Resilient roads: sector cooperation is the key

Now is the time for national road agencies and the private sector to cooperate on building more climate resilient roads, urges Dr Erik Denneman*.
Asphalt Paving, Compaction & Testing / March 11, 2021 1 minute Read
By Dr Erik Denneman
Yesterday’s road designs served their purpose but the tides of change mean highway structures must be more resistant to damage, from whatever source (photo: David Arminas/World Highways)

There is no doubt the impact extreme weather has on local infrastructure can be hugely detrimental to the population and economy. Now, with the increase in these events due to climate change, road construction needs to adapt to make roads that will stand the test of time.

But how does climate change impact roads?

Expected changes in the climate, such as more extreme temperatures, increase in precipitation and intensifying storms can push environmental conditions outside the range for which roads were designed. This necessitates changes in design, materials, construction and operating and maintenance practices.

Bitumen and bituminous products such as asphalt soften as the temperature increases. Therefore, an often-quoted risk of climate change is an increase of deformation and softening of road surfaces. However, a couple of degrees in pavement temperature plays a relatively minor role in the overall performance of bitumen.

To put it in perspective, in the US bitumen specification system, the temperature differences between two grades of bitumen is 6°C, as measured during the hottest week of the year. This means it would take a significant rise in temperature as a result of climate change for different grades of bitumen to be necessitated.

In many regions of the world, the increase of moisture in road structures and more frequent flood events, whether due to increase in rainfall, or sea level rise, pose the greatest threat to road infrastructure.

Moisture-related pavement and road failures following severe rainfall events or floods can be costly to repair. As an example, the 2010–2013 floods in the Australian state of Queensland cost the government AU$6.4 billion (nearly US$5 billion) in repairs to the road network, with half for reconstruction of pavements.

Other more localised climate change-related risks to road infrastructure include increases in the occurrence of landslides, rock fall and avalanches, drought, bush fires and loss of support due to melting of permafrost.

What can be done to mitigate the impact of flooding and wetter weather on roads?

Flooding

Mitigation strategies are highly dependent on the local conditions and the original structure of the road. Thick road structures in urban areas are typically more flood and moisture resistant than rural roads. However, there may still be a need to improve drainage or increase the road level to new flood safe levels. This is because critical rainfall patterns and flood risk for which the road was built may have changed since the original design.

In rural settings where roads carry less traffic, road structures tend to be shallow and more prone to moisture and flood damage. For these roads appropriate drainage is even more important than for their urban counterparts.

Many countries, especially in the developing world, have a large proportion of unpaved gravel roads in rural areas. These are particularly vulnerable and climate adaptation strategies include paving the road surface, often with a sprayed seal.  

Caught off guard: extreme weather occurrences where few have happened are becoming more common (photo: World Highways)
Caught off guard: extreme weather occurrences where few have happened are becoming more common (photo: World Highways)

Cost effective measures to improve the flood resilience of rural roads include stabilising the road base using foamed bitumen. In Queensland this technology is used in regions receiving more than 500mm of rainfall annually. This measure proved its worth during Cyclone Debbie in 2017 with only minimal remedial works required on pavements stablised with foam bitumen.

Australia is not alone in this regard. Government transport departments across the world are developing strategies to mitigate the impact of flooding.

It is clear that to achieve the most successful and desirable long-term outcomes, companies such as Puma Bitumen must work in partnership with transport departments and apply their combined expertise to better manage the impact of climate change upon public infrastructures.

Sustainable solutions

To avoid the bitumen industry contributing to climate change itself, it is hugely important that the industry looks at ways it can reduce carbon emissions. It is encouraging to see the continued transition of our economy from a linear model (take – make – use – dispose) to a circular one (make – use – reuse – remake –  recycle). Given asphalt is 100% reusable, we are well on our way to achieving the goal of a truly circular economy within the sector.

One of the best examples that demonstrates how the industry is recycling other waste materials is the use of tyre-derived crumb rubber modified binders. Puma Bitumen has been using this sustainable and resilient technology to provide improved performance in sprayed seals and asphalt, especially in severe and challenging conditions.

Increasingly road authorities are investigating opportunities to use of these high-performance crumb rubber binders on their road networks. It reduces waste while maintaining good quality infrastructure.

Puma Bitumen is continually striving to make our operations and materials more sustainable. We recently created Olexocrumb, this innovative binder combines both tyre-derived rubber with styrene-butadiene-styrene. It performs as strongly as conventional polymer modified binders and has been successfully used in multiple Australian state road and local government trials last year. It has now become a standard binder.

Importantly, this asphalt binder solution is sustainable, as it incorporates 10% recycled tyre rubber. Furthermore, for every tonne of Olexocrumb binder produced, the equivalent of 15 passenger tyres will be recycled. Such new innovations are essential to support sustainability objectives and for governments to build longer lasting infrastructures that meet climate targets.

Looking to the future

The importance of adequately considering the more frequent extreme weather events being experienced cannot be overstated. This is especially true for rainfall. Less rain due to climate change is a likely scenario in many countries. However, for countries where flooding is becoming more common, there will be a detrimental effect on the performance of roads and pavements if the materials selection and design process are not properly accounted for.

Unfortunately, with a predicted increase in the probability of extreme wet weather, the costs associated with flash floods and heavy rain look set to increase across the world in the coming years.

As a result, policy makers and providers of critical infrastructure need to work together to ensure they are designing roads that can stand the test of time. Co-operation, open discussions into the new more sustainable materials and plans to build resistant roads is needed. Otherwise, policy makers will find that the cost of repairs will be detrimental to business performance in the long term.

Erik Dennman*Erik Denneman is the technical manager for the Middle East and Asia Pacific with Puma Bitumen, part of Puma Energy, a global midstream and downstream energy company based in Singapore and in Geneva, Switzerland. Denneman is a leading expert within the global asphalt and bitumen division of Puma Bitumen’s Global Technology Centre in Altona, Melbourne, Australia. Before joining Puma, he was director of technology and leadership with the Australian Asphalt Pavement Association.