To establish an optimum surface protection system with silane type water repellents, experimental investigations were conducted for 2 kinds of water repellents that had shown good water absorption controlling effect in a previous exposure test in an actual structure carried out by the authors. The effects of the age of application of water repellents and the effects of the curing conditions before and after the application on the penetration depth of water repellents and the water absorption controlling effect were investigated for concretes of different mix proportions with four different W/C, of 35%, 42%, 50%, 65%. Furthermore, the specimens used for the water absorption tests were subjected to a weathering test to examine the durability of the water absorption controlling effect.In dry concrete, both water repellents showed a good water absorption controlling effect. While it is generally considered desirable that the water repellents be applied at an early age to obtain a better water absorption controlling effect, the authors propose that water repellents should be applied not too early for low W/C concrete, in order to ensure a penetration depth of at least 1 to 2 mm. The penetration depth and water absorption controlling effect are affected by the curing conditions before and after application of the water repellents. When the specimens with water repellents were subjected to a weathering test using a Xenon arc lamp for 98 days (equivalent to 2.8 years of weathering in Tokyo), no degradation of the water repellent layer was observed. Considering the experimental results in this study, an optimum surface protection system for newly constructed structures is proposed.
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