No description available.

No description available.

Accurately modeling damping in engineering structures has plagued scientist and engineers for decades. The integration of viscoelastic materials into engineering structures can reduce undesired vibrations and serve as an effective passive control mechanism. Various techniques have been developed to model viscoelastic materials. The growing popularity of finite element analysis in the 1980s and 1990s spawned new techniques for modeling damping in complex structures. The technique defined in this dissertation can be incorporated into finite element models. In metals, the modulus of elasticity can be modeled as a constant. That is, the modulus of elasticity is not treated as a function of frequency in dynamic models. For viscoelastic materials, the modulus of elasticity can be assumed to be constant for static forces and sinusoidal forcing functions. However, when viscoelastic materials undergo excitations from a random or transient forcing function the constant modulus of elasticity assumption may not be valid. This is because the second order equation of motion has non-constant coefficients or coefficients that vary as a function of frequency. The Golla-Hughes-McTavish (GHM) method is a technique used to incorporate the frequency dependency of viscoelastic materials into finite element models. The GHM method is used as a way to alleviate working with second order differential equations with non-constant coefficients. This dissertation presents the theory for a new material modulus function suitable for application within the framework of the GHM method. However, the new material modulus function uses different assumptions and is referred to as the Modified GHM method or MGHM method. The MGHM method is shown to improve the curve fit and damping characteristics of the GHM method. Additionally, the MGHM method is shown to reduce to the GHM method when the original GHM assumptions are imposed. / Ph. D.

The major Hot-Mix Asphalt (HMA) input for mechanistic-empirical (M-E) flexible pavement design is the dynamic complex modulus obtained from either the uniaxial or triaxial compressive dynamic modulus test. Furthermore, as part of the performance-based mix design process, the triaxial dynamic modulus has been selected to predict rutting and fatigue cracking, and the Indirect Tension (IDT) creep compliance test to predict low-temperature thermal cracking. The creep compliance and dynamic modulus are measured responses (viscoelastic functions) of viscoelastic materials under transient and cyclic loading, respectively. Under the assumptions of linearity, linear viscoelastic functions are equivalent. Moreover, these properties should be the same whether they are obtained from a uniaxial compressive or IDT test. For this dissertation, we tested the applicability of linear viscoelastic (LVE) theory to HMA mixes and determined whether HMA need to be modeled as a bimodular material to analyze IDT creep compliance test results. The need to model HMA as a bimodular material is a result of a number of studies that suggest that HMA tensile and compressive properties are different. A testing program was developed to experimentally measure the uniaxial compression, and IDT creep compliance, and the uniaxial compression dynamic modulus for different HMA mixes. The uniaxial compressive creep compliance and dynamic modulus master curves are constructed and the shift factors obtained from each test are compared. Interconversion between the creep compliance and dynamic modulus experimental results confirm the applicability of LVE theory for the HMA mixes investigated. Based on the applicability of LVE theory, a methodology to determine HMA LVE properties from the combined creep compliance and dynamic modulus test results was developed. As a practical application that is relevant to the M-E flexible pavement design procedure, LVE theory was used and compared to proposed approximate methods to perform the conversion of testing frequency to loading time. Specifically, dynamic modulus results were converted to relaxation modulus, creep compliance, and resilient modulus. Finally, the HMA IDT creep compliance test results at low and intermediate temperature (<20oC) were successfully analyzed using a HMA bimodular material model based on the Ambartsumyan model. The difference between the compressive modulus and the modulus calculated from the IDT test using Hondros' stress distribution is calculated. In addition, a method to determine the compressive-to-tensile modulus ratio using uniaxial compressive and IDT test results is illustrated for one of the tested HMA mixes. / Ph. D.

