Effect of alkalis on products of enforced carbonation of cement paste

An approach based on enforced, wet carbonation of cement fines obtained from recycled concrete and its application as an SCM in new composite cements is presented as a new carbon capture and utilization technology. While the carbonation products are stable at a wide range of conditions, it is found that alkalis have a strong impact on product properties, as shown by carbonation in NaOH solutions in this study. Calcium carbonate precipitates mainly as calcite, regardless of the alkali concentration, however, the alkalis influence the size of the calcite crystals, which are smaller at low alkali concentrations. Alkalis modify also the structure of the alumina-silica gel, as a result of absorption of either sodium or calcium ions in this phase. Furthermore, alkali ions present in the solution influence directly the sulphate content of the carbonated cement paste, since a higher alkali concentration in the solution promotes leaching of sulphate. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study presents a new carbon capture and utilization technology by enforcing wet carbonation of cement fines from recycled concrete, and applying them as SCMs in new composite cements. Alkalis have a significant impact on the properties of carbonation products, affecting the crystal size of calcium carbonate precipitates and altering the structure of alumina-silica gel. Additionally, alkalis in the solution directly influence the sulphate content of the carbonated cement paste.