A comparison of methods for chemical assessment of reactive silica in concrete aggregates by selective dissolution

This work is a part of a project developing a method to predict the potential expansion of concrete containing alkali-reactive aggregates. The method is based on an original approach which combines laboratory tests on sample cores and finite element calculations to assess the chemical ASR-advancement of aggregates. The chemical advancement of the reaction is linked to the reactive silica content in the aggregates and this work uses chemical methods to evaluate the proportion of reactive silica in different types of aggregates: opal, siliceous limestone, quartzite and quartz aggregate. The evaluation includes (1) mineralogical studies (XRD and petrography) to characterise the reactive sites, (2) chemical methods using acid and/or basic attacks (NaOH–HCl, HCl–KOH, HF) to measure the reactive site content. When these methods are discussed and compared, HF attack is found to give relevant results in short periods of time.