Effect of pore size distribution on drying shrinkage of alkali-activated slag concrete

Higher drying shrinkage has been observed in alkali-activated slag concrete (AASC) than comparable ordinary Portland cement concrete (OPCC). However, the OPCC samples lost more moisture during the period of shrinkage measurements than the AASC samples. This is contradictory to the commonly accepted relationship between shrinkage and moisture loss. This paper provides an explanation for this phenomenon by studying the effect of pore size distribution on the drying shrinkage. The investigation showed that AAS pastes have a much higher proportion of pore sizes within the mesopore region than OPC pastes. Further, the radius of pores where the meniscus forms seems to be an important parameter in determining the magnitude of shrinkage, rather than the amount of moisture loss. This also supports the theory that the capillary tensile forces set up during drying is an important contributory factor for the drying shrinkage of concrete.