Influence of Shrinkage-Reducing Admixtures on Early-Age Properties of Cement Pastes

Because most shrinkage-reducing admixtures (SRAs) significantly reduce the surface tension of a cement paste pore solution, they will naturally influence all physical properties and processes that are dependent in some way on surface tension. Such properties include internal relative humidity, capillary stresses, and freezing point depression, all via the Kelvin equation and its variants (Kelvin-Laplace, Gibbs-Thomson). Processes that will thus be strongly influenced by the presence of SRAs include drying, autogenous stress and strain development, and freezing. In this paper, experimental measurements of these processes in cement pastes and mortars with and without SRA additions will be presented in light of the Kelvin equation. The experimental measurements that are applied to early-age specimens include X-ray absorption measurements to quantify drying profiles, bulk mass loss measurements, measurements of internal relative humidity, assessments of autogenous deformation under sealed curing conditions, and low temperature calorimetry scans to quantify freezable water content. The results indicate that SRAs can provide benefits in several new applications beyond their conventional usage to reduce drying shrinkage.