高性能混凝土工作性及耐久性试验研究

结合福建当地材料,配置C50等级高性能混凝土,研究不同矿物质及掺量对拌合物工作性、劈裂强度及耐久性等影响。试验得到粉煤灰、矿粉在改善拌合物工作性、抗渗性及劈裂强度等指标的较优掺量及影响规律。双掺性能更优,体现了其在粒形级配改善,工作性提高及火山灰效应的复合优势。提出可综合考虑质量变化率、相对动弹性模量及强度等的混凝土损伤程度指标,对混凝土在快速冻融、盐水腐蚀等因素共同作用下的损伤情况进行半定量评估。结果表明,素混凝土损伤程度最大,而矿粉掺量20%和粉煤灰掺量15%的损伤指标明显降低,表明该掺量下混凝土的耐久性能明显提高。     

对提高混凝土耐久性的思考

长期以来从单方面因素考虑是混凝土耐久性研究的误区。笔者通过分析影响混凝土耐久性的诸多因素后，提出了合理应用新技术混凝土以保持其高度体积稳定性；掺入添加剂，有效改善混凝土的性能；运用质量良好、技术性能指标合格的砂石骨料；严格控制水胶比等提高混凝土耐久性的措施，有一定的工程实用价值。     

Influence of surface treatments on fatigue life of a two-stroke free piston linear engine component using random loading

INTRODUCTION Fatigue durability has long been important issues in the design of a two-stroke free piston linear engine structure (Torres and Voorwald, 2002; Rahman et al., 2005a; 2005b). Durability assessment is traditionally done in the later part of the product development stage when prototypes are available, and heavily re- lied on in confirming ground durability tests. This process is very time consuming and often results in over-design with weight penalties, which is the major obsta…     

Evaluation of university teaching as sound performance appraisal

As research on student evaluations of teaching (SET) has dominated our understanding of teaching evaluation, debate over SET implementation has turned attention away from basic principles for appraising employee performance as established in human resources literature. Considering SET research and its practical significance in isolation from relevant human resources literature not only risks unlawful remedies for issues such as bias in SET but also risks replacing one form of bias with another. Meanwhile, the full potential of human resources tools to support consistent evaluation of teaching remains unrealized. To address this gap, this article clarifies how teaching evaluation can be conducted as sound performance appraisal by deploying SET and peer review of teaching within a larger framework of established human resources techniques. A review of recent literature articulates prominent themes in research on SET and peer review of teaching and outlines key principles for performance appraisal and performance management. Those principles are used to analyze representative faculty evaluation policies and procedures and clarify the weaknesses of both traditional and recently revised approaches to teaching evaluation. The final section elaborates performance appraisal techniques relevant to teaching evaluation. These include planful use of results and/or behavior approaches to performance appraisal, robust rating instruments for behavioral performance appraisal, targeted collection of information from multiple stakeholders, and job analysis. Efforts to de-emphasize quantitative SET data to address issues such as bias can be strengthened through the incorporation of performance appraisal tools that clearly articulate performance criteria and standards and that gather both qualitative and quantitative data on employee performance.     

Experimental study on behaviors of polypropylene fibrous concrete beams

Synthetic fibers made from nylon or polypropylene have gained application when loose and woven into geo textile form although no information on the matrix＇s mechanical performance is obtained so that more understanding of their structural contribution to resist cracking can be determined. This paper presents the results of an experimental investigation to determine the performance characteristics of concrete reinforced with a polypropylene structural fiber. In this investigation ＂Fiber mesh＂ brand of fibers manufactured by SL Concrete System, Tennessee, USA and marketed by M/S Millennium Building System, Inc., Bangalore, India are used. The lengths of the fibers used were 24 mm. Fiber dosages used were 0.9, 1.8, 2.7 kg/m^3. A total of three mixtures, one for each fiber dosage were made. A standard slump cone test was conducted on the fresh concrete mix with and without fibers to determine the workability of the mix. The test program included the evaluation of hardened concrete properties such as compressive, split tensile, modulus of rupture and flexural strengths. The increase in compressive strength is about 36.25%, 26.20%, and 23.75% respectively that of plain concrete. This increase in strength was directly proportional to amount of fibers present in the mix. The increase in flexural strength for Mixes I-III is about 21%, 16.6%, and 23% respectively that of plain concrete specimens. An experimental investigation was also made to study the behaviors of reinforced fibers concrete beams （with longitudinal reinforcements） under two-point loading. The deflection and crack patterns were also studied. The improvements in strength and ductility characteristics were discussed.     

