International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
International Journal of Research and Innovation in Civil and Construction Engineering (IJRICCE) AN EXPERIMENTAL ANALYSIS ON PROPERTIES OF RECYCLED AGGREGATE CONCRETE WITH SUPPLEMENTARY MINERAL ADMIXTURES Tiramdas Manisha1, A.Karthik2. 1 Research Scholar, Department of Civil Engineering, Aurora’s Technological and Research Institute, Hyderabad, India. 2 Sr. Assistant professor , Department of Civil Engineering, Aurora’s Technological and Research Institute, Hyderabad, India.
Abstract Nowadays protection & pollution of environment is the major problem of our society. In Construction and Demolition (C&D) sector, huge amount of waste materials are produced. Aggregates, mortar mixture are wasted, though these are used in land fill, back fill, sub-base course roads. Still, a huge amount of this waste is unused. On the other side, quarrying the rocks for stones and digging the sand reaches has been happening which is causing severe energy and environmental loss. Natural Resources are diminishing rapidly. There is a need to protect the natural resources and recycle the C&D waste through more research and studies on them. Research on Recycled aggregates, as a replacement of the natural aggregates was carried out vigorously in 20th century. In this project, the potential benefits and drawbacks of using recycled aggregate in concrete have been extensively studied. The use of recycled aggregate generally increases the drying shrinkage, creep and water absorptivity and decreases the compressive strength and modulus of elasticity of concrete compared to those of natural aggregate concrete. When Recycled Aggregate Concrete (RAC) mixed with admixtures such as Fly ash/Silica fume, these properties are improved. Fly Ash is a by-product of the combustion of pulverized coal in electric power generation plants. Silica fume is a byproduct of producing silicon metal or ferrosilicon alloys. Because of its chemical and physical properties, it is a very reactive pozzolana. Concrete containing silica fume can have very high strength and can be very durable. In this project, Mix design of concrete as per Indian code IS: 10262-1982 will be adopted. By trial and error method for M-30 mix, amount of the concrete proportions are calculated. Cement will be replaced by 10% admixture (Fly ash/Silica fume) in each case. Recycled aggregates of 0%, 20%, 50% and 100% are to be replaced, in place of coarse aggregates. Properties of fresh and hardened RAC with admixture are to be tested as per IS codes and are compared. Key words: Recycled aggregate (RA), Natural aggregate (NA), Fly ash (FA), Silica fume (SF), M-30 design mix, Workability, Compressive strength, Split tensile strength. *Corresponding Author: Tiramdas Manisha, Research Scholar, Department of Civil Engineering, Aurora’s Technological and Research Institute, Hyderabad, India. Email: manishatiramdas@gmail.com
Year of publication: 2016 Review Type: peer reviewed Volume: III, Issue : I Citation: Tiramdas Manisha, Research Scholar, "An Experimental Analysis on Properties of Recycled Aggregate Concrete With Supplementary Mineral Admixtures" International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET) (2016) 247-254
INTRODUCTION Due to modernization, demolished materials are dumped on land & not used for any purpose. Such situations affect the fertility of land. As per report of Hindu online of March 2007, India generates 23.75 million tons demolition waste annually. As per report of Central Pollution Control Board (CPCB) Delhi, in India, 48million tons solid waste is produced out of which 14.5 million ton waste is generated from the construction waste sector, of them only 3% waste is used for embankment. Out of the total construction demolition waste, 40% is of concrete, 30% ceramic, 5% plastics, 10% wood, 5%metal, & 10% other mixtures.
As per Hindu article 2014, India’s first plant (at Delhi) that recycles construction waste has saved 15.4 lakh tones of debris, which was supposed to be dumped on the land causing severe land pollution. Much research has been made to improve the quality of Recycled Aggregate Concrete (RAC). By different mixing approaches like pre-soaked slurry mix, two stage mixing approach (TSMA), heat treatment, the performance of RAC can be enhanced. Steam curing can give early strength but after 90 days its effect is normal. By supplementing admixtures such as fly ash, silica fume, ground granulated blast furnace slag GGBS, rice husk ash, super plasticizers etc to some percent in the place of cement, the strength of the RAC can be improved. This thesis focuses on properties of recycled aggregate (RA) which are replaced by 20%, 50%, 100% coarse aggregates (RA20, RA50, RA 100) in structural concrete which are mixed with mineral admixtures(10% replacement of cement). Concrete: Concrete usually contains 60-70% coarse aggregates, 1525% fine aggregate and 10-15% cement. The shape, size, surface texture, water absorption, abrasion and impact values are very important basic properties to make the concrete perform better.
