Drying shrinkage and microstructure characteristics of mortar incorporating ground granulated blast furnace slag and shrinkage reducing admixture

Abstract

This paper presents an experimental study of the effects of cement type, ground granulated blast furnace slag (GGBFS) fineness, curing age, and use of shrinkage reducing admixture (SRA) on the drying shrinkage property and microstructure in mortar. The relationship between drying shrinkage and the microstructure characteristics is determined, and an equation that can reasonably predict the drying shrinkage behavior is also proposed according to the dependent variables. The test results revealed that the drying shrinkage evolution can be significantly affected by the GGBFS powder fineness, the cement type – ordinary Portland cement (N), moderate heat Portland cement (M), and low heat Portland cement (L), and the SRA dosage and pore volume of the mortar, but not the curing age (7 and 28days). For mortar samples without GGBFS, the N and L mortar samples exhibited greater shrinkage strain evolution compared to the M sample. For the case of mortar samples incorporating GGBFS, the L mortar sample exhibited the greatest drying shrinkage strain among the investigated mortar mixes. In addition, the drying shrinkage increased significantly with the increase in the GGBFS fineness for the M and L Portland cement mortars. Moreover, the addition of SRA could effectively reduce the drying shrinkage, which is mainly controlled by the pore size distribution and mass loss. In the case of mortar without and with SRA, the drying shrinkage was found to have a high correlation with the pore size ranges of 6–30nm and 0–20nm in diameter, respectively. As a result of the high correlation of pore volume and mass loss observed in this study, the prediction equation for the drying shrinkage of GGBFS mortar is proposed, which verifies good accuracy compared to the test results.