A full-scale experiment at harvey road, derby, has provided evidence about the performance of several types of roadstones when used as 3/4 in. Coated chippings at a nominal 100 sq yd/ton in rolled asphalt. Despite considerable variation in the coverage and degree of embedment of the chippings actually obtained, the experiment has shown that the polished-stone value is the most important property of the aggregate affecting the sideway force coefficient of the surfacing. A minimum polished-stone value (1965) of the order of 45 was needed to ensure maintenance of a mean summer sideway force coefficient of 0.40, the recommended value for this category c site. The traffic was 25,000 ton/day without well-defined wheel lanes. Most of the roadstones provided an asphalt with a good depth of texture after 12 years. Although all of the sections treated with stone of low abrasion resistance gave rather small texture depths, these depths (0.016-0.018 in) were still adequate for this speed-restricted site. Stones that crushed readily in the laboratory test have cracked on the road, but this has not affected their suitability as chippings for rolled asphalt in the conditions of the experiment.
Abstract