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

Beyond Warm Mix Asphalt
Several new technologies have been
developed that reduce energy usage for
asphalt manufacture with a consequent
lowering of production and placement
temperatures. These materials are
called “warm mix asphalt”, or WMA
and the major Validation trial of these
technologies is decribed in page 18 of this
edition of Asphalt Review. However, trials
are also being conducted in New Zealand
into asphalt mixes that can be produced
at even lower temperatures. These are
referred to as half-warm asphalt.
The following paper, prepared by Dr
Bryan Pidwerbesky - Fulton Hogan, Alan
Beuzenberg - Christchurch City Council,
and John De Bono - Christchurch
International Airport, reports on the
reasons for using warm and half-warm
mixes, including operational and technical
benefits, reduction in greenhouse gas
emissions and improvements to worker
safety.
The paper was delivered at AAPA’s 13th
International Flexible Pavements Conference
in November 2009 at Surfers Paradise in
Queensland. (Condensed version - full
version available from Conference papers
2009 - aapa@asn,com.au)
1. Introduction
Climate change and the increased
awareness of greenhouse gas emissions
focusses industry and the community’s
attention on the combustion of fossel
fuels. Therefore although bitumen
is not consumed in the production
of flexible pavements, infact remains
100% recyclable”, the industry does
recognise that it must constantly look at
technologies to even further reduce the
energy concumed in producing asphalt
materials. The industry also recognises
the cost saving associated with lower
fuel consumption. Recognising this,
Fulton Hogan in New Zealand has
identified an advanced Half Warm
asphalt technology and has obtained a
licence for its use.
2. Background to Warm Mix
Asphalts
The drive to reduce greenhouse gas
emissions from hot-mix asphalt
production by reducing fuel usage
is not new. A number and variety of
manufacturing techniques that reduce
the energy used to manufacture asphalts
have been developed beginning in the
1990s. They are generally classified into
two categories:
- Additive based systems, where a
proprietary additive is used to allow a
reduction in energy usage; and
- Alternative manufacturing techniques
such as foaming.
Some processes use a combination
of both techniques, i.e. a proprietary
additive in conjunction with modified
manufacturing processes.
Warm Mix asphalt offers a significant
reduction in production temperature of
up to 40 C and a reduction in greenhouse
emissions associated with the production
of in the order of 20%.
3. Half-Warm Mixes
In 2006, Fulton Hogan identified a
new process that would use even less
fuel for producing asphalt mixes. This
process, developed in Europe, but
licensed worldwide, combines the use
of an additive with plant and process
modifications, resulting in asphalt
produced below 100°C, and able to be
placed at temperatures as low as 60°C.
This new process was radically
different to the Warm-Mix asphalts
previously considered. It involved a
patented system, using proprietary
chemical additives with a change to the
asphalt production process. While the
process change requires modification
to asphalt plants, the degree of
modification is substantially less than
alternative processes and is hence more
ASPHALT REVIEW
A warm mix asphalt produces almost zero fumes and is safer to handle
economically viable. Because the asphalt
mix is produced at temperatures below
100°C, energy demands are significantly
reduced. Experience in Europe
demonstrated that burner fuel savings in
the order of 50% are achievable.
Because this new process differs
so significantly from previous Warm-
Mix asphalts, a new term was coined
to describe the material: “Half-Warm
Mix Asphalt”. This term highlights the
substantial reduction in production
temperature of at least 70°C compared
with similar hot-mix asphalts, and 30° C
cooler than Warm-Mixes.
The significant reduction in burner fuel
usage reduces greenhouse gas emissions
by as much as 50%. In addition, the
cooler asphalt does not emit the “blue
smoke” fumes from production and
handling.
Field crew also benefit from the Half-
Warm asphalt process as the lack of
blue smoke emissions reduces worker
exposure to fumes, and the lowered
placement temperatures virtually remove
the risk of serious burns.
Economically, the costs of the additive
and plant modifications offset the
savings in fuel usage. At the moment the
process is borderline economic, but as
fuel costs continue to rise, the use of the
Half-Warm process will reduce the effect
on the price of asphalt.
Substantial quantities of Half-Warm
asphalt pavements have been constructed
in Europe and the United States. Much
ROADS JUNE 2010/JULY 2010 25