混凝土环境中BFRP筋耐久性能试验研究(英文)

针对玄武岩纤维增强树脂基复合筋(BFRP)在混凝土环境中的耐碱性能进行了加速腐蚀试验研究.腐蚀试验环境包括3种,分别为自来水、盐水及室内空气环境,将包裹有混凝土保护层的BFPR筋试件分别放置在上述3种环境中,试验同时采用碱溶液直接浸泡BFRP筋作为对比,对直接碱溶液浸泡环境与混凝土包裹环境之间的加速系数进行了研究.试验采用60℃的高温进行加速.试验结果表明:自来水和盐水浸泡对于包裹有混凝土的BFRP筋试件没有明显差异.分析认为,与混凝土内部高碱性的孔隙溶液接触是BFRP筋退化的主要原因,当经受高温和高湿环境共同作用时,混凝土环境中BFRP筋的退化将明显加速;BFRP筋的退化速率在初期较快,随着龄期的增长,退化速率降低.基于试验数据分析表明,对于所采用的BFRP筋,60℃饱和吸湿混凝土环境下,BFRP筋2.18 a的退化程度与60℃碱溶液直接浸泡环境下1 a的退化程度相当.     

基于物元评判模型的网络课程评价研究

网络课程是进行在线学习的重要教育资源,其质量直接关系到学习者的学习效果。文章从物元分析理论出发,将物元评判模型和网络课程评价结合,建构了可定量化评价的网络课程物元评价模型,并通过案例展示了该模型对网络课程的评价过程,为网络课程评价提供一种新的方法。     

Effects of surface finish and treatment on the fatigue behaviour of vibrating cylinder block using frequency response approach

INTRODUCTION Due to market pressures for improvements in productivity, reliability, ductility, wear resistance and profitability of mechanical systems, manufacturers are placing increasing demands on available materials.Economic constraints require that these materials are inexpensive and easily available. In order to enhance the surface properties of today’s materials, producers of components are turning to different surface finish and treatments. There are several techniques available …     

Beyond conceptual change learning in science education: focusing on transfer,durability and metacognition

The frequently encountered problems of students being unable to utilize schoollearned science in different contexts, and of students forgetting what they have learned in a short time after initial instruction, are two important problems for classroom practitioners. This paper advocates a shift in focus of conceptual change learning research in order to address these problems. It draws upon four overlapping areas: conceptual change learning is the broad subject area that sets the epistemological background; transfer and durability of scientific conceptions are the two problem areas under scrutiny, while metacognition is seen as potential mediator of improvement. The paper offers a brief review of existing literature on the four areas; it proposes confronting the two problems by incorporating metacognitive instruction in the learning environment of primary school science; and it reports on recently completed research.     

Fire's effect on chloride ingress related durability of concrete structure

This paper describes the effects of fire on durability of reinforced concrete structures, and points out that fire not only damages the chemical composition and physical structure of concrete by high temperature, but also leads to an additional risk due to the generation of polyvinyl chloride (PVC) combustion gases. A mathematical model is proposed to calculate chloride ingress profiles in fire damaged concrete, so as to explore the service life prediction of the structure. Rapid Chloride Migration (RCM) test was carried out to determine the chloride diffusion coefficients for the application of the mathematical model. Finally, the detected results of a reported case testified to the validity of the mathematical model.     

Enhancement of durability of glass fiber-reinforced cement with PVA

The main thrust of this research was to determine the effectiveness of polyvinyl alcohol (PVA) powder in enhancing the durability of short GFRC materials. Accelerated aging of the materials was achieved through low-pressure steam curing in a moist chamber. The strength and ductility of GFRC were measured by the direct tension test, which showed that incorporation of PVA powder into GFRC could improve its mechanical behaviour and turn it from brittle to ductile. To investigate the mechanism of the tensile strength enhancement, the fiber-matrix interface was examined by polarizing optical microscopy and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX). It was found that PVA powder tended to migrate to the fiber-matrix interfacial zone and thus prevented the accumulation of calcium hydroxide in this area. PVA film around the fiber resulted in a more ductile interfacial microstructure and better bonding between fiber and matrix, which should be responsible for enhancing the tensile property and preventing the aging of GFRC. Furthermore, PVA powder reduced the microhardness and brittleness at the interface.     

模糊综合评价法下的信用担保机构实力评价

随着中小企业信用担保体系建设的不断推进,对担保机构的实力评价日益显得重要,评价指标体系分为基本素质、信用能力、财务能力、业务能力、成长与发展、社会效益六个方面.以模糊数学理论为基础的模糊综合评价法,有利于解决评价过程中出现的一些不确定事项.运用模糊综合评价法对担保机构实力进行评价,可明确知晓该机构的实力,在与其合作或对其进行监管中,能更加有的放矢,提高决策的科学性和准确性.     

