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Conclusions

It has been shown that curing environments can have a significant effect on cement hydration kinetics. Even exposure to a 90% RH environment, after 6 or 12 hours of curing at 100% RH, can effectively terminate the hydration process as all remaining capillary water is removed from the specimen. While curing under sealed conditions may be adequate for systems with w/c ratios greater than 0.4, for lower w/c ratios, a significant reduction in the achieved degree of hydration has been observed. The best curing practice, similar to that originally suggested by Powers [12], may be to maintain surface saturated conditions until the capillary porosity depercolates, which will occur at different curing ages for different w/c ratios, and then seal the surface to prevent any moisture loss. The NIST cement paste hydration and microstructural model has provided valuable insights into the effects of sealed conditions and the resultant chemical shrinkage on hydration kinetics and microstructure.