Abstract:
The proper densification of the separate pavement layers forms an integral part of road
construction. Many problems, are, however, experienced in this area. Because of a lack of
knowledge the compaction of untreated roadbuilding materials in problem situations is usually
approached on a ''trial and error'' basis rather than basing possible solutions on scientific
evidence of the collective influence of the material properties and site conditions.
The purpose of the study was to place the compaction of untreated roadbuilding materials on
a more scientific basis. An investigation was therefore launched to determine the effect of
measured material properties on their compactability. A non-standard vibratory compaction
test was used to compact the samples in one layer. New test parameters to quantify the
shape and texture of the material were also developed, namely the shakedown bulk density
and the shape factor. The CBR values of the materials at moulding moisture content were
determined for each material for a range of densities and moisture contents. The maximum
dry densities (MOD) (vibratory and mod. AASHTO) and optimum moisture content (OMC)
(vibratory and mod. AASHTO) were also determined.
The measured values were then evaluated in terms of the following physical properties of the
materials: grading, Atterberg limits, linear shrinkage, shakedown bulk density (SBD), loose
bulk density (LBO), shape factor (SF) and specific rugosity (Srv). In the extensive laboratory
study of 21 different untreated roadbuilding materials, varying from TAB classes A-7-6 to A-1,
it was found that both the maximum dry densities and moisture regimes can be quantified in
terms of the grading, liquid limit and linear shnnkage of the materials. These relations were modelled by means of regression analysis. Besides this a general bearing capacity model was found for all these materials where the
CBR is a function of the dry density and moisture content of the material. This model was
further refined to take account of the influence of shape and texture of the particles so that
it is possible to determine reasonable estimates of the bearing capacity for a range of
densities and moisture contents from the grading, Atterberg limits, linear shrinkage,
shakedown bulk density and shape factor.
This investigation has shown that physical laws govern both the compactability and bearing
capacity of untreated roadbuilding materials, irrespective of their composition or nature,
making it possible to approach the compaction of untreated roadbuilding materials in a more
generalised manner.
