FGSV Colloquium // InLine Pave® Rooted in the German Catalogue of Construction Methods
Part 2: Expert Interviews
There is a Future for Compact Asphalt Pavements
Talking with the experts
Compact asphalt pavements yield advantages for planning engineers, road operators, contractors and road users. All road construction experts agree on this point. During the colloquium of the German Road and Transportation Research Association (FGSV), RoadNews discussed the technology’s possibilities, advantages and future with four experts from very different areas of road construction.
“An economical construction method with a service life
of at least 20 years.”
Publicly appointed and sworn expert for asphalt paving in road construction and lecturer for further education courses on asphalt technology at Darmstadt Technical University, Germany.
RoadNews: Mr Schäfer, you headed the working party investigating compact asphalt pavements. How long have you been working on this subject?
Volker Schäfer: Road construction engineers have been considering the idea since the mid-1990s. I have also been working on the subject since then. In 2006, the FGSV set up a working party under my leadership. Our job was to define the paving method and monitor its integration into the German technical rules and standards.
RoadNews: This working party was discontinued in early 2012. Why?
Volker Schäfer: Due to the positive experiences and the method’s technical possibilities, it has now been recognized as a standard method in Germany and consistently described. All the tools needed for tendering and invoicing compact asphalt pavements are available. Our job is done. It is now the turn of the authorities and the construction industry to invite tenders for this technology, to offer it and to use it accordingly.
RoadNews: Why do we need compact asphalt pavements?
Volker Schäfer: Quite simply because the stresses to which our roads are being subjected are increasing constantly. Take for instance the “just-on-time” deliveries in industry and trade which have resulted in a growing number of transports. The roads have not grown, but the vehicles’ capacity utilization and hence their actual axle loads are increasing. In short, our roads are increasingly having to cope with ever heavier loads.
The stresses imposed on our roads by these axle loads are rising disproportionately – by the power four, to be precise. For example: a lorry with an axle load of 10t is equivalent to about 160,000 cars with an axle load of 0.5t, while one with an axle load of 12t produces twice the stress, and an axle load of 13t results in three times the load, and so on.
That is why we need road structures capable of bearing these loads in the long term. Precisely that is achieved with compact asphalt pavements. What’s more, they have a service life of at least 20 years.
RoadNews: Are compact asphalt pavements only suitable for roads with high traffic loads?
Volker Schäfer: Most definitely not. Compact asphalt pavements are just as suitable for roads with light traffic. In this case, the compact pavement comprises the base course and the wearing course.
“Saving resources – improving long-term durability.”
Rudi Bull-Wasser, Executive Senior
Government Official at the Federal
Highway Research Institute (BASt),
Bergisch Gladbach, Germany
Head of the BASt’s asphalt construction department, for over 20 years actively involved in many national and international working parties on the further development of road construction technology.
RoadNews: Mr Bull-Wasser, as a representative of the Federal Highway Research Institute (BASt), you view the subject of compact asphalt pavements from a government vantage. What does the Federal government expect of this innovative construction method?
Rudi Bull-Wasser: We make sure that the people in our country can use the best possible infrastructure for their commercial and private purposes. As the “owner” of the motorways, we are therefore interested in durable pavements on which traffic can flow safely and without disruptions.
Saving resources is another important aspect. It is also a political objective in Germany. Compact asphalt pavements are a step in the right direction, for they save resources. They are also sustainable on account of their optimum bond between layers and consequently their better long-term durability.
RoadNews: What has your authority done to promote this technology and help it become a standard method?
Rudi Bull-Wasser: Federal and Land governments have consistently promoted this technology; the BASt has selected suitable test roads for it in collaboration with Land authorities and taken over scientific monitoring of the paving process and further development of the asphalt pavements. At the same time, we have worked in various committees to establish the formal basic conditions needed to build more roads using this method in the future.
RoadNews: What was your greatest challenge?
Rudi Bull-Wasser: As a public authority, we want to promote innovation but tight budgets make it impossible to support every technology. In such a situation, it is therefore vital to identify the most promising ideas and to pursue their development. That is the greatest challenge. For if we do not recognise a good idea when we see it, we could miss out on some great opportunities.
RoadNews: What part do the machine manufacturers play in this process?
