house effect and the global warming of the planet, the developed countries are considering very server regulations and limitations on the CO2 emissions. In view of the global sustainable development, it is imperative that supplementary cementing materials be used to replace large proportions of cement in the concrete industry and the most available supplementary cementing material worldwide is fly ash, a byproduct of thermal power stations. In order to increase considerably the utilization of fly ash that otherwise is being wasted and to have a significant impact on the production of cement, it is necessary to advocate the use of concrete that will incorporate large amounts of fly ash as replacement for cement. However, such concrete will have to demonstrate performance comparable to that of conventional Portland cement concrete and must be cost effective. In 1985, CANMET developed a concrete incorporating large volumes of fly ash that has all the attributes of high performance concrete i.e., excellent mechanical properties, low permeability superior durability and that is environmentally friendly. This paper gives an overview of the type of concrete that is believed to be a very promising alternative for the industry seeking to meet the sustainable objectives.
Bridgar er al.,: (4) have conducted investigations into fly ash concrete proportioned on modified replacement method. Nominal mix proportioning of concrete was made with ratios being 1:2:4 and water-cement ratio is 0.52. The amount of fly ash substituted was 1.5 times to 2.5 times by weight of cement replaced. Other ingredients were kept constant thereby reducing the water to total binder ratio comparable results have been obtained at 20% replacement of cement with 1.5 times fly ash.
38
Further tests were conducted on re-tempering the above mixes with the addition of super plastisizer at 0.25% for each hour for hrs. To investigate the suitability of fly ash concrete production in Ready Mix Plants. Results indicate that re-tempering has compensated the slump loss and returned the slump of the concrete to original levels.
Seshagiri Rao et al., :
(39)
this paper presents the behaviour of high volume fly
ash concrete made with fly ash obtained from Ramagundam Thermal Power Plant in AP, India and 43 grade Portland cement by using high volume of fly ash as a partial replacement and as additional ingredients upto 100% by weight of the cement. Experimental investigation were carried out on concrete cubes, beams and cylinders of M20, M30 grades with fly ash as an additional material upto 100% by weight of cement and fly ash as partial replacement of cement upto 60% for finding out the properties of concrete under normal curing. From the first results, for high volume fly ash concrete with fly ash as a partial replacement for cement, it is observed that the increase in fly ash content has resulted in decrease in compressive and tensile strength of concrete. In the second series of experiments conducted with fly ash as an additional ingredient it is concluded that the 28 days strength are found to be improved in both grades of concrete. The splitting tensile strength, flexural strength and modulus of elasticity of high volume fly ash concrete are found to be more.
Mehta : (26) in this paper, a brief review is presented of the theory and construction practice with concrete mixtures containing more than 50% fly ash by mass of the cementitious material. Mehanisms are discussed by which the incorporation of high volume fly ash in concrete reduces the water demand, improves the workability, minimizes cracking due to thermal and drying shrinkage, and enhances durability to reinforcement corrosion, sulfate attack, and alkali-silica expansion. For countries like china and India, this technology can play an important role in meeting the huge demand for infrastructure in suitable manner. Higher amounts of fly ash on the order of 25%-30% are recommended when there is a concern for thermal cracking , alkali-silica expansion, or sulfate attack. Such 39
high proportions of fly ash are not readily accepted by the construction industry due to slower rate of strength development at early age. The high volume fly ash concrete system overcomes the problems of low early strength to great extent through drastic reduction in the water-cementitious materials ratio by using a combination of methods, such as taking advantage of the superplactisizing effect of fly ash when used in a large volume, the use of a chemical super plasticizer, and a judicious grading, Consequently, properly cured high-volume concrete products are homogeneous in microstructure, virtually crack-free, and highly durable.
Madan et al.,:
(24)
have studied the development of bond of steel reinforcement in
the structural fly ash concrete, having fly ash ranging from 5 to 25% as part replacement of cement in steps of 5%. They observed the compressive strength development with curing period of concrete without fly ash and concretes with various percentage replacement of cement by fly ash on one for one basis by weight. From their observations they have come to the following conclusions. Early strength at 7 days and 14 days goes on decreasing rapidly with an increase in the content of fly ash. The effect is such that when 15% of cement is replaced by fly ash, the 7 day strength is less than 0.6 times the strength of concrete without fly ash and this effect is more marked with 20 and 25 percent replacement. For obvious reasons, nominal replacement of cement up to 5% has enough early strength (through not equal to concrete without fly ash) on 7 and 14 days which improve further at 21 and 28 days when it is on par, or greater than that of normal concrete. It is noted that the 21 day strength for 10% to 25% replacement of cement with fly ash is again very low, and this does not permit its use in those ranges where form work is required to be stripped off at 28 days or earlier.
Walariat Bumrongjareon et al.,:
(49)
has carried out studies on “ A Figure of
Merit for Fly Ash Replacement of Portland Cement� based on his study the following results are reported.
40
The replacement of Portland cement by fly ash produces competing effects: it contributes C-S-H gel through the pozzolanic and alkali-actived reactions, but it also dilutes the contribution of the main Portland cement reaction the reactive importance of these individual effects depends on the chemical composition of the glassy phase of the fly ash. All of them must be taken in to account in proportioning the fly ash/cement mix. Therefore, A Figure of Merit for Fly Ash Replacement has been developed. Given a fly ash chemical composition, and a specified replacement factor, the algorithm for computing the individual C-S-H Contribution has several steps modeling the consumption of the CaO, SiO2 and Al2O3 contents of the fly ash. If the figure of merit is greater than unity, then the replacement should provide a beneficial effect, i.e.more C-S-H gel. If it is less than unity, then the fly ash replacement would degrade the performances of concrete. This algorithm can be iterated using different replacement factors to find optimum value. An example of this approach is presented using a typical lignitic-type (class C) fly ash and bituminoustype (Class F) one. In most cases the figure of merit was less than unity. 2.2 REVIEW OF LITERATURE ON ACCELERATED CURING
OF PLAIN CEMENT CONCRETE: In construction industry, strength is a primary criterion in selecting a concrete for a particular application. Concrete used for construction gains strength over a long period of time after pouring. The characteristic strength of concrete is defined as the compressive strength of a sample that has been aged for 28 days. Neither waiting 28 days from such a test would serve the rapidity of construction, nor neglecting, it would serve the quality control process on concrete in large construction sites. Therefore, rapid and reliable prediction for the strength of concrete would be of great significance. For example, it provides a chance to do the necessary adjustment on the mix proportion, used to avoid situation where concrete does not reach the required design strength or by avoiding concrete that is unnecessarily strong and also, for more economic use of raw materials and fewer construction failures, hence reducing construction cost.
41
Prediction of concrete strength, therefore, has been an active area of research and a considerable number of studies have been carried out. Some of them are presented here.
Akroyd et al., : (1) has developed a method for accelerated curing of concrete. The method procedure is as follows, cube moulds, along with the cover plates were placed in water at 60C half an hour after casting. The water was then raised to boiling temperature and the cubes kept in water for a total of 7 hours. The cubes were tested one hour after their removal from the boiling water. The method was later modified by changing the curing regime to 24 hours normal curing followed by 3 ½ hours of boiling. The strength tests were carried out one hour after removal from water. The relation of accelerated cured strength to normally cured strength was found to be affected by changes in cement and aggregate.
King :
(50)
conducted an experiment on accelerated curing of concrete specimens
(cubes). In this test, standard cubes were made and moulds are immediately covered by top plates, sealed with grease in order to prevent drying. Within 30 minutes of casting the cubes with their cover plates were placed in an air tight oven. The oven should reach 930C (2000 F) in one hour. The cubes were kept at this temperature for a further time of 5 hours making a total of six hours. At the end of this period the cubes were removed from the oven, striped allowed to cool and tested for compressive strength. In this experiment the accelerated curing cycle is 7 hours after casting the cubes. Based on this experimental procedure the following conclusions are made. 1.
The accelerated strength shows good correlation with
the 7 and 28 days strength of normally cured concrete. 2.
The reliability of the results so obtained were high, but
because of the variation in the rate of strength gain of cements, it was not possible to use the 7 days strength to predict 28 day values.
Malhotra et al.,: (28) has studied the boiling water method in detail applied curing for 24 hours at 23+1.7C and 100 percent relative humidity, and then in boiling water for 3 ½ hours. The strength tests were carried out 28 ½ hours after casting. They suggested following hyperbolic relationship between accelerated strength R and 28
42
day strength R28, (both in psi) for the prediction of 28-day compressive strength of concrete: R28=
Ra 0.000078 Ra + 0.29
The accuracy of the prediction was about +12 percent. The admixtures employed did not significantly affect the general relationship. It was also found that the gain in strength of accelerated cured specimens depended upon the strength characteristics of cement and the strength level of concrete. The ratio of accelerated to 28-day strength varied from 0.24 at low strength level to 0.65 at high at high strength level.
Smith et al.,: (40) made an extensive study on autogenously curing which makes use of the heat of hydration of cement for accelerated curing. According to this method, immediately after moulding, the specimens are covered with metal plates and are sealed in plastic bags. They are then placed in insulated containers. At the age of 48 + Âź hours the specimens are removed and demoulded and tested in compression one hour after removal. The regression equation suggested is: R28= 1.35 R + 82.97 kg/cm2, with a standard deviation of 21.2 kg/cm2
Hansen et al.,:
(10)
carried out studies on “Physical and Chemical Properties of
Cement Mortar Cured at Elevated Temperatures�. Through his study it was observed that by curing at temperature above 45 0C, the hydration of C3S was accelerated in particular and in cases where this process starts before the hydration of C 3A, the mechanical properties might be affected. In conclusion, nothing for certainty is known regarding the influence of the type of cement and other mix parameters on the correlation between accelerated strength and 28-day normally cured strength of concrete, although, in case of steam curing the strength development is found to be influenced by the physical and chemical characteristics of cement.
Malhotra et al.,: (27) carried out further investigation on boiling water method and founded the following results. The boiling water method was extensively used at several construction projects in Canada and based on the results a new relationship between Ra and R28 was suggested.
43
R28=126.6+1.286 Ra kg/cm2 For the combined data, when various brands of normal Portland cement, Various types of aggregates and a number of kinds of admixtures had been used, the 28-day compressive strength could be predicted with an accuracy of + 15 percent.
Orchard et al.,: (34) from this experimental investigation it was observed that in all procedures developed for accelerated testing of concrete, the effect of the coefficient of thermal expansion of coarse aggregate on the correlation between accelerated and 28-day normally cured strength had been ignored. An accelerated test would tend to underestimate the potential strength of normally cured concrete made from coarse aggregate with a low coefficient of thermal expansion. The use of moderate curing temperature would minimize their effects and was therefore preferable. A low C 3A content in the cement appeared to be very important for best results with accelerated curing.
Nasser:
(32)
invented an accelerated strength testing method and apparatus for
concrete in which a concrete mix sample is subjected to elevated temperature and pressure to accelerated curing. In this preferred embodiment, a prediction of 28-day strength is provided in about five hours. The apparatus comprises a container for the sample comprising a cylinder and piston. Closure, means for applying force to the closure to pressurize the sample and seal the container, and heating means for heating the sample within the container pressurizing the sample prevents it from separating as it is heated. In previously proposed accelerated tests involving heating , in order to prevent separation or boiling, the sample is partially cured to prior to the heating step. This procuring step consumes considerable time which avoided by present invention. Maintaining the sample at constant pressure facilitates consistent curing conditions for successive tests. After the predetermined heating time has elapse, heating is discontinued and the cured specimens are allowed to cool, or cooled mechanically. After cooling the pressure was released and the containers removed. The specimens were ejecting apparatus previously described. The uncapped specimens were then tested for compressive strength, again using the same jack. Preliminary tests showed that the relationship between the accelerated cured and the 28 day standard cured strength can be represented by a linear equation with an accuracy of + 15% and that
44
the relationship appears to be independent of the type of aggregates and admixtures used.
