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

ASPHALT REVIEW
research and quality control testing has
been carried out in association with this
work, with considerable successes being
obtained.
4. Benefits of Half-Warm Mixes
The two main benefits of Half-Warm
asphalt mixes are:
1. Reduction in greenhouse gas
emissions; and
2. Improvement in field crew health and
safety.
A closer examination of the technology
reveals additional benefits for both
producers and purchasers of Half-Warm
asphalt mixes.
4.1 For the producer
Producing mix at a lower temperature
means that the differential between
ambient and mix temperature is reduced.
This means that the Half-Warm asphalt
mix will cool more slowly compared
with hot mix asphalts. A slower rate of
cooling allows longer cartage distances,
extended workability time in the field
and the ability to place and compact in
cooler conditions.
Because the Half-Warm asphalt cools
more slowly, the formation of a chilled
‘crust” on the surface of payloads does not
form to the same degree. Another benefit
of the Half-Warm asphalt technology is
cleaner truck decks and hand tools.
4.2 For the Client
Conventional hot-mix asphalts are
produced at around 165° C so that
the viscosity of the bitumen binder is
lowered enough to permit adequate
workability of the mix. A negative effect
of this high production temperature is
the aging of the bitumen due to reaction
with atmospheric oxygen. This is a well
known phenomenon and is controlled
by including aging tests in bitumen
specifications
The chemical additives in the Half-
Warm process contain active adhesion
promoters. Thus the risk of water
damage in the asphalt pavement is
reduced or eliminated. This use of
adhesion promoters is contrasted with
some Warm Mix systems that depend
on the use of water, potentially trapping
water in the mix and degrading longterm
performance. The Half-Warm
process provides for long-term adhesion
of bitumen to the aggregate by including
active chemistry in the additive
chemicals.
The reduction in temperature
differential between the half-Warm
asphalt and ambient temperatures,
the extended workability and the
minimisation of “crust” formation means
that compaction is more readily achieved
in the field minimising the risk of rutting,
permeability and binder oxidation.
The Half-Warm asphalt process is
a means for the production of asphalt
paving mixes. The same material is being
manufactured and placed; it’s only the
manufacturing process that has changed.
5. New Zealand Experience with
Half-Warm Mixes
In 2005, Fulton Hogan began assessing
warm mix and half-warm mix
technologies available around the world,
and selected the low emissions asphalt
(LEA) process to implement in the
company’s New Zealand asphalt plants.
Following laboratory development and
early pilot trials constructed on a haul
road within one of Fulton Hogan’s
quarries in Christchurch, some high
profile/high-demand sites were paved:
1. Buckley’s Road, Christchurch,
December 2007
2. Montreal Street, Christchurch,
March/April 2008;
3. Christchurch International Airport
taxiway, February 2008.
To date the performance of all the
trials has been exemplary. Cores were
taken of the trial sections in August
2008 (4 months after they were laid),
and tested in Fulton Hogan’s laboratory
wheeltracking device. The AC14 initially
had a higher rate of rut development
compared with the CoolPave, but after
10,000 passes they had similar rut
depths.
Our experience to date is that the
Half-Warm process allows asphalt
pavements to be placed at a quality
equal to, or better than, conventional
hot mix asphalt pavements.
Fulton Hogan has produced Coolpave
in 5 of its 14 fixed plants, all of which
are continuous drum plants.
Fulton Hogan has produced
approximately 6000 tonnes of Coolpave,
mostly a standard 14 mm dense mix.
Small runs of 7mm and 10 mm mix
have been produced for hand work trials
which worked successfully.
Mixes have been laid to date on minor
city streets, multi-lane city arterials,
airport taxiways and factory yards/
carparks.
Compaction results in the field show
that Coolpave compacts similar to hot
mix, and the workable time and time to
compact increases using Coolpave.
Minimal laboratory-based performance
testing has been conducted, although
one wheel tracking test showed that after
10,000 passes the AC14 Coolpave had
almost exactly the same degree of rutting
as hot mix AC14. The Coolpave product
reported total rutting equal to 96% of the
hot mix value after 10,000 passes.
6. Clients’ Perspectives
6.1 Christchurch City
Christchurch City Council leads and
strongly supports local environmental
initiatives in transportation and other
fields – particularly where these initiatives
may have benefits for the wider regional
and national community.
The production of standard asphalt
has a high energy requirement due to
the need for materials to be heated
during production and the need for
high temperatures to be maintained
through to final placement. The high
temperatures required to manufacture
asphalt also result in high emissions
to atmosphere as well as temperaturerelated
safety issues for site staff and the
public during the laying-down process.
This initiative by Fulton Hogan meets
council’s expectations for practical
solutions to both environmental and
safety issues. The material met initial
trial requirements and meets all council
asphalt test needs. The full scale trials at
the two sites have to date demonstrated
that material design, manufacture,
cartage and laying methodologies are
similar to standard asphalt; resulting in
burner fuel savings during manufacture
due to lower energy requirements,
reduced emissions, easier achievement
of density requirements when laying
in cooler air temperatures and greater
safety during placement.
Council tendering and contract
methodologies encourage innovation and
Fulton Hogan’s proposal was developed
within this framework. Council works
with the local contracting industry to
explore new initiatives. The local industry
has demonstrated a willingness to work
with council to meet both community
and industry needs and has shown great
passion in their endeavours.
6.2 Christchurch International
Airport
Christchurch International Airport
Limited (CIAL) has worked with Fulton
Hogan for the last 18 years on Airfield
Pavement Maintenance Works (APMW).
In 2006, CIAL encouraged Fulton Hogan
to undertake a process of innovation
to reduce the total cost of ownership
and reduce the carbon footprint in the
delivery of the APMW programme. CIAL
is a CarbonZero Airport, the first in the
26 ROADS JUNE 2010/JULY 2010