Recycled coarse aggregate from parent concrete with supplementary cementitious materials under freeze-thaw environment: Recyclability, environment and economic evaluation

Abstract

In order to improve the utilization efficiency of waste concrete in cold regions, this paper studied the properties of parent concrete (PC) and its recycled coarse aggregate (RCA) based on ordinary Portland cement (OPC), fly ash (FA), silica fume (SF), and ground granulated blast-furnace slag (GGBS) combination optimization in freeze-thaw (F-T) environment. The influence of supplementary cementitious materials (SCMs) on the frost resistance of PC was analyzed by compressive strength and relative dynamic elastic modulus. The recyclability potential of RCA was evaluated by the apparent density, water absorption, crushing index and attached mortar content. In addition, the phase composition and microstructure of RCA were analyzed by XRD and SEM, respectively, and the degradation mechanism of PC during F-T process was analyzed. Finally, the environment and economic benefits from cradle to cradle is analyzed. The results showed that PC containing SCMs had good frost resistance. The PC with a binder system of 75 % OPC +15 % FA + 10 % SF had the smallest F-T damage at 0.068, and its RCA quality could be upgraded from Class III to II after mechanical grinding. This combination of cementitious materials reduced harmful pores in concrete and inhibits the development of cracks during F-T cycles. In addition, it had a carbon emission 18 % lower than that of traditional concrete, with cost-effectiveness of 1.054. This research can provide a low-carbon and economic strategy for the preparation and recycling of waste concrete in cold regions.