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