Long-term superhydrophobic coatings for concrete by producing bonds with cement matrix

Water is the main vehicle of decay agents in concrete due to its highly permeable and hydrophilic nature. In recent years, numerous superhydrophobic treatments, combining hydrophobicity and repellence, have been developed. Their main drawback is their poor durability, especially at outdoor conditions. Herein, an advanced material with long-lasting superhydrophobic performance has been developed. Specifically, an organically modified silica (ormosil) based sol, with ability to penetrate into pores and cracks of concrete and spontaneously react with portlandite to produce C-S-H gel, the main component of cementitious materials, was successfully prepared. A comprehensive study of interaction processes of the sol with portlandite demonstrated that it creates chemical bonds with cementitious substrates through two complementary mechanisms: direct reaction of the silica precursors and pozzolanic reaction of the silica xerogel produced. Performance and durability of cement mortars treated with the sol were validated at laboratory conditions, confirming that superhydrophobic properties (static angle of 160° and sliding angle <5°) are obtained due to the combined effect of a surface energy reduction, by the organic components, and creation of a regular nanoroughness produced by silica nanoparticles also incorporated to the sol. Durability, which is maintained after a heavy rain test, is linked to its capacity to bond with the substrate. Finally, validation was carried out on site in a concrete-based memorial in Lithuania. The performance was maintained after 21 months. • An advanced material to preserve concrete has been successfully developed. • A starting sol was optimized to penetrate into concrete pores. • The sol is able to produce C-S-H gel in presence of portlandite. • Long-lasting superhydrophobic performance is promoted. • On-site validation was successfully carried out in a concrete memorial in Lithuania.