A dissipated energy comparison to evaluate fatigue resistance using 2PB

Flexural fatigue due to repeated traffic loading is a process of cumulative damage and one of the main failure modes of flexible pavement structures. Typically, micro-cracks originate at the bottom of an asphalt concrete layer due to horizontal tensile strains. Micro-cracking starts to propagate towards the upper layers under repeated loading which can lead to pavement failure. Different approaches are usually used to characterise fatigue resistance in asphalt mixtures including the phenomenological approach, the fracture mechanics approach and the dissipated energy approach. This paper presents a comparison of fatigue resistance calculated for different dissipated energy models using 2 Point Bending (2PB) at IFSTTAR in Nantes. 2PB tests have been undertaken under different loading and environmental conditions in order to evaluate the properties of the mixtures (stiffness, dissipated energy, fatigue life and healing effect)

Fatigue resistance: is it possible having a unique response?

The mechanical characterisation of the asphalt concrete in terms of both the fatigue resistance and the stiffness modulus is necessary to use any design method of the flexible road pavements. Different kinds of test are usually used in experimental work such as bending tests, uniaxial tests, etc., but sometimes they do not give the same answer. In this paper mechanical characterization was carried out by means of fatigue tests undertaken with two most used testing machines for asphalt material: two point bending (2PB) test at IFSTTAR in Nantes (France) and four point bending (4PB) test at University of Palermo, in Palermo (Italy). Different strain controlled tests were undertaken for the same material under the same loading conditions, frequency and temperature (15 Hz and 20˚C), according to the European standard 12697 part 24 and 26. The first results of this interlaboratory activity are showed in this paper

Motivators and barriers for older people participating in resistance training: A systematic review

Regular participation in resistance training is important for older people to maintain their health and independence, yet participation rates are low. The study aimed to identify motivators and barriers to older people participating in resistance training. A systematic review was conducted including quantitative, qualitative and mixed-method studies. Searches generated 15,920 citations from six databases, with 14 studies (n=1,937 participants) included. In total, 92 motivators and 24 barriers were identified. Motivators specific to participating in resistance training included preventing deterioration (disability), reducing risk of falls, building (toning) muscles, feeling more alert and better concentration. Looking too muscular and thinking participation increased the risk of having a heart attack, stroke or death, despite the minimal likelihood of these occurring, were barriers. The analysis indicates that increasing participation in resistance training among older people should focus on the specific benefits valued by older people and the dissemination of accurate information to counter misperceptions

Moisture susceptibility of high and low compaction dry process crumb rubber modified asphalt mixtures

The field performance of dry process crumb rubber-modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures

Использование инструментов Data Mining для анализа успеваемости студентов университета

В результате выполнения работы произведен анализ характеристик студентов и их успеваемости с помощью инструментов Data Mining. Были построены и сравнены между собой прогнозные модели, а также спроектировано и разработано веб-приложение.As a result of the work, the analysis of students' characteristics and their academic performance was performed using Data Mining tools. Predictive models were built and compared, and a web application was designed and developed

Evaluation of bio-materials’ rejuvenating effect on binders for high-reclaimed asphalt content mixtures

The interest in using bio-materials in pavement engineering has grown significantly over the last decades due to environmental concerns about the use of non-recoverable natural resources. In this paper, bio-materials are used together with Reclaimed Asphalt (RA) to restore some of the properties of the aged bitumen present in mixtures with high RA content. For this purpose, two bio-materials are studied and compared to conventional and polymer modified bitumens. Blends of these materials with RA bitumen were produced and studied to simulate a 50% RA mixture. The rejuvenating effect of the two bio-materials on RA has been assessed and compared with the effect of the conventional binders. Apparent Molecular Weight Distribution of the samples (obtained by the ?-method) and different rheological parameters were used for this purpose. Results revealed the power of bio-materials to rejuvenate RA bitumen, showing their capability to be used as fresh binders in high-RA content mixtures

Ferromagnetic GaMnAs/GaAs superlattices - MBE growth and magnetic properties

We have studied the magnetic properties of (GaMnAs)m/(GaAs)n superlattices with magnetic GaMnAs layers of thickness between 8 and 16 molecular layers (ML) (23-45 \AA), and with nonmagnetic GaAs spacers from 4 ML to 10 ML (11-28 \AA). While previous reports state that GaMnAs layers thinner than 50 \AA are paramagnetic in the whole Mn composition range achievable using MBE growth (up to 8% Mn), we have found that short period superlattices exhibit a paramagnetic-to-ferromagnetic phase transition with a transition temperature which depends on both the thickness of the magnetic GaMnAs layer and the nonmagnetic GaAs spacer. The neutron scattering experiments have shown that the magnetic layers in superlattices are ferromagnetically coupled for both thin (below 50 \AA) and thick (above 50 \AA) GaMnAs layers.Comment: Proceedings of 4th International Workshop on Molecular Beam Epitaxy and Vapour Phase Epitaxy Growth Physics and Technology, September 23 - 28 (2001), Warszawa, Poland, to appear in Thin Solid Films. 24 pages, 8 figure

Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders

Bitumen is a viscoelastic material that exhibits both elastic and viscous components of response and displays both a temperature and time dependent relationship between applied stresses and resultant strains. In addition, as bitumen is responsible for the viscoelastic behaviour of all bituminous materials, it plays a dominant role in defining many of the aspects of asphalt road performance, such as strength and stiffness, permanent deformation and cracking. Although conventional bituminous materials perform satisfactorily in most highway pavement applications, there are situations that require the modification of the binder to enhance the properties of existing asphalt material. The best known form of modification is by means of polymer modification, traditionally used to improve the temperature and time susceptibility of bitumen. Tyre rubber modification is another form using recycled crumb tyre rubber to alter the properties of conventional bitumen. In addition, alternative binders (synthetic polymeric binders as well as renewable, environmental-friendly bio-binders) have entered the bitumen market over the last few years due to concerns over the continued availability of bitumen from current crudes and refinery processes. This paper provides a detailed rheological assessment, under both temperature and time regimes, of a range of conventional, modified and alternative binders in terms of the materials dynamic (oscillatory) viscoelastic response. The rheological results show the improved viscoelastic properties of polymer- and rubber-modified binders in terms of increased complex shear modulus and elastic response, particularly at high temperatures and low frequencies. The synthetic binders were found to demonstrate complex rheological behaviour relative to that seen for conventional bituminous binders

Films and critical pedagogy in management education: A tourism studies context

This article examines and critically assesses the role of films in the practice of critical pedagogy in undergraduate management education, using tourism studies as a context. Utilising online focus groups, it aims to gain an in-depth knowledge and understanding of the role of films as an effective pedagogical medium in enhancing experiential approaches to learning. It argues that films play an important role in facilitating critical analyses of the studied phenomenon, illustrating and problematising abstract concepts and ideas, as well as in facilitating students’ ability to discern multiple and alternative discourses about management. The findings highlight the role of films in context-specific critical engagement with the studied content and in stimulating emotionality in learning development, thereby enhancing deep approaches to learning. Emotional responses, even negative ones, prove to be critical in engaging with intellectual and critical reflection after watching films. The findings yield new and empirical insights into the pedagogic use of films in management education, thereby contributing to some of the goals of critical management studies