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For concrete to be good concrete it has to be satisfactory in its hardened state and also in its fresh state while being transported from the mixer and placed in the formwork. The requirements in the fresh state are that the consistence of the mix is such that the concrete can be compacted and also that the mix is cohesive enough to be transported and placed without segregation. As far as the hardened state is considered, the usual requirement is a satisfactory compressive strength. Many properties of concrete are related to its compressive strength such as density, impermeability, durability, resistance to abrasion, resistance to impact, tensile strength, and resistance to sulphates. Recycled Aggregate Concrete The concrete containing cement, sand, new and used coarse aggregates, water is termed to be Recycled aggregate concrete (RAC). The recycled aggregates can be obtained from the construction and demolition (C&D) waste. They are available in cheap price. If unused, they are dumped on the land (landfill) creating land pollution. New aggregates are quarried and used extensively. Due to this natural resource of aggregates (rocks) is diminishing rapidly creating ecological imbalance. RAC Applications Traditionally, the application of recycled aggregate is used as landfill. Recently, the applications of recycled aggregate in construction areas are wide. The applications differ from country to country. The recycled aggregates are used in non-structural applications such as concrete kerb and gutter mix, granular base course materials, embankment filling, paving blocks, backfill materials, building blocks. Admixtures IS: 1343 - 1980 allows using admixtures that conform to IS: 9103 - 1999, Concrete Admixtures Specification. The admixtures can be broadly divided into two types: chemical admixtures and mineral admixtures. In this project mineral admixtures class F Fly ash and Silica fume are used. Cost of fly ash and silica fume in local Indian market Approximate price of Fly ash in India (2016) is Rs 700 / metric ton. For 1 Kg, fly ash cost is less than 1 Rupee, whereas cement 50 kg bag costs around Rs 350/- (1 Kg Cement approximate cost is around Rs 7/-) Finer the silica fume, the cost will appear more. Approximate price of Silica fume in India (2016) is Rs 10/- to 30/per Kg. The cost is more when compared with cement but the recycled aggregate concrete with this supplement performed well. Fly ash is a cheaper by-product. In economical point of view and for exhibiting good properties with cement, fly ash is used extensively in construction industry. Research Objectives The principle objective of this thesis is to improve the RAC properties which can be used for structural applications. Addition of admixtures in RAC may show enhanced behavior in strength and durability properties.
This study is conducted to analyze the fresh and hardened properties of RAC made with different recycled coarse aggregate (RA) replacement levels with those of natural aggregate concrete (NAC) by considering M-30 design mix. Investigating the potential of fly ash / silica fume in recycled aggregate concrete and comparisons are to be made between the properties of two admixtures in the Recycled aggregate concrete and will suggest the best mix. LITERATURE REVIEW The literature review presents the current state of knowledge and examples of successful uses of alternative materials in concrete technology, and in particular the use of Recycled aggregate (RA) as a coarse aggregate fraction in nonstructural and structural concrete. Many researchers have dedicated their work to describe the properties of these kinds of aggregate, the minimum requirements for their utilisation in concrete and the properties of concretes made with recycle aggregates. Initial slump: Poon et al. (2004) studied the moisture condition of the aggregate on initial slump, showed that the initial slump of recycled aggregate concrete was significantly affected by the moisture condition of aggregates. Ismail and Ramli (2013) pre-soaked the RAC in acid of different molarity and studied the slump values of both treated and untreated RCA, no significant difference in the slump values was observed. It has been reported that angular and rough surface of RCA decreases the slump values as compared to natural aggregates concrete. In accordance with Hansen et al. (1983) and Ravindrarajah et al. (1985), recycled aggregate concrete made with recycled coarse aggregates and natural sand needs 5% more water than conventional concrete in order to obtain the same workability. If the sand was also recycled, 15% more amount of water was necessary to obtain the same workability. Compressive strength: The most of authors reported that fresh and hardened properties of different mix grade RAC are lower than the Natural aggregate concrete such as Katz et al.