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This thesis investigates the effects of using various percentages of RAP and asphalt binder contents on the dynamic modulus and fatigue resistance of asphalt concrete. Two RAP percentages (20% and 40%) and three binder percentages (plant-mixed, plant-mixed + 0.5%, and plant-mixed + 1.0%) were evaluated. A Superpave gyratory compactor and an asphalt vibratory compactor were used to prepare dynamic modulus samples and fatigue beam samples at 7% air voids. Three replicate samples for each percentage of RAP and asphalt binder content were prepared for testing purposes. An Interlaken Technology Corporation servohydraulic testing machine and a Material Testing System servohydraulic machine were used to determine the dynamic modulus and fatigue resistance of the asphalt samples. Analysis of variance (ANOVA) was used to determine if any of the factors (air voids, percent RAP, and percent asphalt binder) affected the performance criteria (dynamic modulus and fatigue life cycles). Results suggest that as the amount of RAP increases in asphalt concrete, both the dynamic modulus and fatigue life will increase. As per the literature, these results were expected for the dynamic modulus, but not for the fatigue life. It is suspected that the increase in fatigue life for the 40% RAP mixes may be due to the use of a softer binder (PG 64-22 instead of PG 70-22).  It was also found that by increasing the amount of binder in the mixture, the stiffness of asphalt concrete will decrease, but the fatigue life will improve. The fatigue life results showed a strong trend of this improvement for the 20% RAP samples, however, the results for the 40% RAP samples were inconclusive. For dynamic modulus, it was found that the percent RAP, additional binder, frequency, and temperature were all statistically significant with 95% confidence. For the fatigue life, ANOVA showed that the percent RAP and additional binder were statistically significant with 95% confidence. These results suggest that by utilizing a higher percentage of RAP and asphalt binder, it is possible to meet or improve upon the dynamic modulus and fatigue life of the lower percentage of RAP samples. / Master of Science

Repeated or prolonged activation of skeletal muscle results in an acute decline in the muscle's ability to produce force, which is typically referred to as fatigue. Muscle fatigue is likely related to the by-products of cellular metabolism, alterations in neural activation and diminished membrane excitability that have been shown to accompany repeated contractions. However, the complicated etiology of the fatigue process makes it difficult to understand the relative influence of these physiological responses. Computational modeling of the skeletal muscle response to repeated activation is an appealing means of gaining insight into the mechanisms of muscle fatigue. A reasonably comprehensive model would include components that represent motor neurons and populations of muscle fibers that reflect the range of metabolic and contractile characteristics known to exist in human skeletal muscle. Consideration of joint and connective tissue mechanical properties will add translational value by predicting whole joint segment behavior that can be validated by in vivo experimentation. The proposed dissertation project involved the development of a computational model incorporating multiple components meant to represent the function of the intact neuromuscular system. The complete model combines previously-validated models of neural activation and contractile behavior with a control function that attempts to match torque output to a pre-determined task. The model uses experimentally-derived functions describing metabolic cost and force inhibition to predict the loss of force generating capacity during repeated activation. Once tested using data from a group of adult men, the parameters of this model were altered to reflect age-related changes in the human neuromuscular system. The model's ability to predict the well-established phenomenon of age-related fatigue resistance during isometric contractions was then tested. The results from this series of studies support the utility of a computational approach to the investigation of muscle fatigue, and provide useful tools for future studies.

