Pore structure and durability of green concrete containing recycled powder and recycled coarse aggregate

Abstract

This study aims to investigate the pore structure, carbonation and chloride ion permeability of recycled aggregate-powder concrete (RAPC), which was prepared synergistically with recycled coarse aggregates (RA) and recycled powder (RP) from construction and demolition waste. RA was used to replace natural aggregates (NA) with rates of 0%, 30%, 50% and 100% and RP was used to replace cement with rates of 0%, 15%, 30% and 45%. The micromechanisms were revealed by mercury intrusion pore (MIP) size measurement, scanning electron microscopy (SEM) and X-ray diffractometer (XRD) tests. The results showed that the carbonation depth and chloride ion permeability of RAPC both increased with the increase of RA replacement rate. The secondary hydration and filling effect of 15% RP refined and partitioned the >200 nm pores in the new mortar, resulting in a 9.27% reduction in the average pore diameter. The carbonation depth was also reduced by 6.33% compared to the RAPC with 0% RP replacement rate. However, the incorporation of 30% and 45% RP was detrimental to both the pore structure and the carbonation resistance. The incorporation of 0–45% RP successfully decreased the chloride ion permeability of all RAPC, and the best result was achieved at 15%. The average chloride diffusion coefficient of RAPC with four RA replacement rates was reduced by 28.32% compared to that without RP incorporation. Taking into account the environment, cost, durability and compressive strength, it was determined that a 30% RA replacement and a 15% RP replacement would be realistically feasible.