To determine the Flexural Strength of Concrete, which comes into play when a road slab with inadequate sub-grade support is subjected to wheel loads and / or there are volume changes due to temperature / shrinking.
IS : 516-1959 – Methods of tests for strength of concrete.
Equipment & Apparatus
- Flexural test machine
- Test specimens shall be prepared by moldings concrete to a beam section, curing and storing in accordance with standard procedure. The section of the beam shall be square of 100 mm or 150 mm. The overall length of the specimen shall be 4d to 5d. The ratio of d to the maximum particle size of aggregate shall be not less than three.
- Circular rollers manufactured out of steel having cross section with diameter 38 mm will be used for providing support and loading points to the specimens. The length of the rollers shall be at least 10 mm more than the width of the test specimen. A total of four rollers shall be used, three out of which shall be capable of rotating along their own axes. The distance between the outer rollers (i.e. span) shall be 3d and the distance between the inner rollers shall be d. The inner rollers shall be equally spaced between the outer rollers, such that the entire system is systematic.
- The specimen stored in water shall be tested immediately on removal from water; whilst they are still wet. The test specimen shall be placed in the machine correctly centered with the longitudinal axis of the specimen at right angles to the rollers. For moulded specimens, the mould filling direction shall be normal to the direction of loading.
- The load shall be applied slowly without shock at such a rate as to increase the stress at a rate of .06 + .04 N/mm2 per second.
The Flexural Strength is given by
fb = pl/bd2
a > 20.0cm for 15.0cm specimen or > 13.0cm specimen.
fb = 3pa/bd2
a <20.0cm but >17.0 for 15.0cm specimen or <13.3 cm but >11.0cm for 10.0cm specimen.
b = width of specimen
d = failure point depth
l = supported length
p =max. Load
The Flexural strength of the concrete is reported to two significant figures.
Safety & Precautions:
- Use hand gloves while, safety shoes at the time of test.
- After test switch off the machine.
- Keep all the exposed metal parts greased.
- Keep the guide rods firmly fixed to the base & top plate.
- Equipment should be cleaned thoroughly before testing & after testing.