The purpose of this study was to examine the relationships between age, gender and fatigue resistance, and further, to determine the relative influence that estrogen status, membrane excitability, absolute force and muscle length have over the development of fatigue. A total of 48 subjects, classified by age and gender participated in this study; 12 young males (25.3 ± 2.1 yrs.), 12 young females (23.5 ± 2.1 yrs.), 12 elderly males (71.7 ± 5.6 yrs.) and 12 elderly females (69.5 ± 4.6 yrs.). The young females were all eumenorrheic, not taking oral contraceptives and tested in the mid-follicular phase of the menstral cycle. None of the elderly females were on hormone replacement therapy. A 3 minute paradigm of intermittent maximal voluntary contractions (MVC) was used to fatigue the adductor pollicis muscle, in which 5s MVC's were alternated with 2s rest periods. In addition, maximal twitches were evoked in each 2s rest period. No gender difference in fatigability was evident between young males and young females when considering the fatigue index of the evoked twitch (FI-PT) (young males: 39.8 ± 26.7%, young females: 36.6 ± 19.0%). There was also no gender difference in fatigability found between elderly males and elderly females when considering the FI-PT (elderly males: 24.9 ± 26.6%, elderly females: 16.4 ± 48.9%). However, potentiation of the evoked twitches during fatigue may have confounded these measures. When considering the changes in voluntary force during fatigue, there was a strong trend for a gender by time interaction between young males and young females.(p=0.06), which suggests that the former were more fatigable. The trend for this gender difference was also apparent in the voluntary fatigue index (FI-MVC) (young males: 44.7 ± 10.5%, young females: 37.8 ± 14.1 %; p=0.12). Similarly, young males had a significant decrease in M-wave amplitude during the fatigue protocol and a trend for a decrease in M-wave area (p=0.08), while young females showed no significant decreases in either M-wave measure during the fatigue protocol. There was no gender difference found between the elderly males and elderly females when considering the FI-MVC (elderly males: 24.2 ± 10.7%, elderly females: 26.3 ± 14.5%). Both groups also showed small but significant reductions in theM-wave amplitude during the fatigue protocol, although M-wave area was well maintained. The fact that a strong trend for a gender difference in fatigability was found in the young subjects but not the elderly subjects, suggests that estrogen may possess fatigue resisting properties, even during short duration exercise in which glycogen depletion is not a concern. With respect to the age-related differences in fatigue, elderly males were found to be significantly more fatigue resistant than young males as indicated by the FI-MVC (p<0.01), and the significant age by time interaction during the fatigue protocol (p<0.01). In contrast, only a trend was found for an age by time interaction between the young and elderly females during the fatigue protocol (p=0.06). This trend for an age-related difference in fatigue amongst women was also reflected in the FI- MVC (p=0.13). / Thesis / Master of Science (MSc)

The physiological responses to exercise depend on intensity, duration, and type of exercise. The muscles in the body have complex regulation responses in order to create a certain resistance and adaptation to the exercise demands without fatigue. In the following study, we used the model of Alaskan sled dogs in order to analyze changes in gene expression within muscle tissue. Gene expression allows us to look more in depth into temporal or long term biological changes that take place in order for the muscle to adapt and maintain homeostasis. Eight dogs were used for the study; four biopsies from the femoris biceps were taken from each at different time points. Time point 1 (Tp1) untrained dogs, time point 2 (Tp2) after mid training, time point 3 (Tp3) fully trained and time point 4 (Tp4) were taken after dogs had completed a 400 mile run in 4 consecutive days. Time point one was used as a control ratio for the other three time points for analysis one, for the second analysis Tp1 was eliminated as a control. Analysis, one compared Tp2-Tp3 and Tp3-Tp4; the subsequent analysis looked at Tp1-Tp3. For Mid trained animals compared to fully trained, we looked at a total of 25 differentially expressed genes, for fully trained compared against acute exercise performance, we looked at total of 52 differentially expressed genes (based on a ≤0.01 p-value and fold change of ≥3), and untrained was compared to fully trained where we looked at a total of 26 differentially expressed genes. Known transcriptional regulators were mapped from these differentially expressed genes, such as exocyst complex, lysyl oxidase, protein tyrosine phosphatase, protein kinase C, creatine kinase, HSP40, cytochrome P450, ACSL6 gene responsible for Acyl-CoA synthesis, myosin chain, ATP binding, and ubiquitin, among others. These transcripts were linked to important biological pathways, and functional analysis of these pathways demonstrated that changes found in gene expression are responsible for muscle tissue remodeling, energy storage and metabolism changes, cardiovascular enhancement, and activation of elements that regulate metabolism via the nervous system. The following study of transcriptional regulation mechanisms helped identify specific responses to exercise stimuli in the organism that allow the athletes to adapt to the demands of exercise.

