Development of sustainable concrete using recycled coarse aggregate and ground granulated blast furnace slag

The present investigation aims to use recycled coarse aggregate (RCA) and ground granulated blast furnace slag (GGBFS) as replacement of natural coarse aggregate (NCA) and ordinary Portland cement (OPC) for developing sustainable concrete. Sixteen numbers of concrete mixes are prepared with 0%, 25%, 50% and 100% replacement of NCA by RCA for each 0%, 20%, 40% and 60% replacement of cement by GGBFS. The effects of RCA and GGBFS on fresh and hardened concrete properties such as workability, compressive strength, split tensile strength, flexural strength, rebound number, density, water absorption and volume of voids are experimentally investigated. The test results obtained in the present investigation show that the workability increases with the use of RCA or GGBFS or both of these two. The compressive, split tensile and flexural strength decrease with increase in the percentages of RCA or GGBFS or both. The reduction in split tensile and flexural strength of the concrete mixes containing RCA or GGBFS or both RCA and GGBFS is less pronounced unlike its compressive strength. The values of rebound number obtained from non destructive test (NDT) show the similar trend with the results of compressive strength. Water absorption and volume of voids of the concrete mixes increases with increase in RCA content. However, the use of GGBFS improves the quality of the concrete mixes by improving the ITZ and bond between mortar and RCA. The concrete mix with 50% RCA and 40% GGBFS achieves values of these properties closer to those of the concrete mix without RCA and GGBFS. Finally, the concrete mix with 50% RCA and 40% GGBFS is considered as the optimum mix which is satisfying the target mean strength of the mix design and producing sustainable concrete by saving 40% of cement and 50% of NCA and utilizing maximum waste products such as GGBFS and RCA.