Dhir : (8) based on his work at Dundee University, felt the necessity of permitting the use of variable pre-and/or post curing periods (upto 8 hours) so that the specimens could be tested for strength at one or two convenient predetermined periods during working hours. He adopted the British Standard Accelerated cuing procedures and suggested accelerated strength correction factors for different pre-and post curing periods to obtain the standard cycle accelerated strength. Regarding the tolerances on curing temperatures and duration of accelerated curing, Dhir concluded that to achieve reliable and reproducible results, variations in temperature and acceleratedcuring time should not exceed + 2 C and + 2.5 percent respectively of the specified temperature and time though it was desirable to be as close to the specified values as possible.
Dhie et al.,:
(9)
studied the influence of constituent materials (cements, aggregates
and admixtures) on accelerated, 7 and 28-day strength of concrete, adopting the British Standard Accelerated Curing Procedure (Warm Water Method). They concluded that different constituent materials gave similar accelerated and normal strength performance relative to one another. In other words, the constituent materials did not significantly affect the ratio of strength of accelerated and normally-cured concrete.
Al-Rawi et al.,: (2) has found that the ratio of accelerated to 28-day normally cured strength increased significantly with increase in the C 3A content of cement in the range 1 to 6 percent. With further increase above 6 percent in the C3A content, however, there was no significant change in the ratio. It was also shown that there was as interaction between the chemical composition of cement and W/C ratio of concrete concerning their effects on the strength of accelerated cured concrete. It was found that for all cements used, the increase in W/C ratio from 0.35 to 0.50 resulted in a significant decrease in the ratio of accelerated to 28-day normally cured strength. With further increase in W/C ratio from 0.50 to 0.70, there was a slight increase in the strength ratio. Regarding C3S/C2S ratio had an adverse effect on the accelerated strength and a favourable effect on the later age strength.
45
Accelerated Curing Procedures:
(15)
the accelerated curing procedures
conformed to the India Standard method of making, curing and determining the compressive strength of accelerated cured concrete test specimens. The summary given by India Standard code is as follows. Traditionally, quality of concrete in construction is calculated in terms of its 28 days compressive strength. This procedure requires 28 days of moist curing before testing, which is too long a period to be of any value for either concrete construction control or applying timely corrective measures. Thus by time the results of 28 day test, or even 7 day test are available, a considerable amount of concrete has been utilized. It is then rather too late for remedial measures if the concrete is too weak or if is too strong. With the assistance of reliable test methods employing accelerated curing techniques, it is now possible to test the compressive strength of concrete within short periods and thereby to estimate whether it is likely to reach the specified strength at 28 days or not. The two methods of such accelerated techniques are given as follows.
1. Warm Water Method: After the specimens have been made, they were left undisturbed in moist air of at least 90 percent relative humidity and a temperature of 27 + 2 C for 1 ½ to 3 ½ hours. The specimens were then gently lowered into the water in the curing tank, maintained at 55 + 2C and cured for 19 hours 50 minutes. The specimens were then removed from the water, demoulded and immersed in the cooling tank at 27 + 2 C before the completion of 20hours 10 minutes from the start of immersion in the curing tank. They shall remain in the cooling in the cooling tank for a period of not less than one hour. Then the specimens were tested for compressive strength as per IS:5161959.
46
Fig. 2.1 Typical relation Between Accelerated and 28 days compressive strength of concrete (Warm Water Method) Courtesy IS : 9013 - 1978 2. Boiling Water Method: After the specimens have been made, they were stored in a place free from vibration, in moist air of at least 90 percent relative humidity and at a temperature of 27 + 20 C for 23 hours + 15 minutes from the time of addition of water to the concrete ingredients. The specimens shall then be gently lowered into the curing tank and shall remain totally immersed for a period of 3 ½ hours + 5 minutes. The temperature of the water in the curing tank shall be a boiling (100 0 C) at sea level. The temperature of water shall not drop 3 C after the specimens are placed and shall return to boiling within 15 minutes. After curing for 3 ½ hours + 5 minutes in the curing tank, the specimen shall be removed from the boiling water, removed from the moulds and cooled by immersing in cooling tank at 27 + 2 C for a period not less than
47
2 hours. Then the specimens were tested for compressive strength as per IS: 5161959.
Fig. 2.2 Typical relation Between Accelerated and 28 days compressive strength of concrete (Boiling Water Method) Courtesy IS : 9013 - 1978 CRI Report
(7)
studied carried out by Cement Research Institute of India on
“Correlation of Strength of Accelerated Cured and Normally Cured Concrete� has revealed the following conclusions. Both accelerated curing methods like boiling water method and warm water method were tried and found suitable. Regression equations for calculating the 28 day strength on the basis of accelerated strength were proposed for both the methods. The influence of parameters like chemical composition, fineness or the 7 day compressive strength were studied. It was also concluded that the effect of admixtures in concrete can be neglected in assessing the 28 day strength using the regression formulae.
48
Sirin Kurbetci et al.,(41) in this study, applicability of accelerated curing to high strength concrete specimens is investigated. In the laboratory, using PC 42.5 cement and super plasticizer, 25 different batches of concrete were made. The accelerated curing used was the “warm water curing method” which is described in the Turkish Standard TS 3223. Results indicated that the warm water curing method can successfully be applied to assess in advance 28-day strength of High Strength Concrete Specimens.
Timothy:
(48)
in this paper the author reported a computer controlled curing
procedure that ensures quality, efficiency, and economy. The procedure is as follows. The computer controls the temperature of the casting bed with respect to time and can control the rate of change or hold the temperature at set point. By inputting the desired time-temperature curve, the temperature can be constantly controlled for efficiency (see side bar). Thermocouples imbedded in the concrete product report the current concrete temperature to the computer. The computer then controls the supply of heat so the actual temperature matches that prescribed by the preset curve. The heat is simply turned on and off when needed.
Calvin:
(6)
this paper discussed about the “Basics of Accelerated Curing” in the
following way. High early concrete strengths are most efficiently produced by increasing the internal temperature of the concrete while maintaining high moisture content in the curing environment. Heating reduces relative humidity of the air surrounding the concrete. Thus, moisture must be added to the heated air to maintain the same relative humidity of the air. If adequate moisture is not maintained in the curing environment, the concrete won’t develop maximum compressive strength and cracking may occur. Durability of the concrete may also be reduced due to inadequate hydration of the cementitious material.
Meyer:
(29)
has carried out studies on “A Statistical Comparison of Accelerated
Concrete Testing Methods”. Through his study it was observed that accelerated curing results, obtained after only 24 hours, are used to predict the 28 day strength of concrete. Various accelerated curing methods are available. Two of these methods are compared in relation to the accuracy of their predictions and stability of the
49
relationship between their 24 hour and 28-day concrete strength. The results suggest that Warm Water Accelerated Curing is preferable to Hot Water Accelerated Curing of Concrete. In addition, some other methods for improving the accuracy of predictions of 28 day strength are suggested. In particular the frequency at which it is necessary to recalibrate the Prediction equation is considered. These results suggest that the simpler warm water method of accelerated curing is preferable to the hot water method and that the equation used to predict 28-day strengths needs to be checked, and recalibrated if necessary. However, this study has also suggested three additional methods for improving the accuracy of 28-day concrete strength predictions.
Hulusi et al., : (13) the results of this experimental investigation was reported in this manner. The relation between 28-day strength of normal cured concrete and accelerated strength is investigated by using an ordinary Portland cement and trass cement under two different accelerated curing conditions, warm water and boiling. Linear regression analysis was applied on the test results and evaluated by using the efficiency concept, i.e., the ratio of accelerated strength and 28-day normal cured strength. It is concluded that the ordinary Portland cement gives higher efficiency than that of the tress cement. The difference due to the cement types is less in the boiling water method than that in warm water method.
Bhatnagar et al.,:
(10)
have conducted investigations on the thermal alteration in
ordinary concrete which involved laboratory study on concrete test samples (representing M15 and M20) exposed to temperatures of 200, 400, 600 and 8000 C in an electric furnace keeping two different exposure periods of 2 and 4 hours duration. If may be noted that exposure of concrete sample to 200 0 C yield marginal gain in compressive strength in both grades of concrete. Hardened cement paste on heating to lower temperatures (upto 2000 C) often shows minor gain in strength properties. It is reported that gain in strength of low temperature heated concrete (upto 200 0 C) is primarily due to thermal alteration of amorphous tobermorite phase into its crystalline/semi-crystalline state. Further heating of test samples between 200 0 C to 8000 C show continuous fall in strength properties irrespective, as exposure of hydrated cement pastes to elevated temperatures beyond 200 0 C lead to excessive loss of constitutional moisture from many of its cementitious phases, besides thermal decomposition of carbonate mineral phases. In addition, thermal expansion and
50
contraction of different constituents of concrete during heating-cooling cycle is yet another factor for the loss in mechanical properties of concrete mass. The magnitude of regain of strength in concrete samples exposed at 6000 C with period of storage was found low in both the grades of concrete. It may be further observed that concrete cubes (M15 and M20) heated to 8000C did not show any significant regain strength properties with storage time. If any therefore be inferred from the above observations that the concrete mass when heated to temperatures more than 6000 C (i.e., the dehydration temperature C-S-H gel) loses most of its structural attributes permanently without any significant increase in strength properties with storage time.
Jee Namyong et al.,
(23)
this paper presents the regression equation for predicting
compressive strength of in-situ concrete. For this purpose, this study used data of mixture proportions of ready-mixed concrete and test results of compressive strength at construction sites. This study used 1442 compressive strength test results obtained from the specimens having 59 different kinds of mixtures with specified compressive strength of 18-27 N/mm2, water-cement ratio of 0.39-0.69, maximum aggregate size of 25mm, and slump 12-15cm. principal factors that influence compressive strength of concrete are selected by a correlation analysis, and then the multiple linear regression analysis is carried out for predicting compressive strength according to water-cement ratio or cement-water ratio, cement contents and cement-aggregate ratio.
Hasan et al.,: (14) the authors concluded the following points based on their research work. Hardened concrete strength can be estimated from accelerated strength with reasonableaccuracy. The relationship between hardened concrete strength and accelerated strength is affected by variation in the W/C ratio especially for high strength concrete with high cement dose. Modulus of elasticity of hardened concrete can be predicted from accelerated one which is equal to 0.49 of E28 days. 2.3 REVIEW OF LITERATURE ON ACCELERATED CURING OF
POZZOLANIC CONCRETE :
51
There are different number of investigations were carried out on quick assessment of 28 day strength of concrete with pozzolanic materials. Some of the recent and significant investigation are presented here.
Sujjavanich et al.,:
(44)
this paper reports the effects of water binder ratio (w/b),
curing temperature and fly ash content on datum temperature for maturity applications on fly ash concrete. This chosen temperature is used to predict the potential characteristics of fly ash concrete within a short time after placing for quality control purpose. It was found that these factors strongly and differently affected the datum temperature of fly ash concrete with different workability. From the three chosen curing temperatures, 26,40 and 600 +C, the datum temperature of no slump roller compacted concrete was -3.2 + C, while those of normal slump fly ash concrete appeared to be higher. The w/c ratios of 0.40 to 0.45 and fly ash content of 20 to 30% yielded a small difference in datum temperature while the higher w/b and higher fly ash content resulted in high datum temperature.
Shweta et al.,:
(43)
carried out an experimental and analytic research, in this
experimental and analytic research, the effect of curing regime on various combinations of silica fume and fly ash was investigated in terms of development of compressive strength. Over 24 mixes were prepared with the water-to-binder ratios of 0.45, 0.35 and 0.25 and with differing percentage of additives uses as a combination of 2 to 3 blinders. The specimens were subjected to five different curing regimes ranging from continuously water cured to continuously air cured. Results show that it is economical to use a combination of silica fume and fly ash rather than using only silica fume for attaining the same strength level. Poor curing condition adversely affect the strength characteristics of pozzolanic concrete than that of OPC concrete. For silica fume concrete, it is necessary to apply water curing for the initial 7 days to explore pozzolanic activity but it is imperative to cure the fly ash concrete for an extended period to utilize its full potential.
Brent Vollenweider
(5)
this research paper reveals some data related
to
Accelerates Curing and Mineral and Chemical Admixtures and High Range Water Reducing Admixtures and self consolidated concrete.
