Air voids in bituminous materials can have a significant effect on many aspects of performance, particularly the durability of surfacings. Full-scale trials have shown that a durable surfacing will result when the air voids content does not exceed 4 per cent at the design stage for rolled asphalt, with minimal in-situ hardening of the bitumen with time. A laboratory study using the ASTM test for directly determining the maximum relative density, and hence the air voids content, was carried out for rolled asphalt surfacings and the results compared with the British Standard calculation method. The comparison showed that the two methods are not statistically significantly different. A degree of compaction (DOC) test has been compaction (DOC) test has been developed, using standard apparatus, that can be used on cores extracted from a surfacing of rolled asphalt with pre-coated chippings. The results from the DOC test also correlate well with the in-situ air voids content. Within the limits of the study, both the ASTM and DOC tests are shown to be very precise. Results from a pilot scale trial showed that, for a rolled asphalt designed to have an air voids content of less than 4 per cent, a well-compacted surfacing with pre-coated chippings will have an air voids content of about 5 per cent and a degree of compaction of about 96 per cent. These criteria could form the basis of part of a performance-related specification for chipped rolled asphalt surfacing, but specification trials would be necessary to ascertain limits which could be applied in practice for acceptance purposes. (A)
Abstract