surface dressings for heavily trafficked roads: results after 10 years of the full-scale experiment on a30 blackbushe, hants

the embedment of surface dressing chippings under traffic can have a marked effect on the performance of the dressings, particularly with regard to maintenance of adequate texture depth. this report describes the performance of surface dressings made with both tar and cut-back bitumen binders and a range of aggregates when laid on a hard substrate on a heavily trafficked road. it is concluded that improved performance is obtained if precautions are taken adequately to render the macadam substrate uniform before surface dressing. both tar and bitumen gave dressings of very good durability but, throughout the lives of the dressings, greater texture depths were maintained with tar binder rather than cut-back bitumen. at speeds below 80 km/h the resistance to polishing of the aggregates used was the main factor determining resistance to skidding which was independent of binder type. recommendations are made for limits for aggregate abrasion and crushing values to be set to avoid excessive wear of the applied chippings under heavy traffic (a).