Asphalt in The Netherlands
The Netherlands has one of the most densely branched road networks in the world, including 130,000 kilometres of paved road. This requires effective building of roads and proper maintenance. That's why we're working on asphalt mixtures, materials, and structures for better roads and on reliably and accurately predicting the service life of asphalt.
What is asphalt?
Most paved roads are made of asphalt. Asphalt consists of aggregate, sand, filler, and bitumen. These components are used to produce different types of asphalt, such as asphaltic concrete, dense asphaltic concrete (DAC), stone mastic asphalt (SMA) and pervious concrete. Each type of asphalt has specific properties regarding elasticity, noise reduction capability, and resistance to rutting. The type of asphalt chosen for a road depends on the traffic situation. Sometimes special mixtures are created, for example at airports and container terminals, often to client specifications.
Effects of air, UV radiation, water, and dirt cause asphalt to age. In the construction stage, you can take measures to protect roads more effectively from these externalities. It’s possible to postpone maintenance and repair using methods we have developed in this area. We are also developing an application to combat asphalt ageing.
New asphalt mixtures
New asphalt mixtures can perfectly match the required application. Using components such as fibres, rubber or synthetics improves the performance of an existing asphalt mixture. The mixtures are also more environmentally friendly. We study the performance of these new mixtures, including fibre-reinforced asphalt and porous elastic road surfaces, and we compare them to standard mixtures. For example, we are developing new technologies for the production of polymer-modified binders and components for sustainable ‘green’ asphalt.
Assessment of the asphalt
Asphalt is made up of different materials and its exact composition and properties are often unknown. So, it’s difficult to know how the asphalt performs. That's why we review and assess the performance of the individual materials, and the asphalt as a whole. This allows us to better identify the quality. In addition, the market has developed a number of maintenance techniques that, depending on the extent of the damage, can be used to extend the service life of a road surface. We assess and validate these repair materials and techniques.
Validation of asphalt deals with technical, economic, and sustainability aspects. We are working on the testing of preventive measures to ensure that national main roads last as long as possible. Using these measures early on extends the service life by as much as 30 percent. When we test repair techniques, we take into account their social costs and benefits. Maintenance decisions are based on more than just the contract price.
Measurement and monitoring of pervious concrete
More than 80% of the national roads in the Netherlands consist of pervious concrete: porous asphalt with 2 layers. The roads must meet the legal requirements for safety, noise, and ride quality. That's why they are monitored to determine when maintenance is needed. In collaboration with the Department of Public Works and Water Management, we are working on an important technique: measuring surface damage.
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Ravelling is the most common type of damage that occurs in pervious concrete road surfaces. In this process, the top stones are squeezed through the road surface. If the damage is too severe, the road must be paved. A road with severe ravelling problems reduces ride quality, increases noise, and increases the risk of windscreen damage.
Automated systems can make a useful contribution to fast, safe road inspections and the timely detection of ravelling. That's why we are conducting research for the Department of Public Works on automated ravelling detection for pervious concrete roads.
Improving Dutch roads
To ensure a sustainable and safe road network in the Netherlands, we at TNO work on solutions and improvements to materials including asphalt, and processes such as maintenance. For example, we are working on:
- Developing new innovative concepts for improving road performance.
- Investigating how existing materials and structures of (national) roads are put together and how they perform.
- Monitoring systems that measure asphalt quality faster and better, as a basis for maintenance and replacement decisions.
- Monitoring and measuring roads, by analysing data and images of the damage to road surfaces measured.
- Developing tests that quickly and properly assess the quality of innovative asphalts.
- Repairing and protecting asphalt by developing products for road maintenance, such as a ‘sun cream’ applied as a protective layer after construction.
- Developing innovative asphalt mixtures, such as mixtures that age less quickly.
- Testing and assessing service life performance of existing asphalt mixtures.
- Accelerated testing of asphalt mixtures by developing methods and procedures to rapidly assess innovative asphalt mixtures for usability.
- Accurately determining the skid resistance of the road surface and early identification of ravelling damage.
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