Complex moduli and Poisson’s ratio have been estimated using extensional and torsional wave experiments. The data were used for assessment of linearity and isotropy of two polymers, polymethyl methacrylate (PMMA) and polypropylene (PP). The responses of both materials were found to be close to linear and isotropic. A statistical analysis of different estimation approaches for complex modulus and Poisson’s ratio was conducted. It was shown that a joint estimation of complex modulus and Poisson’s ratio improves the estimated results. Considerable improvement was achieved in the frequency range 5-15 kHz for Poisson’s ratio. A non-equilibrium split Hopkinson pressure bar (SHPB) procedure for identification of complex modulus has been developed. Two simplified procedures were also established. Both overestimated the magnitude of the complex modulus. The complex modulus of PP was identified using PMMA and aluminium bars, and the estimated complex modulus was in good agreement with published results. The procedure was found to be accurate regardless of the specimen size or the specimen-to-bar impedance ratio. The procedure was also used to analyze the mechanical response of four compacted pharmaceutical tablet materials. A Debye-like relaxation was observed for all tested materials. Utilizing SHPB effectively requires knowledge about the impact process that is normally used for excitation. Therefore the impact between a cylindrical striker and a long cylindrical bar of viscoelastic material was studied theoretically and experimentally. Strains measured at three locations along a PMMA bar impacted by strikers of the same material agreed well with the theoretical results. A method for identification of complex shear modulus from measured shear strains on a disc subjected to a transient torque at its centre has been established. The two-dimensional wave solutions used are exact in the sense of three-dimensional theory. The results from experimental tests with different load amplitudes and durations agree well with each other.

Viscoelastic materials can today be found in a wide range of practical applications. In order to make efficient use of these materials in construction, it is of importance to know how they behave when subjected to dynamic load. Characterization of viscoelastic materials is therefore an important topic, that has received a lot of attention over the years. This thesis treats different methods for identifying the complex modulus of an viscoelastic material. The complex modulus is a frequency dependent material function, that describes the deformation of the material when subjected to stress. With knowledge of this and other material functions, it is possible to simulate and predict how the material behaves under different kinds of dynamic load. The complex modulus is often identified through wave propagation testing, where the viscoelastic material is subjected to some kind of load and the response then measured. Models describing the wave propagation in the setups are then needed. In order for the identification to be accurate, it is important that these models can describe the wave propagation in an adequate way. A statistical test quantity is therefore derived and used to evaluate the wave propagation models in this thesis. Both nonparametric and parametric identification of the complex modulus is considered in this thesis.  An important aspect of the identification is the accuracy of the estimates.  Theoretical expressions for the variance of the estimates are therefore derived, both for the nonparametric and the parametric identification. In order for the identification to be as accurate as possible, it is also important that the experimental data contains as much valuable information as possible. Different experimental conditions, such as sensor locations and choice of excitation, can influence the amount of information in the data. The procedure of determining optimal values for such design parameters is known as optimal experiment design. In this thesis, both optimal sensor locations and optimal excitation are considered.

This thesis present novel non-destructive laboratory test methods to characterize asphalt concrete. The testing is based on frequency response measurements of specimens where resonance frequencies play a key role to derive material properties such as the complex modulus and complex Poisson’s ratio. These material properties are directly related to pavement quality and used in thickness design of pavements. Since conventional cyclic loading is expensive, time consuming and complicated to perform, there has been a growing interest to apply resonance and ultrasonic testing to estimate the material properties of asphalt concrete. Most of these applications have been based on analytical approximations which are limited to characterizing the complex modulus at one frequency per temperature. This is a significant limitation due to the strong