碳纳米管水泥基复合材料耐久性及力学性能研究

为解决复杂环境下混凝土材料的耐久性以及力学性能等问题,以纳米材料作为水泥基材料的增强组份,添加碳纳米管(CNTs)制备了一种碳纳米管水泥基复合材料。研究了该水泥基复合材料的力学性能、流变性能,采用氯离子渗透深度来对该水泥基复合材料的耐久性能进行了评价。通过测试分析了不同碳纳米管掺量的水泥基复合材料的力学性能和耐久性,并通过SEM(扫描电镜)分析了碳纳米管水泥基复合材料的微观结构。结果表明CNTs能显著提高水泥基材料的力学性能以及耐久性,改善水泥基材料孔结构,同时能提高水泥基材料的抗氯离子渗透性能。     

水泥基胶凝材料氯离子扩散性的研究

借助X射线衍射（XRD）、扫描电镜（SEM）、水银压汞法等测试技术,从水泥熟料矿物组成、石膏种类及掺量、混合材掺量以及混合材优化匹配、粒度分布等几方面分析水泥砂浆氯离子扩散能力,并结合28d水化产物、水泥石孔隙特征等微观结构分析,探讨影响水泥氯离子扩散性的主要因素及其机理。研究表明,〉100nm孔总量与总孔隙率比值（硬化水泥石有害大孔相对含量）与水泥氯离子扩散系数有较好相关性,是影响氯离子扩散系数的最主要因素。同时提出用水泥组成特征参数（n）表征水泥氯离子扩散性的新观点。     

水泥基材料中氯离子结合机理及其影响因素研究进展

氯离子侵蚀是造成钢筋混凝土中钢筋锈蚀的主要原因,水泥基材料中氯离子的结合可以有效延缓钢筋的锈蚀.本文主要从三个方面进行了综述:(1)氯离子结合机理;(2)氯离子结合的测试方法及表征;(3)氯离子结合影响因素.具体研究了水泥组分及水化产物对氯离子的结合情况,以及不同测试方法及表征的应用范围、优缺点等,分析了辅助胶凝材料、...     

高掺量矿物掺合料对水泥基材料固化氯离子能力的影响

本文研究了高掺量矿物掺合料对水泥基材料固化氯离子能力的影响,并借助XRD、DTG等进行了分析,研究结果表明:在水泥掺量为20％情况下,随着矿粉和NaCl的掺量的增加,提高了水泥基材料的强度.高掺量的矿粉促进了水泥基材料中的F盐和镁铝水滑石的生成提高了其对氯离子的固化能力,增加浆体的水灰比对氯离子的固化也起到了促进作用.     

氧化石墨烯复合PVA纤维增强水泥基材料的力学性能及耐久性研究

为解决混凝土耐久性差、脆性大等问题,研究了氧化石墨烯(GO)复掺聚乙烯醇(PVA)纤维对低水灰比水泥基材料力学性能及耐久性能的影响.利用Hummers法制备GO,并表征GO的结构和性能,通过测试分析了不同配合比砂浆的力学性能和耐久性,并通过MIP(压汞法)和SEM(扫描电镜)分析了氧化石墨烯以及PVA纤维对水泥基材料的改性机理.结果表明GO和PVA纤维均能提高水泥基材料的力学性能以及耐久性.GO复掺PVA纤维可以显著改善水泥基材料孔结构,降低孔隙率,提高水泥基材料抗氯离子渗透性能并降低水泥基材料收缩率.     

水泥基材料氯离子渗透性能研究

本文采用ASTM C 1202及NEL氯离子渗透性测试方法,水银浸入(MIP)孔结构测试方法,以强度、渗透性系数及孔结构特征为指标,分析了不同胶凝材料组成及不同配合比水泥基材料在氯离子作用下性能的变化,系统研究了水泥矿物组成、矿物掺合料种类对水泥基材料氯离子渗透性能的影响;对比分析了高性能与传统水泥基材料在氯离子渗透下抵抗破坏的能力及其失效机理。     

水滑石复合水泥基材料氯离子吸附能力的研究进展

以氯离子为诱导的钢筋锈蚀是造成混凝土耐久性问题的主要原因,其本质是氯离子通过材料基体的多孔结构在水泥基材料中扩散,并逐步迁移到钢筋表面,发生不利的物理化学反应。水滑石即层状双金属氢氧化物(LDHs)是一种新型延缓钢筋锈蚀的外掺材料,具有独特的层状结构和离子交换性质,可在特定的介质溶液中将客体阴离子与层间阳离子进行交换,达到吸附氯离子、延长混凝土结构服役寿命的目的。本文介绍了水滑石的结构性质、制备方法及氯离子吸附机理,总结了不同类型水滑石的氯离子吸附能力及相关研究成果。研究结果表明：水滑石复合水泥基材料的氯离子吸附性能受LDHs材料制备工艺、水泥基材料中孔隙液pH值及氯离子浓度影响,高温焙烧处理的水滑石对氯离子吸附效果更好;当LDHs掺量控制在1%～3%(质量分数)时,有利于改善水泥基材料的抗氯离子渗透性能。     

