Recycling low-noise SDA asphalt

Why SDA surfaces pose a challenge

SDA 4 surfaces are made from particularly high-quality aggregates and bitumen, which are crucial for their acoustic performance. However, their fine aggregate grading differs significantly from that of conventional dense asphalt mixtures. As a result, recycling SDA materials into standard reclaimed asphalt pavement (RAP) is not straightforward.

At present, SDA surfaces are handled differently depending on the producer: some are incorporated into lower pavement layers, others are stored separately. For cantons, this leads to limited planning certainty, additional effort and unresolved questions regarding the future use of these materials.

The opportunity: circularity instead of disposal

With clear technical foundations and reliable data, low-noise SDA 4 surfaces could in future be reintroduced into new SDA mixtures. This would:

• conserve valuable primary resources
• reduce CO₂ emissions
• lower costs for cantonal authorities
• promote sustainable infrastructure

The RESDA project: a nationwide initiative

To unlock this potential, the Federal Office for the Environment (FOEN) initiated the REcycling SDA (RESDA) project, supported by the Environmental Technology Fund. The project is led by G+P, in collaboration with Consultest AG as laboratory partner.

Since spring 2024, SDA surfaces of different types and ages have been selectively milled and collected in six cantons. A key aspect of the process is that only the top layer, the wearing course, is recovered to ensure high-quality recycled material.

Currently, seven Swiss cantons support the project through the provision of material, financial contributions and technical expertise: Neuchâtel, Thurgau, St. Gallen, Zurich, Basel-City, Aargau, Fribourg and Bern.

What happens to the collected material

The recovered material is subjected to comprehensive laboratory testing at Consultest, including:

• aggregate grading
• bitumen content and properties
• water sensitivity
• low-temperature cracking resistance
• rutting resistance
• aggregate loss

These tests assess the degree of ageing of the material and determine the proportions in which it can be incorporated into new SDA 4 mixtures without compromising acoustic or mechanical performance.

Why G+P plays a key role

For many years, G+P has been supporting cantons, cities and municipalities in the development and assessment of low-noise road surfaces and in the reduction of noise emissions more broadly.

Within RESDA, we bring together:

• expertise from measurements, predictions and optimisation
• in-depth knowledge in the assessment of road construction materials
• project leadership and methodological development for nationwide application
• extensive experience in the acoustic performance of low-noise road surfaces

This provides cantonal authorities with the foundations they need for future tenders, long-term strategies and sustainable decision-making.

Benefits for the target group

For cantonal, urban and municipal road authorities, RESDA delivers:

• clear, scientifically substantiated recycling recommendations
• reduced uncertainty in the future handling of SDA surfaces
• a basis for future technical specifications and guidelines
• support in achieving environmental and cost objectives

And for society?

Less waste, reduced use of primary materials, lower CO₂ emissions, better use of existing resources and continued low-noise roads. This directly supports Switzerland’s climate strategy and the transition towards a circular economy.

What comes next

The laboratory results are expected at the beginning of 2026. Based on these findings, practical threshold values for RAP content will be defined and initial field test sections implemented. This marks an important step towards a sustainable future for Switzerland’s low-noise roads and asphalt wearing courses in general.