7.1.1 Primes
The performance of primes and subsequent seals applied to granular pavements is dependent on the adequacy of the underlying pavement in respect to surface condition, strength and stability. These issues are discussed in Austroads (2010b).
The prepared pavement surface should be swept, to remove surface dust and provide a surface that is free of foreign material, with the larger-sized stones at the surface of the pavement exposed but not loose or dislodged. Guidance on surface preparation (homogeneity, exposed aggregate, avoidance of laminating materials or a build-up of fines) is provided in the Guide to Pavement Technology Part 8: Pavement Construction (Austroads 2009b).
Pavements to be primed should be surface dry, and no more than damp to the required depth of primer penetration. Excess moisture will inhibit the penetration of the prime, as voids filled with moisture cannot be filled with primer (Austroads 2009b).
It is critical to attain a satisfactory level of dry-back or removal of moisture from the compacted and prepared basecourse pavement layers to present a suitably hard surface for priming. Guidance in controlling moisture in pavement construction and specifying and measuring dry-back is provided in Austroads Pavements Reference Group (2003).
Poor surface hardness can lead to excessive aggregate embedment and flushing. This can be due to a number of factors including excess moisture in the pavement or a layer of fines at the surface. The ball penetration test (Austroads 2010c) is a useful indicator of both the level of surface hardness and dry‑back that has been achieved in the basecourse. It provides an input to the determination of the binder application rate in seal design, allowing for the potential embedment of the sealing aggregate into granular pavements.
Photographic examples of good, marginal and poor granular pavement preparation are provided in Appendix A.