Comparative performance of ordinary and recycled aggregate concrete incorporating CFA as SCM

Abstract This study aims to explore the feasibility of using circulating fluidized bed fly ash (CFA) as a supplementary cementitious material in both ordinary concrete and recycled aggregate concrete (RAC). Various properties of both concretes, including compressive strength, drying shrinkage, carbonation resistance, surface resistivity, were evaluated. Additionally, the economic and environmental benefits were assessed. Findings indicated that increasing CFA content (mass fraction) progressively increases drying shrinkage rate and carbonation depth in both concretes. At 30% CFA, ordinary concrete showed 10.9% higher 180-day shrinkage and 4.3% greater 28-day carbonation compared to the control, while RAC exhibited 14.7% higher shrinkage and a significant 34.4% increase in carbonation compared to its control. However, at 10% CFA, both concretes showed no significant reduction in compressive strength compared to their respective controls. Up to 20% CFA, a decline of 13.1% and 9.0% was observed in the 28-day compressive strength of ordinary concrete and RAC, respectively. The results indicate that RAC demonstrates better compatibility with CFA compared to ordinary concrete. Additionally, the economic and environmental benefit analysis showed that the lowest cost (8.6 and 7.4 yuan for ordinary concrete and RAC, respectively) and carbon emission (6.2 and 6.7 kg for ordinary concrete and RAC, respectively) for both concretes (normalized per unit of strength) occurred at 10% and 20% CFA, respectively. This study investigated varying CFA dosages to balance performance trade-offs against cost and carbon emissions, establishing the feasibility of CFA utilization in both ordinary concrete and RAC.