Discontinuity in pore structure and its effect on mass transfer through hardened cement paste

grantor: University of TorontoToday, the mass transfer characteristics of concrete is measured by permeability testing or measured ionic diffusivity under saturated condition. However, saturation is not usually found in concrete in the field. The mass transfer characteristic of concrete is dependent on its pore structure and the boundary conditions. In this study, low pressure permeability test, high pressure permeability tests and water vapor transmission tests were conducted to evaluate the postulated effect of discontinuous pore structure in hardened cement paste (HCP) on two different mass transfer mechanisms: saturated water transfer and water vapor transfer. The low pressure permeability test is unable to determine permeability values below 1E-13 m/s, while the high pressure permeability test extends this lower limit to IE-16 m/s by using the modified high pressure permeameter. The pore structure of HCP was deemed to be discontinuous when "zero" flow was measured in the high pressure permeability test. However, water vapor transmission test shows significant mass transfer of water vapor through HCP even those having discontinuous pores according to high pressure permeability test results. Finally, the permeability models examined in this study give inaccurate estimates of permeability for HCP with discontinuous capillary porosity.M.A.Sc