Effect of different wind speeds and sealed curing time on early-age shrinkage of cement paste

Abstract

The influence of different wind speeds and sealed curing time on early-age shrinkage of cement paste was investigated. The 72-h early-age total shrinkage of cement paste after sealed curing for 0 h, 3 h, 6 h, 9 h, 12 h, and 24 h starting from the initial setting time under different wind speeds was studied. Water loss, autogenous shrinkage, tensile strength, pore size distribution (PSD) and hydration degree were measured. Elastic modulus, cracking strain, and radius of the pores where the meniscus forms were calculated based on the data obtained. For mixtures that did not undergo sealed curing, the wind speed could considerably increase the drying shrinkage and total shrinkage of the cement paste. The wind speed also reduced the early tensile strength, hydration degree, and elastic modulus of the cement paste. Within 1 day, the cracking strain was reduced by wind speed. According to the experimental data, a fitting formula for the early total shrinkage of cement paste is proposed, and the wind speed influencing factor βw is also proposed for the first time. Considering the PSD and water loss to study the mechanism of early drying shrinkage of cement paste, we found that there is a good correlation between rs and drying shrinkage. The exponential formula is given between rs and drying shrinkage. For mixtures with sealed curing, the total shrinkage and water loss decreased with increasing sealed curing time. However, the effects of water loss at different stages on drying shrinkage were different. Water evaporation in the early stage led to more drying shrinkage than water evaporation in the later stage. Sealed curing also weakened the increasing effect of wind speed on total shrinkage, so that at the same wind speed, the shrinkage increment was considerably reduced. After analysis and comparison, it was found that it is economical and reasonable to adopt sealed curing for 6 or 9 h, which can effectively decrease the early total shrinkage and improve the cracking strain of the cement paste in the wind environment.