浇注式沥青混凝土现状与发展

为进一步确定浇注式沥青混凝土科学合理的性能评价指标及要求,全面梳理了国内外浇注式沥青混凝土相关规范,对比评价了不同规范中的技术指标要求及级配范围,系统地调查了大量实体工程及研究动态,厘定了浇注式沥青混凝土钢桥面铺装结构层组合、原材料类型和技术指标要求及级配类型,为浇注式沥青混凝土规范完善与质量控制奠定了基础.结果表明:推荐钢桥面铺装结构层组合为30~35 mm GA-10+35~40 mm SMA-10,GA基础沥青为SBS改性沥青+TLA(15%~30%),采用2%降粘剂;推荐性能评价指标要求范围为油石比7.9%~8.5%、流动度10~17 s、贯入度1.4~2.5 mm、贯入度增量不超过0.25 mm、弯拉应变不小于7 000με、动稳定度不小于1 000次/mm(参考指标);疲劳性能试验以控制应变模式进行,结果以实测为准.     

循环荷载作用下钢桥面铺装疲劳损伤失效行为研究

针对钢桥面铺装工程中普遍采用的改性沥青(Stone Matrix Asphalt,SMA)、浇筑式沥青(Guss asphalt,GA)、环氧沥青(Epoxy asphalt,EP)混合料双层铺装结构,进行了循环车载作用下钢桥面与沥青混凝土铺装疲劳损伤特性理论分析与试验研究。基于疲劳损伤度,研究了钢桥面铺装疲劳损伤失效行为和疲劳开裂过程中损伤场、应力和应变场动态演变机制,推导出疲劳失效时的损伤场、应力和应变场计算表达式,并给出钢桥面铺装疲劳寿命理论公式。以三座钢箱梁桥桥面铺装(润扬长江大桥2005,南京长江三桥2005,苏通大桥2008)为例,对不同铺装结构组合方案下的复合梁进行疲劳试验分析和使用寿命理论预测。实例研究结果表明,钢桥面铺装疲劳损伤失效行为预估模型合理可行;相较于改性沥青、浇筑式沥青,环氧沥青混合料具有较强高的强度低变形能力,更适合于大跨径钢桥面铺装抗疲劳的设计要求;由环氧沥青混合料组合而成的“双层环氧沥青混凝土”和“浇注式沥青混凝土(下层)+环氧沥青混凝土(上层)”的抗疲劳性能优于其它沥青混合料铺装结构组合方案,同等厚度组合情况下疲劳使用寿命可延长1倍~2倍以上;“双层环氧沥青混凝土”已应用于润扬长江大桥、南京长江三桥和苏通长江大桥钢桥面工程,并已成功运行10年以上,其跟踪观测结果良好。     

浇筑式沥青混凝土性能影响因素研究

浇筑式沥青混凝土具有较高的变形随从性而在钢桥面铺装上得到了很多的应用,为研究浇筑式沥青混凝土的性能影响因素,采用4种合成级配、3种沥青用量,系统评价了各因素对浇筑式沥青混凝土性能的影响。通过流动度试验和贯入度试验确定最佳含油量,由高温车辙试验和低温弯曲试验进行路用性能检验。研究表明,级配形式和沥青含油量变化对混合料的性能指标的影响较大,因此,实际施工时应严格控制混合料的级配和沥青用量。     

