Interlayer Stress Absorbing Composite (ISAC) for Mitigating Reflection Cracking in Asphalt Concrete Overlays

1979191PDFTech ReportUILU-ENG-96-2006Reflection crackingOverlays (Pavements)Properties of materialsGeosyntheticsGeotextilesAsphalt cementCrumb rubberComposite materialsLaboratory testsMukhtar, Muhammad T.Dempsey, Barry J.University of Illinois at Urbana-Champaign. Dept. of Civil EngineeringUnited States. Federal Highway AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-MaterialsUS Transportation CollectionTo approach the reflection cracking problem in AC overlays systematically the properties of the materials intended to be used in an ISAC system were first identified. Various thermal/structural models and laboratory equipment were used for this purpose. A number of woven and nonwoven geotextiles were selected and tested for their engineering properties such as tensile strength, initial modulus, modulus at failure, and percent shrinkage. Several samples of rubber asphalt were prepared by blending different ratios of crumb rubber with various types and ratios of asphalt cements at 400 F. These rubber asphalts were tested at different temperatures and the effects of temperature and rate of deformation on their stiffness were evaluated.An interlayer stress absorbing composite, ISAC layer was fabricated in the laboratory using the materials considered appropriate. Testing equipment was developed to evaluate the interfacial shear strength and laboratory testing was performed to determine the shear strength of the fabricated ISAC layer under an AC overlay. The ISAC layer was evaluated for its effectiveness against reflection cracking. A laboratory pavement section with an AC overlay over a jointed PCC slab was constructed and placed in an environmental chamber. A mechanical device was used to simulate thermal strain in the slab and the joint was opened and ciosed at an extremely slow rate. The testing was conducted at 30F and deterioration in the overlay was monitored using a sensitive LVDT device.The results from the laboratory evaluation testing program indicated that the ISAC layer was highly effective in preventing reflection cracking in a 2.5 in. AC overlay. When compared to a control test section and a section using a commercially available reflection cracking control material the ISAC layer provided for superior performance. A field pavement test section utilizing the ISAC layer was constructed in the Summer 1994 and field evacuation is ongoing