Square concrete columns strengthened with carbon fiber reinforced plastics sheets at low temperatures

Twenty-one square concrete columns were constructed and tested. The testing results indicate that bonded carbon fiber reinforced plastics(CFRP) sheets can be used to increase the strength and improve the serviceability of damaged concrete columns at low temperatures. The failure of the specimens,in most cases,takes place within the middle half of the columns. And the failure of strengthened columns is sudden and explosive. The CFRP sheets increase both the axial load capacity and the ultimate concrete compressive strain of the columns. The ultimate loads of strengthened columns at-10,0 and 10 ℃ increase averagely by 9.09%,6.63% and 17.83%,respectively,as compared with those of the control specimens. The axial compressive strength of strengthened columns is related to the curing temperatures. The improvement of axial compressive strength decreases with reducing temperature,and when the temperature drops to a certain value,the improvement increases with falling temperature.

Experimental Study on Electric Properties of Carbon Fiber Reinforced Concrete

According to the phenomenon that the physical properties have,a great effect on the electric capability of carbon fiber reinforced concrete, the author researched the relationship between DC resistance of carbon fiber reinforced concrete and curing age using the two-probe method. Then the effect of insulative area, location and quantity on DC resistance of carbon fiber reinforced concrete was investigated at different curing age with analysis of hydration. The results suggest that DC resistance increases greatly with its curing age, which illustrates the relationship like Gaussian curve. In every curing ages the electric capability of carbon fiber reinforced concrete weakenes with the increase of insulative area. In same curing ages, section and insulative area, the more the quantity of insulation, the stronger the conductibility. The insulative location in optimal position can only result in optimal conductibility.

Detecting the Resistivity Distribution of Carbon Fiber Reinforced Concrete by Electrical Resistance Tomography Method

According to the principle of electrical resistance tomography （ ERT）, the resistivity distribution of the carbon fiber reinforced concrete （CFRC） in the sensing field can be measured by injecting exciting current and measuring the voltage on the sensor electrode arrays installed on the surface of the object. Therefore, measurement of the resistivity distribution of CFRC is divided into first measuring the boundary conditions and then inversely computing the resistivity distribution. To reach this goal, an ERT system was constructed, which is composed of a sensor array unit, a data acquisition unit and an image reconstruction unit. Simulations of static ERT was performed on set-ups with many objects spread in a homogeneous background, and a simulation of dynamic ERT was also done on a rectangular board, the resistivity of which was changed within a small domain of it. Then, the resistivity distribution of a CFRC sample with a circlar hole as the target was detected by the ERT system. Simulation and experimental results show that the reconstructed ERT image reflects the resistivity distribution or the resistivity change of CFRC structure well. Especially, a small change in resistivity can be identified from the reconstructed images in the simulation of dynamic ERT images.

Investigating Some Parameters Affecting Flexural Behavior of Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer Laminate

In this paper,the influence of some important parameters affecting the flexural behavior of reinforced concrete beams strengthened with one layer of carbon fiber reinforced polymer(CFRP)laminate has been studied.For this purpose,six reinforced concrete beams were cast and tested in the laboratory.Based on the obtained data,when CFRP laminate is applied to the tension face,too close to the steel rebar,the flexural strength of the strengthened beam is reduced.In general,the performance of the beam strengthened with one wide CFRP strip is better than that strengthened with two equivalent narrow strips.Ultimate load capacity of each strengthened beam was calculated based on the method given by the ACI 440.2R and compared with the test one.It is concluded that,to avoid the steel rebar-CFRP laminate interaction effect,the CFRP laminate depth-to-the effective depth ratio(df/d)should not be smaller than about 1.17.

