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#19-09 Update to NZTA M1-A specification for performance-graded asphalt binder

Published: | Category: Technical advice note | Audiences: Road traffic engineers & consultants, Roading contractors

This notice advises that the new performance-graded asphalt binder specification is available to be used for all future asphaltic concrete works.  The new specification will come into effect immediately and should be applied to all upcoming asphaltic concrete surfacing works in the state highway programme.

Publication details

  • Author:
  • Published: 24 June 2019
  • Reference: 19-08
  • Version: 1
  • Contact: pavements@nzta.govt.nz

Purpose

This notice advises that the new performance-graded asphalt binder specification is available to be used for all future asphaltic concrete works.  The new specification will come into effect immediately and should be applied to all upcoming asphaltic concrete surfacing works in the state highway programme.

Use of M1-A: 2016 over the past three years has highlighted the need for some fine tuning, hence this revision of the specification.  This update enhances the specification by aligning it with other NZTA specifications, providing more direction on binder grade selection and matching the selected binder grade to site climate conditions.

This notice replaces Technical Advice Note #16-03.

This document describes binders for asphalt mixes using sophisticated performance-related criteria, replacing traditional means of specifying bitumen.   M1-A specification was developed as changes in the bitumen supply chain showed that the traditional criteria for specifying bitumen did not adequately predict its performance as an asphalt binder.  It was based on outputs from research and modern bitumen specifications in the USA.  It linked bitumen properties to site traffic loadings.

The specification is now available online at https://www.nzta.govt.nz/resources/asphalt-binders/

General information

The update to NZTA M1-A has included several changes. 

Firstly, it introduces a New Zealand climate map by dividing the country into three broad climate zones, designated “warm”, “moderate” and “cool”.  The asphalt binder grades are matched to the climate zones, with stiffer binders used in warm zones and softer binders in cool zones.

Secondly, binder grades are linked to traffic categories with loading specified in Equivalent Standard Axles (ESA).  Softer binders are specified for light traffic situations and harder binders where heavy traffic or longer loading times (for example, slow moving traffic) are experienced.
Thirdly, the updated M1-A specification is more specific on sampling and testing.

Finally, the specification references AASHTO M 332, published by the America Association of State Highway and Transportation (AASHTO) rather than explicitly containing the specific binder properties criteria.

Changes to the selection process

The update to M1-A and notes provide more advice for identifying and specifying the correct grade of binder for a job location.  A flow chart has been developed and provided in these documents to assist with this process.  The documents also include discussion of binder selection for other asphalt mix types such as stone mastic asphalt and open-graded porous asphalt.

User benefits

The use of a performance-based specification for asphalt binders has immediate benefits:

  • It links the binder properties to the site loading and temperature conditions.
  • This means that the binder will be matched to the asphalt mix requirements over the life of the pavement, giving surety of performance and durability.
  • The specification is “composition blind”.  This means that standard bitumens, polymer modified bitumens or other proprietary materials can be evaluated on a similar basis and the correct binder selected.  This provides a rational and scientific basis for assessing binders and allows the selection of modified binders where they are needed.
  • Linking M1-A to AASHTO M 332 means New Zealand rapidly benefits from research outputs in the United States.

Support and advice

It’s important to remember that, while M1-A uses sophisticated criteria to specify the performance-related binders, in most cases it is still the same, or very similar, to the bitumen that has been traditionally used.  The advantage of the change is that binders produced from different crude oil feedstock, or using different techniques, or modified with polymers are compared on the same engineering basis.  This reduces the risk of inappropriate binder selection and hence optimises the performance of the asphalt binder.

Publication details

Author: New Zealand Transport Agency
Published: June 2019
Version: 1
Found at: https://www.nzta.govt.nz/resources/asphalt-binders/

Further information

To submit documents or if you have any questions or feedback, please contact the NZTA Principal Surfacings Engineer, Grant Bosma at pavements@nzta.govt.nz

 

David Darwin                 Vanessa Browne

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