frequency dependency of asphalt concrete. In this thesis, numerical methods are applied to develop a methodology based on modal testing of laboratory samples to characterize material properties over a wide frequency and temperature range (i.e. a master curve). The resonance frequency measurements are performed by exciting the specimens using an impact hammer and through a non-contact approach using a speaker. An accelerometer is used to measure the resulting vibration of the specimen. The material properties can be derived from these measurements since resonance frequencies of a solid are a function of the stiffness, mass, dimensions and boundary conditions. The methodology based on modal testing to characterize the material properties has been developed through the work presented in paper I and II, compared to conventional cyclic loading in paper III and IV and used to observe deviations from isotropic linear viscoelastic behavior in paper V. In paper VI, detailed measurements of resonance frequencies have been performed to study the possibility to detect damage and potential healing of asphalt concrete.  The resonance testing are performed at low strain levels (~10^-7) which gives a direct link to surface wave testing of pavements in the field. This enables non-destructive quality control of pavements, since the field measurements are performed at approximately the same frequency range and strain level. / <p>QC 20141117</p>

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Road transport is of great importance for many countries, in Brazil it can be even more extreme, by excessive movement of cargo through this modal. We know that the maintenance costs of roads are high, forcing researchers to find always new alternatives to improve the use of materials, reduce energy consumption, speed up restoration interventions, among others. The goal of this study is to evaluate the behavior of conventional asphalt mixtures of polymers and modified for resistance and deformability. For this study, we used a crushed mineral aggregate skeleton of volcanic origin with framed particle size in the range of C DNIT, coming from the quarry of Santo Antonio da Patrulha RS. 4 types of asphalt binders were used, the CAP 50/70, the TLA CAP, the CAP 60/85 and the TLA FLEX, and the latter two are modified polymers. Compression was done according to Superpave methodology. Tests were carried out to check the mechanical behavior (test Tensile Strength for Diametral Compression (RT) assay Resilience Module (MR) and Dynamic Module test Uniaxial) and later held one performance analysis of mixtures studied by AASHTOWare software. From these investigations it was possible to verify the behavior of the mixtures studied for their resistance, deformability and especially as its durability. It can be said that the choice of the mixture to be used will depend on its applicability. The tests showed that mixtures with TLA Flex achieved the best results, a fact that was confirmed by performance analysis that demonstrated the mixture of TLA Flex with a thickness of 18 cm coating meets all requirements evaluated. / O transporte rodoviário é de grande importância para muitos países, no Brasil isso pode ser ainda mais extremo, pelo excesso de movimentação das cargas através deste modal. Sabe-se que os custos de manutenção das rodovias são elevados, forçando os pesquisadores a encontrar sempre novas alternativas para melhorar o aproveitamento dos materiais, diminuir o consumo de energia, agilizar as intervenções de restauração, entre outros. O objetivo do presente trabalho é avaliar o comportamento de misturas asfálticas convencionais e modificadas por polímeros quanto à resistência e deformabilidade. Para este estudo foi utilizado um esqueleto mineral agregado britado de origem vulcânica com granulometria enquadrada na Faixa C do DNIT, advindos da pedreira de Santo Antônio da Patrulha, RS. Foram utilizados 4 tipos de ligantes asfálticos, o CAP 50/70, o CAP TLA, o CAP 60/85 e o TLA FLEX. A dosagem e compactação foram feitas segundo a metodologia SUPERPAVE. Foram realizados ensaios para verificação do comportamento mecânico (ensaio de Resistência à Tração por Compressão Diametral (RT), ensaio de Módulo de Resiliência (MR) e ensaio de Módulo Dinâmico Uniaxial) e posteriormente realizada uma análise desempenho das misturas estudadas através do software AASHTOWare. A partir destas investigações foi possível verificar o comportamento das misturas estudadas quanto a sua resistência, deformabilidade e principalmente quanto ao seu desempenho. Pode-se afirmar que a escolha da mistura a ser utilizada dependerá do cumprimento de uma série de quesitos de projeto. Os ensaios evidenciaram que as misturas com TLA Flex obtiveram os melhores resultados, fato este que foi confirmado através da análise de desempenho que comprovou que esta mistura, com espessura de 18 cm de revestimento cumpre com todos os requisitos de projeto.

