Study on simultaneous heat and mass tranfer in concrete at elevated temperature

本研究通过实验和分析，探讨了高温下混凝土中热传导和水分扩散同时发生的现象。对混凝土的材料性能进行了试验研究。此外，还对高温加热混凝土的干燥过程进行了分析研究。根据实验研究结果，估计了水分含量和温度对这些材料性能的影响。特别是，混凝土的热传导、比热和比重主要受水分条件的影响，并且吸附等温线和水分传导不仅受相对湿度的显著影响，而且受温度的显著影响。利用吸附等温线和水分传导的结果对扩散系数进行了讨论。胶凝材料的扩散系数受温度的影响，在70℃时的扩散系数与在20℃时的扩散系数的变化趋势有显著的不同。通过将混凝土中的传热传质过程分为两个过程，并采用有限元方法模拟混凝土中的传热传质过程。

In this study, experiments and analysis were carried out to investigate the phenomena of simultaneous heat conduction and moisture diffusion in concrete at elevated temperatures.Material properties of concrete for these phenomena were studied experimentally. Furthermore, analytical studies were carried out to describe the drying process of heated concrete at elevated temperature.As the results of the experimental studies, influence of moisture content and temperature on these material properties were estimated. Especially, it was shown that heat conduction, specific heat, and specific gravity of concrete are mainly affected by moisture condition, and that the sorption isotherm and moisture conduction are significantly influenced not only by relative humidity but also by temperature.Diffusion coefficient was discussed by using the results of the sorption isotherm and moisture conduction. The diffusion coefficient of cementitious material is influenced by temperatures, and it's tendency at temperature 70 degree C is remarkably different from at 20 degree C.Simultaneous heat and mass transfer process in concrete can be simulated by separating the phenomenon into two processes and by means of finite element method.