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Title:Fracture characterization of thin bonded asphalt concrete overlay systems
Author(s):Ahmed, Sarfraz
Director of Research:Buttlar, William G.
Doctoral Committee Chair(s):Buttlar, William G.
Doctoral Committee Member(s):Al-Qadi, Imad L.; Carpenter, Samuel H.; Dave, Eshan V.; Exline, Marvin
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Thin Bonded Overlays
Compact Tension Fracture Test
Asphalt Concrete Pavement
Abstract:Asphalt overlays provide an economical means for treating deteriorated pavements. Thin bonded overlay (TBO) systems have become popular options for pavement rehabilitation. In addition to functional improvements, these systems ensure a high degree of waterproofing benefits. Conventional asphalt concrete fracture tests were developed for pavements with homogeneous asphalt concrete mixtures, and typically their thicknesses exceed two inches. The use of spray paver technology for construction of TBO leads to continuously varying asphalt binder content, up to approximately one-third of the layer thickness. The graded properties of asphalt concrete and thickness of the TBO (typically less than 50 mm) pose challenges for the use of conventional fracture test geometries. For example, obtaining the beams for SEN[B] specimens from pavement may not practical because of insufficient layer thickness of the TBO or may lead to excessive pavement damage. Applications of the other established test geometries, the DC[T] and SC[B] tests, are limited because of the material nonhomogeneity caused by nonuniform distribution of asphalt binder and smaller as-constructed thicknesses of TBO, which are usually less than 25 mm (1 inch) for gap-graded and 50 mm (2 inch) for dense-graded hot mix asphalt (HMA) mixtures. Both the DC[T] and SC[B] tests simulate movement of the crack fronts in transverse or longitudinal directions in the pavement. Use of these tests on field-procured samples of TBO yields a crack front that encounters nonhomogeneous material through the specimen thickness. The crack moves perpendicular to the axis of material nonhomogeneity, which makes data interpretation and fundamental material fracture characterization challenging. In addition, the crack in the specimens is correlated to a crack channeling across the pavement width rather than a more anticipated bottom-up or top-down direction. New test procedures for fracture characterization of graded asphalt pavement systems that have significant material property gradients through their thicknesses have been proposed. Suitable specimen geometry and testing procedures were developed using ASTM E399 and ASTM D7313-07 as a starting point. Laboratory tests were performed using an optimized compact tension C[T] test geometry for field cores as well as laboratory-fabricated composite specimens. Laboratory testing using the proposed procedure clearly showed distinction in the fracture characteristics for specimens prepared with varying material compositions. This capability of distinguishing different materials combined with stable crack growth makes the proposed testing procedure ideal for fracture characterization of thin and graded pavement systems. Statistical analysis of test data revealed that the proposed C[T] test procedure is capable of detecting differences in fracture energy results across a wide range of pavement systems and yields a low test variability. Finite element simulations of the test procedure further indicate the suitability of the test procedure as well as demonstrate a procedure for extraction of fundamental material properties. The suitability of the proposed C[T] test in the context of warmer temperatures was also evaluated. Changes in the loading rate were suggested to minimize the creep energy dissipation during the test at different test temperatures. Composite specimen fabrication procedure has been developed to optimize the design of TBOs. The proposed procedure can also be used to prepared composite specimens for interface bond strength and rutting resistance tests with emulsion and asphalt cement as tack coat material. Suggested wet application of tack coat emulsion on textured base, compacted with heated Superpave gyratory compactor top plate closely resembles field installation of TBOs. Moreover tack coat emulsion permeation effects on mixture fracture and bulk properties were also evaluated in an experimental study. Image analysis technique was utilized to characterize the tack coat emulsion impregnation gradient through the thickness of the overlays. An integrated approach to predict cracking performance of TBOs was presented combining laboratory test results, numerical simulations and early field performance.
Issue Date:2011-05-25
Rights Information:Copyright 2011 Sarfraz Ahmed
Date Available in IDEALS:2013-05-26
Date Deposited:2011-05

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