Mathematical model for kinetics of alkali-silica reaction in concrete

Vast though the literature on the chemistry of the alkali-silica reaction ( ASR) in concrete has become, a comprehensive mathematical model allowing qu antitative predictions seems lacking. The present study attempts a step tow ard this goal. While two distinct problems must be dealt with, namely, (1) the kinetics of the chemical reaction with the associated diffusion process es and (2) fracture mechanics of the damage process, only the former is add ressed here. The analysis is focused on the recent attempts by C. Meyers an d W. Jin to incorporate ground waste glass: (mainly, bottle glass) into con crete. With minor adjustments, though, the model can be applied to ASR in n atural aggregates as well. A characteristic unit cubic cell of concrete con taining one spherical glass particle is analyzed. A spherical layer of basi c ASR gel grows radially inward into the particle, controlled by diffusion of water toward the reaction front. Modification of the solution for the ca se of mineral aggregates with veins of silica is also indicated. Imbibition of additional water from the adjacent capillary pores, which causes swelli ng of the gel, is described as a second diffusion process, limited by the d evelopment of pressure due to resistance of concrete to expansion. The wate r used up to form the basic ASR gel and imbibed to cause its swelling appea rs as a sink term in the non-linear diffusion equation for the global water transport through a concrete structure. The differential equations are int egrated numerically. The study of the effects of various parameters provide s improved understanding of the ASR, and especially the effect of glass par ticle size. Full prediction will require measurements of some parameters of the reaction processes. (C) 2000 Elsevier Science Inc. All rights reserved .