Aging of bituminous binders in asphalt pavements and laboratory tests

Abstract

Aging of bituminous binders is one of the key factors affecting the performance and durability of asphalt pavements. To simulate binder aging in laboratory, a number of methods are available. In this paper, RTFOT (Rolling Thin-Film Oven Test), PAV (Pressure Aging Vessel) and RCAT (Rotating Cylinder Aging Test) using different aging times and temperatures were employed to age two straight-run bitumens and a styrene-butadiene-butadiene (SBS) polymer modified binder. For field aging, a number of asphalt pavements of different years in service were investigated. The binders (virgin, laboratory aged, and extracted from asphalt pavements) were evaluated by penetration and softening point tests, rheological measurements with a Dynamic Shear Rheometer (DSR), as well as chemical analyses using Fourier Transform Infrared Spectroscopy (FTIR) and Gel Permeation Chromatography (GPC). It was confirmed that the rheological changes upon laboratory aging and the formation of chemical functionalities were strongly temperature dependent. Great differences were found between the unmodified and SBS polymer modified binders in the rheological response upon aging. For the modified bitumen, different chemical reactions of the two components (bitumen and polymer) may compensate each other in some ways, making the binder less age-hardening and more durable. Apparently, the standardized PAV and RCAT simulate about 10 years of field aging for the unmodified bitumens when used in a dense asphalt surface layer, but for open graded mixes a longer PAV or RCAT aging time is necessary. However, for polymer modified bitumen the relationship between laboratory and field ageing when studying both mechanical and chemical compositional changes is less trivial.