Whilst most developed countries have moved away from cutting back hot binders with kerosene to construct spray seals, it is still common practice in Australia. The continuation of this practice raises concerns about potential hazards which could result in incidents causing harm to people from explosions and the emission of volatile vapours into the atmosphere.
The primary reason for cutting back hot binders is to reduce their viscosity on a temporary basis to:
- Allow uniform lateral dispersion of modified binders during spraying to prevent tramlining,
- Assist with the binder ‘wetting’ the cover aggregate during spreading when the pavement temperatures are lower,
- Prevent brittle fracture with the onset of lower overnight temperatures which can result in aggregate whip off under traffic.
On the other hand, the presence of cutter entrapment in the binder can lead to flushing during high surface temperatures under heavy traffic in summer. The increase in the traffic density on our spray seal network has led to a reduction the amount of cutter that is used compared to past years to mitigate against the occurrence of flushing.
This presentation will look at practices which can be used to eliminate the use of cutters to construct spray seals which have been implemented in Australia by the COLAS Group. These include:
- Establishing boundaries when cutting back of hot binders is not necessary to construct spray seals
- Use of the OB Vario syncronised sprayer which simultaneously sprays the binder and applies the cover aggregate.
- The spraying of low viscosity S45R crumb rubber binder without cutters
- The use of a high float emulsions to accelerate the cohesion development so the seal can be opened to traffic earlier than conventional emulsions
- The construction of emulsion seals not immediately exposed to traffic such as under asphalt overlays or in winter on new granular bases
- The replacement of kerosene with bio oils in emulsions for priming granular base courses.
- The replacement of diesel with bio oils for producing aggregate precoating fluids
It is hoped that the above initiatives will provide the Industry with confidence to consider moving toward practices which will lead to the elimination of cutters in spray sealing practices.
