Paving interlayer history

50 years ago, the first geosynthetic interlayer was launched – a needle-punched nonwoven polymer-based paving fabric, such as specified in AASHTO M 288 as Type II.  This technology quickly grew in popularity because it cost effectively provided a pavement moisture barrier and resistance to reflective and fatigue cracking. Today more than one billion square yards have been installed.

Recyclability Concerns

In the last several years, it has become standard practice to mill existing pavement and replace it with new asphalt concrete pavement.  During this process, paving fabric interlayer did not always mill up well and could result in millings that were not suitable for reuse in new asphalt concrete. In some cases this created additional disposal costs. 

Recyclable Alternatives Introduced

In response to these recyclability concerns, manufacturers introduced fiberglass-based interlayers.  Because of their brittle nature, fiberglass interlayers easily mill and recycle.  However, the product’s brittleness also makes it more susceptible to fracturing and tearing during installation.  Glass-based products are also significantly more expensive and do not perform as well paving interlayers.  Several key limitations include the inability to be placed onto milled surface without a leveling course, strength loss from installation damage, and a thin structure that does not hold adequate asphalt cement tack coat.

Consequences

These changing dynamics in interlayer technology have resulted in pavement engineers and owners dissatisfied with the performance and cost effectiveness of the glass-based interlayers.  It has also lead to an unwarranted fear of using traditional paving fabric.  This has slowed the use of the beneficial interlayer technology in the US, causing many overlays and mill-and-fills to install without interlayers. The result is limited pavement service life.

The New Solution—PETROMAT Enviro

In 2019 Propex introduced a state-of-the-art solution—PETROMAT Enviro.  This product is a modified polymer-based paving fabric with all the performance characteristics of the original PETROMAT paving fabric system, but it has been re-engineered to be easily millable and recyclable into new asphalt concrete should the need arise.  The advantages of this technology over glass-based interlayers are; the ability to be placed directly onto any milled surface, the high asphalt retention capacity, the thickness to absorb stresses to minimize reflective and fatigue cracking, and better asphalt concrete performance when recycled.  PETROMAT Enviro is also a more easily installed and cost-effective interlayer solution.