Internal Curing of High-Performance Blended Cement Mortars:

In the twenty-first century, most high-performance concretes, and many other ordinary concretes, are now based on blended cements that contain silica fume, slag, and/or fly ash additions. Because the chemical shrinkage accompanying the pozzolanic and hydraulic reactions of these mineral admixtures is generally much greater than that accompanying conventional portland cement hydration, these blended cements may have an increased demand for additional curing water. When such water cannot be supplied efficiently by external curing, internal curing becomes necessary, if the maintenance of saturated hydration conditions in the blended cement paste is desired. In this paper, the internal curing of three different high-performance blended cement mortars is evaluated with respect to measured autogenous deformation and compressive strength development. Internal curing is particularly beneficial for the mortars containing silica fume or slag blended cements. For the blended cement containing a Type F fly ash, less autogenous deformation is observed, due to the maintenance of a more open (percolated) pore structure containing larger pores, as supported by low temperature calorimetry measurements on hydrated paste specimens. In addition to providing a substantial reduction in autogenous shrinkage at early ages, internal curing also provided a significant increase in long term (28 d and beyond) compressive strength in the three mortars investigated in this study.