Comparison of Coarse Matrix High Binder and Dense-Graded Hot-Mix Asphalt

Coarse matrix high binder (CMHB) is a gap-graded hot mix consisting of a large proportion of coarse aggregate with an asphalt binder-filler mastic. CMHB and dense-graded mixtures were compared in terms of their resistance to rutting (permanent deformation), moisture damage, aging, and water permeability. A static creep test was performed to evaluate relative rutting susceptibility. Moisture damage was assessed with the tensile strength ratio (TSR) and a boiling-water test. The effects of aging were evaluated with indirect tensile strength and resilient modulus testing. Penetration and complex shear modulus (G*) of the recovered, aged asphalt were measured. Permeability was determined with Darcy's Law for flow through saturated, porous media. The static creep test did not indicate that CMHB mixtures were consistently more resistant to rutting in comparison with dense-graded mixtures. CMHB mixtures were found to be more resistant to moisture damage, which was indicated by higher TSR values and less visible stripping than corresponding dense-graded mixtures. The dense-graded mixtures exhibited higher resilient moduli and indirect tensile strengths after short-term and long-term aging. Penetration of binder extracted from aged CMHB mixtures was greater than that from dense-graded mixtures. Binder extracted from aged dense-graded mixtures exhibited higher G* values. The permeability of CMHB mixtures was greater than that of the dense-graded mixtures with comparable air voids.