Assessing the long-term durability of silanes on reinforced concrete structures

Concrete is a porous material. The size and distribution of pores in concrete varies, depending upon the quality of compaction, the materials, the water-to-cement ratio and the degree of hydration. Many of these pores are inter-connected creating larger and more complex pore systems. Water can penetrate this network and cause deterioration of the concrete structure. Silanes have been generally used in the past to help protect reinforced concrete exposed to an aggressive environment. The treatment works as a pore liner, thus making the concrete hydrophobic. This action helps prevent water ingress and can significantly reduce chloride penetration - a major cause of corrosion of the steel reinforcement in concrete. This study was initiated after it was identified that long-term performance data of silanes is scarce and lacking in-depth analysis. Most of the research work previously undertaken aimed to illustrate their viability using different proprietary products and in a variety of exposure conditions. Maintenance Agencies have yet to reliably establish the protective period provided by silanes, and as such the whole life cycle costs are relatively unknown, resulting in a general lack of enthusiasm to their use in the last decade. Twelve structures were selected for investigation, which were treated with silane more than 10 years ago. Cores were extracted and their capillary suction measured in the laboratory in order to assess their permeability when compared to control cores from similar un-treated structures, all constructed during the same time period. The study is ongoing and this paper presents the findings with regard to the long-term performance of the silanes. These show that silanes have a residual protective effect even after 20 years of service. The results improve our understanding of the effective duration of the hydrophobic protective effect, and thus contribute to future whole life cycle costing of such treatments. In turn this can improve the overall corrosion management strategy available for reinforced concrete structures.