A laboratory study has been made to determine the effect of degree of compaction on some properties of two different types of dense bituminous wearing course; these were rolled asphalt, which is gap-graded, and asphaltic concrete, which is continuously graded. The various levels of compaction of the materials, made with a range of binder contents, were achieved using (a) Marshall compaction apparatus and (b) a laboratory roller-compactor. The richer asphalts, of both types, compacted more easily than the drier mixtures to produce impervious surfacings; as a class, the rolled asphalts compacted more readily than the asphaltic concretes. In the Marshall test (60 degrees c) increased compaction led to lower optimum binder contents and higher stabilities the differences being more marked in the asphaltic concretes than in the rolled asphalts. Although the resistance to deformation of both types of asphalt, as measured by the wheel-tracking test (45 degrees c), increased with increasing compaction it was possible to "over-roll" the asphaltic concretes so that the materials became less stable when the void content of the mix was reduced below 3.5 per cent. This effect was not observed with rolled asphalt. (Author/publisher)
Abstract