Rudi Bull-Wasser: What we need is innovative companies who develop new technologies and who will pursue the idea with a great deal of initiative and ingenuity. In addition to a good team of innovative engineers, this requires courage, farsightedness and perseverance in order to survive the difficult times when developing a new product. VÖGELE is one manufacturer who contributed a great deal towards the development of this construction method.
“I expect a clear extension in a road’s durability.”
Head of Department in the
Motorway Directorate in Southern
Bavaria, Munich, Germany
Responsible for road construction excluding roadbase, preservation management, road database, as well as construction and geo-technology in the department of central affairs.
RoadNews: Mr Schmerbeck, you are responsible for affairs on the motorways of southern Bavaria. What do you expect of compact asphalt pavements?
Rupert Schmerbeck: Our expectations are very specific. One concerns the time required for paving, for example. It can be significantly reduced by using this method. To us as the people responsible for the operation of roads, this is a matter of particular importance, for we want to minimize or preferably avoid any kind of nuisance leading to traffic congestions. We also have high expectations as regards stability. Some forecasts claim a two-fold extension in durability – so far, that has neither been proved nor disproved ... but it is certainly possible.
The extent to which the layers interlock is definitely better than in a conventionally built pavement. We also know that the thicker packages make for more efficient heat distribution inside the asphalt package during the paving process. The layer package cools very much more slowly than the individually paved layers. This promises better compaction and consequently a longer service life.
RoadNews: What do you expect with regard to preservation measures?
Rupert Schmerbeck: On the whole, we expect the roads to last considerably longer due to the bond between layers, on the one hand, and the good compaction on the other. We also expect lower costs for pavement rehabilitation, as it will only be necessary to mill off and repave a very thin surfacing.
RoadNews: In your opinion, which kinds of construction project are particularly suitable for this method?
Rupert Schmerbeck: I consider compact asphalt pavements to be a good alternative when building new roads and for extension projects, as well as for extensive rehabilitation of wearing courses. I hope that this method will soon be used for more projects in Bavaria. We will certainly not obstruct contractors and also welcome alternative bids.
“Efficient construction, long use, little need for pavement rehabilitation.”
Technical Director of Johann Bunte
Bauunternehmung GmbH & Co. KG,
He learned construction from the ground up and has worked in the construction industry since graduating.
RoadNews: Mr Renze, what does the future hold for compact asphalt pavements?
Helmut Renze: The breakthrough will come in PPP projects (PPP = Public Private Partnership). This method is extremely economical due to the high quality of the roadways, especially in the long term. Unfortunately this finding is not yet reflected in public invitations to tender today.
As a contractor in the industry, however, we set great store on the advantages of this construction method. Firstly because it produces roads of high quality and secondly because it significantly reduces the time needed for paving, with savings of up to 50%. Together, these two factors yield a major advantage for all partners in a project.
RoadNews: Your company has built numerous compact asphalt pavements. What has been your experience to date?
Helmut Renze: Our experience has been very good. We are exceedingly pleased that this method has now become firmly established as a standard method in Germany. One point that must be mentioned is that all customers have so far been highly satisfied with the quality of the asphalt pavement.
RoadNews: You swear by its durability. Why?
Helmut Renze: High compaction and the resultant lower voids content of the finished layer ensure perfect conditions for excellent resistance to ageing. What’s more, shear forces are optimally discharged into the lower layers through the interlocking between wearing course and binder course. That is a point which, so far as we know today, contributes greatly to the long-term stability of a road structure.
This is also confirmed by the fact that, even after many years, rutting effectively does not form on roads with compact asphalt pavements. This ensures high cost-efficiency and greater traffic safety.
RoadNews: Are there any other advantages for you as a contractor?
Helmut Renze: The paving season has become longer, as the heat storage properties of compact asphalt pavements allow us to respond a great deal more flexibly in the transitional period than ever before. This is excellent news for public authorities, as their budgets are often only determined during the course of the year, meaning that several projects have to be postponed until the colder months.
RoadNews: What is the key to successful paving?
Helmut Renze: The construction sections should not be too small. For us, cost-efficiency starts with 40,000m2. For rehabilitation projects, I also recommend creating a level base by 3-dimensional profile milling of the asphalt layers.