52
In these tests , 7.5% by weight of cement was replaced with microsilica. It can be seen that the combination of heat cured concrete with the addition of microsilica has much higher early strength than any of the combinations. The primary mechanism to which the increased strength is attributed is not unique to the early stages of curing, however,” the Inclusion of Dry-Densified form of Microsilica increased cohesiveness and Reduced segregation and bleeding of fresh concrete”,(French et al.,1998).The use of the microsilica seemed to improve the transition zone characteristics of the concrete, increasing the bond strength between the aggregate and the matrix, Unlike microsilica, however, fly ash does not result in improved early strength of concrete. In fact, the results of the same study mentioned previously in which microsilica was shown to increase concrete strength show that the replacement of cement by fly ash resulted decreased early strengths (French et al., 1998). For moist-cured specimens, decrease in compressive strength was limited to early ages, upto 180 days, while nearly all the specimens subjected to heat-curing exhibited lower compressive strengths at all ages (upto 365 days). While the use of fly ash may improve other properties of concrete, namely plasticity of the mix (Concoran, 2004), the discussion which is beyond the scope of this paper, it should not be used as a curing accelerator. Nonetheless, studies have shown that calcium chloride has significant impact on early strength gain of concrete. The use of 1% of calcium chloride relative to the weight of cement in a mix has resulted in and increase of strength after 24 hours of 300% (Levitt, 1982). On the other hand, very small concentrations of calcim chloride, on the order of 0.0005-0.05% by weight of cement can have a server retarding effect on the hydration process. In applications in which metal is not embedded in concrete, the use of calcium chloride as an accelerator is still permitted. Although not technically characterized as accelerators high range water reducing (HR WR) admixtures contribute to, “large increases in early concrete strengths under both normal and accelerated curing conditions”, (Hester, 1978). The use of these admixtures results in either increased concrete workability while maintaining a target strength concrete workability while maintaining a target strength level, or increased strength while maintaining a desired workability. When compared with standard concrete mixes, the inclusion of HR WR admixtures has showed a marked increase in early strength gain when exposed to a variety of curing temperatures. Figure 5 clearly demonstrates the relationship observed between compressive strength and time for a
53
HR WR mix compared to a normal mix, for two different maximum curing temperatures (Hester, 1978). In both cases the HR WR mix displays significantly greater strength than the plain mix displays significantly greater strength than the plain mix. The early strength achieved as a result of the greater maximum curing temperature is nearly double that of the lower temperature and the initial rate of strength gain is significantly greater as well. A similar product involving the use of highly advanced HR WR admixtures is self consolidating, or self-compacting concrete (SCC). Initially developed in Japan, in the 1980s in response to a lack of skilled laborers for placing traditional concrete, “SCC is highly workable concrete that can flow through densely reinforced or geometrically complex structure elements under its own weight and adequately fill voids with out segregation or excessive bleeding without need for vibration to consolidate it”, (Lanier etal., 2003). The development of this product has the potential to significantly alter the current precast industry. Regarding accelerated curing, the use of SCC has primarily an indirectly potential impact. The use of ‘SCC’ can greatly reduce the time required for placing concrete. To an extent, this can possibly reduce the need for accelerated curing (Lanier et al., 2003). While it is unlikely that the need for accelerated curing will be eliminated altogether, it is possible that the process will require less energy, and thus become more economical. The implementation of elevated curing temperatures is a relative straight forward process, and can be achieved without the need for a great deal of research and development. As a result, this is primary method currently employed by commercial precast manufacturers.
Sudarat Jraratsongkiti :
(42)
has conducted studies on accelerated tensile
strength of fly ash concrete and reported the following. From the test results, the relationship of all accelerated strength and strength and 28-day standard cure appeared to be linear. Accelerated splitting-tensile strength by modified boiling water provided the co-efficient of determination ranging between 0.9367 to 0.9698 with percent error of predicted splitting-tensile strength at 28 days standard cure -8.335 to 6.89%. accelerated flexural strength by modified boiling water provided the coefficient of determination ranging between 0.9508 to 0.9667 with percent error of
54
predicted flexural strength at 28 days standard cure -8.01% to 8.82%. Using accelerated splitting-tensile strength at 28 days standard cure -8.01% to 8.82 %. Using accelerated splitting-tensile strength for prediction, the flexural strength at 28 days standard-cure by modified boiling water provided the coefficient of determination ranging between 0.8691 to 0.8884 with percent error of predicted flexural strength at 28 day-standard cure -7.84% to 9.13%. accelerated splitting-tensile strength by microwave heated curing provided the coefficient of determination of 0.9684 with percent error of predicted splitting-tensile strength at 28 days standard cure -7.07% to 2.95%.
Neil Lee:
(36)
this experimental investigation revealed that, accelerated curing
generally has a significant for supplementary cementitious material (SCM) concretes. Thus seven days water curing is till recommended after the completion of the accelerated curing cycle. Anecdotal reports from the industry suggest this recommendation is not widely observed. Consequently BRANZ Ltd, funded through the building research levy, has undertaken a limited investigation of the durability detriment resulting from the failure to follow this recommended practice. Only small benefits to concrete performance are likely to be achieved by subsequent water curing of heat-cured concrete elements. This would appear to justify current precast industry practice, although the procedure recommended by NZS 3101 should still be considered where durability is critical. It must be stressed that any suggestion that water curing can be dispensed with applies strictly to concrete cured at elevated temperature.
Srinivasa Rao et al.,:
(45)
the paper reports results of laboratory investigations
carried out to study the effects of elevated temperatures ranging from 50 0 C to 2500C on the compressive strength of high strength concrete (HSC) made with both ordinary Portland cement (OPC) and Portland pozzolana cement (PPC). Based on the results obtained the authors concluded the following. Both OPC and PPC concrete concrete gained compressive strength on heating till temperature of 150C at early ages of 1 and 3 days. This could be due to acceleration in hydration process on heating. The increase in percentage residual compressive strengths are in the range of 10 to 30 percent for OPC and PPC concretes when exposed to elevated temperatures for 3 hours. Both concretes experienced
55
reduction in residual compressive strength at the age of 1 and 3 days beyond 150C temperature. The residual compressive strength of OPC and PPC concretes at the age of 7,28,56 and 91 days decreased steadily with increase in temperature. OPC concrete retained more percentage of residual compressive strength compared to PPC concrete at early age’s upto 7 days. However, PPC concrete performed better by retaining more residual compressive strength compared to OPC concrete at later ages. PPC concrete appeared to have lower decrease in percentage residual compressive strength than OPC concrete for similar conditions. OPC concrete exhibited maximum decrease of 40 percent residual compressive strength at 250C whereas, PPC concrete exhibited maximum decrease of 18 percent in residual compressive strength.
Saifuddin et al.,:
(46)
studied the influence of different curing methods on the
properties of microsilica concrete. Based on this study the following results are reported. Test results indicate that water curing as well as wrapped curing provided much better results than Dry-air curing. The rate of moisture movement was significant when the specimens were, subjected to dry-curing. It hampered the hydration process, and thus affected the compressive strength, and other properties of concrete. The over all findings of this study suggest that microsilica concrete should be cured by water curing to achieve good hardened properties. Water curing was the most effective method of curing it produced the highest level of compressive strength, dynamic modulus of elasticity and ultrasonic pulse velocity, and the lowest of initial surface absorption. This is due to improved pore structure and lower porosity resulting from greater degree of cement hydration and pozzolanic reaction without any loss of moisture from the concrete specimens. Micro silica concrete should be cured by water curing in order to achieve good hardened properties. Water curing produces no loss of moisture, and therefore enhances cement hydration and pozzolanic reaction. In case of water shortage, wrapped curing can be adopted instead of dry-air curing.
56
Elsageer et al.,:
(30)
conducted research to study the strength development of
concrete containing fly ash admixture under different curing conditions and reported the following. The strength development of Portland cement and fly ash concrete with the target mean strength of 70 N/mm2 at 28 days has been investigated under isothermal (100 C, 300 C, and 400 C, 500 C) curing regimes and compared to the strength development using standard curing conditions. At 10C and 20C, the strength development of fly ash concrete with target 28-day strength of 70 N/mm 2 was found be equivalent to that of Portland cement concrete. At an elevated curing temperature all concrete samples were observed to gain strength more rapidly than at 20C and had higher 32-day strength with increasing levels of fly ash. However, the longer term strength is detrimentally affected by the higher curing temperatures with Portland cement concrete being more detrimentally affected than fly ash concrete. This work indicates that fly ash concrete could be used in projects when early age strength is required without having a determental effect on the early or later age strength development. Its early age strength was found to be equivalent to that of Portland cement concrete. The later age strength in a structural element, where temperatures are likely to exceed standard 200 C curing temperatures, may be significantly higher than the target mean strength of the concrete when fly ash is used. In contrast to slag cement, which is detrimentally affected by cold temperatures, fly ash concrete showed same strength development 100 C as Portland cement concrete and could potentially be used at significant levels even in colder conditions without causing delays to construction schedules. This applies fro this particular fly ash and that it may be different for fly ash from another source. The effect of temperature on the particular fly ash seems to be the same as that for Portland cement at early agesirrespective of whether the temperature is higher than or lower than normal curing temperatures.
CHAPTER – 3 EXPERIMENTAL INVESTIGATION The following are the details of experimental investigation carried out on the accelerated strength characteristics of fly ash concrete.
57
3.1 Materials used in the Investigation: The following materials are used in the present investigation. A brief description is given below regarding the materials used.
3.1.1
1.
Cement OPC (53 Grade) and PPC
2.
Fine Aggregate
3.
Coarse Aggregate
4.
Fly Ash
5.
Super Plasticizer (Complast SP – 430)
6.
Water
Cement Locally available 53 grade ordinary Portland cement (OPC) & PPC of
ULTRATECH brand has been used in the present investigation for all concrete mixes. The cement used was fresh and without any lumps. The cement thus procured was tested for physical and chemical requirements in accordance with IS 12269-1987 (21)
. The details of various physical and chemical properties of cement are reported in
Table 3.1. 3.1.2
Fine Aggregate In the present investigation locally available river sand is used as fine
aggregate. The sand is free from clayey matter, still and organic impurities. The physical properties of fine aggregate such as gradation, specific gravity and bulk density are tested in accordance with IS 2386-1963. The sand used confirms to Zone II of IS 383-1970
(17)
. The various physical properties of fine aggregate are given in
Tables 3.2 to 3.3
3.1.3
Coarse Aggregate The crushed coarse aggregate of 20 mm maximum size obtained from the
local crushing plants is used in the present investigation. It is free from impurities such as dust, clay particulars and organic matter etc. The physical properties of coarse aggregate such as gradation, specific gravity and bulk density are tested in accordance
58
with IS 2386-1963.
(22)
. The details of physical properties are presented in Tables 3.4
to 3.5. 3.1.4
Fly ash In the present investigation work, the fly ash used is obtained from
Vijayawada Thermal Power Station in Andhra Pradesh. The specific surface area of fly ash is found to be 475 m2/Kg by Blaine’s permeability Apparatus. The typical oxide composition and physical and chemical requirements of fly ash are shown in Tables 3.6 to 3.8. 3.1.5
Water This is the least expensive but most important ingredient in concrete. The
water, which is used for making concrete, should be clean and free from harmful impurities such as oil, alkali, acid etc. in general, the water is fit for drinking should be used for making concrete.
Table 3.1 Physical properties of ordinary Portland cement : SL.NO.
PROPERTIES 59
RESULTS
1 2 3
4 5 6
Normal Consistency Specific gravity Setting Times (a) Initial setting time (b) Final setting time Soundness (Expansion)
29% 3.15 90 min 340 min
Le-chatilier method Fineness of cement (90Âľ sieve) Compressive Strength (28 days)
1 mm 3.5% 54 N/mm2
Table 3.2 Chemical composition of ordinary Portland cement Lime (cao) Silica (Sio2) Alumina (Al2o3) Iron Oxide (Fe2o3) Magnesia (Mgo) Sulphur Trioxide
63.70% 22.00% 4.25% 3.40% 1.50% 1.95%
Table 3.3 Sieve Analysis of fine aggregate : (Weight of fine aggregate sample taken = 1000 gms.) SI.N O
IS SIEVE NO
WEIGHT CUMULATIVE CUMULATIVE CUMULATIVE RETAINED WEIGHT PERCENTAGE PERCENTAGE (gms) RETAINED RETAINED PASSING
1.
