Concrete construction methods and practices influence the final in-place quality of concrete. A low permeability concrete mixture does not alone ensure quality in-place concrete. If the concrete mixture is not transported, placed and cured properly, it may not exhibit the desired durability and mechanical properties. This study investigates the in-place permeation properties of low permeability concrete bridge decks mixtures used in the Commonwealth of Virginia. Permeation properties were assessed in both the laboratory and in the field using 4-point Wenner array electrical resistivity, surface air flow (SAF), and chloride ion penetrability (ASTM C 1202-97). Laboratory test specimens consisted of two concrete slabs having dimensions of 280 x 280 x 102-mm (11 x 11 x 4-in) and twelve 102 x 204-mm (4 x 8-in) cylinders per concrete mixture. Specimens were tested at 7, 28 and 91-days. Thirteen cylinder specimens per concrete mixture underwent standard curing in a saturated limewater bath. The simulated field-curing regimes used wet burlap and plastic sheeting for 3 (3B) and 7 days (7B) respectively and was applied to both slabs and cylinder specimens. Slab specimen were tested on finished surface using the SAF at 28 and 91 days, and 4-point electrical resistivity measurements at 1, 3, 7, 14, 28 and 91 days. Compressive strength (CS) tests were conducted at 7 and 28 days. Chloride ion penetrability tests were performed at 7, 28, and 91 days. Statistical analyses were performed to assess the significance of the relationships for the following: Total charge passed and initial current (ASTM C 1202-97); 3B resistivity and 7B resistivity; Slab and cylinder resistivity; Slab resistivity and ASTM C-1202-97 (Total Charge and Initial current); and Surface Air Flow and ASTM C-1202-97. Field cast specimens, test slabs and cylinders, were cast on-site during concrete bridge deck construction. The slab dimensions were 30.5 x 40.6 x 10.2-cm (12 x 16 x 4 in.), and the cylinders were 10.2 x 20.4-cm (4 x 8-in). In-situ SAF and resistivity measurements were taken on the bridge deck at 14, 42 and 91 days. In-place SAF and resistivity measurements on laboratory field cast slabs were taken at 7, 14 and 28-days. ASTM C 1202-97 specimens were prepared from field cast cylinders and tested at 7 and 28 and 42-days. The relationship between in-place permeation measures from field specimens was compared to laboratory data. Results indicated no difference in chloride ion penetrability (Figures 7.4 and 7.5) and 28-day compressive strength (Figure 7.2) with regard to differing simulated field curing regimes, for same age testing. There was no significant difference at the 95 % confidence level between 3B resistivity and 7B resistivity specimens tested at the same age (Figures 7.9 and 7.10). A well defined relationship was observed between total charge passed and initial current (Figure 7-6). An inverse power function was found to describe the relationship between charge passed/initial current and electrical resistivity for all laboratory mixtures used in this study (Figure 7.17 – 7.22). Field data was used to validate laboratory established models for charge passed/initial current and electrical resistivity. Laboratory established models were able to predict 30 to 50% of the field data (Figures 7.31 – 7.34). Results indicate that the SAF lacked the sensitivity to classify the range of concretes used in this study (Figure 7.24). / Ph. D.

According to a 1999 Federal Highway Administration statistic, the U.S. has around 8.2 million lane-miles of roadways that need to be maintained and rehabilitated periodically. Therefore, in order to reduce rehabilitation costs, pavement engineers need to optimize the rehabilitation procedure, which is achieved by accurately knowing the existing pavement layer thicknesses and localization of subsurface defects. Currently, the majority of departments of transportation (DOTs) rely on coring as a means to estimate pavement thicknesses, instead of using other nondestructive techniques, such as Ground Penetrating Radar (GPR). The use of GPR as a nondestructive pavement assessment tool is limited mainly due to the difficulty of GPR data interpretation, which requires experienced operators. Therefore, GPR results are usually subjective and inaccurate. Moreover, GPR data interpretation is very time-consuming because of the huge amount of data collected during a survey and the lack of reliable GPR data-interpretation software. This research effort attempts to overcome these problems by developing new GPR data analysis techniques that allow thickness estimation and subsurface defect detection from GPR data without operator intervention. The data analysis techniques are based on an accurate modeling of the propagation of the GPR electromagnetic waves through the pavement dielectric materials while traveling from the GPR transmitter to the receiver. Image-processing techniques are also applied to detect layer boundaries and subsurface defects. The developed data analysis techniques were validated utilizing data collected from an experimental pavement system: the Virginia Smart Road. The layer thickness error achieved by the developed system was around 3%. The conditions needed to achieve reliable and accurate results from GPR testing were also established. / Ph. D.

