A New Approach to Evaluating the Effectiveness of Pozzolanic and Blastfurnace Cements against Alkali-Silica Reaction in Concrete

摘要

In this study, a new approach for the evaluation of the effectiveness of pozzolanic and blastfurnace cements against Alkali-Silica Reaction (ASR) in concrete is proposed. This approach is based on the concepts of the Threshold Alkali Level (TAL) of the aggregates and the driving force (DASR) for ASR development. The TAL is defined as the minimum concrete alkali content above which deleterious ASR expansion is developed by a specific aggregate. The DASR is defined as the concrete alkali content exceeding TAL. Thus, it is possible to derive a performance parameter specific for every blended cement, represented by the tolerable driving force (Dtol), i.e., the maximum concrete alkali content exceeding TAL that does not produce deleterious expansion. Such an approach was validated experimentally through different sets of expansion tests on concrete mixes made with four Italian blended cements conforming to EN197-1 (two pozzolanic cements made with natural pozzolana, one pozzolanic cement with siliceous fly ash, one blastfurnace cement) and three Italian aggregates of different alkali reactivity (TAL). Three different concrete expansion tests were used: the expansion test at 38°C and 100% R.H., the accelerated expansion test at 60°C and 100% R.H., and a new ultra-accelerated expansion test in alkaline solutions at 150°C. The experimental results indicate that: 1) the tolerable driving force, Dtol, is a suitable parameter for qualifying the efficacy of blended cements against ASR; 2) the cements tested in this study are very effective in counteracting deleterious ASR expansion, being all characterized by very high Dtol values (2.9 – 4.6 kg Na2Oeq/m3); 3) there exists a good correspondence between the Dtol values determined with the three concrete expansion tests; 4) the ultra-accelerated concrete expansion test in alkaline solutions at 150°C has proved to be a rapid and reliable test method for evaluating the effectiveness of blended cements against ASR.