Use of DMA to Characterize the Aging of Asphalt Binders: Fid-Bau Portal

Use of DMA to Characterize the Aging of Asphalt Binders

W. H. Daly / I. I. Negulescu / L. N. Mohammad / I. Chiparus

This report presents issues associated with long-term aging of polymer modified asphalt cements (PMACs) as reflected by dynamic mechanical analysis (DMA) data. In this study a standard SBS (styrene-butadiene-styrene block copolymer) polymer modified asphalt cement containing 3% copolymer (PMAC) meeting LADOTD specifications for PAC-40HG and PG 76-22M was selected and subjected to accelerated laboratory aging. Procedures were developed for simulation of long term aging of asphalt binders using multiple pressure aging vessel (PAV) operations in the absence and in the presence of water. Three, five and seven year old field aged asphalt samples originally of similar PMAC composition as that of PG 76-22 listed above were recovered from a wearing course mixture located on interstate I-55 near Granada, MS. All binders were characterized with respect to their composition and rheological properties. The extent of oxidation of both laboratory- and field-aged aged samples was estimated from Fourier transform infrared (FTIR) spectroscopy analysis and non-aqueous potentiometric titration data.. Changes in the molecular mass of the asphalt cement components were estimated from gel permeation chromatography (GPC) measurements. Aging determined a drastic reduction of molecular mass of SBS species and an increase in the content of large molecular species (LMS) asphalt components. Dynamic viscoelastic properties were determined using a high torque instrument. The asphalt architecture has been simulated with that of a gel. The cross-over temperature at which G equals G at a frequency of 10rad/s as temperature increases was considered as the critical temperature, Tc, and chosen as a criterion to assess the advancement of hardening (aging). Oxidative aging in the presence of water promoted an increase in the carbonyl content of aged samples, primarily as acid groups, but the high humidity aging reduced the extent of asphalt hardening. Critical temperature of the field 3 year old I-55 paving sample correlated better with the laboratory wet 0.5xPAV aged PMAC sample, Tc of the field 5 year sample was intermediate between Tc of the dry 0.5xPAV and that of the dry 1.0xPAV laboratory aged PMAC samples and Tc of the field 7 year old sample correlated better with the laboratory dry 1.0xPAV aged PMAC sample. This type of correlation was used to determine if a binder extracted from the damaged LA 3234 Hwy road pavement was excessively aged after three years of service.