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24 May 2004
Materials and Construction Research Division
Building and Fire Research Laboratory
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA
Degree of hydration and differential scanning calorimetry (DSC) measurements are used to characterize the effect of early exposure to a 90 % relative humidity (RH) environment on cement paste hydration. Early exposure to a 90 % RH environment can lead to the consumption of freezable water and altered microstructural development. The minimum duration of 100 % RH curing required to eliminate the effects of an unsaturated environment on microstructural development coincides with the appearance of a DSC peak near -30 ºC that occurs in the range 1 d to 14 d for the pastes studied. The Jennings colloidal microstructural model is used to argue that the -30 ºC peak coincides with the cessation of capillary pore percolation. Alternatively, all samples cured under 100 % RH conditions for 7 d prior to 90 % RH exposure hydrated at the same rate as those continuously exposed to 100 % RH. Application of these results to the formulation of separate curing practices for durability and strength is discussed.
Keywords: A. Calorimetry; A. Curing; B. Degree of Hydration (Nominated); A. Humidity; B. Microstructure.