Destructive tests of concrete

Destructive tests (DT) are tests in which the concrete specimen is loaded or cut to failure, so it is damaged or destroyed. They give the direct measure of strength and are the basis of acceptance (IS 456, Cl. 15 and 16).

1. Compressive strength test on 150 mm cubes or 150 × 300 mm cylinders (IS 516): the main test.
2. Split tensile test on cylinders (IS 5816): indirect tensile strength.
3. Flexural strength test on beams 150 × 150 × 700 mm (IS 516): modulus of rupture.
4. Core test (IS 516, ASTM C42): 100 mm cores drilled from the structure and tested in compression; the average of cores should be at least 85% of $f_{ck}$, no core below 75%.
5. Pull-out and bond tests: a steel bar pulled from concrete to find bond strength.
6. Load test on the structure or member (IS 456, Cl. 17.6): the member is loaded with the full dead load plus 1.25 times the imposed load for 24 hours, and the deflection and recovery are checked.
7. Modulus of elasticity test and shear tests.

Comparison with NDT: DT is accurate but expensive, slow and damages the member, while NDT is quick, cheap, and non-damaging but gives only indirect results.