An evaluation of interlayer stress absorbing composite (ISAC) reflective crack relief system

1006336Final reportPDFResearch PaperFHWA/IL/PRR 150Physical Research No. 150NTIS-PB2006102781IHR-R07Asphalt concreteBituminous concrete pavementsBituminous overlaysCost effectivenessCostsEvaluationGeotextilesPavement jointsPavement layersPavement maintenanceRehabilitation (Maintenance)StressesIllinoisIllinois. Dept. of Transportation. Bureau of Materials and Physical ResearchVespa, Joseph W.Illinois. Dept. of Transportation. Bureau of Materials and Physical ResearchUS Transportation CollectionReflective cracking of bituminous concrete overlays has long been a problem in pavement rehabilitation. Various types of interlayer systems and fabrics have been used to eliminate or slow the development of reflective cracks. These methods and products have had mixed results. In 1993, the University of Illinois completed research directed by the Illinois Department of Transportation on a prototype Interlayer Stress Absorbing Composite (ISAC). A prototype test section was placed on IL 38 near Rochelle, IL in 1993. Other ISAC test sections were placed on five asphalt concrete overlay (ACOL) projects between 1997 and 2000. Some of these ACOL sections contain other reflective crack control methods, such as Sand Anti-Fracture (SAF) layer, strip, and area-wide reflective crack control fabric. ISAC consists of a three-layer system. The top layer is a high strength woven geotextile to resist stresses caused by underlying pavement movements. This layer has the ability to, due to its weaving, expand like a chain link fence. This movement dissipates the stress caused by the movement of the underlying pavement. Typically, this geotextile has a tensile strength greater than 4,000 lb. /in. (700 N/mm) at 5% strain (ASTM D 4595). High strength is needed to ensure that, when the geotextile is expanded to its full extent, the geotextile strength is greater than the strength of the bituminous concrete overlay. The bottom layer is a low strength, nonwoven, geotextile (meeting AASHTO M-288-92). The middle layer is a modified rubberized asphalt layer to absorb the strain energy and bond the two geotextiles together. The system bridges across the joint or crack and dissipates stresses resulting from opening or closing movements. ISAC is bonded to the existing pavement using a tack coat and then the overlay is placed. The formation of reflective cracks and the subsequent deterioration of these cracks were delayed at ISAC treated joints and cracks. This statement was true for all five test sites. This delay ranged from over one year to close to three years when compared to the untreated and other crack control methods. Of special note, the ISAC areas consistently outperformed the System B products, PavePrep and Roadtac. When compared with SAF, the ISAC delayed reflective cracks by about two years. The two sections performed the same after the cracks were routed and sealed. The cost analysis indicated that the higher the total cost of the asphalt concrete the higher the number of cracks and joints that could be treated with ISAC. The present cost of the ISAC strips, $10 - $14 per foot, limits the conditions under which it would be cost effective to use ISAC. If asphalt costs are high or the cost of ISAC were to decline, there would be more projects that could benefit from using ISAC. Described herein are details of the various experimental field installations and a discussion of performance and results. Recommendations for the use of ISAC are included. /Abstract from report summary page