86,640 research outputs found
Discussing the feasibility of improving fatigue performance of asphalt mixtures by incorporating high recycled asphalt pavement
No full textThe application of Recycled Asphalt Pavement (RAP) is one of the most accepted strategies in pavement communities due to instability in natural sources and environmental issues, however the performance of substitute materials is still the main concern of producers. Structural properties of produced mixtures such as rutting resistance, strength and fatigue life have the main role in the durability of asphalt mixtures which strongly depend on aggregate and bitumen contents. This paper presents a review of recent studies and results on fatigue performance of asphalt mixtures containing different percentages of Recycled Asphalt Pavement (RAP). The aim of this paper is to emphasize the role of RAP in fatigue performance— which is one of the main distresses of bituminous mixtures- of asphalt mixtures and also to highlight benefits and disadvantages (limitation) of using high RAP content in asphalt mixtures. In addition, the possibility of using a high portion of RAP is discussed. Based on literature review, it can be inferred that including RAP could affect the fatigue performance of asphalt mixtures. © 2019 Taylor & Francis Group, London
Improving runway strip performance to fulfill international requirements through eco-efficient soil treatments: Case study of a major italian airport
No full textThe paper presents a case study of a significant intervention conducted on a major Italian airport for improving the structural and functional properties of the runway safety STRIP in order to fulfill specific national and international standards. The STRIP had to accomplish strict requirements in terms of the maximum longitudinal and transversal terrain slope and minimum values of bearing capacity; in particular, soil bearing capacity was identified as the main lack and thus the most urgent action to be carried out in the airport. However, the STRIP itself is located in a very critical area due to its closeness to the runway and several constraints were therefore identified during the design stage. The optimal strategy was identified as the one that minimized the intervention timing and costs, reducing the handling of construction material to/from the airport, avoiding delays to the air traffic, and maximizing the performance of the treated soils in terms of bearing capacity. In this framework, an energy-controlled stabilization technique of in-situ soils was developed. Several measurements, in both laboratory and field environment, were also conducted at different stages: i) before the intervention took place, ii) during the construction stage, and iii) at the conclusion of the work to monitor and validate the expected results. The intervention was able to provide the STRIP areas with a smooth surface presenting terrain slopes and bearing capacity in accordance with the standards. The illustrated methodology could also be applied to other airports saving time, costs, materials, and limiting air traffic delays
Deterioration trends of asphalt pavement friction and roughness from medium-term surveys on major Italian roads
No full textDeterioration models are the key factor for effective Pavement Management Systems, helping out road agencies to assess the actual pavement condition and forecast future performance of the asset. Among pavement condition characteristics, friction should be taken into account due to its important effect on user safety, while roughness could be used to express user comfort. The purpose of this study was to provide a reasonable case study for future improvements of Italian road management, even if the length of the analyzed highways was not intended to be representative of the overall Italian network. This research studied the friction trend (Side Force Coefficient) depending on traffic levels (ESALs) and pavement aging for Italian highways, combining the data with roughness and macrotexture. Surface characteristics were monitored during a seven-year time span. A selection of different road sections with homogeneous traffic levels, similar environmental conditions and surface material was performed and high-speed/high-quality road surveys were used for distress data collection. Pavement deterioration models for Italian road sectors were developed at project level, as starting point to advance pavement management practices in Italy. Degradation curves showed the same trends for similar pavement structures, materials and traffic levels; on the other hand, differences in pavement characteristics, increased ESALs and various maintenance treatments significantly altered those trends
Application of rejuvenators and virgin bitumen to restore physical and rheological properties of RAP binder
No full textBoth chemical and rheological aspects of aged bitumen in reclaimed asphalt pavement ( RAP) material play an important role in the final performance of bituminous mixtures containing recycled asphalt material. This must be especially considered in the case of pavements containing high RAP content. The use of rejuvenators and/or virgin bitumen in recycled mixtures helps improving the properties of aged bitumen. This research study investigates RAP oxidised bitumen and its possible rejuvenation with virgin bitumen and addition of various additives as rejuvenator agents. Tests were conducted to analyse the chemical, rheological and physical behaviours of several binder mixes before and after laboratory ageing processes. Longterm ageing of rejuvenated binder mixes was also investigated to assess the effectiveness of rejuvenation over time. The results showed that the addition of virgin bitumen and rejuvenators could improve the performance of oxidised bitumen and increase its resistance to further ageing
History of cardiac embolism
No full textFrom 1742, the first time Gerhard van Swieten postulated that embolism might arise inside the heart chambers and great vessels, another century was needed before that clinicians became accustomed to the concept that an embolism can lead to an occlusion of a brain artery. In fact, in 1875, Gowers described a case of blindness and contralateral hemiplegia in a patient with mitral stenosis. At autopsy, emboli were found in the middle cerebral artery and in the central retinal artery. Specifically, the emboli were found to originate from clots on the auricular appendices. Subsequently, in 1954, Fisher demonstrated that a thromboembolic mechanism underlies most ischemic strokes and that the source of thrombus might be the heart rather than a proximal arterial lesion. He suggested that the embolus might have arisen after myocardial infarction, in the fibrillating atrial appendage.