(2003) concluded that the Concrete made with 100% recycled aggregates was weaker than concrete made with natural aggregates at the same w/c ratio. Tam et al. (2005) experimentally shows that the two-stage mixing approach can provide an effective method for enhancing harden properties [compressive strength, splitting tensile strength and flexural strength] and durability properties [creep, shrinkage, permeability, chloride penetration] and other mechanical performance. Kou et al. (2012) used commercial recycled aggregates at 0%, 25%, 50% and 100% replacement levels on natural aggregates. At 28 days the compressive strength of 100% recycled aggregate concrete was 12.2% lower than natural aggregate concrete. After 90 days the values of recycled aggregate concrete was better and even more at 20% replacement level of natural aggregate. Yang et al (2008) had shown inverse relationship between compressive strength and water absorption in RAC. If water absorption of recycled aggregate is more, compressive
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strength of that concrete is less. Frondistou-Yannas (n.d) in their study shown that there is a decrease in compressive strength of recycled aggregate concrete (RAC) of about 4-14% when compared with NAC. Dibas et al. (2014) investigated recycled aggregate concrete with silica fume for compressive strength. Two types of recycled aggregates were used, composed of concrete, tiles and bricks. The replacement levels of aggregates were 30% and 40%, later both types were used simultaneously taking replacement of 70%. Silica fume replaced was 5% and 10% by weight of cement. The results showed that impurities in recycled aggregates can reduce the effect of silica fume. Despite that concrete containing separate recycled aggregates exhibited good results using 5% and 10% silica fume when compared with traditional concrete Split Tensile Strength: Dabhade (2014) by taking two w/c ratios such as 0.38 and 0.45 and using 53 OPC cement and zone-2 sand stated that up to 40% RA and 10% fly ash yields good tensile strength when compared with natural aggregate concrete. He also stated that RAC based concrete with 10% fly ash gives higher compressive strength than natural RAC based concrete in 90 days. This may due to bonding between the old mortar and fly ash. Lima et al. (2013) presented the splitting tensile strength property of concrete made with recycled aggregate and fly ash. The percentage of recycled aggregates was 30, 60 and 100. Both coarse and fine recycled aggregates were used in concrete mixtures. To keep the water available for chemical reaction constant, extra amount of water was added in various mixes calculated from water absorption capacity of aggregates. The content of fly ash was kept as “Low”, “Medium” and “High”. The specimens containing 60% and 100% recycled aggregates showed strong reduction in tensile strength. Addition of medium level of fly ash at 30% recycled aggregates gave the best values in recycled aggregate concrete mix. Need of the Present Investigation A review of literature presented shows that recycled aggregates are being investigated for proper use in concrete. The total use of recycled aggregates in concrete with positive results has been done in very few studies. Moreover the strength values of mineral admixtures such as fly ash and silica fume, when replaced (10%) in the place of cement in recycled aggregate concrete (RAC) have not been mutually analyzed. In this thesis, the strength properties are analyzed and it will suggest the best mix to obtain M-30 concrete strength, which can be used for structural applications.
Jaw Crusher used for crushing of old concrete
Code IS 3812-1 (2003) gives standards specifications on properties of Fly ash. Class C and Class F fly ash which differ by CaO percentage. IS 456 (2000) suggests maximum of 30% fly ash replacement of cement can be taken. Code IS 15388 gives standards on properties of silica fume. Usually 5%-15% of silica fume replacement in place of cement constitutes good results. Interfacial transition zone will be improves because of the fineness and surface area of silica fume. It gives the dense mixture when mixed with cement and fills the voids to a greater extent, thereby improving strength characteristics. Mix design (Procedure IS 10262:2009) For M-30 design mix, we have to mix the proportions as per desired slump and target mean strength. Casting of Specimens Moulds: The mould shall be of metal, preferably steel or cast iron, and stout enough to prevent distortion. It shall be constructed in such a manner so as to facilitate the removal of the moulded specimen without damage, and shall be so machined that, when it is assembled ready for use, the dimensions and internal faces shall be accurate as per the limits stated in the code IS 516 (1959). Concrete is poured into the moulds and are vibrated so as to minimize voids. They are hardened for 1 day and the iron moulds are removed. The concrete cubes and cylinders are cured in the water at a temperature of 27° ± 2°C. They are taken out for testing of strengths at 7 days and 28 days.
