Asphalt Review - Volume 29 Number 2 (June / July 2010)

ASPHALT REVIEW
AAPA/Austroads Warm Mix Asphalt Validation Protocol
In order to validate the performance
of WMA (including WMA with varying
amounts of RAP) against hot mix, AAPA
and the sate roads authorities developed
an evaluation protocol.
This protocol was developed through
the Asphalt Research Reference Group, a
group comprising state road authorities and
the AAPA National Technology Committee,
which was established to advise the
Austroads Pavement Technology Review
Panel.
The scope of the protocol was confined
to wearing courses consisting of densegraded
asphalt and conventional binders.
Recycled asphalt pavement (RAP), if
included in the WMA, could also be
addressed.
The key issues addressed by the
protocol were:
• the testing of asphalt containing
additives and surfactants, both in the
laboratory and during production;
• the testing of asphalt containing foamed
bitumen: during production only;
• desirable site conditions for a field trial;
• the timeframe for the evaluation; and
• data and information exchange.
The Protocol specified four stages in a
Validation Project – Initial Testing; Field
Validation; Performance Monitoring,
Reporting and Data Sharing.
Initial Testing
• WMA Incorporating Additives and
Surfactants - Testing of (laboratory)
design mixes.
The Protocol proposed that a series
of tests be conducted on both WMA with
additives and surfactants, and the same
asphalt mix composition without additives
and surfactants (the control hot mix).
The protocol includes the following
asphalt tests:
• resilient modulus (indirect tensile);
• moisture sensitivity (stripping potential);
• wheel tracking;
• fatigue;
• maximum density (voids free bulk
density);
• Marshall stability and flow;
• air voids at the design binder content;
• bulk density at the design binder
content; and
• recovered binder viscosity.
Optimisation of an additive may then be
further investigated by varying the amount
of additive and reducing the production
temperature.
• WMA Incorporating a Foaming Process
Foamed asphalt must be produced
22 ROADS JUNE 2010/JULY 2010
through the asphalt plant as it cannot be
readily replicated in the laboratory.
Once the mix design and production
criteria (i.e. production temperature) have
been established, the same procedures
as for WMA incorporating Additives and
Surfactants should be adopted with the
following two additions:
• moisture content; and
• moisture content of aggregates used in
production mixes.
Field Validation
Site selection
Field validation requires that a suitable
site is identified that would enable the
performance of the WMA materials to be
compared against hot mix controls.
Suitable sites should meet the following
criteria:
• minimum hot mix and WMA sections of
length of 100 metres;
• straight section, consistent crossfall and
longitudinal grade;
• reasonable shape (assessed visually
and by roughness and shape testing
using a Multi-Laser Profilometer (MLP);
• strong structural condition (assessed
visually and by pavement strength
testing);
• uniform distress condition;
• known traffic counts and commercial
vehicle percentage;
• medium to heavy traffic conditions; and
• minimum level of rutting and uniform
rutting.
Once a site is selected the following
information should be recorded:
• site ID (a suitable site ID should be
assigned for easy reference);
• road name and location;
• lane number (where appropriate) and
lane width;
• direction of travel;
• chainage; and
• other relevant information, e.g.
drawings, other reference points, the
location of structures, intersections, etc.
Production and Placement details
Once a validation site has been selected,
the following detailed information must be
recorded on the production and placement
of materials:
• Production details:
o mix and bitumen type;
o bitumen content;
o other additives used (if any);
o WMA type and concentration;
o date and time of production;
o production temperature;
o mix design details;
o tonnage of asphalt produced; and
o haulage time (from plant to site).
• Placement details:
o site details, eg. site ID, road name,
etc;
o overlay, or mill and replace;
o thickness of asphalt laid;
o asphalt temperature upon arrival at
the site;
o temperature at first compaction;
o paver type;
o shuttle buggy (if used); and
o roller type and pattern.
Performance Monitoring
The field performance under traffic is the
key factor in validating WMA. Trial sites
must therefore be monitored for a number
of critical performance parameters.
Field monitoring
Given the importance of demonstrating
the viability of WMA and its adoption into
practice by road authorities in Australia
and New Zealand as soon as possible, the
protocol recommended that validation sites
initially be monitored for two summers.
This recognised that should there be any
early problems with WMA they would be
identified during that period. At the end
of that period, the following performance
parameters would be measured and
recorded:
• cracking;
• rutting at 10 metre interval;
• texture at 10 metre interval; and
• stripping potential.
Reporting and Data Exchange
It was noted in the introduction that the
purpose of the protocol was to assess
the performance of WMA and share data,
experience and knowledge among the
road authorities and industry in Australia
and New Zealand using the Austroads
framework. The Protocol recommended
that all information be readily shared
between all participants as a means of
ensuring a consistent understanding of the
performance of WMA.
Reporting
All information related to the evaluation of
WMA should be collated for processing and
to ensure a consistent and comprehensive
report. This information includes:
• Process type (eg. foamed, additive)
and name of additive (if used) of WMA
technology/processes considered;
• asphalt mix type and aggregate size;
• bitumen grade and percentage;
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