Influence of CSH carbonation on the porosity of cement paste

Abstract

Thermogravimetric analysis and mercury intrusion porosimetry were used to determine the relationship between cement paste porosity and calcium silicate hydrate (CSH) carbonation during the carbonation process. A method that is not based on the chemical formula of CSH was developed to calculate porosity variation during CSH carbonation. This method is based on the variation of calcium hydrate volume and total volume to obtain the CSH volume variation during carbonation, as well as the porosity variation caused by CSH carbonation. The CSH carbonation results showed that the main factor in the variation of paste porosity was CSH carbonation, which accounted for more than 70% of the total porosity variation. A transition point was observed on the CSH volume variation curve. CSH generated calcium carbonate during the early carbonation process, at which a volume expansion also occurred. The volume shrinkage and calcium carbonate content reached maximum when the carbonation process was completed.