Influence of Pretreatment Methods for Coarse Recycled Aggregates on the Performance of Alkali-Activated Concrete

Coarse recycled aggregates (CRAs) could be potentially used as aggregates for construction, providing an alternative option to expensive natural aggregates (NA). CRAs are of meager strength, with a weak interfacial transition zone, which has limited their widespread use as a substitute for NA. This study aims to investigate the effectiveness of different pretreatment techniques for CRAs and their potential to enhance the mechanical properties of alkali-activated concrete (AAC). Three distinct pretreatment techniques-mechanical, chemical, and hybrid processes-were employed to address the issue of adhered mortar in CRAs. The study maintained a fixed 0.1 M acidic solution to ensure treatment consistency. Data collection involved assessing residual mortar content (RMC), microstructural changes, durability, and fundamental properties. Among the three pretreatments, the hybrid process (HP) demonstrated the highest efficiency, effectively removing a significant portion of the RMC and resulting in CRAs with superior microstructural properties, including an 81% reduction in water absorption potential and a specific gravity of 98%, comparable to NA. Freeze-thaw and soundness tests revealed the enhanced durability of HP, with 50% less loss during freeze-thaw and 76% better soundness properties compared to unprocessed CRAs. The compressive strength of AAC incorporating 100% hybrid-processed coarse recycled aggregates (HPCRAs) reached 47.49 MPa. The findings suggest that HP is a promising method for enhancing the CRA's fundamental properties. It also shows that HPCRAs have the potential to improve the mechanical properties of AAC significantly. These outcomes pave the way for more sustainable construction practices, reducing reliance on NA and promoting the use of CRAs in AAC.