Freeze-thaw damage deterioration mechanism of rice husk ash concrete based on pore volume fractal dimension

Under the increasingly severe environmental pressure, the application of agricultural by-products such as rice husk ash (RHA) in concrete has attracted widespread attention. In order to study the effect of rice husk ash partial replacement (0%, 10%, 20%, 30%) of Portland cement by equal mass on the frost resistance of concrete, the apparent morphology, mass loss, dynamic elastic modulus and compressive strength of rice husk ash concrete under the action of freeze-thaw cycles were conducted, while the spatial distribution pattern of cement paste pores was explored by establishing the pore volume fractal dimension model, and the freeze-thaw damage deterioration mechanism of rice husk ash concrete was revealed. The results show that with the increase of the number of freeze-thaw cycles, the surface spalling damage of concrete gradually intensifies, the mass loss rate tends to decrease and then increase, while the relative dynamic elastic modulus and relative compressive strength show a decreasing trend. In addition, since the hardened cement paste before and after freeze-thaw cycles shows obvious multifractal characteristics, its pore structure can be divided into two categories: Small pores and great pores. Under the action of freeze-thaw cycles, the existence of the mesoporous structure of rice husk ash will improve the pore size distribution of concrete, resulting in an increase in the fractal dimension of the small pores. The great pores are more sensitive to freeze-thaw cycles, and their pore structures will be subject to freeze-thaw damage due to the gradual accumulation of swelling pressure.