The final evaluation of the performance of 17 bituminous test sections constructed in 1978 on highway 7 near lindsay, ontario, is reported. The objective ofthe trial was to develop suitable surface friction course mixes for highways carrying moderate volume of traffic (about 5, 000 aadt) at posted speed limit of 80km/h. These mixes would provide and maintain adequate levels of surface friction to reduce wet pavement skidding accidents. Both open- and dense-graded type mixes were included in the evaluation. Two standard mixes were incorporated for control purposes. A specialty patented mix called delugrip was also placed in the trial. Aggregates used consisted of crushed gravels, local sand, and screenings of various blends. Frictional properties of the test sections were measured three times within the 6-year monitoring period. Samples of the surface course mixes were periodically taken for laboratory testing and evaluation. Friction results indicate that the coarse aggregate content and quality is a major factor for determining the level of friction achievable in a mix. The mixes found suitable for moderate traffic are those containing at least 25% of hard igneous coarse aggregate with the coarse aggregate content in the mix greater than 60%. Open friction course mixes using granite/basalt coarse aggregate (without limestone) were found to perform best, but some of the dense friction course mixes also performed satisfactorily. Mixes containing a high proportion of limestone coarse aggregate from local supplies were found unsatisfactory both in terms of friction number and, in most cases, durability. This paper appears in transportation research record no. 1259, Chip seals, friction courses, and asphalt pavement rutting 1990.
Samenvatting