Enhancement mechanism of wet-carbonated recycled concrete aggregates subjected to calcium-rich and magnesium-rich industrial reclaimed wastewater sources

Abstract

While efficient in enhancing recycled concrete aggregates' (RCAs) performance, wet carbonation demands significant amounts of water. Addressing this, we investigated carbonation of RCAs in tap-water (TW), concrete batching plant wash-water (WW), and reject brine (RB). Composition and microstructure of carbonated RCAs and their impact on reaction and mechanical properties of recycled aggregate concrete (RAC) were examined. Although the dissolution of Ca-containing components in RCAs was slower in WW, the high Ca(OH)₂ content in WW enhanced carbonation, leading to the formation of large calcite particles (1–2 μm). Despite a 56 % increase in RAC strength compared to the control, WW-RAC revealed slightly lower strengths than TW-RAC, which contained finer calcite particles (0.1–0.3 μm). The presence of Mg²⁺ in RB accelerated the dissolution of Ca components in RCAs due to the lower solubility product constant of Mg(OH)₂ compared to Ca(OH)₂, thereby promoting early-stage carbonation. As carbonation progressed, Mg²⁺ was recovered from the carbonation product into the solution, with a recovery rate of 94 %. This Mg-modification resulted in the formation of 0.1–0.3 μm calcite particles along with needle-shaped Mg-calcite, enhancing bond strength. Results demonstrated feasibility of using reclaimed industrial wastewater in enhancing CO₂ sequestration, while significantly improving RCAs’ properties.