Water Sorption of Hardened Cement Pastes

Hardened cement paste (hcp), binding the components in cementitious composites, usu- ally controls most strength, transport, and durability properties of these materials. Water sorption in hcps can cause durability problems such as sulfate and chloride ingress, frost deterioration, and esthetic problems. Replacement of air by water in the pores can also increase the thermal conductivity of the material and affect the energy efficiency. Capillary suction test as a simple method for characterization of the material resistance to water sorption is described in this chapter. Different factors affecting water sorption of hcps such as changing water to cement ratio (w/c), using pozzolanic materials, and internal hydrophobation are also discussed. Furthermore, resistance number, capillary number, and pore protection factor as different criterions for characterizing the mois ture transport in cement-based materials are described. Since cement-based materials modified for reducing water sorption have different behavior in capillary suction test compared to ordinary materials, the abovementioned criteria may become inapplicable for characterizing these materials. Thus, “effective moisture transport ( EMT )” factor is introduced here which can be a more comparative measure for modified cementitious materials with denser or internally hydrophobed pore structure.