While the oxidation of binders in hot mix asphalt (HMA) pavements and its subsequent detrimental effects on pavement life have been well recognized in the last few years, many important issues have not yet been investigated. Understanding how best to design mixtures taking this phenomenon into account and achieving maximum durability is an important and complex issue. This study was aimed at characterizing the effects of oxidative aging on durability in terms of mixture fatigue resistance of laboratory mixed-laboratory compacted (LMLC) samples. Direct tension tests were conducted on HMA samples to measure mixture stiffness and a Modified Calibrated Mechanistic with Surface Energy (CMSE*) analysis method was used to predict fatigue life. The effect of various mix design parameters was evaluated to understand their importance with respect to the aging phenomena and mixture fatigue resistance. Analysis of the results showed that aging has a significant negative effect on mixture fatigue resistance. Considerable increase in the stiffness modulus (Eve) of the mixtures was observed with age for all three mixtures analyzed. Air voids (AV) played a substantial role in affecting the fatigue resistance with aging, but a difference of 0.5% in binder content near the optimum level did not statistically change mixture durability in terms of fatigue resistance with aging. For the three mixtures in Texas included in this study, when comparing Eve, one month of artificial aging in the laboratory was equivalent to 10.5 months of natural aging in the field. A good correlation was also found between the Eve of the mixture and the Carbonyl Area (CA) and Dynamic Shear Rheometer (DSR) function of the extracted binder. Thus, a connection exists between the properties of the extracted binder, laboratory mixtures and field mixtures. This relationship will facilitate development of a more mechanistic aging component in pavement performance prediction models.

In Deutschland werden Verkehrsflächenbefestigungen größtenteils auf der Grundlage empirisch gewonnener Erkenntnisse dimensioniert und ausgeführt. Die Dimensionierung der Dicken der gebundenen und ungebundenen Schichten von Straßenbefestigungen erfolgt unter Anwendung der RStO 12. Des Weiteren wird das Gebrauchsverhalten der Baustoffgemische dieser Schichten indirekt über ihre Zusammensetzung und einige wenige leistungsbezogene Prüfverfahren beschrieben. Da die Beanspruchung der Straßenbefestigungen in Deutschland aufgrund der Verkehrsentwicklung in den nächsten Jahren weiter zunehmen wird, reichen die traditionellen Prüfverfahren der indirekten Ansprache der Asphalteigenschaften jedoch nicht mehr aus, das Performance-Verhalten von im Straßenbau eingesetzten Asphalten zuverlässig prognostizieren zu können. Um dennoch die noch vorhandenen Ressourcen (z. B. Bitumen) effizienter zu nutzen, den Verkehrsteilnehmern ein weitgehend sicheres und dauerhaftes Verkehrsnetz zu bieten, weniger Verkehrsstaus aufgrund von Erhaltungs- bzw. Erneuerungsmaßnahmen von Straßen und der damit verbundenen Beeinträchtigung der Mobilität zu erzeugen, ist es von großer Bedeutung, die einzelnen Konstruktionsschichten von Verkehrsflächenbefestigungen aus Asphalt ihrer Beanspruchung entsprechend zu konzipieren. Die daraus resultierende Notwendigkeit weiterführender Untersuchungen definiert das Ziel dieser Arbeit. Das Ziel besteht darin, Kenntnisse über die Auswirkungen der Veränderung der Zusammensetzung von Asphaltgemischen auf die Ermüdungsbeständigkeit von Asphaltbefestigungen zu erlangen. Während bisher durchgeführte Forschungsvorhaben zum Einfluss der Zusammensetzung auf das Ermüdungsverhalten von Asphalten bei der Bewertung dieser Eigenschaft nur die Lastwechselzahl bei bestimmten Beanspruchungsgrößen (z. B. Spannung) herangezogen haben, bei der das Versagen eines Probekörpers (z. B. Bruch) eintritt, sollen die in dieser Arbeit durchgeführten Untersuchungen das gesamte Spektrum an möglichen Belastungen aus Verkehr und Temperatur, welche auf eine Asphaltbefestigung einwirken können, berücksichtigen. Zunächst erfolgt eine theoretische Einführung zum Material- und Ermüdungsverhalten von Asphalt, den in Deutschland angewendeten