METHODOLOGY General Properties such as Specific gravity, water absorption, fineness modulus, Los Angels Abrasion value, Crushing value are to be obtained through tests which are conducted according to the code IS: 2386 (Part I, III)-1963. The aggregates are cleaned properly so as to remove the chemicals, dust attached to it. The surface texture is rough and the shape of the 70% recycled aggregates is angular. Sieve analysis is carried out. 20mm maximum nominal size is taken.
Empty150mm*150mm size cube moulds
Cylindrical 150mm dia*300mm long
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bution of this applied load and to reduce the magnitude of the high compressive stresses near the points of application of this load. Concrete cylinder split into two halves along this vertical plane due to indirect tensile stress generated by Poisson’s effect. Split tensile strength is calculated by the formula Split-tensile strength Fck=2P/πLd where P is the maximum load (in N) L is the average measured length of the specimen (in mm) d is the cross sectional diameter of the specimen (in mm) 1. Curing site 2. Collecting concrete cubes and cylinders
Testing of Specimens Workability Workability means simplicity in relocating concrete and how much it opposes segregation. It is determined via slump test and confirmed via its consistency. Procedure for Slump test: Slump cone of 100mm*200mm*300mm. Fresh concrete mixture is taken into the Slump cone by 3 levels. Each level is tamped 25 times. On immediate lifting of the cone, the shape obtained is noted: true, shear, collapse..etc. The depth of the concrete which is spread towards bottom is taken as the value of slump Compressive strength Test The cubes of size 150x150x150mm were casted. After 24 hours, the specimens are removed from the moulds and subjected to curing for 7 days and 28 days in portable water. Procedure - Specimens stored in water shall be tested immediately on removal from the water and while they are still in the wet condition. Surface water and grit shall be wiped off the specimens and any projecting fins removed. Loads are applied at a constant increasing rate as per IS 516:1959, Compressive strength is calculated using the following formula Compressive strength (N/mm2) = P/A Where, P = Maximum applied load just before load, (N) A = Plan area of cube mould, (mm2)
EXPERIMENTAL WORK Materials and its properties: Cement Cement used in this experiment is Ordinary Portland Cement grade 43 maintaining IS 8112 (1989) Standards. Specific gravity of cement obtained is 3.12. Sand By sieve analysis, well graded sand belonging to zone-2 of IS 383 (1970) is used in these tests. Physical properties of fine aggregates Property
Fine Aggregate
Specific Gravity
2.68
Fineness Modulus
3.61%
Bulk Density
1436 Kg/m3
Coarse Aggregate Maximum nominal size of aggregate used is 20mm. These are crushed from granite rocks. Sieve analysis is carried out and the properties of aggregates are according to the code IS 383 (1970). Recycled Aggregate Recycled aggregates are obtained from the 40 year old demolished building in Hyderabad. The aggregates are adhered to the old mortar. These aggregates are taken in the jaw crusher to remove the old mortar surrounded on the aggregate in the lab.
