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Effect of Cement Proportion on Strength of Recycled Aggregate Concrete

Ahsanul Kabir 1, Nizam Uddin Ahmed 2, and Md. Shariful Alam 2
1. Department of Civil Eng, Bangladesh Univ. of Engineering & Tech, Dhaka, Bangladesh
2. D Stichting Bangladesh Accord Foundation & BWDB, Dhaka, Bangladesh

Abstract—This is an attempt to study the effect of normal and higher cement proportion on the properties of concrete made with Recycled concrete aggregate without adding any water reducing admixture. Workability and concrete strength was the principal target of investigation. Recycled aggregates were prepared from the concrete laboratory wastes of concrete cylinders/cubes dumped after routine strength tests in the Lab courtyard for disposal. Simultaneously, concrete specimen with fresh natural aggregates were tested to compare the properties of Recycled Aggregate Concrete (RAC) with Natural Aggregate Concrete (NAC). Waste concrete cylinders were usually tested at their 28th day’s strength but their waste life span in the courtyard ranged from 2 months to 2 years. Several sets of RAC were made by varying the percentage of RCA from zero to 100 percent. After mixing the RCA in different proportions (0, 25, 50, 75 and 100%) with required amount of fine aggregate (sand) the combined gradation of each batch was determined. Three different water cement (w/c) ratio of 0.41, 0.46 and 0.5 were used for each group of mix proportion. Relatively low slump was observed for concrete mixes with normal cement content of 370 kg/m3 for w/c less than 0.5. But workability (slump) increased reasonably with higher cement amount for all the mixes. Strength gain pattern with ages was found to be similar to normal aggregate concrete in all cases with different RCA replacement. Concrete strength with RCA was found to be lower compared to NAC for normal cement content. But with 30% increase in cement concrete strengths increased and were found comparable for all RCA replacement with that of NAC for a particular age. 
Index Terms—recycled course aggregate, gradation, workability, natural course aggregate, recycled aggregate concrete, strength of concrete

Cite: Ahsanul Kabir, Nizam Uddin Ahmed, and Md. Shariful Alam, "Effect of Cement Proportion on Strength of Recycled Aggregate Concrete," International Journal of Structural and Civil Engineering Research, Vol. 4, No. 4, pp. 341-346, November 2015. doi: 10.18178/ijscer.4.4.341-346