Susceptibility of bituminous concrete towards permanent deformations can be determined in laboratory by means of a wheel track test. Several devices exist to perform this trial. In Switzerland, no one is normalized, however the LAVOC is using the French device developed by the LCPC for more than 20 years.
Although EMPA and 2 other private laboratories have recently acquired the same device, actually, only rutting susceptibility can be evaluated by performing such trial. Behaviour in place depends not only on mechanical properties of the mixture, but also on conditions of laying, on traffic characteristics, and on the climatic conditions. The LCPC testing process does not take into account the modulation of these parameters.
A method deserves to be developed, which takes into account in the testing process the traffic characteristics and climatic conditions to which the bituminous mixture will be exposed when in place.
The project has two basic objectives:
- Prediction of in situ rutting behaviour of bituminous mixture by means of the LCPC wheel track test.
- Assessment of the limit values for the LCPC wheel track testing applicable to standardized bituminous mixtures.
This research focused on the prediction of the average rut depth on Swiss territory. It sheds new light on the determination of the average rut, taking into account changes that may be characteristic of the material used, the characteristics of traffic and climatic conditions of the site.
In the framework of the research project a method for predicting rutting was developed. The proposed method is simple and can be applied by several laboratories in Switzerland. After an introductory period, it will be possible to refine the prediction and apply it to other types of coatings.
A standard is currently not necessary but might be considered after the introduction of a European standard on laboratory rutting for determining the equipment.
These are main conclusions of the project:
The traffic is constituted by the heavy traffic load expressed by equivalent axles which passed on the pavement during its service period. The mean speed adopted by heavy vehicles on the considered section provides some information about the loading time.
The bituminous pavement is taken into account by the material resistance to rutting parameter measured with the LPC traffic simulator.
Various laboratory tests were carried out with the LPC traffic simulator on pavement samples taken from roadways that were in service for variable lengths of time. With the aim of having a representative sampling of the Swiss roadways, different types of pavements were selected.
The pavements represent the variability and the range of climatic solicitations in Switzerland, as well as the specificities of heavy traffic.