A Combination Waterbound Macadam and Dense-Graded Aggregate Base for Flexible Pavements

This paper is concerned with a flexible base designed primarily to improve the riding qualities of high-type bituminous pavements. Difficulties in control of grades and sections with modern methods of macadam base construction have emphasized needs for effective finishing procedures. In the project described, an 8-in. base was built in two courses, the lower waterbound macadam being overlain by a densegraded aggregate material suitable for spreading and shaping with a power grader. The base was then surfaced with two courses of a hot bituminous plant mix. Observations and measurements showed that the combination could be built satisfactorily; construction entailed more equipment but less manpower for the blade-spread course than for the waterbound macadam; the dense-graded aggregate produced a high base density; and the possibilities for finishing to uniform section were much better with the dense-graded aggregate than with the macadam