The role of composition in the structure and water-binding in alkali-silica reaction sol and gel

The discrepancy between alkali cation (Na+) used in accelerated assessments of potential alkali-silica reactivity (ASR) and those predominant in portland cements (larger amounts of K+ than Na+) leads to questions regarding the reliability of standardized test methods to predict concrete field performance. To better understand the role of alkali cation type in ASR, this study investigates the influence of alkali cation type on the structure and water-binding ability of ASR sols and gels of varying composition. Results obtained by small-angle neutron scattering, H-1 NMR relaxometry, and rheological measurements indicate the formation of densified agglomerate structures with increasing silica-to-alkali molar mass ratios (S/A). However, Na-based sols exhibit a greater tendency to agglomerate and a higher dynamic viscosity than K-based ones. Furthermore, at high S/A, H-1 NMR relaxometry shows the greater ability of K-based gels to bind water, suggesting the better dispersion of siliceous structures and the development of finer porosities.