analytischen Verfahren der Dimensionierung von Ver-kehrsflächenbefestigungen aus Asphalt sowie eine Zusammenfassung bisheriger Forschungsarbeiten zum Einfluss der Zusammensetzung von Asphaltgemischen auf ihr Steifigkeits- und Ermüdungsverhalten (dimensionierungsrelevante Materialeigenschaften). Weiterhin werden die erforderlichen statistischen Analysen zur Auswertung der Ergebnisse zum Einfluss der Variation der Asphaltzusammensetzung in ihren Wirkungen auf diese Materialeigenschaften geschildert. Es werden die zu untersuchenden Asphaltvarianten, die Bestimmung des Ermüdungs- und Steifigkeitsverhaltens mit dem Spaltzug-Schwellversuch und die Festlegungen für die Durchführung der rechnerischen Dimensionierung einer fiktiven Asphaltbefestigung erläutert. Im Hauptteil der Arbeit werden die Ergebnisse der Variation der Zusammensetzung der untersuchten Asphaltgemische auf die versuchstechnisch ermittelten dimensionierungsrelevanten Materialeigenschaften, dargestellt. Die Ergebnisse der Dimensionierungsberechnungen unter Verwendung der versuchstechnisch ermittelten Materialeigenschaften zeigten, dass die Ermüdungsbeständigkeit von Asphaltbefestigungen erheblich durch die Zusammensetzung von Asphalttragschichtgemischen beeinflusst wird. / In Germany, pavement structures are commonly designed based on empirical knowledge. The thickness design of the bound and unbound pavement layers in Germany is currently chosen using the empirical design guideline RStO 12. Furthermore, the performance of the materials used in the pavement structure is described indirectly through the composition, and the results of defined performance-based test methods. Because the traffic volume in Germany will increase in future, the traditional testing methods (indirect testing methods) to describe the asphalt properties are no longer sufficient to be able to predict the performance of asphalt mixes used in pavements reliable. In order to use the still existing resources (e.g. bitumen) efficiently, to offer users a mostly safe and sustainable transport network, to minimize traffic congestion resulting from maintenance and renewal measures of pavements and the associated impact of mobility of the users, is required to design the pavement layers according to their stress and strain condition in the pavement. For this reason, the thesis aims to gain knowledge about the impact of the change in the asphalt mix composition on the fatigue resistance of asphalt pavements. Research projects previously conducted have used the influence of the mix composition on the fatigue behavior of asphalt the number of load cycles at certain loading parameters (e.g. stress) only in which the failure of a test specimen (e.g. failure) occurs. However, the tests conducted in this research covered the entire range of possible traffic loads and temperature conditions, which can act on a asphalt pavement in reality. Firstly, a theoretical introduction regarding the material and fatigue behavior of asphalt mixes and the German analytical design method for asphalt pavements are presented. In addition, a summary of previous research on the influence of the asphalt mix composition in terms of stiffness and fatigue behavior as well as the design relevant material properties is given. Furthermore, the statistical analyzes necessary to evaluate the results in dependence on the variation of the asphalt mix composition and their effects on these material properties are described in detail. The asphalt mixes investigated, the procedure to determine the fatigue and master curve using the results of indirect tensile tests and the analytical design procedure for a “fictive“ asphalt pavement structure are explained in detail The main part of the dissertation presents the influence of the asphalt mix composition on the design relevant material properties which were determined experimentally using the results of appropriate laboratory tests. The results of the pavement design analysis taking into the material properties which were determined using the result of laboratory tests showed, that the fatigue resistance of asphalt pavements is significantly affected by the composition of asphalt basecourse.

