Dominic Browne talks to global product technology manager Dr Richard Taylor and technical manager Connor Campbell of Shell Bitumen to find out what lies just inside, and just beyond, the horizon.
Speaking to Shell sometimes feels a bit like speaking to an engineering or chemistry oracle – one that deals with well-respected research, hard data and science of course. Nonetheless, visions of the future emerge but no-one can be sure how they will be interpreted.
As Dr Taylor points out Shell invented the synthetic rubber Styrene Butadiene Styrene (SBS) and subsequently SBS modified bitumen in the 1960s.
Richard Taylor
However it took decades to become an established product and is now the ‘most commonly used polymer modified bitumen (PMB) in the world’ he says.
‘The more recent adoption of warm mix [asphalt] by the industry was markedly quicker. As product life cycles shorten, the adoption rate of new solutions is getting quicker. This is an encouraging development that means more innovation for roads.’
Mr Campbell adds: ‘There is certainly a greater adoption of warm mix asphalt. One of the benefits is that you reduce surface tension between the binder and the aggregate so the compatibility is improved. Depending on the plant, you can also considerably lower your mixing temperature, potentially up to 30 degrees. This means you are using less energy and the lower temperature means you can open the road sooner.’
When Highways spoke to Shell major issues arose for the future of the sector: Will roads remain part of the construction industry or are they an emerging services industry?
Dr Taylor says: ‘There is an emerging question around the future of roads as a potential service provider. It raises interesting points around the purpose and functionality of roads that goes beyond the transportation of goods and people. As a result, the development of roads and wider infrastructure will be viewed through this lens and its value judged accordingly.’
This functionality includes electrification – generating electricity and charging electric cars – active roads, which can take emissions out of the atmosphere, and coloured or glow in the dark roads that help with demarcation and communication of various hazards. All of which Shell has shown are possible for some years now.
Dr Taylor says: ‘The Shell group as a whole is gearing up for a new future. There are exciting developments taking place across the business that are focused on developing new solutions for the energy transition. On electric vehicle charging, we recently purchased a Dutch company, NewMotion, that is a specialist in this field and we have also entered the wholesale electricity market.
‘From a bitumen perspective, this opens up a lot of possibilities for greater innovation. We can explore ways to make it easier to install induction charging systems or investigate asphalts that are more efficient at transferring the induction charge. Once such technologies are installed, there are practical aspects to consider too such as demarcation of the charging lane by making it a different colour. We are approaching these prospects with a holistic view and in doing so the reality of how a road becomes a service does not seem too distant in the future.’
Back in the here and now, Dr Taylor says around 95% of Shell’s research is ‘still thinking about how countries can maintain a safe, efficient, durable transport system’. However even this is subject to some major debates, not least the use of recycled asphalt pavement (RAP).
Dr Taylor says: ‘The use of RAP appears to be on the rise. Methods also differ on how to soften the RAP, ranging from lighter potentially vegetable based oils to heavier products from the refinery. Asphalt today is markedly different to the 1970s. For example, where your traditional road would consist of aggregate, bitumen and some filler, today, there is a much greater variety of components in the asphalt mixture. For rejuvenators, my preference would be for the heavier end of the spectrum, something that is more alike to bitumen.’
There is some debate over how far RAP can or should go into the mixture. Again this is a debate Shell is leading with important research.
‘It’s certainly possible today to make an asphalt mixture that is 100% RAP but that does not necessarily mean it’s always the best option to pursue.
Connor Campbell
Aside from availability, a chief issue is understanding what has happened to that bitumen over time,’ Dr Taylor says.
‘We have looked into this in great detail through a major study and found that asphaltenes take on oxygen as they get older. In extreme cases, some of the RAP we measured was around 10 years old and had about 5% oxygen in the asphaltenes. Since the asphaltenes now have the oxygen molecule attached to it, it is possible that they arrange themselves more readily so that, as we have seen from our own studies, steric hardening occurs.
‘The short-term effect is that the material stiffens and there could be a greater potential for cracking in future if the steric hardening we observe in the binder translates to the mixture performance. In the binder, you will get the intended penetration initially but over a few days it will become quite a bit harder than originally thought.
‘If you have 80% of the bitumen coming from a new binder you can pretty much tolerate 20% of binder from the RAP without too many quality concerns. If you start moving on that to 100% rap mixes you are entirely relying on that old binder, plus whatever is added, acting like a new binder. This in itself raises another question – does a binder that’s hard and has been softened to meet rheological specification behave like a new binder? Our initial conclusion is that it does not.’
According to Dr Taylor, on the lecture circuit two schools of thought are being debated on how best to tackle the issue of RAP – one a lot more complicated than the other.
‘On the one side, there are advocates for the bio component rejuvenator, RAP and standard bitumen, and on the other there is the emphasis for PMB solutions. I personally see the future for PMB as being healthy since, even with RAP, it ensures that a road has high performance. Generally speaking, adding polymer will improve the rutting and the cracking issues.’
The move towards RAP may mean we have to look at specifications and testing in a new light and Dr Taylor suggests that parts of America are taking a different and perhaps more practical approach.
‘For us it is still very much a volumetric design with one or two indicative performance tests. In the US there is an emerging thinking that they don’t need a restriction on RAP but a balanced mix design. It’s a very rational approach and in doing so they are balancing rutting, cracking and ageing. The ageing step is important. We still live in a world where things are designed against fresh bitumen but in reality, a certain amount of severity goes through the plant and paver. They are therefore designing for what ends up in the pavement rather than the lab situation.’
Another issue that has caused some heated debate behind the scenes is the use of recycled plastic in roads. One company in particular has become synonymous with the process. While the process has been celebrated by some for trying to tackle a recycling issue, others have made the point that we cannot know at this stage what impact it will have on the durability of the asphalt mix.
Dr Taylor says: ‘Although it’s an attractive development and I approve of the innovative thinking that is being applied, there is little evidence to support durability improvement in asphalt pavements using polyethylene. This is a story worth watching closely as long-term service evidence arises which sheds light on improving durability of pavements using this particular route.’
All this adds up to make a picture of a sector willing to take on innovation and willing, dare we say it, to try and fail a little bit more.
Mr Campbell says: ‘In my conversations with customers, I sense a real appetite for innovation that hasn’t always been there. Recent solutions such as the warm mix have helped spur this in my opinion. The benefits it brought to customers and their bottom lines has meant everyone is now hungry for more.
‘What I find most exciting is the new-found passion to test and learn – we are getting a pull from the industry asking ‘what do you have?’ and ‘let’s test and prove this together before we take it to market’. That mentality has the potential to produce some really exciting results.’
Dr Taylor concludes: ‘As an industry, we are at an important crossroads. For decades we have been iteratively improving our technologies and solutions for application on roads, the purpose of which hasn’t changed since Roman times.
‘Now we look towards a future that has the potential to fundamentally alter the purpose of our end-product and the solutions required from us as an industry to make it possible. At Shell we are planning for that eventuality today, from the group level down to bitumen specifically, and the green shoots are already visible.’
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