A new approach for assessing the potential alkali expansivity of slowly reactive siliceous aggregates in concrete

The combination of a petrographic analysis with the ASTM C1260-94 mortar-bar expansion test in a 1 M NaOH solution at 80°C and the current standard concrete prism expansion test at 38°C and 100% relative humidity (RH) appears to be the best guidance for evaluating the potential alkali reactivity of siliceous aggregates. To ascertain the reliability of this test methodology, concrete prism expansion tests are performed both in accordance with the standard test procedure and by varying the alkali content of the concrete in the range 2.3 to 9.0 kg Na2Oeq/m3 of concrete. Based on the results, a modification of the test methodology is suggested for better evaluating the potential alkali reactivity of slowly expanding aggregates.