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Title:Evaluation of viscous effects in crack tip fields in recycled asphalt pavement materials using digital image correlation
Author(s):Doll, Berangere
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Digital Image Correlation (DIC)
Recycled Asphalt Shingles (RAS)
Asphalt Binder Replacement (ABR)
Fracture Process Zone (FPZ)
Aggregate structure
Abstract:In this work, we investigated the fracture behavior of asphalt, a heterogeneous mixture of hard aggregates (usually rock) with a polymeric binder (also called asphalt), used in paving applications. Specifically we studied the dependence of asphalt fracture response on loading rate, temperature, and recycled content in the binder. Fracture tests were conducted on Semi Circular Bend (SCB) edge cracked specimens obtained from mixes with different compositions, and the tests were recorded with a camera to allow for Digital Image Correlation (DIC) measurements. DIC measured the strain and displacement fields both at the far-field scale (40 microns/pixel) and at a near-field scale (8 microns/pixel), and allowed a local characterization of fracture mechanisms depending on the aggregate structure. Initial efforts focused on characterizing the material behavior by quantifying its viscosity and fracture properties. The viscoelasticity correspondence principle was used to extract viscous and elastic components from the full-field DIC-measured viscoelastic strain and displacement fields. Stress intensity factor and J-integral were used to study the fracture properties, as well as the viscoelastic equivalents. It was seen that the viscosity of the material was a dominant factor in the material behavior, and the loading rate and RAS (Recycled Asphalt Shingles) content affected viscous response. The second part of this work focused on comparing different mixes regarding energy dissipation, strain recovery, crack propagation and fracture process zone (FPZ). Energy dissipation was studied on two different aspects: first was the dissipation under the loading head due to crushing of the specimen; the second was dissipation in the bulk of the material. No crushing of the material was observed around the loading head, thus indicating minimal energy loss there. Bulk material dissipation, quantified through the area contained within loops in the path followed by each point in the stress-strain space, was seen to decrease with increasing RAS content. Strain recovery at the far-field was studied as well, it was done by comparing how the strains unloaded when the crack propagated, and how much strain was recovered at the end of the test. There was less recovery for lower RAS content material. We also looked at the influence of the microstructure on the fracture properties. It started by comparing the crack path with the aggregate structure showing that the crack propagated mostly between aggregates. We also studied the Fracture Process Zone (FPZ) that developed between aggregates and whose size was increasing for lower RAS content or intermediate temperature. In the end, this study showed that the increase of RAS content considerably embrittles the material meaning less viscous effects, less energy dissipated in the bulk.
Issue Date:2015-05-01
Rights Information:Copyright 2015 Berangere Doll
Date Available in IDEALS:2015-07-22
Date Deposited:May 2015

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