40mm
0
0
0
100
2.
20mm
0
0
0
100
3.
10mm
0
0
0
100
4.
4.75mm
20
20
2
98
5.
2.36mm
55
75
7.5
92.5
60
6.
1.18mm
205
280
28
72
7.
600µ
345
625
62.50
37.50
8.
300 µ
295
920
92
8
9.
150 µ
60
980
98
2
Fineness Modulus of Fine aggregate = (Cumulative percentage Retained/100) 288/100 = 2.88 Confirming to IS: 383 – 1970 the sand used comes under category of course sand. Sand used confirms to Zone-II.
SIEVE ANALYSIS DURING THE PROJECT
61
SIEVING OF COARSE AGGREGATE
62
SIEVING OF FINE AGGREGATE
63
Table 3.4 Physical properties of Fine Aggregate : SI.NO 1.
PROPERTIES Specific Gravity
2.
Fineness Modulus
3.
Bulk Density (Kg/m3)
Fine aggregate 2.62 2.88
γ losse
γ dense
= 1610 kg/m3 = 1715 kg/m3
Table: 3.5 Sieve Analysis of for coarse aggregate : (Weight of course aggregate sample taken = 5000 gms) SI. NO
IS SIEVE WEIGHT CUMULATIVE CUMULATIVE CUMULATIVE NO. RETAINED WEIGHT PERCENTAGE WEIGHT (gms) RETAINED RETAINED PERCENTAGE
1.
40mm
0
0.0
0.0
100
2.
20mm
400
400
8
92
3.
10mm
4600
5000
100
0
4.
4.75mm
0
5000
100
0
5.
2.36mm
0
5000
100
0
6.
1.18mm
0
5000
100
0
7.
600 µ
0
5000
100
0
8.
300 µ
0
5000
100
0
9.
150 µ
0
5000
100
0
Fineness Modulus of coarse aggregate = (Cumulative percentage Retained / 100) 708/100 = 7.08
64
Table 3.6 Properties of Coarse aggregate: SI.NO
PROPERTIES
Coarse aggregate
1.
Specific Gravity
2.60(20mm)
2.
Fineness Modulus
7.08 (20mm)
3.
Bulk Density (kg/m3)
γ losse
= 1410 kg/m3
γ dense = 1560 kg/m3 Table 3.7 Typical oxide composition of Indian Fly ash: S.No 1 2 3 4 5 6 7 8
Characteristics Silica, SiO2 Alumina, Al2O3 Iron oxide, Fe2O3 Lime, CaO Magnesia, MgO Sulphur trioxide, SO3 Loss on ignition Surface area, m2/Kg
Percentage 40-67 16-28 4-10 0.7-3.6 0.3-2.6 0.1-2.1 0.4-1.9 230-600
Table 3.8 Chemical requirements of fly ash : (As given by Vijaywada Thermal Power Station) Sl.No
Characteristics
Requirement in %
65
Present in the fly
ash used in the 1 2 3 4 5
Silica (SiO2) plus Alumina (Al2O3) SiO2 percent by mass MgO percent by mass Total sulpher as SO3 percent by mass Available alkali as sodium oxide Na2O3
70.0 (min) 35.0 (min) 5.0 (max) 2.75 (max) 1.50 (max)
investigation % 86.7 54.0 0.10 0.11 2.11
6
percent by mass Loss on ignition percent by mass
12.0 (max)
4.0
Table 3.9 Physical requirements of fly ash: (As given by Vijayawada Thermal Power Station) Sl.
Characteristics
Requirement for Grade of fly ash Class ‘C’ Class ‘F’
No.
Experimental results
1
Fineness-specific surface in m2/kg, by blains Permeability method, minimum
320
250
475
2
Lime reactivity-average compressive strength In N/mm2, minimum Compressive strength at 28 days in N/mm2, Minimum
4.0
3.0
4.0
3
4
Drying shrinking percent, maximum
5
Autoclave maximum
expansion
percent,
Not less than 80% of the strength of corresponding plain cement mortar cubes 0.15 0.10 0.80
0.80
> 80% of the corresponding plain cement mortar cubes 0.08 0.68
3.2 MIX DESIGN OF FLY ASH CONCRETE In the present investigation work four grades of concrete mixes were tried for different cements like OPC and OPC replaced with 20% Fly ash. They are M 30, M 40, M50, M60 & M70grades of concrete. The Indian standard mix design procedure is adopted (i.e., IS:10262-2009
(20)
) in the present investigation to arrive the mix
proportions for each grade of concrete. The detailed mix design procedure of all four
66
grades of concrete are given in Appendix. In each grade of concrete mix 22% of cement is replaced by fly ash.
MIX DESIGN AS PER IS 10262-2009
SPECIMEN CALCULATION FOR M 30 DESIGN MIX STIPULATIONS FOR PROPORTIONING a)
Grade designation
:
M30
b)
Type of cement
:
OPC 53 grade
c)
Maximum nominal size of aggregate :
20mm
d)
Minimum Cement content
:
300 Kg/m3
e)
Workability
:
Medium
TEST DATA FOR MATERIALS a)
Cement used
:
OPC 53 Grade
b)
Specific gravity of cement
:
3.15
c)
Specific gravity of : i) Coarse aggregate
:
2.60
ii) Fine aggregate
:
2.60
i) Coarse aggregate
:
Conforming to Table 2 of IS 383
ii) Fine aggregate
:
Conforming to grading Zone-II of Table of 4 of IS 383
d)
Sieve Analysis
TARGET STRENGTH FOR MIX PROPOTIONING f1 ck = f ck + 1.65 s Where f1 ck = target average compressive strength at 28 days f ck = characteristic compressive strength at 28 days and s = standard deviation
67
From table 1 standard deviations, s = 5.0 N/mm2 Therefore, target strength = 30 + 1.65 x 5 = 38.25 N/mm2
SELECTION OF WATER CEMENT RATIO From table 5 of IS 456, maximum water-cement ratio = 0.50 Based on experience, adopt water-cement ratio as 0.45, hence O.K.
SELECTION OF WATER CONTENT From table 2, maximum water content
= 186 Litters
for 20 mm aggregate Hence the water content for 75mm slump
= 191.58Litters
Using super plasticizer reduction of water 15% so required water content =162.843liters
CALCULATION OF CEMENT CONTENT Water-cement ratio
=
0.45
Cement content
=
162.843/0.45 = 346.47 Kg/m3
From table 5 of IS 456, minimum cement content for ‘moderate’ exposure condition = 300 Kg/m3
POROPOTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone-II) for water –cement ratio of 0.5 = 0.62 In the present case water-cement ratio is 0.55. Therefore, volume of coarse aggregate is required to be decrease to increase the fine aggregate content. As the water-cement ratio is higher by 0.05, the proportion of volume of coarse aggregate is decreased by 0.01 (at the rate of -0.01 for every + 0.05 change in water-cement ratio). Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.455 = 0.62 +0.01 = 0.63 Volume of coarse aggregate
=
Volume of fine aggregate content =
0.63 1 - 0.63 = 0.37
68
MIX CALCULATIONS The mix calculations per unit volume of concrete shall be as follows. a)
Volume of concrete
=
b)
Volume of cement
=
=
1 m3 Mass of cement
1
Specific gravity of cement
1000
346.47 3.15
1 1000
= 0.11 m3 c)
Volume of water
=
Mass of Water Specific gravity of Water
=
162.84 1
1 1000
1 1000
= 0.163 m3 d)volume of super plasticizre @2% of cement =
346.47*2% 1.145*1000
=0.00302m3 e) Volume of all in aggregate
= [ a – (b + c+d) ] = 1 – (0.11+0.163+0.00302) = 0.72 m3
f)
Mass of coarse aggregate
= e x Volume of coarse aggregate x Specific gravity of coarse aggregate x 1000 = 0.72 x 0.63 x 2.60x 1000 = 1180 Kgs
g) Mass of fine aggregate
= ex Volume of fine aggregate x Specific gravity of fine aggregate x 1000 = 0.72 x 0.37x 2.60 x 1000 = 693Kgs
69
MIX PROPORTIONS FOR TRIAL NUMBER Cement
=
346047 Kgs
Water
=
162.84 Litters
Fine aggregate
=
693 Kgs
Coarse aggregate
=
1180 Kgs
Water-cement ratio
=
0.45
SPECIMEN CALCULATION FOR M 40 DESIGN MIX STIPULATIONS FOR PROPORTIONING a)
Grade designation
:
M40
b)
Type of cement
:
OPC 53 grade
c)
Maximum nominal size of aggregate :
20mm
d)
Minimum Cement content
:
300 Kg/m3
e)
Workability
:
Medium
TEST DATA FOR MATERIALS a)
Cement used
:
OPC 53 Grade
b)
Specific gravity of cement
:
3.15
c)
Specific gravity of : i) Coarse aggregate
:
2.60
ii) Fine aggregate
:
2.60
i) Coarse aggregate
:
Conforming to Table 2 of IS 383
ii) Fine aggregate
:
Conforming to grading Zone-II of Table of 4 of IS 383
d)
Sieve Analysis
TARGET STRENGTH FOR MIX PROPOTIONING f1 ck = f ck + 1.65 s Where f1 ck = target average compressive strength at 28 days 70
f ck = characteristic compressive strength at 28 days and s = standard deviation From table 1 standard deviations, s = 5.0 N/mm2 Therefore, target strength = 40 + 1.65 x 5 = 48.25 N/mm2
SELECTION OF WATER CEMENT RATIO From table 5 of IS 456 Based on experience, adopt water-cement ratio as 0.38, hence O.K.
SELECTION OF WATER CONTENT From table 2, maximum water content
= 186 Litters
for 20 mm aggregate Hence the water content for 75mm slump
= 163
Litters
Using super plasticizer reduction of water 15% so required water content =162.843liters
CALCULATION OF CEMENT CONTENT Water-cement ratio
=
0.38
Cement content
=
162.843/0.38 = 428 Kg/m3
From table 5 of IS 456, minimum cement content for ‘moderate’ exposure condition = 300 Kg/m3
POROPOTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone-II) for water –cement ratio of 0.5 = 0.62 In the present case water-cement ratio is 0.55. Therefore, volume of coarse aggregate is required to be decrease to increase the fine aggregate content. As the water-cement ratio is higher by 0.05, the proportion of volume of coarse aggregate is decreased by 0.01 (at the rate of -0.01 for every + 0.05 change in water-cement ratio). Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.0.38 = 0.62 +0.024 = 0.644
71
Volume of coarse aggregate
=
Volume of fine aggregate content =
0.644 1 - 0.644 = 0.356
MIX CALCULATIONS The mix calculations per unit volume of concrete shall be as follows. a)
Volume of concrete
=
b)
Volume of cement
=
=
1 m3 Mass of cement
1
Specific gravity of cement
1000
428 3.15
1 1000
= 0.136m3 c)
Volume of water
=
Mass of Water Specific gravity of Water
=
162.84 1
1 1000
1 1000
= 0.163 m3 d)volume of super plasticizre @2% of cement =
428*2% 1.145*1000
=0.00374m3 e) Volume of all in aggregate
= [ a – (b + c+d) ] = 1 – (0.136+0.163+0.00374) = 0.697 m3
f)
Mass of coarse aggregate
= e x Volume of coarse aggregate x Specific gravity of coarse aggregate x 1000 = 0.697x 0.644 x 2.60x 1000 = 1167 Kgs
g) Mass of fine aggregate
= ex Volume of fine aggregate x Specific gravity of fine aggregate x 1000
72
= 0.697 x 0.356x 2.60 x 1000 = 645Kgs
MIX PROPORTIONS FOR TRIAL NUMBER Cement
=
428 Kgs
Water
=
162.84 Litters
Fine aggregate
=
645 Kgs
Coarse aggregate
=
1167Kgs
Water-cement ratio
=
0.38
SPECIMEN CALCULATION FOR M 50 DESIGN MIX STIPULATIONS FOR PROPORTIONING a)
Grade designation
:
M50
b)
Type of cement
:
OPC 53 grade
c)
Maximum nominal size of aggregate :
20mm
d)
Minimum Cement content
:
300 Kg/m3
e)
Workability
:
Medium
TEST DATA FOR MATERIALS a)
Cement used
:
OPC 53 Grade
b)
Specific gravity of cement
:
3.15
c)
Specific gravity of : i) Coarse aggregate
:
2.60
ii) Fine aggregate
:
2.60
i) Coarse aggregate
:
Conforming to Table 2 of IS 383
ii) Fine aggregate
:
Conforming to grading Zone-II of Table of 4 of IS 383
d)
Sieve Analysis
TARGET STRENGTH FOR MIX PROPOTIONING f1 ck = f ck + 1.65 s Where f1 ck = target average compressive strength at 28 days f ck = characteristic compressive strength at 28 days and 73
s = standard deviation From table 1 standard deviations, s = 5.0 N/mm2 Therefore, target strength = 50 + 1.65 x 5 = 58.25 N/mm2
SELECTION OF WATER CEMENT RATIO From table 5 of IS 456 Based on experience, adopt water-cement ratio as 0.33, hence O.K.