苯丙乳液对水泥基材料氯离子固化能力的影响

研究了不同掺量苯丙乳液对水泥基材料氯离子固化能力的影响.将苯丙乳液分别以水泥质量的1％和3％掺入到水泥净浆中,分别研究7 d和28 d不同龄期和不同苯丙乳液掺量条件下的水泥基材料氯离子固化能力.研究发现1％苯丙乳液掺量下,7 d和28 d氯离子固化率对空白组提高率分别为11.69％和12.06％,而3％掺量下,7 d和28 d的氯离子固化率提高率分别为12.59％和13.39％.通过XRD、TG、SEM等测试方法研究表明苯丙乳液会促进水泥水化生成更多的C-S-H凝胶吸附水泥中的自由氯离子,提高氯离子物理吸附率;并且能够促进水泥基材料中F盐和K盐的生成,使氯离子参与形成稳定的水化产物,提高了氯离子化学固化率;以上两方面综合作用使得苯丙乳液加入水泥中之后能够提高水泥对氯离子的固化率.     

纳米压痕在水泥基材料微观结构与力学性能研究中的应用

纳米压痕测试结果是材料微观力学性能本质属性的体现.本文简述了水泥基材料中应用纳米压痕技术的测试要求,揭示了水化浆体中各物相的微观结构与力学性能,尤其对水化硅酸钙(C-S-H)凝胶在纳米尺度的结构特征与力学性能进行了重点分析.同时利用纳米压痕在界面区微结构特征测试方面的优势,介绍了不同组分水泥基材料界面区的微观力学性能差异.另外概述了水泥基材料中加入矿物细掺料、纳米材料后C-S-H的变化规律,这为后续纳米压痕在水泥基材料微观力学性能研究、宏观性能优化等方面提供参考和依据.     

水泥基材料氯离子结合机理及影响因素研究综述

水泥基材料的氯离子结合能力主要取决于水化硅酸钙(C-S-H)凝胶和Friedel's盐的含量及其稳定性,两者的含量越高、稳定性越好,水泥基材料的氯离子结合能力越强。对水泥基材料氯离子结合能力的分析需考虑多种因素的影响,如水泥种类、矿物掺合料种类、温度、氯离子浓度、阳离子类型、硫酸盐侵蚀和碳化等因素,它们会通过直接影响C-S-H凝胶和Friedel's盐的生成量,或间接影响孔隙液pH值和离子浓度改变C-S-H凝胶和Friedel's盐的稳定性,进而影响其物理吸附能力与化学结合能力,促使氯离子重新结合或释放,导致氯离子结合能力变化显著。本文综述了上述影响因素下,水泥基材料中C-S-H凝胶和Friedel's盐含量、稳定性的变化,及其对氯离子结合能力的影响,并为今后的研究方向提出了建议。     

Modeling of chloride diffusivity coupled with non-linear binding capacity in sound and cracked concrete

The objective of this research is to establish a model that can predict chloride transport phenomena in sound and cracked concrete. The chloride diffusivity is formulated based on computed micro-pore structure, which considers tortuosity and constrictivity of porous network as reduction factors in terms of complex micro-pore structure and electric interaction of chloride ions and pore wall. In the real environment, concrete structures are not always crack-free, therefore chloride transport in cracked concrete is also simulated by section large void spaces in a control volume to represent the crack and by proposing a model of chloride diffusivity through the cracked region The proposed models are implemented into a finite-element computational program DuCOM, which simulates the early-age development process of cementitious materials. The calculated concentration profiles of total chloride ions are verified through a comparison with experiments results.     

Fundamental salt and water transport properties in directly copolymerized disulfonated poly(arylene ether sulfone) random copolymers

Water and sodium chloride solubility, diffusivity and permeability in disulfonated poly(arylene ether sulfone) (BPS) copolymers were measured for both acid and salt form samples at sulfonation levels from 20 to 40 mol percent. The hydrophilicity of these materials, based on water uptake, increased significantly as sulfonation level increased. The water permeability of BPS materials in both the salt and acid forms increases more than one order of magnitude as sulfonation level increases from 20% to 40%, while NaCl permeability increases by two orders of magnitude. The water and salt diffusivity and permeability were correlated with water uptake, consistent with expectations from free volume theory. In addition, a tradeoff was observed between water/salt solubility, diffusivity, and permeability selectivity and water solubility, diffusivity and permeability, respectively. This finding suggests a water/salt permeability/selectivity tradeoff, similar to that operative in gas separation polymers, in this family of polymers.     

