Effects of early hydration of alite and belite phases on subsequent accelerated carbonation

To better understand the early hydration impact of cement phases on subsequent accelerated carbonation, this study mixed alite (C3S) and belite (beta-C2S) with 40 wt% of water for 2, 4, 8, 18 h hydration before exposing to 2 h accelerated carbonation. The results indicated that early hydration exerted a significant impact on C3S (particularly 4-8 h), which accelerated the subsequent carbonation degree (CD) with maximum of 57.27%. Over 8 h, however, packed hydrates impeded CO2 ingress, leading to a decelerated CD and co-existence of different calcium carbonate polymorphs: calcite (dominant for short hydration), aragonite and vaterite (dominant for long hydration). Differently, beta-C2S samples with marginal hydrates continuously accelerated CD with time (32.23% after 18 h), and indicated a direct beta-C2S carbonation. Detection of calcite and vaterite in carbonated beta-C2S samples revealed that carbonates polymorphs varied with calcium silicate and their resulting hydrates participation. This study provides a viable strategy for CO2 storage and microstructure densification, distinct from conventional cement carbonation regime.