An insight of carbonation-hydration kinetics and microstructure characterization of cement paste under accelerated carbonation at early age

Accelerated carbonation of cement and concrete at early age is an essential technique for both of carbon sequestration and performance improvement, while the core carbonation heat and the interplay with the subsequent hydration process remain unclear. This study aims to develop a method to explore carbonation-hydration heat evolution using a modified isothermal calorimeter, microstructure characterization of carbonated pastes was revealed by multi-techniques of TG/DTG, XRD, SEM and thermodynamic modelling. Carbonation heat was confirmed and the intensity of this heat was much higher than that of hydration heat. Interestingly, the main hydration peak flow overlapped with the front carbonation flow, while three factors including prior-hydration time, w/c ratio and superplasticizer (SP) were found to be the key factors to obtaining independent carbonation-hydration flow in this process. Furthermore, prior-hydration of 2 h promoted CO2 uptake of paste to 14.9%, and the generation of 1–4 μm calcium carbonate crystals with irregular graininess and rhombohedral-like shape were also observed in carbonated pastes.