Long-term volume changes and microcracks formation in high strength mortars

Volume changes of high strength mortars cured in water were investigated. Effects of characteristic microstructure on the volume stability were considered in relation to the formation of microcracks. Mortars without silica fume exhibited swelling at early ages while the ones with silica fume started to swell at long ages after a certain period of initial shrinking in water. Cracking at long ages was confirmed for the both mortars with and without silica fume. However, there were distinct differences in the characteristics of crack patterns, such as the situation for cracking and their effects on the strength development between both. It was suggested that a mechanism other than autogenous shrinkage was involved in volume changes which occurred in mortars with an extremely low water/binder ratio. Generation of the internal expansive pressure due to the late cement hydration should be taken into account for a mechanism to cause microcracks in mortars at long ages.