Asphalt in the Netherlands

Thema:
Road structures

The Netherlands has one of the most densely branched road networks in the world, including 130,000 kilometers of paved roads. This requires effective road construction and good maintenance, with attention to minimising environmental impact and costs. Therefore, we work on asphalt mixtures, materials, and constructions for better-laid roads, using materials with a low environmental impact. Additionally, we focus on reliably and accurately predicting the lifespan of asphalt so that maintenance can be performed at the right time.

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 dense asphaltic concrete (AC), 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 and the environment. Sometimes special mixtures are created, for example at airports and container terminals, often to client specifications.

Asphalt ages over its lifespan due to exposure to air, UV radiation, water, and dirt. During the construction phase, measures can be taken to make the asphalt more resistant to this aging. With methods we have developed in this area, maintenance and repairs can be postponed.

New asphalt mixtures

New asphalt mixtures can perfectly match the required application. We focus on circular, bio-based solutions. Besides technical performance, we also consider safety and environmental performance (LCA) for these solutions. We investigate the performance of these new building materials, such as algae or PHBV (biopolymer), in asphalt mixtures and compare them with standard mixtures. This way, we develop new technologies for the production of 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 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

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 percent of the national roads in the Netherlands consist of ZOAB: asphalt with 20% voids allowing water to drain and reducing noise. These roads must meet legal requirements for safety, noise, and ride quality. The roads are monitored to determine when they no longer meet the requirements and maintenance is needed. In collaboration with the Department of Public Works and Water Management, we are working on an important technique: accurately and automatically measuring surface damage.

Surface damage

Raveling is the most common form of damage that occurs in ZOAB road surfaces. The top stones are driven out of the road surface. If the damage is too severe, the road must be replaced. A road with severe raveling problems reduces ride quality, increases noise production, and increases the risk of windshield damage.

Automated systems can make a useful contribution to quick, safe road inspections and the timely detection of raveling. Therefore, we are researching automated raveling detection for ZOAB roads for the Department of Public Works and Water Management.

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:

  • Investigating how existing materials and constructions of (national) roads are composed and how they perform.
  • Developing monitoring systems that measure the quality of asphalt faster and better by analysing data and images of the damage measured on the road surface as a basis for maintenance and replacement decisions.
  • Developing innovative asphalt mixtures, such as mixtures that age less quickly or asphalt mixtures with bio-based components.
  • Testing and assessing the lifespan performance of existing asphalt mixtures.
  • Developing lifespan models for asphalt layers.
  • Accelerated testing of asphalt mixtures by developing methods and procedures to quickly assess the usability of innovative asphalt mixtures.
  • Testing and assessing the effectiveness of new maintenance methods.