<p dir="ltr">Ultrasonic testing (UT) is a commonly used inspection method for buildings and bridges, yet variability in inspector performance has brought the validity of the UT process into question. While practical tests and performance testing are required as part of most UT certification processes and some industry standards, the building and bridge industries currently have no standardized testing body to verify the qualification of UT technicians. This research aimed to develop and implement a possible standardized testing protocol based on the American Welding Society (AWS) structural welding codes. Results from performance tests conducted in this research demonstrated high variability and low precision in UT measurements and generally poor performance amongst the 20 technicians that took part in the tests. It is clear from this research that certification from the existing certification programs do not always indicate qualification. Therefore, standardized performance testing would add value and increase the reliability of UT inspections by identifying those technicians that are clearly unqualified.</p>

This thesis demonstrates the use of fiber optic methods for nondestructive testing of composite materials and aluminum specimens using the acousto-ultrasound approach. A noncontact method using a hybrid interferometer is devised for measuring absolute surface acoustic wave (SAW) amplitudes. The J1..J4 spectrum analysis technique is used for calibrating the piezoelectric transducer cylinder (PZT) and JO/J2 spectrum analysis technique is used for demodulating the SAW signal from the interferometer. An extrinsic Fabry-Perot interferometric (EFPI) sensor is utilized for sensing acoustic emission, measuring speed and attenuation in aluminum and composite specimens. A broadband preamplifier is designed for amplifying signals from the EFPI sensor. Theoretical and practical minimum detectable air gap change of an EFPI sensor are calculated for the system. The directional sensitivity of the EFPI sensor to SAW is studied. / Master of Science

As a nondestructive examination, the acoustic emission technique is used to detect the presence of discontinuities inside of pressurized components. However, doubts still exist concerning the loading procedure to accomplish the acoustic emission testing, especially, in a pressure vessel where a uniform pressure can produce a nonuniform stress distribution due to the presence of the singularities such as the nozzles and supports. The combined loading of vapor and hydrostatic pressure can also generate a nonuniform stress distribution throughout the pressure vessel. According to the Kaiser effect, a structure with a nonuniform stress distribution should have a different acoustic emission testing result when compared to a structure with a uniform stress distribution. In this present study, the necessity to perform a stress analysis prior to the acoustic emission testing is examined. Furthermore, for the purpose of the stress analysis, two approaches are discussed, the membrane stress analysis and the finite element approach. By means of the membrane stress analysis, it is shown that the combined loading of the hydrostatic and vapor pressure does not produce a significant variation of stress throughout the spherical vessel. Actually, a computer program based on the membrane stress analysis is written to determine the stress distribution due to the combined loading. The limitation of the membrane stress analysis to handle problem with the presence of bending stress is also indicated. The finite element approach is used to perform the stress analysis of the singularities where the bending stress is important. The finite element computer program ABAQUS is used to perform the finite element stress analysis, and the mechanical computer-aided engineering program PATRAN is also used to construct the finite element model and to interpret the stress analysis results. The convenience and the success of these computer programs to handle this kind of problem are confirmed. The application of different types of finite elements to perform the stress analysis is also discussed. Results from the experiments performed by Gill, Catching and Paine [9] to measure the stress distribution of a pad reinforced nozzle is used as a benchmark to determine the performance of these finite elements. As a consequence, concrete recommendations concerning the selections of the finite elements and the stress analysis procedure are given. Finally, the influence of the stress distribution throughout the spherical pressure vessel on the acoustic emission is discussed, and the actual interpretation of the acoustic emission testing results based on the level of activity of acoustic emission without considering the nonuniform stress distribution throughout the structure is questioned. / Master of Science

The need for sensors demonstrating both high sensitivity and electromagnetic noise immunity has prompted the development of sensing systems based on optical fiber technology. This presentation opens with a short review of fiber optic sensing methods, including a discussion of several devices developed in prominent laboratories. The theoretical and empirical results of a particular technique of distributed pressure sensing appear next. This sensing approach, aimed towards the nondestructive testing of graphite/epoxy composite structures, relies on optical time - domain reflectometry in imbedded optical fibers. The method is investigated primarily in terms of its sensitivity and its effect on the mechanical integrity of the host composite. The work concludes with a discussion of results and ideas relating to microbending sensor research, as well as the design of several novel sensing devices. / M.S.

