Mechanism of Water-Resistant Performance Enhancement in Paraffin Phase-Change Film–Forming Cement-Based Materials

The effects of the baking temperature and paraffin content on the water resistance and degree of phase change of paraffin phase-change film–forming cement-based materials (PPFCMs) were studied by observing the phase-change melting state of paraffin in cement-based materials mixed with paraffin powder under the action of baking and measuring the water absorption and degree of seepage of specimens immersed in water for an extended period. The hydrophobic characteristics of the cement matrix and microscopic morphology of its internal phase-change paraffin film were studied. The results indicated that the water absorption of the PPFCM immersed in water for a long time (30 days) decreased significantly at first and then decreased gently with the increase in the paraffin content and baking temperature. The specimens could achieve the effect of blocking water infiltration with a decrease in the water absorption to a stable value. When the baking temperature was high (>80°C), the paraffin inside the cement-based material could be melted into the best colorless and transparent adhesion state. The phase-change paraffin in the cement matrix exhibited a relatively dense, smooth, and film-like structure at the microlevel. These films firmly adhered to the surface of the cement stone structure, endowing the PPFCM with excellent hydrophobic properties (water contact angle >90°).