Characteristics of CSH under carbonation and its effects on the hydration and microstructure of cement paste

This paper investigated the characteristics of synthesized calcium silicate hydrate (CSH) during the carbonation process and the effects of CSH and carbonated C-S-H (CCSH) seeds on the performance of cement pastes. The result showed that the CCSH is composed by 68.4% calcite and 31.6 % silica gel with Ca/Si of 0.09 and can absorb 301 g CO2 per kg C-S-H, which had a high potential for CO2 capture. please modifed to The result showed that the CCSH is composed by 68.4% calcite and 31.6 % silica gel and can absorb 301 g CO2 per kg C-S-H, which had a high potential for CO2 capture. The addition of CCSH showed more significant improvement on the cement hydration due to the higher surface area and the generated calcite and silica gel after carbonation treatment in comparison to CSH. A new hydration product of calcium aluminate mono-carbonate was generated in CCSH sample with the reaction between calcium carbonate and aluminate. Different from the only additional nucle-ation sites provided by CSH seeds, the generated calcite after carbonation provided nucleation effect, chemical effect and finer effect, and the silica gel had a high pozzolanic reaction degree, which significantly accelerated the hydration and led to a denser pore structure. Therefore, the CCSH seeds significantly accelerated the early hydration and increase the early compressive strength without an obvious decrease of the later compressive strength due to the coupling effect of calcite and silica gel.