Carbonation strengthening mechanism of dry cement-based materials under supercritical carbon dioxide

Long-term stability of concrete as a wellbore sealing material is enhanced by the interaction between Portland cement and supercritical carbon dioxide. This study is to explore the mechanism of the strengthening effect of supercritical carbon dioxide on cement-based materials. After supercritical carbonation curing, the compressive strength of dry samples is increased by 93 %∼123 %. By using regional characterization analysis, the relationship between chemical reaction process and local mechanical property changes is established. The supercritical carbonation process and reaction kinetics are uncovered. On the one hand, the carbonation products form a compacted layer in the external area of cement paste, with a local microhardness increase of 30 % for 7d and 102 % for 28d, playing hoop effect on strengthening; On the other hand, the inward aggregation of carbonation produced water promotes the local “rehydration”, increasing the degree of hydration by 3.89 %∼15.98 %, which benefits strength development. The transport and accumulation of the produced water are the main limiting factors which obstruct the continuous penetration of supercritical carbonation.