Strength parameters of concrete containing recycled aggregate

STRENGTH PARAMETERS OF CONCRETE CONTAINING RECYCLED AGGREGATE Deepa P.R1, Anup joy2 1

2

PG Scholar, Structural Engineering, Sree Buddha College of Engg, Pattoor, Alappuzha, Asst. Professor, Dept of Civil Engg, Sree Buddha College of Engg, Pattoor, Alappuzha, Kerala

Abstract— Concrete is the most extensively used construction material in the world. Demand for concrete as a construction material is increasing day by day. Construction industry utilizes large amount of concrete every day. Since concrete is widely used in construction, there is huge demand for aggregate and cement. It leads to massive exploitation of natural resources and environmental pollution. Utilisation of waste materials in concrete instead of raw materials reduces environmental pollution. This study presents the possibility of producing concrete with recycled aggregate and Ground Granulated Blastfurnace Slag(GGBS). In this experimental study cement is replaced with 10%, 20%, 30% and 40% of GGBS. Fresh and hardened properties of each mixes are studied. With the optimum percentage of GGBS, coarse aggregate is replaced with 10%, 20%, 30% and 40% of recycled aggregate. The results from various tests are compared and found out the optimum percentages of recycled aggregate and GGBS in concrete Keywords—recycled aggregate; Ground Granulated Blastfurnace Slag (GGBS); environmental pollution; natural resources; concrete.

I. INTRODUCTION Construction industry utilizes large amount of concrete every day. It is estimated that 25 billion tonnes of concrete is manufactured each year. Concrete usage around the world is second only to water. The main reason behind its popularity is its high strength and durability. With the advancement of technology and increased field application of concrete and mortar, the strength durability and other characteristics of the ordinary concrete is continually undergoing modifications to make it more suitable for any situation. Concrete is a composite material composed of aggregate, cement and water. The aggregate are bonded together with fluid cement which hardened over time.

Since concrete is widely used in construction, there is huge demand for aggregate and cement. This will causes the scarcity of natural aggregate. On the other hand demolition of old concrete structures are increasing day by day. These demolition wastes are dumped in to the land. It will causes land pollution. Coarse aggregates are the major constituents of this demolished waste. Recycling these aggregate in concrete, requirement of natural aggregate and land pollution can be reduced to some extent. The main ingredient of conventional concrete is ordinary Portland cement, which is not an environment-friendly material. The large amount of energy was also consumed for the cement production. These identified problems clearly, contribute to climate change. Utilisation of supplementary cementitious material is the only solution to reduce cement production.

Ground Granulated Blastfurnace Slag (GGBS) is a by-product of iron and steel industry. It is a glassy, non-metallic granular material which exhibits cementitious properties. It is off-white in colour. GGBS is shown in figure 1. The main constituents of GGBS are CaO, SiO2, Al2O3 and MgO. Increasing the percentage of CaO in the slag results in raised slag basicity and an increase in compressive strength. Use of GGBS in concrete causes high compressive strength, low heat of hydration, resistance to chemical attack, better workability and cost-effectiveness.

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Recycled aggregate is generally produced by crushing of demolished concrete, screening and removal of contaminants. Strength of concrete is affected by type of aggregate used. Recycled aggregate is also called as Recycled Concrete Aggregate (RCA). Recycled aggregate normally has higher water absorption and lower specific gravity. Workability of concrete is decreased with increasing the percentage of recycled aggregate. It is due to the presence of attached mortar. To improve the workability of recycled aggregate concrete one option is to first saturate recycled aggregate to the condition saturated surface dry. Second is to use dried recycled aggregate and to add additional water quantity during mixing. Recycled aggregate is shown in figure 2

Figure 1. Ground Granulated Blastfurnace Slag (GGBS)

Figure 2. Recycled aggregate

II. LITERATURE REVIEW Parthasai Reddy (2014) Conducted an experimental study to determine the mechanical properties of concrete containing recycled aggregate and fly ash. IS 10262:2009 method of mix design is adopted. Mix design was made for M 20 grade concrete. From the experimental results they concluded that 15% of recycled aggregate and 10% of fly ash gives strength close to control concrete. And they found that as increasing the percentage of fly ash workability increases.

R. Kumutha et al. (2010) Investigated the possibility of using recycled aggregates as the replacement of natural coarse aggregates and fine aggregates in concrete. In this study natural coarse aggregate was replaced with 0%, 20%, 40%, 60%, 80% and 100% of crushed concrete aggregates. Natural fine aggregate in concrete was replaced with 0%, 20%, 40%, 60%, 80% and 100% of crushed brick aggregates. Mix was designed for M20 grade. The water cement ratio for all the mixes was 0.5.From the experimental results they found that as the percentage of crushed concrete coarse aggregates and crushed brick fine aggregates was increased, strength of the concrete gets decreased.

P.Saravan Kumar, G.Dhinakaran et al(2013) studied the flexural behavior of reinforced concrete beam containing recycled aggregate and high volume fly ash. Found that the workability of concrete increased by increasing the fly ash content. The load carrying capacity of High volume fly ash recycled aggregate beam is lesser than control beam and also the deflection & crack width was higher than control beam.

