As the frequency of heat waves and their damaging effects to human health and infrastructure increase, clever solutions to beat the heat are beginning to crop up.
A Climate Council of Australia report
Heatwaves: Hotter, longer, more often found during the period 1971–2008, both the duration and frequency of heatwaves increased, and the hottest days during heatwaves became even hotter.
The Federal Government has
flagged increasing “urban canopies” to help cool cities.
In the inner western-Sydney municipality of Marrickville, a trial into the heat-combating effects of a lighter coloured road surface are being trailed in collaboration with Monash University.
A relatively new product called Ascrete has been used to resurface Cecilia St. Climate stations have been installed to monitor the road surface temperature and changes in the micro-scale thermal environment of the street. Monash University's monitoring commenced in January, with results expected in the coming months.
Jan Orton, Manager Infrastructure Works and Services says Marrickville is one of only three councils in Australia to trial the product so far, along with City Of Sydney and Canada Bay Council.
“Council has joined with Monash University as part of the CRC for Water Sensitive Cities to monitor the lighter road surface temperatures in Cecilia Street Marrickville,” Orton says.
At this stage, Ascrete installation is a specialised process, only available through Downer EDI Works.
The process involves laying an open graded asphalt (nominally a 10mm stone size asphalt at 40mm thickness) over a sound base course. This new asphalt is allowed to cool overnight with minimum trafficking.
The following day, a cement slurry with latex grout additive is added to the pavement, from a concrete agitator truck and screeded and vibrated into the porous surface.
Depending on environmental conditions the grouting can require as little as four hours to cure. The pavement can typically be trafficked the following day. The idea is that the grout penetrates the open graded asphalt and then forms an integral part of the material matrix.
As Ascrete is a relatively new product, Orton says the exact life-span is unknown, although it will be dependent on factors such as traffic loading, condition of base course and sub-grade, and the adequacy of surface and sub-surface drainage.
“We expect Ascrete should have a service life of approximately 20 years, if not more,” Orton says. “Ascrete should reasonably have the same service life as any other well-constructed local road surfaced in asphalt.”
Although costing more than an ordinary dense grade hot mix, Orton says Ascrete is a more cost-effective option than concrete.
Resealing Cecilia Street with Ascrete pavement cost approximately $90 per m² (finished product, for a project sized 810m²).
A significant part of the cost (about $20 per m² of the $90 per m²) in this instance was due to specific nature of the site – several shifts were required to maintain vehicular access to properties with their only access by Cecilia St.
Reconstructing a similar area of pavement in concrete (which would have similar reflectivity, and the concrete to be 200 mm thick, 40Mpa, SL82 mesh) would typically cost approximately $300 per m².
Resealing Cecilia Street with ordinary dense grade hot mix by mill and fill, such as 40 mm AC10 would typically cost approximately $35 per m².
The Ascrete trial is part of a range of adaptive and mitigation measures the council is trialling to combat increased temperatures.
“Council has long had a serious commitment to tackling climate change and more recently seriously address rising temperatures in our suburbs,” Orton explains. “Using new materials like Ascrete and changing the way we plan and design streets, introducing water and vegetation will help equip communities and infrastructure to adapt to higher temperatures.”
The council is undertaking thermal hotspot and social vulnerability mapping to assist in identifying priority locations for green infrastructure to cool the landscape. It is then hoped that initiatives like the Ascrete trial can be used to manage heat at these locations.