Arjstcce 02 002

Advanced Research Journals of Science and Technology

ADVANCED RESEARCH JOURNALS OF SCIENCE AND TECHNOLOGY

(ARJST)

EXPERIMENTAL STUDY ON STRESS STRAIN BEHAVIOR OF RECYCLED AGGREGATE CONCRETE

2349-3645

Dhanavath Gopal1, M Rajshekar Reddy2, K Mythili3, 1 Research Scholar, Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad, India.

2 Assistant professor , Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad, India.

3 Assistant professor , Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad, India.

Abstract In this paper, the compressive strength and the stress–strain curve (SSC) of recycled aggregate concrete (RAC) with different replacement percentages of recycled coarse aggregate (RCA) are investigated experimentally. Concrete specimens were fabricated and tested with different RCA replacement percentages of 0%, 20%, 40%, 60%, 80% and , respectively.

Uniaxial compression loading is applied in the experiments. Special attention of the analysis is devoted to the failure behaviour and the influences of the RCA contents on the compressive strength, the elastic modulus, the peak and the ultimate strains of RAC. Analytical expressions for the peak strain and the stress–strain relationship of RAC are given, which can be directly used in theoretical and numerical analysis as well as practical engineering design of RAC structures.

*Corresponding Author: Dhanavath Gopal, Research Scholar, Department Of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad, India.

Published: December 10, 2015 Review Type: peer reviewed Volume: II, Issue : II Citation: Dhanavath Gopal,Research Scholar (2015) EXPERIMENTAL STUDY ON STRESS STRAIN BEHAVIOR OF RECYCLED AGGREGATE CONCRETE

INTRODUCTION Recycling of waste concrete is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. For the effective utilization of waste concrete, it is necessary to use waste concrete as recycled aggregates for new concrete. To make this technology feasible, a significant amount of experimental works has been carried out. Various investigations mainly engaged in the processing of demolished concrete, the mixture design, the physical and the mechanical properties as well as the durability aspects. It is shown that some properties of recycled aggregate concrete (RAC) may be generally lower than those of normal concrete (NC), but they are still sufficient for some practical applications in Civil Engineering.

The most important mechanical properties of RAC are the compressive strength, the tensile and the flexural strengths, the bond strength and the elastic modulus of such concrete. In particular, the stress–strain relation of RAC is especially important in theoretical and numerical analysis as well as engineering design of RAC structures. The peak value of the stress–strain curve yields the compressive strength, and the area under the descending portion of the curve provides a measure of the toughness resistance of RAC. The descending portion of the stress– strain curve is essential when a RAC structure is subjected to impact, earthquakes, or fatigue loading.

In the past, recycled aggregates were used mainly in low utility applications such as general fill. Recently, these aggregates started to be used for intermediate utility applications such as foundations for building and roads.

Nowadays, the aggregates are used, to a very limited extent, in high utility applications such as for the elements of buildings or structural layers of roads.

The advantages of recycling construction and demolition wastes (C&DW) are numerous: • • • • •

Reduces the amount of C&DW entering landfill sites.

Reduces the use of natural resources in construction.

Contributes to the environment.

Provides a renewable source of construction material.

If used in situ, reduces haulage costs.

CONSTITUENT MATERIALS The major components for finding the stress-strain relation of recycled aggregate concrete are Portland cement, normal aggregates of 20mm and 12mm size, recycled aggregate of 20mm and 12mm sizes, water.

