Tensar InterAx® NXAC™ Underlayer Geogrid: Advancing Asphalt Concrete Performance

Risks to pavement performance often begin where the asphalt concrete interfaces with the supporting base layer. Fatigue cracking can emerge sooner than expected, especially when the pavement experiences high loads or when pavement’s foundation lack uniformity. The industry has long needed a smarter, more efficient method to address these uncertainties to improve asphalt performance.

Tensar developed the new InterAx NXAC Underlayer as an alternative to traditional interlayers that are placed between layers of asphalt concrete and geogrids that are placed below or within aggregate base layers. The purpose of the InterAx underlayer is to seamlessly integrate with and enhance traditional rehabilitation methods of “mill and fill”, full depth reclamation or complete reconstruction.

The Underlayer consists of an InterAx geogrid bonded to a heat treated nonwoven geotextile. Contractors will place the Underlayer at the interface between the pavement foundation and hot-mix asphalt concrete.

Engineered for Better Outcomes

Confining the aggregate within the asphalt, NXAC underlayer:

• Increases rutting resistance
• Improves lifetime fatigue 
• Enhances reflective crack mitigation

There is no other product that provides the overall performance improvement of InterAx NXAC. It reduces strain at the bottom of asphalt layers, resulting in long-term enhanced pavement performance, and reduced maintenance costs over time.

Putting NXAC™ underlayer to the test

Tensar’s new product development process includes a variety of validation methods, including: 

• Laboratory testing 
• Field trials 
• Numerical modelling 
• Accelerated pavement testing 
• Real-world validation

To validate our testing and observed performance, Tensar is partnering with select clients to test NXAC on specific projects.

Tensar’s GeoVision™ technology, which employs energy harvesting techniques, wirelessly captures and reports strains within a pavement system. By installing a section of NXAC underlayer alongside a comparable unstabilized section in the same trafficked area, the effect of NXAC in reducing strain on the system can be assessed. NXAC installations with GeoVision technology already show substantial benefits to pavement life relative to control sections. NXAC validation for structural quantification is ongoing through full-scale accelerated pavement testing that is expected to be completed in 2026. However, due to early positive performance results and market demand, Tensar is offering this product to the market on a limited basis.

NXAC validation for structural quantification is ongoing through full-scale accelerated pavement testing that is expected to be completed in 2026. However, due to early positive performance results and market demand, Tensar is offering this product to the market on a limited basis.

Data that Drives Confidence

Tensar’s research shows the optimized geometry and advanced material science of the NXAC underlayer promotes lateral confinement of the aggregate within the asphalt concrete matrix, limiting the formation of cracks, and extending pavement life.

Using constant stress fatigue, a loaded wheel tracker lab test showed asphalt concrete fatigue life improvement ranging between 89 to 102%. The NXAC-stabilized sections had a maximum crack width of ¼ inches, while the unstabilized sections had cracks ranging from ¼–¾ inches.

Tensar Recognized for Pavement Innovation

MR Tanner received an award, given by Southwest Pavement Technology Consortium, at the 2025 Arizona Pavement Materials Conference.

The City of Phoenix’s submission spotlighted the use of InterAx NXAC Underlayer for its Grovers Street Overlay project. The project included construction of a test section using InterAx NXAC underlayer alongside a control section to measure performance differences over time.

Getting Results

Learning about NXAC and how it performs in varying paving thicknesses is ongoing so no detailed calculation was provided. Tensar lab results show that the NXAC pavement section is 3 to 6 times more resilient and longer lasting than the regular pavement section.

Tensar. For Strength You Can Build On.

Pavement durability is determined well before the first lift of asphalt is placed. Our InterAx NXAC Underlayer is a proven way to strengthen asphalt concrete helping you improve performance, reduce long-term maintenance, and deliver a better return on investment.

To learn more about NXAC, contact Tensar today.