Performance of high alkali slag concretes in the context of alkali-silica reaction

The depletion of natural resources, the requirement for sustainable development and environmental restrictions, such as those associated with the Kyoto Agreement, makes the re-use of waste materials increasingly important as we enter the new millennium. The use of one such material in concrete, ground granulated blast furnace slag is well-accepted in many parts of the world. However much research and experience of use is based on slags with low alkali levels and low chloride contents. Environmental and economic constraints may force the increased use of slags with higher alkali levels and chloride contents in future works. The alkali level parameter raises concern in respect of alkali-silica reaction (ASR) where susceptible aggregates are used. The performance of high alkali slags in the context of ASR was assessed by a modified version of the concrete prism expansion test, X-Ray diffraction and scanning electron microscopy. Variables in the test programme were binder combination, slag alkali level, aggregate combination, and storage temperature. Previous research by the authors had identified Irish argillaceous limestone aggregate as potentially classifiable as ASR-vulnerable, despite a low silica content and a satisfactory service record. The performance, in the context of ASR, of argillaceous limestone slag concretes was specifically studied. The study found that inclusion of slag in concrete can be beneficial in inhibiting ASR irrespective of the alkali content of the slag. The particular case of argillaceous limestone slag concrete is commented on.