Combined effect of shrinkage reducing admixtures (SRA) and superabsorbent polymers (SAP) on the autogenous shrinkage, hydration and properties of cementitious materials

Abstract

This paper examines the combined effect of superabsorbent polymers (SAP) and shrinkage reducing admixtures (SRA) on the autogenous shrinkage, hydration, microstructure, and properties of cementitious materials. The addition of SRA was found to reduce the absorption of SAP in the extracted pore solution as well as in the cement pastes. It was shown that the cement pastes with both SAP and SRA exhibited a higher shrinkage than the cement paste with SAP, more notably at the early age. The hydration temperature peak of the cement paste with both SRA and SAP occurred sooner than that of the cement paste with SRA at early age. The non-evaporable water content measurement indicated a higher degree of hydration for the cement paste with both SRA and SAP than the cement paste with SRA due to the internal curing effect of SAP. The compressive strength and electrical resistivity of the cement paste with both SRA and SAP were shown to be lower than those of the cement paste with SAP and the cement paste with SRA. Addition of SAP appeared to promote increased Ca(OH)2 formation in the hydration product. SEM examination indicated a distribution of microvoids in the range of 10–20μm in the microstructure of the cement paste with SAP and SRA at 28days, which could be responsible for a lower compressive strength of the cement paste with SAP and SRA compared to the cement paste with SAP at this age.