Appendix E 1.5 Spraying of Binder, Spreading and Rolling of Aggregates
The time available to incorporate the aggregate into a PMB or multigrade bitumen is relatively short. Keeping aggregate spreading and rolling operations as close as possible behind the sprayer is more critical than when spraying C170 bitumen and may necessitate shorter-than-usual sprayer runs.
There must be sufficient rollers to cover the full sprayer run width with one pass and additional rollers may be required as compared to conventional bitumen work.
Some of the more viscous (high consistency) modified binders will require the use of larger spray nozzles, depending on binder viscosity, to ensure a uniform transverse binder application.
When field mixing crumb rubber binders, the material must be continually circulated to minimise settling out of any rubber particles. Failure to do this may result in blockages of the spraying jets and/or pipe work or spraying of a segregated product.
Field-produced crumb rubber mixtures should not be stored in bitumen sprayers, road tankers or bulk storage due to the potential problem of segregation and settling out of the rubber particles which may result in blocked pipe work.
In locations where a potential for early damage to a new single/single seal exists (e.g. farming entry points, minor intersections), the use of a scatter coat of small size aggregate (7 mm for a 14 mm seal and 5 mm for a 10 mm seal) or double/double seal should be considered.