Effects of Temperature Segregation on the Denisity and Mechanical Properties of Asphalt Mixtures

Temperature differentials (TD) between the target laydown and actual laydown temperatures of asphalt paving mixtures have been noticed and measured since the late 1990s. Since then, numerous research studies conducted on the phenomena found inconclusive conclusions regarding the effects of TD on the initial pavement quality and the long-term performance. The objective of this study was to evaluate the effects of different levels of TD on the initial quality and the long-term performance of asphalt pavements by evaluating the core density and laboratory measured performance characteristics, respectively. Through the evaluation, it was also aimed to ascertain and establish allowable TD range, which would not adversely affect the quality and performance of the pavements. In addition, impacts of construction related factors such as using different types of material transfer vehicles (MTV), different contractors, ambient temperature, etc. on temperature and density differentials were also evaluated. Seven asphalt rehabilitation projects across Louisiana were selected for this study differing in use of mixture type, laydown temperature, mix layer, month of paving, etc. A multi-sensory infrared temperature scanning bar (IR-bar) system and a hand-held portable thermal camera were used to measure the temperature differentials. Field core samples were collected from thermally segregated areas, which were then evaluated in the laboratory using the Density test, Semi-Circular Bending (SCB) test, Loaded Wheel Tracking (LWT) test, and Indirect Tensile Dynamic Modulus (IDT|E*|) test. Two distinct temperature patterns were observed throughout all projects. Cyclic temperature patterns showing regular high-low temperature fluctuations while irregular patterns caused by work stoppages were present in all thermal profiles. Laboratory test results showed pavement density and SCB Jc values correlated strongly with the temperatures measured prior to compaction. LWT, and IDT|E*| test results showed a decreasing trend in rut depth and stiffness with increasing TD severity level. Furthermore, IR-bar temperature readings were used to measure consistency by defining one qualitative (standard deviation) and one quantitative (%severity levels) parameter. Comparisons with construction factors showed that use of MTV increased consistency in temperature. Based on the results of this study, IR-bar system was found useful to monitor consistency in laydown temperatures. However temperature monitoring at breakdown compaction was observed to present actual effect of temperature differential on pavement performance. To ensure that asphalt mixture gets compacted at target temperature, it was strongly advised to instruct breakdown compactor operator to follow the paver closely. Additionally, the use of tarps over un-compacted portion of asphalt mat is strongly advised to prevent significant temperature loss during paver stops

Oral application of L-menthol in the heat: From pleasure to performance

When menthol is applied to the oral cavity it presents with a familiar refreshing sensation and cooling mint flavour. This may be deemed hedonic in some individuals, but may cause irritation in others. This variation in response is likely dependent upon trigeminal sensitivity toward cold stimuli, suggesting a need for a menthol solution that can be easily personalised. Menthol’s characteristics can also be enhanced by matching colour to qualitative outcomes; a factor which can easily be manipulated by practitioners working in athletic or occupational settings to potentially enhance intervention efficacy. This presentation will outline the efficacy of oral menthol application for improving time trial performance to date, either via swilling or via co-ingestion with other cooling strategies, with an emphasis upon how menthol can be applied in ecologically valid scenarios. Situations in which performance is not expected to be enhanced will also be discussed. An updated model by which menthol may prove hedonic, satiate thirst and affect ventilation will also be presented, with the potential performance implications of these findings discussed and modelled. Qualitative reflections from athletes that have implemented menthol mouth swilling in competition, training and maximal exercise will also be included

How Heat Affects Human Hair: Thermal Characterization and Predictive Modeling of Flat Ironing Effects

Many people with curly hair experience heat damage – loss of curls and structural degradation of hair – after repetitive use of flat irons. While an array of relevant studies provide insight into thermochemical processes behind the phenomenon, practical tools for flat iron users are unavailable. As a result, people shun heat for fear of unpredictable amount of heat damage while adopting other laborious methods to satisfy a persevering need for temporary hair straightening. Thus three overarching research projects emerge to address the problem. In Part 1, I develop an empirical approach to mathematically correlate four flat ironing parameters (a temperature setting, gliding speed, the number of passes, and exposure time) with three metrics of flat ironing results (reduction in fatigue strength, straightening efficacy, and permanent curl loss). The objective is to establish user-friendly predictive models for flat ironing results to help users make informed decisions. Hair samples are exposed to various flat ironing conditions to evaluate the impact of each parameter thereby formulating predictive models. In the subsequent study, the impact of heat protectants on the flat ironing results is exclusively investigated to provide insight into better utilizing the widely marketed products for protecting hair from heat damage. In Part 2, thermal characterization of human hair and heat transfer modeling serve as a practical tool for predicting the amount of heat damage due to flat ironing in conjunction with the previously developed predictive models. To measure thermal diffusivity of hair, I develop and validate a non-contact infrared thermography measurement technique based on the Angstrom Method. Then, these properties are integrated into a 2D heat transfer model of the thermal transport between a hair bundle and flat iron utilizing the finite difference method. Experimental validation of the model follows to complete the overarching goal of providing practical tools for decision making before flat ironing. This work provides a practical tool that assists flat iron users in making decisions regarding the use of flat irons. It also introduces novel empirical and modeling approaches for understanding the effects of flat ironing. Furthermore, it presents a novel measurement technique for thermal characterization of polymer fibers

