Pavements Unbound

Pavements Unbound

The requirement for a performance based test for unbound
and weak hydraulically bound materials (HBMs), which is also simple to
use in comparison with research based apparatus, was identified some
years ago as being key to characterising non standard and stabilised
pavement foundation materials. Resilient modulus and permanent
deformation resistance were identified as key material performance
properties to be determined, both for input into new UK design
procedures (where pavement thickness will depend on foundation class),
and for assessing potential constructability prior to more expensive trials.
Design features for such a test include the incorporation of an aggregate
size up to 40 mm, the ability to cure HBM samples other than in the
compaction mould or the test equipment itself, and utilisation of the
standard Nottingham Asphalt Tester (NAT) loading frame, which is
widely used for the testing of asphalt samples.

In recent years, there has been a strong tendency throughout civil engineering to move
away from traditional “recipe and method” specifications and towards those that are
“performance related” (Fleming, et al 2000). The determination of fundamental
engineering properties of materials is key to their inclusion within analytical or
mechanistic pavement designs.
An overview of laboratory test method indicated a lack of recognised mechanical tests
in the UK applicable to unbound and weakly bound pavement materials (Edwards, 2003).
Specialist tests are available such as the Repeated Load Triaxial (RLT) test and Hollow
Cylinder Apparatus (HCA), as are much simpler techniques such as the California
Bearing Ratio (CBR).
A need was therefore identified for a relatively simple test which was capable of
generating the required mechanical properties for input into analytical pavement design,
most notably stiffness modulus, but also resistance to permanent deformation.


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