A study of the influence of slag alkali level on the alkali-silica reactivity of slag concrete

Ground granulated blast furnace slag (ggbs), can reduce the alkali load in concrete, despite its relatively high alkali content. Most research has been devoted to the efficacy of slag with an alkali content of less than 1.0% and this is reflected in guidance documents. A comparative assessment was made of the effect, if any, of the alkali level of ggbs on potential alkali-silica reactivity. Expansion tests were performed on a matrix of concrete mixes using Irish normal Portland cement, two slags of differing alkali content, three aggregates and alkali loads of 5 and 6 kg Na2Oeq./m3. A replacement level of 50% was used throughout. No significant difference in behaviour was apparent, irrespective of aggregate type or alkali load, indicating that the alkali level of the slag is not a contributory factor at the 50% replacement level.