Effects of treated wastewater from recycled aggregate processing on the microstructure and mechanical properties of cement mortar

This study investigated the effects of various treatment methods applied to recycled aggregate wastewater on the microstructure and mechanical properties of cement mortar. Industrial wastewater collected from a construction waste processing facility was treated using membrane filtration (MF), activated carbon adsorption (AC), ion exchange (IEX), and their combinations (MF+IEX, AC+IEX). The treated and untreated wastewater, along with tap water as a reference, were used as mixing water for mortar production. Physicochemical and microstructural analyses, including X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and X-ray micro-computed tomography (micro-CT), revealed that water quality significantly affected hydration products and pore structure. Compressive strength was reduced by approximately 15% when using wastewater treated with MF or AC alone due to high concentrations of organic matter (TOC > 45 mg/L) and suspended solids. In contrast, specimens using IEX-treated water achieved higher compressive strength (up to 8% increase) and reduced porosity (as low as 4.66%) due to lower chloride and sulfate ion concentrations. The results highlight that appropriate wastewater treatment — particularly involving IEX — can enable the sustainable reuse of industrial wastewater in cement-based materials without compromising performance.