Behavior and Residual Stress Development in Mortar Containing Shrinkage Reducing Admixture (SRA’s)

Concrete shrinks as a result of drying, self-desiccation, chemical reaction, or temperature reduction. If this shrinkage is prevented by restraint, tensile stresses develop which may result in cracking. Various alternatives have been proposed to reduce the cracking propensity of a mixture including the use of commercial chemical admixtures called shrinkage reducing admixtures (SRA). To date however, little information has been presented to describe how the performance of mixtures containing SRA’s could be predicted. In addition, little guidance exists to determine the dosage rate of SRA that should be used to achieve a specific level of performance. This paper describes initial research results from a study that has been aimed at quantifying the role of SRA at early-ages. The surface tension of various solutions of water and SRA was measured. In addition, free shrinkage measurements were conducted for specimens exposed to sealed and drying conditions from the time of set. Results indicate that shrinkage can be directly related to the concentration of SRA. Restrained ring experiments were performed to investigate the influence of a SRA on residual stress development and cracking in mortar. It has been observed that the residual stress reduction is not directly proportional to the reduction in free shrinkage since the specimens with SRA demonstrate less stress relaxation.