Frequently Asked Questions
Cement & Concrete
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Strength/Modulus of Rupture
Q: What is the recommended value for the flexural
strength (modulus of rupture) of a 28 MPa (4000 psi) concrete to
be used in the design of a slab on grade?
A: The approximate relationship
between flexural strength (modulus of rupture), tested in accordance
with ASTM C 78, and compressive strength (fc)
of concrete is:
In inch-pound units, k is typically estimated to be between 9 for
rounded gravels and 11 for crushed or angular stone (metric: between
0.7 and 0.8).
It is very common to use a k value of 9 (0.74, metric) for design
purposes. Therefore, for a 28 MPa (4000 psi) concrete, the corresponding
flexural strength would be 3.9 MPa (570 psi).
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| Compressive Strength Testing |
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Flexural Strength Testing |
This information is published in Concrete
Floors on Ground, Table 4-6a and 4-6b and in Concrete
Technology Today, Vol. 6, No. 4, December 1985.
There are many additional papers, articles, and opinions on the
correlation between different strength test types. The American
Concrete Pavement Association (ACPA) has compiled some of them here:
http://www.pavement.com/PavTech/Tech/FATQ/fatq-strengthtests.html
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