Construction Materials Why the modulus of rupture of a concr

Solution

Modulus of rupure is equal to the tensile strength only when material is homogeneous. but in the case of concreate bolck is composition of sand, cement and aggregate. When Concrete structure is bent only the extreme fibers are at the largest stress so, if those fibers are free from defects, the flexural strength will be controlled by the strength of those intact \'fibers\' but concrete structure subjected to only tensile forces then all the fibers in the material are at the same stress and failure will initiate when the weakest fiber reaches its limiting tensile stress.

Therefore, it is common for flexural strengths to be higher than tensile strengths for the same material.