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Physicochemical Interactions at the Binder-Aggregate Interface
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Asphalt mixtures undergo chemical and mechanical changes with environmental weathering, most specifically due to moisture damage and oxidative aging. Degradation through weathering compromises asphalt mixture integrity and leads to early failure. It has been reported that potential for moisture damage is related to physicochemical properties of binder, aggregate, and resulting interface. Oxidative aging literature suggests that the aggregate could be a catalyst to the oxidation process and/or that the aggregate could selectively absorb softer functional groups from within the asphalt binder, resulting in an additional age-hardening effect of the asphalt mixture. This study characterized mechanical and physicochemical properties of asphalt binders and aggregates and resulting mechanical responses of corresponding asphalt mixtures subjected to moisture and aging effects. The experimental plan involved 20 binder-aggregate combinations including warm-mix asphalt technologies, neat and polymer-modified binders, and two aggregates with different mineralogies and morphologies. Experiments were conducted at various length scales: full mixtures, fine aggregate mixtures, asphalt binder, and aggregates. Additionally, this study proposes a modified microcalorimetry experiment to evaluate binder-aggregate interaction over the range of in-service temperatures and with moisture present at the interface. This study concludes that physicochemical characteristics of the binder-aggregate interface and aggregate microtextural features affect moisture damage. It was found that increasing temperature reduces binder-aggregate bond strength and that a uniform layer of moisture prevents binder-aggregate interfacial bonding. Inclusion of warm-mix asphalt additives with adhesion promoters can improve mixture performance in terms of moisture resistance, and additive dosage should be optimized. In terms of age-hardening, it was found that warm-mix asphalt can exhibit greater age-hardening in the first 3 months of laboratory aging, but longer-term aging is comparable to that of hot-mix asphalt. Additional findings conclude that aggregate type can significantly alter the age-hardening process of asphalt mixtures. Gabbro aggregate catalyzes the oxidation process of the asphalt binder, while inclusion of limestone aggregate produces increased stiffening of the asphalt mixture, possibly due to selective absorption. Based on these findings, it is recommended to pursue a deeper understanding of an interphase region formed due to binder interlocking with the aggregate surface and with diffusion of binder into the aggregate.
Garcia Cucalon, Maria Lorena (2016). Physicochemical Interactions at the Binder-Aggregate Interface. Doctoral dissertation, Texas A & M University. Available electronically from