Next-generation paving

With the Middle East embarking on a massive infrastructure modernisation programme, governments and transport authorities will be keen to upgrade the region’s road networks. Can emerging surfacing technologies help?

The panel
Professor John Read has worked in the bitumen and asphalt industry for over 20 years. He is currently the Global Bitumen Development and Product Manager for Shell Bitumen.
Jean-Pascal Planche has been working with Total for 23 years in the bitumen field. Since 2005, he has been responsible for Total’s international bitumen technical strategy and R&D coordination.
Chris Southwell, Technical Director of the Refined Bitumen Association, has 30 years of experience in the bitumen and roads industry.

INFRA. Road authorities are constantly looking at how to improve the lifecycle of their road networks. How can this best be achieved? Are polymer-modified bitumens (PMBs) the answer?
John Read. Polymer modified bitumens are widely hailed as the universal panacea to all pavement problems; this is a fallacy in the same way that supercars are automatically considered the best cars in the world. By this I mean that PMBs will address many of the problems of the road, but not all, just as a supercar is great on high-speed straights and corners but not as a family car. The product must meet the requirements for which it is to be used.

To extract the maximum value from a PMB, you must ensure that the lower layers of the road are properly constructed, compacted and drained and that the traffic loading, climate and desired life of the pavement is understood. Only once all of this is ensured can the choice of PMB be made.

Jean-Pascal Planche. Improving the lifecycle of road networks requires consideration of the global picture: traffic loads and evolution, climatic conditions, pavement techniques and materials, recycling and economical constraints. Pavement design models help to optimise the road construction and maintenance process by taking into account all these parameters.

PMBs are a major part of the answer but not the silver bullet. They have to be adequately employed in the appropriate asphalt mixture and pavement designs according to best practices. But all PMBs are not equal. Field survey studies, like the one carried out recently by the LAVOC laboratory, have shown PMBs performing extremely well under severe conditions whereas others did poorly – well below base bitumen, even. Using a good performing PMB does help a great deal to improve pavement life expectancy. Styrelf from Total is one of the best, with a fantastic 30-year track record worldwide.

Chris Southwell. Extending the life of any road network involves a combination of a number of contributory factors. The answer does not just lie in the use of new binder technologies. Enhancement is available through the use of polymer-modified bitumen to improve, for example, resistance to fatigue cracking and resistance to deformation in warmer weather conditions.
  
In the UK, Road Note 42 was recently published by the Transport Research Laboratory as a guide for highway authorities and contractors to promote the adoption of best practice in the specification, manufacture and laying of asphalt materials. Failure to implement these best practice guidelines can negate the benefits available through higher-performance bitumen grades. Appropriate material selection, mix design and correct installation of the pavement are critical to achieving durability. Assuming these factors have been correctly optimised for the prevailing traffic conditions, extending pavement life even further can be achieved through the use of polymer-modified bitumen or hard paving grades like 10/20 and 15/25 pen, which enable much stiffer base and binder course materials such as EME (enrobé á module élevé) developed in France. 

INFRA. What challenges are there in communicating the benefits of these next-generation bitumens to the contracting community? Does this differ from region to region?
JPP. Challenges mainly lie in the technical background differences between local users and international suppliers. Teaching a new user what a PMB is, and what makes one PMB better than another, is one such challenge. What makes the need worth the value? This crucial discussion, occurring under different technical references, can be challenging for suppliers; the lack of universally approved performance-based specification systems does not help.

This issue is region-dependant; considering that road authorities expect material and maintenance savings, the benefits depend on how much a new binder will contribute to the extension of the pavement life. The specification topic sets the pace for PMB development. The fastest-growing PMB adopters are those with PMB specs, such as Germany, USA, Japan and China. Total is at the forefront of these developments, participating in standardisation committees and actively addressing the development of performance-related specifications and test methods.

JR. Not all PMBs are the same, so this requires that the PMB supplier be clearly able to demonstrate which mechanical properties of the PMB (and therefore asphalt) are improved by the modification; this necessitates that the PMB supplier has this type of information, can provide technical support as required, can develop fit-for-purpose solutions at short notice and can demonstrate a long track record.

Proof that PMBs really work is always difficult to come by as it is rare that a modified and unmodified section of road are laid together so that they experience exactly the same conditions. However, the Asphalt Institute in the US recently produced a book entitled Quantifying the Effects of Polymer Modified Asphalt for Reducing Pavement Distress that provides a lot of convincing independent evidence to this effect. Additionally, there are many instances around the world where PMBs have been used because other solutions have failed and the PMBs have stood up to the onerous conditions.