CRUSHING AND SIEVING TECHNOLOGY OF WASTE CONCRETE Hou et al.(2002) designed one cycled aggregate production process with a set of wind grading equipment, which can sieve out the recycled aggregate with 0.15~5mm in diameter ,and it laid a good foundation to use recycled fine aggregate in China. Li et al.(2001)proposed a production process to establish a practical continuous production line, which can produce clean recycled aggregate with different materials and diameters. Xiao et al. (2005) compared and analyzed different production processes for recycled aggregate in different countries and proposed a new production process according to the situation in China. It used manual method to remove reinforced bars and wood in waste concrete because the labor cost in China is relative low and processing big concrete block with machine is difficult. The reycled aggregate with diameter less than 0.5mm is considered as micro-powder because recycled fine aggregate has not been studied in-depth. Fer-

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Advanced Research Journals of Science and Technology

romagnetic separator and separation desk are used to improve the purity of recycled aggregate. Sieving machine is applied to produce recycled aggregate with different diameters. The recycled aggregate with5~31.5mm in diameter is often washed at last.

LITERATURE REVIEW

PROPERTIES OF RECYCLED COARSE AGGREGATE (RCA)

The investigation on recycling of concrete waste was initiated by Glushge in Russia in 1946, and in the following years, a number of experimental investigations have been carried out in 2006.

Xu et al. (2006) compared and analyzed the test results of many scholars, and found that for RCA, the apparent density and stacking density are between 2.31~2.62 (kg/ m3) and1.29~1.47 (kg/m3), water absorption is 4%~10%, crush index is 14.2%~23.1%. Xiao (2008)and Li (2005) investigated on the RCA from primary concrete with different strength, and found that the apparent density of RCA increases with the increase of primary concrete strength. Shen (2006) found that the water absorption for some RCA can be as much as 15%.Li (2004) investigated the properties of RCA systematically and it showed that the bulk density, apparent density and soundness of RCA are lower than that of natural coarse aggregate, while the water absorption, crush index and sediment percentage of RCA are also higher.

MIX RATIO OF RAC Xiao (2008) investigated the approach for the mix design of recycled aggregate concrete (RAC). It is proposed that the proportion of cement, sand and aggregate in RAC can be calculated based on the mix design code for conventional concrete, but the high water adsorption of waste concrete aggregates should be considered and the water should be added together with water content calculated according to the approach for conventional concrete. RAC using this method can meet the requirement of national code on workability and strength. Shi (2001) proposed an approach for the mix design of RAC based on free watercement ratio to solve the problem of high water adsorption of waste concrete aggregate. Total water of RAC comprise of two parts. One part of water all absorbed by RCA is called additional water. The other part of water used for the mortar is called free water. Both of the two methods are used to consider the effect of high water adsorption in waste concrete aggregates COMPRESSIVE STRENGTH OF RAC Li et al. (2006), Tang (2007) and Jin et al. (2008) had conducted experimental investigations on the compressive strength of RAC. The results show that the RCA content has obvious influence on the compressive strength of RAC. The relationship between the RCA replacement percentage and the relative compressive strength, which is defined as the ratio of the compressive strength of RAC to that of RAC with 0% replacement percentage (namely conventional concrete), is shown in Fig.1. It indicates that the compressive strength of RAC decreases with the increase of the RCA replacement percentage. However, the effect on the compressive strength is not obvious when the RCA replacement percentage is less than 30%. A special phenomenon was found by Li et al. (2006) that the compressive strength of RAC with 50% replacement percentage is larger than that of 30%. It needs to further studied to demonstrate it is the real property of RAC or just because the random city of the test. Li et al. (2006) also pointed out that it is quite possible to obtain RAC with a desirable compressive strength by adjusting the waster/cement ratio.

In this chapter research work related to stress-strain relations of recycled aggregates concrete was reported by various authors has been presented in respective sequence.

A study (Bairagi & Kishore 1993) revealed that the replacement ratio [RA/(NA+RA)] has a marked influence on stress-strain relations, particularly at higher ratios, it was found that for concrete containing higher proportions of RA, strain increases at a faster rate than the applied stress.

