Friction course surfacing has been used on New Zealand road pavements since the early 1970s. The porous nature of this surfacing gives advantages of high skid resistance when wet, low noise, and excellent spray suppression when compared to other surfacings. Although the surfacing will last in excess of eight years, the voids in the surfacing tend to clog within three years, so that its full benefits are not available for over half its life.
A literature review was carried out in 1992 to identify techniques that could be used to maintain the porous nature of friction course for a longer period of its life than it currently gives.
Factors that contribute to the loss of the porous nature have been identified and the entry of detritus is suggested as the primary mechanism affecting New Zealand mixes.
Recommendations for research and field trials into techniques to increase the effective life are given. These techniques are based on increasing the initial void content by changes to the mix design and by increasing the layer thickness.
Keywords: Clogging, friction course, New Zealand, pavements, permeability, porosity, roads, voids