Prolonged rainy conditions in the efficacy of concrete protection

Abstract

Hydrophobic impregnation is the most widely employed method to combat chloride attack for concrete structures. According to the UK Design Manual for Roads and Bridges, it is required to apply impregnates onto dry surfaces, after natural drying for 24 h following wet conditions. Achieving a dry surface in this manner results only in superficially dry concrete in a structure that has been exposed for a prolonged period of wet conditions. In this study, a silane-based material and a water-based material were evaluated, each applied on concrete cubes subjected to moisture pre-conditioning for up to 48 h. The test cubes were all surface dried prior to the application of the impregnate, and then submerged in sodium chloride solution for 60 d, before collecting dust samples at various depths, by dry drilling. When applied in dry conditions, the silane-based impregnate was more effective than the water-based one. The performance of both impregnates was significantly reduced when the concrete was subject to wet conditions for long periods. Internal moisture thus has a significant effect on the performance of the impregnates. A practical interpretation is that the specified 24 h drying period may not be sufficient to secure the benefit from hydrophobic impregnation.