Split-Cylinder Test It is the standard test, to determine the tensile strength of concrete in an indirect way. This test could be performed in accordance with IS 5916:1970. The cylinders are of size 150 mm diameter and 300mm length are casted. After 24 hours, the specimens are removed from the moulds and subjected to curing for 28 days in portable water. Surface water and grit shall be wiped off the specimens and any projecting fins removed. The concrete cylinders are placed horizontally between the loading surfaces of Universal Testing machine. The compression load is applied diametrically and uniformly along the length of cylinder until the failure of the cylinder is along the vertical diameter. To allow the uniform distri-
Recycled aggregates
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International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
Physical properties of the recycled and natural coarse aggregate Property
Coarse Aggregate
Recycled Aggregate
Remarks
Specific Gravity
2.72
2.3
Water absorption
0.6%
5.7%
Bulk Density
1460 Kg/m3
1228 Kg/m3
Los Angel’s Abrasion value
14.5%
25.67%
<30% O.K (IS 383: 1970)
Crushing value
18.89%
23.5
<30% O.K (IS 383: 1970)
Finenes modulus
2.41%
2.48%
Step 3: Take W/C = 0.40 (By 3rd trial and error method) From table 2 of IS 10262: 2009, For 20mm aggregate, Maximum water content = 186kg For that target slump,
RA>CA
Admixtures
We obtained water content = 172 Kg Therefore, cement content = 172/0.4 = 430 Kg/m3 (O.K) Note: Cement content should not exceed 450 Kg/m3 as per clause 8.2.4.2 in IS 456:2000 Step 4: From table 3 of IS 10262:2009, Volume of coarse aggregate in total aggregate is taken as 0.62. (Sand conforming to zone-2) Volume of Fine aggregate in total aggregate = 1- 0.62= 0.38 Volume of concrete = 1 m3
Fly ash Class F fly ash taken which is as per IS 3812-1 (2003) Specific gravity = 2.15 Fines passing 150 micron sieve = 99.2% Fines passing 90 micron sieve = 97 % Silica fume Silica fume with specific surface area 20,000 m2/Kg and maximum particle size 0.1 micron is taken. Its Specific gravity is around 2.2. Water Normal water without any injurious amounts of oils, acids, alkalis, salts, sugar, organic materials or other substances that may be deleterious to concrete/steel is considered. pH of water used is more than 6. Okay to use as per IS 456 (2000). Design procedure For M-30 Design mix, as per code IS 10262 (2009) Step 1: Assumed std. deviation = 5 N/mm2 Target mean compressive strength (Ft) Ft = Fck + 1.65S = 38.25 N/mm2 Step 2: Stipulations for proportioning a) Grade Designation=M30 b) Type of cement: OPC 43 grade conforming to IS 8112(1989) c) Max Nominal size of aggregate = 20mm d) Min. Cement content = 320 Kg/m3 ( Table 4 and 5, IS 456 (2000)) e) Max. Cement content = 450 Kg/m3 f) Max. W/C ratio = 0.45 g) Workability = 60mm (target slump) h) Exposure condition = severe i) Type of aggregate = crushed angular aggregate.
Step 5: Mass of Coarse aggregate = e*Volume of C.A*Specific gravity of C.A*1000 = 0.691 * 0.62 * 2.72 * 1000 = 1165.302 Kg Mass of Fine aggregate = e*Volume of F.A*Specific Gravity of F.A*1000 = 0.691 * 0.38 * 2.68 * 1000 = 703.714 Kg Therefore, Cement: 430kg; F.A = 703.714 Kg; C.A = 1165.302 Kg are found in 3rd trial mix for w/c at 0.4. Mix proportion of control sample The period of mixing shall be not less than 2 minutes after all the materials are in the drum, and shall continue till the resulting concrete is uniform in appearance. 1:1.64:2.71 was obtained for M-30 mix for the desired slump of 60mm at w/c ratio 0.4 For each test, average of 3 specimen test values are taken. Therefore for 0%, 20%, 50% and 100% replacement with recycled aggregate, a total of 12*2 = 24 cubes casted (7days and 28days). Similarly for RAC(10% FA) and for RAC(10% SF), a total of 48 cubes casted. 48 Cylindrical moulds are casted to test split-tensile strengths. RESULTS Workability Slump values RAC
Slump
RA 0%
60mm
RA 20%
56mm
RA 50%
49mm
RA 100%
44mm
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International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
Compressive strength
Analysis of Strength values between RAC and NAC
Compressive strength of NAC (Natural Aggregate Concrete) 1. 7days curing strength = 23.34 N/mm2 2. 28days curing strength = 40.81 N/mm2
i) The tested strength value of RAC is less, when compared with NACâ&#x20AC;&#x2122;s. The compressive strength of NAC at 7 and 28 days are 23.34 and 40.81 N/mm2 respectively. ii) The average decrease in strength of RAC (20% to 100% RA replacement), when compared with NAC is around 12.51 % (7 days) and 12.17% (28 days). iii) The reason for the decrease in strength of RAC is because of the adhered old mortar and inorganic chemicals on Recycled aggregate. RA used is of high absorption property. iv) Up to 20% replacement of coarse aggregate with the recycled aggregate can be used in the concrete, when normal mixing method and normal curing is adopted. 20% RA taken concrete shown strength of 38.15 N/mm2. The target mean strength for the mix is designed has value 38.25 N/mm2 v) The tensile strength of RAC is less, when compared with NAC. The 28days split tensile strength value of NAC is 3.78 N/mm2 vi) The decrease in split tensile strength of RAC is around 11.91%. This is due to high drying shrinkage and high permeability characteristics of recycled aggregate.