With an increasingly aging population, a significant challenge in implantology is the creation of biomaterials that actively promote and accelerate tissue integration while offering excellent mechanical properties. Engineered surfaces with superimposed micro and nanoscale topographies showed great potential to control and direct biomaterial-host tissue interactions. However, these modified surfaces require a careful assessment to prevent potential adverse effects on the fatigue resistance, a factor which may ultimately cause premature failure of biomedical implants. In this context, the surfaces of two widely used biocompatible metals, namely CP Ti and Ti-6Al-4V, were engineered through simple yet efficient chemical treatments which demonstrated the ability to confer exciting new bioactive capacities. The qualitative and quantitative assessments of the fatigue resistance of polished and treated metals were carried out. Results from this study highlight the importance of mechanical considerations in the development and evaluation of nanoscale surface treatments for metallic biomedical implants.

With an increasingly aging population, a significant challenge in implantology is the creation of biomaterials that actively promote and accelerate tissue integration while offering excellent mechanical properties. Engineered surfaces with superimposed micro and nanoscale topographies showed great potential to control and direct biomaterial-host tissue interactions. However, these modified surfaces require a careful assessment to prevent potential adverse effects on the fatigue resistance, a factor which may ultimately cause premature failure of biomedical implants. In this context, the surfaces of two widely used biocompatible metals, namely CP Ti and Ti-6Al-4V, were engineered through simple yet efficient chemical treatments which demonstrated the ability to confer exciting new bioactive capacities. The qualitative and quantitative assessments of the fatigue resistance of polished and treated metals were carried out. Results from this study highlight the importance of mechanical considerations in the development and evaluation of nanoscale surface treatments for metallic biomedical implants.

In Deutschland werden Verkehrsflächenbefestigungen größtenteils auf der Grundlage empirisch gewonnener Erkenntnisse dimensioniert und ausgeführt. Die Dimensionierung der Dicken der gebundenen und ungebundenen Schichten von Straßenbefestigungen erfolgt unter Anwendung der RStO 12. Des Weiteren wird das Gebrauchsverhalten der Baustoffgemische dieser Schichten indirekt über ihre Zusammensetzung und einige wenige leistungsbezogene Prüfverfahren beschrieben. Da die Beanspruchung der Straßenbefestigungen in Deutschland aufgrund der Verkehrsentwicklung in den nächsten Jahren weiter zunehmen wird, reichen die traditionellen Prüfverfahren der indirekten Ansprache der Asphalteigenschaften jedoch nicht mehr aus, das Performance-Verhalten von im Straßenbau eingesetzten Asphalten zuverlässig prognostizieren zu können. Um dennoch die noch vorhandenen Ressourcen (z. B. Bitumen) effizienter zu nutzen, den Verkehrsteilnehmern ein weitgehend sicheres und dauerhaftes Verkehrsnetz zu bieten, weniger Verkehrsstaus aufgrund von Erhaltungs- bzw. Erneuerungsmaßnahmen von Straßen und der damit verbundenen Beeinträchtigung der Mobilität zu erzeugen, ist es von großer Bedeutung, die einzelnen Konstruktionsschichten von Verkehrsflächenbefestigungen aus Asphalt ihrer Beanspruchung entsprechend zu konzipieren. Die daraus resultierende Notwendigkeit weiterführender Untersuchungen definiert das Ziel dieser Arbeit. Das Ziel besteht darin, Kenntnisse über die Auswirkungen der Veränderung der Zusammensetzung von Asphaltgemischen auf die Ermüdungsbeständigkeit von Asphaltbefestigungen zu erlangen. Während bisher durchgeführte Forschungsvorhaben zum Einfluss der Zusammensetzung auf das Ermüdungsverhalten von Asphalten bei der Bewertung dieser Eigenschaft nur die Lastwechselzahl bei bestimmten Beanspruchungsgrößen (z. B. Spannung) herangezogen haben, bei der das Versagen eines Probekörpers (z. B. Bruch) eintritt, sollen die in dieser Arbeit durchgeführten Untersuchungen das gesamte Spektrum an möglichen Belastungen aus Verkehr und Temperatur, welche auf eine Asphaltbefestigung einwirken können, berücksichtigen. Zunächst