混凝土结构耐久性研究综述

本文从钢筋的锈蚀机理、钢筋锈蚀对混凝土构件的影响、钢筋混凝土结构耐久性的评估以及提高耐久性的措施这四个方面对近几年的研究进行综述。     

Durability of Chinese Repair Bamboo Papers under Artificial Aging Conditions

ABSTRACT

To study the life expectancy and difference in aging resistance properties of different modern repair bamboo papers, hydrothermal/dry-heat ageing experiments on repair bamboo paper samples were conducted. The mechanical strength (tensile strength and folding endurance) of different papers during the ageing process were analyzed. Furthermore, the chemical properties (degree of polymerization and pH) of the samples were tested to search for the immanent cause of paper ageing. The results indicated that the ageing resistance ability and durability of modern repair paper are strongly related to their production process, which corresponds with the initial properties of the paper. Mechanical pulp had a low degradation resistance, which was further exacerbated by the chemical bleaching process. In the long run, traditional handmade papers with solar bleaching processes will have longer-term stability and durability.     

The properties of potassium silicate/ fly ash slurry used in the conservation of adobe structures

The work reported here is a systematic study to evaluate the compatibility of using PS-F (potassium silicate with high modulus – fly ash) slurry in the conservation of adobe structures. Firstly, the optimum mixing proportion (0.47) was determined by flow meter. Then the experimental program was divided into two parts: one part studied changes in physical and mechanical properties with increase in setting time by means of the measurement of moisture content, compressive and flexural strength, elastic-wave velocity, density, and porosity; the other part studied the durability of PS-F slurry through temperature and humidity cycles, freeze–thaw cycles, water stability, tensile testing, and alkali resistivity tests. The results show that the consolidation process with the slurry can meet the requirements of conservation applications and provide a timely anchoring force, and the slurry and soil mass of adobe-based structures have good compatibility in physical and mechanical properties. In addition, the slurry can strongly resist freeze–thaw cycles, temperature-moisture cycles, and tensile stress and has a relatively weak resistance to alkali solutions and water immersion. In conclusion, PS-F with a mixing ratio of 0.47 is a suitable slurry for conservation of adobe structures.     

强力缓冲型档案纸张纤维素螯合与脱酸保护研究

本文论述的BDM保护液在中和纸张中酸的同时,在纸张中沉积微量沉淀,既能使纸张保持7—7.5之强力缓冲的中性,又能与纸张纤维素、半纤维素基环上的羟基与羰基形成稳定螯合物,通过测试其与传统碳酸氢镁溶液处理的纸张老化前后耐折度、抗张强度、撕裂度及白度的保持率,证明该螯合保护液能使纸张耐久保存。     

无碳复写纸档案字迹材料耐久性研究

无碳复写纸档案字迹材料耐久性与环境温湿度、酸碱性物质、有机溶剂、微胶囊牢度、显色剂性能等保存环境和内在因素密切相关。本文就影响无碳复写纸档案字迹材料耐久性的温湿度、酸碱、有机溶剂、微胶囊牢度、显色剂性能等因素进行研究和分析。     

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.     

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。     

Evaluation of the performance of surface treatments on concrete durability

This paper reports on a laboratory-based study carried out to evaluate the effectiveness of surface treatments on the durability of concrete and suggests a number of different evaluation methodologies for assessing the performance of various surface treatments. Durability of untreated and treated concrete specimens was evaluated by measuring chloride diffusion, charge passing capacity, air permeability and water absorption. A total of six concrete surface treatments were selected to represent different generic types, including coating, penetrant and mixed-use treatments. Results show that the concrete specimens with a coating procedure have a better long-term performance and effectiveness than the specimens with the penetrant treatments. This work also indicates that the wetting and drying cycles test can be used to assess the weatherability of the surface treatments. The ASTM C 1202 and the Autoclam air permeability test can be used to evaluate the effectiveness of surface treatments quantitatively. Further work is needed, however, to assess the longevity of the various surface treatments.     

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.     

加固材料对纸质档案耐久性的影响研究

以草酸/乙醇—氢氧化钡/甲醇保护液、水性氟碳乳液和明胶—甘油溶液三种加固材料为研究对象,采用中性纸、宣纸为载体材料,墨汁、碳素墨水为字迹材料,分别对加固前后纸张的耐折度、色差变化以及字迹材料的耐干热老化、耐紫外老化、耐酸碱和耐氧化等性能进行综合分析比较,进而探讨三种加固材料对纸质档案纸张和字迹材料耐久性的综合影响。实验结果表明:三种加固材料均能提高纸张和字迹材料的耐久性。其中,水性氟碳乳液加固效果最佳,草酸/乙醇—氢氧化钡/甲醇保护液最差。水性氟碳乳液对宣纸和墨汁的加固效果较中性纸和碳素墨水更为理想。