In-life prediction of hygrometric behaviour of buildings materials: an application of fractal geometry to the determination of adsorption and suction properties

In order to describe the hygrometric behaviour of a porous material such as mortar, it is quite common to resort to the diffusion process theory [1]. The equations that are obtained depend on the parameters that linearise the dependence on the gradient of the potential P adopted. Such parameters are not constants, but they greatly depend on the hygroscopic content of humidity inside the material. The hygroscopic content u inside the material depends on the relative humidity of the environment φ in a non-linear way. In short, we indicate the mass flux by m: m=f(u)×grad P,with u=u(φ). Current research obtains the constitutive link between u and φ by fitting experimental data and there is no theoretical model which can interpret the curves obtained. This paper shows the results of research that, on the basis of fractal geometry, has worked out a mathematical model in order to express the existing link between the water content inside a porous material and the relative humidity of the environment at a given temperature. It shows that the knowledge of the fractal dimension of the pores’ space in a porous medium is enough to work out the suction and adsorption curves characteristic of the medium.