Une nouvelle methodologie de qualification des granulats siliceux vis-a-vis de l'alcali-reaction dans le beton

摘要

In this study, the reliability of both the French (AFNOR P18-542) and the Canadian (CSA A23.2-27A) test methodologies for the qualification of aggregates susceptible of alkali-silica (A-S) reaction in con-crete was verified on some Italian natural siliceous sands of known long-term field performance. A new test methodology, based on the utilization of the petrographic examination (ASTM C295), the mortar-microbar expansion test (AFNOR P18-588) and a method of determination of the threshold alkali level, TAL, was also developed. It was found that the Canadian test methodology does not appear to be appropriate for evaluating the potential alkali-reactivity of the tested sands. Conversely, a correct diagnosis for the A-S reactivity of these sands is obtained through the use of the French test methodology. However, both test methodologies do not appear suitable for strictly predicting the expansive behaviour of a given aggregate when subjected to variations of composition and/or environmental exposure conditions of concrete. The proposed test methodology, which is essentially based on the use of the threshold alkali level, TAL, as a reactivity parameter, appears to be more appropriate for such a prediction, at least for the sands investigated.