a full-scale experiment was begun in july 1973 on a20 at swanley, kent, with the object of determining whether higher levels of surface texture and resistance to skidding can be maintained in surface dressings on heavily trafficked high-speed roads when using truly single-sized chippings rather than chippings conforming to the present gradings of bs63: 1971. six experimental sections, each each about 75m long, have been laid using three different gradings of each of two aggregate types. earlier experiments on bituminous substrates have shown the degree of embedment of chippings to have more effect on performance than variations in grading of the applied aggregate. for this reason a concrete road where no embedment would take plaece was chosen. the work is complementary to a series of full-scale experiments planned for less heavily trafficked roads by the british standards institution's committee responsible for the amendment of bs63. (a)

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