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…     

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.     

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 …     

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。     

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.     

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.     

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.     

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,…     

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。     

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.     

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。     

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。     

关于高职院校评估工作的思考

高职人才培养工作水平评估在取得明显成效的同时,也存在一些问题。完善高职教育评估要摆脱单一的评估模式,建立适应高职教育的人才培养评估指标体系和评价体系。     

AK320齿轮传动箱的热功率评估

根据齿轮传动箱的发热机理和热功率评估理论,采用箱体三维实体造型所生成的相关数据,分析估算了AK320齿轮传动箱的热功率数值,在此基础上针对运行中的问题提出了改进措施,保证了该齿轮传动箱的正常运行.     

研究生素质评价的实践探索

研究生素质评价是研究生培养中一项必要的管理环节。本文在研究生教育实践经验的基础上,提出了基于发展观点的研究生评价方法,探索一种既考虑历史积累又关注未来发展的研究生素质评价模式。     

形成性评价在基础教育教学中的应用研究

教育评价作为衡量教育优劣的手段,是随着教育的产生而发展的,随着基础教育新课改的进行,教育评价越来越引起人们的关注,重视形成性评价是现代教育评价的发展趋势。本文首先介绍了教育评价中的形成性评价的概念、类型以及作用,然后通过具体实例,详细阐述其在教学中的具体应用。     

水泥混凝土结构外观质量控制与耐久性

水泥混凝土结构外观是衡量混凝土内在质量优劣的一个重要方面,水泥混凝土结构外观质量控制决定了混凝土的外观、质量和使用寿命,耐久性是检验水泥混凝土结构外观质量控制的标准和手段.分析了混凝土结构外观与耐久性之间的关系、水泥混凝土结构外观存在的主要问题及原因,初步提出了解决混凝土结构外观质量与耐久性问题的思路及注意事项.