The testing machine shall be capable of applying load with a permissible error of less than ± 0.5% of the applied load when a high degree of accuracy is required. In commercial use the applied rate of loading is less than ± 1.5 percent of the applied load.
The bed of the testing machine is provided with two steel rollers, 38 mm in diameter , on which the beam specimen is supported. The rollers shall be so mounted that the distance from centre to centre is 60 cm for 15.0 cm specimens or 40 cm for 10.0 cm specimens. Load is applied through two similar rollers mounted at the third points of the supporting span, that is, spaced at 20 or 13.3 cm centre to centre. The load shall be divided equally between the two loading rollers.
Procedure:
1) Concrete is mixed in manner a similar to compression test cube specimens.
2) The standard size of cubes are casted of size 15 × 15 × 70 cm. Alternatively, if the largest nominal size of the aggregate is less than 19 mm, specimens 10 × 10 × 50 cm may be used.
3) The joints between the sections of the mould shall be thinly coated with mould oil.
4) The interior faces of the assembled mould shall be thinly coated with mould oil to prevent adhesion of the concrete.
5) Test specimens stored in water at a temperature of 24° to 30°C for 48 hours before testing, shall be tested immediately on removal from the water while they are still in a wet condition.
6) The specimen shall then be placed in the machine in such a manner that the load shall be applied to the uppermost surface as cast in the mould along two lines spaced 20.0 or 13.3 cm apart.
7) Axis of the specimen shall be carefully aligned with the axis of the loading device.
8) No packing shall be used between the bearing surfaces of the specimen and the rollers.
9) Load shall be applied without shock and increasing continuously at a rate such that the extreme fibre stress increases at approximately 7 kg/cm2/min.
10)The rate of loading of 400 kg/min for the 15.0 cm specimens and at a rate of 180kg/min for the 10.0 cm specimens
11) Load shall be increased until the specimen fails, and the maximum load applied to the specimen during the test shall be recorded.
12) The appearance of the fractured faces of concrete and any unusual features in the type of failure shall be noted.
