Suspended hydration and loss of freezable water in cement pastes exposed to 90% relative humidity

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 t9 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 .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 .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. Published by Elsevier Ltd. Keywords; Calorimetry; Curing; Degree of Hydration (Nominated); Humidity; Microstructure