Alteration of sorption properties of hardened cement paste under drying process

Hydrated hardened cement paste samples using white cement were cured under different relative humidity con- ditions. After 180-day drying, Adsorption and desorption isotherms as well as chemically bound water of cured hard- ened cement paste were measured. Based on the adsorption data, it was concluded that drying process has two dif- ferent effects on a sorption property. One effect was seen in drying process over 70%RH. Capillary pore with more than 2nm size was collapsed and amount of capillary condensation is decreased as it is dried in the lower relative humidity. The second effect was seen in drying process under below 60%RH. The vapor BET surface area was dra- matically decreased as cement paste cured in lower relative humidity. From the change of chemically bound water and vapor BET surface area, it was deduced that a reaction of silanol to siloxane bond in C-S-H poses decrease in vapor adsorption sites.