Fibers from Recycled Tire as Reinforcement in Hot Mix Asphalt

Previous laboratory and field research has demonstrated that virgin synthetic and cellulose fibers provide important attributes for hot mix asphalt (HMA): reduced asphalt (mastic) draindown during construction for certain types of mixtures, reinforcement which significantly reduces cracking; and, in some cases, reduced rutting. By-product fibers from grinding of scrap tires offer an excellent, low-cost alternative to virgin and cellulose fibers. Currently, most of these fibers are being disposed of in landfills or incinerated. Two types of recycled tire fibers were evaluated to determine whether they can be used in different types of HMA mixtures as a replacement of currently used cellulose fibers or mineral fiber. The researchers tested three different types of mixtures: stone mastic asphalt (SMA), permeable friction course (PFC), and coarse mix high binder (CMHB) mixtures with two different types of recycled tire fibers, one cellulose fiber, and no fiber. HMA specimens were prepared using all of these combinations and tested using several common laboratory test procedures. The laboratory tests used to evaluate the mixtures were: draindown test, dynamic modulus test, overlay test, indirect tensile strength test, and Hamburg wheel tracking test. Mixtures containing tire fibers, in most cases, outperformed the mixtures containing cellulose fiber and mixtures with no fiber. Draindown test results clearly revealed that recycled tire fiber can be used in SMA and PFC mixtures as a replacement for cellulose fiber (or mineral fiber) to prevent asphalt draindown during construction. Researchers examined the availability of by-product tire fibers and found them to be readily obtainable in various parts of the USA. The incorporation of recycled tire fiber into HMA does not require any special technique or equipment beyond that typically used for handling other fiber products. The cost of tire fiber will probably be less than cellulose fiber, particularly when tire fiber is available locally.