Au Québec, lors de la période de gel et dégel, l’enrobé bitumineux, constituant le revêtement de la chaussée, est soumis à des conditions sévères qui le dégradent. Ces conditions sont : précipitations de pluie et fontes de neige générant une saturation partielle du matériau, présence de sel déverglaçant, passages de véhicule lourd sollicitant mécaniquement le matériau, variations de températures engendrant la création de déformations et de contraintes au sein du revêtement, et présence de cycles de gel-dégel.A cet effet, la revue de la littérature porte sur l’étude : des conditions sévères (sollicitations mécaniques, climatiques, hydriques et chimiques), et des caractéristiques physiques de l’enrobé qui affectent sa durabilité, ses comportements mécaniques (viscoélastique linéaire et en fatigue) et thermomécaniques (coefficient de dilatation-contraction thermique).Notamment, un programme expérimental de laboratoire a été réalisé en vue de vérifier l’influence de ces conditions sévères sur la dégradation et le comportement de l’enrobé. Premièrement, des essais thermiques, incluant des cycles de gel et dégel, ont été réalisés sur des éprouvettes d’enrobé à l’état sec et partiellement saturé en eau ou en saumures. Les éprouvettes sont instrumentées d’une jauge axiale et de deux thermocouples. L’éprouvette partiellement saturée en eau, comparativement à celles partiellement saturées en saumures, est soumise à des dilatations et des contractions nettement plus importantes lors de la formation et la fonte de la glace. De +10 à +23°C, les coefficients de dilatation linéique des éprouvettes partiellement saturées sont assez similaires, mais supérieurs à celui de l’enrobé à l’état sec, ce qui implique que l’enrobé partiellement saturé se contracte et se dilate un peu plus que celui a l’état sec à ces températures.Deuxièmement, les éprouvettes ont été soumises à des essais mécaniques, de module complexe, afin d’évaluer l’évolution de leur endommagement suite aux cycles de gel et dégel. Les résultats des essais et du modèle rhéologique 2S2P1D ont été utilisés afin de simuler le comportement de l’enrobé selon les divers états. Au fil des cycles de gel et dégel, un endommagement est observable pour l’ensemble des éprouvettes, mais nettement supérieur pour l’éprouvette partiellement saturée en eau. De plus, pour les éprouvettes partiellement saturées, un comportement distinct est observable en dessous et au-dessus de la température de solidification des liquides.Pour terminer, l’étude du comportement à la fatigue de l’enrobé suivant l’état sec et partiellement saturé en eau est réalisée. A +10°C et 10Hz, seules des diminutions légères ont été observées au niveau du module (3%) et de la résistance à la fatigue (ɛ6 de 105 vs 109ƒμdef) pour l’enrobé partiellement saturé en eau. Ces faibles diminutions sont attribuables à la faible période d’immersion des éprouvettes d’enrobé dans l’eau, à la faible température de l’eau et de l’essai, à la faible teneur en vides des éprouvettes, au bitume modifié et aux granulats de qualité utilisés / During winter and spring in the province of Quebec, hot mix asphalt (HMA) pavement could be subjected to sever conditions over their design life. These conditions are: 1) rainfall and snowmelt, which generates the partial saturation of the HMA, 2) winter maintenance requiring the presence of de-icing salt, which acting chemically on HMA, 3) traffic, which acting mechanically on HMA, and 4) temperature changes and presence of freeze-thaw cycles (FTC) creating thermal stress and deformation (thermo-mechanical coupling) within the pavement, and pressure, within the material, generated by freezing water or brines. More specifically, the literature review of this work focuses on the study of: 1) severe conditions such as climatic, chemical and mechanical solicitations, 2) physical characteristics of HMAthat affect its durability, mechanical properties (viscoelastic and fatigue) and thermomechanical properties (coefficient of thermal contraction).An experimental laboratory program was conducted to verify the influence of these severe conditions on the degradation and behavior of HMA. First, thermal testing (-18 to +23°C), including freeze-thaw cycles (FTC, -18 to +10°C) were performed on samples under dry (D)and partially saturated (PS), with water or brine, states. The samples were instrumented with an axial gauge and two thermocouples. During FTC (-18 to +10°C), sample partially saturated with water, compared to those partially saturated with brines, is subject to expansions and contractions significantly greater during formation and melting of ice. In the temperature range from +10 to +23°C, the linear