Modelling and optimisation of concrete containing recycled concrete aggregate and waste glass

Recycling of waste materials plays a significant role in waste management strategies, but the interactive properties of recycled aggregates in concrete have been considered by only a few researchers. The experimental study reported in this paper focused on the effects of recycled concrete aggregate (RCA) and waste glass (WG) on the properties of concrete. The response surface methodology was used to optimise and model the results of tests for compressive strength, tensile strength, slump, water absorption, electrical resistivity and hardened unit weight. The effective variables of the experiment were RCA (0-65%) as coarse aggregate replacement and WG (0-40%) as fine aggregate replacement. The results obtained indicate that high volumes of waste materials could be used in concrete without a significant reduction in the mechanical and durability (namely water absorption and electrical resistivity) properties of the concrete. Moreover, when WG was substituted in the mixture, the water absorption, electrical resistivity and workability of the concrete improved and the use of RCA had a significant influence on the mechanical properties of the concrete. Based on statistical analysis, all the proposed models were adequate, with coefficients of determination above 0.95. The optimum condition in which all response targets performed properly was found to be 17% of RCA and 35% of WG.