Flexural Strength of Concrete (Modulus of Rupture)

The flexural strength (modulus of rupture, fcr) is the maximum tensile stress in the extreme fibre of a plain concrete beam at failure under bending, measured per IS 516 on a 150 × 150 × 700 mm beam under two-point (third-point) loading. It characterises concrete's resistance to bending-tension cracking and is the design strength parameter for concrete pavements and slabs-on-grade, where flexure rather than crushing governs.

For mix design and where testing is not done, IS 456 Cl. 6.2.2 gives fcr = 0.7√fck MPa. IRC 58 (rigid pavement design) is explicitly based on the 90-day flexural strength of pavement-quality concrete (commonly specified around 4.5 MPa), making this the controlling acceptance test for PQC and white-topping. The third-point loading arrangement keeps the central third of the span in pure bending so the recorded rupture occurs at the genuine weakest section within that zone.