CS. The primary challenge is the variability in awareness of new technologies and the declining asphalt technical and engineering skills across the community. This can hinder the correct use of polymer-modified bitumens and delay their more widespread adoption. In periods of economic recession, new technologies are less readily adopted so it is often the more buoyant markets that are able to take advantage of improved materials and pave the way for others. It is the responsibility of industry institutions and representative bodies to take a collaborative approach to improving highway engineering knowledge across the supply chain, ensuring that clients and consultants are included in this process.

INFRA. Sustainability is a key concern right now across the infrastructure development community. How is the bitumen industry addressing the issue of sustainability, and why is taking a greener approach so important?
JR. The need for PMBs is increasing all the time, with increasing traffic volumes, axle loads, tyre pressures and temperatures all having a detrimental effect on the pavement, as well as with the environmental drive towards all industries being sustainable. In the long-term it is entirely feasible that we will move towards PMBs in all bound layers of the road to ensure that we get the maximum performance with the minimum thickness and reduced disruption due to maintenance, and indeed this is already happening in some countries.

PMBs such as the Shell Cariphalte range can be more sustainable in that if they are properly designed into the overall structure, then pavement life can be significantly extended – saving money in whole-life terms, reducing the amount of construction materials used, reducing energy consumption and reducing the number of vehicle movements associated with construction and maintenance (thinner structures and longer maintenance periods).

JPP. The industry addresses the sustainability issue at various levels, depending on which step of the bitumen life is being considered. One must try to find solutions to work under the safest conditions, using a minimum of energy, delivering safe products that will last longer and that save as much raw materials as possible – both mineral aggregates and bitumen.

To tackle these issues, the industry is getting organised and sustainable development is the main driver. For instance, bridges are set to follow occupational health studies on the effects of bitumen fumes in preparation of the new IARC bitumen monograph. In the US, warm-mix asphalts are fast developing under the auspices of joint task forces involving the Asphalt Institute and bitumen user associations. Eurobitume has developed a model to conduct the lifecycle inventory of bitumen for one application. Taking a greener approach is unavoidable from both a professional and citizen perspective. Expectations are high.

CS. Development of asphalt materials that provide durability or longer life is the first step towards greater sustainability. The industry is developing more sustainable asphalts and products such as semi-warm mix and warm-mix asphalts. In the longer-term, the bitumen industry is contributing to joint industry research into creating a common framework for assessing the carbon footprint of bituminous materials.

INFRA. How is this reflected in R&D operations? What new developments can we expect to see over the next few years in this industry?
JPP. Our R&D is mainly driven by sustainability issues. One can expect to see growing use of warm-mix asphalt mixtures, an increased bio component in bitumen (one that does not compete with food demand), PMB-based solutions for longer-life pavements, a higher rate of recycling materials for asphalt pavements, reuse of wastes from other industries (provided it does not affect the classification of bituminous materials, and various combinations of these sustainable solutions.

Total R&D is active in all these fields and has dedicated a significant budget to sustainability. Sustainable development (SD) is part of Total’s bitumen strategy, together with innovation and geographical development. Just one example is our Total 360-degree SD approach where, after an internal evaluation, we interviewed a wide cross-section of stakeholders to know their expectations in terms of bitumen-related SD. The action plan that followed induced R&D studies that are now delivering patents, publications and new products.

JR. PMBs are becoming widespread, with developing nations using them to build their infrastructures and developed nations using them for maintenance. The next generation of PMBs adds functionality beyond improved mechanical properties, an example of which is Shell Cariphalte Fuelsafe, a PMB designed to provide all the benefits of a traditional PMB, as well as significantly increased resistance to damage by fuel – particularly important in areas such as airports, where loose material caused by a fuel spillage could cause foreign object damage. So what comes after PMBs? The answer to this question forms the basis of our extensive research and development programme, where we have more than 100 bitumen, asphalt and pavement experts working with our customers to find the sustainable solutions of tomorrow.

CS. The bitumen industry’s commitment to sustainability manifests itself through its co-operation with customer representative bodies and the Highways Agency. One such recently completed three-year programme resulted in the TRL Road Note 42, already mentioned, providing guidance on best practice for the achievement of durable asphalt pavements. A current research programme is looking into the development of a transparent framework for the delivery of sustainable construction including standard protocols for the calculation of key measures such as the carbon footprinting of materials and processes.

As in other European markets, the UK bitumen industry is working on the standardisation of test methods and specifications for bitumen across the continent, along with meeting the challenging requirements of the REACH chemical registration legislation. All of this highly detailed work will ultimately lead to greater technical clarity for the customer, enabling improved health and safety, as well as sustainability.