159 research outputs found
Effect of Selected Antiretroviral Drugs on Malondialdehyde (MDA)and Catalase Levels in Healthy Rat Tissues
No full textThe study assessed the effect of selected antiretroviral drugs used in the management of HIV/AIDS on the oxidative stress marker malondialdehyde (as TBARs) and the antioxidant enzyme, Catalase, of the liver and kidney tissues of healthy albino rats. 0.43, 0.43, 0.27, and 0.21mg/kg of Efavirenz, Abacavir, SNP 40 and Lamivudine respectively, were orally administered to four different groups of albino rats for seven days. The control group received normal saline. On the eighth day, the rats were sacrificed and the liver and kidney tissues were collected for Lipid peroxidation and Catalase activity analysis. Efavirenz and Lamivudine caused significant decrease (P0.05) compared to the control. All the drugs caused significant increase (P<0.05) in Catalase activity in the liver and a significant decrease (P<0.05) in Catalase activity in the kidney. Taken together, the present observation suggests that the effects of antiretroviral drugs on oxidative stress markers (such as MDA) and on antioxidant enzymes (such as catalase) in healthy as well as in HIV infected humans (by way of extrapolation) may vary from drug to drug and from organ to organ. We therefore advocate for extensive clinical research to investigate the influence of antiretroviral drugs on antioxidants enzymes in HIV and HIV/AIDS patients. Keywords: antiretroviral drugs, lipid peroxidation, liver, kidney, catalase
Anti-reflective cracking design of (reinforced) asphaltic overlays
No full textCivil Engineering and Geoscience
Characterization of Unbound Granular Materials for Pavements
No full textThis research is focused on the characterization of the mechanical behavior of unbound granular road base materials (UGMs). An extensive laboratory investigation is described, in which various methods for determination of the mechanical properties of granular materials are examined for their applicability, particularly in developing countries. Further, the mechanical behavior of unbound granular materials as a function of the moisture content and the degree of compaction is investigated. A study into the modeling of the stress dependent mechanical behavior of granular materials is presented. Finally, verification and validation of a relatively simple characterization technique, the repeated load CBR test (RL-CBR), by the results of cyclic load triaxial testing are provided and overall practical implications of the research are presented. The laboratory investigation involves a large range of granular materials, mainly (sub-)tropical road base and subbase materials. The performed tests yield fundamental parameters that describe the strength, stiffness and resistance to permanent deformation of the materials tested. In addition to the (sub-)tropical road base and subbase materials, a recycled mix-granulate widely used in pavement construction in the Netherlands and a base course and frost protection material from Austria are incorporated to a limited extent in the laboratory testing program. Most roads in developing countries are either unpaved or have a thin asphalt surfacing, and as a consequence the granular base and subbase layers provide the bulk of the bearing capacity. Although the important structural contribution of these unbound granular layers is understood, engineering practice still greatly relies on tests which mainly give index properties of these materials. Pavement structures are designed based on empirical design methods related to a single design chart, restricting the incorporation of marginal materials or new materials for which the empirical data sets are not available. The reasons that pavement design and construction in developing countries rely on empirical design procedures that are basically developed for completely different conditions are: - the affordability and complexity of the cyclic triaxial tests required to determine the stress dependent mechanical behavior of granular materials; - the perceived complexity and unfamiliarity with the computational tools (non-linear multilayer or finite element analysis) required to model the performance of pavements using this mechanical behavior despite the availability of powerful digital computers and their penetration even to remote places. In order to promote the introduction of Mechanistic-Empirical design methods in developing countries, this research was set up with two goals: i. to make the characterization technique for the mechanical behavior of granular road base materials more accessible to practice through the development of a simple and effective characterization technique; ii. to further develop the understanding of the stress dependent mechanical behavior of unbound (sub-)tropical base and subbase materials. To achieve the first aim an innovative and relatively simple testing procedure, the RL-CBR test, is developed to characterize the mechanical behavior of the UGMs. RL-CBR testing is performed on the various granular materials in steel moulds without and with strain gauges. With the strain gauges the confining condition and hence the stress state of the