Study of Asphalt and Polymer-Modified Asphalt: Microstructure, Compatibility and Reinforcement Effect.
Date of Award
Doctor of Philosophy (PhD)
William H. Daly
Eight asphalt samples with grades ranging from 10 to 30 from four different sources were examined using NMR, FTIR, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and constant stress rheometry (CSR). The crystallization process of asphalt is very time dependent. Slow heating or annealing before analysis in order to experimentally realize a close-to-equilibrium state is necessary in order to study the system with more thermodynamic rigor. The DSC method developed in this research shows a possible application in asphalt identification with respect to crude and manufacture source. Dynamic mechanic analysis shows in asphalts only those segments primarily composed of linear aliphatic units contribute to the glass transition process. Note that at 50 Hz all asphalt samples cracked at temperature above their Tg at the same frequency, which implies that Tg can be considered the limit of brittle temperature of asphalt when the loading frequency and the frequency under which the Tg is measured are the same. The eight asphalt samples shows characteristics of pseudoplastic substance at temperature lower than 100$\sp\circ$C. Activation energy analysis of the viscous state of the asphalts reveals that a three dimensional network that extends throughout asphalt may exist via molecular interactions. Maleic anhydride grafted polyethylenes were synthesized through both solution and melt reactions in the presence of free radical initiators and characterized with FTIR, NMR and DSC. Copolymers of maleic anhydride and aliphatic alpha olefins with carbon atom numbers from eight to eighteen were prepared and characterized. Among the alpha olefins used in this research, the olefin having more carbon atoms will have higher ratio in the copolymer composition when the feeding ratio is higher than two (olefin: maleic anhydride). The copolymers probably have an alternating or close to alternating structure. The chlorinated polyethylene and maleated polyethylene prepared in this lab and used in present study prove to be better asphalt modifiers than polyethylene, since most of them can show better results in increasing strength and elasticity at higher temperatures or lower frequencies, and are less temperature or frequency sensitive. Chlorinated polyethylenes containing less than 15 wt% chlorine interact more extensively with an asphalt matrix than that of polyethylene. The maleated polyethylene is more compatible with asphalt through chemical bonding and dramatically increased creep recovery capability of the asphalt. Low molecular weight copolymers of maleic anhydride and aliphatic alpha olefins can reduce crystallinity of the asphalt quite significantly. Chemical bonding of the copolymer additives to the asphalt molecules through the anhydride group is a favorite factor in reducing the crystallinity of the asphalt.
Qiu, Zhaoyao, "Study of Asphalt and Polymer-Modified Asphalt: Microstructure, Compatibility and Reinforcement Effect." (1994). LSU Historical Dissertations and Theses. 5812.