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3. Road Surface Types
3.1 Description
In the last decade, thin surfacing systems, which are a diverse set of proprietary asphalt materials, have become the predominant surfacing option. For use on trunk and most county roads, a thin surfacing system must have a Roads and Bridges certificate under the Highway Authorities Product Approval Scheme (HAPAS) from the British Board of Agrément (BBA)1. For the purpose of this scheme, a thin surfacing system is defined as a proprietary bituminous product with suitable properties to provide a surface course that is laid at a nominal depth of less than 40 mm (BBA(2000)). An example of a document that gives further information on thin surfacings is Nicholls (2002).
Because the definition of thin surfacings is relatively wide, it is impossible to identify definitive properties for these systems. However, those currently on the market are designed with the preference for low-noise surfacings and have relatively open surfaces. As such, there are marked differences from the surfacings previously used for major roads which, in general, were of hot rolled asphalt with pre-coated chippings.
BBA-HAPAS certificates can be downloaded from the relevant page in the BBA site on the web, www.bbacerts.co.uk/. The relevant page can be found by searching either for the name of the product or supplier or for thin surfacing to get a current list of the pages for all relevant certificates.
3.2 Advice on temporary markings for thin surfacings
When selecting the type of temporary marking to use on a particular scheme with newly laid asphalt, the properties of the asphalt layer should be taken in consideration. The acceptable options, based on a limited survey reported in Appendix A, are given in Table 3, but other factors, such as the type of site, may also have a significant effect but were not observed because of the similarity within the data reviewed.
The method for removing such markings should be considered before application is started.
| Layer thickness | Max. nom. agg. size | Binder type* | Binder content | Temporary Studs** | Temporary Tape |
|---|---|---|---|---|---|
| < 35 mm | 14 mm | Unmodified | > 6.0 % | Suitable | Suitable |
| 6.0 % | Suitable | Possible | |||
| < 6.0 % | Suitable | Unsuitable | |||
| Modified | > 4.9 % | Suitable | Suitable | ||
| 4.9 % | Suitable | Possible | |||
| < 4.9 % | Suitable | Unsuitable | |||
| 10 mm | Unmodified | > 5.4 % | Suitable | Suitable | |
| 5.4 % | Suitable | Possible | |||
| < 5.4 % | Suitable | Unsuitable | |||
| Modified | > 3.5 % | Suitable | Suitable | ||
| 3.5 % | Suitable | Possible | |||
| < 3.5 % | Suitable | Unsuitable | |||
| 35 - 40 mm | 14 mm | Unmodified | > 6.0 % | Possible | Suitable |
| 6.0 % | Possible | Possible | |||
| < 6.0 % | Possible | Unsuitable | |||
| Modified | > 4.9 % | Possible | Suitable | ||
| 4.9 % | Possible | Possible | |||
| < 4.9 % | Possible | Unsuitable | |||
| 10 mm | Unmodified | > 5.4 % | Possible | Suitable | |
| 5.4 % | Possible | Possible | |||
| < 5.4 % | Possible | Unsuitable | |||
| Modified | > 3.5 % | Possible | Suitable | ||
| 3.5 % | Possible | Possible | |||
| < 3.5 % | Possible | Unsuitable |
* Definitions:
- Unmodified binder: Paving grade bitumen in accordance with BS EN 12591: 2000 (Bitumen and bituminous binders - Specification for paving grade bitumens)
- Modified binder: Polymer-modified bitumen
** Based on small 100mm x 50mm (4" x 2") studs in use at the time of writing.