Compressive strength (N/mm2) of specimen at 7 and 28 days RAC
RAC + 10% Fly ash
RAC +10% Silica fume
7 days
28 days
7 days
28 days
7 days
28 days
RA 0%
23.34
40.81
24.21
41.52
24.50
42.90
RA 20%
21.74
38.15
24.46
39.86
24.89
40.36
RA 50%
20.89
36. 67
23.05
37.24
23.43
38.10
RA 100%
18.61
32.70
20.56
36.12
20.61
35.26
Split Tensile Strength Split tensile strength of NAC (Natural Aggregate concrete) of M-30 mix at 28 days obtained as 3.78 N/mm2 Split Tensile Strength (N/mm2) of specimen at 28 days RAC
RAC + 10% Fly ash
RAC + 10% Silica fume
RA 0%
3.78
3.80
3.82
RA 20%
3.54
3.62
3.73
RA 50%
3.31
3.35
RA 100%
3.15
3.20
Variations of Compressive strength (7days and 28days) shown in percentages when compared with NAC (Natural Aggregate Concrete) RAC
3.41
C.C: 7 days (23.34 N/mm2) 28 days (40.81 N/ mm2)
7days
28days
3.28
RA 0%
0%
0%
DISCUSSION
1.RA 20%
-6.85%
-6.15%
2.RA 50%
-10.49%
-10.14%
Effect of Recycled Aggregate, Silica Fume and Fly-ash on Properties of Concrete
3.RA 100%
-20.2%
-19.87%
*Average (1+2+3)
-12.51%
-12.17%
Analysis of physical properties between RA and NA i) Water absorption of Recycled aggregate (RA) is 5.7%, which is less than 6%. It can be used in the concrete for non-structural and structural applications. ii) Natural aggregate has high bulk density (1460 Kg/m3) when compare with Recycled aggregate (1228 Kg/m3). This states that RA is highly porous and permeable. Fineness modulus of RA is more. It is because of the weak aggregate taken from old concrete. Rough and angular stones are obtained from the crushing process. iii) The abrasion value and the crushing value of the RA are more, when compared with NA. The reason is RA (used aggregate) has taken enough loads in the old concrete structure. But the tested values are less than 30%, which are satisfying the code IS 383: 1970.
(* + means increase of strength, - means decrease of strength) Variations of Split Tensile strength 28days shown in percentages when compared with NAC (Natural Aggregate Concrete) C.C (28 days) = 3.78 N/mm2
RAC 28 Days
RA 0%
0%
1.RA 20%
-6.34%
2.RA 50%
-12.43%
3.RA 100%
-16.67%
* Average (1+2+3)
-11.91%
Analysis of Workability property between NAC and RAC
(* + means increase of strength, - means decrease of strength)
i) Slump value of NAC desired and obtained is 60mm, which is a medium slump. On increasing the RA content from 0% to 100%, the slump value decreased from 60mm to 44mm. This decrease is not abnormal. ii) The decreasing nature of RAC slump values is due to use of low quality of RA in the concrete. Due to high water absorption, slump loss is observed.
