The points in favour of the process: it’s cost-effective, time-saving and durable. Cost-effective because the thinner layer significantly reduces milling and material costs. Besides which, there is no need for costly adjustments and the installation of new curbs. Time-saving because spraying the high-quality polymer-modified bitumen and paving the surface course can take place in a single pass. Last but not least, the pavements rehabilitated by paving thin overlays are exceedingly durable. The sprayed binder forms a continuous film on the lower layer, effectively sealing the road structure against water and significantly extending the service life of the new pavement.
Paving thin overlay on spray seal
In order to produce a particularly high-quality bond between layers when overlaying the surface course, Sorigué used an emulsion called ELASTAM which was developed by the company itself and contains 65% of polymer-modified bitumen and 35% of water. The polymer-modified emulsion guarantees very rapid “breaking” so that the film of emulsion can be overlaid with hot asphalt immediately after spraying. The SprayJet module ensures that the emulsion is always sprayed in exactly the right quantity. Unlike the case when using conventional methods, job site vehicles and paver do not drive over the film of emulsion so that it remains intact over the full width.
The set rate of spread was relatively high, at 1.1kg/m². Alfredo Bobis, product developer for Sorigué explains why this was so: “Using a high rate of spread produces a reliable tack coat on all bases and ensures a strong bond between the layers. In addition, it also allows more bitumen to be mixed into the asphalt retroactively. All in all, this extends the service life of the new surfacing in line with demands for sustainable road construction.”