We’re pleased to feature this insight from Steve Halligan at Road Surfacing SOLUTIONS, who brings experience in sustainable road construction and asphalt technologies to explore the topic of Extreme Stress Seal (XSS) application using a PGXpand® modified binder.
What the Asset Owner Wanted
This section of road is currently surfaced with a sprayed seal carrying 19,000 vehicles per day over two lanes along with the movement of a high proportion of heavy trucks plus an intersection servicing a quarry. The seal is flushing in the wheelpaths along with cracking.
The asset owner wanted to apply a reseal that would manage the cracking to waterproof the road and would be fit for purpose for the high traffic volume plus the intersection servicing the quarry. Looking at the Austroads publication, Guide to Pavement Technology Part 4K: Selection and Design of Sprayed Seals, it advises https://austroads.gov.au/publications/pavement/agpt04fthat a sprayed seal for this environment would be an Extreme Stress Seal (XSS).
Why Use PGXpand
A typical treatment for an XSS seal could be a 14/7mm double/double seal with a modified binder. However, with the high and increasing traffic volume along with many heavy vehicles and the intersection the asset owner wanted a more robust seal treatment.
The incorporation of PGXpand into a seal binder can achieve improved seal performance through the binder having enhanced properties including:
- Higher softening points so the binder does not soften too much in extreme summer weather; and
- Higher consistency than other modified binders; plus
- Reduction in viscosity at typical spraying temperatures, thus improving binder/aggregate adhesion, reducing the likelihood of seal stripping assuming the aggregate is not wet or dirty with dust.
Other seal binders may not provide the same outcomes as a PGXpand modified binder. PGXpand is introduced to the seal binder at the depot where it can be mixed into the binder at its source. PGXpand travels well without any separation of the components and does not degrade during transport or heating.
What was Done to Construct the Extreme Stress Seal
The works were to reseal 1.0km of the main road over two days. The first day was a 550m section with a 20/7/7mm XSS seal applied using an S18RF binder without PGXpand. On the 2nd day, a 450m section abutting the seal from the first day was applied with PGXpand in the S18RF binder. The section with PGXpand included the intersection to the quarry with turning trucks and is ideal for Sripath to demonstrate the performance of PGXpand in comparison to the seal applied on the first day.
The 20/7/7mm XSS seal on both days comprised of the following coats:
- Spray binder at 1.0 L/m2 cold and cover with 20mm aggregate, roll, traffic and then sweep lightly.
- Cover with 7mm aggregate without binder and lightly roll/traffic.
- Spray binder at 0.9 L/m2 cold and cover with 7mm aggregate, roll, traffic and sweep.
PGXpand was used in all binder applications on the 2nd day and the aggregates were precoated with a bitumen based black precoat on both days. An adhesion agent was added to the binder on each day. A total of 4-6% cutter was added to the S18RF on the first day and 2% cutter was added to the PGXpand modified binder on the 2nd day. The use of less cutter on the 2nd day was because the day was hotter but it also reflected the impact PGXpand has on the viscosity of the modified binder at the time of spaying. PGXpand can assist with a reduction in the amount of cutter oil used in the application of the binder or by reducing the spraying temperature.
For more information about spray seals and PGXpand, contact info@sripathapc.com.
