Correlating the permeability of mortar under compression with connected porosity and tortuosity

Abstract

This paper describes the influence of pore structure parameters – connected porosity and tortuosity – on the water permeability coefficient of cement mortar. Plain and fibre-reinforced mortar specimens were prepared to evaluate the permeability and characterise the microstructure. Polypropylene microfibres were incorporated at 0·25% volume fraction in the fibre-reinforced mortar specimens. The permeability of the mortar specimens was determined using an in situ method where hollow cylinders were subjected to uniaxial compressive stress. The specimens were loaded in the range of 0–90% of the ultimate compressive strength in five different stages. X-ray computed micro-tomography was employed to characterise the pore system of the mortar specimens. By analysing the tomographic images, both connected porosity and tortuosity of the pore network were evaluated. The results showed that the coefficient of water permeability has a correlation with connected porosity across the load levels. While no significant correlation was found with tortuosity alone, the water permeability was found to depend on the ratio between connected porosity and tortuosity as expressed by the Kozeny–Carman formulation.