Spectrometric Investigation of Aged Polymer-Modified Asphalts

Oxidative aging of asphalt pavements occurs due to diffusion of atmospheric oxygen into asphalt followed by radical chemical reactions. Chemical changes due to oxidation result in increase of asphalt viscosity, or hardening. Hardening of asphalt increases its susceptibility to cracking and moisture damage, thus reducing riding quality and service life of asphalt pavements. While it has been agreed that polymer-modified asphalts (PMA) improve performance of flexible pavements, more research needed to evaluate their long-term performance and resistance to oxidation. Furthermore, laboratory procedures developed for simulating long-term aging of non-modified asphalts often fail to adequately rank performance of PMA. Those laboratory procedures are also expensive, time-consuming, and hazardous in terms of personnel health and safety.;This dissertation employs recent advances in spectroscopic testing of asphalts and simulation of asphalt aging to 1) investigate chemical changes in aged PMA and the effect of aging on their long-term performance and 2) develop a compact accelerated aging procedure capable of adequate performance ranking of modified and non-modified asphalts. Infrared spectroscopy, gel permeation chromatography, and nuclear magnetic resonance are utilized to compare chemical composition of unaged and aged PMA samples in laboratory, while viscoelastic properties of asphalts are evaluated using dynamic mechanical analysis. Statistical analysis of spectroscopic and mechanical testing results is employed to develop regression models for predicting viscosity of aged PMA from its chemical composition. The analysis of variance reveals that severity of aging procedure affects PMA viscosity greater than polymer composition and concentration do. Furthermore, it appears feasible to predict dynamic viscosity of PMA at a given temperature and aging test severity from relative content of oxidized functional groups and polymer composition elucidated from infrared spectrum.;A compact aging apparatus proposed in this dissertation uses a compact Attenuated Total Reflection spectrometer and airflow Aging Cell (ATRAC) equipped with a temperature controller to oxidize ultrathin asphalt samples within an hour. Preliminary results show a good correlation between oxidation rates of binders aged by the ATRAC and oxidation rates of asphalt mixes collected from the existing pavements in Connecticut and Rhode Island. Furthermore, oxidation rates induced by ATRAC system can be used as an alternative ranking parameter for performance grading of asphalts.