Obtaining pore size distribution of porous stone using non-Newtonian fluids

The characteristics of the pore space are considered a key factor in susceptibility of the stone to various weathering processes. The pore size distribution can be determined by a number of methods such as mercury intrusion porosimetry or computed topography. None of them is without disadvantages, namely the mercury intrusion porosimetry – despite being very popular – is the object of some critics due to the harmful effects of the mercury. Within the last decade, there has been a growing interest in the use of non-Newtonian fluids for obtaining the pore size distribution of the porous materials (see, e.g., Abou Najm and Atallah, 2016; Rodríguez de Castro et al., 2016). The principle exploits the behaviour of non-Newtonian fluids whose viscosity changes with shear rate. This is manifested by the fact that saturated flow of different fluids under different hydraulic gradients is distributed differently in the pore space. Therefore, conducting a set of saturated flow experiments with different fluids and/or under different hydraulic gradients allows – using a numerical model – to determine an approximation of the pore size distribution.

Our goal is to test feasibility of determining the pore size distribution using saturated flow experiments with low-concentration water-xanthan solutions (<1 g/l) under relatively small hydraulic gradients (<5). We have now completed a set of laboratory experiments for three types of sandstone and we are performing a sensitivity analyses of the parameters used in the numerical model. The presented approach is low-cost, easy-to-use and can serve as an alternative to mercury intrusion porosimetry in geoscience and various cultural heritage studies.

 

The research is funded by the Czech Science Foundation [21-27291S].

 

References:

Abou Najm, M.R., Atallah, N.M., 2016: Non-Newtonian Fluids in Action: Revisiting Hydraulic Conductivity and Pore Size Distribution of Porous Media. Vadose Zone Journal, 15(19), 1–15.

Rodríguez de Castro A., Omari, A., Ahmadi-Sénichault, A., Savin, S., Madariaga, L-S., 2016: Characterizing Porous Media with the Yield Stress Fluids Porosimetry Method. Transport in Porous Media, 114, 213–233.