Measuring permeability of rigid materials by a beam-bending method: I, theory

When a saturated porous material is deformed, pressure gradients are create d in the Liquid, and the liquid flows within the pores to equilibrate the p ressure. This phenomenon can be exploited to measure permeability: A rod of saturated porous material is instantaneously bent by a fixed amount, and t he force required to sustain the deflection is measured as a function of ti me. The force decreases as the liquid flows through the pore network, and t he rate of decrease depends on the permeability. This technique has been ap plied successfully to determine the permeability of gels, as well as their viscoelastic properties; in this paper the method is extended to ceramic ma terials, such as porous glass and cement paste. The theory has been modifie d to take account of the compressibility of the solid and liquid phases (wh ereas, those factors are negligible for gels), Analyses are presented for c onstant deflection, constant rate of deflection, and sinusoidal oscillation , where the solid phase is either purely elastic or viscoelastic, and the b eam is either cylindrical or square. Experimental tests on Vycor(R) glass a nd cement paste will be presented in companion papers.