Use of Recycled and Waste Fibers in Asphalt Concrete

Abstract

A significant problem associated with asphalt concrete mixtures is the lack of durability resulting from an inadequate asphalt cement content. Additional asphalt cement added to increase durability results in flushing, bleeding and a significant loss in stability. Fibers have been used in stone matrix asphalt and open-graded friction course pavements successfully throughout Europe to allow higher asphalt cement contents for many years. The presence of recycled and waste fibers in mixtures offer the potential of durable, longer lasting roads. This paper summarizes the findings of two independent studies. One investigation studied four fiber types in an asphalt concrete with a polymer modified asphalt cement to measure the effectiveness of commercial and recycled/waste fibers. All four fibers; commercial cellulose and polyester and waste nylon and ground carpet, were added to an asphalt concrete mixture at the same proportions. Stabilities, air voids and "voids in the mineral aggregate" (VMA) were measured to evaluate mixture properties as affected by the different fiber types. Stripping resistance tests, Resilient Modulus and indirect tensile stress tests were conducted according to the Asphalt-Aggregate Mixture Analysis System (AAMAS) to measure performance of the fiber mixtures. A comparison study was conducted on mixtures compacted to densities simulating the densities achieved at construction. Indirect Tensile Strengths and Resilient Modulus were measured. Evaluation of overall performances of the different fiber types suggests all fibers can be used in asphalt concrete mixtures. The waste nylon fibers and the ground carpet showed a higher VMA and an increase in stability versus the commercial fibers. All of the fibers were effective in increasing the asphalt cement content by 0.3 to 0.4 percent.