coefficients of thermal contraction of partially saturated samples are quite similar, but higher than that of HMA in dry state. At such temperature range, this implies that the partially saturated HMA contracts and expands a little more than that in dry state. Secondly, the samples were subjected to mechanical testing.The complex modulus test was performed in order to evaluate the damage of samples due to FTC. The test results and rheological model 2S2P1D were used to simulate the behavior of the HMA according to the various states. Over FTC, damage is observed for all samples, butmuch higher for the PS sample with water. Moreover, for PS samples, a distinct behavior is observable below and above the solidification temperature of the liquid. Finally, the study of the fatigue behavior of HMA under PS, with water, and D states is performed. At +10°C and 10Hz, only slight decreases were observed for complex modulus (3%) and fatigue (ε6 = 105 vs 109μstrain) for HMA partially saturated with water. These small decreases are due to the low period of immersion of samples in water, lowers temperatures of water and test, low void content of the samples, modified bitumen and good aggregates used.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The degradation of the pavement has grown considerably due to the modification of traffic characteristics. It was increased the volume of traffic, the transported load and the tire inflation pressure, which added to the lack of load inspection on the load transport causes the asphalt coating the early appearance of defects. In order to seek progress on knowledge of the behavior of asphalt mixtures this study aimed to analyze the influence of the dosing method, of the granulometry and binders in the mechanical behavior of asphalt mixtures and determinate which of these three variables most influence on the mechanical behavior of the material. It was used two dosing method, Superpave and Marshall, four granulometries, two of them determined by Bailey method (range B and range C) and two by trial (range B and range C- simple framework on the ranges) and two type of asphalt binders: CAP 50-70 and the CAP 60-85, totalizing sixteen asphalt mixtures. The mixtures were evaluated in indirect tensile strength, stiffness in the resilient modulus testing and complex modulus, which used the 2SDP1D modeling to the composition of the master curves, and the permanent deformation by Flow Number test. The obtained results indicated that the factor that alter the stiffness and resistance to permanent deformation of the mixtures was the type of asphalt binder, wherein the modified binder increased the stiffness and damage resistance of the mixtures. The Bailey method of granulometric selection has also improved the behavior of the mixtures on a smaller scale of influence than the type of asphalt binder, followed by the dosing method Superpave that reduced the design binder content of the mixtures. / A degradação sobre o pavimento cresceu consideravelmente em virtude da modificação das características do tráfego. Aumentou-se o volume de tráfego, as cargas transportadas, a pressão de inflação dos pneus, que somados a falta de fiscalização sobre o transporte de carga ocasionam no revestimento asfáltico o surgimento precoce de defeitos. No sentido de buscar uma evolução sobre o conhecimento do comportamento das misturas asfálticas, este trabalho teve por objetivo analisar a influência do método de dosagem, da granulometria e do ligante no comportamento mecânico de misturas asfálticas e determinar quais dessas três variáveis mais influenciam no comportamento mecânico do material. Utilizaram-se dois métodos de dosagem, Superpave e Marshall, quatro granulometrias, duas determinadas pelo método Bailey (Faixa B e Faixa C) e duas por tentativa (Faixa B e Faixa C- simples enquadramento nas faixas) e dois tipos de ligantes asfálticos: CAP 50-70 e o CAP 60-85, totalizando dezesseis misturas asfálticas. As misturas foram avaliadas na resistência à tração indireta, na rigidez pelo ensaio de módulo de resiliência e módulo complexo, que utilizou a modelagem 2S2P1D para composição das curvas mestras, e a deformação permanente pelo ensaio de Flow Number. Os resultados obtidos indicaram que o fator que mais alterou a rigidez e a resistência à deformação permanente das misturas foi o tipo de ligante asfáltico, no qual o ligante modificado aumentou a rigidez e a resistência ao dano das misturas. O método Bailey de seleção granulométrica também melhorou o comportamento das misturas em uma menor escala de influência que o tipo de ligante, seguido pelo método de dosagem Superpave que reduziu o teor de ligante de projeto das misturas.