Another investigation carried out by (Jianzhuang in 2005) focused on failure behaviour and the influences of the RA content on compressive strength, elastic modulus, peak and ultimate strains of RAC. This study revealed that the stress–strain relationship for RAC was quite similar to that of NAC. (Topcu & Guncan 1995) produces complete stress–strain curves for RAC with replacement percentages of 0, 30, 50, 70 and 100%. It was concluded that with the increased amount of RA, values of compressive strength, toughness, elastic energy, plastic energy and the elastic modulus were decreased. Research indicates that the elastic modulus of RAC is about 30% less than NAC concrete attaining equal compressive strength.

It was reported (Khaldoun 2007) that strains at peak compressive stress in RAC were 5.5% larger than in NAC, but would not have significant implications for structural design. Shear strength of concrete depends significantly on the ability of the coarse aggregate to resist shearing stresses. RA used is relatively weaker than NA in most cases and yielded reduced shear strength. Experimental data has shown that for NAC, shear cracks propagate in the hardened cement matrix and around the relatively stronger coarse aggregate. For high strength concrete HSC where the matrix is relatively stronger, shear cracks pass through the matrix as well as the aggregate, forming a smoother crack surface. The modulus of elasticity for RAC has been reported to be in the range of 50-70% of the normal concrete.

Hansen & Narud, in their empirical studies however stated that recycled aggregate gave similar test results to natural aggregates. These researchers concluded that in concretes obtained from waste material the percentage of waste mortar stuck on aggregates changed between 30 and 60 %, and these mortars affected the properties of concrete, elasticity, deformations like creep and shrinkage and, water absorption of aggregate. Such composite mixes required 10 % more water in comparison to natural aggregates. They also stated a decreased workability and loss of slump in a short time With respect to abrasion resistance (Gilpin 2004; Khalaf & DeVenny 2004) reported that recycled aggregates are extensively used in USA, UK and other countries as new material for rigid pavements.

For shrinkage, (Amnon 2003) reported that the shrinkage could be about 0.55-0.8 mm/m, whereas the comparable value for NAC is only 0.30 mm/m. The use of RA in concrete includes a large shrinkage due to the high absorption.

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Advanced Research Journals of Science and Technology

With respect to creep, (Ajdukiewicz & Kilszczewicz 2002) states that some studies have shown that creep of RAC after one year, in a reverse tendency, was about 20% lower than similar NAC. A reduction of up to 10% in the bond strength of the RAC has been reported at 100% RA replacement.

Durability properties can be improved by the use of supplementary cementitious admixtures such as fly ash, condensed silica fume, etc. (Ajdukiewicz & Kilszczewicz 2002; Akash 2007). Concretes made with RAC using RA derived from air-entrained concrete were highly frost resistance, and the carbonation depth of RAC was found to be 1.32.5 times greater than that of the reference concrete.

GENERAL The experimental programme consisted of casting and testing of 54 cube specimens {150x150x150 mm} and 54 cylinder specimens {150x300 mm} with varying percentages of recycled aggregate concrete. The specimens have been tested for compressive strength and stress-strain behavior.

The main objective of this study is to develop stress-strain curves, to investigate compressive strength.

NAME OF THE MATERIAL USED ORDINARY PORTLAND CEMENT 53GRADE COARSE AGGREGATE

AGGREGATES

RECYCLED COARSE AGGREGATE

20mm 10mm 20mm 10mm

FINE AGGREGATE

Cement, fine aggregate, Normal coarse aggregate, recycled coarse aggregate and water are used throughout the investigations, had following properties.

CEMENT

PHYSICAL PROPERTIES OF ORDINARY PORTLAND CEMENT

1 2

Characteristics

IS-specifications (IS:122691987

Standard consistency Setting time in minutes i.Initial setting time ii.Final setting time

Test results

Remarks

Mix design changes accordingly Satisfactory Satisfactory Satisfactory

>27 >37 >53

25.25 37.6 54.0

SIEVE ANALYSIS OF FINE AGGREGATE Weight of sample = 1000gm S.no

1.

2.

3.

IS sieve designation

Weight retained (g)

4.75mm 2.36mm 1.18mm

Percentage retained

Percentage passing

Cumulative percentage retained

20

2

2

98

50

5

7

93

125

12.5

19.5

80.5

4.

