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This paper presents findings of a research study focused on investigating influences of coarse aggregate morphologies on the strength and permanent deformation behavior of unbound aggregate materials. Angularity and surface texture properties of six different types of aggregates were evaluated using two shape indices, angularity index (AI) and surface texture index (ST), based on image analysis. Twenty-one unbound aggregate blends having the same gradation and voids content but different crushed percentages were prepared by mixing the imaging evaluated aggregates and tested using triaxial tests for strength and permanent deformation. The laboratory permanent strain--load application ([[epsilon.sub.p]-N) curves evaluated using a phenomenological power model showed the A and b parameters to be heavily dependent on applied stress levels. Aggregate blends with higher AI and ST indices were consistently associated with lower magnitudes of A and b. The angularity property was found to contribute mainly to the strength and stability of aggregate structure through confinement by bulk stress, whereas the surface texture property tended to mitigate the dilation effects through increasing friction between individual aggregate particles. DOI: 10.1061/(ASCE)0899-1561(2008)20:9(617) CE Database subject headings: Aggregates; Imaging techniques; Deformation; Shear strength; Pavements.

This paper defined a complete set of imaging based indices for different levels of coarse aggregate morphologies, i.e., the flat and elongated (FE) ratio, angularity index (AI), and surface texture (ST) index, and investigated their effects on permanent deformation behavior of hot mix asphalt (HMA). Image analyzed coarse aggregates were used to prepare eighteen Superpave HMA specimens using job mix formulas from ten State highway agencies and tested for permanent deformation at a specified high temperature. The permanent deformation data when linked to the morphological indices of the coarse aggregate, showed the best correlations with the ST index. The FE ratio demonstrated no measurable effects on the permanent deformation due to low percentage of flat and elongated particles used in the mixes. The influences of the AI and ST indices on the permanent deformation were especially significant when differences in the asphalt mix aggregate gradations were properly considered. A possible mechanism of coarse aggregate morphology affecting the stability and permanent deformation behavior of HMA was proposed in terms of particle geometrical interference in HMA. CE Database subject headings: Aggregates; Shape; Asphalt mixes; Deformation.

With a proper approximate solution to the Schrödinger Equation of a multi-electron system, the method ofab initiomolecular dynamics (AIMD) performs first-principles molecular dynamics analysis without pre-defining interatomic potentials as are mandatory in traditional molecular dynamics analyses. The objective of this study is to determine the oxidative-ageing pathway of petroleum asphalt as a typical hydrocarbon system, using the AIMD method. This objective was accomplished in three steps, including (1) identifying a group of representative asphalt molecules to model, (2) determining an atomistic modelling method that can effectively simulate the production of critical functional groups in oxidative ageing of hydrocarbons and (3) evaluating the oxidative-ageing pathway of a hydrocarbon system. The determination of oxidative-ageing pathway of hydrocarbons was done by tracking the generations of critical functional groups in the course of oxidative ageing. The chemical elements of carbon, nitrogen and sulphur all experience oxidative reactions, producing polarised functional groups such as ketones, aldehydes or carboxylic acids, pyrrolic groups and sulphoxides. The electrostatic forces of the polarised groups generated in oxidation are responsible for the behaviour of aged hydrocarbons. The developed AIMD model can be used for modelling the ageing of generic hydrocarbon polymers and developing antioxidants without running expensive experiments. [ABSTRACT FROM PUBLISHER]