Performance of silane impregnants for the protection of reinforced concrete

Silanes can act as hydrophobic pore liners for reinforced concrete (RC) structures. They can significantly reduce the depth of chloride penetration, a major cause of steel reinforcement corrosion. There is little published information however, on their long-term performance. For this study, 32 concrete cores were extracted from eight full-scale RC bridge supporting cross-beams which had been treated with silane 20 years ago. Their rate of water absorption by capillarity was measured and compared with 16 control cores extracted from four non-silane treated RC cross-beams constructed at the same time. Results show that these silanes provide a residual protective effect against water even after 20 years of service. The performance of silane impregnations on concrete incorporating blended cements, and the effects of different formwork, ages of concrete and curing conditions prior to impregnation were also investigated. Concrete specimens were cast with CEM III/A (Portland cement with 50% ground granulated blast furnace slag) cement. The performance of the silane impregnation was assessed by the rate of water absorption due to capillary action. The results indicate that improvements in performance were identified within the sample groups of lower w/c ratios, steel finishes, outside curing and double coatings of silane treatment. The findings from both research programmes indicate that silane impregnations can provide a significant reduction to the water absorption characteristics of both site retrieved and laboratory cast concrete samples. It was observed that performance was reduced with increasing the age of the silane impregnation service life. In addition, silane impregnations applied at specimens with plywood or tampered finish demonstrated a greater reduction on water absorption than specimens with a steel finish.