Self-compensating autogenous shrinkage in Portland cement—metakaolin—fly ash pastes

Abstract

For concrete containing high amounts of cement, particularly for (but not restricted to) hot climatic conditions, the rate of hydration may be high enough to cause shrinkage problems. Use of some admixtures such as silica fume and pulverized fuel ash (PFA) may further increase shrinkage. Blending Portland cement (PC) with metakaolin (MK) has shown expansive tendencies which may be applicable in suppressing early shrinkage. By blending MK with PFA partially to replace PC, shrinkage may be regulated. The current work is particularly directed towards regulation of autogenous shrinkage. Paste bars in which PC was replaced by up to 20% MK, 30% PFA and 30% MK plus PFA blends were monitored for autogenous shrinkage for up to 200 days during sealed moist curing at room temperature and 100% relative humidity. The results reported show reduced autogenous shrinkage, although cement type was also found to be an important factor in influencing shrinkage. The use of PC-MK-PFA blends should provide technological, economic and environmental advantages by reducing PC production and its associated greenhouse gas emissions, and improving concrete durability