Title:
Alkali-Silica Reaction, Part I: Use of the Double-Layer Theory to Explain the Behavior of Reaction-Product Gels
Author(s):
Monica Prezzi, Paulo J. M. Monteiro, and Garrison Sposito
Publication:
Materials Journal
Volume:
94
Issue:
1
Appears on pages(s):
10-17
Keywords:
alkali-aggregate reactions; concretes; expansion; mineral admixtures;
DOI:
10.14359/280
Date:
1/1/1997
Abstract:
An understanding of the expansion mechanisms resulting from the alkali-silica reaction is essential to the assessment of 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 counter-ions 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 (aqueous solution). Experimental results available in the literature support the double-layer model. According to these results, the expansion of mortar bars in the 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.