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.