The use of hydrophobicity and pozzolanic reactivity of the PMHS/nanosilica hybrid composites on the water absorption of cement mortar

the durability of cement-based materials can be significantly improved by surface treatment with organic or inorganic silica-based treatment agents. in this paper, silica-based organic and inorganic hybrid composites (polymethylhydrosiloxane/nanosilica, pmhs/ns) were synthesized for surface treatment and their performances on hardened cement-based material were determined by measurements of the water absorption rate, water contact angle, and resistance to detachment by rain-washing. the thermogravimetric analysis results showed that 88.33, 65.38, 77.68, and 79.78% of pmhs are physically attached to ns in mixtures at pmhs/ns mass ratios of 1.2, 0.95, 0.7, and 0.6. moreover, through calorimetric measurement and thermogravimetric analysis, the reaction of the hybrid material with hardened cement-based material was simulated and evaluated by its reaction with ca(oh)2, i.e., the pozzolanic reaction. results showed that hydrophobicity has been introduced to the surface of cement-based material after surface treatment and the water absorption rate can be reduced by over 80%. moreover, the involving of ns could make the hybrid material more rain resistance: hybrid material with pmhs-to-ns mass ratio of 0.6 showed a superior water proofing effect (introduced by its in situ pozzolanic reaction) after simulated rain-washing. this work demonstrated the potential of taking advantages of the hydrophobicity and pozzolanic reactivity of the silica-based hybrid material synergistically in endowing an improved durability of cement-based materials.