Richard Ashton, UK market development manager for TotalEnergies' Bitumen Division, gives advice on how to handle the summer ahead in road maintenance.
The impact of increasingly volatile and extreme weather conditions is showing up on our roads and creating year-round risks and responsibilities. While the wetter conditions and cold snaps of winter usher in a new wave of potholes each year, summer temperatures in excess of 40 degrees – which some parts of the UK saw last year - are melting the very ground we drive on. This is a vicious cycle of degradation, and a short-term focus on remedial road work is not enough.
The national government, local councils, and contractor stakeholders all share a responsibility to climate-proof our highways and futureproof asset management strategies, operating on a principle of ‘sustainability through durability’ that can accommodate weather extremes and lower the cumulative maintenance load over time.
In good news, there is no better time to kickstart a ‘horizon’ approach to road maintenance than the summer, not least because the work done in the warmer months will largely determine the volume and severity of road maintenance for the remainder of the year. Survey and prioritise road maintenance
Filling potholes is top of the agenda for many local authorities, bolstered by a £200m injection of funds in the Spring Budget. But the need to fill potholes at all is, in many respects, a sign of systemic failure. Early issues detection and prevention is the ‘stitch in time’ that can save nine potholes.
Although appraising roads is a year-round task, tackling early or medium-stage microcracks in the summer months through resurfacing or Emulsis surface treatments can considerably reduce the development of potholes over the wetter, colder periods.
This, in turn, reduces the amount of remedial pothole work required the following summer, freeing up budget and resources for councils to undertake longer-term highway projects, and minimising disruption to road users.
Technological advances such as computerised highway asset management systems allow local councils to regularly monitor, assess and triage road conditions, using data and sensors to detect issues well ahead of time.
Unfortunately, statistics from the Department for Transport show that the percentage of A, B and C roads receiving surface dressing treatment has declined 30% since 2016, potentially suggesting decision-making and funding are becoming more short-term and reactive rather than longer-term, proactive and preventative.
Bitumen material selection
The selection of the appropriate bitumen grade is critical in ensuring the durability of the asphalt pavement during hot summer days. The softening point is the temperature at which bitumen becomes malleable and loses its load-bearing capacity and is a critical parameter that influences the pavement's resilience under high-temperature conditions.
In hot summer conditions, the temperature of the road surface can increase significantly, causing the bitumen to soften and become less viscous – as typified by the closure of Luton Airport in 2021.
When the bitumen becomes too soft, it may not be able to support the weight of heavy vehicles, leading to deformation and rutting of the road surface. When the softening point is exceeded, the bitumen can become loose within the mixture and rise up, filling in gaps between the top-level aggregates, which takes away the texture of the road and reduces skid resistance.
To counter the effects of longer, hotter summer on roads, the emphasis should be on durable material selections – in particular the use of bitumen with a softening point of 80+ that incorporates a bitumen-polymer mix.
A high softening point is desirable for asphalt pavements that will be exposed to high temperatures because it provides greater resistance to deformation. Selecting bitumen products which have a softening points of 80 degrees or higher, as opposed to those with 40-60 degree ranges, allows a much larger safety margin in case of extreme heat.
Roads are most prone to heat damage in their early years, and cold damage in their later years as bitumen oxidises – and becomes more brittle – as it ages. Investing in a bitumen-polymer mix such as Styrelf delays the oxidative ageing process, while reducing the roads vulnerability to heat at the outset and less prone to cracking long-term – markedly reducing the need for intervention or resurfacing compared to pure bitumen products.
While investing in quality materials that can withstand weather conditions may cost more upfront, it can save money in the long run by reducing the need for frequent repairs and maintenance by 10-30%, according to a 2019 Rutgers study.
Warm-mix asphalt
Warm mix asphalt (WMA), which can be produced at temperatures 40°C lower than traditional hot mix asphalt (HMA), offers seasonal advantages in productivity, safety and sustainability.
Newly laid asphalt cannot be trafficked until it is around 10 degrees cooler than its softening point, and as the warm mix asphalts are produced at a lower temperature, they take less time to cool and reach their service temperature during the summer months. While normal asphalt can take up to two hours to cool, warm mix asphalt can cool to optimum temperature in slightly less than an hour.
This allows more material to be laid in a single shift without compromising the application of multiple layers in a short period of time. Further, it allows the finished surface to be opened earlier to traffic without the risk of the material deforming under heavy loads.
Secondly, warm mix asphalt creates a more comfortable environment for workers during the summer months. The lower production temperatures of WMA mean that the asphalt mix is less hot and produces less steam aiding visibility around the site.
As summer days get hotter, we need to consider the needs of construction workers on site, and this offers obvious wellbeing advantages while reducing the risks or severity of burns and reducing energy costs (as well as associated carbon footprint).
Managing ambient temperature
Without appropriate interventions, major roadways risk becoming ‘urban heat islands’ due to an absence of natural surfaces or shade that can reduce the surrounding air temperature.
Darker colours absorb more heat, so selecting brighter roadway materials can have a cooling effect on the area. In terms of roadway maintenance, areas subject to extreme heat should consider using a clear synthetic binder with a light colour asphalt to lighten and subsequently cool the surface area.
While elevated road surface temperatures are the culprit behind the majority of summer road damage, managing the ambient temperature of the surrounding area can have a meaningful impact on general road maintenance needs.
Urban planning around roadways that incorporates more vegetation, soil, and bodies of water into the surrounding area can assist the evaporative cooling process while trees or roadside design elements can provide shade. Taken alongside material upgrades to road surfaces, this can mitigate the intensity of heat the roads are exposed to.
Reducing carbon footprint
Stepping back further, part of summer road maintenance is also taking an industry-wide look at efforts to reduce carbon emissions. Hot summers pose a threat to our roadways in asset management terms, and every sustainable step can slow the trajectory towards increasingly hot summers and extreme weather conditions overall.
Indeed, the 2019 Rutgers University study found that proactive road maintenance can reduce greenhouse gases by up to 2%, while National Highways has found that warm mix asphalts can reduce carbon emissions by around 15% compared to their hot-mix alternatives.
Tackling road issues before they become critical, investing in high quality materials that are fit-for-purpose in more extreme conditions, preferencing the lower carbon footprint and productivity gains of warm mix asphalts, and managing ambient temperature in a bid to reduce surface temperature pressures are all part and parcel of a ‘sustainability through durability’ approach.
Making smart material and maintenance decisions reduce the need for ad-hoc issues management and helps lengthen the time between interventions thus reducing the total environmental impact of the roadway across its lifecycle.
By taking a long-view of highway asset management through season-specific maintenance and upgrades in summer, we can reduce the load on road maintenance needs for the seasons that follow to future proof our most valuable infrastructure asset.
