Experimental Placement of Stone Matrix Asphalt Project STP-8724 (00) X South Portland January 2004

In September 2003 the Maine Department of Transportation used stone matrix asphalt and Superpave to renovate two intersections in South Portland, Maine. The experimental placement of stone matrix asphalt (SMA) and Superpave with modified binder was a part of pavement project STP-8724(00) X. The primary focus of this experiment is to look at the rutting resistance of SMA versus Superpave with modified binder. SMA mixtures consist of a large coarse aggregate content, fine aggregate, high filler content, asphalt cement with or without a modifier and usually a cellulose or mineral fiber. These mixtures contain a large coarse aggregate content (approximately 70 percent) and enough fine aggregate to help fill the voids in the coarse aggregate. The strength of this mix is gained from stone on stone contact. This mix is designed to have 3-4 percent air voids, and it has a relatively high asphalt content due to the high amount of voids in the mineral aggregate. The mix contains a high filler content (approximately 10 percent passing the No. 200 sieve), and it typically contains a polymer in the asphalt cement or fiber (cellulose or mineral) in the mixture to prevent drainage of the asphalt cement. This mixture has a surface appearance similar to that of an open graded friction course, however it has low in-place air voids similar to that of a dense graded HMA. The high asphalt content produces a mixture that is easily compacted and that should be durable. If the asphalt content is excessive it will tend to push the aggregate apart and prevent stone on stone contact. An asphalt content that produces 3-4 percent air voids in laboratory compacted samples is desirable. The intersections are at the junction of Route 1 and Turnpike Spur (703) and the junction of Route 1 and Westbrook Street. The pre-existing pavement conditions had moderate rutting and cracking. The goal of the experiment is to compare how the SMA and Superpave perform relative to each other.