Multi-criteria optimization of recycled aggregate concrete mixes

This study intends to develop a sustainable strategy for selection of recycled aggregate concrete (RAC) through a series of experiments and using multi-criteria decision-making (MCDM) techniques. The mechanical, environmental and economic aspects of RAC were integrated to evaluate the most sustainable concrete, which may be appropriate for varied concrete applications. 25 mixes were prepared by replacing natural coarse aggregate with recycled concrete aggregate (RCA) at mass ratios of 0%, 25%, 50%, 75% and 100%, to span a target compressive strength range of 17-35 MPa. RCA were derived from uncontaminated precast structural members only, which may have superior properties to aggregate from construction and demolition waste. The fresh and hardened properties of RAC were assessed. Varying superplasticizer contents were used to control the reduction in workability, as well as to examine the correlation between 1-day compressive strength of mixes with superplasticizer and 7- and 28-day strength of corresponding mixes without superplasticizer. The CO2 footprint and volume of raw materials were quantified as environmental impact and cost was also evaluated for each mix. The results indicated that with RCA content the compressive strength reduced but within acceptable range, CO2 footprint and cost was also declined, and raw material conservation was recorded. Finally, a framework was employed for sustainable selection (considering technical, environmental and economic parameters) of RAC, with target compressive strength as the main goal. Three compressive strengths (20, 25 and 30 MPa) were set as target and the corresponding ranking of mixes was established using two MCDM techniques; AHP and TOPSIS. Some variation in the results was found, but both techniques allowed sustainable selection of RAC. (c) 2020 Elsevier Ltd. All rights reserved.