Assessing Moisture Susceptibility of Open-Graded Friction Course Mixes Containing Styrene-Butadiene-Styrene and Epoxy Modified Asphalt Binders under Varied Aging and Moisture Conditioning Levels

Open-graded friction course (OGFC) is a thin asphalt mixture surface layer designed primarily to improve the functionality of a roadway. It is designed with a special aggregate structure with high air voids and stone-on-stone contact that accelerates rainwater drainage. It has many advantages, such as reducing hydroplaning, splashing, and spray, and enhancing roadway visibility and skid resistance under wet weather conditions. However, these mixtures exhibit premature failures and moisture damage that limit their usage in pavement construction. Further, the current specifications might inaccurately reflect field conditions. Therefore, this study was aimed at evaluating and comparing the effect of various asphalt binder types on the performance of OGFC mixtures under different aging and moisture conditions. Three types of asphalt binder were utilized: conventional styrene-butadiene-styrene asphalt binder performance grading (PG) 76-22M and diluted epoxy asphalt (EA) binder with two different dosages. A suite of physical and mechanical tests was conducted to evaluate OGFC mixtures, namely, draindown, permeability, Hamburg wheel tracking (HWT) test for rutting and moisture susceptibility, Cantabro abrasion loss test for durability, semi-circular beam (SCB) for fracture resistance, and indirect tensile strength (ITS) test for tensile strength and moisture susceptibility. Results indicated that EA mixtures exhibited improved draindown results, compared with 76M mixture. Further, the developed cross-linked network associated with EA binder might explain the improved rutting and abrasion loss resistance. EA mixtures showed significantly better moisture resistance, as measured by HWT, ITS, and SCB tests. Cost-effectiveness ratio results showed higher effectiveness for EA mixtures than conventional 76M mixture.