Evaluation of mechanical weakening of calcarenite building stones due to environmental relative humidity using the vapour equilibrium technique

Previous studies have evaluated the water-weakening effect of rock materials after immersion in water during different periods of time. However, the water transference between the environment and the building stones frequently occurs in vapour form when changes in the relative humidity of the air involve little variations in moisture content of stones. In this sense, the novelty of this work lies in assessing the impact of the environmental relative humidity (RH) on Unconfined Compressive Strength (UCS), Young's modulus (E st ), Brazilian Tensile Strength (BTS) and Point Load Strength Index (I s(50) ) of three calcarenite building stones. To this aim, calcarenite specimens were exposed to five different environments with RH values ranging from 10 to 93% which were devised in laboratory through a novel modified Vapour Equilibrium Technique (VET) by using water-glycerol solutions at different concentrations and then, they were mechanically tested. The results indicated that, despite the water content (w) and the degree of saturation (S r ) inside the pore network of calcarenites were relatively small for all RH environments (w = 0.03–1.79% and S r  = 0.2–35.6%), important reductions of UCS (28.2–34.7%), E st (20.0–31.3%), BTS (17.0–41.3%) and I s(50) (23.9–37.6%) were found when the RH varied from 10 to 93%. Furthermore, negative linear relationships were established between the values of the mechanical properties and the environmental RH while negative tri-parametric exponential functions were proposed between the mechanical parameters and w. In addition, the mechanisms involved in the observed behaviour were discussed and relationships between the different mechanical properties were also proposed.