This thesis contains the results of Phase-1 of a project funded by Ford Motor Company. The objective is to study the feasibility of Acousto-Ultrasonics (AU) as a nondestructive technique for assuring the quality of adhesively bonded sheet-metal used for automobiles. Other nondestructive (NDT) techniques were also applied viz., ultrasonics. radiography and thermography to supplement and verify the results of the AU technique. The AU Technique demonstrated the best results in terms of its sensitivity to the variations in the properties of the interface. Regions having kissing bonds or regions lacking adhesive were easily identified by this technique. These regions contribute to the mixed mode failure. A bond quality (BQ) model is suggested to take into account the mixed mode failure. Destructive testing results show fairly consistent correlation of BQ values with the breaking strength of the adhesive joint failing in mixed mode failure. The BQ values were calculated from the SWF (stress wave factor) values generated by the AU technique. No correlation was observed between the SWF values and the breaking strengths of the bonds failing cohesively. Cohesive failures occur at higher loads than those for mixed mode failures. These are, of course, governed by the maximum possible strength of a joint. More work needs to be done to develop a better way to analyze signals for differentiating total cohesive failure, at least for academic interest. The results strongly suggest the potential of this technique for quantitative evaluation of such types of bonding. Automation of this technique can be developed for application on the assembly line of the motor-car industry. Future work to make this technique more efficient and sensitive is suggested. / Master of Science

O objetivo desta pesquisa é avaliar uma metodologia utilizando ondas de ultrassom para estimar a resistência de peças estruturais de madeira de peroba-rosa, Aspidosperma polyneuron Müll. Arg. A metodologia pode ser utilizada para orientar projetos de restauro de estruturas de madeira do patrimônio histórico, onde de acordo com os critérios da restauração, a avaliação por métodos destrutivos não são recomendados. A verificação foi realizada em três amostras retiradas de edificações construídas há 122 anos, 50 anos e peças sem uso de madeira da espécie perobarosa, que foram submetidas à sequência de ensaios não destrutivos e destrutivos. Os corpos-de-prova ensaiados tiveram suas dimensões definidas de acordo com os métodos de ensaio de resistência à compressão e à flexão da norma ABNT 7190:1997 e o teor de umidade estabilizado na condição padrão de referência a 12%. Os ensaios com o uso de equipamento de ultrassom com freqüência de 100 KHz e transdutores de ondas longitudinais e transversais foram utilizados para a determinação da velocidade ultrassônica nos três eixos da madeira (longitudinal, radial e tangencial). Em seguida, os mesmos corpos-de-prova foram submetidos aos ensaios de determinação da resistência e da rigidez à compressão e à flexão de acordo com a norma NBR 7190:1997. O resultados dos ensaios dinâmicos e estáticos foram correlacionados, tendo, portanto sido definido o coeficiente de correlação R²= 0,56 na direção do eixo longitudinal. / The objective of this research is to evaluate a methodology by making use of ultrasound waves to estimate the strength of structural timber of peroba-rosa, Aspidosperma polyneuron Müll. Arg. This methodology can be used to provide guidance in restoration projects of wooden structures of historical buildings, where the assessment by destructive methods is not recommended, according to the restoration criteria. The sequence of tests was performed by using both non destructive and destructive analysis methods on samples from three buildings constructed 122 years ago, 50 years ago and non used wood. The specimens tested had their dimensions defined according to the test methods of ABNT 7190:1997 for resistance to compression and bending and their moisture content was stabilized at 12%. The tests using ultrasound equipment with a frequency of 100 kHz transducers and longitudinal and transverse waves were used to determine the ultrasonic velocity in three axes of the wood (longitudinal, radial and tangential). Afterwards, the same specimens were tested to determine the strength and stiffness to compression and bending in accordance with NBR 7190:1997. The test results of dynamic and static modulus were correlated, obtaining thus the correlation coefficient of R²=0.54 in the longitudinal direction.

