Influence of evaporation rate on pore size distribution, water loss, and early-age drying shrinkage of cement paste after the initial setting

Abstract

The influence of the water evaporation rate on early-age drying shrinkage of cement paste is investigated. To measure shrinkage, three mixed groups with different water–cement ratios (w/c’s) were studied over a period of 72 h. The 72-h early-age drying shrinkage, starting from the initial setting time, was measured. The pore size distribution (PSD) was measured using mercury intrusion porosimetry. The results show that the increase of the evaporation rate leads to a large increase in the early-age drying shrinkage. During the first six hours, each group had a good positive relationship between the shrinkage ratio and water loss ratio, and the shrinkage ratio was slightly greater than water loss ratio. Different water evaporation rates influence the most probable pore diameter of cement paste, which increases as the water evaporation rate increases. However, the porosity of the bulk paste and volume of mesopores was not consistent with the rule of the most probable pore diameter. A higher water evaporation rate resulted in a lower pore volume within 26 nm. Therefore, a parameter rs, which can explain the contradiction between the increase of shrinkage and volume of mesopores, was calculated from the water loss and cumulative PSD. The total volume of mesopores may not be the dominant factor in early-age shrinkage, but the most probable pore diameter, parameter rs, and relationship between them can provide a better index of drying shrinkage for the early-age of cement-based materials. Furthermore, in the paste with a w/c of 0.28, rs and drying shrinkage show a linear relationship.