Relation between humidity and chemically combined water under self-desiccation condition

In this study, high-performance concrete was exposed to self-desiccation condition to investigate the correlation between chemically combined water (CCW) and internal humidity. The results indicate that the reduction in internal humidity over the first 28 d accounts for over 86% of the total decrement in 112 d, and the increase in CCW in the first 7 d accounts for more than 76% of the total increase over 112 d. It was also found that admixing of fly ash can postpone the decrease in internal humidity, make the matrix maintain the moisture saturation stage for over 20 d and significantly decrease the content of CCW at early age. A mathematical formula was developed to describe the quantitative relation between internal humidity and CCW of concrete under self-desiccation.