Analysis of strength values between RAC (10% FA) and RAC (10% SF): i) The compressive strength values of RAC (10% silica fume) are more. But the increasing trend of 100% RA10% FA is more when compared with 100% RA-10% SF. Average increase of 5.83% compressive strength is shown in RAC 10% SF, where as 5.5% increase of compressive strength is shown in RAC 10% FA. ii) The increase is more in silica fume due to its high fineness quality. The surface area of silica fume used is 252
International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
around 20,000 m2/Kg. Even the 0.1micron pore can be filled with silica fume particle. iii) ITZ gets stronger in both cases. This is because these mixtures when reacted with cement and water produce C-S-H gel. The C-S-H gel is very active in RAC 10% SF. iv) The early days (7day) compressive strength of 10% silica fume RAC is more, as stated C-S-H gel is very active. v) In economical point of view, 20% RA replacement and 10% fly ash is best mix which can satisfy the target mean strength ( Fly ash cost is less) vi) 20% RA replacement and 10% silica fume is best mix as it enhances properties of RAC in a faster rate when compared with fly ash. Since silica fume is highly costly when compared with cement, this is used less in construction fields. vii) Split tensile strength of RA 10% SF is quite more (around 4.17%), when compared with RAC 10% FA (around 1.68%). Variations of Compressive strength (7 days and 28 days) shown in percentages when compared with RAC RAC + 10% Fly ash
RAC +10% Silica fume
7 days
28 days
7 days
28 days
RA 0%
+3.73%
+1.74%
+4.97%
+5.12%
1.RA 20%
+12.51%
+4.48%
+14.49%
+5.79%
2.RA 50%
+10.34%
+1.55%
+12.15%
+3.90%
3.RA 100%
+10.47%
+10.45%
+10.8%
+7.82%
*Averagae(1+2+3)
+11.1%
+5.5%
+12.5%
+5.83%
Bar diagram showing 28 days Split-Tensile strength
CONCLUSION 1. In this project, water absorption value of RA obtained is 5.7%, which is more when compared with NA obtained value (0.6%). Recycled aggregates are taken from 40 year old construction debris. Because of high water absorption, RA is highly porous and permeable. 2.Los Angelâ&#x20AC;&#x2122;s Abrasion value and crushing value of RA are in permissible limits as per IS 383:1970 code. 3.In NAC, Slump value obtained is 60mm. RAC (0% RA to 100% RA) with normal mixing approach, Slump value decreased up to 44mm. This implies that RAC has low workability when compared with NAC. This is due to low weight of RA, high water absorption, initial chemical reactions of the cementitious materials, and loss of water by evaporation in RAC.
(* + means increase of strength, - means decrease of strength)
4.Compressive strength of RAC (0% RA to 100% RA) tested values are low. At 28 days, the compressive strength of NAC for design M30 mix (1:1.64:2.71) obtained is 40.81 N/mm2. For 20% RA, the strength value is 38.15 N/ mm2. Up to 20% RA replacement with coarse aggregate is satisfactory for non-structural applications and low-rise buildings. Split tensile strength values of RAC are less, when compared with NAC. 5.For the structural applications, RAC strength values can be improved by adding admixtures, lowering watercement ratio, adopting different mixing and curing techniques.
Bar diagram showing 7days Compressive strength
6.When 10% Fly ash is replaced with cement in RAC (0% RA to 100% RA), though the strength values show decreasing trend, they are better when compared with RAC strengths. For 20% RA-10% FA concrete mix, the 28 days compressive strength is 39.86 N/mm2. This value is more than the target mean strength of concrete (38.25 N/ mm2). The increase in strength is due to fewer voids between cement particles and the aggregate. Concrete mixture becomes dense, when we add the spherical shaped fly ash. The pozzolonic activity of fly ash with cement and its fineness enhances the strength properties. 7.Split tensile strength values of RAC-10% Fly ash are more when compared with RAC strengths. At 28 days curing, 20% RA-10% FA concrete has tensile strength of 3.62 N/mm2, where as 20% RAC has 3.54 N/mm2. The difference in tensile strength values is very less (1.68% more)
Bar diagram showing 28days Compressive strength
8.For 10% silica fume replacement and 20% RA, the compressive strength for 28 days curing is 40.36 N/mm2. At conventional dosage rates, silica fume containing con253
International Journal of Research and Innovation on Science, Engineering and Technology (IJRISET)
crete always has higher strength than ordinary port land cement concrete at a comparable water-cement ratio. This is due to the active C-S-H (calcium-silica-hydrated) gel which is obtained from the reactions of silica fume and concrete mixture on heat of hydration. Interfacial transition zone (ITZ) between them is very stronger as the micro structure of the mixture is free from voids, due to high specific surface area of silica fume. 9.The difference in tensile strength values when compared with RAC is of 4.17% more. The effect of silica fume is most pronounced on strength between 3 and 28 days, after which its influence on strength is minimal. The water required for the chemical reactions between the silica fume and the concrete is used up very rapidly, thereby getting early strength values. 10.Both fly ash and silica fume has the properties to reduce drying shrinkage, creep, permeability, chloride-ion penetration and to increase strength values when added as replacement of cement. IS 456: 2000, suggests maximum of 30% fly ash can be replaced with cement. Silica fume enhances good properties when used in lesser percentages (5%-15%). 11.20% RA-10% FA concrete mixture is better mix for medium strength structural applications of RAC. Also the cost and environmental energy will get reduce on use of fly ash and recycled aggregate. 12. 20% to 30% RA and 10% silica fume is best mix to get the early strengths in a faster rate. REFERENCES 1.Poon C.S., Shui Z.H., Lam L., Fok H., Kou S.C. (2004). “Influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete.” Cement and Concrete Research Vol. 34 pp 31-36.
