Modelling carbonation of fly ash concrete using system dynamics

Abstract

Steel reinforcement corrosion is the most frequent threat to concrete durability. Carbonation is considered to be one of the prominent precursors to steel corrosion in concrete. The introduction of fly ash concrete increases the amount of hydration product; hence the permeability is less and the durability is improved. In this study, system dynamic software (Vensim PLE) is used to model the carbonation of fly ash concrete. The relations between porosity, diffusivity of carbon dioxide and the carbonation depth are modelled as feedback loops and the influences of significant external factors are also incorporated. The model predicts the carbonation depth propagation over 100 years and the results are validated against the available experimental studies. The model also concludes that the fly ash replacement between 20% and 30% would optimize durability. Carbonation itself creates a balancing loop causing a reduction in the rate of carbonation over the years.