Demolished concrete is a large carbon sink which has not been utilized yet. Carbonation of hydrated cement paste from old concrete can effectively store CO₂, and in addition, the resulting carbonated cement paste can be used as a pozzolanic material in new composite cements. This concept reduces the CO₂ footprint of cement and promotes circularity and recycling. This work investigates a semi-dry gas-solid process for the carbonation of recycled cement paste. Decreasing gas humidity and hence the content of water adsorbed on the solid cement grains limits the transport of reactants from the dissolving hydrates and the overall reaction kinetics. It also leads to co-precipitation of the carbonation products, i.e., calcium carbonate and the alumina-silica gel, into a single dense matrix within the original grains. A decreasing water availability increases also the complexity and heterogeneity of the microstructure formed, since calcium carbonate precipitates as different polymorphs, including an amorphous form, and because the final phase assemblage comprises intermediate phases such as decalcified C-(A)-S-H, remains of the original hydrates in addition to the final carbonation products.

拆除的混凝土是一个尚未被利用的大型碳汇。旧混凝土水合水泥浆体的碳化可有效储存CO ₂，​​此外，所得碳化水泥浆体可用作新型复合水泥中的火山灰材料。这个概念减少了 CO ₂水泥足迹，促进循环和循环利用。这项工作研究了一种用于再生水泥浆碳化的半干气固相工艺。降低气体湿度并因此降低固体水泥颗粒上吸附的水含量，从而限制了反应物从溶解的水合物中的传输和整体反应动力学。它还导致碳酸化产物，即碳酸钙和氧化铝-硅胶共沉淀成原始晶粒内的单一致密基质。由于碳酸钙沉淀为不同的多晶型物，包括无定形形式，并且由于最终相组合包含中间相，例如脱钙C-(A)-SH，减少的水可用性也增加了所形成微结构的复杂性和异质性，