Effect of environmental relative humidity in the tensile strength of layering in slate stone

Abstract

Slate is a natural stone widely used for building, for which is subjected to regulations and standards in order to be commercialized. As far as the influence of water is considered, only detailed studies are compulsory when the water absorption is higher than 0.60%. However, the mechanical behavior of this layered material depends on water content, which is function of the relative humidity of the environment, and not considered in existing standards. In order to investigate its influence on foliation tensile strength, an experimental study was performed, which consists on carrying out Brazilian tests in slate samples with known water content, applied and controlled by using vapor equilibrium technique. This technique allows controlling the relative humidity of the environment surrounding the material and that of the air on its pores. Relative humidities between 55% and 92% were applied during the tests and defined considering climate data from the north of Spain. Despite the maximum water content tested in the slates was low (0.10%) in comparison with its saturation content (0.57%), the experimental results show a decreasing of the foliation tensile strength that reaches up to three times less with an increment of the environmental relative humidity of 37%. The results achieved can be important in order to quantify the layering weakness due to a natural alteration factor such as the environmental relative humidity. Moreover, the procedure employed is proposed as a convenient method for adequating each variety of slate stone to different climates according to its vulnerability to water.