Hydrophobic impregnation of geopolymer composite by ethoxysilanes

Anotace: A geopolymer composite was impregnated by incorporating the hydrophobic alkyl group on the outer surface and in the inner structure of the geopolymer. Ethoxysilanes 1H,1H,2H,2H perfluoroctyltriethoxysilane and hexadecyltrimethoxysilane were used as the source of hydrophobic groups. Three types of solutions based on the ethoxysilanes were prepared according to adapted procedures. The modification of the geopolymer composites was done by their immersion into the hydrophobic solutions followed by drying at a laboratory or elevated temperature. The effectivity of the procedure was evaluated by measuring the water contact angle on the surface of the modified composite and by measuring the water uptake and stiffness of the composite. The results confirmed that the silanes hydrolyzed in sol containing SiO2 nanoparticles have a higher hydrophobization effect than solutions of simply hydrolyzed silanes. The resulting impregnation procedure led to the change of the geopolymer composite surface from hydrophilic to hydrophobic.