A STUDY ON THE PREDICTION MODEL OF CONCRETE CARBONATION USING CEMENT HYDRATION MODEL INCORPORATING GROUND GRANULATED BLAST FURNACE SLAG

Abstract

Concrete carbonation that is one of main causes for corrosion of reinforced concrete and deterioration, lowers pH value of concrete by reacting with atmospheric CO2. This reaction destroys the film on passive state metals of rebar surface and causes corrosion of rebar. Recently, due to the continuous increase in the atmospheric CO2 concentration, carbonation problem of concrete is reaching a situation where it becomes more serious. Therefore, many concrete carbonation prediction formulas by regression analysis are suggested to evaluate concrete carbonation. However, as these formulas are the results of regression analysis by experiments that consider to achieve that goal some factors, to accurately evaluate concrete carbonation, it is difficult because scientific grounds are lacking and deviation by each formulas is noticeable. On the other hand, as interest in utilization of industrial waste is increasing considering the resource depletion and the recycling of resources, the use of blast furnace slag (hereafter GGBFS) has been increasing. Therefore, specific prediction method of concrete carbonation considering the effects of GGBFS in cement paste is needed. In this study, to resolve problems like mentioned above, prediction model of concrete carbonation using cement hydration model incorporating GGBFS to adopt cement hydration model based on the chemical reaction was suggested. This thesis is organized in five chapters. In chapter 1, situation of GGBFS, carbonation reaction of concrete, background and necessity of this study about cement hydration, objectives and contents of this study, method and scope of this study were described. In chapter 2, properties of GGBFS such as outline, pros and cons of GGBFS were analysed and then hydration model of cement and cement incorporating GGBFS were analysed. Concrete carbonation reaction such as mechanism of concrete carbonation, Fick's law of diffusion, carbonation model of Papadakis were investigated and concrete carbonation prediction formulas by regression analysis were analyzed. In chapter 3, cement hydration model that is based on cement hydration model incorporating GGBFS suggested in this study was analyzed and cement hydration model incorporating GGBFS was suggested to apply to the carbonation model. Then cement hydration model incorporating GGBFS was verified by experiments. In chapter 4, reaction between cement hydrate and GGBFS, carbonation reaction mechanism of cement concrete incorporating GGBFS were described and prediction model of concrete carbonation using cement hydration model incorporating GGBFS was suggested. For accelerated carbonation experiment, carbonation of cement concrete was evaluated and verified. Results of experiment were compared and analyzed with results simulated for carbonation model. In chapter 5, conclusions deduced from this study were summarized. Carbonation model that resolve existing problems of carbonation prediction formulas, was suggested considering mix proportion of concrete incorporating GGBFS, type and chemical compositions of binder, amount of hydrate, concentration of CO2, porosity, temperature, relative humidity. Finally, carbonation model suggested in this study was verified by experiments.