Reshma Rughooputh et al(2014) investigate the effect of GGBS in the mechanical properties of concrete. Compressive strength, flexural strength, and split tensile strength was tested. And found that GGBS improves the workability of concrete. There is an increase in compressive strength, flexural strength, & split tensile strength with the increase of GGBS. Yogendr O. Patil et al. (2013) Studied the strength characteristics of concrete containing GGBS as partial replacement for cement. Mix design was done as per IS 10262:2009.Water cement ratio is taken as 0.5 for all mixes. From the experimental results they found that 20% of GGBS gives strength comparable to conventional concrete and 20% replacement of GGBS with OPC results in 14% reduction in cost of concrete.

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III. OBJECTIVE OF STUDY 1. Study on normal concrete by replacing cement with 10%, 20%, 30% & 40% of GGBS and find out the optimum percentages of GGBS 2. With optimum percentages of GGBS replace 10%, 20%, 30% & 40% of coarse aggregate by recycled aggregate and study the fresh and hardened properties and find out the optimum percentage of recycled aggregate.

IV. EXPERIMENTAL INVESTIGATION 4.1. Materials 4.1.1. Cement Ordinary Portland cement of 43 grade conforming to IS 8112-1989 is being used. Table 1 shows the test results.

Table 1.Properties of cement

Properties Fineness Specific gravity Standard Consistency Initial setting time Final setting time

Cement 1% 3.2 33% 60 minutes 360 minutes

4.1.2. Ground Granulated Blastfurnace Slag (GGBS) GGBS was collected from JSW plant, Mumbai. Table 2 shows the properties of GGBS. Table 2. Properties of GGBS

Properties Fineness Sulphide sulphar (%) Insoluble residue Magnesia content (%) Sulphite content(%)

Values 1% 0.51 0.46 7.57 0.42

4.1.3. Fine aggregate Manufactured sand conforming to zone II is used as fine aggregate. Table 3 shows the properties of fine aggregates.

Table 3. Properties of Fine aggregate

Properties Specific gravity Fineness modulus

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Fine aggregate 2.61 2.67

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4.1.4. Coarse aggregate Natural aggregate with 20 mm size is used as coarse aggregate. Table 4 shows the properties of coarse aggregate 4.1.5. Recycled aggregate Recycled aggregates are obtained from a 20 year’s old demolished building. Recycled aggregate normally has higher water absorption and lower specific gravity. For reducing the water absorption saturated surface dry aggregates are used. Properties of recycled aggregates are given in Table 4.

Table 4. Properties of coarse aggregate and Recycled aggregate

Properties Specific gravity Water absorption Fineness modulus

Coarse aggregate 2.77 0.5% 7.06

Recycled aggregate 2.5 7% 7.63

4.1.6. Water Locally available purified drinking water was used for making concrete and curing.

4.2. Mix Proportion Mix design can be defined as the process of selecting suitable ingredients of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength. The mix proportion for M30 grade of concrete was arrived through trial mixes. The mix design was based on IS 10262:2009.Mix proportion is 1:1.59:2.52:0.45.

In this experimental study cement is replaced with 10%, 20%, 30%, & 40% of GGBS and found out the optimum percentage of GGBS. With the optimum percentage of GGBS, replacing coarse aggregate with 10%, 20%, 30%, & 40% of recycled aggregate and found out the optimum percentage of recycled aggregate.

Reference mix is designated as A. The optimum percentage replacement of GGBS was found by replacing cement with 0%, 10%, 20%, 30%, and 40% of GGBS. It was designated as A, A10, A20, A30, and A40. The optimum percentage of GGBS was found and this was used further to find the optimum percentage of recycled aggregate. Coarse aggregate was replaced with 0%, 10%, 20%, 30%, and 40% of recycled aggregate to find the optimum percentage. For this experimental study, various concrete specimens were prepared for different mixes using rotating drum mixer. The specimens prepared were demoulded after 24 hours of casting and were kept in a curing tank for 28 days. After 28 days of curing hardened properties are tested.

V. RESULTS AND DISCUSSION 5.1. Effect of GGBS. The cement is replaced with 10%, 20%, 30% and 40% of GGBS. The specimens are casted and cured. Workability tests are conducted for fresh concrete. Slump and compaction factor tests are conducted for each mix and found that as increasing the percentage of GGBS, workability of concrete increases. The slump and compaction factor values for different percentages of GGBS are given in table.5. Figure 3 and figure 4 shows the graphical representation of slump and compaction factor test results. Compressive strength is tested for finding the optimum percentage of GGBS.

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Table 5. Workability of concrete for different percentages of GGBS

Mix A A10 A20 A30 A40

Compaction factor 0.950 0.952 0.956 0.960 0.966

Figure 3. Slump of mix with GGBS

Slump(mm) 110 113 115 118 120

Figure 4. Compaction factor of mix with GGBS

5.1.1. Compressive strength for different percentages of GGBS The compressive strength test was conducted on cubes of size 150 x 150 x150 mm at 7 days and 28 days. For each mix three cubes are tested. Figure 5 shows the comparison of compressive strengths of different proportions of GGBS. From the figure maximum compressive strength is observed as 26.29 N/mm2 and 40.5 N/mm2 at 7 day and 28 day when cement is replaced by 20% of GGBS. That is for A20 mix. The presence of GGBS in concrete leads to lower early strength gain but higher later strength.

