IMPACT OF DEMOLDING AGE AND DRYING PERIOD ON DEGREE OF HYDRATION OF EARLY AGE CEMENT PASTE

Abstract

This study investigates the effects of demolding age and drying period on the early-age hydration behavior of cement paste, with a focus on depth-dependent moisture evolution and phase transformation. A combination of single-sided ¹ H NMR relaxometry and micro-XRD mapping measurement were employed to monitor moisture content and quantify hydration products at different depths. Specimens were categorized by demolding age and subjected to controlled drying conditions （60％RH, 20℃）. The results show that shorter demolding ages more significant moisture loss and a lower degree of hydration within the shallow region （0-5mm）under identical hydration durations. In comparison, hydration in the deep regions （9-15mm）was scarcely influenced, indicating that the influence of drying gradually weakens with increasing depth. Extended drying periods suppress hydration reactions in the shallow region, with the inhibitory effect being more pronounced at shorter demolding ages. Under the present experimental conditions （20℃, 60％RH）, five days is the optimal time for demolding. Specimens with longer demolding ages develop a denser C-S-H structure, which enhances moisture retention and lessens the suppression of hydration reactions due to drying.