Experimental investigation on fractal characteristics of pores in air-entrained concrete at low atmospheric pressure

This study intends to investigate the characteristics of pore structure of air-entrained concrete at low atmospheric pressure (0.7P₀ = 0.7 atm) and standard atmospheric pressure (P₀ = 1 atm) through in situ experiments. By using the data obtained from mercury intrusion porosimetry (MIP) test, the surface fractal dimension in different pore size regions is computed and linear regressed based on thermodynamic model. The results show that low atmospheric pressure has great impact on the fractal properties of pores and pore volume. The surface fractal dimension of pores <10 nm prepared at 0.7P₀ is 4.5%–27.6% smaller than that at P₀; the surface fractal dimension of pores >1000 nm at 0.7P₀ is 4.5%–13.6% bigger than that at P₀. The volumes of pores <10 nm and >1000 nm at 0.7 P₀ is respectively 9.4%–38.9% and 38.5%–66.7% lower than that at P₀; and the volume of pores within 10–1000 nm at 0.7P₀ is 19.8%–41.8% higher than that at P₀. The mechanisms behind the abnormal structure of pores at 0.7P₀ are discussed from perspectives of cement hydration and mechanical equilibrium of air bubble.