Application of resin-TiO2 nanoparticle hybrid coatings on travertine stones to investigate their durability under artificial aging tests

• Performance of resin-TiO 2 NPs hybrid coatings in protecting travertine stones was studied. • Samples coated by resin-anatase NPs had the best durability against the aging tests. • The use of coatings on the stone samples significantly increased their surface hardness. • The addition of nanoparticles to resin increased the durability of stone. Three different stone coating products including industrial resin, resin-anatase nanoparticles and resin-rutile nanoparticles (NPs) were used to evaluate their stone surface protection effect against thermal shock and salt crystallization on three types of porous travertine stones. The results showed that the use of nanoparticles of both TiO 2 polymorphs (rutile and anatase) dispersedly in resin, significantly increased durability of the stones surfaces during the aging tests. No color change in the sample surfaces is another advantage of the resin-TiO 2 NPs hybrid coating. Product with anatase nanoparticles shows by far the best performance in protecting the stone surfaces. In both aging tests, samples coated by resin-anatase NPs had the lowest mass changes and the highest surface hardness compared to samples coated by the other coatings. Mineralogy, porosity and microbial activity textural features controlled the durability of the studied stones. Mono-mineral composition and macro porosity of studied samples explain their significant durability against the thermal shock process. On the other hand, the growth of salt crystals in the pore space of the stones in some cases induced macroscopic cracks, particularly in Abarkooh sample with high porosity and microbial textural features Scanning electron microscopy observation confirms that the samples underwent microcracking processes related mainly to salt crystallization pressures. Finally it can be concluded that the resin-TiO 2 NPs hybrid coating had a good compatibility with the stone substrate and could be very promising to protect the porous stone façades against natural aging processes.