Chemical Sequence and Kinetics of Alkali–Silica Reaction Part II. A Thermodynamic Model

Abstract

This manuscript describes development of a thermodynamic model for the chemical sequence of the alkali–silica reaction (ASR) process in the model, closed reactive system consisting of mixture of reactive silica mineral, calcium hydroxide, and alkali hydroxide solution. The focus of the first part of the study is on formulating the kinetic rate law for silica dissolution as a function of several factors, including pH, temperature, concentration of alkalis in solution, and type of the reactive silica mineral. This kinetic rate law was then incorporated into the commercial modeling software (Geochemist's Workbench®) in an attempt to simulate the chemical sequence of the ASR process. Once the proper input data and parameters were selected, the model generated reasonably accurate predictions of the distribution of species in the reacting system and captured distinct features of experimental data. In addition, this model suggested that the thermodynamic equilibrium condition among reactant (reactive silica mineral), products, and ionic species in the solution resulted in the threshold value of alkali concentration needed for the ASR to take place. Though the application of the proposed model is currently limited to the closed ASR system, the model may offer the possibility of the establishment of the unified theory which can bridge the gap between fundamental (chemical) mechanisms of ASR and the mechanical responses of concrete by providing the kinetic basis for the evolution of ASR process.