Method for determination of slake durability index of rocks
1981 Edition

The test drum must be constructed from 2.0 mm wire mesh, measuring 100 mm in unobstructed length and 140 mm in diameter. It should have a solid fixed base and a removable solid lid, capable of withstanding temperatures up to 105°C. The drum needs to maintain structural integrity without internal or external reinforcements obstructing the mesh surfaces. It is mounted horizontally in a trough filled with slaking fluid, positioned so that the fluid level is approximately 20 mm below the drum’s axis, with a 40 mm clearance between the trough and the drum base mesh, ensuring consistent and reliable testing conditions according to IS 10050.

As per IS 10050 Clause 4.1, select ten rock fragments weighing between 40 to 60 grams each, with a total sample mass of 400 to 600 grams. The pieces should be roughly spherical in shape, with edges rounded off to prevent stress concentrations and to ensure uniformity during testing. This preparation allows for consistent evaluation of rock durability through cycles of wetting and drying, facilitating accurate and comparable slake durability index results.

While tap water at 20°C is the standard slaking fluid specified by IS 10050, alternative fluids may be employed depending on environmental simulation requirements. These include acidic solutions to mimic acidic conditions, seawater to replicate marine environments, and corrosive groundwater for specific field scenarios. The choice of fluid and its temperature must be documented as they significantly influence the durability outcomes.

The slake durability index (Id2) for the second cycle is calculated using the formula: Id2 = ((A - D) / (C - D)) × 100%, where A is the dry weight after the second cycle, C is the initial dry weight before testing, and D is the weight of non-rock fines separated after testing. Higher Id2 values close to 100% indicate highly durable rocks with minimal breakdown, values between 80% and 100% suggest good durability, while values below 60% reflect poor durability and susceptibility to weathering.

The weighing apparatus must have an accuracy of ±0.5 grams when measuring the drum and sample combined, as stated in Clause 3.5 of IS 10050. Drying should be conducted in an oven maintained at 105 ± 5°C until a constant weight is achieved, generally requiring at least 12 hours, ensuring precise moisture content measurement and consistent test results.