Dimensional change of cement paste subjected to carbonation in CO2 sequestration and utilization context: A critical review on the mechanisms

With the utilization of mineral CO2 sequestration technology, the volume stability of cement paste exposed to carbonation is catching significant interest. This review attempts to summarize the state-of-the-art knowledge on the volume stability of cement paste upon carbonation and thereby benefit the decision-making process in the utilization of CO2 sequestration technology in the concrete industry. In this work, the dimensional change caused by carbonation of each major cement hydration product was analyzed individually, with a special focus on the carbonation of calcium silicate hydrate (C-S-H). Key parameters affecting carbonation reactions and the associated volume stability of cement paste were examined, e.g. CO2 concentration, temperature, relative humidity, and supplementary cementitious materials. On that basis, the typical evolution of dimensional change of cement paste upon carbonation was presented and elucidated, with the critical research gaps identified. Overall, carbonation of calcium hydroxide and calcium silicate (C2S and C3S) tends to cause a volume expansion, whereas carbonation of ettringite and C-S-H phases leads to the opposite. The change in micropore structures of cement paste upon carbonation depends mainly on the competition between the clogging of capillary pores filled with calcium carbonate and the formation of additional capillary pores induced by the decalcification of C-S-H. To assess the volume stability of cement paste carbonated at early ages, the coupling effect between hydration and carbonation requires further studies. For the measurement of linear carbonation deformation of cement-based materials, a standard test procedure is urgently needed.