Microscopic effects on chloride diffusivity of cement pastes—a scale-transition analysis

For estimation of the durability of structures, it is highly desirable to quantify and simulate the chloride diffusion process in concrete. To this end, diffusion–cell experiments delivering the chloride diffusivity of cement pastes with different water–cement ratios (related to different microporosities) are evaluated in a scale-transition analysis. For prediction of the apparent chloride diffusivity, cement paste can be modelled by means of a differential homogenization scheme involving nondiffusive spherical inclusions in a diffusive matrix. As a result, chloride diffusivity of cement paste is obtained as a function of the microporosity and the chloride diffusivity in the micropore solution. Remarkably, the latter turns out to be one order of magnitude smaller than the chloride diffusivity in a pure salt solution system. The smaller diffusivity is probably caused by structuring of water molecules along the pore surface of cement paste.     

Diffusion of electrolytes in dilute polymer solutions

The diffusion of sodium chloride in dilute solutions of carboxymethylcellulose (CMC) was studied using the porous frit technique. It was found that at relatively low CMC concentrations the diffusivity of sodium chloride (D) is higher than that in water (D₀); with increasing CMC concentration, the diffusivity decreases gradually and reaches a value lower than that in water. The relation between the diffusivity (D) and CMC concentration (C_p) was represented by the equation D = a – bC_p. The effect of temperature on the diffusivity of sodium chloride in CMC solutions was found to obey the Arrhenius equation with an activation energy of 2230 cal/mol.     

Thermal diffusivity of fiber-reinforced composites using the laser flash technique

The applicability of the flash technique for measuring thermal diffusivity of fiber-reinforced composites has been examined. While the usefulness of this technique has been demonstrated previously for randomly dispersed composites and for layered structures, problems arise from preferential heat paths in fibrous-reinforced composites. For these materials the concept of diffusivity must be expanded to include dependencies upon sample thickness to unit cell ratios and transient times in addition to the usual constituent property ratios and temperature dependencies of properties. Nevertheless, the flash technique has been shown to be a powerful tool for examining heat flow in these materials. It is possible to obtain diffusivity data which are equivalent to steady-state properties. In addition, it is possible to determine in situ properties for the fiber and matrix and to examine defect structures.     

氯化聚氯乙烯的研究、生产和应用现状

简要介绍了国内外氯化聚氯乙烯(CPVC)的研究、生产和应用现状,从原料、生产工艺和配方以及加工技术等方面分析了国内外CPVC行业的差距,并提出了促进国内CPVC行业发展的建议.     

循环冷却水中氯离子的腐蚀影响探析

介绍了循环冷却水中的氯离子的来源及其危害,用氯离子腐蚀实验和实际应用数据对比不同材质下的腐蚀影响程度。从材料选用,操作规程,维修及管理方面介绍了氯离子腐蚀性的防护措施。     

Effect of Microcracking on the Thermal Diffusivity of Fe2TiO5

The effect of microcracking on the thermal diffusivity of polycrystalline Fe₂TiO₅ subjected to a range of annealing treatments was investigated. At fine grain size (∼1 μm), the thermal diffusivity exhibited the decrease with increasing temperature common for dielectrics. Extensive microcracking in the larger-grain-sized materials significantly decreased their thermal diffusivity. On heating, the microcracked materials exhibited increased thermal diffusivity at elevated temperatures which can be attributed primarily to microcrack closure and healing; on cooling, they exhibited a pronounced hysteresis, attributable to irreversible crack opening and closing. Thermal cycling closed the hysteresis curves, which suggests permanent changes in microcrack morphology. It appears that microcracking is a promising technique for tailoring ceramic materials to a combination of high thermal shock resistance and good insulating capability.     

Surface Chemical Study of Sheet Molded Composite (SMC) as Related to Adhesion

Surfaces of commercial sheet molded composite (SMC) materials have been characterized by X-ray photoelectron spectroscopy (XPS) before and after various surface treatments. Surface treatments included cleaning with methylene chloride, abrasion using methylene chloride and a Scotch Brite ® abrasive pad, and application of an isocyanate primer. The pretreated SMC materials were bonded using a polyurethane adhesive. Bonded coupons were tested under a variety of conditions using the lap shear technique. Lap shear test results for specimens bonded following the abrasion and primer pretreatment indicated a favorable fracture force and mode of failure. Surface analysis studies were used to characterize the pretreated and failed surfaces.