specimen is estimated through mould deformation measurements. The finite element method (FEM) is used to model the RL-CBR testing and interpret the test results into mechanical behavior. Due to the non-uniform complex stress distribution in the RL-CBR compared to the triaxial test, fundamental material properties such as the stiffness modulus are less easy to determine. Extensive triaxial testing on the various granular materials is performed to realize the second goal. The result of this investigation is also used to validate and verify the results of the RL-CBR tests. Moreover, the effect of influence factors such as moisture content, degree of compaction, material type etc. on the mechanical behavior is investigated. For the unbound granular road base materials, particularly the natural gravels, the effect of the moisture content on the mechanical behavior was found to be more significant than the effect of the degree of compaction. Relative to the failure and permanent deformation behavior the resilient deformation behavior is less affected by the moisture content and the degree of compaction. The RL-CBR testing serves well its purpose to get a good estimate of the fundamental mechanical properties of granular road base materials from a rather simple characterization technique. The practical accessibility of characterizing the mechanical behavior of UGMs can therefore be enhanced through RL-CBR testing. This is proven by the fact that good correlations have been found between the stiffness results of the two characterization techniques, i.e. the complex triaxial test and the newly developed repeated load CBR test.Design and ConstructionCivil Engineering and Geoscience
Performance related characterisation of the mechanical behaviour of asphalt mixtures
No full textAbstract not availableCivil Engineering and Geoscience
Design principles of surfacings on orthotropic steel bridge decks
No full textThis dissertation describes the research into surfacings of orthotropic steel bridge decks. The motive for this research is the frequently reported problems of this type of structures including cracking and rutting of surfacing materials and fatigue related cracks in the steel plate. An intensive experimental program was carried out on three wearing course materials, namely mastic asphalt, guss asphalt and an open synthetic material. The program also included on a bituminous based membrane material. The results of the experimental program were analysed to characterise the complex mechanical behaviour of the different materials. Within the framework of this research, models that describe the response of the surfacing materials were developed, including a newly developed unified model that describes the time-temperature characteristics of many road materials. Furthermore, constitutive relations for elastic as well as inelastic response of the materials were developed. All the developed models were implemented in the Finite Element System CAPA-3D. For verification of the different models results of laboratory tests and full-scale experiments in the LINTRACK APT facility were used. Furthermore, a scientific approach in which the non-linear response of the materials, the geometry and the load are well presented, was used to give an insight into the interaction between the different components of the structure and the vehicle at different temperatures. Because this scientific approach is too sophisticated and expensive for routine analyses and design of the structure, a practical design concept is proposed. In this concept, the geometry and the load are well presented, but the material behaviour is simplifiedCivil Engineering and Geoscience
Development of an Evaluation Protocol for Self-Cementing Secondary Road Base Materials
No full textIn congested areas around the world, traffic has significantly grown beyond expectation in terms of both volume and weight. Any hinder to the traffic causes severe delays resulting not only in economic loss but also in extra pollution of the environment. Therefore, the number of times maintenance work have to be performed should be reduced as much as possible. Application of self-cementing, secondary materials such as Blast Furnace Slag (BFS) for base courses is one of the methods to reduce the need for maintenance, since such base courses can provide an increase of the stiffness and the strength of the pavement structure. The long-term performance of this type of self-cementing, secondary material is however not fully understood. Because this type of stabilization appears to be associated with undesired deformations and distresses such as heaves formation and cracking. These undesired defects, which appear at random in terms of severity and moment of occurring, requires an assessment of the long-term physical and mechanical performance of these materials. However, long-term behaviour is often difficult to predict. In general, field-scale trials monitored over a long period of time, are needed to provide information whether these materials can be used without significant risk or not. As an alternative to field trials, which are time consuming and expensive, reliable methodologies are needed to estimate the