SELECTION OF WATER CONTENT From table 2, maximum water content
= 186 Litters
for 20 mm aggregate Hence the water content for 75mm slump
=
163 Litters
Using super plasticizer reduction of water 15% so required water content =162.843liters
CALCULATION OF CEMENT CONTENT Water-cement ratio
=
0.38
Cement content
=
162.843/0.33 = 494Kg/m3
From table 5 of IS 456, minimum cement content for ‘moderate’ exposure condition = 300 Kg/m3
POROPOTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone-II) for water –cement ratio of 0.5 = 0.62 In the present case water-cement ratio is 0.33. Therefore, volume of coarse aggregate is required to be decrease to increase the fine aggregate content. As the water-cement ratio is higher by 0.05, the proportion of volume of coarse aggregate is decreased by 0.01 (at the rate of -0.01 for every + 0.05 change in water-cement ratio). Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.33 = 0.62 +0.034 = 0.654
74
Volume of coarse aggregate
=
Volume of fine aggregate content =
0.654 1 - 0.654 = 0.346
MIX CALCULATIONS The mix calculations per unit volume of concrete shall be as follows. a)
Volume of concrete
=
b)
Volume of cement
=
=
1 m3 Mass of cement
1
Specific gravity of cement
1000
494 3.15
1 1000
= 0.157m3 c)
Volume of water
=
Mass of Water Specific gravity of Water
=
162.84 1
1 1000
1 1000
= 0.163 m3 d)volume of super plasticizre @2% of cement =
494*2% 1.145*1000
=0.0043m3 e) Volume of all in aggregate
= [ a – (b + c+d) ] = 1 – (0.157+0.163+0.00432) = 0.68m3
f)
Mass of coarse aggregate
= e x Volume of coarse aggregate x Specific gravity of coarse aggregate x 1000 = 0.68x 0.654 x 2.60x 1000 = 1150Kgs
g) Mass of fine aggregate
= ex Volume of fine aggregate x Specific gravity of fine aggregate x 1000 = 0.68 x 0.356x 2.60 x 1000 = 612Kgs
75
`MIX PROPORTIONS FOR TRIAL NUMBER Cement
=
494 Kgs
Water
=
162.84 Litters
Fine aggregate
=
612 Kgs
Coarse aggregate
=
1150Kgs
Water-cement ratio
=
0.33
SPECIMEN CALCULATION FOR M 30 DESIGN MIX BY 22%REPLACEMENT OF CEMENT BY FLYASH STIPULATIONS FOR PROPORTIONING a)
Grade designation
:
M30
b)
Type of cement
:
OPC 53 grade
c)
Maximum nominal size of aggregate :
20mm
d)
Minimum Cement content
:
300 Kg/m3
e)
Workability
:
Medium
TEST DATA FOR MATERIALS a)
Cement used
:
OPC 53 Grade
b)
Specific gravity of cement
:
3.15
c)
Specific gravity of : i) Coarse aggregate
:
2.60
ii) Fine aggregate
:
2.60
flyash
:
2.2
:
1.145
super plasticizre d)
Sieve Analysis i) Coarse aggregate
:
76
Conforming to Table 2 of IS 383
ii) Fine aggregate
:
Conforming to grading Zone-II of Table of 4 of IS 383
TARGET STRENGTH FOR MIX PROPOTIONING f1 ck = f ck + 1.65 s Where f1 ck = target average compressive strength at 28 days f ck = characteristic compressive strength at 28 days and s = standard deviation From table 1 standard deviations, s = 5.0 N/mm2 Therefore, target strength = 50 + 1.65 x 5 = 58.25 N/mm2
SELECTION OF WATER CEMENT RATIO From table 5 of IS 456, maximum water-cement ratio = 0.50 Based on experience, adopt water-cement ratio as 0.47, hence O.K.
SELECTION OF WATER CONTENT From table 2, maximum water content
= 186 Litters
for 20 mm aggregate Hence the water content for 75mm slump
= 191.58Litters
Using Flyash+ super plasticizer reduction of water 20% so required water content =153.264liters
CALCULATION OF CEMENT AND FLYASH CONTENT Water-cement ratio
=
0.47
Cement +flyash
=
153.264/0.47 = 326.09Kg/m3
From table 5 of IS 456, minimum cement content for ‘moderate’ exposure condition = 300 Kg/m3 Increase cementitious material by 10% as per code so cement+flyash=326.09*1.1=358.7Kg/m3
W/C=153.264/358.7=0.43
77
Flyash @22% replacement of cement =78.914kg/m3 Cement
=279.786kg/m3
PROPOTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone-II) for water 窶田ement ratio of 0.5 = 0.62 In the present case water-cement ratio is 0.43 Therefore, volume of coarse aggregate is required to be decrease to increase the fine aggregate content. As the water-cement ratio is higher by 0.05, the proportion of volume of coarse aggregate is decreased by 0.01 (at the rate of -0.01 for every + 0.05 change in water-cement ratio). Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.43 = 0.62 +0.01 = 0.63 Volume of coarse aggregate
=
Volume of fine aggregate content =
0.63 1 - 0.63 = 0.37
MIX CALCULATIONS The mix calculations per unit volume of concrete shall be as follows. a)
Volume of concrete
=
b)
Volume of cement
=
=
1 m3 Mass of cement
1
Specific gravity of cement
1000
279.786 3.15
1 1000
= 0.089 m3 c)
Volume of water
=
Mass of Water Specific gravity of Water
=
153.264 1
1 1000
= 0.1533 m3 d)volume of flyash =78.914/(2.2*1000)=0.03587 e)volume of super plasticizre @2% of cement =
358.7*2% 1.145*1000
78
1 1000
=0.00636m3 e) Volume of all in aggregate
= [ a – (b + c+d+e) ] = 1 -(0.089+0.1533+0.003587+0.00636) = 0.69m3
f)
Mass of coarse aggregate
= e x Volume of coarse aggregate x Specific gravity of coarse aggregate x 1000 = 0.69 x 0.63 x 2.60x 1000 = 1131.09Kgs
g) Mass of fine aggregate
= ex Volume of fine aggregate x Specific gravity of fine aggregate x 1000 = 0.72 x 0.37x 2.60 x 1000 = 664.261Kgs
MIX PROPORTIONS FOR TRIAL NUMBER Cement Flyash
=
279.786Kgs
=
78.94kg
Super plasticizre
=
7.168lit.
Water
=
153.264Litters
Fine aggregate
=
664.261Kgs
Coarse aggregate
=
1131.039 Kgs
Water-cement ratio
=
0.43
SPECIMEN CALCULATION FOR M 40 DESIGN MIX BY 22%REPLACEMENT OF CEMENT BY FLYASH STIPULATIONS FOR PROPORTIONING a)
Grade designation
:
M40
b)
Type of cement
:
OPC 53 grade
c)
Maximum nominal size of aggregate :
20mm
d)
Minimum Cement content
:
300 Kg/m3
e)
Workability
:
Medium
79
TEST DATA FOR MATERIALS a)
Cement used
:
OPC 53 Grade
b)
Specific gravity of cement
:
3.15
c)
Specific gravity of : i) Coarse aggregate
:
2.60
ii) Fine aggregate
:
2.60
flyash
:
2.2
super plasticizre
:
1.145
d)
Sieve Analysis i) Coarse aggregate
:
Conforming to Table 2 of IS 383
ii) Fine aggregate
:
Conforming to grading Zone-II of Table of 4 of IS 383
TARGET STRENGTH FOR MIX PROPOTIONING f1 ck = f ck + 1.65 s Where f1 ck = target average compressive strength at 28 days f ck = characteristic compressive strength at 28 days and s = standard deviation From table 1 standard deviations, s = 5.0 N/mm2 Therefore, target strength = 40 + 1.65 x 5 =8.25 N/mm2
SELECTION OF WATER CEMENT RATIO From table 5 of IS 456 Based on experience, adopt water-cement ratio as 0.38, hence O.K. 80
SELECTION OF WATER CONTENT From table 2, maximum water content
= 186 Litters
for 20 mm aggregate Hence the water content for 75mm slump
= 191.58Litters
Using Flyash+ super plasticizer reduction of water 20% so required water content =153.264liters
CALCULATION OF CEMENT AND FLYASH CONTENT Water-cement ratio
=
0.47
Cement +flyash
=
153.264/0.38 = 403.26Kg/m3
From table 5 of IS 456, minimum cement content for ‘moderate’ exposure condition = 300 Kg/m3 Increase cementitious material by 10% as per code so cement+flyash=403.326*1.1=443.65Kg/m3
W/C=153.264/443.65=0.345 Flyash @22% replacement of cement =97.64kg/m3 Cement
=346.04kg/m3
PROPOTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone-II) for water –cement ratio of 0.5 = 0.62 In the present case water-cement ratio is 0.43 Therefore, volume of coarse aggregate is required to be decrease to increase the fine aggregate content. As the water-cement ratio is higher by 0.05, the proportion of volume of coarse aggregate is decreased by 0.01 (at the rate of -0.01 for every + 0.05 change in water-cement ratio). Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.38 = 0.62 +0.22= 0.644 Volume of coarse aggregate
=
Volume of fine aggregate content =
0.644 1 - 0.644 = 0.356
81
MIX CALCULATIONS The mix calculations per unit volume of concrete shall be as follows. a)
Volume of concrete
=
b)
Volume of cement
=
1 m3 Mass of cement
1
Specific gravity of cement
1000
=
346.04 3.15
1 1000
= 0.1098m3 c)
Volume of water
=
Mass of Water Specific gravity of Water
=
153.264 1
1 1000
1 1000
= 0.1533 m3 d)volume of flyash =78.914/(2.2*1000)=0.03587 e)volume of super plasticizre @2% of cement =
443.65*2% 1.145*1000
=0.00774m3 e) Volume of all in aggregate
= [ a – (b + c+d+e) ] = 1–
(0.1098+0.1533+0.00774+0.003587) = 0.688m3 f)
Mass of coarse aggregate
= e x Volume of coarse aggregate x Specific gravity of coarse aggregate x 1000 = 0.688 x 0.644 x 2.60x 1000 = 1152.09Kgs
g) Mass of fine aggregate
= ex Volume of fine aggregate x Specific gravity of fine aggregate x 1000 = 0.72 x 0.37x 2.60 x 1000
82
= 636.8Kgs
MIX PROPORTIONS FOR TRIAL NUMBER Cement
=
Flyash
346.448Kgs
=
97.60kg
Super plasticizre
=
8.873lit.
