Also called modulus of rupture, it is tested by loading a 6 by 6 in beam at its third points (ASTM C78) until it cracks. Typical paving mixes reach 550 to 750 psi, roughly 10 to 15 percent of compressive strength. Highway and airfield pavements are designed on flexural strength because slabs fail by bending under wheel loads, not by crushing.
Heard on the job
Airport spec is 650 psi flexural strength, so the beams get broken at 28 days and the cylinders are for information only.
Also heard as
- modulus of rupture
- MR
- beam strength
Related terms
Compressive strength
The crushing load concrete can carry per unit area, the main property specified and tested for concrete.
Cylinder
A cast concrete test specimen, usually 4 by 8 in or 6 by 12 in, crushed to measure compressive strength.
Break
A cylinder strength test result, or the crushing of cylinders in the lab.