4.8 Selecting an Initial Seal
Table 4.6 is a preliminary guide to selecting initial seals, based on traffic, equivalent heavy vehicles (EHV(%)), and climatic conditions. Specialist advice should be sought to manage variations based on local experience.
Further guidance for the selection of an appropriate binder and aggregate size is provided in Section 4.8.1 and Section 4.8.2 respectively.
Consideration should be given to the average seasonal temperature that the pavement will be subjected to during the day of sealing, and the following weeks.
Table 4.6: Preliminary guide to the selection of initial seals
| EHV(%) | Average seasonal temperature | Low traffic | Medium traffic | High traffic |
|---|---|---|---|---|
| Typical binder(5) and seal type | ||||
| Low (< 25%) | Cool(4) | AMC4 (S/S) | AMC5 (S/S) | AMC6 (S/S, D/D) |
| Warm | AMC5 (S/S) | AMC6 (S/S) | AMC7 (S/S, D/D) | |
| Hot | AMC6 (S/S) | AMC7 (S/S) | AMC7 (S/S) | |
| High (≥ 25%) | Cool(4) | AMC5 (S/S) | AMC6 (S/S) | CRS67 (D/D) |
| Warm | AMC6 (S/S) | AMC7 (S/S) | AMC7 (S/S) | |
| Hot | AMC7 (S/S) | AMC7 (S/S) | AMC7 (S/S) | |
- Guidance to field application of PMBs for sprayed seals (including cutting practice) is provided in Appendix E.
- Care must be taken when using PMBs (especially SBS) because it is difficult to achieve sufficient adhesion to the base and aggregate wetting. To date successful trials have been undertaken only with crumb rubber binders (Austroads 2014a), and as yet other binders are unproven in this application, pending further trials.
- When low or medium traffic is coupled with high-stress situations such as intersections, turning lanes, and grades, consider following guidance for the ‘high traffic’ category instead.
- As sealing in cool and damp conditions increases the risk of seal failure, consideration should be given to postponing works if possible until weather conditions have improved.
- Cutback bitumen grades nominated in the table are based on typical pavement materials used in Australia. Adjustment to the proportion of cutter oil content may be required for very porous (less cutter oil) or tightly bonded (more cutter oil) pavement surfaces. For tightly bonded surfaces (including stabilised pavements), pavement surface preparation is essential to achieving an adequate bond, particularly when emulsions, low cutter content cutback bitumen and PMB grades are used.