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Title:An analysis of impact factors on the Illinois flexibility index test
Author(s):Barry, Maxwell K
Advisor(s):Al-Qadi, Imad L.; Ozer, Hasan
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):llinois flexibility index test (I-FIT)
Recycled asphalt pavement (RAP)
Recycled asphalt shingles (RAS)
Asphalt binder replacement (ABR)
Brittleness mitigation
Hot-in-place recycling (HIR)
Abstract:The use of recycled materials in asphalt pavements has become widespread in recent years. Materials such as recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) have been incorporated into the material design of typical pavements. The use of these materials is both economically and environmentally friendly, at least initially. However, asphalt concrete materials with high recycled content have been shown to have some performance issues, leading to deterioration before the end of the design life. This early deterioration may negate any environmental or economic benefit initially obtained from the use of recycled materials. The typical modes of failure for asphalt pavements with high recycled content are thermal cracking or early fatigue cracking. While RAP and RAS contribute a significant amount of recycled asphalt binder, that is asphalt binder replacement (ABR), the binder may be too stiff for the given application. For this reason, standard Superpave design may be insufficient to prevent cracking when ABR is present. As a result, the Illinois Center for Transportation has developed the Illinois Flexibility Index Test (I-FIT) to evaluate the cracking potential of an asphalt concrete mixture. The I-FIT method is in its early stages, and various impact factors on the test’s output need to be understood. While laboratory-produced specimens can be easily controlled, the qualities of field core specimens are typically out of the researcher’s control. Two main parameters, while controlled for laboratory-produced specimens, will typically be uncontrolled for field core specimens. These parameters are the specimen thickness and the air void content. It is vital to understand the effect of these parameters on the I-FIT method; therefore, these effects are a main focus of investigation in this thesis. Another main focus of this thesis is the mitigation of asphalt concrete mixture stiffness. The I-FIT method was developed specifically to evaluate the flexibility of an asphalt concrete mix. It is ideal for identifying mixtures of excessive stiffness as a result of high levels of ABR. It is also ideal for evaluating the success of methods of stiffness mitigation, that is, increasing flexibility to reduce cracking potential. Typical methods of stiffness mitigation—for example, virgin binder softening—are evaluated in terms of the I-FIT method. Additionally, atypical methods of stiffness mitigation are evaluated, specifically mix-applied rejuvenation. Mix-applied rejuvenation, which closely resembles hot-in-place recycling, is evaluated on a large scale. Rejuvenation of plant mix, laboratory-produced specimens, and field cores is evaluated, and the effectiveness of mix-applied rejuvenation is analyzed via the I-FIT method. Preferable methods of mix-applied rejuvenation are determined, and field applications are suggested. This thesis provides an understanding of the effect of mix and test specimen geometry parameters on I-FIT results. Additionally, the effect of aging on I-FIT results is presented.
Issue Date:2016-11-14
Rights Information:Copyright 2016 Maxwell Barry
Date Available in IDEALS:2017-03-01
Date Deposited:2016-12

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