long-term physical and mechanical performance within a short period of time. In this research, a protocol is proposed as a means of exploring the long-term mechanical and physical performance of secondary materials. A slag mixture which is routinely used in the Netherlands in road (sub-)bases was selected as study material. The slag mixture consisted of fresh Air-cooled Blast Furnace Slag (AC-BFS), steel slag and Granulated Blast Furnace Slag (GBFS) sand. The A32 motorway in the Netherlands was used as a source of field aged Blast Furnace Slag and steel slag materials. The pavement structure of this motorway experienced serious failure after about 20 years of service life and the base layer material caused this failure. In order to prevent similar problems to occur in the future, this research suggests different methods to detect at an early stage potential poor material performance. The first step of exploring the long-term performance of self-cementing materials in road applications implies obtaining a better understanding of the physical, mechanical and microstructural features of the materials when used as road base material and to analysis its possible effects on the pavement performance. Consequently, the influence of different potential degradation conditions, which can be mimicked in the laboratory was investigated. Numerous failure mechanisms have been hypothesized, including chemical reactions and increased stresses due to obstructed deformations. Additionally, other physical failure mechanisms including frost action damage were investigated. The results show that there is a linkage between the secondary material performance and temperature, moisture, chemical composition and time. The measured data indicate a relationship between some major chemical compositions and the mechanical properties of slags. The response of the laboratory prepared samples to the proposed tests were similar to the A32 base material failure, suggesting that the evaluation method did a reasonable job of producing in an accelerated way in the laboratory a material which behaves similar as the A32 material. The developed procedure (protocol) suggests that it is possible on the basis of material characterization, steam aging tests and freezing – thawing tests to trace in a rather short period of time materials which may attribute to the failure process of base layers in pavements.Structural EngineeringCivil Engineering and Geoscience
The effect of aging on binder proporties of porous asphalt concrete
No full textIn this dissertation, the results of a research on the effects of aging on the binder properties of porous asphalt concrete (PAC) are described. The research has been done on laboratory and field aged specimens. In addition to the conventional aging methods for short and long term aging of the binder in the laboratory, a new mixture aging protocol in a 'weatherometer' was proposed that combines the main environmental factors influencing field aging, i.e. temperature, UV light, and humidity/moisture. The field binders were recovered from specimens taken from road sections immediately after construction and after 1, 3, 7, and 12 years service life. Rheological, mechanical, and chemical characterization of the binders was conducted on the laboratory and field binders to understand the effects of aging. To this end, the determination of fundamental rheological binder properties was performed in addition to conventional empirical properties such as penetration and softening point. Low temperature tensile and stiffness properties of the binder/mastic were determined using the Direct Tensile Test (DTT) and Bending Beam Rheometer (BBR). The Dynamic Shear Rheometer (DSR) was used to determine the viscoelastic properties (complex modulus and phase angle) of the binders in a wide range of temperatures. Furthermore, the DSR was used to determine the fatigue properties of the binders using strain controlled repeated loading at different strain levels. Chemical characterization using Infrared spectroscopy (IR) and Gel-Permeation Chromatography (GPC) were performed to determine, respectively, the development of the functional groups responsible for aging and the Molecular Weight Distribution (MWD). All the test results have provided insight into laboratory and field aging simulations, the impact of the filler, and at the same time has provided material properties for constitutive modelling. An important finding in this research signifies that aging greatly influences the low temperature performance of the binding material leading to a higher rate of damage accumulation (fatigue) and ultimately ravelling of PA. To illustrate the implications of the research results, a limited number of finite element calculations have been made to determine the stress conditions in the binder/mortar due to traffic loads. Because aging has a negative influence on the fatigue resistance and relaxation behaviour of the binder, aging negatively influences the performance of PAC.Civil Engineering and Geoscience
Accelerated testing and surface cracking of asphaltic concrete pavements
No full textCivil Engineering and Geoscience
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