Oscillating asphalt

To celebrate Barbagallo Raceway’s 50 anniversary, the West Australian Sporting Car Club enlisted the help of Asphaltech to resurface the entire track — its first upgrade in 14 years.

When the Western Australian Sporting Car Club (WASCC) set out to explore its first resurfacing project in 14 years, they wanted to keep their options open. Submissions were requested for three different combinations of stone, bitumen and polymer.

Submissions were then independently evaluated by technical advisors Golder Associates and WASCC with both coming to the same conclusion – Asphaltech would be awarded the contract.

Given Asphaltech worked on the last resurfacing project in 2004, WASCC called the award unsurprising.

Asphaltech decided the most suitable technology for compaction on this specific project was oscillation — and utilised two HAMM oscillating rollers, the HAMM HD+70iVO and the HAMM DV+70iVO to complete the work.

According to WASCC, the critical question of the project was whether to use the conventional and currently utilised 10-millimetre Dense Graded Asphalt (DGA) or change to newer 7-millimetre Stone Mastic Asphalt (SMA) technology.

DGA typically starts off smooth, developing texture as more stones are exposed. Over time, however, the fine material between stones begins to dislodge in a process called ravelling —a significant issue for tyre wear.

Alternatively, SMA is a single-style mix of stone particles bound by a higher per cent of bitumen. While this makes SMA marginally more expensive, it also makes it stronger and less reliant on fine binding material.

This combination of factors means SMA tracks have a better early life grip when wet, a more durable and consistent high-grip surface and a longer service life.

According to Wirtgen Product Manager, Marc Fernandes, oscillation is the compaction technology best suited for SMA, meaning HAMM compaction equipment was the obvious choice for the raceway project.

The relationship between Wirtgen and Asphaltech started in early 2015 when Asphaltech was looking to renew their roller and paver fleet.

According to Mr. Fernandes, Asphaltech wanted to find the most cost-efficient way to compact asphalt.

“Given there are various types of asphalt mix’s that require various types and sizes of rollers, we wanted to get an all-round mix of rollers that would get high utilisation,” says Asphaltech General Manager WA Peter Rimpas.

Following various trials, meetings and phone calls, Asphaltech selected Wirtgen Group as its key supplier.

“We had a lot of suppliers to choose from and we put them through a great deal of scrutiny but in the end, Wirtgen came out on top, says Mr. Rimpas. “Now, we use oscillation rollers on all of our projects daily.”

HAMM, part of the Wirtgen Group, first developed the technology 35 years ago — becoming the first roller manufacturer to use an oscillation drum in tandem rollers.

In the past five years alone, HAMM have delivered more than 3,000 machines that use this particular technology — and today, one in five of the tandem rollers leaving the HAMM factory in Germany is equipped with an oscillation drum.

“Vibration is not the preferred compaction style when compacting SMA due to the risk of flushing and bleeding of the bitumen,” Mr. Fernandes says.

“Following various trials, we found that we could achieve compaction quicker and eliminate the risk of flushing or bleeding of the bitumen on SMA by using oscillation”

Through oscillation, two unbalanced shafts rotate synchronously, with the unbalances offset by 180 degrees.

Mr. Fernandes says the benefits of the oscillation method are numerous, highlighting HAMM equipment’s high compaction power, lack of over-compaction, tight joints and efficient compaction rate.

“Tandem Rollers equipped with one oscillation and one vibrating drum are used across all types of asphalt mix designs. Both features can be switched off and the roller then utilised in static.

“The oscillation drum moves both in a forward and backward movement and the drum directs its compaction force into the ground in the form of tangential shear forces. In doing so, the drum never lifts off the ground — the area is therefore compacted dynamically without interruption,” Mr. Fernandes says.

Vibration compaction increases the risk of destroying material structure and grain crushing because of the level of rigidity. This, however, is not the case with oscillation, as aggregate particles are redistributed non-destructively.

“Surfaces compacted using oscillation also exhibit excellent longitudinal evenness. And because the drum remains in constant contact with the ground, no impacts occur that could produce irregularities in the ground or asphalt,” Mr. Fernandes says.

On the first race day post resurfacing, Asphaltech’s new track delivered on its promise, with the lap record being broken multiple times.

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