Job # 11:
Determination of the Tensile Strength of Concrete by Double Punch Test
Significance:
- It is an indirect method through which tensile strength of concrete is estimated.
Apparatus:
- Denison Leeds, England Compression testing machine
- Testing Samples
- Punches of diameter 37 mm (2 in number, to be placed at the top and bottom of the sample)
Related theory:
Difficulties in measurement of tensile strength:
There are considerable experimental difficulties in determining the true tensile strength of concrete. In direct tension test following are the difficulties:
- When concrete is gripped by the machine it may be crushed due the large stress concentration at the grip.
- Concrete samples of different sizes and diameters show large variation in results.
- If there are some voids in sample the test may show very small strength.
- If there is some initial misalignment in fixing the sample the results are not accurate.
Indirect methods for the determination of tensile strength of concrete:
- Split cylinder test
- Double punch test
- Modulus of rupture test
Double punch test:
In this test, a concrete cylinder is placed vertically between the loading platens of the machine and is compressed by two steel punches placed parallel to top and bottom end surfaces. The sample splits across many vertical diametrical planes radiating from central axis.
Tensile strength can be defined as