erfolgt eine theoretische Einführung zum Material- und Ermüdungsverhalten von Asphalt, den in Deutschland angewendeten analytischen Verfahren der Dimensionierung von Ver-kehrsflächenbefestigungen aus Asphalt sowie eine Zusammenfassung bisheriger Forschungsarbeiten zum Einfluss der Zusammensetzung von Asphaltgemischen auf ihr Steifigkeits- und Ermüdungsverhalten (dimensionierungsrelevante Materialeigenschaften). Weiterhin werden die erforderlichen statistischen Analysen zur Auswertung der Ergebnisse zum Einfluss der Variation der Asphaltzusammensetzung in ihren Wirkungen auf diese Materialeigenschaften geschildert. Es werden die zu untersuchenden Asphaltvarianten, die Bestimmung des Ermüdungs- und Steifigkeitsverhaltens mit dem Spaltzug-Schwellversuch und die Festlegungen für die Durchführung der rechnerischen Dimensionierung einer fiktiven Asphaltbefestigung erläutert. Im Hauptteil der Arbeit werden die Ergebnisse der Variation der Zusammensetzung der untersuchten Asphaltgemische auf die versuchstechnisch ermittelten dimensionierungsrelevanten Materialeigenschaften, dargestellt. Die Ergebnisse der Dimensionierungsberechnungen unter Verwendung der versuchstechnisch ermittelten Materialeigenschaften zeigten, dass die Ermüdungsbeständigkeit von Asphaltbefestigungen erheblich durch die Zusammensetzung von Asphalttragschichtgemischen beeinflusst wird. / In Germany, pavement structures are commonly designed based on empirical knowledge. The thickness design of the bound and unbound pavement layers in Germany is currently chosen using the empirical design guideline RStO 12. Furthermore, the performance of the materials used in the pavement structure is described indirectly through the composition, and the results of defined performance-based test methods. Because the traffic volume in Germany will increase in future, the traditional testing methods (indirect testing methods) to describe the asphalt properties are no longer sufficient to be able to predict the performance of asphalt mixes used in pavements reliable. In order to use the still existing resources (e.g. bitumen) efficiently, to offer users a mostly safe and sustainable transport network, to minimize traffic congestion resulting from maintenance and renewal measures of pavements and the associated impact of mobility of the users, is required to design the pavement layers according to their stress and strain condition in the pavement. For this reason, the thesis aims to gain knowledge about the impact of the change in the asphalt mix composition on the fatigue resistance of asphalt pavements. Research projects previously conducted have used the influence of the mix composition on the fatigue behavior of asphalt the number of load cycles at certain loading parameters (e.g. stress) only in which the failure of a test specimen (e.g. failure) occurs. However, the tests conducted in this research covered the entire range of possible traffic loads and temperature conditions, which can act on a asphalt pavement in reality. Firstly, a theoretical introduction regarding the material and fatigue behavior of asphalt mixes and the German analytical design method for asphalt pavements are presented. In addition, a summary of previous research on the influence of the asphalt mix composition in terms of stiffness and fatigue behavior as well as the design relevant material properties is given. Furthermore, the statistical analyzes necessary to evaluate the results in dependence on the variation of the asphalt mix composition and their effects on these material properties are described in detail. The asphalt mixes investigated, the procedure to determine the fatigue and master curve using the results of indirect tensile tests and the analytical design procedure for a “fictive“ asphalt pavement structure are explained in detail The main part of the dissertation presents the influence of the asphalt mix composition on the design relevant material properties which were determined experimentally using the results of appropriate laboratory tests. The results of the pavement design analysis taking into the material properties which were determined using the result of laboratory tests showed, that the fatigue resistance of asphalt pavements is significantly affected by the composition of asphalt basecourse.