Fly Ash and Granulated Blast Furnace Slag to Mitigate the Alkali Silica Reaction in Concretes

Abstract

The alkali silica reaction (ASR) is a pathological manifestation of chemical origin and high gravity that can negatively affect the mechanical properties and durability of important concrete structures, even with short time in service. The reaction results from the interaction of Portland cement alkalis and other sources (internal and external to concrete) with the reactive silica of the aggregate. Several studies are under development about the best approach for the mitigation of ASR. The use of supplementary cementitious materials (SCM) has been widely accepted. One of the first SCM studied was the fly ash and, in recent years, the granulated blast furnace slag has also been fairly addressed in research. To have the expected efficacy, fly ash and granulated blast furnace slag must present some peculiar characteristics such as high total concentration of silica, alumina and hematite, high fineness and reduced alkalis content. The protection mechanism offered by fly ash and granulated slag involves not only the pozzolanic action, but also the possibility of fixing the alkalis in the pozzolanic C-S-H, reducing the CaO/SiO2 ratio of the C-S-H formed by the Portland clinker and reducing the permeability of the concrete. Currently, the use of SCM is still the best approach in the ASR mitigation because, in addition to offering technical advantages, it also contributes to reducing the environmental impact caused by industries in different segments, either by reducing the CO2 released into the atmosphere or by reusing by-products.KeywordsAlkali-silica reaction mitigationFly ashGranulated blast furnace slagProtection mechanism