Alkali-Silica Reactivity Potential of Aggregate and Concrete Evaluated by Dilatometer Method

Abstract

Undesirable expansion of concrete due to a reaction between alkalis and certain type of reactive siliceous aggregates known as alkali-silica reactivity (ASR) continues as a major problem worldwide. Renewed interest in minimizing distress resulting from ASR emphasizes the need to develop predictable modeling of concrete ASR behavior under field conditions. Current test methods are either incapable of that or need long testing periods, which offer only limited predictive estimates of ASR behavior in a narrow band of field conditions. Therefore, an attempt was made to formulate a robust performance approach based on basic aggregate and concrete ASR material properties derived from dilatometry and a kinetic-based mathematical expression for ASR behavior. Since ASR is largely an alkali as well as a thermally activated process, the use of rate theory (Arrhenius relationship between temperature and alkali solution concentration) on the dilatometer time-expansion relationship provides a fundamental aggregate ASR material property known as activation energy. Activation energy is an indicator of aggregate reactivity, which is a function of alkalinity, particle size, crystallinity, calcium concentration, and so on. The studied concrete ASR material properties represent combined effects of mixture-related properties (e.g., water-cementitious material ratio, porosity, presence of supplementary cementitious materials) and maturity. A performance-based approach provides direct accountability for various factors affecting ASR, such as aggregate reactivity, temperature, moisture, calcium concentration, solution alkalinity, and water-cementitious material ratio. From test results, it was determined that the proposed model provides a means to predict ASR expansion development in concrete.