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Pavement Air Void Property Determination and Incorporation of Pavement Air Void Properties in Pavement Oxidation Modeling with an Emphasis on X-Ray CT Image Analysis
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Pavement oxidation modeling has been used to predict pavement aging, or more specifically, asphalt oxidation and hardening. A key aspect of such modeling is the transport of oxygen into the asphalt from pavement air voids. To improve upon previous modeling efforts, this work investigated measurement of pavement air void properties and incorporation of air void properties in pavement oxidation modeling. A method for analyzing x-ray computed tomography (CT) images of pavement cores to determine air void properties relevant to pavement oxidation modeling, which relies on only image processing toolbox enabled MATLAB software, was developed. Method variations are applied in each of the studies presented. In a first study, x-ray CT image analysis was applied to validate a new method for measuring total air void (TAV) variation over pavement depth. Pavement cores were cut horizontally to create slices, and TAVs were measured following techniques developed for whole cores. Because the slices are insufficient to meet standard method specimen size requirements, precision was evaluated and alternative maximum theoretical specific gravity methods were compared. A vacuum dryer increased efficiency without oxidizing the binder. Air void distributions compared favorably with x-ray CT measurements. This effort represents a step away from reliance on x-ray CT for pavement oxidation modeling. In a second study, the assumption that only x-ray CT-identified accessible air voids (AAVs) are accessible to oxygen was examined. Analysis of nine field cores shows TAV and AAV variation with depth to be generally similar; nevertheless, two cores had especially low AAV content in their lower slices. Oxidation in these lower slices was not correspondingly low. These results suggest that a recent diffusion depth (dD) oxidation modeling approach may be improved by defining a new dD based on TAVs. Use of a TAV dD provided superior overall predictions. In a third study, the dD approach for incorporating pavement air voids in modeling analysis was compared with another recent approach, the cylindrical approach. The two approaches were compared with a multiyear, multisite set of field data. The dD approach produced field calibration factor values that were closer to theory, and was better able to predict aging variation with pavement depth. Based upon these studies the following future work is recommended: (1) obtain field cores from a pavement aged approximately to the point of failure and study the ability of oxidation modeling to predict the final state of the binder, (2) improve upon the current oxidation modeling approaches by incorporating an oxygen flux at the pavement surface, (3) image cores or core portions using higher resolution x-ray CT, (4) work toward a means for determining the parameters required for oxidation modeling without the need for x-ray CT, and (5) incorporate air void variation with time into oxidation modeling.
Subjectpavement oxidation modeling
pavement air void property measurement
total air voids
accessible air voids
volumetric measurement precision
air voids distribution
core slice air voids
x-ray CT image analysis
core vacuum drying
asphalt carbonyl area
Rose, Avery Atticus (2016). Pavement Air Void Property Determination and Incorporation of Pavement Air Void Properties in Pavement Oxidation Modeling with an Emphasis on X-Ray CT Image Analysis. Doctoral dissertation, Texas A & M University. Available electronically from
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