The fractal characteristics of pore size distribution in cement-based materials and its effect on gas permeability

To study the influence of the pore structure of cement-based materials on macroscopic features (gas permeability), mercury intrusion porosimetry (MIP) and nitrogen adsorption (NA) were applied to 8 groups of paste and mortar samples (including adding mineral admixtures or not and standard or sealed curing conditions). Pore size distribution has a great influence on gas permeability. By calculating pore surface fractal dimensions based on Zhang's fractal model, the obvious fractal characteristics of micropores (<100 nm) and macropores (> 10⁵ nm) have been found. The pore diameter of the paste is mostly distributed in the micropores, and the average critical pore diameter is 82 nm. For mortar, the pore diameter is mostly distributed in the micropores and transition pores, and the average critical pore diameter is 121 nm, which means that the seepage pore diameters of the paste and mortar are 82 nm and 121 nm, respectively. The pore surface fractal dimensions of the visible pores are larger than those of the micropores, and there is an inverse relationship between the pore surface fractal dimensions and gas permeability. An important guide for engineering production is to use standard curing and add mineral admixtures to mortar materials to improve the impermeability as much as possible, while a contrary condition exists for paste materials.