Effects of Mineral Composition and Texture on Durability of Sulfate Rocks in Gachsaran Formation, Iran

Slake Durability is one of the most important engineering properties which is investigated by many researchers. Several correlations have been proposed between the slake durability index (SDI) of some rocks and their engineering properties. The purpose of this research is to determine the SDIs of sulfate rocks, including gypsum (GP), anhydrite (AN), and clay bearing gypsum and to investigate the effect of mineral composition and rock texture on the SDI. In order to carry out this research study, rock blocks were collected from the outcrops of the Gachsaran formation in 4 under construction reservoir dam sites in Iran. Rounded rock samples were prepared according to standard methods. Due to the specific characteristics of sulfate rocks, a thorough research was carried out on the determination and application of appropriate drying and saturation methods of sulfate rocks. The slake durability tests were performed in 5 cycles of 10 min using ionized water under dry and saturated conditions. These experiments have shown that in a rock composed of GP and AN, the durability of a rock is affected by its mineral composition and as a result, the durability index in both dry and saturated conditions decreases with increasing the GP percentage, and inversely, increases with increasing the AN content. In an almost pure GP or AN rock, there is a strong linear correlation between the number of slaking cycles and the SDI. Presence of clay-sized carbonates or microcrystalline carbonates in the mineral composition of GP rocks, increases the durability of rock in both dry and saturated conditions, especially in higher test cycles. Rock texture also has an important effect on the durability index, so that in a similar mineral composition, a rock with a porphyry texture is more durable than a rock with alabaster texture.