Difficulty in Determining the Alkali Threshold Based on CPT Results

In order to control alkali-silica reaction (ASR), various standards set an upper limit for the total alkali content (Na₂O_eq) of concrete, and performance tests of specific aggregates have been conducted to determine the alkali threshold (AT) to be tolerated in terms of ASR risk. It well established that ASR expansion does not always show a positive correlation with concentration or quantity of Na₂O_eq. In other words, AT is not simply fixed at a constant value. In JASS 5N, the construction specification for nuclear power plants by Japan Architectural Society Standard, the case where the expansion would be greater at smaller Na₂O_eq is also considered. However, it is unclear under what conditions the expansion becomes greater when the Na₂O_eq is smaller. Therefore, in this study, alkali-wrapped concrete prism test (AW-CPT) was conducted for a long period of time on Norwegian cataclasite and four types of Japanese reactive aggregates with different Na₂O_eq and temperatures to identify ATs. The test results strongly suggested that AT cannot be simply determined. The difficulty of determining AT by CPT under a single condition was clearly shown in this paper.