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Suspended Hydration and Loss of Freezable Water in Cement Pastes Exposed to 90% Relative Humidity.


pdf icon Suspended Hydration and Loss of Freezable Water in Cement Pastes Exposed to 90% Relative Humidity. (3071 K)
Snyder, K. A.

Cement and Concrete Research, Vol. 34, No. 11, 2045-2056, November 2004.

Keywords:

cement pastes; hydration; water; humidity; calorimetry; curing; microstructure

Abstract:

Degree of hydration (DOH) 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% RHcuring required to eliminate the effects of an unsaturated environment on microstructural development coincides with the appearance of a DSC peak near -30 deg C that occurs in the range 1-14 days for the pastes studied. The Jennings colloidal microstructural model is used to argue that the -30 deg C peak coincides with the cessation of capillary pore percolation. Alternatively, all samples cured under 100% RH conditions for 7 days prior to 90% RH exposure hydrated at the same rate as those continuously exposed to 100% RH. The application of these results to the formulation of separate curing practices for durability and strength is discussed.