Effects of Slaking fluid pH on the Index Properties of Carbonate Rocks

The physical and chemical characteristics of water critically influence the mechanical and chemical breakdown of rocks. The physical properties of rocks, such as porosity (n), water content (w_a), apparent specific gravity (G_s(A)), and dry and saturated densities (ρ_d, ρ_s, respectively), may be adversely affected by the acidity/alkalinity of water. This study aimed to investigate the variability of certain physical properties of carbonate rocks using the second-cycle slake durability index (second-cycle SDI, I_d2) under acidic and alkali conditions. Laboratory SDI tests were conducted on 21 rock samples (seven from each of the Rus, Asmari, and Dammam carbonate rock formations) using slaking fluids with various pH levels, i.e., 2–14 (acidic to basic). Results show that the n and w_a values were negatively correlated with pH for carbonate rocks from the Rus, Asmari, and Dammam Formations. However, the G_s(A), ρ_d, and ρ_s values of carbonate rocks from the Rus Formation showed decreasing trends with pH, whereas increasing trends were observed for the Asmari and Dammam Formations. This may have been either due to variations in the mineralogical and textural features of the carbonate rocks or chemical reactions with CaCO₃ caused by the different pH levels of the slaking fluid, especially under acidic conditions. Such findings will likely improve our understanding of the durability of carbonate rocks in the study region and elsewhere.