Enhancing the accelerated carbonation of recycled concrete aggregates by using reclaimed wastewater from concrete batching plants

Accelerated carbonation is regarded as an efficient and economical way to improve the mechanical properties of recycled concrete aggregates (RCAs) through strengthening the attached mortar/cement paste. However, the property enhancement is usually limited due to the pore-filling effect at the surface of the attached mortar/cement paste. In this study, a series of pretreatment methods were employed on both laboratory prepared cement pastes and real RCA samples to enhance the accelerated carbonation process. This involved the use of a saturated Ca(OH)₂ solution and wastewater generated from a ready-mixed concrete plant. The hypothesis was that with the additional introduction of Ca²⁺ and OH⁻ into RCAs through either soaking or spraying, the carbonation products can be enriched. The physico-chemical and microstructural properties of the samples were investigated by using mercury intrusion porosimetry (MIP), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) analysis, microhardness, scanning electron microscopy (SEM)-back scattered electron (BSE) imaging techniques. Moreover, the density and water absorption values of the samples were evaluated. The experimental results showed that the properties of both the cement paste and RCA samples were further improved with the use of the pretreatment methods before carbonation.