It is more than 30 years since ASR (Alkali Silica Reaction) problem was recognized in Japan. In port and harbor structures, the first report on the ASR problem was issued as a PHRI technical note more than 10 years ago1). In the last decade, the concern to the ASR problem in the concrete engineering field was dissipated. However, in recent years, a serious real structures, damage due to ASR was newly found, and, the significance of the ASR problem is recognized again. The research work described in this report, is focused on the effectiveness of surface coating on the prevention of ASR reaction and expansion. The main objectives of this study are, 1) to check the effectiveness of surface coating on the expansion prevention for ASR affected concrete, and 2) to check the effectiveness of surface coating on the internal stress of ASR-affected RC beams and RC columns under sustained load. The main conclusions obtained in this study are as follows:
1) The ASR-affected concrete located under very severe wettingconditions in which concrete surface is always wetted, such as submerged or tidal zones, could not be thoroughly protected from expansion by surface coating.
2) The best surface coating material is varied depending on the environmental conditions. Therefore, the choice of coating material should be based on these conditions.
3) Under mild wetting conditions in which concrete surface is exposed to wetting and drying, surface coating can protect concrete from ASR reaction and expansion.
4) Surface coating effects can be obtained when concrete is coated before the initiation of ASR reaction and expansion.
5) Surface coating effects can be obtained when all area of concrete surface is coated.