Abstract:
Surfacing seals consist of a combination of bitumen and aggregate, and are used to provide
an all-weather surfacing to protect underlying layers and provide safe access to vehicles
traveling on a road. Analysis of a number of sections in Gauteng, South Africa, has shown
that surfacing seals lost a large proportion of their aggregate where the road was crossed by a
bridge. As all original properties of the seal components as well as the traffic on the road
were similar, it was deduced that the micro-climate where the road traveled underneath the
bridge should have caused this localized failure condition. In this paper the phenomenon is
investigated through analysis of the micro-climate underneath the bridge, the material
properties of the surfacing seal, and the combined effect of these factors on the performance
of the seal. It is shown that the micro-climate can affect the performance of an otherwise
suitable surfacing seal to such an extent that the performance of the seal is severely
compromised. A procedure for the analysis of potential micro-climate effects is described in
the paper.
