Austroads Seal Design

I am presenting here some Austroads documents related to seal design. Please take these as reading materials and you need to refer to Austroads for latest revision and current versions.

Review of Australasian and Overseas Specifications and Performance Tests for Bitumen

This report describes a literature review on the bitumen/binder specifications and test methods used in Australasia, USA, Europe and South Africa. The project investigated whether the Australian and New Zealand bitumen specifications are adequately related to performance, and appropriate for evaluating the current generation of bitumens.

The Australian bitumen specification (AS 2008) and PMB specification (AGPT/T190) were found to be able to rank the performance of binders at high road temperatures (e.g. 60 °C), and also could account for regional climatic variations. Concerns have been raised in New Zealand about the New Zealand bitumen specification (NZTA M1) as bitumens are increasingly being imported into the country. As a result of these concerns, new bitumen/binder specifications have been under development in New Zealand. Preliminary New Zealand validation studies appear to suggest that the new specifications may be appropriate for evaluating the performance of asphalt and sprayed sealing grade binders in New Zealand.

The current Australian and the proposed New Zealand bitumen specifications were not immediately interchangeable in their current forms, and thus further studies would be required if a common specification is to be developed for the two countries in the future.

A review of international development work into performance-based specifications indicated that traditional binder tests (e.g. viscosity at 60 °C and penetration at 25 °C) were generally considered suitable for ranking the performance of bitumens. A number of potential performance-based tests are currently under development in various countries to characterise the properties of PMBs. The results of this research are expected to provide useful information when the Australian and New Zealand PMB specifications are updated.


Effect of Heavy Vehicle Traffic in Sprayed Seal Design

The principal aim of this work was to examine the effect of heavy vehicle loading on sprayed seals, in order to incorporate such loading impacts into the Austroads sprayed seal design method.

The current sprayed seal design method uses an equivalent heavy vehicle factor (EHV(%)) to account for the effects of heavy traffic on sprayed seals which is calculated using a simple equation using information from traffic counts. The seal design results obtained using the simple equation were compared to those obtained when EHV(%) values were determined using a detailed analytical method that utilised weigh-in-motion (WIM) data and seal deterioration models. WIM data was obtained from rural areas of Australia between 2007 and 2011.

Four seal design examples were used to compare the different EHV(%) calculation methods. There was either none of very little variation in EHV(%) values when the different methods of calculation were used. This resulted in either none or insignificant variations to the design binder application rates determined by the method (if expected construction tolerances were considered). Considering the increased complexity associated with the WIM-based methods, it appears that the current simple equation to determine EHV(%) will yield results which are suitable for use in the Austroads sprayed seal design method.

A comparison of the results obtained using the simple equation to calculate EHV(%), and a commonly used alternative interpretation also indicated that the use of either method had minimal effects on design binder application rate.


Selection and Design of Initial Treatments for Sprayed Seal Surfacings

This document is an update of the design of initial treatments for sprayed seal surfacing.

The information contained within this document supersedes that found in Austroads AP-T68-06 Update of the Austroads Sprayed Seal Design Method, and replaces Section 12 in that document.

The terminology used to describe applying sprayed seals directly onto a pavement basecourse has also been updated.

Previously there has been no formal design method used for initial sealing. The typical seal design method may be used for this purpose, with specific adjustments based on the requirements of applying a seal directly to a pavement basecourse.


Seal Design Improvement for Low Volume Roads

The current version of the Austroads sprayed seal design method was published in 2006 and has been in use for the last nine years. During recent times, a number of sprayed sealing practitioners have indicated that the basic voids factor for single/single seals in the current Austroads sprayed seal design method is too high for low volume roads. To address these concerns, a questionnaire was initially distributed to jurisdictions and local councils to determine the extent of the concerns. The results obtained during a literature review of the derivation of Austroads basic voids factor for single/single seals, and the equivalent factor in the New Zealand seal design method, were used as a basis to propose changes to the Austroads basic voids factor.

The responses to the questionnaire indicated that the main issue associated with the Austroads sprayed seal design method was that the basic voids factor for single/single seals was too high for low volume roads. The results obtained during the literature review indicated that the Austroads basic voids factor has developed empirically over time based on observations by sealing experts and practitioners, while the current New Zealand equivalent factor is based on quantitative measurements obtained during an extensive series of road trials. As the New Zealand equivalent of the basic voids factor was based on quantitative measurements, the New Zealand seal design approach was used to propose changes to the Austroads basic voids factor.

A new version of the Austroads basic voids factor has been proposed for single/single seals which will require lower basic voids factors to be used for low volume roads. The new version of the Austroads basic voids factor was compared with recent Australian seal data/observations in order to investigate whether its use would result in issues with sprayed seals. Based on these comparisons, it appears unlikely that use of the new version of the Austroads basic voids factor will result in issues with sprayed seals.

Errata: On 14 September 2015, Equation 20 of this report was corrected.

AP-T302-15_Seal_design_improvement _for_low_volume_roads

Penetration of Road Based by Bituminous Primers or Primer Binders

This test method sets out the procedure for assessing the degree of absorption of a primer or primerbinder by a given road gravel in bituminous surfacing work.


Seal Behaviour

This method describes the procedure for the recovery of sprayed seal samples from the pavement without disturbing the sealing aggregate orientation. The method stipulates how the void content of the sample is determined.