Pavement
- Publication no: AP-T384-26
- ISBN: 978-1-922994-91-2
- Published: 27 February 2026
- PDF (free) Download
This report presents updates to the Austroads Guide to Pavement Technology Part 4K: Selection and Design of Sprayed Seals, aiming to refine the sprayed seal design method to better suit evolving traffic loads, pavement structures, and material technologies across both countries. It incorporates findings from workshops held in Australia and New Zealand, as well as a targeted literature review.
The Austroads sprayed seal design method, widely used in Australia, provides guidance on materials and methods for calculating binder application rates and aggregate spread rates. In New Zealand, the chipsealing design method is detailed in Chipsealing in New Zealand.
Ongoing changes in traffic loadings, pavement structures and materials have prompted updates to the Guide. Continued research is crucial due to the unique road infrastructure challenges in Australia and New Zealand. This ensures the design methods are tailored to local environments, optimising performance and cost-effectiveness.
To ensure the design methods remain reliable and that sprayed seals can perform under increased traffic volumes, contributions were sought from seal designers, transport agencies, consultants, and contractors as part of the workshops held in Australia and New Zealand. The New Zealand workshop also explored the potential for a unified guidance document that satisfies both Australian and New Zealand practices.
This report highlights areas for immediate implementation and further research. Key topics include refining aggregate spread rates and developing robust seal design procedures.
Watch a recording of the webinar to learn more.
- 1. Introduction
- 1.1 Background
- 1.2 Purpose
- 1.3 Scope
- 1.4 Methodology
- 2. Workshops
- 2.1 Overview
- 2.2 Australian workshop outcomes and suggested topics for review
- 2.2.1 Sections 1 and 2 – Introduction and operating environment
- 2.2.2 Section 3 – Types of sprayed seal treatments
- 2.2.3 Section 4 – Selection of treatments
- 2.2.4 Section 5 – Design method
- 2.2.5 Section 6 – Seal design input parameters
- 2.2.6 Section 7 – Construction
- 2.3 New Zealand workshop outcomes
- 2.3.1 New Zealand sealing overview
- 2.3.2 Overview of sprayed sealing in Australia
- 2.3.3 Treatment types and classifications
- 2.3.4 Selection of sprayed seals/chipseals
- 2.3.5 Design method
- 2.4 Discussion
- 2.4.1 Major research projects
- 2.4.2 BSTG consideration and further research projects
- 2.4.3 Unification of Australian and New Zealand design guides
- 3. Literature Review
- 3.1 Measurement of Average Least Dimension (ALD)
- 3.2 Aggregate spread rate
- 3.2.1 Austroads
- 3.2.2 New Zealand
- 3.2.3 South Africa
- 3.3 Aggregate size compatibility
- 3.4 Robust seals
- 3.4.1 South African examples
- 3.4.2 Victorian approach
- 3.5 Seals under asphalt
- 3.5.1 Strain Alleviating Membrane Interlayers
- 3.5.2 Other seals under asphalt
- 3.6 Otta seals
- 4. Technical Basis for Guide Update
- 4.1 Overview
- 4.2 Suggested updates
- 4.2.1 Remove obsolete treatment type
- 4.2.2 Review accuracy of terminology comparing Australian and New Zealand seal types
- 4.2.3 Update figures to better reflect good practice
- 4.2.4 Remove foamed bitumen as binder type
- 4.2.5 Remove calculation (nomograph) method of ALD measurement
- 4.2.6 Typical binder retention allowance for geotextile reinforced seals
- 5. Findings and Conclusions
- References
- Appendix A Meeting Agendas
- A.1 Australian workshops
- A.2 New Zealand workshop
- Appendix B Workshop Minutes
- B.1 Melbourne, Victoria
- B.2 Adelaide, South Australia
- B.3 Perth, Western Australia
- B.4 Brisbane, Queensland
- B.5 Sydney, New South Wales
- B.6 Auckland, New Zealand