Thermodynamic Modeling Study of Carbonation of Portland Cement.

The assessment of the extent of carbonation and related phase changes is important for the evaluation of the durability aspects of concrete. The phase assemblage of Portland cements with different clinker compositions is evaluated using thermodynamic calculations. Four different compositions of cements, as specified by ASTM cements types I to IV, are considered in this study. Calcite, zeolites, and gypsum were identified as carbonation products. CO content required for full carbonation had a direct relationship with the initial volume of phases. The CO required for portlandite determined the initiation of carbonation of C-S-H. A continual decrease in the pH of pore solution and a decrease in Ca/Si is observed with the carbonation of C-S-H. Type II cement exhibited rapid carbonation at relatively less COfor full carbonation, while type III required more CO to carbonate to the same level as other types of cement. The modeling of carbonation of different Portland cements provided insights into the quantity of CO required to destabilize different hydrated products into respective carbonated phases.