无损状态下钢桥面沥青铺装材料变形恢复特性

钢桥面铺装用高性能材料的组成及性能差异较大,目前对钢桥面铺装材料性能的研究主要集中在加载阶段的强度规律及损伤行为,而对卸载阶段材料的变形恢复特性研究甚少.为评价钢桥面铺装材料在卸载阶段的变形恢复能力,针对蠕变逐级加载试验方法存在的不足,提出了重复蠕变逐级加载恢复试验,对浇注式沥青混合料、环氧沥青混合料、沥青玛蹄脂碎石混合料三种典型钢桥面铺装材料,在卸载阶段不同时刻的内应力及对应时刻的残余应变进行测试.根据恢复模量的定义,计算三个不同蠕变应力水平下的恢复模量,依次来评价三种材料驱动变形恢复的能力.同时,基于粘弹性基本理论,确定蠕变柔量的拟合参数,并计算不同间隔时间下三种材料的应变恢复率,评价其变形恢复的速度.试验结果表明:无损状态下材料的恢复模量不同于内应力,不随蠕变荷载大小的变化而变化,环氧沥青混合料的恢复模量最大,约为沥青玛蹄脂碎石混合料、浇注式沥青混合料的7倍和4倍,环氧沥青混合料材料自身驱动变形恢复的能力优于浇注式沥青混合料和沥青玛蹄脂碎石混合料;但在相同时间间隔时间下,浇注式沥青混合料的应变恢复率最快,在3.6 s内,应变恢复率即可达到82％.     

钢桥面铺装在行车荷载与环境温度共同作用下疲劳损伤分析

用损伤力学原理及方法,从力学近似法角度分析了环境温度和循环车辆荷载共同作用下钢桥面沥青混合料铺装的疲劳损伤特性,推导出疲劳试验复合梁的损伤场、应力和应变场。以长江一大桥钢桥面环氧沥青混凝土铺装体系复合梁疲劳试验为例,进一步推导出复合梁的疲劳寿命预测公式。实例分析表明,考虑环境温度和车辆荷载共同作用下钢桥面铺装体系的疲劳寿命要小于单一考虑行车荷载的计算结果,二者相差最大可达44%。研究认为温度变化会导致铺装层的劲度不断发生变化,从而直接影响钢桥面沥青混合料铺装的力学行为和疲劳寿命,因此仅考虑交通荷载的作用进行钢桥面沥青混合料铺装体系疲劳损伤的分析是过于简化的,应予以重视。此外,指出了环氧沥青混凝土铺装具有很好的抗疲劳性能。     

环氧沥青混凝土桥面铺装材料研究与应用进展

随着桥梁设计理念、结构分析、施工技术等不断更新发展与完善,目前桥梁正逐渐朝着大跨度、高强度、长寿命、高耐久等方向发展,同时,未来桥梁也将面临更复杂的建设环境、更多的功能需求,因此必须加强研发与新型桥梁设计体系相匹配的特种桥面铺装材料。环氧沥青混凝土桥面铺装材料以高强度、耐高温、抗疲劳、抗老化等优异路用性能脱颖而出,逐渐受到关注。然而,环氧沥青混凝土制备工艺复杂、施工条件严苛、耐久性不足等问题日益凸显,这些缺点使得其在桥面铺装领域的推广受到一定阻碍。为此,研究者们针对如何提升环氧沥青混凝土使用品质及耐久性进行了深入研究并取得了一定成果。这一系列成果先后在大量桥面铺装实体工程中得以应用,良好的使用效果也为环氧沥青混凝土的进一步推广奠定了基础。环氧沥青混凝土在桥面铺装领域的研究成果可以概括为三个方面:铺装结构组合优化、制备工艺优化、混凝土原材料优化。其中铺装结构组合从早期的单质单层结构逐渐过渡到单质双层、异质双层结构,趋于合理的铺装结构组合使环氧沥青混凝土材料的性能得以充分发挥。制备工艺从热拌法发展到温拌甚至冷拌,在保证环氧沥青混凝土使用性能的同时减少了对环境的污染,并且在一定程度上降低了施工难度。而在原材料应用方面,研究者们不断对双组分环氧沥青与三组分环氧沥青的性能进行对比分析;同时,环氧沥青的改性方式趋于多样化,从单独使用改性沥青发展到同步使用改性环氧树脂,改性剂从纤维发展到高分子聚合物、超支化聚合物等。这些措施不仅改善了沥青与环氧树脂的相容性,也增强了环氧沥青混凝土的相关性能。此外,为使环氧沥青混凝土具有更好的稳定性,在级配优化方面也进行了深入研究。然而目前环氧沥青混凝土的一系列研究成果较为散乱,缺乏对其系统的总结与梳理,且环氧沥青混凝土的性能评价指标及要求仍需深入研究与完善。为进一步确定环氧沥青混凝土桥面铺装材料科学合理的性能评价指标及要求,本文全面梳理了国内外环氧沥青混凝土相关规范,系统调查了大量实体工程及研究动态,对比分析了不同主要原材料的环氧沥青混凝土对其路用性能的影响,最终推荐了环氧沥青混凝土桥面铺装结构组合、原材料类型、级配范围和性能评价指标及要求,为环氧沥青混凝土桥面铺装材料规范完善与质量控制奠定了基础。     

