Water vapor sorption and its mechanical effect on clay-bearing conglomerate selected from China

Water sorption is one of the most important causes for rock deformation and failure. In the present study, water vapor sorption experiment was carried out on clay-bearing conglomerate rock samples collected from northeast China to investigate dynamics of water vapor sorption and vapor-induced strength softening effect. The experimental results have shown that the amount of water vapor sorbed by each conglomerate sample kept increasing with time until finally reached to a plateau, generally following an exponential law. The greater abundance of clay minerals, especially smectite, allowed more water sorption. By analyzing correlation relationships between the porosity characteristic parameters of conglomerate samples and the sorbed water content, it was found that vapor sorption was positively correlated with rock porosity (diameter > 0.2 μm). This result indicated that the total volume of pores with diameter > 0.2 μm was an important factor influencing water sorption of conglomerate rocks. Negative correlations between water content and uniaxial compressive strength (UCS) as well as modulus of elasticity suggested that with increasing water content induced by vapor sorption conglomerate rock strength tended to decrease, and meanwhile it was more prone to deformation. Furthermore, microstructure images of scanning electron microscope (SEM) analyses for conglomerate rocks before and after water vapor sorption showed that after vapor sorption conglomerate rocks have undergone significant changes in microscopic morphology which may be an important cause for rock softening and deterioration.