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

Abstract

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.