Optimisation of welding parameters to mitigate the effect of residual stress on the fatigue life of nozzle–shell welded joints in cylindrical pressure vessels.

Doctoral Degree. University of KwaZulu-Natal, Durban.The process of welding steel structures inadvertently causes residual stress as a result of thermal cycles that the material is subjected to. These welding-induced residual stresses have been shown to be responsible for a number of catastrophic failures in critical infrastructure installations such as pressure vessels, ship’s hulls, steel roof structures, and others. The present study examines the relationship between welding input parameters and the resultant residual stress, fatigue properties, weld bead geometry and mechanical properties of welded carbon steel pressure vessels. The study focuses on circumferential nozzle-to-shell welds, which have not been studied to this extent until now. A hybrid methodology including experimentation, numerical analysis, and mathematical modelling is employed to map out the relationship between welding input parameters and the output weld characteristics in order to further optimize the input parameters to produce an optimal welded joint whose stress and fatigue characteristics enhance service life of the welded structure. The results of a series of experiments performed show that the mechanical properties such as hardness are significantly affected by the welding process parameters and thereby affect the service life of a welded pressure vessel. The weld geometry is also affected by the input parameters of the welding process such that bead width and bead depth will vary depending on the parametric combination of input variables. The fatigue properties of a welded pressure vessel structure are affected by the residual stress conditions of the structure. The fractional factorial design technique shows that the welding current (I) and voltage (V) are statistically significant controlling parameters in the welding process. The results of the neutron diffraction (ND) tests reveal that there is a high concentration of residual stresses close to the weld centre-line. These stresses subside with increasing distance from the centre-line. The resultant hoop residual stress distribution shows that the hoop stresses are highly tensile close to the weld centre-line, decrease in magnitude as the distance from the weld centre-line increases, then decrease back to zero before changing direction to compressive further away from the weld centre-line. The hoop stress distribution profile on the flange side is similar to that of the pipe side around the circumferential weld, and the residual stress peak values are equal to or higher than the yield strength of the filler material. The weld specimens failed at the weld toe where the hoop stress was generally highly tensile in most of the welded specimens. The multiobjective genetic algorithm is successfully used to produce a set of optimal solutions that are in agreement with values obtained during experiments. The 3D finite element model produced using MSC Marc software is generally comparable to physical experimentation. The results obtained in the present study are in agreement with similar studies reported in the literature

The mechanics of defect detection in vibrothermography

Vibrothermography is a nondestructive evaluation (NDE) technique that is used to detect surface and sub-surface defects such as cracks, disbonds, and delaminations through observations of vibration-induced frictional heat generation at defects. Frictional heating is observed using an infrared (IR) camera and is used to determine the presence and location of defects. There is a large industrial interest in vibrothermography due to its ability to rapidly detect defects over a large area. Another motivation for using this technology is its ability to find defects, such as tightly-closed cracks, that can be missed using other common NDE techniques. A major hindrance to the widespread application of vibrothermography has been an inability to quantify the reliability and capability of the inspection due to insufficient knowledge of the underlying physics of vibrothermography. The purpose of this work is to further understand the physics controlling defect detection in vibrothermography. The influence of vibration was studied through the use of synthetic defects and noncontact measures of vibration. Numerous samples of aluminum, brass, titanium, and carbon fiber-reinforced polymer composites were used to study the physics of heat generation to isolate the different sources of heat generation in metals and composites. The effects of crack closure on heat generation were studied and a method was developed to accurately measure crack closure stresses using vibrothermography. Finally, the effect of friction and heat generation on rubbing crack faces was observed using techniques such as profilometry, optical microscopy, and scanning electron microscopy. This work describes some of the fundamental parameters affecting heat generation and methods to improve defect detection reliability. This research provides a foundation for creating statistical models to improve the defect detection process using vibrothermography

Evaluation of short-term conservative treatment in patients with tennis elbow (lateral epicondylitis): A prospective randomised, assessor-blinded trial.

