LABORATORY EVALUATION OF SELECTED FABRICS FOR REINFORCEMENT OF ASPHALTIC CONCRETE OVERLAYS

Asphaltic concrete overlays are often used in an attempt to restore the riding quality of a roadway and extend its useful life. However, these overlays are susceptible to premature deterioration as a result of transverse reflection cracking, whereby a cracking pattern existing in the original pavement is extended into and through the new overlay. Reflection cracking occurs in new overlays due to their inability to withstand shear and tensile stresses created by movements of the underlying pavement. These damaging movements may be caused by traffic loading, thermally induced contractions of the paving materials, or a combination of these. Various "engineering" fabrics have been used in recent years to provide reinforcement and undersealing for overlays in attempting to prevent and/or delay the occurrence of reflection cracking, and the subsequent penetration of water into the sublayers. Fabrics reduce the amount of water that enters the sublayers of a pavement both by reinforcing and by undersealing the overlay. Reinforcing delays the appearance of the reflection cracking and reduces the width of cracks that develop. Undersealing may not prevent water from entering the pavement structure below the overlay but usually reduces the amount of water that penetrates into the sublayers. Six commercially available engineering fabrics were tested in an effort to develop a reinforced overlay design that could withstand the reflective cracking forces. Laboratory testing consisted of subjecting fabric reinforced laboratory prepared overlay specimens to cyclic tensile loads. (FHWA)