Effects of Fluid Salinity and Composition on Subcritical Crack Growth in Marble

Subcritical fracture growth of rocks in fluid-chemical environments played a crucial role in the weathering process of rocks and the preservation of stone building heritage. Fracture mechanics properties of marble under different fluid compositions and salinity conditions were investigated by carrying out double torsion tests. The subcritical crack growth index (SCI) exhibited different salinity dependencies in two salt solutions. In NaCl solution, the SCI decreased by 1.97 % - 40.50 % with increasing salinity due to the increase in solubility of calcite. The SCI decreased by 4.60% and 14.01 % respectively as the Na2SO4 salinity increases from 0.01 mol/L to 1 mol/ L, and then increased with the increase in salinity, which was related to the relationship between calcite solubility and salinity. Compared to Na2SO4 solution, the weakening effect of NaCl solution on Ka was smaller. In contrast, the fracture toughness (KIC) was insensitive to fluid composition and salinity in the short term, with KIC ranging from 0.65 to 0.79 MPa m1/2 in all salt solutions. The three-dimensional morphology results of the fracture surfaces indicated that the effect of salinity on the roughness of both fracture types was negligible. However, the microstructure of the marble was significantly affected by salinity, and apparent dissolution was observed. The results highlighted the dependence of the subcritical fracture behavior of marble on fluid chemistry, which had implications for the weathering assessment of stone masonry buildings and the permanent protection of stone heritage monuments. In these applications, fluid chemistry could either strengthen or weaken the rock, depending on variations in fluid composition and salinity.