D41 38
3. Tips regarding material laying
Especially when laying bitumen materials, the quality of the material is of great
importance. Cold material lumps produce an open structure (holes, nests) that
requires unnecessary reworking. Using the wrong grain size can also cause open
structures if there are stones in an otherwise fine grained material (especially when
laying the final wear course).
The thickness of the layer should usually be triple or at least one and a half times
the maximum grain size of the material being laid!
Spraying the foundation must be done with the required care. Spraying too much
material can cause oversaturation of the surface. This is especially important with
vibration screeds.
Laying material on slopes or inclines is better done by working up the slope or
incline. In wet weather, however, it may be more advantageous to work down the
slope or incline so that water is pushed aside. Generally, however, work should be
stopped during heavy rain falls.
When paving one side of a road at a time, the working width of each successive
layer should be varied by approx. 20 cm. When the final wear course is laid, the
seam must, of course, be in the middle of the road.
3.1 Layer thickness
The thicker the individual layers are and the smaller the number of layers is, the
greater must be the care to be taken when laying the foundation. By using a large
number of layers, it is possible to compensate any unevenness and obtain a good,
i.e. level wear course - even with an uneven subsoil of less load-bearing capacity.
On many construction sites, an additional layer of material is manually spread on
top of the wear course to get a better surface. However, this produces exactly the
opposite result. Owing to the rapid cooling rate of the additional layer, the road
roller cannot fully compact and flatten the material so that the result is an uneven,
rough surface which has holes in some places.
The compaction of a wear course by the different types of road rollers is of crucial
importance for the stability and durability of an asphalt carriageway. Often,
careless compacting noticeably impairs the quality of the layers laid by the paver
finisher.
The temperature of the material depends on the type of bitumen and the
composition of the asphalt. If possible, the values given in the following table should
always be adhered to. For different types, the stipulated pertaining temperatures
must be heeded.
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