钢桥面铺装损伤病害的调查及分析

钢桥面铺装病害产生的原因包括外部因素和铺装自身因素,外部因素主要是铺装温度、交通荷载、桥面板刚度;铺装内部自身因素主要包括混合料的胶结料性能、混合料级配类型、混合料配合比、施工控制质量等因素。本文针对我国典型的钢桥面铺装:双层SMA、浇注式、环氧沥青铺装进行病害调查,分析引起病害的原因,为制定病害处治方案提供依据。     

浇注式导电沥青混凝土组合结构热传导效应预估模型

为进一步确定浇注式导电沥青混凝土组合结构热传导效应及融雪化冰工作时间,系统研究了浇注式导电沥青混凝土组合结构传导热基本原理,建立了浇注式导电沥青混凝土组合结构上面层热传导效应预估模型,分别实测和预估了不同环境温度、结构层厚度及通电时间等条件下组合结构上面层的表面温度,确定了浇注式导电沥青混凝土融雪化冰工作时间,并采用pearson相关性检验方法,对比分析及验证了浇注式导电沥青混凝土组合结构的热传导效应预估模型的准确性,为浇注式导电沥青混凝土在桥面铺装领域的推广应用奠定基础。结果表明:浇注式导电沥青混凝土组合结构传导热过程是一种瞬态非稳态导热过程,不同环境条件下,组合结构上面层表面温度在初期上升、中期转折、后期下降等三阶段的预估误差分别维持在0.2～0.8℃、0.3～1.2℃和0.7～5.5℃,其融雪化冰工作时间预估误差则维持在16 min左右;不同环境温度、结构层厚度和通电时间等条件下,预估模型得出的组合结构上面层表面温度的预测值与实测值相关系数介于0.974 0～0.989 0之间,相应P值均小于0.01,判定系数R~2介于0.948 7～0.978 1之间,两者为显著相关,拟合优度较高,预估结果较为准确。     

浇注式沥青混合料(GMA)标准化施工工艺控制研究

钢桥面的施工环境较为严苛且对施工质量的要求较高,为了保证施工工艺寿命以及质量,对钢桥面的标准化施工工艺控制至为重要。本文研究了浇注式沥青混合料的最佳拌和施工工艺,以拌和速率、温度和时间作为主要考察指标,测试不同条件下浇注式沥青混合料的性能。     

基于冲击韧性的钢桥面铺装环氧沥青混凝土疲劳性能设计研究

针对钢桥面铺装环氧沥青混凝土出现的疲劳开裂问题,分析现有设计理论和方法的不足之处。基于断裂力学和能量法原理基础上,提出以冲击韧性作为环氧沥青混凝土配合比设计的评价指标,通过试验验证了该指标的可行性;采用剩余劲度模量比来反映环氧沥青混凝土的疲劳性能,并建立起冲击韧性和剩余劲度模量比之间的关系。研究结果表明,冲击韧性和疲劳性能之间有良好的线性相关性,采用冲击韧性指标能够有效地评价环氧沥青混凝土的配合比设计和疲劳性能,该方法操作简单、快捷、准确,为环氧沥青混凝土的设计理论和方法提供一种新的思路。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.