سيد رضا متولي عنبراني

This study investigates the rheological, mechanical, and microstructural properties of self-compacting concrete (SCC) incorporating recycled concrete aggregates (RCA) and recycled brick aggregates (RBA) derived from construction and demolition waste. RCA was substituted at replacement levels of 25%, 50%, 75%, and 100%, while RBA was incorporated at replacement levels of 10%, 20%, 30%, 40%, and 50%. Additionally, the effectiveness of treatment methods to improve the quality of recycled aggregates (RA), including pre-saturation with sodium silicate and a two-stage mixing approach (TSMA), was eva‎luated. The results revealed that increasing the replacement levels of RCA and RBA led to an increase in the static yield stress (τ_0s ), dynamic yield stress (τ_0d ), and plastic viscosity (μ) compared to the reference mix (τ_0s=10.75 Pa ,τ_0d=9.34 Pa ,μ=49.13 Pa.s). However, pre-saturation with sodium silicate, combined with TSMA, reduced these values and significantly enhanced flowability, passing ability, and segregation resistance. For RCA-containing mixtures, the reductions in static yield stress, dynamic yield stress, and plastic viscosity were 28.07%, 23.89%, and 7.01%, respectively, while the reductions for RBA-containing mixtures were 18.57%, 17.38%, and 4.1%, respectively. In terms of mechanical properties, the 7-day and 28-day compressive strengths decreased with increasing recycled aggregate (RA) replacement levels compared to the reference mix (f ́_(c,7)=45.1 Mpa ,f ́_(c,28)=56.8 Mpa). However, the pre-saturation of RA with sodium silicate mitigated this reduction, particularly in RBA-containing samples, by reducing water absorption and porosity. Microstructural analysis demonstrated that sodium silicate treatment decreased the Interfacial Transition Zone (ITZ) porosity by reducing calcium hydroxide content and promoting a more uniform distribution of calcium silicate hydrate (C-S-H). The combined effect of these modification techniques enhanced the mechanical properties of SCC incorporating RA by reducing voids and increasing density. This study demonstrates that the utilization of treated recycled aggregates not only improves concrete properties but also offers a sustainable and cost-effective solution for managing construction waste and reducing dependence on natural resources.

بتن خودتراكم , سنگدانه بازيافتي , روش‌هاي بهبود كيفيت , خواص رئولوژيكي , خواص ريزساختاري

Self-Compacting Concrete , Recycled aggregate , Treatment methods , Rheological properties , Microstructural properties

Reza Moteva‎lli Anbarani

Dr. Parviz Ghoddousi