The complexity of the pathophysiology of tennis elbow is reflected by the lack of consensus on management and remains a therapeutic challenge. This study was a prospective randomised, assessor-blinded trial. 64 patients with tennis elbow referred by their GP to either the physiotherapy, orthopaedic or MSK CAT services, subject to eligibility criteria, were randomised into one of 3 treatment arms: injection, ultrasound or exercise, to which the assessor remained blinded. The outcome measures of thermal difference, median frequency (MDF), patient-rated tennis elbow evaluation questionnaire (PRTEE), pain-free grip strength (PFG) and patient preference were assessed twice at baseline, at 10 days, 6 weeks and 6 months and analysed as an intention to treat analysis. In the short term of 6 weeks injection was the most effective treatment demonstrating both statistically significant and minimum clinically important differences (MCID) for PFG and PRTEE in comparison to ultrasound and exercise. Patients had a strong preference for injection and a strong aversion for exercise. No statistically significant differences were found between ultrasound and exercise although a MCID was found in favour of ultrasound for thermal difference and MDF at 10 days. In to the long term of 6 months, although this was on a limited subgroup, no statistically significant differences were found between any of the groups. A MCID was found in favour of ultrasound for MDF and a MCID was found in favour of exercise over injection for all aspects of PRTEE and over ultrasound for PRTEE pain only. This research supports the superior effectiveness of injection in the short term of 6 weeks and should be advocated for patients who present early with severe limiting pain and have important short term goals, although patients need to be warned that a 1/3rd will have a recurrence of symptoms within 6 months. In contrast, for those patients who present with moderate to low pain physiotherapy including exercise and/ or ultrasound should be advocated. Thermal difference is a sensitive outcome measure for tennis elbow. Continuous 3 MHz therapeutic ultrasound at 2W/cm2 for 5 minutes utilises thermal effects which optimise the healing process and demonstrate an accumulative effect of ultrasound in to the long term. Further research on the effectiveness of a combination of injection with physiotherapy is required

Condition Assessment of Concrete Bridge Decks Using Ground and Airborne Infrared Thermography

Applications of nondestructive testing (NDT) technologies have shown promise in assessing the condition of existing concrete bridges. Infrared thermography (IRT) has gradually gained wider acceptance as a NDT and evaluation tool in the civil engineering field. The high capability of IRT in detecting subsurface delamination, commercial availability of infrared cameras, lower cost compared with other technologies, speed of data collection, and remote sensing are some of the expected benefits of applying this technique in bridge deck inspection practices. The research conducted in this thesis aims at developing a rational condition assessment system for concrete bridge decks based on IRT technology, and automating its analysis process in order to add this invaluable technique to the bridge inspector’s tool box. Ground penetrating radar (GPR) has also been vastly recognized as a NDT technique capable of evaluating the potential of active corrosion. Therefore, integrating IRT and GPR results in this research provides more precise assessments of bridge deck conditions. In addition, the research aims to establish a unique link between NDT technologies and inspector findings by developing a novel bridge deck condition rating index (BDCI). The proposed procedure captures the integrated results of IRT and GPR techniques, along with visual inspection judgements, thus overcoming the inherent scientific uncertainties of this process. Finally, the research aims to explore the potential application of unmanned aerial vehicle (UAV) infrared thermography for detecting hidden defects in concrete bridge decks. The NDT work in this thesis was conducted on full-scale deteriorated reinforced concrete bridge decks located in Montreal, Quebec and London, Ontario. The proposed models have been validated through various case studies. IRT, either from the ground or by utilizing a UAV with high-resolution thermal infrared imagery, was found to be an appropriate technology for inspecting and precisely detecting subsurface anomalies in concrete bridge decks. The proposed analysis produced thermal mosaic maps from the individual IR images. The k-means clustering classification technique was utilized to segment the mosaics and identify objective thresholds and, hence, to delineate different categories of delamination severity in the entire bridge decks. The proposed integration methodology of NDT technologies and visual inspection results provided more reliable BDCI. The information that was sought to identify the parameters affecting the integration process was gathered from bridge engineers with extensive experience and intuition. The analysis process utilized the fuzzy set theory to account for uncertainties and imprecision in the measurements of bridge deck defects detected by IRT and GPR testing along with bridge inspector observations. The developed system and models should stimulate wider acceptance of IRT as a rapid, systematic and cost-effective evaluation technique for detecting bridge deck delaminations. The proposed combination of IRT and GPR results should expand their correlative use in bridge deck inspection. Integrating the proposed BDCI procedure with existing bridge management systems can provide a detailed and timely picture of bridge health, thus helping transportation agencies in identifying critical deficiencies at various service life stages. Consequently, this can yield sizeable reductions in bridge inspection costs, effective allocation of limited maintenance and repair funds, and promote the safety, mobility, longevity, and reliability of our highway transportation assets