InfraStructures - November 2005

Compact Asphalt

Jean-François Dubois

During the past several years, the Erfurt University of Applied Sciences in Germany has been developing a new technology that makes it possible to apply two layers of paving simultaneously. Currently in the testing phase, this new technology offers advantages deserving our attention.

A key obstacle in the compaction of asphalt is the loss of heat sustained by the surface layer once it is applied to the cooled mat or base layer. This heat loss has a serious effect on the compaction desired. The smaller the degree of compaction, the larger the percentage of void content potentially affecting the waterproof qualities of the top layer. A porous layer allows for water to seep in, contributing to the deterioration of the pavement during the freezing and thawing cycles.

The new method developed by professor Elk Richter's team has, as its primary objective, to improve the degree of compaction at the time of paving by utilizing the heat released by the base coat. During preliminary tests, the research team used a first paver followed immediately with a second, rolling directly on the base coat. Since this method created a number of problems, Hermann Kirchner, the contractor collaborating on the project, decided to build a prototype paver which would allow for simultaneous paving. This modular paver can be attached to a conventional paver thus making it possible to use two storage bins, two conveyors and two asphalt screw-type conveyors with independent systems of compaction. Another advantage is that this module can be easily removed, making it possible to use the basic paver in a conventional manner.

The objectives set by this new method are:

A superior degree of compaction while using the same method of compaction. By using the heat emanating from the base coat, the period of compaction is increased.
An increase in the structural properties of asphalt. Studies have shown that increasing compaction by 1% results in an increase of 15% of the mechanical properties of asphalt.
To create a thin, dense, and waterproof surface. This layer is only 2 cm thick.
To minimize the risks of quality loss at the time of spreading during cold weather.
To improve the bond between the base coat and the surface.
A reduction in application time.

Test strips were carried out throughout Germany on several types of road surfaces, including highways, which demonstrated an increase of 3% in the degree of compaction compared to the standard method. For example, wheel tracking tests were carried out and results of 9,6 mm were reached after 19 200 passes with this method contrary to 3500 passes with the standard method.

This new German technology, called compact asphalt (kompakt asphalt) is currently the subject of a study by the BAST (federal institute of road research in Germany). The study should validate whether the results meet the designer's expectations in the medium and long term.

While this new technology is still in the developmental stage, it is obvious that it has already generated a lot of interest from people of the industry.

Cet article est également publié en français