Traditional pothole repair involves cutting out a rectangle of asphalt around the hole using saws and jackhammers, to create vertical edges against which new asphalt can be compacted. But where do all those road planings go?
The answer is likely to be to join other road planings in a stockpile somewhere. From the stockpiles, the planings will probably go on to be used elsewhere. What that use is depends on the homogeneity of the pile and how much the planings are graded and processed.
The most common use for planings is as a low-quality fill for farm roads, hard standing or temporary roads. The size of the planings is often too varied for it to be used as a sub-base. Screening can produce a more homogenous product, but of course adds to the cost. Planings aren’t generally used as sub-base for buildings because the bitumen in them degrades over time which could lead to settlement.
Although there is lots of talk of the use of RAP – recycled asphalt planings – in road construction, in reality, its use is limited. The figures for asphalt production and recycling in Great Britain, which are collated by the European Asphalt Pavement Association (EAPA) suggest that the amount of RAP being reused in roads is pretty low.
EAPA’s latest statistics, Asphalt in Figures 2020, show that Great Britain produced 23 million tonnes of hot and warm-mix asphalt in 2020. In that same year there was 5 million tonnes of reclaimed asphalt available for re-use. The statistics also say that 63% of recycled asphalt goes into unbound road layers and other civil engineering applications with only 37% going into hot and warm mixes.
Where RAP is used in road construction in the UK, it is most likely to be used in the base and binder courses of roads where specifications allow for up to 50% RAP. For surface courses, specifications set the proportion at 10% because of issues such as achieving the required skid resistance. Recently, National Highways has been trialling the use of higher proportions of RAP in surface courses – for instance on the A1 I Mill Hill where FM Conway used an asphalt course with 50% RAP.
Any RAP used in asphalt mixes for roads must be carefully sourced, analysed and treated. It cannot just come from any old stockpile. In countries that don’t have sufficient primary aggregate sources, such as the Netherlands or Finland, RAP is treated like a precious resource, sorted and stored to optimise its reuse and value.
The proportion of RAP which can be used in an asphalt mix is also constrained by the technology at the asphalt plant. The higher the proportion of RAP to be used, the greater the modifications to the plant are needed, with specialist plants needed at the higher end. RAP contains moisture – especially if it has been hanging around in outdoor stockpiles – so must be pre-heated when used in larger proportions, and this has to be done in a certain way to avoid overheating the bitumen in the RAP which makes it brittle.
It is worth noting that some road planings may not be easily reusable because they contain potentially carcinogenic substances. Roads laid before the early 1980s may contain coal tar which in turn contains polyaromatic or polycyclic hydrocarbons and is hence potentially hazardous.
Clearly, although road planings can be reused, they are likely to be downcycled rather than recycled. Prevention is at the top of every waste hierarchy, which is what Thermal Road Repairs’ technology was designed to do. Because the process heats up and uses the existing material, there are no waste planings. This in turn also helps reduce carbon emissions and vehicle movements on the roads to remove any waste material for stockpiling. It also reduces noise pollution as no jackhammering or saw cutting is required to break up and remove the unwanted asphalt.
A permanent repair means that the area that was a pothole or defect will last as long as the road surface around it. When the whole road reaches the end of its life, the entire surface can be removed – and hopefully treated as a resource to go into the next road surface.
Thermal Road Repairs is a green technology company which supplies systems to improve the quality, cost and time efficiency of road repairs and paving – at a far lower environmental cost than traditional methods. We invest significantly in R&D, to create new technologies and to continuously improve our existing ones.
High output. Low emission. Permanent solution.
Sources
https://096.wpcdnnode.com/eapa.org/wp-content/uploads/2021/12/asphalt_in_figures_2020.pdf
https://adeptnet.org.uk/system/files/documents/ADEPT%20Guide%20to%20Managing%20Reclaimed%20Asphalt%20Version%202019%20Rev%201.pdf