# Property Analysis of Slag Composite Concrete Using a Kinetic-Thermodynamic Hydration Model
## 5 Conclusions  
This study demonstrates a procedure for analyzing the development of properties in slag composite concrete. * First, we performed an experimental study on the isothermal hydration heat of blends of cement-slag. As the replacement percentages of slag increased from 0% to 30% and 50%, the rate of hydration heat decreased. For specimens with 30% and 50% slag, the third peak for the dissolution of aluminum was much higher and sharper than the second peak. Moreover, using the experimental results for the isothermal heat of hydration, we determined the reaction extent of slag. The analysis found that, as the replacement percentage of slag increased, the reaction extent of the slag was reduced. In addition, because the proposed model covers the interactions between the individual reactions of slag and cement, the coefficients of the slag reaction model and the cement hydration model are constant for various mixtures. * Second, during the isothermal calorimetry test, both cement hydration and slag reaction contribute to heat release. Because the proposed kinetic hydration model can separate the slag reaction from cement hydration, the contribution of the slag reaction on heat release can be determined. Moreover, the reaction degree of slag can be calculated. Thus, based on the use of the kinetic hydration model, the isothermal calorimetry test can be used as an indirect method for determining the reaction degree of slag. * Third, the reaction extents of slag and cement were used as input parameters for the thermodynamic equilibrium model, and the phase assemblage of the hydration of cement-slag was determined. Using the experimental results for strength and the analysis results of GEM-Selektor, we found that the strength of paste is linearly dependent on the combined water content or CSH content. The coefficients of determination for the combined water-based strength model and the CSH-based strength model were 0.82 and 0.87, respectively. The combined water-based strength model cannot reflect the strength crossover between plain paste and blended paste, while the CSH-based strength model can reflect the strength crossover. The CSH-based strength model showed that as the slag content increased, the time of the strength crossover grew longer. Compared with the combined water content, the CSH content is more suitable for the evaluation of the strength of cement-slag blends. * Fourth, the specific contributions of this study are summarized as follows: (1) we proposed a kinetic hydration model to evaluate the reaction extent of slag and cement based on an isothermal calorimetry test, (2) we used the calculation results of the kinetic hydration model as input data for a thermodynamic model and evaluated the phase assemblage of hydrating cement-slag composite, and (3) we evaluatedthe strength development of hardening concrete using phase assemblage of composite concrete. In summary, the evolution of the phase assemblage (chemical compositions) of cement-slag blends can be calculated based on the integrated kinetic-thermodynamic model. Moreover, the development of the compressive strength (mechanical property) of composite concrete can be evaluated using a phase assemblage, such as CSH content or combined water content. Thus, the proposed model is useful for analyzing the chemical and mechanical properties of cement-slag blends. Conceptualization, K.-B.P. ; methodology, Y.-S.W. and X.-Y.W. ; vali-dation, K.-B.P., Y.-S.W. and X.-Y.W. ; writing--original-draft preparation, K.-B.P. and X.-Y.W. ; writing--review and editing, K.-B.P., Y.-S.W. and X.-Y.W. ; visualization, Y.-S.W. and X.-Y.W. ; supervision, K.-B.P. and X.-Y.W. All authors have read and agreed to the published version of the manuscript. This study has been worked with the support of a research grant of Kangwon National University in 2017. This study is supported by the National Research Foundation of Korea (NRF-2015R1A5A1037548, NRF-2020R1A2C4002093, NRF-2020R1A2C1102871). This study is supported by BK21 FOUR (Fostering Outstanding Universities for Research).