Multiscale Theoretical Model of Thermal Conductivity of Concrete and the Mesoscale Simulation of Its Temperature Field.

Temperature field analysis is the precondition of studying the heat and mass transfer and durability of a concrete building; thermal conductivity is a key parameter that affects the distribution of the temperature field of concrete. Through reasonable assumptions and simplifications, the relationship between the micro-microscopic composition of concrete and its macroscopic thermal conductivity is established, and a multiscale theoretical model of thermal conductivity considering the influence of interface transition zone (ITZ) is proposed. The model can predict the thermal conductivities of concrete and its components at an arbitrary saturation. Subsequently, the influence of saturation, water-cement ratio, volume fraction and type of coarse aggregate, and sand ratio is researched. Moreover, according to the prediction results of the proposed model, a mesoscale simulation of the concrete temperature field is carried out. The results demonstrate that the presence of aggregate and ITZ leads to the isotherm deflection and abruption at the junction of the phases. Meanwhile, the heat flux density at the corners of the polygonal aggregate is significantly higher than at other positions; the phenomenon, first named the "corner effect" in the research, causes the temperature field distribution of concrete containing polygonal aggregates to be more uneven than that of circular and elliptical aggregates, and it is more likely to produce temperature-induced cracks. The research helps explain the influence mechanism of material components on the thermal conductivity of concrete and the distribution of its temperature field and provides a basis for the fine simulation of concrete thermal crack growth and creep at variable temperatures. [ABSTRACT FROM AUTHOR]