600m (microns)

310

31

50.5

49.5

5.

300m (microns)

460

46

96.5

3.5

6.

150m (microns)

35

3.5

100

0

1000

-

-

tal

To-

∑F=275

Total percentage retained, ∑F = 275 Fineness modulus of fine aggregate, ∑ F/100 = 275/100 F.M = 2.75 (this is between acceptable limit of 2.0 and 3.5) By viewing column no.5 (percentage passing) of table, sand confirmed to zone-II of IS:383-1970 classifications.

COARSE AGGREGATE

32.5% >30 <600

Compressive strength in N/mm2 i.3 days ii.7 days iii.28 days

3.12

Tests performed on the fine aggregate yielded the properties of fine aggregate which are given in table

7.

Ordinary Portland cement of grade-53 (source JAYPEE cement) conforming to Indian standards IS: 12269-1987 has been used the present study. The results of the various tests on cement properties are given in table

S.NO

4

3.15

FINE AGGREGATE

MATERIALS USED

CEMENT

Specific gravity

Locally available sand has been used as fine aggregate.

The particle size distribution and properties are given in table 3.3. other foreign matters present in the sand has been separated before use.

EXPERIMENTAL PROGRAMME

CONSTITUENTS

3

112 240

Satisfactory Satisfactory

Locally available crushed stone aggregate of maximum size 20 mm has been used. The properties are listed in table 3.4. coarse aggregate has been sieved through IS: 150-micron sieve to remove dirt and other foreign materials.

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Advanced Research Journals of Science and Technology

SIEVE ANALYSIS OF COARSE AGGREGATE

COMPACTION

Sample taken = 5000gms

For compacting the concrete usual methods of mechanical vibrator such as table vibrator can be used. Table vibrator is the most suitable as it gives proper tendency to align the aggregates in the specimen. A mix generally requires much less vibrations to move the mix and consolidate it into the moulds. The compaction of the specimens have been done on a platform vibrating table.

Sieve no.

Wt retained

80mm

%of wt retained

0

Cumulative % of wt retained

0

0

% passing

100

40mm

0

0

0

100

20mm

2.995

59.9

59.9

41.1

39.8

10mm 4.75mm

1.99 0.015

99.7

0.3

0.3

100

0

2.36mm

0

0

100

0

1.18mm

0

0

100

0

600m

0

0

100

0

300m

0

0

100

0

150m

0

0

100

0

CURING Identification marks have been etched into the specimens after 2 to 3 hours of casting. They are allowed to set in the moulds for 24 hours after which they have been taken out of the moulds and immersed in fresh water for curing for a specified period of time(28 days). The specimens have been then removed from water and stored in a room till their time of testing.

TESTING PROCEDURE

•Fineness modulus of C.A = (cumulative % wt retained)/100 = 7.596 •Fineness modulus should lie between 6-8 for economical mix.

The testing of cubes and cylinder specimens for compressive strengths as well as stress-strain has been done at early ages of 28 days, the following tests were performed in the present research work.

SIEVE ANALYSIS OF RECYCLED COARSE AGGREGATE

Stress-strain behaviour, Compressive strength test.

Equipments used : Compression testing machine.

Compressometer with 2 dial guages.

Sample taken = 5000gms

STRESS-STRAIN BEHAVIOUR Sieve no.

80mm

Wt retained

%of wt retained

0

Cumulative % of wt retained

0

0

% passing

100

40mm

0

0

0

100

20mm

2.995

56.9

58.9

42.1

42.8

99.2

0.8

10mm 4.75mm

1.96

0.3

100

0

2.36mm

0.018 0

0

100

0

1.18mm

0

0

100

0

600m

0

0

100

0

300m

0

0

100

0

150m

0

0

100

0

• Fineness modulus of R.C.A = (cumulative % wt retained)/100 = 6.966 • Fineness modulus should lie between 6-8 for economical mix.

