BFRL ICON 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.



Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899