Slake durability and mineralogical characteristic of carbonaceous rocks

The slake durability and the related deterioration mechanism of carbonaceous rocks exposed to adverse external environment are of a great importance to the stability of infrastructure. A series of laboratory tests were conducted to determine their slake durability index I_di, fractal dimension D, total organic carbon (TOC) content, and mineralogical characteristic. The results demonstrated that I_di value decreased rapidly within the first 4 cycles, and then reached a relatively stable state as the test cycle further increased, indicating that effective protective measures should be conducted at the earlier stage of wetting-drying process to minimize the durability deterioration of carbonaceous rock. The discrepancy of carbonaceous rocks in terms of mineralogical characteristic accounted for different slake durability responses at a given cycle. Carbonaceous rock with lower clay minerals content w_c possessed superior slake durability performance, and a power correlation between I_d6 and w_c was obtained. Fractal dimension D was found to be an indicator to indirectly describe the durability characteristic of carbonaceous rock. The organic matter imposed negative impact on the slake durability, which was manifested by the carbonaceous rock with higher TOC content exhibited inferior disintegration resistance. The microstructure changes, including an increase in pore volume, pore size, layer spacing, and the presence of new crystalline-like substances, demonstrated the minerals/salts dissolution and chemical reactions within the rock matrix occurred during the slake durability test. These changes were mainly attributed to the hybrid influence of mineralogy and microstructure of carbonaceous rock.