LICENTIATE THESIS - Luleå tekniska universitet

Sleeper No. 17 looks more like the yellow sleepers because only the ends had a lot of
cracks. Sleeper No. 16 looks more like sleeper No. 7 due to the fact that it has long
horizontal cracks. As mentioned above it does not have the vertical crack at the
fastener.
For sleepers No. 5, 7-16a and 17 the tests have been performed according to Figure 21,
i.e. with a steel pad between the end of the sleeper and the vertical girder. For sleeper
No. 16b and 18 the steel pad was removed to be able to see the influence of this steel
pad. In Figure 20 it is shown that for a sleeper of class 2 or 3 (compare with sleeper
No. 18) it does not influence the test. For a sleeper that is in class 1 (red sleepers) that
have severe cracking the steel pad may influence the test, compare No. 16a and 16b.
Steel pad Vertical girder
Figure 21 Test set-up. Illustration showing the steel pad used in the tests.
Material properties
The material properties of the concrete have been determined from uniaxial tensile and
compression tests on drilled out cores with a diameter of 68 mm, see Figure 22.
The concrete was specified to have a cube strength of 60 MPa. The cement content
was ordinarily 420 kg/m 3 . In order to increase the production speed, the cement
amount was increased to 500 kg/m 3 and heat was used during the hardening process in
some of the production plants. The test results are summarised in Table 2.
i = sleeper no.
i:1 = tensile test
i:2 = compression test
i:3 = reserve
a)
i:3
i:2
i:1
- 17 -
Mid section
sleeper
9:1p
18:1
9:1
b)
12:1p
Figure 22 Test of material properties. (a) Location of cores. (b) Crack planes for
the test specimens 9:1p, 9:1 and 12:1p.
The mean value for 22 compression tests was 100.4 MPa with a standard deviation of
6.6 MPa and a coefficient of variation of 0.07 (the lowest value was 85 MPa).