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#16-03 Performance specification for asphalt binders M1-A

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

The M1 specification for bitumen is based around the measurement of penetration and basic viscosity.

This technical advice is superseded by #19-09 Update to NZTA M1-A specification for performance-graded asphalt binder.

Publication details

  • Author:
  • Published: 23 March 2016
  • Reference: 16-03
  • Contact: pavements@nzta.govt.nz
  • Amendments: This technical advice is superseded by #19-09 Update to NZTA M1-A specification for performance-graded asphalt binder.

The M1 specification for bitumen is based around the measurement of penetration and basic viscosity.

While this served us well for many years, premature shoving and rutting has shown that these
measures are insufficient to ensure asphalt performance, particularly in heavy traffic and high
temperature conditions.

To address this issue, the Transport Agency and industry have agreed to adopt a performance based specification for asphalt binders, M1-A. M1-A specifies properties that predict binder performance in asphalt with respect to traffic volumes and speed within the New Zealand temperature range.

The performance based binder specification is aimed at lowering the risk to the Agency and the contractor and, as such, binders in asphalt for state highways must be specified to M1-A.

Selecting a binder

The specification sets out four performance levels, Standard (S), Heavy (H), Very Heavy (V) and
Extreme (E) based on traffic in equivalent standard axles (ESA) and traffic speed (refer table 1).

Table 1 – Guide to traffic category

Bitumen grade category NZ traffic level Traffic level, ESAs (see note) Shear rate
Standard ‘S Low to medium < 10x106 Traffic level and more than the standard traffic speed (>70km/h). For example arterial roads
Heavy ‘H Heavy to very heavy 10x106 - 30x106 Traffic level or slow moving traffic (20 to 70 km/h). For example, climbing lanes or congested routes
Very heavy ‘V Very heavy and higher > 30x106 Traffic level or standing traffic (<20km/h). For example, heavy duty roadways/ motorways/ industrial estates
Extreme ‘E Industrial and ports > 30x106 and standing traffic Traffic level and standing traffic (<20km/h) such as industrial and port facilities

ESAs can be calculated from annual average daily traffic (AADT) and commercial vehicle counts. For new pavements or rehabilitation works this information will be in the pavement design report. For other works the asphalt supplier will need to be able to show evidence the binder proposed is appropriate based on the traffic for the site. Guidance on calculating the ESAs can be found in the Austroads Guide to pavement technology, part 2 ‘Pavement structural design’ and the associated New Zealand supplement.

Next, the speed which heavy vehicles will be travelling will need to be considered. This can be
different to the posted speed limit particularly for curved alignments or steep climbs. In some cases the traffic speed rather than the ESAs will dictate the grade of binder used. A summary of the binder grades for the various traffic and speed ranges is presented in table 2.

Table 2 – Binder grade selection matrix

Traffic level ESAs Traffic speed range
>70km/hr 20-70km/hr <20km/hr
< 10x106 S H V
10x106 - 30x106 H H V
> 30x106 V V E

Note: Please refer to the specification and guide notes for further details

In general, the binders currently used will slot into one of the four traffic grades, therefore current mix designs should not be affected. It is recommended that the asphalt supplier simply update the binder referred to in their mix designs to an equivalent from the new specification.

Specifying modified binders

There is no need to specify a polymer type and percentage. The specification applies to both straight run bitumen and polymer modified binders (PMBs). It is up to the supplier how to meet the specification, however for some grades, particularly the ‘V’ and ‘E’ grades, the asphalt supplier is more likely to use additives, such as polymers, to meet the properties.

There are times where a type of binder is desirable in surfacing mixes to improve other aspects of performance that are not related to traffic. For example, a PMB in open graded asphalt may be desirable to allow thicker binder films in the mix without the risk of binder drain down.

In these cases a binder grade different to that indicated by the traffic category in table 1 may be needed. It is recommended to consult with the asphalt supplier on an appropriate binder for these situations. Advice on binder selection is also available from the NZ Transport Agency Pavements team.

Quality control

While binders are a significant contributor to asphalt performance it should not be forgotten that selection, mix design, production and construction processes also have a major impact on how the asphalt will behave.

Appropriate levels of surveillance and auditing are recommended to ensure that specifications and the contractor’s quality plan are followed in all areas. For binders, quality assurance requirements are outlined in RNZ 9803 ‘Code of practice: quality assurance of bitumen as binders’ available through the Civil Contractors NZ web site(external link).

Chip sealing and asphalt for local government

Work is underway to develop a similar specification for chip seal binders. In the meantime, the M1 specification will still be available with the full range of penetration grade binder currently specified for chip seals.

Local government is encouraged to adopt the M1-A specification however the current asphalt grades in M1 will be retained for local government users with low traffic levels who have seen good performance with the binders they are currently specifying.

Publication details

Author: NZ Transport Agency – Pavements team
Published: March 2016
Version: 1
Also known as: M1/A, M1-A
Found at: http://hip.nzta.govt.nz/technical-information/pavements/surfacings/surfacing-specifications

Further information

Contact the Highways and Network Operations Pavements team at pavements@nzta.govt.nz.

Kevin Reid

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