Influence of Shrinkage-Reducing Admixtures on Development of Plastic Shrinkage Cracks

Abstract

Cracking that forms between concrete placement and concrete setting is generally described as plastic shrinkage cracking. The authors discuss how concave menisci may form on fresh concrete surfaces due to water evaporation. Potential development of plastic shrinkage cracks may occur when concrete surface tensile stress and concrete settlement develop because of the menisci. The authors focus on how mortars containing a shrinkage-reducing admixture (SRA), which is commercially available, develop plastic shrinkage cracks. When exposed to the same environmental conditions, fewer and narrower plastic shrinkage cracks are shown in SRA-containing mortar than plain mortar. The authors propose that pore fluid of SRA-containing mortar has lower surface tension, which can result in lower crack-inducing stresses at the mortar's topmost layer, reduced capillary tension, reduced settlement, and less evaporation.