Site investigation · Laboratory: rock & aggregates

Brazilian tensile strength calculator

Indirect tensile strength of rock discs σt = 2P/(π D t), averaged over the set.

Standard: ISRM suggested method · ASTM D3967

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
Discs: load P (kN), D (mm), t (mm)	18.2, 54, 27 16.9, 54, 26.5 19.5, 54, 27.4

Result	Value	Unit
Mean tensile strength	7.95	MPa
Coefficient of variation	5.48	%

Diagram for the worked example

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.
Slake durability index — Second-cycle slake durability index and Gamble durability class.
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.