Enhancing mixed recycled aggregate properties using water glass coating: optimization and performance in concrete applications

The rapid advancement of global infrastructure has resulted in a significant increase in construction and demolition (C&D) waste, raising urgent environmental issues stemming from inadequate disposal and management strategies. Recent research has focused on recycling C&D waste as mixed recycled aggregate (MRA) in concrete, majorly in developing countries, to promote sustainability. This study investigates a novel method for improving MRA characteristics by treating it with a water glass (WG) coating solution. A central composite design (CCD) model was used to identify the best treatment conditions considering WG concentration, water-to-aggregate ratio, and soaking duration as independent variables to facilitate treatment in MRA. The model’s performance was evaluated using water absorption, Los Angeles (LA) abrasion resistance, and apparent density. The microstructural analysis demonstrated that WG treatment enhanced MRA by forming calcium silicate hydrate (C-S-H) gel, which improved the pore structure and interfacial transition zone (ITZ). The optimised treated MRA was incorporated into the concrete at replacement levels of 0, 25, 50, 75, and 100% to assess workability, mechanical properties, and microhardness. The results indicated that substituting 25% of natural coarse aggregate with treated MRA led to significant enhancements in workability by 11.76%, compressive strength by 4.83%, split tensile strength by 2.94% and flexural strength by 3.43% while maintaining comparable hardness values to conventional concrete. The improvement was linked to the densification effect of the WG coating, resulting in enhanced bonding and mechanical performance. The results demonstrate a viable way to recycle C&D waste while maintaining structural integrity in concrete applications.