Final PERSUADE seminar at BRRC, Sterrebeek

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Poroelastic road surface

On 24th August 2015, about seventy delegates from fifteen countries gathered in BRRC’s auditorium at Sterrebeek to attend the final PERSUADE seminar (acronym of PoroElastic Road SUrface: an innovation to Avoid Damages to the Environment).

The objective of this six-year European research project (September 1, 2009 – August 31, 2015) led by BRRC was to develop a safe and durable poroelastic road surface, as a means to control road traffic noise.

A poroelastic road surface is composed of rubber granules (from recycled car tyres), small-sized stone aggregate and a number of additives, which are bound with an elastic synthetic resin (polyurethane). It contains no bitumen and must, therefore, not be confused with rubberized asphalt.

Earlier experiments had demonstrated that such a road surface can reduce road traffic noise by 7 to 12 dB. For comparison, a 4 m high noise screen has a noise-abating effect of about 8 dB.

However, durability was inadequate, especially for fretting and adhesion to the underlying layer. Further extensive research was necessary to improve those aspects and to find the answers to a number of pending questions.

Comprehensive approach

Laboratory tests “Pilot” test section at Sterrebeek Full-scale test section at Herzele

An all-inclusive comprehensive approach was opted for right from the outset of the project.

More specifically a noise-abating application of a poroelastic material was aimed at, which moreover was required:

  • to be durable and cost-effective;
  • to produce a sufficiently skid-resistant and even road surface, in order to ensure the safety and driving comfort of road users;
  • to be harmless to man and the environment, under all circumstances (laying, vehicle fire, etc.); - not to cause a significant increase in rolling resistance, so as to avoid extra fuel consumption.

Furthermore, the research programme comprised:

  • tests in the laboratory;
  • the construction of “pilot” test sections with little or no traffic (for example, on BRRC’s parking area at Sterrebeek);
  • the construction and monitoring of full-scale test sections on trafficked roads (for example, on regional road N464 at Herzele).

Results

The objectives were reached to a large extent. The partners were successful in designing two mixtures with a good resistance to fretting. The strength values obtained in laboratory tests were comparable with those of high-quality thin asphalt surfacings. Although it was not possible to monitor the test sections for as long as planned, the findings in the field confirmed the results of the laboratory tests.

The quality of the underlying layer proved to be an important factor for the adhesion of the poroelastic surface material.

Noise reductions from 7.5 dB(A) to 10 dB(A) were actually measured on eight test sections in five of the participating countries (Belgium, Denmark, Poland, Slovenia, and Sweden).

Skid resistance is fair to good, and rolling resistance is comparable to that of an SMA 0/16 mixture.

A poroelastic road surface is not toxic and (somewhat surprisingly) much safer in a vehicle fire with leaking fuel than “conventional” dense road surfaces. The idea has already been suggested that this material could help improve safety in tunnels. Poroelastic material is more expensive in use than “conventional” materials. It may, however, be advantageous in comparison with other measures (such as noise screens) that have a similar noise-reducing effect. Also, it can be used in places where few or no other noise control solutions are possible.

To sum up, it can be stated that the elements to produce a poroelastic road surface with good noise-reducing characteristics, fair durability and all the other properties to be reasonably expected from a road surface are now available and well documented.

However, further test sections are required to enable road contractors to gain the necessary experience with poroelastic material and to refine the laying techniques.

Future prospects

The final report on this European research project is due by the end of this year (www.persuadeproject.eu).

On behalf of the consortium, Luc Goubert presented the PERSUADE project to the Working Party on Noise (GRB) of the United Nations Economic Commission for Europe (UNECE) in Geneva on 1st September 2015.

As part of the urban project SToLA (STille TopLagen voor Antwerpen, or low-noise road surfaces for Antwerp), a poroelastic test section 128 m in length will be constructed in the formerly independent municipality of Zandvliet. The objective is to investigate the usefulness and feasibility of low-noise road surfaces in an urban area. In addition, roadside residents will be surveyed for their views on this kind of application.