Laboratory studies of skid resistance and rutting of low cost bituminous wearing courses

Two important aspects of low cost bituminous wearing courses are skid resistance and rutting. Normally, the polished stone value (PSV) of the aggregates used in the surface keep in check the effect of wearing out of the surfaces on the skid resistance. An effort is made in this laboratory study to assess the skid resistance of various wearing courses (Premix Carpet with Sand/Liquid Seal Coat, Mix Seal Surfacing Types 'A' and 'B' and Surface Dressing) using the British Portable Skid Resistance Tester. In addition, indigenous equipment is designed and fabricated in order to discover the effect of wearing out of the surfaces on skid resistance as a whole by directly providing the wheel passes over the prepared sample from the surface being tested. The rut depth after a given number of wheel passes is also studied in order to assess the resistance of the surface being tested to rutting. Variations on the testing include using both iron wheel and rubber tyre wheels, as well as using another sample for each surface with 10% extra bitumen tested with the rubber tyre wheel. Samples were prepared following specifications of rural roads by the Ministry of Rural Development. Results of the study show that Premix Carpet with Sand Seal Coat is the best surface for skid resistance and is further improved by adding 10% extra bitumen to the mix. Mix Seal Surfacing Type 'A' shows the best resistance to rutting, however there is no improvement by adding extra bitumen. The other surfaces do, in fact, show improvement by adding extra bitumen.