基于细观力学的延性构件的设计

本文阐述了依据细观力学原理设计高性能纤维增强水泥基复合材料(HPFRCC)的原则。普通钢筋或FRP筋混凝土构件需设置大量的箍筋保证延性。HPFRCC强度较高，受拉和受剪时延性较好，作为基体配置钢／FRP筋后，与相同配筋条件的混凝土梁相比，承载力和延性均提高。     

纤维增强混凝土连接的装配式混凝土结构节点性能综述

装配式混凝土建筑在国内外已有广泛的应用,预制混凝土构件的连接是装配式结构性能的重要影响因素之一.本文在装配式建筑节点连接研究进展的基础上,总结了普通纤维增强混凝土、超高延性纤维增强水泥基复合材料(ECC)和超高性能混凝土(UHPC)连接的装配式混凝土构件承载力、裂缝和破坏形式、刚度退化和耗能等特性.纤维增强混凝土连接预制混凝土构件均能提高装配式结构的承载力,避免梁-柱节点核心区发生剪切破坏,在梁端形成塑性铰,实现"强节点弱构件"的需求;普通纤维增强混凝土连接的预制混凝土构件在新旧混凝土界面处的破坏仍较明显;超高延性纤维增强水泥基复合材料连接的预制混凝土构件整体延性增大,且在循环荷载作用下,承载力和刚度退化速率较小;超高性能混凝土连接较大程度缩短连接处钢筋搭接和现浇段长度.     

高性能PVA纤维增强水泥基复合材料研究进展及应用

高性能PVA(聚乙烯醇)纤维增强水泥基复合材料(PVA-ECC)是一种具有应变硬化、多缝开裂能力和高能量吸收能力的超高韧性纤维增强水泥基复合材料。文中阐述了高性能PVA纤维增强水泥基复合材料的研究背景、进展以及基本性能。得出:与普通水泥基复合材料相比,PVA-ECC的抗弯抗拉以及抗压性能均有所提高,同时具有良好的延性和耐久性。目前,PVA纤维增强水泥基复合材料已成功应用于实际工程中。     

高延性水泥基复合材料的断裂性能分析

实验测试了不同纤维掺量下的高延性水泥基复合材料的载荷—挠度曲线,并对试件加载过程中的声发射信号进行收集,分析了试件断裂后的裂纹分布及纤维在基材中的破坏形式。结果发现:(1)当纤维体积掺量2.0%时,水泥基材的极限挠度、极限抗弯承载力分别可达20.16mm、19.47MPa;(2)高延性水泥基复合材料破坏主要来自于微裂纹的萌生、扩展以及损伤积累过程,试件从加载至完全破坏的时间为素水泥基复合材料破坏持续时间的2~5倍;(3)高延性水泥基复合材料中纤维的破坏以纤维被拔出和纤维被拉断两种模式,试件表现出明显的多缝开裂特征。     

玻璃钢筋增强水泥基复合材料的试验研究

本文采用对裸玻璃钢筋进行表面处理的方法提高水泥对玻璃钢筋的握裹力；研究了挤拉玻璃钢筋增强水泥基复合材料的结合性能，制备出抗压强度49.6MPa、抗折强度25．8MPa的优质玻璃钢筋增强水泥基复合材料；初步探讨了用玻璃钢筋增强水泥的可行性。     

浅谈高性能水泥基复合材料研究现状

经过单掺、双掺或者三掺矿物掺合料等掺入技术,制备出高性能水泥基复合材料。又通过复掺纤维技术,制备出高性能多功能水泥基复合材料。本文主要从以上两个因素对研究现状做了总结,并得到了重要结论,为以后研究高性能水泥基复合材料提供了理论基础和指导方向。     

高性能水泥基复合材料研究综述

本文以国内外大量学者的研究成果为基础,对高性能水泥基复合材料性能的主要影响因素,进行了归纳总结。结果发现,水胶比、胶凝材料用量、矿物掺合料以及纤维掺量等影响因素与高性能水泥基复合材料性能的有很大关系,同时通过本文的总结,也为后期高性能水泥基复合材料的进一步发展提供了很好的参考。     