Water
=
153.264Litters
Fine aggregate
=
636.8Kgs
Coarse aggregate
=
1152 Kgs
Water-cement ratio
=
0.345
SPECIMEN CALCULATION FOSPR M 50DESIGN MIX BY 22%REPLACEMENT OF CEMENT BY FLYASH STIPULATIONS FOR PROPORTIONING a)
Grade designation
:
M50
b)
Type of cement
:
OPC 53 grade
c)
Maximum nominal size of aggregate :
20mm
d)
Minimum Cement content
:
300 Kg/m3
e)
Workability
:
Medium
TEST DATA FOR MATERIALS a)
Cement used
:
OPC 53 Grade
b)
Specific gravity of cement
:
3.15
c)
Specific gravity of : i) Coarse aggregate
:
2.60
ii) Fine aggregate
:
2.60
flyash
:
2.2
super plasticizre
:
1.145
d)
Sieve Analysis i) Coarse aggregate
:
83
Conforming to Table 2 of IS 383
ii) Fine aggregate
:
Conforming to grading Zone-II of Table of 4 of IS 383
TARGET STRENGTH FOR MIX PROPOTIONING f1 ck = f ck + 1.65 s Where f1 ck = target average compressive strength at 28 days f ck = characteristic compressive strength at 28 days and s = standard deviation From table 1 standard deviations, s = 5.0 N/mm2 Therefore, target strength = 50 + 1.65 x 5 =58.25 N/mm2
SELECTION OF WATER CEMENT RATIO From table 5 of IS 456 Based on experience, adopt water-cement ratio as 0.33, hence O.K.
SELECTION OF WATER CONTENT From table 2, maximum water content
= 186 Litters
for 20 mm aggregate Hence the water content for 75mm slump
= 191.58Litters
Using Flyash+ super plasticizer reduction of water 20% so required water content =153.264liters
CALCULATION OF CEMENT AND FLYASH CONTENT Water-cement ratio
=
0.47
Cement +flyash
=
153.264/0.33 = 464043Kg/m3
From table 5 of IS 456, minimum cement content for ‘moderate’ exposure condition = 300 Kg/m3 Increase cementitious material by 10% as per code so cement+flyash=464.43*1.1=510.75Kg/m3
W/C=153.264/510.75=0.3 Flyash @22% replacement of cement =112.4kg/m3 84
Cement
=398.48kg/m3
PROPOTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE CONTENT From Table 3, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone-II) for water 窶田ement ratio of 0.5 = 0.62 In the present case water-cement ratio is 0.3 Therefore, volume of coarse aggregate is required to be decrease to increase the fine aggregate content. As the water-cement ratio is higher by 0.05, the proportion of volume of coarse aggregate is decreased by 0.01 (at the rate of -0.01 for every + 0.05 change in water-cement ratio). Therefore, corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.38 = 0.62 +0.034= 0.654 Volume of coarse aggregate
=
Volume of fine aggregate content =
0.654 1 - 0.654 = 0.346
MIX CALCULATIONS The mix calculations per unit volume of concrete shall be as follows. a)
Volume of concrete
=
b)
Volume of cement
=
=
1 m3 Mass of cement
1
Specific gravity of cement
1000
398.48 3.15
1 1000
= 0.1265m3 c)
Volume of water
=
Mass of Water Specific gravity of Water
=
153.264 1
1 1000
= 0.1533 m3 d)volume of flyash =112.393/(2.2*1000)=0.0511 e)volume of super plasticizre @2% of cement =
85
510.758*2%
1 1000
1.145*1000 =0.00892m3 e) Volume of all in aggregate
= [ a – (b + c+d+e) ] = 1 – (0.1265+0.1533+0.00892+0.0511) = 0.66m3
f)
Mass of coarse aggregate
= e x Volume of coarse aggregate x Specific gravity of coarse aggregate x 1000 = 0.66x 0.654 x 2.60x 1000 = 1122.264Kgs
g) Mass of fine aggregate
= ex Volume of fine aggregate x Specific gravity of fine aggregate x 1000 = 0.66 x 0.346x 2.60 x 1000 = 593.74Kgs
MIX PROPORTIONS FOR TRIAL NUMBER Cement Flyash
=
398.48Kgs
=
112.94kg
Super plasticizre
=
10.21lit.
Water
=
153.264Litters
Fine aggregate
=
593.74Kgs
Coarse aggregate
=
1122.624 Kgs
Water-cement ratio
=
0.3
86
MIX DESIGN AS PER DOE METHOD DESIGN OF PROCEDURE HIGH STRENGTH CONCRETE BY DOE METHOD: The DOE method was first published in 1975 and then was revised in 1988, as per the BS code 1988 year. The DOE method is applicable to concrete for most purposes. The method can be used for concrete using fly ash. Since DOE method presently is the standard British method of concrete mix design, the procedure and steps involved in this method is described below. MATERIALS: Cement
: OPC 53 grade
Coarse aggregate : crushed stone Fine aggregate
: natural river sand
PARAMETERS: Assume standard deviation = 5 N/mm2 Assume slump of concrete = 75 mm
Step 1: Find the target mean strength from the specified characteristic strength Target mean strength = specified characteristic strength + standard deviation x risk factor. Step 2: Calculate the water/cement ratio. Using table and figure shown below. Table gives approximate compressive strength of concrete made with a free w/c ratio of 0.50. Using this table find 28 days strength for the approximate type of cement and types of C.A. mark a point on the Y-axis in fig equal to the compressive strength read from the table which is at a W/C ratio of 0.50. through this intersection point, draw a
87
parallel doted curve nearest to the intersection point. Using the new curve we read of W/C ratio as against target mean strength. Step 3: Decide water content water require workability express in terms of slump or vee-bee time taking into consideration the size of aggregate and its type. Step 4: Find the cement content knowing the W/C ratio and the water content. Step 5: Find out the total aggregate content and find out wet density of fully compacted aggregates. The value of specific gravity of 2.7 for crushed aggregate can be taken. The aggregate content is obtain by subtracting the weight of cement and water content from weight of fresh concrete. Step 6: Proportion of fine aggregate is determine in the total aggregate. Maximum size of C.A the level of workability, W/C ratio, and the %age of fine passing 600Âľ sieve. Once the proportion of FA is obtained multiplying by the weight of total aggregate gives the weight if fine aggregate. Then the weight of the CA can be found out
DESIGN CALCULATIONS FOR M60 MIX Design concrete mix for a reinforced concrete work which will be exposed to the moderate condition. The concrete is to be designed for a mean compressive strength of 60MPa at the age of 28 days. A requirement of 25mm cover is prescribed. Maximum size of aggregate is 20mm uncrushed aggregate will be used. Sieve analysis shows that 50% passĂŠ through 600micron sieve. The bulk specific gravity of aggregate is found to be 2.65. Cement used OPC 53 Grade STEP 1 Mean compressive strength
60MPa at 28
days STEP 2 Adopt water cement ratio as
0.33
88
STEP 3 Water content for slump of 75mm for 20mm uncrushed metal is
195 Kg/m3
STEP 4 Cement content
195/0.33
590.91
Kg/m3 STEP 5 Density of fresh concrete from 11.4 for 195 Kg/m3 of water 20mm uncrushed and specific gravity wet density 2450 Kg/m3
2450 Kg/m3
STEP 6 Weight total aggregate from fig 11.3 the water Cement ratio is 0.33
2450-(195+590.91)
1664.09
Kg/m3 STEP 7 From fig 11.3b the water cement ratio is 0.33 For 20mm aggregate and 50% passing through 600 microns sieve % of fine aggregate
38%
STEP 8 Weight of fine aggregate
1664.09 x 38/100
632.35
kg/m3 STEP 9 Weight of coarse aggregate
1664.09-632.35
kg/m3
89
1031.74
STEP 10 Estimated quantities of materials per m3 of concrete CEMENT
590.91
Kg FINE AGGREGATE
632.35
Kg COARSE AGGREGATE
1031.74
Kg WATER
195.00
Kg WET DENSITY OF CONCRETE MIX 2450.00
Kg
STEP 11 Mix proportions CEMENT
1.00
FINE AGGREGATE
1.07
COARSE AGGREGATE
1.75
WATER
0.32
90
DESIGN CALCULATIONS FOR M70 MIX Design concrete mix for a reinforced concrete work which will be exposed to the moderate condition. The concrete is to be designed for a mean compressive strength of 60MPa at the age of 28 days. A requirement of 25mm cover is prescribed. Maximum size of aggregate is 20mm uncrushed aggregate will be used. Sieve analysis shows that 50% passĂŠ through 600micron sieve. The bulk specific gravity of aggregate is found to be 2.65. Cement used OPC 53 Grade STEP 1 Mean compressive strength
70MPa at 28
days STEP 2 Adopt water cement ratio as
0.31
STEP 3 Water content for slump of 75mm for 20mm uncrushed metal is
195 Kg/m3
STEP 4 Cement content
195/0.32
609.38Kg/m3
STEP 5 Density of fresh concrete from 11.4 for 195 Kg/m3 of water 20mm uncrushed and specific gravity wet density 2450 Kg/m3
2450 Kg/m3
STEP 6 Weight total aggregate from fig 11.3 the water Cement ratio is 0.33
2450-(195+609.38)
Kg/m3 STEP 7 From fig 11.3b the water cement ratio is 0.33 91
1645.63
For 20mm aggregate and 50% passing through 600 microns sieve % of fine aggregate
36%
STEP 8 Weight of fine aggregate
1645.63 x 36/100
592.43
kg/m3 STEP 9 Weight of coarse aggregate
1645.63-592.43
1053.20
kg/m3 STEP 10 Estimated quantities of materials per m3 of concrete CEMENT
609.38
Kg FINE AGGREGATE
592.43
Kg COARSE AGGREGATE
1053.2
Kg WATER
195.00
Kg WET DENSITY OF CONCRETE MIX 2450.00
Kg
STEP 11 Mix proportions CEMENT
1.00
FINE AGGREGATE
0.97
COARSE AGGREGATE
1.73
WATER
0.32
92
DESIGN CALCULATIONS FOR M60 MIX WITH 22% REPLACEMENT OF OPC WITH FLYASH Design concrete mix for a reinforced concrete work which will be exposed to the moderate condition. The concrete is to be designed for a mean compressive strength of 60MPa at the age of 28 days. A requirement of 25mm cover is prescribed. Maximum size of aggregate is 20mm uncrushed aggregate will be used. Sieve analysis shows that 50% passĂŠ through 600micron sieve. The bulk specific gravity of aggregate is found to be 2.65. Cement used OPC 53 Grade STEP 1 Mean compressive strength
60MPa at 28
days STEP 2 Adopt water cement ratio as
0.33
STEP 3 Water content for slump of 75mm for 20mm uncrushed metal is
195 Kg/m3
STEP 4 Cement +flyash
195/0.33
590.91 Kg/m3
STEP 5 130kg/m3
Flyash@22% replacement of opc Now cement content
460.69kg/m3
STEP 6 Density of fresh concrete from 11.4 for 195 Kg/m3 of water 20mm uncrushed and specific gravity wet density 2450 Kg/m3
93
2450 Kg/m3
STEP 7 Weight total aggregate from fig 11.3 the water Cement ratio is 0.33
2450-(195+590.91
1664.09
Kg/m3 STEP 8 From fig 11.3b the water cement ratio is 0.33 For 20mm aggregate and 50% passing through 600 microns sieve % of fine aggregate
38%
STEP 9 Weight of fine aggregate
1664.09 x 38/100
632.35
kg/m3 STEP 10 Weight of coarse aggregate
1664.09-632.35
1031.74
kg/m3 STEP 11 Estimated quantities of materials per m3 of concrete CEMENT
460.9
Kg FLYASH
130.00
Kg FINE AGGREGATE
632.35
Kg COARSE AGGREGATE
1031.74
Kg WATER
195.00
Kg
94
WET DENSITY OF CONCRETE MIX 2450.00
Kg
STEP 11 Mix proportions CEMENT
1.00
FINE AGGREGATE 1.372 COARSE AGGREGATE
2.24
FLYASH 0.282 WATER
0.33
DESIGN CALCULATIONS FOR M70 MIX BY 22% REPLACEMENT OF OPC WITH FLYASH Design concrete mix for a reinforced concrete work which will be exposed to the moderate condition. The concrete is to be designed for a mean compressive strength of 60MPa at the age of 28 days. A requirement of 25mm cover is prescribed. Maximum size of aggregate is 20mm uncrushed aggregate will be used. Sieve analysis shows that 50% passĂŠ through 600micron sieve. The bulk specific gravity of aggregate is found to be 2.65. Cement used OPC 53 Grade STEP 1
95
Mean compressive strength
70MPa at 28
days STEP 2 Adopt water cement ratio as
0.32
STEP 3 Water content for slump of 75mm for 20mm uncrushed metal is
195 Kg/m3
STEP 4 Cement+Flyash
195/0.32
609.38Kg/m3
STEP 5 134.06kg/m3
Flyash@22% replacement of opc Now cement content
475.32Kg/m3
STEP 5 Density of fresh concrete from 11.4 for 195 Kg/m3 of water 20mm uncrushed and specific gravity wet density 2450 Kg/m3
2450 Kg/m3
STEP 6 Weight total aggregate from fig 11.3 the water Cement ratio is 0.33
2450-(195+609.38)
1645.63
Kg/m3 STEP 7 From fig 11.3b the water cement ratio is 0.33 For 20mm aggregate and 50% passing through 600 microns sieve % of fine aggregate
36%
96
STEP 8 Weight of fine aggregate
1645.63 x 36/100
592.43
kg/m3
STEP 9 Weight of coarse aggregate
1645.63-592.43
1053.20
kg/m3
-STEP 10
CEMENT
475.32
Kg FLYASH
134.06
Kg FINE AGGREGATE
592.43
Kg COARSE AGGREGATE
1053.2
Kg WATER
195.00
Kg WET DENSITY OF CONCRETE MIX 2450.00
Kg
STEP 11
Mix proportions 97
CEMENT
1.00
FINE AGGREGATE
1.24
COARSE AGGREGATE
1.73
FLYASH
2.21
WATER
0.32
The material quantities obtained as per mix design method (i.e., IS:10262-2009) are given in Tables 3.9 to 3.11. The quantities of materials required per one cubic meter of concrete including fly ash percentages are given in Tables 3.12 to 3.14. The details of experimentations carried out in the laboratory.
