Ceramics-Silikáty 62, (4) 332 - 341 (2018)

The surface treatment of existing concrete structures with silica-based organic and inorganic agents is often used to improve the durability of the structures, but their effects vary from each other, thus the recognition of their strengths and drawbacks could help to make good use of the techniques under various environments. In this work, tetraethyl orthosilicate (TEOS), an organic precursor for manufacturing silica sol, together with other two normally used silica-based agents, Na₂SiO₃ and silane, was used for the surface treatment of concrete. Their effects on the durability were studied and compared by investigating the compressive strength, the water absorption rate, the carbonation, the chloride penetration and the sulfate attack of cement concrete samples. The results showed that TEOS decreased the transport properties of concrete significantly: reductions of 49.0% of the water absorption rate, 28.5% of the chloride ion penetration depth, and 20% of the carbonisation degree to that of the control sample were found, while the corresponding values of 42%/80%, 39%/71%, and 23%/10% of Na₂SiO₃/silane-treated samples were shown. The compressive strength and visual observation showed that the samples treated by TEOS exhibited the best performance for long term exposure in the 5 wt. % sodium sulfate solution when compared with silane-treated and Na₂SiO₃-treated samples. The variation of the in-situ Ca(OH)₂ consuming capability of the agents, as well as their effects on the hydration and hardening properties of the cement-based material could be ascribed to their differences in improving the durability.