MIXING, COMPACTION AND CURING MIXING After weighting accurately cement, sand , normal coarse aggregate and recycled coarse aggregate these have been mixed to get uniform color. Recycled aggregates is added and mixed such that the recycled aggregate are distributed uniformly throughout. Water has been added to mix and proper mixing is ensured. Balling of lump formation if found anywhere has been lossened to achieve a homogenious mix.

In the present research, specimens have been tested under the 2000 KN capacity compression testing machine (CTM). This machine fulfills the entire requirement for compression testing as per IS: 516-1959.

Specimens stored for curing have been tested immediately on removal from the water, while they are in wet condition. Surface water and grit has been wiped off the specimens. The bearing surfaces of the testing machine also have been wiped clean and any loose sand or other material is removed. Cylinder specimens have been placed centrally in the machine in such a manner that the load is applied to opposite sides of the cylinder as cast that is top and bottom. The load is applied in a continuous and uniform fashion without shock. To get the stress-strain curves, average values of three specimen for each mix have been used.

COMPRESSIVE STRENGTH TEST compressive strength of RAC. The results show that the RCA content has obvious influence on the compressive strength of RAC. The relationship between theRCA replacement percentage and the relative compressive strength, which is defined as theratio of the compressive strength of RAC to that of RAC with 0% replacement percentage(namely conventional concrete), is shown in Fig.It indicates that the compressive strength of RAC decreases with the increase of the RCA replacement percentage. However, the effecton the compressive strength is not obvious when the RCA replacement percentage is less than 30%. A special phenomenon was found by Li et al.

(2006) that the compressive strength of RAC with 50% replacement percentage is larger than that of 30%. It needs to further studied to demonstrate it is the real property of RAC or just because the random city of the test. Li et al.

(2006) also pointed out that it is quite possible to obtain

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Advanced Research Journals of Science and Technology

RAC with a desirable compressive strength by adjusting the waster/cement ratio Compressive strength measurements are primary concern in the testing of normal aggregate concrete and as well as recycled aggregate concrete. In the above same test the maximum loads carried by each specimen during test have been recorded. Compressive strength is calculated by dividing the maximum load obtained by the cross-sectional area of the specimen.

To get the compressive strength, average values of three (cube and cylinder) specimens have been used.

DETAILS OF TESTS Name of test

Size of specimen

No. of mix

No.of specimens for each mix

Total no. of specimens

Compressive strength test

150x150x150 mm cube

3

18

54

Stress strain behaviour

150x300mm cylinder

3

18

54

For M60 Grade S.no

Percentage of recycled aggregate

Compressive strength Mpa

1

plain

52.75

2

20%

45.78

3

40%

48.56

4

60%

48.50

5

80%

52.17

6

100%

44.4

Graphs related to different grades of concrete

RESULTS AND DISCUSSIONS This chapter includes the test result in respect of the recycled aggregate concrete cubes and cylinders. It includes the effect of addition percentage of recycled aggregate to concrete on its compressive strength and stress-strain relationship.

COMPRESSIVE STRENGTH The compressive strength of recycled aggregate concrete has been measured by compression test as per IS: 5161959. The compressive strength for plain and recycled aggregate concrete have been summarized in table 4.1. graph is plotted between percentage of recycled aggregate concrete vs. compressive strength for chosen percentage of recycled aggregate concrete as shown in fig .

