Analysis of Inherent Anisotropy in asphalt Concrete mixtures
Creators: name: Zakariyas Mussie Amanu
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2022
Subjects: Asphalt Concrete, Aggregates, inherent anisotropy, orientation, internal structure, Vector magnitude, X-ray CT images

description: Asphalt Concrete mixtures were characterized by one of mechanistically modeling technique, inherent anisotropy of the material. The performance of AC<br> mixtures is influenced by the arrangement of aggregates and their associated<br> air voids. The main objective of this study to analyze aggregate orientation<br> and evaluates inherent anisotropy in AC mixtures using X-ray CT images<br> by means of microstructure parameter. There are three AC mixture designs:<br> coarse graded CMHB Type C, gap graded PFC and fine graded Superpave<br> Type C AC mixtures. They are prepared with hard limestone aggregate and<br> compacted with SGC, having a PG 76-22 modified binder.<br> Digital image processing algorithm is adopted for this study to process X-ray<br> CT scanned images and effectively separate the connected or overlapping aggregates using MATLABr 2018b, image processing toolbox. It includes for<br> both coarse and fine aggregate particles ranging from 1.18 mm to 19 mm. The<br> aggregate orientation, size and area can be used to define internal structure<br> parameters (i.e., modified Vector magnitude) to evaluate inherent anisotropy<br> of AC mixtures.<br> Aggregates have three dominant average orientations having 20% of the aggregates has an inclination angle between (-10o-10o), 65% of the aggregates<br> have an inclination angle between (-45o-45o) and 15% of aggregates have<br> an inclination angle between (-45o-90o) for three AC mixtures. Small inclination angle indicates the aggregates lies flat in the horizontal direction that<br> is perpendicular to the compaction direction. In addition, statistical analysis was performed for AC mixtures within AC layers. It results, aggregate<br> orientation varies within AC layers. Variation of aggregates orientation is<br> performed using Scheffe multi-comparison test.<br> Vector magnitude is an internal microstructural index, which is used to quantify the average inherent anisotropy of AC mixtures. For three AC mixtures;<br> a Vector magnitude doesn’t exceed a value of 0.25 as well as modified Vector<br> magnitude value of 0.6. The composition of aggregates for CMHB Type C is<br> coarse, for PFC is a gap and for Superpave Type C is fine graded aggregates.<br> Due to this, for three AC mixtures; CMHB Type C has greater microstructural<br> parameter than PFC and Superpave Type C AC mixtures. Based on the results, the undamaged zero month aging AC mixtures was inherently anisotropic. Aggregate morphological properties (i.e., orientation,<br> area and aspect ratio) increase microstructural parameter than considering<br> only orientation of aggregates to quantify inherent anisotropy of AC mixtures. It indicates that the Vector magnitude substantially underestimates the<br> inherent anisotropy of the AC mixtures. The study include challenges in<br> visualizing images as matrix form, creating what if scenarios, executing algorithm and identifying causes of algorithm failure in MATLABr software.<br> The future scope may include; varying compaction level and angle of gyration, changing compaction methods, using aging AC mixtures, varying image<br> resolution and specimen height.