A semi-empirical model for predicting carbonation depth of RAC under two-dimensional conditions

Abstract Recycled aggregate concrete has been widely used in practical engineering construction, and the carbonation resistance of buildings within their allowable strength range is currently urgently needed to be considered. By constructing a time prediction model for the carbonation depth of recycled concrete, the time when the complete carbonation zone reaches the depth of the steel bar inside the concrete can be determined, and then the carbonation life of the building can be determined. However, the current carbonation model for recycled aggregates (RAs) has theoretical and practical limitations. The existing semi-empirical model has not quantitatively considered the influence of particle sizes of RAs on the carbonation depth, but only qualitatively analyzed the effect of particle size on the carbonation depth. In practical applications, the existing models usually only determine the structural life under one-dimensional carbonation conditions in laboratory conditions, ignoring the fact that two-dimensional carbonation mainly occurs in actual engineering. In order to overcome these limitations, a semi-empirical model for predicting the carbonation depth of recycled concrete is proposed for life prediction of structural carbonation. Based on the replacement rate of RAs, external environmental influences, and the stress state of components, the particle size of RAs is considered in the carbonation depth prediction model, and model parameters are fitted by performing carbonation experiments on specimens with different mix ratios. The model is then validated by applying a large amount of existing experimental data to the fitted model, and the results show that the model has good applicability for the constructed components. Furthermore, the model is used to predict the carbonation life of the main components in actual engineering and considers two-dimensional carbonation. It was found that when the replacement rate of RAs was 40%, the predicted life of the main components after carbonation in actual engineering was close to the design life.