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A model for predicting time-dependent chloride binding capacity of cement-fly ash cementitious systems was proposed. The proposed model took into account both chemical binding and physical binding. Chemical binding was considered to depend on the amount of unhydrated aluminate and aluminoferrite phases while physical binding depended upon the quantity of hydrated and pozzolanic products. The concept of time-dependent chloride binding capacity was introduced in the model with the consideration of curing time and chloride exposure period. The chloride binding of cement pastes and cement-fly ash pastes under different curing times and chloride exposure periods were tested. Three types of cement and two types of fly ash were used.From the experimental results, time-dependent behavior of chloride binding capacity was observed. At the same chloride exposure period, pastes with longer curing time prior to chloride exposure bound less chloride than those exposed with shorter curing time. Longer exposure period of paste resulted in larger chloride binding capacity. The analytical results from the model were verified with the experimental results from the authors mad other researchers. The verification showed that the proposed model was satisfactory for predicting the chloride binding capacity of various cement and cement-fly ash cementitious systems. RI~SUMI~

Abstract.A method for estimating mix proportion of hardened OPC concrete is proposed in this study. A set of mass balance equations was formed to calculate content of concrete compositions including cement, water, sand, and coarse aggregate. The degree of hydration of cement was taken into account in the analysis in order to cover the effect of age of concrete. In order to verify the accuracy of the proposed method, the determination of mix proportion of concrete was conducted on concrete specimens prepared in the laboratory with known mix proportions. Moreover, the mix proportion of concrete at different ages were calculated both with and without consideration of time-dependent degree of hydration in the analysis to clarify the enhanced capability of the proposed method when the effect of age of concrete is considered. It was found from the analytical results that the proposed method could be used to estimate mix proportion of concrete, with a satisfactory precision, at any age. The calculation of mix proportion of hardened concrete with consideration of time-dependent degree of hydration provided less error than that without consideration of the degree of hydration. The percentage of error of the mix proportion prediction of the concrete samples was less than 5%.

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