Unified determination of relative molecular diffusivity and fluid permeability for partially saturated cement-based materials

Abstract

From conductivity theory, general models for relative molecular diffusivity and fluid permeability are first derived with unknown tortuosity function and modification coefficient, which can be respectively deduced from hydraulic diffusivity and water retention curve (WRC). Based on empirical laws for hydraulic diffusivity and WRC of cement-based material, unified models for relative molecular diffusivity and fluid permeability are further formulated with only two measurable parameters. Because of practical difficulty for measuring water permeability and pure gaseous molecular diffusivity, only relative gas permeability and relative chloride diffusivity models are verified by the reported data. It is found that the predicted relative gas permeability agrees with measured values and exponential law is a little more preferable than power law for quantifying hydraulic diffusivity. Moreover, relative chloride diffusivity from the unified model also agrees well with experimental data derived via Nernst–Einstein Equation. However, the unified model doesn't capture the possibly overestimated relative chloride diffusivity from Fick's law.