Effect of SiO2 oligomers on water absorption of cementitious materials

SiO2 oligomers, a kind of intermedium between silane and SiO2 nanoparticles, reveal small size, hydrophilic property, and high affinity with cement paste. In cement-based materials, the SiO2 oligomers transform into SiO2 nanomaterials. This is first time to report SiO2 oligomers created by the hydrolysis and condensation reactions of tetraethyl orthosilicate in an acetic acid solution to reduce the water absorption rate and modify the surface microstructure of cement-based materials. Mild acetic acid makes the stable formation of SiO2 oligomers which promote the reaction with cement phases. Linear, branched and 3D-chain structures of SiO2 particles can be formed in sequence during the condensation of oligomers. The water absorption rate of cement mortars treated with SiO2 oligomers was reduced to 46.4%. The SiO2 oligomers were ideal candidate as a surface-treated agent which resulted in surface densification of cement-based materials.