Precise Permeability Measurement for High Strength and Ultra Low Permeability Concrete under Controlled Temperature

Abstract

High strength and ultra low permeability concrete (HSULPC) is being considered as a material used to package transuranic (TRU) waste for disposal in geological repositories. Therefore, information on the permeability of HSULPC is essential. Permeability tests need to be highly accurate to determine the hydraulic conductivity of HSULPC because of its ultralow permeability. In our study, we measured the permeability of HSULPC samples using the transient pulse method. The temperature of the concrete was finely controlled and held constant. The hydraulic conductivities were determined from the measurements to be around 10 ¹13 to 10 ¹12 m/s for confining pressures between 2 and 10 MPa. The pore pressure was a constant 1 MPa. The results further showed that the permeability of HSULPC had a hysteretic dependence on the effective confining pressure. We found that the hydraulic conductivity of HSULPC is comparable to or less than that of intact Toki granite obtained from Gifu Prefecture in central Japan. It was also considered that the hydraulic conductivity of HSULPC stabilized at around 10 ¹13 m/s after being buried and stressed. The high density and impermeability of HSULPC would enable it to effectively confine 14 C radionuclides found in TRU waste.

Effect of Reinforcing Steel Fiber on Permeability of High Strength and Ultra-Low Permeability Concrete

“…The influence of hydraulic conductivity on effective confining pressure is then explored. The coefficients (ratios) of the effective confining pressure dependency of hydraulic ing pressure for HSULPC without fiber, 15,16) HSULPC with steel fiber, Horonobe mudstone, and Toki granite. 17) conductivity were computed for HSULPC with and without steel fibers and Horonobe mudstone using the following equations.…”

“…This study's permeability test apparatus (Fig. 4) was the same as that used previously by Kato et al 15,16,20) Because the values of water pressure and differential pressure are temperature sensitive, 20) the experimental apparatus was placed in a triple-insulated chamber. During the measurethe temperature changes around the pressure vessel were kept to within «0.1°C/h.…”

“…The transient pulse permeability measurement procedure is based on Kato et al 15,16) However, there are some differences in the procedure for the steel-fiber reinforced concrete specimen. Some thin grooves were generated from the mold on the side of the steel-fiber reinforced concrete specimen, which could be water flow pathways during the permeability measurement.…”

“…Finally, cylindrical specimens with diameters of 50 mm and heights of 25 mm were created. Kato et al 15,16) previously reported the results of permeability tests on HSULPC without fibers.…”

Effect of Reinforcing Steel Fiber on Permeability of High Strength and Ultra Low Permeability Concrete

“…Fig.2Photos of cylindrical specimens for permeability test: (a) HSULPC without fiber 15),16) , (b) HSULPC with steel fiber, (c) Horonobe mudstone, (d) Toki granite18) . Diameter and length of the specimens are 50 and 25 mm, respectively.…”