Controlling ASR in concrete by surface treatment - Field performance investigation

Several concrete structures in Denmark have been built with potentially ASR-reactive aggregates. Most of these concrete structures have been constructed in the 60's and 70's and includes more than 600 large concrete bridges. Unfortunately, during the last 10 to 20 years an increasing number of these concrete structures have become severely deteriorated due to alkali-silica reaction (ASR). Since it can be extremely expensive to replace these concrete structures, it is desirable to develop and implement better economic methods to prolong the service life of these concrete structures. Surface treatment of concrete samples in the laboratory shows promising results by controlling the moisture content. The surface treatment can delay or even prevent the ASR from developing. In this study, it is investigated whether silane-based surface treatment can reduce the relative humidity inside the concrete. Eight concrete cubes (0.3x0.3x0.3m³) with water/cement-ratios of 0.45 and 0.55 have been casted and exposed to outdoor climate conditions over a period of nearly three years. Half of the concrete cubes contain ASR-reactive aggregates (porous opaline flint) and half of the concrete cubes have been impregnated with a silane-based surface treatment. Moisture and temperature sensors (HumiGuard) measure the relative humidity and the temperature inside the concrete cubes during outdoor exposure (field exposure). The results of this study show that the surface treatment can significantly reduce the relative humidity inside the concrete. Furthermore, it is shown that the ASR expansion was delayed or even prevented by avoiding external moisture contribution to the ASR development. The wlc-ratio has a significant influence on the initiation of cracking in the concrete cubes.