CT4860 STRUCTURAL DESIGN OF PAVEMENTS

The irregular temperature results in internal concrete stresses, which are only
relevant for very thick concrete slabs. For normal concrete slab thicknesses
they also can be neglected.
On the contrary, the temperature gradients ∆t cause flexural stresses in the
concrete pavement that are in the same order of magnitude as those caused
by the traffic loadings, and thus cannot be neglected at all. Paragraph 3.3.2
deals with the magnitude and frequency of occurrence of temperature
gradients. In 3.3.3 and 3.3.4 the calculation of the flexural stresses due to a
temperature gradient will be discussed.
3.3.2 Temperature gradients
The temperature gradient ∆t is defined as (figure 9):
T Tb
∆ t =
(13)
h
t −
where: Tt = temperature (°C) at the top of the concrete layer
Tb = temperature (°C) at the bottom of the concrete layer
h = thickness (mm) of the concrete layer
In case of a negative temperature gradient the concrete slab curls. Due to the
deadweight of the concrete slab there are flexural tensile stresses at the top of
the slab. Generally a negative temperature gradient (that occurs during night)
is not taken into consideration in the design of a concrete pavement, because:
- the negative gradient is smaller than the positive gradient (figure 10 and
table 7)
- during night there is only a small amount of heavy traffic
- in the mostly dominating location of the concrete slab (in case of plain
concrete pavements the centre of the longitudinal edge and in case of
reinforced pavements along the transverse crack in the wheel track or in
the centre of the slab width) the traffic loadings cause flexural compressive
stresses at the top of the slab.
A positive temperature gradient (that occurs during day) causes warping of
the concrete slab. Due to the deadweight of the concrete slab, in this case
there are flexural tensile stresses at the bottom of the slab. These stresses
are called ‘warping stresses’.
Table 8 shows the standard temperature gradient frequency distribution that is
included in the current Dutch method for the structural design of concrete
pavements (5).
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