The polishing properties of aggregate have until now not been considered in Sweden, as in the rest of the Nordic countries. In the wintertime wear of studded tyres has roughened up the aggregate surfaces and thus provided the microtexture necessary. Also, the most polish susceptible aggregates as limestones etc. have not been used. However, in the last few years, the wear of studs on road surfacings has been reduced because very hard aggregates as porphyry and quartzite have come in use, most often also in stone mastic asphalt that has a high amount of coarse aggregate. Another development has been that at present only light-weight studs, with a reduced wearing action, are allowed to be marketed. The reduced wear has in recent time resulted in poor skid resistance, in wet conditions especially in locations as sharp bends, round-abouts, etc. The microtexture of the aggregate surfaces is poor and this is especially the case with porphyry which is extremely hard. The special Swedish conditions, with wear of studs wintertime, hinders experience from other countries to be utilised in a full extent. Investigations have recently begun at VTI, both laboratory work, experiments in road simulator and skid resistance measurements on experimental sections. Preliminary results are presented and means to improve the skid resistance to an acceptable level and especially avoiding dangerous "black spots" are discussed. (A)
Abstract