In 1977, a necropsy study provided additional evidence supporting the role of atrial fibrillation as a crucial cause of cerebral embolism which was later confirmed by large epidemiological studies. Finally, in the first part of the 1990’s, several studies reported that oral anticoagulants consistently reduced the risk of stroke in patients with atrial fibrillation. Oral anticoagulants currently remain the most powerful stroke prevention strategy available for patients with atrial fibrillation
Probability contour map of landing overrun based on aircraft braking distance computation
No full textRunway excursions have formed the biggest share of runway-related accidents compare to all possible types of airport recorded events worldwide. Out of different possible event scenarios of excursions, runway overrun, which may occur in both landing and take-off phases of flight, is the most frequent one. Therefore many studies have been conducted focusing on determination of the contributing factors which have influence on the probability of runway overrun occurrence. This probability is directly related to the difference between aircraft Landing Distance Required (LDR) and real-time braking distance. In this regard, aircraft braking distance under certain circumstances should be computed. Runway surface condition as a result of previous studies is known to be one of the most contributing factors in runway overrun accidents. Existence of different water-film thicknesses on the pavement decreases the pavement skid resistance which leads to lower friction, for instance; consequently, longer aircraft braking distance is needed and greater risk for aircrafts to overrun is expected. Skid resistance strongly depends on the complex relationship between the aircraft operating conditions and pavement surface properties. Braking distances for a selected set of aircrafts were calculated and plotted in probability distribution format. Based on the probability distribution compared to LDR for the selected set of aircrafts, the landing overrun probability contour map and safety/risk probability distribution is presented
Life-cycle analysis of a new composite material for bridge pavementwaterproofing
No full textone of the most critical issues related to bridge management and preventive maintenance is deck waterproofing. Infiltration of meteoric and rain-wash water into the bridge asphalt pavement through unsealed cracks could produce a series of chain events that leads towards an accelerated decay of the bridge structural adequacy. Actions like crack sealing and general waterproofing are main activities; they can in fact slow down the deterioration and reduce the life-cycle costs. An effective protection system against water is one of the key factors for a functional and efficient bridge management plan. However, benefits associated
with such maintenance activities are seldom correctly accounted and, in many instances, they are not even considered at all. Consequently many road bridge authorities do not include pavement preventive maintenance activities in their infrastructures management programs. Recent research has resulted in the development of new technologies in the field of crack sealing and pavement waterproofing. In this context, a new composite material for waterproofing interlayer membranes, to be “cold applied” (with great benefit for environment and workers) was studied and also tested in full scale experiments by Politecnico of Milano researchers. This paper presents the main characteristics and the performances of this new technology, applied to bridge pavements, followed by a life-cycle analysis to quantitatively show the savings of the road bridge authority and the benefits of the users (in terms of improved condition of the bridge pavement surface). The results obtained are of general validity as they can be extended to all similar technologies
A less invasive, selective, functional neck dissection for papillary thyroid carcinoma
No full textHypothesis: To describe an alternative lateral neck access in order to perform neck dissection in papillary thyroid carcinoma (PTC) with lymph node involvement. Design: Prospective (January 2000 to December 2003), 36-month study. Setting: Catholic University of Rome and University of "Tor Vergata", Rome, Italy. Patients and methods: Twenty-four consecutive patients with PTC and cervical lymph node metastases were included. Functional neck dissection (FND), unilateral or bilateral, was performed acceding via a lateral dissection through a traditional Kocher incision, running along the superficial fascia of the neck and posteriorly to the sternocleidomastoideus muscle. Results: Mean age was 39.04 +/- 13.69 years. Twenty patients were women and four were men. Mean tumour size was 2.5 +/- 1 cm, while the greatest metastatic lymph node size was 4.5 cm. Minimally invasive, selective FND was performed in all patients associated to total thyroidectomy and central compartment lymph node clearance. Metastatic lymph nodes were found in 142 out of 340 of the lymph nodes dissected. Conclusions: Minimally invasive neck dissection seems to carry a lower risk in terms of specific morbidity and allows a quicker recovery and a better aesthetic result. This access has to be considered as a less invasive procedure compared to the other surgical accesses for the radical or modified lateral neck dissection
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