Eco-, economic- and mechanical- efficiencies of using precast rejects as coarse aggregates in self-compacting concrete

Abstract

This paper investigates the eco-, economic- and mechanical- properties of self-compacting concrete (SCC) containing recycled coarse aggregates generated from prefabricated concrete rejects (PRA) or construction and demolition wastes (CRA). A total of 720 specimens from 36 unique SCC mixes are prepared and tested. The effects of the key parameters including, water-to-binder ratio (w/b), fly ash replacing ordinary Portland cement weight ratio, recycled coarse aggregate replacing natural coarse aggregate volume ratio, heat curing temperature, mixing method or the addition of steel fibers, on the fresh and hardened properties of SCC are experimentally explored. In addition to the experimental study, cradle-to-gate life cycle cost (LCC) analysis and life cycle assessment (LCA) of the SCC are carried out, where these are done through considering different levels of functional units. Based on the results of the experimental work, LCA and LCC, it is found that the PRA based concrete shows ecological-, environmental- and economic- benefits over conventional SCC with slightly compromised rheological and mechanical properties. When considering only the volumetric equivalence, it is observed that a higher w/b, the inclusion of higher amount of recycled coarse aggregate (RCA), or fly ash, or using a lower curing temperature can efficiently reduce the cost and environmental impacts of SCC with PRA. PRA concrete products are more eco-friendly and less cost intensive than those associated with the CRA ones due mainly to the shorter distance to transport PRA compared to CRA. Beyond the volumetric functional unit, the results of LCC and LCA show that, as indicated by carbon dioxide equivalent-, embodied energy- or cost- intensity, a higher w/b, the incorporation of higher content of RCA or fly ash, and using a lower curing temperature no longer benefit the eco-, environmental and mechanical performance of recycled coarse aggregate SCC (RCASCC) and the effect of curing temperature becomes ambiguous.