Structural Design of Pavements PART VI Structural ... - TU Delft

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Preface:
Pavements deteriorate due to damaging effects of traffic and environmental loads and at a
given moment in time maintenance is needed. Maintenance activities can grossly be divided
into two categories.
The first category is the so called routine maintenance which is mainly applied to keep the
pavement surface in such a condition that it provides good service to the public but also to
limit the effects of ageing. Routine maintenance consists e.g. of crack filling, local repairs and
the application of surface dressings. Normally this type of maintenance is not too expensive.
The costs of a surface dressing are approximately fl 6/m 2 while filling of cracks costs
approximately fl 2.5/m ’ . Routine maintenance is done on a regular basis; the time period
between two successive applications depends of course on the rate of deterioration which in
turn is affected by the damaging power of traffic and climate and by the workmanship of the
maintenance crews.
The second category is much more capital intensive. Now we are dealing with strengthening
of the pavement for which overlays are needed or partial or complete reconstruction. This
type of maintenance is less often required than routine maintenance.
Because pavement strengthening is such a costly affair, investigations to determine precisely
the extent and severity of the damage and the rate of progression are strongly recommended.
If a pavement surface e.g. shows severe cracking, removing this layer and replacing it by a
new one seems to be a sensible solution. If however the cracking is due to the very low
stiffness of the base and no measure are taken to improve the bending stiffness of the base
layer, then the cracking will soon reappear.
This simple example already illustrates that, in order to be able to make a proper selection of
the maintenance treatments available, one not only should know where something is going
wrong but also why.
Understanding why the pavement fails means that one needs knowledge on the stresses and
strains in the pavement as well as the strength of materials. The process of gaining this
knowledge is called “evaluation of the structural condition of pavements”.
As it will be shown in these lecture notes, deflection measurements are an extremely useful
tool in the assessment of the structural condition of the pavement. During a deflection
measurement, the bending of the pavement surface due to a well-defined test load is measured.
This is called the measurement of surface deflections. It is clear that the magnitude of
the deflections and especially the curvature of the deflection bowl reveal important information
on the bending stiffness of the pavement.
In the notes ample attention is paid to the techniques for measuring deflections, the way how
the measurement results can be processed to obtain information on the stiffness of the
individual pavements layers and how they can be used to determine the required thickness of
the overlays to be applied.
Although all possible care has been given during the preparation of these notes to avoid
typing errors etc., it is always possible that some “bugs” are still present. Furthermore the
reader can have suggestions about certain parts of the material presented. It would be highly
appreciated if you could send your comments to the author using the following email address.
a.a.a.molenaar@citg.tudelft.nl