玄武岩纤维网增强海砂水泥基薄板的力学性能研究

水泥混凝土构件中利用纤维材料替代钢材,不但可以起到增强效果,还可以有效避免钢筋锈蚀的发生。本文利用我国自主研发的玄武岩纤维网对海砂水泥基薄板进行增强,试验结果表明,玄武岩纤维网的抗拉强度决定了水泥基薄板的拉伸强度,随纤维网层数的增加薄板拉伸强度大幅提高,纤维网增强薄板的拉伸强度略低于钢丝网增强薄板,但延性较好;利用玄武岩纤维网增强的薄板其弯曲韧性和抗弯承载力均优于钢丝网增强薄板,且相应的指标显著高于规范要求。     

高性能水泥基复合材料的研究与发展状况

高性能水泥基复合材料既是在近代科技成就的基石上发展起来的，又将在高新工程技术领域中开发应用。本文对近年来出现的几种高性能水泥基复合材料进行了初步综述。     

钢-PVA混杂纤维水泥基复合材料抗压力学性能及经济性研究

纤维增强延性水泥基材料(ECC)造价昂贵,在实际工程应用中尚未被推广。在传统ECC体系中加入钢纤维,并按照不同体积分数(0%、25%、50%、75%、100%)将国产PVA纤维替代日产PVA纤维,制备极具性价比的钢-PVA混杂纤维增强延性水泥基材料,通过立方体轴心抗压试验研究混杂纤维延性水泥基材料的单轴受压力学性能。结果表明：随着国产PVA纤维的增加,钢-PVA混杂纤维水泥基复合材料的抗压强度先减小后增加,抗压韧性指数先增强后减弱,而峰值应变提升效果较为显著;相较于普通水泥基材料,钢-PVA混杂纤维水泥基复合材料具有更好的完整性和延性;综合材料抗压性能与材料造价,国产PVA纤维替代日产PVA纤维配制钢-PVA混杂纤维水泥基复合材料可以实现功能价值和经济价值的协同最大化。     

聚乙烯醇纤维增强水泥基复合材料研究进展

普通混凝土具有许多优点,但其脆性大、易产生开裂,这将导致外界化学介质向内部扩散的速度加快,使建筑结构的使用寿命大幅度降低.加入聚乙烯醇纤维是解决这一问题的一种有效途径,并且能够显著改善水泥基材料的性能.论文介绍了聚乙烯醇纤维增强水泥基复合材料的国内外研究现状、动力学特性以及自愈合情况,探讨了该材料的微观设计理论,介绍了其应用,并对聚乙烯醇纤维增强水泥基复合材料研究进行了展望.     

热处理对聚合物改性纤维增韧水泥基复合材料物理力学性能的影响

采用环氧乳液、乳胶粉制备了聚合物改性纤维增韧水泥基复合材料,研究了200℃、400℃、600℃、800℃热处理对材料物理力学性能的影响.结果表明:掺加聚合物可以改善试样的高温体积稳定性,使得试样在800℃高温下热处理时不发生爆裂;室温冷却条件下,聚合物使得材料峰值残余强度对应的温度由400℃降低至200℃,而在水冷却条...     

单/双层水泥基平板的微波吸收性能

依据阻抗匹配原理与电磁波传播规律,提出表层透波、内层吸波的双层法设计,该设计具有电磁波吸收性能的层状水泥基平板结构.研究了硅灰和橡胶粉对表面层阻抗匹配的影响;同时还对碳纤维、钢纤维、碳纤维与铁氧体粉复合以及钢纤维与碳纤维复合作为内层吸收剂时,水泥基平板材料在8～18GHz频段内的吸波性能进行了研究.结果表明:硅灰和橡胶颗粒可以明显地改善水泥平板与自由空间的阻抗匹配:与单层相比,在相同碳纤维掺量时,双层吸波砂浆反射率下降-3dB左右;30%质量分数铁氧体与碳纤维复合作为吸波材料的损耗层的吸收剂,反射率在-10dB以下(12.5～18.0GHz),且随着入射频率的增加反射率下降.     

Improving the interface bond between fiber mesh and cementitious matrix

The use of continuous fiber mesh as reinforcement of cementitious composites is attractive for various applications. In this paper, fracture toughness was used to evaluate the flexural behavior of glass concrete reinforced with either AR-glass or polypropylene fiber mesh. AR-glass fiber mesh was found to be much more efficient, but polypropylene fiber mesh is less expensive and has no aging problem. A research project is underway at Columbia University to improve the bond between the polypropylene fiber mesh and cementitious matrix. Results obtained so far indicate a great improvement of the mechanical properties of the fiber mesh-reinforced material.     

