Geochemical Method for Identifying Alkali-Silica-Reaction Gel

Abstract

A geochemical method for staining various products of the alkali-silica reaction is presented. The method is based on both the composition of alkali-silica-reaction (ASR) gel and one of its properties (the ability to exchange cations with a fluid). Specifically, one stain (sodium cobalt-initrite) reacts with exchangeable potassium in the gel to form a bright-yellow precipitate on the gel surface. The other class of stains (a variety of rhodamine compounds) reacts with calcium-rich portions of the gel (and, for some compounds, with other calcium-rich components of the concrete) to form a pink-stained gel. The significance of the pink staining is twofold. First, it can provide a high contrast to the yellow-stained gels, making them easier to observe. Second, some rhodamine compounds react predominantly with Ca-rich ASR gels. Some aspects of staining by rhodamine remain the subject of continued study and may be useful for a more detailed understanding of ASR progression and other deterioration mechanisms. However, a positive diagnosis of ASR is indicated by the presence of yellow-stained gel within aggregate, at the aggregate-paste interface, along fractures, or in air voids. The technique can be used as a rapid field screening method or as a useful aid for detailed petrographic examinations.