One of the most cost effective ways to increase the service life of a pavement system is the utilization of a pavement interlayer geotextile
during pavement resurfacing.
By John Lostumbo, Director of Technical Marketing, TenCate Geosynthetics
The American Society of Civil Engineers (ASCE) Report Card for America’s Infrastructure gave a grade of D to America’s Roads. “Over 42% of Americas roads are congested costing the economy an estimated $101 billion in wasted time and fuel annually.” It is estimated that over $170 billion needs to be spent annually just to maintain America’s roads and bridges (ASCE Infrastructure Report Card). The 2015 Transportation Reauthorization and Reform Act of 2015 provides only $46 billion per year. These kinds of budget deficits require innovative solutions to provide more efficient and sustainable road system solutions. One technology that can provide efficient and longer lasting pavement systems are geotextiles. Geotextiles offer multiple solutions to pavement construction and rehabilitation, including: cost effective ways to address soft soil conditions, manage drainage in pavements, provide reinforcement to the pavement system and solutions for rehabilitation and overlays of existing pavements.
Many pavement systems throughout the world are now long past the intended service life of the system. As these roads deteriorate, public agencies are struggling with declining budgets but increasing maintenance requirements of these crumbling roads. Geotextiles can provide several solution options in many different methods, often increasing service life on the order of 20-50% depending on project conditions. One of the most cost effective ways to increase the service life of a pavement system is the utilization of a pavement interlayer geotextile during pavement resurfacing.
Pavement interlayer geotextiles are typically made from nonwoven geotextiles. Often these nonwoven geotextiles are produced by needle punched staple polypropylene (PP) fibers. Interlayer geotextiles can be used effectively when overlaying (resurfacing) concrete, asphalt or composite pavement systems. They are also very effective in chip seal applications in lower volume road systems.
Pavement interlayer geotextiles provide significant economic and performance benefit to pavement systems, however, selecting the correct material and method of resurfacing is paramount to sufficiently extending the life of the pavement. The most common method of traditional resurfacing projects is utilizing a bonded overlay system. In a bonded overlay system, the interlayer geotextile is adhered to the underlying existing pavement using a tack coat prior to resurfacing. The surface overlay is then placed and creates a bonded system where the new overlay is adhered to the underlying pavement system. The key to a bonded overlay system is the underlying existing pavement system that is contributing to the structural performance of the new composite system. In order for satisfactory performance, the existing pavement system condition must be sufficient enough to still provide structural support. Unfortunately, in some cases, a bonded overlay system is utilized when the existing pavement section is in fair to poor condition. In these situations, premature deterioration and reflective cracking could occur in the new overlay. This would be an inefficient use of limited maintenance dollars. In order for the highway system to get ahead of this maintenance crisis, the rehabilitation ratio of dollars spent versus service life of the system must increase. If the underlying pavement is too deteriorated for the more conventional bonded overlay system an unbonded overlay should be considered.
Unbonded concrete overlay systems are a relatively new technology. First utilized in Germany and now utilized in multiple countries throughout the world, it provides a cost-effective solution to resurfacing pavements in poor conditions. The system utilizes a heavyweight nonwoven polypropylene needle punched geotextile (14 oz./sy) to act as the bond breaker and drainage material between the old pavement and new unbonded concrete overlay. The geotextile is installed directly on top of the existing concrete pavement and is mechanically secured using bolts and washers.
Concrete overlays previously utilized approximately 1 inch of hot mix asphalt (HMA) between the existing pavement and the new concrete overlay system. This asphalt layer acts as a bond breaker between the two systems for improved performance. It has been found that a better solution to using HMA is to use a nonwoven geotextile bond breaker. The benefits are lower material cost compared to HMA, better performance and a faster installation. This process has been endorsed by the Federal Highway Administration, AASSHTO and the National Cooperative Highway Research Program.
The bond breaker geotextile is specifically engineered to perform several functions. First, it must meet specific permeability requirements. The geotextile must be able to move water in-plane and under load. It is important that the geotextile can move water out and away from the pavement layers. Second, the geotextile prevents the bonding of the new and old pavements. Lastly, the geotextile provides a shear plane that mitigates reflective cracking of the new pavement surface.
Unbonded concrete overlays using geotextiles provide significant cost savings. Recently, Interstate I-16 had to be replaced by the Georgia Department of Transportation. Approximately 30 miles near Dublin, Ga. required full replacement and utilized TenCate Mirafi® 1450BB bond breaker nonwoven in lieu of a hot mix asphalt separation layer. The Mirafi 1450BB allowed for faster installation, a reduction in material cost and material transportation. The bond breaker geotextile provides improved drainage and helps to manage water infiltration in the system, particularly at the pavement joints. The construction was performed in 4 mile increments and the bond breaker geotextile allowed for expeditions and economical construction in regard to preparation, pouring, curing and re-opening of the lane sections. The Mirafi 1450BB provided a saving of approximately $7.50/SY of lane area, with over 1,400,000 square yards installed, the use of this technology saved the state of Georgia approximately $10,500,000.
Many pavement systems throughout the world are in service well beyond their intended service life. Due to tightening budgets, maintenance schedules for pavements often are not able to keep up with the demand of deteriorating pavements. This results in more and more pavements falling into the fair to poor classification condition assessment. These roadways are excellent candidates for unbounded overlay treatments. Instead of doing a very costly full depth reclamation of the pavement system, an unbonded overlay could be an economical and faster solution. The use of a nonwoven geosynthetic bond breaker only improves upon this rehabilitation method at significant savings to the road owner.
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