Water Removal by Freeze-Drying of Hardened Cement Paste

This paper investigates the water removal extent of freeze-drying (F-drying) technique on hardened cement pastes. Two cement pastes with w/c = 0.5, 0.3 were prepared, and the authors measured the hydration degree, specific surface area, porosity, and solid skeleton density of the material samples at curing ages from 7 days to 180 days. From these results, the C-S-H gel volumes of samples are predicted from Jennings model and also evaluated from drying data. The good agreement between the results of two approaches confirms that F-drying removes only partially the water in gel pores of LD C-S-H structure. At the age of 180 days, the residual porosity saturated by water after F-drying is evaluated as 28% (w/c = 0.5) and 55% (w/c = 0.3) with dried C-S-H estimated as 28% (w/c = 0.5) and 13% (w/c = 0.3).