Shear strengthening of pre-damaged reinforced concrete beams with carbon fiber reinforced polymer sheet strips

This paper presents the results of an experimental investigation on the response of pre-damaged reinforced concrete (RC) beam strengthened in shear using applied-epoxy unidirectional carbon fiber reinforced polymer (CFRP) sheet. The reasearch included four test rectangular simply supported RC beams in shear capacity. One is the control beam, two RC beams are damaged to a predetermined degree from ultimate shear capacity of the control beam, and the last beam is left without pre-damaged and then strengthened with using externally bonded carbon fiber reinforced polymer to upgrade their shear capacity. We focused on the damage degree to beams during strengthening, therefore, only the beams with side- bonded CFRPs strips and horizontal anchored strips were used. The results show the feasibility of using CFRPs to restore or increase the load-carrying capacity in the shear of damaged RC beams. The failure mode of all the CFRP-strengthened beams is debonding of CFRP vertical strips. Two prediction available models in ACI-440 and fib European code were compared with the experimental results.

Flexural rigidity evolvement laws of reinforced concrete beams strengthened with carbon fiber laminates

Extensive research has shown that externally bonded carbon fiber reinforced polymer (CFRP) laminates are particularly suitable for improving the fatigue behavior of reinforced concrete (RC) beams. This paper presents the research on flexural rigidity evolvement laws by testing 14 simple-supported RC beams strengthened with carbon fiber laminates (CFL) under cyclic load, and 2 under monotone load as a reference. The cyclic load tests revealed the peak load applied onto the surface of a supported RC beam strengthened with CFL is linear to the logarithm of its fatigue life, and the flexural rigidity evolvement undergoes three distinct phases: a rapid decrease from the start to about 5% of the fatigue life; an even development from 5% to about 99% of the fatigue life; and a succedent rapid decrease to failure. When the ratio of fatigue cycles to the fatigue life is within 0.05 to 0.99, the flexural rigidity varies linearly with the ratio. The peak load does not affect the flexural rigidity evolvement if it is not high enough to make the main reinforcements yield. The dependences of the flexural rigidity of specimens formed in the same group upon their fatigue cycles normalized by fatigue life are almost coincident. This implies the flexural rigidity may be a material parameter independent of the stress level. These relationships of flexural rigidity to fatigue cycles, and fatigue life may be able to provide some hints for fatigue design and fatigue life evaluation of RC member strengthened with CFL; nevertheless the findings still need verifying by more experiments.

Influence of Carbon Fiber Contents on the Temperature Sensibility of CFRC Road Material

The relationship between the electrical resistivity of carbon fiber reinforced concrete(CFRC) containing different carbon fiber contents and temperature was studied.it is found that carbon fiber contents influence greatly on the temperature sensibility of CFRC road material.Only with a certain amount of carbon fiber can CFRC show a sensitive and stable temperature sensibility.

Experimental study on slender reinforced concrete columns wrapped with CFRP

By axial compression tests on 6 reinforced concrete slender columns wrapped with carbon fiber-reinforced plastic (CFRP),with slenderness ratio(SR) from 4.5 to 17.5,the results show that when SR increases the retrofitting effect declines. In the case of same SR,the stability coefficient (SC) for the reinforced concrete(RC) columns with CFRP is much less than that without CFRP. There is 20% increase of stable bearing capacity to the former as compared with the latter when the SR in less than 17.5. The study summarized the simplified formula for SC,which provides a reference for engineering designers.

CFRC道面板电热效应模拟研究

为探究碳纤维混凝土(CFRC,carbon fiber concrete)道面的除冰效果,通过室内试验与ABAQUS电热效应分析结果进行对比,验证数值模拟CFRC道面板电热升温过程的可靠性,研究有、无隔热层情况下,不同输入电压、碳纤维含量、外界温度、风速等级条件下的道面升温规律。模拟结果表明:碳纤维含量越高,道面板的升温速率受输入电压的影响越小,当碳纤维含量达到1.7%时,对道面板升温速率的影响将不再明显;外界初始温度对道面板升温速率影响不大;外界风速等级越高,道面板升温速率越慢,当外界风速等级高于三级时,电压对道面板的升温效果影响较大,当风速等级达到六级时,90 V以下的输入电压作用下道面板难以升温到0℃;当外界温度为-10℃时,有隔热层道面板的升温速率比无隔热层的更快;当风速等级低于三级时,有、无隔热层对道面板的除冰效果影响较小。通过研究不同影响因素下的模型升温曲线,可为寒冷地区碳纤维混凝土机场道面的建设提供借鉴。

