LABORATORY DESIGN AND FIELD COMPACTION OF DENSE BITUMEN MACADAM. DURABILITY AND PERFORMANCE OF BITUMINOUS HIGHWAY MATERIALS, HATFIELD POLYTECHNIC, 3-4 APRIL 1989

This paper presents the results of a laboratory investigation which evaluates the percent refusal density (prd) as a method of control for compaction. It also discusses the use of the Leeds design method (ldm) for the determination of the optimum binder content of dense bitumen macadam and heavy duty macadam and for controlling compaction by a modified prd. The aggregates used in the investigation were single sized crushed limestone and crushed basalt (nominal sizes of 28 mm, 20 mm, 14 mm, 10 mm, 6 mm and 5 mm). A limestone filler was also used to increase the filler content of the two dense and heavy duty macadams. The tests for characterisation of the aggregates were particle size distribution, specific gravity, and water absorption. The bitumen binders used were of nominal penetration 100 for the dense bitumen macadam and 50 for the heavy duty macadam. The refusal density test was carried out in duplicate specimens at 3 binder contents (3.4%; 4.0% and 4.6%). For the ldm, specimens were prepared at 5 bitumen contents from 3% to 5% in order to determine optimum binder content. The results show that the pdr method gives repeatable results, and that the ldm is adequate for the design of dense bitumen macadams. The ldm should be modified to allow design of mixes containing aggregate size particle up to 28 mm diameter. For the covering abstract of the conference see IRRD 823743.