Performance of fibers embedded in a cementitious matrix

Reinforcement of cementitious materials with short fibers has been proved to be an economical and effective way to convert these brittle materials to ductile products. Many fibers with different geometries have been used as reinforcement materials. Fibers bonding to cementitious materials play an important role in mechanical performance of these composites. This article describes the performance of (homemade) fibers as reinforcement in cement‐based materials by investigation on bonding characteristic of fiber to cement matrix. To this end, the fibers (glass, polypropylene, polyacrylonitrile (PAN), and high strength nylon 66 (N66)) are characterized using microscopy analysis, tensile strength, and alkali attack tests. The fibers embedded in the cement matrix, then, pulled‐out to evaluate their bonding to cementitious materials. SEM analysis is used to study fiber/cement interfacial transition zone. The results show that PAN fibers have the advantages of preparing for cementitious reinforcement. It was found that the reinforcing efficiency of fibers‐reinforced cementitious composites was strongly depending on interfacial contact area in fiber/matrix interface and chemical/physical properties of fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Compressive fatigue damage and failure mechanism of fiber reinforced cementitious material with high ductility

The fiber reinforced cementitious material with high ductility has potential use in particular environments and structures that undergo repeated or fatigue loads. In this study, a series of monotonic and fatigue tests were performed to investigate the compressive fatigue behavior of this material. It is found that the fatigue life of this material is higher than that of plain concrete and steel fiber reinforced concrete under the same stress level. In addition, the failure deformation of fiber reinforced cementitious material with high ductility under fatigue load was larger than the monotonic envelope, while the envelope coincides with the monotonic loading curve for concrete or fiber reinforced concrete. The failure surface and damage process were investigated and a new failure mode of polyvinyl alcohol fiber with crushed end was discovered. The fatigue failure surface could be divided into three regions, including fatigue source region, transition region and crack extension region.     

不同龄期钢纤维增强水泥砂浆纤维拉拔试验与模拟研究

钢纤维增强水泥基复合材料作为一种多相复合材料,其增强增韧效果的发挥依赖于钢纤维与基体之间的界面粘结性能。通过开展不同龄期的钢纤维增强水泥基复合材料单根纤维拉拔试验及数值模拟研究,分析了龄期对钢纤维增强水泥砂浆界面粘结性能的影响,建立了不同龄期的单根纤维拉拔细观模型,通过将模拟结果与试验结果进行对比验证模型的有效性。根据所建立的细观模型分别对不同龄期钢纤维增强水泥砂浆纤维-基体间的界面粘结作用机理及纤维-基体间粘结表面在纤维拔出过程中的应力变化进行了分析。结果表明:所建立细观模型模拟得到的纤维最大拉拔力及荷载-滑移曲线与试验结果吻合较好,钢纤维的最大拉拔力及钢纤维-水泥砂浆基体的界面粘结强度均随着龄期的增加而增加;在7 d龄期内界面粘结强度的增长速度较快,7 d龄期后增长速度放缓;随着龄期的增加,不同龄期段的界面粘结强度的增长率逐渐减小并趋于稳定。采用拟合得到的粘结表面材料参数能够有效模拟各龄期下单根钢纤维从水泥砂浆中的拔出过程。     

Surface treatments of subdenier monofilament polypropylene fibers to optimize their reinforcing efficiency in cementitious composites

The surface properties of polypropylene (PP) fibers have an important effect on their reinforcing efficiency in cementitious composites. Two new methods of modifying the surface of subdenier monofilament polypropylene fibers were introduced, as well as the performances of the fiber‐reinforced mortar. The results show that the surface modification improved the mechanical performance of the fiber‐reinforced mortars, such as compressive strength and flexural strength, and the reinforcing efficiency depends on the adopted method. The enhanced interfacial bonding between treated fibers and the cementitious matrix, compared with that of unmodified fibers, was investigated using scanning electronic microscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2637–2641, 2004     

The effect of high content of fly ash on the properties of glass fiber reinforced cementitious composites

The objective of this paper was to study glass fiber reinforced cementitious composites (GFRCC) with Portland cement, a high content of fly ash as matrix. The effect of fly ash content, the initial curing time, and accelerated ageing on the flexural strength of GFRCC was investigated. The suitability of the accelerated ageing method was queried by analyzing the results from SEM observation, XRD analysis, and deflection testing.