Alkali-silica reaction in finnish swimming pools

Finland has traditionally been considered an alkali-silica reaction (ASR) free country. This was thought to be due to the exceptional quality of the mostly coarse crystalline igneous rocks. However, during the last few years dozens of cases of ASR have been reported. The scope of this study was to survey the occurrence and the propagation time of ASR in recent investigations of swimming pool structures. The research data consists of 9 condition investigation reports, and the reports of 144 thin section analyses, 188 tensile strength analyses and 29 compressive strength analyses made during 2005-2018. According to the research data, the occurrence of ASR is spread all over Finland. The reacting aggregates consist of rock types which are considered relatively stable or low reacting in literature. This may explain the relatively late emergence, usually around 40 years, of ASR. However, the swimming pool environment, with relatively high temperatures and humidity, is more favourable for ASR than the average Finnish outdoor climate. In most cases ASR has been incipient. Only few of the tensile strength tests made have indicated local weathering in the leaking concrete pool. ASR can be reliably detected in a petrographic thin section analysis, but evaluating the degree of ASR -caused damage also requires tensile strength testing. Observations of silica gel, or reacting aggregate, do not necessarily indicate serious damage or direct correlation with the degree of cracking. Therefore, parallel test methods, i.e. thin section analyses and tensile strength tests, are needed to diagnose the ASR in a concrete structure and the possibility of repair.