RSM-based optimized mix design of recycled aggregate concrete containing supplementary cementitious materials based on waste generation and global warming potential

Abstract

Rapid increase in waste generation is one of the biggest environmental problems in the construction industry. Special attention has been given to using industrial wastes such as supplementary cementitious materials (SCMs) and recycled aggregates (RA) in concrete. In this research, optimizing the mix design of concrete containing recycled concrete aggregate (RCA), silica fume and ground granulated blast furnace slag (GGBFS) with different compressive strengths was performed in terms of global warming potential (GWP) and service life. In fact, the environmental impacts (GWP, waste generation and recycling potential and consuming natural resource) of plain concrete and optimal recycled concretes were compared for mixes having similar compressive strength (CS) and service life. First, an experimental investigation on the mechanical and durability properties of concrete was conducted using response surface method (RSM). Next, optimization technique was used to determine optimal mix designs with maximized service life and minimized GWP and waste generation for 6 classes of compressive strength. According to the results, comparison without considering the service life of mixes (even in equal range of CS) could lead to a significant underestimation. For instance, without considering the service life, the reduction in GWP for optimal mix designs was 41% whereas this reduction considering an equal service life was 80%. Also, compared to the plain concrete, waste generation of the optimal mix was reduced from 6412 kg to 2605 kg in a 110-year period, and 425 kg of waste per 1 m3 is recycled in this mix design.