Table 3.10 : Quantity of materials required per one cubic meter of different grades of concrete : S.No.
Quantity Kg/m3
Material Grade
M30
M40
M50
M60 590.91
M70
1
Cement (OPC)
346.47
428
494
2
Fire aggregate
693
645
612
632.35
592.43
3
Coarse aggregate
1180
1167
1150
1031.74
1053
4
Water
162.84
162.64
163.02
195
Table
609.38
195
3.11 : Quantity of materials required per one cubic meter of
different grades of Fly Ash replaced concrete : S.No 1
Material Grade Cement (OPC)
M30 279.79
98
Quantity kg/m3 M40 M50 346.45 464.43
M60 460.9
M70 475.3
2
Fly ash
3 4
Fire aggregate Coarse aggregate
5
Water
78.91
97.6
112.4
130.02
134.06
664.26 1131.039
636.8 1152
593.74 1122.26
632.35 1031.74
154.24
139.15
139.32
195
592.43 1053 195
3.3Preparation of Test Specimens: The following procedure is adopted to prepare the test specimens 1. Mixing 2. Casting 3. Normal Curing 3.3.1
Mixing :
In the present investigation machine mixing was adopted. In the process of mixing the materials are weight with the designed mix proportions, various ingredients of concrete namely, cement, fly ash, fine aggregate, coarse aggregate and water have been calculated for the required number of cube specimens of 150 mm size. The required quantity of fly ash and cement content are thoroughly blended with hand and then all the ingredients are poured into the pan mixer. The materials are thoroughly mixed in their dry condition before water is added. Then calculated amount of water is gradually added and wet mixing is done until a mixture of uniform colour is achieved. Generally the mixers are designed to run at a speed of 15 to 20 revolutions per minute. For proper mixing, it is seen that about 25 to 30 revolutions are required. Mixing was done in batches in each batch the amount of materials required to prepare eighteen test specimens are weighted, based on the designed mix proportions of each concrete mix (i.e., M30, M40 , M50, M60and M70) for different cements like OPC and OPC replaced with 22% Fly ash. Before casting the specimens, workability of the mixes were found out by slump test. It is seen from the experiments that the quality of concrete in terms of compressive strength will increase with the increase in the time of mixing, but for mixing time beyond two minutes, the improvement in compressive strength is not very significant.
99
MIXING OF INGRADIENTS OF CONCRETE
3.3.2
Casting :
For casting the test specimens, standard size of 150 x 150 x 150 mm cubes made with cast iron, metal moulds are used to cast the test specimens. The moulds have been cleaned to remove the dust particles from the mould and mineral oil is applied on all sides of the mould, before concrete is poured into the mould. Thoroughly mixed concrete is filled into the mould in three layers of equal height
100
followed by vibration with table vibrator. Excess concrete was removed with travel and top surface is finished level and smooth. In the present investigation a total number of four grades (i.e., M30, M40, M50 ,M60and M70) of concrete mixes were tried for different cements like PPC, OPC and OPC replaced with 22% fly ash. For each type of cement in every grade of concrete 6 cube specimens are casted. For the above three types of cement 60 cube specimens are casted for all the four grades of concrete mixes (i.e. M30, M40, M50 ,M60& M70).
PREPARING OF MOULDS FOR CASTING OF SPECIMENS 3.3.3. Fresh Property of Concrete : All mixes are designed to have medium workability and attained same during casting mixes. 3.3.4. Normal Curing : After casting, the moulded specimens are stored in the laboratory free from vibration, in moist air and at room temperature for 24 hours. After this period, the specimens are removed from the moulds and immediately submerged in clean, fresh water of curing tank. Two different periods of water curing i.e., 7 days & 28 days have been adopted in the present work. 101
PLACING OF SPECIMENS IN THE NORMAL CURING TANK
3.4 Details of Accelerated Curing : In the present investigation accelerated curing method is adopted to study the accelerated strength of different mixes made of different cements. For accelerated curing, boiling water method is used which confirms to IS 9013-1978. (16).
102
3.4.1 Description of Accelerated Curing Tank: The accelerated curing tank used in the present investigation was manufactured and supplied by M/S AIMIL CO. the curing tank is shown in Fig. 3.1. The tank was fabricated as per the requirements of IS 9013-1978. It is a metallic rectangular tank polished inside and is sufficient to accommodate at least six numbers of 15 cm cube moulds or twelve numbers of 10 cm cube moulds. The tank is provided with an electrical heating element for increasing the temperature of water in the tank. The tank is having all the accessories like pump drive, valve, lid, thermostant, recirculation pumps, control panel, thermometer etc. by switching on, the temperature gets gradually increased and can be kept constant at any desired level.
ACCELERATED CURING TANK 3.4.2 Procedure of Accelerated Curing : For conducting accelerated curing test, firstly accelerated curing tank is cleaned and fresh water is poured into the accelerated curing tank up to the marked
103
level. Then the power button of the accelerated curing tank is switched on to increase the temperature of the water gradually up to 1000 C. After reaching the temperature at 1000C the power button of the accelerated curing tank is switched off. Then the test specimens prepared one day (i.e., 23 hrs + 15 minutes) prior to accelerated curing are kept inside in the boiling water (i.e., 1000 C) along with their moulds for a period of 3 ½ hours + 5 minutes. In this period of keeping the test specimens in the curing tank the temperature in the curing tank is slightly reduced (i.e., not more than 3 0 C) this reduction in temperature is seen in control panel of the curing tank. This reduced temperature has to be covered within 15 minutes after placing the test specimens in the curing tank. For this purpose again the power button of the accelerated curing tank is switched on and boiling continues in the curing tank for a period of 3 ½ hours + 5 minutes. After completing this boiling period time the power button of the accelerated curing tank is switched off and test specimens are taken out from the curing tank. Then the test specimens are removed from the moulds, the removed test specimens are cooled in a cooling tank at 27 + 20 C temperature for a period not less than two hours. Finally specimens are tested for compressive strength at the age of 28 ½ hrs + 20 minutes.
104
PLACING OF SPECIMENS IN THE ACCELERATED CURING TANK
3.4.3 Accelerated Strength Prediction by the Codal Procedure: The Indian Standard codal procedure (i.e., IS 9013-1978) is adopted in the present investigation to study the accelerated strength characteristics of all the concrete mixes. To predict the accelerated strength, IS code has given a regression equation and correlation curve on the basis of the experimental work carried out using only Normal OPC Concrete. In the present experimental study, a new correlation have been tried to establish using the specimens prepared with fly ash concrete, in which fly ash is used as a replacement material to cement in various percentages, and for same fly ash concrete a check is also made, whether the same IS code regression equation or correlation curve can be used to predict the 28 days strength. The IS code regression equation or correlation curve can be used to predict the strength of fly ash concrete when fly ash is used in small percentages as a replacement material to cement. But the same IS code regression equation or correlation curve is not applicable when fly ash is used in higher percentages as a replacement material to cement. An attempt is also made to assess the strength of fly ash concrete at longer ages on the basis of accelerated curing. 3.4.4 Curing of Test Specimens In the present investigation for each grade of concrete mix (i.e., M 30, M40, M50, M60& M70) with OPC and OPC replaced with 22% of fly ash were tried. For each mix a total number of eighteen test specimens are prepared. In those eighteen specimens six test specimens are used for accelerated curing purpose and the remaining twelve test specimens are cured by normal wet curing. Two different periods of water curing (i.e, 7 and 28 days) have been adopted in the present work. In the present experimental work a total number of 60 test specimens are prepared, in that twenty test specimens are used for accelerated curing purpose, and the remaining 40 specimens are used for normal wet curing purpose.
3.5. Testing of Specimens :
105
The test specimens are cured as explained above were taken out from the water after the specified period of curing and air-dried, tests for compressive strength were carried out according to IS 516-1959. (19).
3.5.1. Description of the Compression Testing Machine: In the present investigation the compression testing machine employed to determine the compressive strength of cube specimens, under micro process based compression testing machine of ELE International Limited., UK. The capacity of the compression testing machine is 2000KN. The compression testing machine has the facility of a clutch and control valve by means of which the rate of loading can be adjusted. The machine has been calibrated to standard rate of loading, the platens are cleaned, oil level is checked and it is kept ready in all respects of testing.
3.5.2 Testing Procedure for Compressive Strength: Among the various strength of concrete, the determination of compressive strength has received a large amount of attention because the concrete is primarily meant to withstand compressive stresses. Generally cubes are used to determine the compressive strength. In the present investigation the standard 150 x 150 x 150 mm cubes are used to determine the compressive strength. The compressive strength test procedure is given below. After the required period of curing, specimens are removed from the curing tank just before testing and cleaned to wipe off the surface water. The cube specimen is placed on the lower platen in such a manner that the load is applied centrally on opposite side of the cube and right angels to that has cast. According to BIS 1881:part 116: 1983, the rate of load is applied is equal to 5 KN/sec or 0.22 N/mm2/sec. the oil pressure valve is closed then the compression testing machine is switched on. The top platen of the compression testing machine is brought into contact with the surface of the cube specimen, then operate the clutch with suitable rate of loading, the load improvements are displayed in digital screen system. The load was applied until the resistance of the specimen to the increasing load broke down and no higher load was sustained, then the digital screen reading starts moving back, at this stage the pressure valve of the compression testing machine is released then automatically the ultimate load is displayed in the digital screen, and the platens are also loosened, now crushed
106
specimen is removed from compression testing machine, and the maximum load applied to the specimen is noted down. The same procedure is repeated for testing all other test specimens.
3.5.3 Compressive Strength Results : The compressive strength of the specimen was calculated by dividing the maximum load applied on the specimen during the test by the cross sectional area, for this purpose at least three specimens of same batch are required. In the present investigation three grades of (i.e., M30, M40 , M50 ,M60& M70) of concrete mixes are tried for different cements like OPC and OPC replaced with 22% Fly ash. The casted specimens are tested for both accelerated curing and normal wet curing purpose (i.e., 7 and 28 days) as described above.
TESTING OF SPECIMENS IN COPESSIVE TESTING MACHINE
107
CHAPTER - 4 Presentation of Results 4.1 General : The present experimental investigation mainly found that a correlation exists between the results obtained on concrete specimens, cured by accelerated curing method and cured by normal curing method for mixes of M 30, M40, M50 , M60 &M70 with OPC and OPC replaced by 22% fly ash. The test results obtained by accelerating curing test and normal curing test of 28 days of the above cements used specimens have been correlated and different correlation curves are obtained for different cements. The details are presented in the form of tables and graphs.
