• Tuesday, May 21st, 2013

What:  An interlayer is the application of a membrane on distressed pavement surfaces before applying a pavement preservation surface treatment.  There are a variety of commercially available materials and techniques, including non-woven geotextile fabrics, non-woven fiberglass/polyester mats, paving grids (made from materials ranging from plastics to chain metal), asphalt rubber chip seals, polymer modified asphalt chip seals, polymer scrub seals, micro surfacing, highly polymer modified ultrathin fine aggregate hot mix interlayers, fiber/polymer asphalt/aggregate blends, and composites of the materials listed above.  The interlayer may then be covered with most available pavement preservation surfaces, from chip seals to thin HMA overlays, with the choice determined by the type of interlayer, traffic, climate and type of pavement.  Some interlayers are referred to as Stress-Absorbing Membrane Interlayers (SAMIs).

Where:  Interlayers have been used successfully on flexible (asphalt) and rigid (Portland Cement Concrete) pavements with moderate to high severity surface cracking caused by surface oxidation and aging.  They may also be indicated for hot mix asphalt overlays on jointed concrete to prevent reflective cracking from the joints.  Candidates should have a sound pavement structure with good drainage.

Why (advantages):  Interlayers are designed to mitigate reflective cracking, prevent surface water from penetrating into the pavement structure, relieve stresses and increase fatigue life.  Some interlayers will also allow for a reduction in thickness of the proposed overlay by providing stress and/or strain relief for the subsequent surface treatment.  Interlayers can help the new pavement surface last longer and provide a smoother ride throughout the life of the pavement.  They reduce cracking and reduce needed future maintenance, providing lower life cycle costs while preserving pavements.

Why not (disadvantages):  Costs for the various products vary greatly; some can be costly.  Some products may prevent future recycling of the pavement, but newer products have answered those concerns.  Interlayers are not designed to address rutting, bleeding, pumping or structural problems.

When:  Interlayers are appropriate when the asphalt or concrete pavement surface has aged sufficiently to exhibit non-load associated alligator, block, longitudinal, and/or transverse cracking.

Estimated life extension: 6-12 years.

For more information on successful fabric interlayers, consult the Fabric Interlayer Checklist put together by the Foundation and FHWA.

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