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《International Journal of Pavement Engineering》2012,13(2):133-144
The context of long-life pavements (LLP) is winning specific international interest the last years; especially in regards to the upgrading of existing pavements to LLP, which constitutes the main focus of the present research study. For this reason, a detailed assessment of the in situ condition of a heavy-duty highway pavement was performed, based on a comprehensive long-term monitoring approach of its structural performance. The main distress mode of the investigated pavement was cracking in the pavement surface. It is shown that the originally designed pavement could be classified as an upgradeable long lasting one and transferred into a context of a full long-life pavement. 相似文献
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《International Journal of Pavement Engineering》2012,13(2):145-152
To provide a totally comprehensive Europe-wide cost benefit analysis for the adoption of long-life pavements (LLPs) is not a straightforward task. This paper proposes a methodology to compare the results of the cost benefit assessment of determinate life pavements with that of LLPs. This approach is relevant but nevertheless raises certain issues such as the determination of residual life. Existing models which are available for the economic evaluation of LLPs are presented but none of them take into account all of the significant parameters, for example, environmental costs. In addition, other parameters may be difficult to assess with sufficient accuracy due to the specific behaviour of LLPs such as the lack of deterioration in the structural layers. An example whole life cost analysis of a part of the UK network suggests the large potential benefits to be obtained from the adoption of the LLP design principles on a heavily trafficked road network even before considering the potential environmental benefits of such an approach. 相似文献
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《International Journal of Pavement Engineering》2012,13(2):121-132
A major mode of deterioration in fully-flexible long-life pavements (LLP) is surface-initiated top–down cracking. If surface maintenance is suspended, surface-initiated cracks may conflict the long-life concept, as they will propagate into the structural layers and structural deterioration will start. The risk of surface-initiated top–down cracking is influenced by a number of interacting factors. Critical stresses may result, e.g. from the 3D loading situation at or near the pavement surface due to contact stresses between the tire and the pavement surface, from a sudden change in the asphalt layer temperature gradient, from traffic loading at low-temperatures and from material related factors like asphalt ageing and particle segregation due to stripping of the binder. Cracks may also be initiated by early construction micro-cracks induced by the asphalt roller. Depending on the respective mechanism of initiation, surface cracks are observed to be orientated in both directions, transversally to the road axis and longitudinally and longitudinal cracks are found inside as well as outside the wheel-path. In this study, the combined effect of tensile stresses resulting from both traffic and thermal loading in a typical fully-flexible LLP structure is investigated. Supposed that the risk of surface-initiated cracking can be minimized by using an appropriate asphalt material, the main objective of this paper is to find important missing links between the characterization of fundamental low-temperature properties of an asphalt mixture, on the one hand, and its in-service behaviour with special regard to the risk of surface-initiated top–down cracking at low-temperatures, on the other hand. Based on fundamental test methods, material modeling and numerical simulation, an overall concept is presented that will enable a better prediction of the low-temperature performance and a better risk evaluation of surface-initiated cracking at low-temperatures. First promising results are given for a typical fully-flexible LLP structure that is exposed to prescribed temperature and loading scenarios. Realistic critical stress distributions at the road surface in consequence of combined thermal and traffic loading are found that allow assessment of the risk of longitudinal surface-initiated top–down cracking at low-temperatures. 相似文献
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小型长寿命核能系统燃料物理性能的研究 总被引：1，自引：0，他引：1