strength of concrete, Bureau of Indian Standard, New Delhi-2004. 10.IS 456 (2000): Plain and Reinforced Concrete - Code ofPractice [CED 2: Cement and Concrete] 11.IS: 5816-1999: Methods of test for Splitting Tensile Strength of Concrete, Bureau of Indian Standard, New Delhi-1999. 12.IS: 8112-1989 (Reaffirmed 2005): Specification for 43 Grade Ordinary Portland Cement, Bureau of Indian Standard, New Delhi-2005. 13. IS 383 (1970): Specification for Coarse and Fine Aggregates From Natural Sources For Concrete [CED 2: Cement and Concrete] 14.N. Sowmith, P.S.S. Anjaneya Babu, (2016) “Influence of Fly Ash on the Performance of Recycled Aggregate Concrete”, IJSR. Volume 5 Issue 6, June 2016. 15.A.N. Dabhade, S.R. Chaudari and A.R. Gajbhaye “Effect of Flyash on Recycle Coarse Aggregate Concrete” ISSN 2278-3652 Volume 5, Number 1 (2014), pp. 35-42 16.M. Kikuchi, T. Mukai, H. Koizumi, “Properties of concrete products containing recycled aggregate, Demolition and Reuse of Concrete and Masonry: Reuse of Demolition Waste”, Chapman and Hall, London, 1988, pp. 595–604. 17.Gambhir, M. L. (2004). Concrete Technology Third Edition, Tata McGraw Hill Companies.BS
Authors
2.Ismail S., Ramli M. (2013). “Engineering properties of treated recycled concrete aggregate (RCA) for structural applications.” Construction and Building Materials Vol. 44 pp 464-476. 3.Kou S.C., Poon C.S., Agrela F. (2011). “Comparisons of natural and recycled aggregates concretes prepared with the addition of different mineral admixtures.” Cement and Concrete Composites Vol. 33 pp 788-795.
Tiramdas Manisha, Research Scholar, Department of Civil Engineering, Aurora’s Technological and Research Institute, Hyderabad, India.
4.Lima C., Caggiano A., Faella C., Martinelli E., Pepe M., Realfonzo R. (2013). “Physical properties and mechanical behaviour of concrete made with recycled aggregate and fly ash.” Construction and Building Materials Vol. 47 pp 547-559. 5.IS: 10262-1982 (Reaffirmed 2004): Recommended guidelines for concrete mix design, Bureau of Indian Standard, New Delhi-2004. 6.IS: 15388-2003: Silica fume specification, Bureau of Indian Standard, New Delhi-2003.
A.Karthik, Sr. Assistant professor, Department of Civil Engineering, Aurora’s Technological and Research Institute, Hyderabad, India.
7.IS: 2386 (Part I, III)-1963: Methods of Test for Aggregates for Concrete, Bureau of Indian Standard, New Delhi-1963. 8.IS: 383-1970: Specification for Coarse and Fine Aggregates from Natural Sources for Concrete, Bureau of Indian Standard, New Delhi-1970. 9.IS: 516-1959 (Reaffirmed 2004): Methods of tests for
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