Doctor of Philosophy (PhD)
A PG 76-22 Polymer Modified Asphalt Cement composition was subjected in the laboratory to accelerated aging using both a standard Thin Film Oven Test and a Pressure Aging Vessel. Conditions simulating wet atmospheres (PAV in saturated water vapors) as well as very long service terms (multiple dry and wet PAV operations) were studied. A Rotating Cylinder Aging Test has been employed as an alternate asphalt aging technique using the same PMAC composition in order to observe the initial phases of the oxidative aging process. The data provided by this technique was correlated with the actual aging in the field of asphalt pavements. The extent of oxidation and changes in the molecular mass of the asphalt cement components of aged samples were estimated using Fourier Transform Infrared Spectroscopy data, Potentiometric Titrations and Gel Permeation Chromatography analyses. FTIR data show that multiple PAV and RCAT aging introduced polar carboxylic acid oxygen species. PT analysis identified the presence of sulfonic acids in commercial PMACs, apparently derived from sulfur used in preparing the blends. GPC data show that even after extensive RCAT aging the polymer did not degrade significantly. In contrast, the polymer is rapidly crosslinked or degraded by PAV or field aging. In order to obtain a better understanding of the role of radicals during oxidative processes both under dry and wet conditions, the chemical impact of aging of PMAC components has been modeled using a cobalt naphthenate/cumene hydroperoxide redox system to generate free radicals. Under these conditions, the polymer served as a sacrificial antioxidant and protected the asphalt components from oxidation. Viscoelastic properties of asphalts were determined from dynamic shear measurements using a high torque instrument. The cross-over temperature at which G" equals G' as temperature increases was considered as the critical temperature and chosen as a criterion to asses the advancement of hardening (aging). The oxidative aging in the presence of water promoted an increase in the carbonyl content of aged samples, primarily as acid groups. Aging in the wet atmosphere had also a retarding effect on asphalt hardening.
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Glover, Ionela Chiparus, "Wet and dry aging of polymer-asphalt blends: chemistry and performance" (2007). LSU Doctoral Dissertations. 2747.
William H Daly