本文在简要说明世界上小型长寿命核能系统研究现状的基础上,提出了使用钍-铀燃料和铅-铋冷却剂构造小型长寿命堆芯的设想,并为此进行了一系列燃料物理性能的研究.对于长寿命核能系统的堆芯物理设计,使反应性随燃耗变动最小非常重要,同时应该尽可能地提高堆芯的燃耗以满足长寿命运行的需求.本文使用MCNP和MCBurn程序详细计算分析了使用不同的初始驱动燃料、不同栅格、燃料成分和类型、富集度条件下,燃料栅元的燃耗反应性变化等性能,并对其进行了能谱、转换比、富集度变化等方面的分析,经过对比初步确定了使用钍-铀燃料构造长寿命堆芯的物理条件,并以此为起点构造出一个堆芯,计算给出了反应性空泡系数等安全参数. 相似文献
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This research aims at modeling the rotary drying of carton packaging waste and analyzing the energy performance of the process. Drying data were obtained in a semi-pilot rotary dryer, 0.45 m diameter and 2.7 m rotating drum long, operating with an air velocity of 1 m/s and air inlet temperature of 90°C and 10 rpm. Under the operating conditions employed, the analysis of the data showed that the energy performance of the drying process increased from 5 to 75% as the inlet wet solid feed rate increased from 1.8 to 19 kg/h. In addition, at this latter wet-solid feed rate, the reduction of the air velocity in the dryer to 0.8 m/s also led to an increase in the performance of drying process from 80 to 94%. Furthermore, with a 95% confidence interval, the model used was adequate to predict the air and solid temperature as well as the air humidity and the solids moisture content. 相似文献
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Toshiro Kamei Jun Sato Yoshie Nakai Akemi Natsume Katsuhiko Noda 《Packaging Technology and Science》1991,4(4):185-193
The microbiological quality of aseptic packaging (the board for long-life milk) was good and viable counts were under 50cfu per package. The percentage of defective samples that had viable microorganisms after 7–14 days of pre-incubation was 54% (one pin-hole) and 54% (ten pin-holes) for coffee beverage packed in board B and 17% (one pin-hole) and 17% (10 pin-holes) for milk packed in board A. The differences in the percentage of defective samples between milk and coffee beverage and between board A and board B were significant, but no difference was observed between one and ten pin-holes. An increase in fat content or a decrease in protein content increased the permeation of milk components through the pin-holes. The microorganisms isolated from the products with artificial pin-holes were f actobacillus sp. (52%), Streptococcus sp. (48 %) and Enterobacteriaceae (34%). 相似文献
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《International Journal of Pavement Engineering》2012,13(2):91-100
This paper explains some of the historical developments that lead to the discovery of the unexpected pavement deterioration modes that are an inherent part of the flexible long life pavement concept. The paper also summarises some recent pavement modelling which attempts to confirm and explain these unexpected deterioration phenomena. A European Long-Life Pavement Group (ELLPAG) has been formed under the auspices of the Forum of European National Highway Research Laboratories (FEHRL) to report on the current state of knowledge on long-life pavements in Europe in particular on the very practical issue of how to design, build and maintain pavements to give long structural lives. The paper summarises the findings of the first two phases of the project which has delivered a report reviewing the current state-of-the-art of fully flexible long-life pavements (LLP) and a corresponding draft review for semi-rigid pavements based on the combined knowledge of the European pavement community. The reports include chapters on: new pavement design, assessment and upgrading, maintenance and treatment design, economics and, finally, identifying knowledge gaps. Future phases will look at the state-of-the-art of other major pavement types as well as promoting research programmes to solve the knowledge gaps identified. The Group is funded by the members' respective road administrations. 相似文献
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本文综述了国际上超灵敏度检漏仪的校准技术进展。超灵敏度检漏仪是高可靠长寿命真空器件封装的重要检漏工具,当前报道的检漏下限可达10−16 Pa·m3/s,但检漏结果的正确性是器件可靠性的关键因素。超灵敏度检漏结果正确性主要取决于检漏仪的自身性能和计量校准,对于后者,国际上先后采用标准漏孔、可变漏率的白金丝漏孔及标准气体流量计作为参考标准来提高检漏结果的正确性。采用标准漏孔的方法是使用当前下限仅为10−11 Pa·m3/s的漏孔作为参考标准,由于漏孔自身的偏差及检漏采用质谱计跨越几个数量级的线性递推方法,在小于10−14 Pa·m3/s范围的检漏结果偏差可达一个数量级;采用可变漏率的白金丝漏孔作为参考标准,可提供（10−10～10−12）Pa·m3/s范围内漏率,与标准漏孔相比对检漏结果的正确性有一定提升;采用近期新研制的宽量程标准气体流量计作为参考标准,可提供下限为10−16 Pa·m3/s范围内漏率,解决了目前超灵敏度检漏仪全量程的校准难题,将检漏结果的合成标准不确定度减小到15%以内,提升了长寿命真空器件的可靠性。 相似文献
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在工业生产中加热对象往往体积庞大,微波功率不够高将直接影响加热效果,并严重制约生产规模,远不能满足大规模工业连续生产的需求。简单将多只磁控管作为独立微波源进行非相干功率合成,造成了功率合成效率低、难以消除磁控管之间相互问的干扰。严重影响微波源的工作稳定性和工作寿命,甚至直接损坏微波源。普通连续波磁控管是一种复杂幅相特性微波器件,通常其幅度易受工作条件的影响、频率和相位随机变化、幅度和相位变化相互牵连,使得进行相干功率合成具有相当大的难度。而随着注入锁频技术的引入,注入锁频连续波磁控管将能很好的解决这些问题,可实现真正意义上的相干功率合成,为微波能大规模工业应用开辟广阔的前景。 相似文献