Title: Effect of Stress on Gas Permeability
Author(s): Takafumi Sugiyama, Theodore W. Bremner, and Thomas A. Holm
Publication: Materials Journal
Appears on pages(s): 443-450
Keywords: compression tests; lightweight concretes; microcracking; per-meability;
The effect of compressive stress on the permeability of concrete was experi-mentally investigated using nitrogen gas as the flowing substance. A uniaxial compressive load was applied to a cylindrical hollow concrete specimen and increased by steps until failure, while a constant nitrogen gas pressure was maintained between the walls of the hollow cylinder and the volumetric gas flow rate was measured in a steady state. Gas permeability was then calculated and compared at increasing stress levels. Structural lightweight concrete with water-cement ratios of 0.4 and 0.6 was compared with normal- weight concrete with equal water-cement ratios and at similar stress levels. The stress level at which gas permeability increased significantly (significant stress level) was 76 to 79 percent of the ultimate strength for normal-weight concrete, whereas it was 82 to 89 percent of ultimate strength for the lightweight concrete. Structural lightweight concrete had both a higher significant stress level and a higher stress level at which dila-tion due to microcracking was noted (critical stress level) compared to nor-mal- weight concrete. Furthermore, normal-weight and structural lightweight concrete with different degrees of water saturation were tested. A higher degree of saturation resulted in a higher significant stress level.