Phase assemblance evolution during wet carbonation of recycled concrete fines

In this work, recycled concrete fine (RCF), one of the major products generated from waste concrete recycling process, was carbonated in water. The carbonation mechanism of RCF is investigated, aiming to bring forward the basic understanding of carbonation mechanism and develop value-added products. It was found that the CO₂ dissolution and calcite precipitation limited the carbonation process for the initial stage. Afterwards, the kinetics was dominated by the dissolution of RCF. Portlandite was firstly consumed and the decalcification of C-S-H involved three steps associated with pH development of the aqueous environment. The main carbonation products were calcite, amorphous calcium carbonate (CC), alumina-silica gel, silica gel and alumina gel. The formed CC was turned from a poorly-crystalline layer into aggregated calcite grains. Meanwhile, a silica-rich layer was still located at the outermost surface of carbonated RCF. The carbonated RCF had a significantly high pozzolanic reactivity, being reused as supplementary cementitious materials.