Asphalt Review - Feb/March 2013 - Australian Asphalt Pavement ...

ASPHALT REVIEW
Sergio Cinerari (left) and
Fergus Cameron (MD of
Phillip Island Operations)
in front of asphalt plant
brought to Phillip Island.
commenced on the asphalt mix design. Records of the job mix from
1998 were still available which served as a valuable reference point
during the development of the new mix design.
As we all know things change with time, and while the previously
used source rock was still readily available, the grading of the
aggregates available now was not the same. Together with this, the
sand incorporated into the mix in 1998 was no longer available.
Considerable effort was put into fine tuning the mix design to ensure
that it did not only meet the specification requirements, but was the
mix that delivered optimal performance from the materials.
The collaborative approach employed by Linfox enabled open
discussion amongst the parties. This ensured all the issues were
investigated, discussed and the “best for track” outcome decided based
on risk and cost. The selection of the binder for the project was an
excellent example of this process.
The current surface placed in 1998 incorporated C320 binder;
however, the decision was made to move to an A35P polymer modified
binder for the 2012 homologation works. The collaborative approach
enabled Linfox to work with Downer and Aurecon to understand the
performance benefits of the modified binder and to be able to weigh
these up against the higher initial cost to arrive at the best value for
money solution.
This process was aided by a visit to Downer’s Research and
Development laboratory in Somerton where the Linfox team were able
to touch and feel the different variants of the mix design and physically
see the difference in performance and surface texture offered by each.
The profiling asphalt production and paving methods followed a similar
decision process before being agreed upon.
While the existing surface of the track was generally in good
condition, several bumps and hollows had developed over the past 13
years, so the team agreed that this was not a project where just milling
off a nominal 40mm and replacing it would meet the brief.
In keeping with best practice which dictates that you attend to ride
issues as early in the process as possible, the decision was made to
mill the track to level. To facilitate this, a laser scan of the track was
undertaken by Aurecon and a new design surface overlayed on the
existing, with the “ideal” design manipulated as required to match
structures such as existing ripple strips. The profiling of the track would
then be undertaken utilising Paveset level control on the profilers with
a Specification tolerance of plus or minus 3mm.
To achieve the original goal, the decision was made to establish a
large mobile plant on site. This decision was reached to enable the track
to be paved full-width with two pavers in echelon, ensuring that each
paver could be fed with enough mix to maintain an ideal consistent
paving speed of five metres per minute. The added advantage of the
plant on site was to minimise the time between production of the
mix and placement. This would ensure consistently optimum asphalt
temperature and promote homogeneous compaction of the mix.
An Astec T400 Double Barrel continuous mixing plant was
transported to site for the task. “The establishment of the plant into
the infield of the track presented its own challenges,” commented
Martin Kinski, Downer Project Manager.
“With the long wheel base and low clearance of the mobile plant
trailers, we had to complete pre-works involving widening and flattening
of the access into the site and demolishing the veranda off the old hay
shed inside the circuit to accommodate the swept path of the mobile
plant trailers. The track is used around 300 days per year, so the window
of opportunity to move the trailers over the track was small.
“A short three-day window existed immediately following the Motto
GP in late October; however, the plant had to be moved in overnight
due to the transport traffic leaving the track during the day with
everything from temporary stands, portable buildings and marquees
all having to be removed over the same three-day day period,”
commented Martin.
“It wasn’t just a case of towing the nine oversized trailers in; firstly
we needed to build a temporary pavement over the track, move the
plant in and then remove the ramp. All this needed be completed and
the site left clean and ready for racing the following day.”
With the plant moved into the site, the erection and commissioning
was performed during early November while the track was still in
operation, followed by mix trials later in the month.
To minimise costs, the RAP profiled from the track was to be utilised
to construct the hardstand area for the virgin aggregates. Once
again, this presented challenges as the profiling of the track was not
commencing until seven days before the new surface was to be placed.
This necessitated the early production, testing and stockpiling of the
aggregates at the quarry so they could be available for transport into
the track over only four days.
The track was closed from Monday 3rd December, with profiling
commencing immediately that morning, utilising two 2m Profilers with
fine milling drums. Despite some ice cold, windy and wet weather
early in the week, the bulk of the track was milled out in only three
days, with final clean-up, patching of laminations and any other defects
occurring over the remainder of the week. The tight tolerance had been
met and the surface rode well. All was ready for the application of the
new asphalt.
The track was planned to be paved in two days totalling 4,700
tonnes. The location of the two transverse joins had been pre-agreed
as part of the planning of the job, so the target for each shift needed
was achieved.
32 ROADS FEB/MARCH 2013