Abstract
The main object of the presented research was to investigate properties of water confined in hardened cement paste with w/c ratio equal to 0.5. The experimental analysis was conducted by means of differential scanning calorimetry on samples containing various moisture content which reflected the equilibrium with ambient air of RH = 11%, 54%, 75%, 84%, 93%, 97%, and 100%. Consequently, the relation between temperature and ice content was provided for partly saturated samples. The recorded thermograms consisted of two main peaks which clearly separated the transitions of liquid confined in capillary pores from that within gel ones. Concerning the molecules migration during freezing the ions concentration in gel pores for various moisture content was increasing. The analysis also involved the phase transition hysteresis between melting and freezing of partially saturated cement paste. It was established that apart from different interfacial curvatures, changeable concentrations of ions contained in pore solution can serve as a supplementary explanation of the hysteresis. Hence, we also investigated how the presence of ions affected the phase transition temperature of pore solution and final ice content in cementitious materials. The arguments for underestimating the pore size of cement-based materials using the Gibbs-Thomson equation were provided.
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