Effects of Fatty Alcohol-Based Shrinkage Reducing Agents on Early-Age Shrinkage under High Temperature Conditions

Arid and tropical climates are prone to the occurrence of drying shrinkage cracking at early ages. Shrinkage reducing agents (SRAs) are often used to mitigate drying shrinkage, whose key action on the reduction of early-age shrinkage was seen to be a reduction of capillary tension. However, the roles of SRAs on reduction of shrinkage that have been reported, throw doubt on the idea that SRAs work solely via capillary tension. In order to clarify the mechanisms of early-age shrinkage in the presence of SRAs, the effects of fatty alcohol-based SRAs on shrinkage strain, capillary pore pressure and crack area of cement-based mortars at early ages were investigated. Our results demonstrated clearly that capillary tension does not directly correlate with shrinkage strain at early ages in the presence of SRAs, even under the same profiles of evaporation and hydration. We interpreted the actions of SRAs on early-age shrinkage as follows: SRA micelles adsorb onto hydrates and/or exist in pores, and form the hydrate matrix with incorporated SRA micelles. The matrix could mitigate the capillary tension as stress absorbers, and thereby shrinkage and crack area are reduced. The concept of the matrix could be experimentally demonstrated by the changes in shear creep.