Laboratory Study of Large Stone Asphalt Mixtures

LABORATORY STUDY OF LARGE STONE ASPHALT MIXTURES Mohammad, Louay, N.;Huang, Baoshan;Abadie, Chris;Raghavendra, Amar

Abstract

Large stone asphalt mixtures (LSAM) generally refer to hot mix asphalt mixtures with nominal aggregate sizes greater than 25-mm (1-in.). The philosophy of using LSAM in pavement is to provide better stone-on- stone contact within asphalt mixtures and thus reduce rutting. Dense or stone-filled LSAMs are mainly used as asphalt base mixtures, whereas, open-graded LSAMs are considered as drainable base layers that can sustain construction traffic. The paper describes the findings of a laboratory study of LSAM carried out at the Louisiana Transportation Research Center (LTRC). Two types of large stone asphalt mixtures: an open-graded LSAM, and a 37.5-mm (1.5-in.) Superpave mix were designed based on both volumetric properties and engineering performance tests. These two mixtures were compared to their corresponding conventional Louisiana Type 508 drainable base mix and Type 5A base mix respectively, through laboratory performance tests. The performance tests considered include indirect tensile strength tests, axial creep test, Asphalt Pavement Analyzer rut test, Superpave frequency sweep at constant height, and permeability test for open-graded LSAM and Louisiana Type 508 drainable base mix. The test results indicated that the open0graded LSAM showed better rut-resistance and durability than the conventional Type 508 drainable base mix while still maintaining permeability. The 3705-mm Superpave base mix exhibited improved performance as measured from the axial creep test and similar performance as measured from the other performance tests when compared to the when compared to the conventional Type 5A base mix.