This contribution discusses a new carbon capture and utilization (CCU) approach based on CO2 mineralization of cement paste from recycled concrete that can balance a significant part of the CO2 emissions associated with cement production. Carbonation of the calcium-bearing phases is achieved in a few hours at ambient temperature and pressure and with a relatively low CO2 gas concentration (< 10 %). The carbonation of cement paste produces calcite and an amorphous alumina-silica gel, the latter being a pozzolanic material that can be utilized as a supplementary cementitious material. The pozzolanic reaction of the alumina-silica gel is very rapid as a result of its high specific surface and amorphous structure, implying that composite cements containing carbonated cement paste exhibit a rapid strength gain. The successful implementation of this CCU approach relies also on improved concrete recycling techniques and methods to separate out the cement paste fines. Full concrete recycling will further improve concrete’s circular utilization by using recycled aggregates instead of natural deposits of aggregates. Although the feasibility of the process has already been demonstrated at the industrial scale, there are still several open questions related to optimum carbonation conditions and performance of carbonated material in novel composite cements.
