Validation of the Wehner/Schulze test : the development of instruments for risk control relating to the development of skid resistance (Track 2)

The new contract types now being used by the Directorate-General for Public Works and Water Management (DPW) provide the contractor with more freedom and responsibility in its choice of products offered. DPW prescribes the function of a particular product, but does not describe in detail what the product should be. With regard to the functional requirement “Wet skid resistance of road surface upon opening”, the Superstructure Component Requirements version of 18 March 2009 state that the surfacing of the road section to be opened to traffi c should have a wet skid resistance of at least 0.40. Over the remainder of its service life, the wet skid resistance of closed surfacing should be at least 0.39 and the wet skid resistance of open surfacing should be at least 0.42. This report describes the validation of the Wehner/Schulze test. This test determines resistance against polishes of the entire asphalt mix and not merely a fraction of the mineral aggregate. The validation is performed on both PA 0/16 mixes and AC 0/16 SURF mixes. The investigation has demonstrated that a close relationship exists between the WSV[0] and the current skid resistance of the road surfaces, measured in accordance with test 150 of the Standard RAW Stipulations 2005. In addition, the investigation has also demonstrated that the Wehner/Schulze test also distinguishes between asphalt mixes from good and bad road surfaces. Asphalt mixes from bad road sections (investigated for drilling cores from hard shoulders that had not been driven on) have a significantly lower WSV[3] than asphalt mixes from good road sections. On this basis, final recommendations are made with regard to the guideline values for the Wehner/Schulze test, which are able to separate new mixes into mixes with a service life expectation of at least 20 years on the one hand, and less than 20 years on the other hand. A further recommendation is to discuss the results of the investigation at an international level, and to coordinate the results with investigation results from other countries. This to determine the joint objectives that must be achieved in order for the Wehner/Schulze test to be accepted as a Type Testing test.