RESUMEN
The present work investigates the effect of both surface roughness and particle morphology on the retention behaviour of granular materials via X-ray micro-computed tomography (µCT) observations. X-ray µCT images were taken on two types of spherical glass beads (i.e. smooth and rough) and two different sands (i.e. natural and roughened). Each sample was subjected to drainage and soaking paths consisting in a multiphase 'static' flow of potassium iodine (KI) brine (wetting phase) and dry air (non-wetting phase). Tomograms were obtained at different saturation states ranging from fully brine saturated to air dry conditions with 6.2 µm voxel size resolution. The data acquisition and pre-processing are here described while all data, a total of 48 tomograms, are made publicly available. The combined dataset offers new opportunities to study the influence of surface roughness and particle morphology on capillary actions as well as supporting validation of pore-scale models of multiphase flow in granular materials.
RESUMEN
Understanding multiphase fluid displacement dynamics in porous media is of great importance in efficiently designing hydrogen storage projects in porous reservoirs. During gas injection and extraction, cyclic evaporation and spontaneous imbibition processes have an impact on storage efficiency. In both imbibition and evaporation, capillary films on the surface of grains play a role in the transport of water through the pore space. In this study, we use atomic force microscopy to study the formation of these films in carbonate rock during imbibition and their dynamic behavior during evaporation. The imbibition dynamics are related to pore-scale processes determined by micro-CT experiments. We find that imbibition through the mesoporous structure of the grains is slower compared to imbibition in macropores. The formation of the water film on the outer grains is also slower, indicating that a film is evolving due to water flow through intragranular mesopores rather than film flow around the grains. Evaporation experiments reveal that the film shows both local swelling and shrinkage behavior, which we relate to pore-scale processes causing disconnection of the water film. Our results show the close relationship between pore-scale processes and water film dynamics during both spontaneous imbibition and evaporation. This work forms a basis for a more quantitative study of the impact of pore structure on wetting and drying dynamics and can be extended to reactive flow processes.
RESUMEN
Air pollution is one of the main actors of stone deterioration. It influences not only the material itself but also prokaryotes colonizing rocks. Prokaryotes can affect rock substrates and biological colonization will most likely become relatively more important during the course of the 21st century. Therefore, it is necessary to understand the effects of air pollution on biological colonization and on the impact of this colonization on rock weathering. For this reason, we studied the prokaryotic community of Lede stone from two deteriorated monuments in Belgium: one in the urban and one in the rural environment. This research conducts 16S rRNA gene Next Generation Sequencing combined with an isolation campaign. It revealed diverse and complex prokaryotic communities with more specialized bacteria present in the urban environment, while archaea were barely detected. Some genera could cause biodeterioration but the isolates did not produce a significant amount of acid. Soluble salts analysis revealed an important effect of salts on the prokaryotic community. Colour measurements at least indicate that a main effect of prokaryotes might be on the aesthetics: In the countryside prokaryotic communities seemed to discolour Lede stone, while pollution most likely blackened building stones in the urban environment.