2017 Volume 71 Issue 1 Pages 440-447
Two kinds of PC beams both containing reactive aggregate and high alkali, one with fly ash（FA）and one without FA, were cast and subjected to a field exposure test. Next, core samples were taken and further subjected to an accelerated expansion test in 80℃ 1N NaOH solution（ASTM C 1260）. The results showed that the addition of FA almost completely suppressed ASR during the exposure test, but that the same FA-enriched concrete significantly expanded during the subsequent accelerated expansion test. Petrographic examination indicated that FA mitigated ASR adequately against internal alkali, limiting deterioration to the formation of minute, thin cracks during the exposure test in the field. However, alkali solution was able to pass through these cracks in spite of FA-caused densification of the cement paste, which usually prevents the infiltration of external alkali. This was considered to be the reason why FA did not suppress ASR in the subsequent accelerated expansion test, during which ASR occurred even in non-reactive granitic rocks. These results from the accelerated expansion test disagree with the field exposure test and real ASR occurrence in the field. Based on the foregoing, it was thought that adapting ASTM C 1260 for judging whether or not deterioration of a structure is due to ASR would not necessarily be appropriate. The length density of minute cracks under polarizing microscope increased and the ultrasonic pulse velocity decreased.
