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Early age delamination in concrete pavements made with gravel aggregatesLiu, Juanyu 02 June 2009 (has links)
Gravel aggregates had been used extensively in the Houston District of Texas Department of Transportation (TxDOT) for continuously reinforced concrete pavements construction for many years. However, some of these pavements have been subject to early age delamination and eventual spalling damage. Therefore, a series of studies funded by TxDOT since the early 1990's has been conducted to gain a better understanding of mechanisms, material properties, and construction practices, and to provide guidelines and recommendations for minimizing early-age delamination in concrete pavements made with gravel aggregates. In this study, a test protocol to measure the bond strength between aggregates and cement mortar was established, and the effects of different material and construction parameters on the bond strength of concrete at early ages using a fractional factorial design were investigated. The significances of each factor to achieve better bonding performance were determined, and the optimum design combination was subsequently chosen and validated. Geometric parameters were proposed to characterize aggregate shape properties relative to bonding performance with the facilitation of the Aggregate Imaging System. A rating system based on utility theory was developed to evaluate the overall contribution of aggregate properties (i.e. physical, geometric, and chemical) to the concrete bonding capability and the feasibility of certain mixture design combinations. As for theoretical representation of the bond strength across the interfacial transition zone, a model of interfacial fracture energy between aggregate and mortar that represents the energy necessary to create a crack along the interface was formulated. This model built the connection between concrete properties at the meso-level (represented by the interfacial fracture energy between aggregate and mortar) and the macro-level (represented by fracture toughness of concrete and significant influencing materials and construction factors). In addition, the moisture effects on stress development of concrete pavements at early ages using field data as inputs were numerically simulated, and a fracture mechanics-based approach was used to predict the occurrence of delamination. A delamination detection protocol for the field was developed to explore the feasibility and potential of utilizing Ground Penetration Radar technology in delamination detection. Research findings from laboratory investigation, field testing, theoretical modeling, and numerical analysis were further validated through field test sections, and the associated framework for delamination guidelines was established.
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Development of a Reaction Signature for Combined Concrete MaterialsGhanem, Hassan A. 2009 May 1900 (has links)
Although concrete is widely considered a very durable material, if conditions are such, it
can be vulnerable to deterioration and early distress development. Alkali-Silica Reaction
(ASR) is a major durability problem in concrete structures. It is a chemical reaction
between the reactive silica existent in some types of rocks and alkali hydroxides in the
concrete pore water. The product of this reaction is a gel that is hygroscopic in nature.
When the gel absorbs moisture, it swells leading to tensile stresses in concrete. When
those stresses exceed the tensile strength of concrete, cracks occur. The main objective of
this study was to address a method of testing concrete materials as a combination to assist
engineers to effectively mitigate ASR in concrete. The research approach involved
capturing the combined effects of concrete materials (water cement ratio, porosity,
supplementary cementitious materials, etc.) through a method of testing to allow the
formulation of mixture combinations resistant to ASR leading to an increase in the life
span of concrete structures.
To achieve this objective, a comprehensive study on different types of aggregates
of different reactivity was conducted to formulate a robust approach that takes into
account the factors affecting ASR; such as, temperature, moisture, calcium concentration
and alkalinity. A kinetic model was proposed to determine aggregate ASR characteristics
which were calculated using the System Identification Method. Analysis of the results
validates that ASR is a thermally activated process and therefore, the reactivity of an
aggregate can be characterized in terms of its activation energy (Ea) using the Arrhenius
equation. Statistical analysis was conducted to determine that the test protocol is highly
repeatable and reliable.
To relate the effect of material combinations to field performance, concrete
samples with different w/cm?s and fly ash contents using selective aggregates were tested
at different alkalinities. To combine aggregate and concrete characteristics, two models were proposed and combined. The first model predicts the Ea of the aggregate at levels of
alkalinity similar to field conditions. The second model, generated using the Juarez-
Badillo transform, connects the ultimate expansion of the concrete and aggregate, the
water cement ratio, and the fly ash content to the Ea of the rock. The proposed models
were validated through laboratory tests. To develop concrete mixtures highly resistant to
ASR, a sequence of steps to determine threshold total alkali in concrete were presented
with examples. It is expected that the knowledge gained through this work will assist
government agencies, contractors, and material engineers, to select the optimum mixture
combinations that fits best their needs or type of applications, and predict their effects on
the concrete performance in the field.
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炭素・酸素同位体分析による実構造物中のコンクリートの中性化進行評価Yoshida, Hidekazu, Maruyama, Ippei, Minami, Masayo, Asahara, Yoshihiro, 吉田, 英一, 丸山, 一平, 南, 雅代, 淺原, 良浩 03 1900 (has links)
第23回名古屋大学年代測定総合研究センターシンポジウム平成22(2010)年度報告
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Characterization of asphalt concrete using anisotropic damage viscoelastic-viscoplastic modelAbdel-Rahman Saadeh, Shadi 25 April 2007 (has links)
This dissertation presents the integration of a damage viscoelastic constitutive
relationship with a viscoplastic relationship in order to develop a comprehensive
anisotropic damage viscoelastic-viscoplastic model that is capable of capturing hot mix
asphalt (HMA) response and performance under a wide range of temperatures, loading
rates, and stress states. The damage viscoelasticity model developed by Schapery (1969) is
employed to present the recoverable response, and the viscoplasticity model developed at
the Texas Transportation Institute (TTI) is improved and used to model the irrecoverable
strain component. The influence of the anisotropic aggregate distribution is accounted for
in both the viscoelastic and viscoplastic responses.
A comprehensive material identification experimental program is developed in
this study. The experimental program is designed such that the quantification and
decomposition of the response into viscoelastic and viscoplastic components can be
achieved. The developed experimental program and theoretical framework are used to
analyze repeated creep tests conducted on three mixes that include aggregates with
different characteristics. An experiment was conducted to capture and characterize the three-dimensional
distribution of aggregate orientation and air voids in HMA specimens. X-ray computed
tomography (CT) and image analysis techniques were used to analyze the microstructure in
specimens before and after being subjected to triaxial repeated creep and recovery tests as
well as monotonic constant strain rate tests. The results indicate that the different loading
conditions and stress states induce different microstructure distributions at the same
macroscopic strain level. Also, stress-induced anisotropy is shown to develop in HMA
specimens.
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Shock vibration resistance and direct tensile strength of concreteZheng, Wei, January 2001 (has links)
Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.
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Shear strengthening of reinforced concrete beams using CFRP and bonding behavior between CFRP and concrete /Zhang, Huiyun. January 2005 (has links)
Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 179-180). Also available via World Wide Web.
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Continuum MDOF model for seismic analysis of wall-frame structures /Huang, Kai. January 2009 (has links)
Includes bibliographical references (p. 217-227).
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Effects of strain gradient on maximun concrete stress and flexural capacity of normal-strength RC membersPeng, Jun, January 2009 (has links)
Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 66-68). Also available in print.
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Strengthening of reinforced concrete two-way slabs /Ebead, Usama Ali Ali. January 2002 (has links)
Thesis (Ph.D.)--Memorial University of Newfoundland, 2002. / Bibliography: leaves 231-245.
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Evaluation of performance graded asphalt binder equipment and testing protocolPumphrey, Michael E., January 2003 (has links)
Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains viii, 106 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 104-105).
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