4.2 Details of Tables. The specimens of various concrete grades of OPC and OPC replaced with 22% fly ash have been cured and tasted for accelerated curing test, 7 days and 28 days of normal curing test. The test results are tabulated in tables
4.1 to 4.2. The
compassion of accelerated curing strength of OPC used concrete with other cements used concrete like OPC and 22% of OPC replaced with fly ash are tabulated in table 4.3 . The Comparison of 7 days strength of OPC used concrete with other cements used concrete like opc and 22% OPC replaced with fly ash are tabulated in tables 4.4. The comparison of 28 days strength of OPC used concrete with other cements used concrete like 22% OPC replaced with Fly ash are tabulated in tables 4.5 The comparison of Accelerated curing strength with 28 days normal curing strength for different grades of concreted made with OPC and OPC replaced with 22% Fly ash are tabulated in tables 4.6 & 4.7.
4.3
Graphs :
108
A comparison graphs for accelerated strength, 7 days and 28 days strength for M30, M40, M50 , M60, &M70 grades of concrete made different cements like OPC and 22% of OPC replaced with Fly ash are shown in figures 4.1 to 4.2.
Relation graph is plotted with accelerated curing strength and 7 days normal curing for concrete used with different cements like OPC and OPC replaced with 22% Fly ash. Analytical expression developed to estimate the strength of concrete at 28 days from accelerated curing strength based on experimental results was shown in figures 4.4 . Graphs are plotted with experimental 28 days normal curing strength and analytical 28 days strength for concrete used with different cements like PPC, OPC and OPC replaced with 20% fly ash and the rank correlation factor arrived and shown in fig.4.5
Table No. 4.1 Compressive Strength results for different grades of concrete used with Ordinary Portland Cement: S.NO
Grade of concrete
Compacting factor
1 2 3 4
M30 M40 M50 M60
0.86 0.87 0.865 0.857
Accelerated Curing Strength (N/mm2) 19.6 24.4 30.2 34.35
5
M70
0.854
38.4
109
Normal curing Strength(N/mm2) 7 Days
28 Days
28.94 35.56 43.45 50.9
40.2 50.8 61.2 70.7
55.62
78.9
Table No. 4.2Compressive Strength results for different grades of concrete used with OPC replaced with 22% Fly ash : S.NO
Grade of concrete
Compacting factor
1 2 3 4
M30 M40 M50 M60
0.85 0.84 0.86 0.85
5
M70
0.87
Accelerated Curing Strength (N/mm2) 16.80 22.4 28.00 33.60 36.20
Normal curing Strength(N/mm2) 7 Days
28 Days
22.70 30.31 36.63 43.68 49.84
32.20 42.10 51.60 62.40 71.20
Table No.4.3: Comparison between Accelerated curing strength for OPC and OPC replaced with 22% fly ash : Sl. No.
Grade of Concrete
Accelerated curing strength with OPC (N/mm2 )
Accelerated curing strength with OPC replaced with 22% Fly ash (N/mm2 )
Percentage of variation in strength
1
M30
19.60
16.80
14.2
2
M40
24.40
22.40
8.19
Average percentage of variation
7.494
5
3
M50
30.20
28.00
7.28
4
M60
34.35
33.60
2.10
M70
38.40
36.20
110
5.70
Table No. 4.4 : Comparison between 7 days curing strength of OPC with OPC replaced with 22% fly ash : Sl. No .
Grade of Concret e
7 Days strength curing strength with OPC (N/mm2 )
7 Days curing strength with OPC Fly Ash (N/mm2 )
Percentage of variation in strength
28.94
22.70
21.56
30.31
14.76
1
M30
2
M40
3
M50
43.45
36.63
15.69
4
M60
50.90
43.68
14.10
5
M70
55.62
49.84
10.39
35.56
Average percentage of variation
15.30
Table No. 4.5 : Comparison between 28 days normal curing strength of OPC with OPC replaced with 22% fly ash: Sl. No .
Grade of 28 Days Concrete normal curing strength with OPC (N/mm2 )
28 Days normal curing strength with OPC 22% Fly Ash (N/mm2 )
Percentage of variation in strength
1
M30
40.2
32.2
19.9
2
M40
50.8
42.1
17.12
3
M50
61.2
51.6
15.68
4
M60
70.7
62.4
11.74
5
M70
78.9
71.2
111
9.76
Average percentage of variation
14.84
Table No. 4.6: Comparison between accelerated curing strength and normal 28days curing strength of OPC for different grades of concrete : S. NO
Grade of concrete
Average Accelerated Curing Strength (N/mm2)
Average Normal 28 days curing Strength (N/mm2)
Percentage of Accelerated Strength in 28 days Normal curing strength
1
M30
19.6
40.2
51.2
2
M40
24.4
50.8
51.96
3
M50
30.2
61.2
50.65
4
M60
34.35
70.7
51.41
5
M70
38.4
78.9
51.33
Average Percentage of Accelerated strength in 28 days normal curing strength
51.31
Table No. 4.7: Comparison between accelerated curing strength and normal 28days curing strength of OPC replaced with 22% fly Ash for different grades of concrete : S. NO
Grade of concrete
Average Accelerated Curing Strength (N/mm2)
Average Normal 28 days curing Strength (N/mm2)
Percentage of Accelerated Strength in 28 days Normal curing strength
1
M30
16.8
32.2
47.82
2
M40
22.4
42.1
46.79
3
M50
28
51.6
45.73
4
M60
33.6
62.4
46.15
36.2
71.2
49.15
5
M70
112
Average Percentage of Accelerated strength in 28 days normal curing strength
47.13
COPRESSIVE STRENGTH OF OPC WITH DIFFERENRTGRADES OF CONCRETE
COMPRESSIVE STRENGTH OF 22% OPC REPLACED WITH FLYASH FOR DIFERENT GRADES OF CONCRETE
RELATION BETWEEN ACCELERATED CURING STRENGTH AND 28-DAY STRENGTH OF OPC
113
RELATION BETWEEN ACCELERATED CURING STRENGTH AND 28-DAY STRENGTH OF OPC+FLYASH
CHAPTER 5 DISCUSSION OF TEST RESULTS 5.1
GENERAL The present investigation has been carried out for predication of 28 days
strength of concrete and used with OPC, OPC replaced with 22% fly ash on the basis of accelerated curing test by boiling water method. The IS Code 9013-1978 specifies a correlation formula and graphical representation for finding 28 days normal curing strength based on accelerated strength for normal cement concrete mixes. This procedure is used for the predication of 28 days normal curing test in hasten manner. The code has not given any reference in the case of concretes blended with admixtures. It is proposed to arrive correlation formula in the case of concrete mixes prepared using OPC and 22% replacement of OPC by fly ash. It is proposed to arrive a correlation formula in the case of OPC and 22% fly ash replaced OPC concrete mixes with this present experimental investigation. Fly ash is a industrial by product contain about 50% of Silica and also pozzolanic in nature and produces cementanious products when mixed with cement during the hydration process. The PPC and fly ash replacement concrete mixes produces lower strength at early ages but it will gain almost full strength at 28 days. The conventional way of determining the strength potential of concrete is a time taking process. In modern construction practices it is inevitable to find out the strength potential of concrete quickly. The sooner results are available the more valuable strength tests become in meeting the twin objects of measuring the variability for quality control purposes and determining compliance with strength specifications. In this context studies have been conducted on accelerated curing of
OPC and OPC replaced with 22% fly ash
concrete mixes. The observations made are as follows.
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5.2 Predicted strength by Accelerated curing of different types of
cements: Table No.4.3
gives the comparison of Accelerated strength between and
0PC& OPC replaced with 22% Fly ash cements based on accelerated curing for various concrete mixes proposed in the present investigation. It is found that the strength obtained through accelerated curing varies from 5.7% to 14.2% with an average of 8% and for OPC replaced 22% Fly ash when compared with OPC strength.
5.3 Predicted strength by 7 days strength for different types of cements. Table No.4.4 gives the comparison of the strength between OPC and OPC replaced with 22% fly ash cements based on 7 days curing for various concrete mixes proposed in the present investigation. IIt is found that the strength obtained through 7 days curing varies from 10.4% to 21.56% with an average of 15.3% and for OPC replaced 22% fly ash when compared with OPC strength.
5.4 Predicted strength by 28 days strength for different types of cements:
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Table No.4.5 gives the comparison of the strength between OPC and OPC replaced with 22% Fly ash cements based on 28 days curing for various concrete mixes proposed in the present investigation. It is found that the strength obtained through 28 days normal curing varies from 9.76% to 19.9% with an average of 19.84% and for OPC replaced 22% fly ash when compared with OPC strength.
5.5 Comparison between accelerated curing strength and 28days
normal curing strength of OPC for different grades of concrete: Table No.4.6gives the comparison between Accelerated curing strength and 28 days normal curing strength of OPC for different grades of concrete. It is found that the percentage of accelerated strength in 28 days normal curing strength is of 51.33% to 51.96% with an average of 51.31% for OPC.
5.6 Comparison between accelerated curing strength and 28days
normal curing strength of OPC replaced with 22% fly Ash for different grades of concrete: Table No.4.7 gives the comparison between Accelerated curing strength and 28 days normal curing strength of OPC replaced with 20% Fly ash for different grades of concrete. It is found that the percentage of accelerated strength in 28 days normal curing strength is of 45.73to 47.82% with an average of 47.13% for OPC 22%Replaced with flyash.
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5.8 Relation between Accelerated curing strength and normal curing
strength of OPC,and OPC replaced with 22% fly ash Concrete. Experimental investigation have been carried out for different concrete mixes such as OPC and OPC replaced with 22% Fly ash through accelerate curing as well as normal curing and their strengths are tabulated vide table No.4.1 & 4.2 analyzed through graphical manner and obtained different relation ships for the above different concrete mixes and are shown in form of graph fig No.4.3 &ig No.4.4 The above experimental results were analyzed and correlated to IS codel recommendation and arrived analytical formula for different types of cements which was given in table No. 5.1. The rank co- relation factors calculated with the experimental results was also shown in fig. 4.5to 4.6and also mentioned in the same table.
Table No. 5.1 Sl. No.
1
Type of mix with
OPC OPC replaced with 22% fly ash
2
Analytical expression for predicted 28 days strength (N/mm2)
Rank correlation factor
2.0428Ra + 0.3227
0.9988
1.9424 Ra+1.3204
0.9898
3
It is revealed from the above observation the accelerated curing strength can also be achieved for blended cement concrete mixes.
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The present Project is useful in prediction of strength through accelerated curing methods for OPC and OPC replaced with 22% fly ash concrete mixes and can be assured through relationships arrived analytically through experimental investigations. CHAPTER 6 CONCLUSION Based on the present experimental investigations. The following conclusions are arrived. 1.
For OPC replaced with 22% fly ash the accelerated curing strength varies from 5.7% to 14.2% with an average of 7.5%. When compared with accelerated
curing strength of OP cement for different grades of concrete. 2.
The 7 days strength of OP Cement replaced with 22% fly ash varies from 10.39% to 21.56% with an average of 15.3%. When compared with 7 days
strength of OP cement for different grades of concrete. 3.
The 28 days strength of OPC replaced with 22% fly ash varies from 9.76% to 19.9% with average of 14.84%. When compared with 28 days strength of OP cement for different grades of concrete.
4..
The percentage of accelerated strength in 28 days normal curing strength is of 51.33to 51.96% with an average of 51.31% for OPC.
5.
The percentage of accelerated strength in 28 days normal curing strength is of 45.73to 49.15% with an average of 47.13% for OPC replaced with 22% Fly
Ash. 6
A regression analysis showed that the relationship between the 28 days strength and the accelerated strengths can be expressed by linear equation for different types of cements also as follows. i)
For 0PC
R28 =2.0428Ra + 0.3227
ii)
OPC replaced with 22% fly ash R28 =1.9424 Ra+1.3204
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