Causes of premature ravelling with single-layer porous asphalt

In the Netherlands the average service life of single-layer Porous Asphalt (PA) 0/16 with standard 70/100 pen grade bitumen is 11 years for the slow lane and 16 years for the fast lane. The end of the service life is mainly caused by the loss of coarse material from the surface (ravelling). However, sometimes the service life is much shorter. This paper discusses an investigation into the causes of premature ravelling problems of a PA road section, which occurred within three years after laying. To find the causes of the premature failing of this road section the mix design, the quality control of the contractor, the end control and the quality of the applied materials were investigated. As a special action the quality of the stone fraction was determined with a petrographic and mineralogical study. The degree of ravelling on the PA road section was measured under traffic with a laser. Based on the laser measurements the remaining service life was predicted. From the research results it can be concluded that the premature ravelling is caused by a complex of factors of which the poor quality of the coarse material plays a crucial role. Recommendations are given to prevent premature ravelling problems in the future.