The alkali-silica reaction, part I: Use of the double-layer theory to explain the behavior of reaction-product gels

TLDR: In this paper, a double-layer model is proposed to explain the volume change behavior of mortar bars containing a reactive aggregate, and the expansion of the reaction-product gels is attributed to swelling caused by electrical double layer repulsive forces.

Abstract: An understanding of the expansion mechanisms resulting from alkali-silica reaction is necessary to assess the susceptibility of a concrete structure to deterioration by these processes and to the planning and implementation of preventive measures. As a result of the alkali-silica reaction between certain reactive aggregates and the highly alkaline pore fluids in a cement paste, a reaction-product gel develops that, in the presence of water, expands and may cause cracking of mortar or concrete. To explain the volume change behavior of mortar bars containing a reactive aggregate, a theoretical model is proposed in this paper. The expansion of the alkali-silica reaction-product gels is attributed to swelling caused by electrical double-layer repulsive forces. For a given colloidal system, double-layer theory indicates that the larger the valence of the counterions in the double layer, or the larger the concentration of these ions, the smaller the double-layer thickness and the repulsive forces that may be generated in the presence of water. Results of experiments from the literature support the double-layer model. According to these results, the expansion of mortar bars in the American Society for Testing and Materials (ASTM) C 1260 test is related to the composition of the reaction product gels. The reaction-product gels containing larger amounts of equivalent sodium oxide (Na2Oe) and smaller CaO/Na2Oe cause larger expansions in the mortar bars.