CUBE COMPRESSIVE STRENGTH OF CONCRETE AT 28 DAYS CURING PERIOD For M20 Grade S.no

Percentage of recycled aggregate

Compressive strength Mpa

1

plain

44.4

2

20%

41.6

3

40%

38.5

4

60%

45.1

5

80%

43.83

6

100%

31.3

S.no

Percentage of recycled aggregate

Compressive strength Mpa

1

plain

52.75

2

20%

42.18

3

40%

48

4

60%

50.78

5

80%

41.6

6

100%

43.8

For M40 Grade

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PHOTOS

Photograph showing casting of specimen CURING OF TEST SPECIMENS

Photograph showing casting of specimen Photograph showing the testing of cylinder and cubes specimen

Photograph showing casting of specimen

Photograph showing casting of specimen Photographs showing the cubes and cylinders after test in

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Advanced Research Journals of Science and Technology

CONCLUSIONS The following conclusions can be drawn from the present study • The complete stress-strain of M20, M40, M60 grades with different replacement percentage of Recycled Aggregate Concrete (RAC) is obtained by the experiment, and the shape of the complete stress-strain of RCA of is similar with that of Normal Aggregate Concrete(NAC), but the peak strain of RAC is much higher than that of NAC. •The addition of Recycled coarse aggregate (RCA) in M20, M40, M60 grades with different percentages(20%,40%,60%,80% nd 100%) there was a decrease in compressive strength of concrete.

•The ultimate stress (σu) of M20, M40, M60 grades of concrete was decreasing from 0% replacement to 100% replacement of RAC.

8. Igarashi, S., Bentur, A., Mindess, S. (1996), “Microhardness testing of cementitious materials.” AdvancedCement Based Materials, 4(2): 48 – 57.

9. Etxeberria, M., Vazquez, E., Mari, A., Barra, M. (2007), “Influence of amount of recycled coarse aggregates and production process on properties of recycled aggregate concrete.” Cement and Concrete Research, 37(5): 735 – 742.

10. R.K. Dhir, M.C. Limbachiya, Suitability of recycled aggregate for use in BS5328 designated mixes, Proc.-Inst.

Civ. Eng. 134 (3) (1999) 257– 274.

11. R.S. Ravindrarajah, C.T. Tam, Properties of concrete made with crushed concrete as coarse aggregate, Mag. Concr. Res. 37 (130) (1985) 29–38.

AUTHOR

•The strain corresponding to ultimate stress (€p) of M20, M40, M60 grades of concrete was increasing from 0% replacement to 100% replacement of RAC. •The breaking stress (σb) after the peak stress of M20, M40, M60 grades of concrete are decreasing from 0% replacement to 100% replacement of RAC. •The ultimate strain (€u) ) of M20, M40, M60 grades of concrete was decreasing from 0% replacement to 100% replacement of RAC. REFERENCES

Dhanavath Gopal Research Scholar, Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad, India.

1. Ajdukiewicz, A.B., Kliszczewicz, A.T. (2007), “Comparative tests of beams and columns made of recycledaggregate concrete and natural aggregate concrete.” Journal of Advanced Concrete Technology, 5(2): 259 – 273.

2. Asnani, P.U. (1996), “Municipal solid waste management in India.” Proceedings of the waste management workshop, 24-28 June 1996, Nicosia, Cyprus.

3. Bairagi, N.K., Kishore, R., Pareek, V.K. (1993), “Behaviour of concrete with different proportions of natural and recycled aggregates.” Resources Conservation and Recycling, 9(1-2): 109 – 126.

4. Hansen, T.C. (1985), “Recycled aggregates and recycled aggregate concrete second state of art report developments 1945 – 9185.” RILEM Technical Committee - 37 - DRC. 5. Sagoe-Crentsil, K.K., Brown, T., Taylor, A.H. (2001), “Performance of concrete made with commercially produced coarse recycled aggregates.” Cement and Concrete Research, 31(5): 707 – 712.

6. Rao, A., Jha, K.N., Misra, S. (2006), “Use of aggregates from recycled construction and demolition waste in concrete.” Resources, Conservation and Recycling, 50(1): 71 – 81.

M Rajshekar Reddy Assistant Professor, Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad, India.

K Mythili Assistant Professor, Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad, India.

7. Padmini, A.K., Ramamurthy, K., Mathews, M.S. (2009), “Influence of parent concrete on the properties of recycled aggregate concrete.” Construction and Building Materials, 23(2): 829 – 836.

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