High Modulus Asphalt (EME2) – Is it fit for purpose?

High Modulus Asphalt or more commonly referenced as EME2 is a developing Australian derivation of a French heavy duty asphalt mix ‘enrobés à module élevé’.

The use of EME2 is aimed at substituting the use of conventional dense graded material (i.e. AC20 – C600 binder) on heavily trafficked, high priority highways and motorways.

The recent advances in pavement technology have identified the benefits of this mix, characterised by enhanced fatigue and deformation resistance and increased constructability. From a design perspective, the use of EME2 is anticipated to exceed the performance of traditional AC20 asphalt mixes for reasons including:

• High relative binder content (≥6% by mass) – Provides enhanced elasticity and elastic response to repetitious wheel loadings
• Stiff, Highly Modified Binder (10-25 Penetration) – Provides additional stiffness to the mix, increasing the design modulus and reducing the resulting critical strain under each standard axle repetition
• Low Air Voids (≤6%) – Provides additional stability to the mix and reduces the likelihood of rutting or shoving in the asphalt layer under heavy traffic loading

In addition to the points above and with reference to the mix composition and relatively low air voids, Queensland Department of Transport and Main Roads (QDTMR) have outlined compacted layer thicknesses up to the 30% greater than the conventional AC20 counterpart.

In a similar context, it is recognised that whilst EME2 exhibits superior characteristics from a theoretical perspective, however there are a number of limitations that currently apply for its use, including:

• Subgrade Support – QDTMR’s current design procedure requires a minimum subgrade support of 70 MPa (CBR 7%) for the working platform to ensure the stringent compaction requirements are met.
• Production and Availability – Given the relatively recent approval of the mix, the use of EME2 has been limited to localised areas and trials and has not comprehensively demonstrated mix availability or contractor capability.
• Cost – Whilst it is anticipated that EME2 can reduce total asphalt thicknesses between 20 and 30%, the economic viability for its use may not be demonstrated in construction savings, particularly in its early stages of use.

When considering the use of EME2 in a pavement design application, the whole of life costs should be analysed in conjunction with suitably qualified contractors to ensure capability and compliance.

For more information on Global Road Technology High Modulus Asphalt (EME2) please contact GRT.