Use of recycled fine aggregates and recycled powders in sustainable recycled concrete

Abstract

The shortage of sand and gravel resources has become a global problem. Processing construction and demolition wastes (CDW) into recycled materials and using them to prepare new concrete is conducive to the sustainable development of the construction industry. In terms of recycled coarse aggregate (RCA), relatively mature technical accumulation and industrialization have been formed, but the utilization technology of recycled fine fractions (RF), accounting for more than 40%, is still scarce. In this study, the feasible use of RF, including recycled fine aggregates (RFA) and recycled powders (RP), in recycled concrete was studied from the perspective of fresh properties (empirical and rheological). The results showed that the reduction in the slump was more prominent in Series with RFA than RP. The highest reduction was observed around 31.71% (30% RP) in Series I at 30mins; and 60.98% (50% RFA) in Series II in mix with 50% RFA, which is due to higher friction and higher interlocking behavior due to their rough surface and higher amount of attached mortar. The mix with RP showed the most significant increase in the static viscosity of 271% at 30% RP and 149% with 100% RFA replacement at 30 min of the time interval. Static yield stress increases greater with RP, which may have caused slump expansion to decrease over time. The friction from RFA's rough surface texture and the mix's extra SP and water content enhance dynamic yield stress and decrease viscosity. The study found that the incorporation of RP and FA in the mixes resulted in a noteworthy reduction in carbon emissions compared to the control mix. Specifically, RPC2 and RPC3 exhibited a decrease of 24.35% and 25.00%, respectively. It is also seen that using recycled fines can lead to stable, low-carbon concrete for leading to a sustainable automated construction industry.