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Title:Development of the Duomorph Asphalt Rheology Tester (DART): a self-contained, portable device for quality assurance testing of asphalt binders
Author(s):Mallela, Jagannath
Director of Research:Carpenter, Samuel H.
Doctoral Committee Chair(s):Carpenter, Samuel H.
Doctoral Committee Member(s):Thompson, Marshall R.; Dempsey, Barry J.; L.M. dos Reis, Henrique
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):asphalt rheology
asphalt binder testing
binder rheology
Superpave binder grading
performance grade
quality control
binder testing
Abstract:This dissertation developed a bench prototype device, named as the Duomorph Asphalt Rheology Tester or DART, for use in quality assurance (QA) testing of asphalt binders. This self-contained, portable device was re-engineered from its original version developed in the 1970s to test the structural integrity of solid rocket propellant fuels. Central to the DART system is a circular piezoelectric duomorph or bimorph with strain sensors that record its response to an applied alternating current (AC) electrical voltage signal. The strain signal’s amplitude and lag relative to the drive signal vary as a function of the properties of the medium it is operating in. The goal of this research was to provide a methodology, using the outputs from the duomorph as a basis, to rapidly and cost-effectively test virgin and modified asphalt binders for specification compliance either at the refinery, the blending terminal, the asphalt plant, or at the job site. The DART was evaluated both as a surrogate test device to the Dynamic Shear Rheometer (DSR) and also as a device capable of directly estimating the AASHTO M320 Table 1 specification parameters—the complex shear modulus (G*) and phase angle (d). The first phase of the research evaluated the physical and operational characteristics of a prototype DART system and its feasibility to test asphalt binders. Various DART gage instrumentation techniques and piezo driving and grounding methods were also examined. It was determined that the DART gage and the associated electronics can withstand normal laboratory use for extended periods of time. Further the DART gage’s primary outputs— bending strains and phase shifts—were repeatable and correlated well with G* and . The gage responses were found to be unique to each asphalt binder grade tested thereby establishing the ability of the system to “fingerprint” asphalt binders and function as an effective QA tool. Finally, the range of asphalt binder storage moduli and phase angles over which the DART was system was effective was established. The next phase involved making direct comparisons of the DART estimated G* and d using an existing data reduction technique developed in the 1970s with those determined from the DSR. These comparisons indicated the need to develop a theoretical framework to more accurately predict asphalt binder G* and d from the DART gage responses. A finite element (FE) model was subsequently configured to simulate the gage behavior in air and when embedded in an asphalt medium. After establishing suitable load equivalencies, the finite element analysis was performed entirely in the mechanical domain. This was done primarily to reduce input complexity associated with performing a coupled piezoelectric-steady state analysis. The FE model’s results compared well with laboratory measured DART responses across a range of binders tested, thereby validating the model. A parametric study was then conducted using the FE model over a range of assumed asphalt binder viscoelastic properties to develop relationships between the DART’s outputs and the asphalt binder G* and d. The relationships were plotted in the form of a nomograph. A limited validation study conducted using the nomograph provide good agreement between the DART predicted G*-d and the corresponding DSR measured values confirming the validity of the proposed data reduction scheme. This research concluded that the DART can be used as a surrogate test device to rapidly evaluate and “fingerprint” the quality of the binders in the field for AASHTO M320 specification compliance. Further, the DART gage responses, combined with the finite element based nomographical solution scheme, can estimate the binder G* and d satisfactorily. Both these findings further the notion that DART can be used for rapid QA testing of asphalt binders along the asphalt binder’s journey from a supplier to the job-site in a cost-effective and rapid manner.
Issue Date:2014-09-25
Rights Information:Copyright 2013 Jagannath Mallela
Date Available in IDEALS:2014-09-25
Date Deposited:2013-12

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