Mathematical modeling of accelerated carbonation curing of Portland cement paste at early age

Accelerated carbonation curing is considered as a promising method to improve mechanical properties and durability of cement-based materials and it also provides a potential for reducing carbon emission. In this paper, a partial differential mathematical model was developed for the coupling behavior of cement hydration and carbonation reaction of both clinker minerals and hydration products when cement paste is exposed to an accelerated carbonation curing at early age. The numerical simulations show that tricalcium silicate is the major reactant for both hydration and carbonation of early age Portland cement paste. The modeling prediction of porosity, carbonation efficiency and pH value of cement paste was verified by measurement results from accelerated carbonation curing test. The prediction values behaved more close to the experimental results with the longer curing age. Dimensionless analysis was performed to figure out the effects of different carbonation mechanisms. Based on the relationship between Thiele modulus and carbonation efficiency, it was found that early age accelerated carbonation curing is a diffusion limiting process initially and then turns into a rate limiting process as the carbonation proceeds. It was also demonstrated that carbonation depth and rate of early age Portland cement paste are mainly controlled by contents of tricalcium silicate and calcium hydroxide while water to binder ratio is kept constant. Therefore, accelerated carbonation curing process of Portland cement paste can be theoretically predicted using this model and influences of mineral admixtures should be further investigated.