Effect of polymer coatings on the freezing–thawing and carbonation resistances of nano-SiO2 and polyvinyl alcohol fiber-reinforced cementitious composites

The inclusion of nano-SiO2 and polyvinyl alcohol (PVA) fibers can improve the strength and toughness of cementitious composites, and the durability can be further enhanced by protecting the surface of the composite with a polymer coating. Herein, three types of nano-SiO2 and PVA fiber-reinforced cementitious composites were prepared with water–binder ratios of 0.35, 0.40, and 0.45. Furthermore, the following three types of polymer coatings were applied to the surfaces of the protective objects: single-layer and double-layer chlorinated rubber coatings, polyurethane coatings, and permeable silane impregnation agents. The effects of the types and number of layers of polymer coatings on water absorption, freezing–thawing resistance, and carbonation resistance of the nano-SiO2 and PVA fiber-reinforced cementitious composites, as well as the effects of the water–binder ratio of the cementitious composites on the protective efficiency of the polymer coatings, were investigated. The results revealed that the three types of polymer coatings could decrease the capillary water absorption of cementitious composites and improve the freezing–thawing resistance and carbonation resistance of the composites. The carbonation depth and mass loss after freezing–thawing cycles of the material coated with a single polymer coating were reduced by 12–66% and 30.2–60.4%, respectively, compared with the corresponding values for the cementitious composites without coatings. Moreover, the effect of the double-layer polymer coatings was superior to that of the single-layer coatings. As the water–binder ratio decreased, the influence of the polymer coating on the durability of the cementitious composites became increasingly apparent.