Figure 5. Compressive strength Vs Mix

From this it is found that 20% of GGBS is the optimum percentage.

5.2 Effect of recycled aggregate With 20% of GGBS coarse aggregate is replaced with 10%, 20%, 30%, & 40% of recycled aggregate. Slump and compaction factor tests are conducted to determine the workability of concrete. The slump and compaction factor values for different percentages of recycled aggregate are given in table.6. Figure 6 and figure 7 shows the graphical representation of slump and compaction

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factor test results. The workability of concrete decreases with increasing the percentages of recycled aggregate.

Table 6. Workability of concrete for different percentages of recycled aggregate

Mix

Compaction factor

Slump(mm)

A

0.950

110

A20,10

0.930

105

A20,20

0.900

95

A20,30

0.880

90

A20,40

0.860

88

Figure 6. Slump of mix containing GGBS and RCA Figure 7.Compaction factor of mix containing GGBS and RCA

5.2.1 Compressive strength for different percentages of recycled aggregate The compressive strength of concrete is decreased by increasing the percentages of RCA. And found that A20,20 mix (20% GGBS+20% RCA) gives maximum strength. Compressive strength for A20,20 mix was observed as 26.5N/mm2 and 39.3 N/mm2 at 7 days and 28 days. That is compressive strength is increased by 5.15% and 2.1% at 7 day and 28 day compared to control concrete.

Compressive strength of recycled aggregate is affected by quality of aggregate used. Graphical representation of compressive strength is shown in figure 8.

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Figure 8. Compressive strength Vs Mix

Note: A x,y-Mix contains x% of GGBS & y% of RCA 5.2.2 Split tensile strength for different percentages of recycled aggregate Cylinder of size 150 mm dia and 300 mm height are casted for split tensile strength. Figure 9 shows split tensile strength values for different percentages of RCA. A20,20 mix gives maximum split tensile strength and is observed as 3.6 N/mm2. Split tensile strength value is increased by 5.8%.

Figure shows that as increasing the percentage of recycled aggregate split tensile strength decreases.

Figure 9. Split tensile strength Vs Mix

5.2.3 Flexural strength for different Percentages of recycled aggregate . Beam of size 500x100x100 mm are casted and tested for flexural strength. Graphical representation of flexural strength is shown in figure 10. A20,20 mix gives maximum strength and is observed as 4.6N/mm2. For A20,20 mix flexural strength is increased by 5.7%.Figure shows that as increasing the percentage of recycled aggregate (beyond 20% ) flexural strength decreases.

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Figure 10. Flexural strength Vs Mix

5.2.4 Modulus of elasticity for different Percentages of recycled aggregate Cylinder of size 150 mm dia and 300 mm height are casted for modulus of elasticity. The maximum modulus of elasticity is showed by concrete mix containing 20% GGBS and 20% recycled aggregate.

Graphical representation of modulus of elasticity is shown in figure 11. From the figure it is clear that upto 20% replacement of recycled aggregate has modulus of elasticity higher than that of control mix. Modulus of elasticity for A20, 20 mix is increased by 4.7%.

Figure 11. Modulus of elasticity Vs mix

From the results obtained, found that mix containing 20% of GGBS and 20% of RCA (A20,20) gives maximum strength.     

VI. CONCLUSIONS Replacement of cement with GGBS yielded maximum strength at 20% replacement level.

Workability of concrete is found to be increases with increasing the percentage of GGBS As increasing the percentage of recycled aggregates decreases the workability.

From various strength tests, found that 20% replacement of cement with GGBS and 20% replacement of coarse aggregate with RCA gives maximum strength Replacing cement with GGBS and coarse aggregate with recycled aggregate is one of the good solutions available to the problem of environmental impacts.

REFERENCES

1. Parthasai Reddy “Determination of mechanical properties of recycled aggregate concrete with fly ash” International Journal of Advancements in Research & Technology, Vol. 3, Issue 2, 2014

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2. Reshma Rughooputh and Jaylina Rana “Partial replacement of cement by Ground Granulated Blast furnace Slag in concrete” Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS),Vol.5,Issue 5, 2014 3. P. Saravankumar, G. Dhinakaran, K.Marimuthu “Performance of sustainable concrete containing HVFA and RCA”Asian Journal of Aplied Sciences 2013,ISSN 1996-3343 4. R. Kumutha and K. Vijai “Strength of concrete incorporating aggregates recycled from demolition waste” ARPN Journal of Engineering and Applied Sciences, Vol. 5, Issue 5, 2010 5. Yogendra O. Patil, “GGBS as partial replacement of OPC in cement concrete – An experimental study”International Journal of Scientific Research” Vol. 2 Issue 11, 2013

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