Independent RMIT Study: ACE XP™ Aramid Fibre More Than Doubles Fatigue Life and Triples Cracking Tolerance in Stone Mastic Asphalt

New laboratory research from RMIT University in Australia provides independent third-party validation of ACE XP™ performance in plant-produced SMA — with no trade-off in rutting resistance.

Surface-Tech | Technical Insights | September 2025

Asphalt pavements live and die by two performance modes: how well they resist permanent deformation under load — rutting — and how long they hold together under repeated traffic and temperature cycles before cracking and fatiguing. Improving one without sacrificing the other is the perennial challenge of mix design.

New independent research from RMIT University in Melbourne offers a striking answer for Stone Mastic Asphalt (SMA): aramid fibre reinforcement with ACE XP™ delivers dramatic gains in cracking and fatigue performance, with no measurable cost to rutting resistance.

The Study

The work was led by Prof. Filippo Giustozzi, Academic Discipline Leader for Materials and Structures at RMIT, and conducted on plant-produced SMAH10 — a premium Australian wearing-course mix registered under VicRoads. Three mixes were compared under identical conditions, varying only the aramid fibre content: a conventional control, a single-dose ACE XP™ mix at 106 g/tonne, and a double-dose mix at 212 g/tonne.

All three mixes used the same heavily polymer-modified A10E binder, aggregate, gradation, and cellulose drain-down inhibitor at 3 kg/tonne. The asphalt was produced under real-world commercial plant conditions at Fowlers Asphalting in Victoria, providing performance data at production scale. For laboratory mix design and agency QC work, Surface-Tech supplies documented mixing protocols that achieve equivalent fibre dispersion in laboratory conditions.

Tests followed three internationally recognised standards: ASTM D8225 for IDEAL-CT cracking tolerance, AGPT-T274 for four-point bending fatigue, and AASHTO T324 for the Hamburg Wheel Tracker rutting and moisture susceptibility test.

The Results

The IDEAL-CT cracking tolerance index — the headline metric — nearly doubled with a single dose of ACE XP™ and more than tripled with a double dose. RMIT attributes the gain to the fibre's crack-bridging action and improved aggregate interlock, with the asphalt's failure mode shifting from brittle to ductile. Supporting parameters reinforce the mechanism: displacement at 75% of peak load rose from 5.81 mm to 8.28 mm, fracture energy increased from 10,120 to 12,469 J/m², and the post-peak slope dropped from 2.52 to 1.49 kN/mm.

Fatigue performance told a similar story. Under four-point bending at three strain levels — 300, 500, and 700 microstrain — the single-dose mix more than doubled fatigue life at every level tested. The ε₆ value, the strain a pavement can sustain for one million load cycles, rose from 244.1 to 286.3 microstrain. That 17.3% improvement translates directly to extended in-service life under traffic loading and a meaningful delay in crack initiation.

Critically, the Hamburg Wheel Tracker results showed no meaningful change in rutting performance: 3.25 mm of rut depth in the conventional mix versus 3.32 mm in the single-dose fibre mix at 20,000 passes under wet conditions at 50 °C. No stripping was observed in either specimen. Initial flexural stiffness dropped just 9.5% with fibre addition — a difference RMIT characterises as not significant given normal test variability.

Why It Matters

Stone Mastic Asphalt is already the premium wearing-course option in Australia, the United Kingdom, Northern Europe, and parts of Asia-Pacific precisely because of its rutting resistance and durability. ACE XP™ reinforcement extends those advantages into the cracking and fatigue domain — areas where SMA's gap-graded structure can otherwise be vulnerable.

The dose-response data is also useful for specifiers. Single-dose reinforcement gives a substantial uplift for standard high-traffic applications; double-dose pushes the cracking tolerance index more than threefold higher than the unreinforced control, offering an option for the most demanding sites where extending service life and deferring major rehabilitation justifies the investment.

About ACE XP™ Aramid Fibre

ACE XP™ is a high-tensile-strength aramid fibre engineered for asphalt reinforcement. Supplied in pellet form — each pellet containing hair-like fibres approximately 38 mm in length, coated in a wax binder — the fibres release and disperse uniformly when introduced at production temperatures. Once dispersed, they form a three-dimensional reinforcement network within the aggregate and bitumen, bridging cracks before they propagate and improving the mix's ability to absorb deformation energy.

ACE XP™ is supplied by Surface-Tech, manufactured to EPD-certified specifications, and produced in accordance with ASTM D8395-23, the international standard specification for aramid fibre used in asphalt mixtures.