Characterization of Aggregate Reactivity by Dissolution

In the context of concrete structures ageing, the study of cementitious material durability is of critical importance, particularly the degradations caused by the Alkali-Silica Reaction (ASR). This reaction is driven by the reactive silica dissolution of the concrete aggregate and can unfold in different manner according to the aggregate. The goal of the study is to improve the evaluation of the aggregate reactivity, in terms of quantity of reactive silica and dissolution rate, linked to the form and state (crystalline, amorphous, micro-crystalline) of the aggregate structure. Four aggregates were selected for this study: Potsdam sandstone, Springhill greywacke, Spratt limestone, and a non-reactive Quartzite (used as a reference). For dissolution properties assessment, the aggregates were immersed in a basic solution to promote the degradation of their reactive structure. To reproduce an idealized highly alkaline solution close to a concrete pore solution, dissolution tests were performed on a 1M NaOH solution. Two particle size fractions for each aggregate: 0.5 mm–1 mm and 1–2 mm (with a solid to solution mass ratio of 1:4) and three temperatures: 25, 38, and 60 ℃ were considered. Silica concentration in the solution was measured by complexometric titration. The study displays the dissolution rate constants and analyses the cause of the differences in dissolution.