A teoria da acustoelasticidade relaciona a variação de velocidade de propagação de ondas mecânicas à variação de tensão em um meio sólido. Em materiais frágeis como concreto, a danificação altera a velocidade de propagação paralelamente ao efeito acustoelástico. O objetivo deste trabalho é identificar e quantificar como a danificação e o efeito acustoelástico agem sobre a Velocidade de Pulso Ultrassônico (VPU) em corpos de prova de concreto submetidos a compressão uniaxial. Para tanto, foram realizadas três fases de ensaio. A primeira fase objetivou gerar dados para a análise da aplicação da interferometria de cauda de onda (Coda Wave Interferometry &#8211; CWI). Duas variações deste método foram estudadas e comparadas, com o propósito de determinar-se qual gera melhores resultados e quais parâmetros devem ser adotados para as análises. Para tal, um código computacional foi desenvolvido utilizando a linguagem Python 3.6.0. Foi constatado que a técnica do alongamento apresenta resultados melhores que a técnica tradicional da interferometria de cauda de onda. A segunda etapa foi dedicada ao estudo da variação de velocidade de propagação devido à recuperação de dano do corpo de prova. A terceira fase abordou a influência da geometria da amostra e da composição do concreto sobre a resposta do material à acustoelasticidade. Além disso, definiu-se um Índice de Dano (D) baseado na redução do módulo de elasticidade devido ao carregamento, a fim de isolar a variação de velocidade causada pelo efeito acustoelástico. Quanto ao estudo da recuperação de dano ao longo do tempo, a variação relativa de velocidade nas primeiras 24 horas após a retirada do carregamento se mostrou muito pequena em relação às variações geradas pelas condições de temperatura e umidade. Concluiu-se também que as amostras cilíndricas apresentaram respostas mais uniformes ao efeito acustoelástico que as amostras prismáticas. Por fim, o Índice de Dano se mostrou eficaz para isolar os efeitos da danificação e da acustoelasticidade sobre a VPU. / The acoustoelasticity theory relates the variation in propagation velocity of mechanical waves to the stress variation in a solid medium. In brittle materials such as concrete, damage affects the propagation velocity parallel to the acoustoelastic effect. This research aims to identify and quantify how damage and acoustoelastic effect act on Ultrasonic Pulse Velocity (UPV) in concrete samples subjected to uniaxial compression. In order to do so, three phases of testing were performed. The first one focused on generating data to analyze the application of the Coda Wave Interferometry (CWI). Two variations of this method were studied and compared, to the purpose of determining which variation shows better results and which parameters should be adopted in the analysis. To enable the analysis, a computational code using Python 3.6.0 language was developed. It was verified that the stretching technique shows better results than the traditional coda wave interferometry technique. The second phase was dedicated to study the variation in propagation velocity due to damage recovery in the sample. The third phase addressed the influence of the sample geometry and the concrete composition over the response from the material to the acoustoelasticity. Furthermore, a Damage Index (D) was defined based on the elastic modulus reduction due to loading, in order to isolate the variation of velocity due solely to the acoustoelastic effect. Regarding the study of damage recovery over time, the relative velocity variation in the first 24 hours following the withdrawal of the loading showed to be too little when compared to the variations caused by temperature and humidity conditions. It was also concluded that the cylindrical samples showed more uniform responses to the acoustoelastic effect than the prismatic samples. Finally, the Damage Index proved itself to be a reliable tool to isolate the effects of damage and acoustoelasticity over the UPV.

L’engouement pour le collage structural est important dans l’aéronautique. Actuellement, il n’existe pas de méthode de contrôle non destructive de l’adhésion dans un assemblage collé. Les méthodes de CND usuelles peuvent détecter au mieux des défauts majeurs de type décollement ou absence de colle. L’objectif de la thèse est donc de déterminer un indicateur ultrasonore en lien avec le niveau d’adhésion et la tenue structurale des assemblages collés.La première étape a consisté en l’élaboration d’éprouvettes étalons à adhésions variables de forme cisaillement simple. Trois traitements de surface différents ont été définis afin d’obtenir trois niveaux de force à rupture et donc trois niveaux d’adhésion distincts. Des cartographies détaillées du joint de colle sont obtenues par ultrasons. A l’issue des essais mécaniques les faciès de rupture sont analysés. Des contrôles supplémentaires par micro-tomographie X ont été réalisés. L’ensemble de ces essais ont permis de valider l’obtention d’éprouvettes homogènes et de niveaux d’adhésion maîtrisé. Un système expérimental spécifique a été réalisé pour développer des mesures d’acoustoélasticité qui permettent l’étude des variations locales de champ des contraintes. Pendant une sollicitation mécanique de type cisaillement simple, les variations de temps de vol dans l’aluminium en mode pulse-écho des éprouvettes sont analysées. Le dispositif est d’abord validé sur une éprouvette d’aluminium. Puis, il est démontré que sur une éprouvette de cisaillement simple, les bords d’un défaut, lieu de concentration de contraintes, sont visibles. Les simulations numériques réalisées donnent les mêmes tendances / The enthusiasm for structural bonding is important in aeronautic. Currently there is no method to test non-destructively the adhesion in a bonded assembly. The usual NDT methods can detect the most common defects like delamination or disbond. The aim of this thesis is to determine an ultrasonic indicator related to the level of adhesion and the structural strength of bonded assemblies.The first step was the development of calibrated samples. The specimens are single lap shear joints. Three different surface treatments have been developed to obtain three different levels of ultimate tensile strength and therefore three distinct levels of adhesion. Detailed cartographies of the adhesive joint are obtained by ultrasound. After mechanical testing the fracture surfaces are analyzed. Additional tests by microtomography were performed. They were used to validate the quality of samples. The objective of standards sample is achieved. A specific control system has been achieved to use acoustoelasticty to study the stress field in the bonded assembly. The variations of time of flight in the aluminum part in pulse-echo mode during mechanical test are analysed. First, the method is validated with an aluminum test piece. Then, it is shown, for a sample with defect, the edges of a defect are visible through the increase of stresses on its borders. Numerical simulations give the same trends.