A strong base for the upper road structure
The bottom
layer essentially comprises an unbound mixture of coarse and fine crushed
stone, as well as crushed sand, to achieve the desired load-bearing capacity
and absorb traffic loads so that the underlying subgrade is not deformed.
A gravel layer protects
against frost
Roads are
exposed to particularly high stresses when the water contained in the pavement
structure begins to freeze. Water expands when freezing, which can lead to
frost damage that will sooner or later have an impact also on the road surface.
This is prevented by a so-called frost blanket which usually consists of a
mixture of gravel and sand, supplemented by crushed mineral aggregate. When
compacted, these layers of frost-resistant materials conduct water away from
the upper pavement layers, reducing tensions very effectively at the same time.
The mix makes all the difference
In many
cases, a bound base course is overlaid over the unbound base course. Bitumen,
cement or lime is predominantly used as binder.
Bituminous bound base layers
Mixes
containing bitumen are referred to as hot-paved or cold-paved asphalt base
courses, depending on whether the mix is hot or cold. The base course is said
to be hydraulically bound when cement or lime is used as binder.
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Hydraulically bound base layers
When the
mineral aggregate mixture is bound with cement or lime, the resulting base
layer is called a hydraulically bound base layer. Mineral aggregate mixtures
used for this type of base layer consist of Un_crushed gravel or coarse
aggregate, chippings, and crushed or natural sand. Ever more frequently, these
mixes also contain a percentage of recycled construction materials.
Paving a hydraulically bound base layer.
Precisely
metered quantities of cement slurry are added via hose connections from the
slurry mixer to the cold recycle.
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