Investigating effects of pore-scale variables and pore geometries on the thermal behaviors of porous concretes

Abstract

Thermal behaviors play significant roles in the design of porous concretes. However, the effects of pore geometries on microscopic thermal behaviors are not still well understood. This work aims to propose a microscopic analysis framework to construct different microstructure models and to study the effects of pore geometries on the thermal behaviors of porous concretes. The microstructures with pore and cement phases are generated using the random generation algorithm (RGA) and compared with realistic microstructures. Digital numerous simulations are conducted to investigate the temperate distribution and heat transfer properties in the pixelated microstructures. Pore-scale variables, such as pore fractal dimension, pore size and porosity, are defined to understand their effects on the thermal behaviors of concretes. Results show that the transient temperature variation behaviors occur in the microstructures, which may be caused by the non-equilibrium heat transfer in the transient time scale. The effective thermal conductivity (ETC) decreases with increasing the pore radius, circularity, porosity and pore number, and it increases as pore fractal dimension increases. The microstructures with square pores have the largest ETC than those microstructures with pentagon, hexagon, and circle pore geometries. Totally, the numerical ETC agrees well with the analytical ETC, showing the accuracy of the proposed microscopic analysis framework. The proposed microscopic concrete analysis framework can provide effective tools to the fire resistance design of concrete constructions used for the green buildings and deep projects such as the deep bury of nuclear wastes.