On the applicability of Washburn law: study of mercury and water flow properties in cement-based materials

This paper deals with flow properties of mercury (Mercury Intrusion Porosimetry, MIP) and water (permeability measurements and capillarity) in building materials. The aim of this work is to study the validity range of the constancy hypothesis of the contact angle, usually admitted in porosity measurements (MIP, and capillarity), by establishing an explicit relationship between the contact angle and the capillary radius. For mercury and water we have showed that: (i) on one hand, for a given value of pressure, the contact angle between the liquid and the capillary walls starts to change significantly only from a 'critical' value of capillary radius R, (ii) on the other hand, in static state, the sphericity of liquid front depends equally on the capillary radius: the water has a spherical form when R # < 10 *mm, mercury has this form only for pores with radius R # < 103 *mm. This expresses the framework of Washburn's law applicability.