Research on Microscopic Pore Structure and Permeability of Air-Entrained Flyâ•fiAsh Concrete Subjected to Freezing and Thawing Action

In this paper, rapid freezing and thawing test of air-entrained fly–ash concrete was carried out. Gas adsorption of concrete pores, mass loss, dynamic elastic modulus, and chloride diffusion coefficient of concrete after different freezing and thawing cycles was tested; scanning electron image was used to study the microscopic pore structure of the specimens. Results show that after certain freezing and thawing cycles, microscopic pores of the sample had a brittle failure, which results in sudden changes of cumulative desorption pore volume and cumulative desorption surface area obtained by Barrett, Joyner, and Halenda method. It was found that the variation of maximum cumulative desorption surface area is in good agreement with that of mass loss rate and chloride diffusion coefficient. At different stages of freezing and thawing, rate of mass loss shows a linear relationship with maximum cumulative desorption pore volume and maximum cumulative desorption surface area. In the range of freezing and thawing cycle between 0 and 150, chloride diffusion coefficient demonstrates a linear relationship with maximum cumulative desorption pore volume and maximum cumulative desorption surface area; in the range of freezing and thawing cycle between 200 and 300, this relationship becomes nonlinear.