Site investigation · Laboratory: rock & aggregates

Slake durability index calculator

Second-cycle slake durability index and Gamble durability class.

Standard: ASTM D4644 · ISRM · Gamble classification

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Input	Value	Unit
Drum + initial dry sample	1620	g
Drum + dry retained after cycle 1	1588	g
Drum + dry retained after cycle 2	1561	g
Drum mass	1110	g

Diagram for the worked example

Id1 = 100*(1588-1110)/(1620-1110) = 93.725 %
Id2 = 100*(1561-1110)/(1620-1110) = 88.431 %
Gamble class = IF(88.431>98,"very high",IF(88.431>95,"high",IF(88.431>85,"medium high",IF(88.431>60,"medium",IF(88.431>30,"low","very low"))))) = medium high

Particle density & water absorption (coarse aggregate) — Oven-dry, SSD and apparent particle densities and water absorption from the basket method.
Rock uniaxial compressive strength & modulus — UCS of a rock core with the L/D correction, tangent modulus at 50% and the ISRM strength term.
Brazilian tensile strength — Indirect tensile strength of rock discs σt = 2P/(π D t), averaged over the set.
Los Angeles abrasion loss — LA abrasion loss of a coarse aggregate grading after 500 revolutions.
Aggregate crushing value — Percentage passing 2.36 mm after crushing at 400 kN.
Ten percent fines value (wet/dry strength) — Load giving 10% fines from a test at x kN producing y% fines: F = 14x/(y + 4); wet/dry variation.
Flakiness index — Flakiness index from the flaky mass in each size fraction.
Bulk density by wax coating — Bulk and dry density of an irregular lump from waxed mass in air and in water.
Sand equivalent — Sand equivalent from clay and sand readings in the graduated cylinder (mean of trials).

For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.