儿童问题行为的评估及其对策

儿童问题行为是国内外心理学和教育工作者共同关注的热点问题,其发生率仍在逐年上升.儿童问题行为不仅影响儿童身心的健康发展,而且影响我国素质教育的进程.在教育过程中,教育者只有对儿童的各种行为表现做出合理的评估,才能够有针对性地实施教育计划.本文对儿童问题行为的评估标准、注意问题和对策等方面作了初步探讨.     

Influence of Different Surface Treatments of H13 Hot Work Die Steel on Its Thermal Fatigue Behaviors

Thermal fatigue checking is general failure of hot work die steels,which is relative with the structures and properties of the steels and the stress alternated during the employment.The Uddeholm test method on thermal fatigue is used to compare the behaviors of different samples,which are treated with plasma nitriding 、plasma sulfur-carbon-nitriding、boronizing or not treated.The results show that the nitriding improves the thermal fatigue property of the tool steel,while the plasma sulfur-carbon-nitriding and the boronizing impair the property.The mechanisms are induced as follows .By increasing the hardness and changing the stress distribution in the surface layer,surface treatment can decrease the plastic deformation and the temsile stress during the cycling.Therefore,the generation and growth of the cracks are restrained.On the other hand,as results of surface treating,in the surface layer the toughness declines and the expanding coefficient ascendes;the latter change caused the strengthening of the tensile and compressive stress during the cycling.Thus the resistance to thermal fatigue is weakened.Whether or not the surface treatment is favor to thermal fatigue of tool steels relies on which factor is dominant.     

基于新课程的物理课堂教学评价体系的完善

对物理课堂教学评价进行理论分析,从课堂教学评价的含义、传统课堂教学评价存在的问题、新课程下课堂教学评价的理念、制定课堂教学评价体系的原则几方面进行了阐述,并结合新课程下中学物理教学特点制定了课堂教学综合评价体系表,尝试对中学物理课堂教学进行试评。     

Method of effective evaluation for examination of chloride ion in concrete

INTRODUCTION For some unknown reasons, perhaps caused bysalt, chlorine ions usually exist in reinforced concreteconsisting of cement, water, aggregate and additionalmaterials, and steel bars. In the presence of water, thechlorine ion reacts with iron existing in concrete andsteel bars to form Fe(OH)2 and FeCl2. The chemicalreactions seriously corrodes the surface of steel barsand damage the concrete, causing gradual decrease ofthe concrete compression and increase of its porosity,…     

Fire＇s effect on chloride ingress related durability of concrete structure

This paper describes the effects of fire on durability of reinforced concrete structures, and points out that fire not only damages the chemical composition and physical structure of concrete by high temperature, but also leads to an additional risk due to the generation ofpolyvinyl chloride （PVC） combustion gases. A mathematical model is proposed to calculate chloride ingress profiles in fire damaged concrete, so as to explore the service life prediction of the structure. Rapid Chloride Migration （RCM） test was carried out to determine the chloride diffusion coefficients for the application of the mathematical model. Finally, the detected results of a reported case testified to the validity of the mathematical model.     

基于评价的命题

本文从理论和实践两方面探讨了实现从考试到评价的跃升的可能性,提出了基于评价的命题的构想;指出它与传统命题方式在命题目标、试题评价的关注点、评价的结果对被试的影响等方面的区别;探索新的试题设计方向,既使试题具有先入为主的清晰的思维能力元素、恰当适度的答题空间和合理而使评价有依据的评分规则。     

Evaluation of blast-resistant performance predicted by damaged plasticity model for concrete

In order to evaluate the capacity of reinforced concrete (RC) structures subjected to blast loadings,the damaged plasticity model for concrete was used in the analysis of the dynamic responses of blast-loaded RC structures,and all three failure modes were numerically simulated by the finite element software ABAQUS.Simulation results agree with the experimental observations.It is demonstrated that the damaged plasticity model for concrete in the finite element software ABAQUS can predict dynamic responses and typical flexure,flexure-shear and direct shear failure modes of the blast-loaded RC structures.     

评价支架对教师在线同伴互评质量的影响研究

教师培训是促进教师专业发展的有效途径,其中,线上培训近些年受到了越来越广泛的关注。以往研究已经证实,同伴互评可以促进教师的在线学习效果,但在应用中仍存在同伴评价参与度低、评分者一致性和评语质量不高等问题。研究将评价支架引入到大规模教师培训类MOOC中,对同伴互评中的整体型评价支架和分析型评价支架进行设计和开发,并采用实证研究的范式,探讨不同评价支架类型对教师同伴互评中评价参与度和评价效果的影响。研究结果表明,分析型评价支架能更好地提升教师学习者同伴互评的评价参与度,提升评价一致性和评语质量。因此,在设计与开发教师培训类MOOC时,可考虑将分析型评价支架纳入同伴互评活动。