EFFECTS OF CEMENT COMPOSITION AND TEMPERATURE OF CURING ON AAR AND DEF EXPANSION IN STEAM-CURED CONCRETE

摘要

Steam-curing of concrete at high temperatures has been reported to have induced deterioration of field concrete structures due to delayed ettringite formation (DEF). However, other researches have found that the deterioration could, at least partly, be attributed to other expansive mechanisms, such as AAR. This issue has remained highly controversial and investigators often differ on the main mechanism of deterioration. Large scale and expensive litigation following the emergence of cases of deterioration, have not helped the controversy, and the opposing parties have been taking sides to blame their legal opponents, rather than genuinely attempting to find a scientific answer to the problem. This paper reports on a study which attempts to address this issue by investigating the effects of many parameters such as sulfate, aluminate, alkali content and curing temperature on the expansion of concrete. This study has shown that most cases of deleterious expansion have been associated with AAR expansion arising from the presence of high alkali content and reactive aggregate in the concrete, regardless of the curing temperature. However, on rare occasions when all the parameters, high aluminate, high sulfate, high alkali and high temperature of curing are concurrently present then DEF expansion may occur in the absence of reactive aggregate. Incorporation of appropriate amounts of supplementary cementitious materials in concrete removes the risk of both AAR and DEF.