Shear capacity of reinforced concrete columns strengthened with CFRP sheet

This paper discusses the results of tests on the shear capacity of reinforced concrete columns strengthened with carbon fiber reinforced plastic (CFRP) sheet. The shear transfer mechanism of the specimens reinforced with CFRP sheet was studied. The factors affecting the shear capacity of reinforced concrete columns strengthened with CFRP sheet were analyzed. Several sug-gestions such as the number of layers, width and tensile strength of the CFRP sheet are proposed for this new strengthening technique. Finally, a simple and practical design method is presented in the paper. The calculated results of the suggested method are shown to be in good agreement with the test results. The suggested design method can be used in evaluating the shear capacity of reinforced concrete columns strengthened with CFRP sheet.

Experimental Investigation on the Properties of Recycled Concrete Using Hybrid Fibers

Due to the inherent property of concrete being very weak in tension, efforts have been made to overcome this deficiency by adding various type of fibers like carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), polypropylene fiber (PPF) and stainlesssteel fiber (SSF) smeared into the concrete mix. The present study involves experimental investigation on the use of GFRP, CFRP and SSF fibers alone or as combination to improve the mechanical properties of concrete. Furthermore, concrete cylinders were cast and tested for compression and tension using 10% fly ash as cement replacement in all specimens. Besides fiber material types, fiber reinforcement ratios of 1% and 1.5% were tested to investigate the mechanical properties of concrete. In all concrete cylinder tests, the fiber reinforcement ratio of 1% had a significant contribution in increasing the tensile strength as oppose to compressive strength. As a result, the tensile and compressive strengths were increased by 26% and 11%, respectively as compared to the control specimen. Increasing the fiber reinforcement ratio from 1% to 1.5%, resulted in diminishing the mechanical properties of concrete. However, reduction in concrete compressive strength was more prominent than the tensile strength. Furthermore, it was observed that, the crack propagation was decreased with the increase of fiber content when compared to the control specimen.

单丝20 mm碳纤维含量对CFRC梁抗弯性能的影响试验

为了提高碳纤维增强混凝土(Carbon Fiber-Reinforced Concrete,CFRC)的动态抗弯性能,研究了低速落锤冲击作用下,单丝20 mm碳纤维的CFRC抗弯性能。试验工况设置为6种碳纤维体积分数(0、0.20%、0.25%、0.30%、0.35%、0.40%)。主要结论如下:提出了结合化学分散剂的多级物理分散法,实现了长度为20 mm碳纤维在混凝土中以单丝态均匀分布,改善了20 mm碳纤维在混凝土中难分散的现状。当冲击速度为3 m/s时,随着碳纤维体积分数由0提高至0.40%,碳纤维体积分数为0.35%的CFRC梁断裂吸收能量最多,约为相同工况下素混凝土梁的2.3倍。长度为20 mm的碳纤维实现在混凝土的水泥相中呈单丝态均匀分散。基于本试验,相较于其他工况,碳纤维体积分数为0.35%的CFRC梁断裂耗能最多。该研究对提高CFRC梁的综合性能具有很好的实际应用价值,易于推广使用。

侧向冲击荷载作用下CFRP型材-方钢管混凝土柱的动力响应

为了研究CFRP型材-方钢管混凝土固简柱的抗侧向冲击性能,采用水平撞击装置对3个CFRP型材-方钢管混凝土柱进行侧向冲击试验.根据柱的破坏模式、局部变形、整体变形及冲击力分析柱的动力响应,研究了CFRP型材、边界条件、冲击能量与冲击冲量对试件动力响应的影响规律.结果表明,CFRP型材-方钢管混凝土固简柱呈现弯曲破坏,具有良好的抗冲击性能,且随着支座约束能力的增大,抗侧向冲击性能增大.增加单位冲击冲量可使悬臂试件的峰值位移下降7%,而两端固支试件峰值位移仅变化1%.随着支座约束能力的下降,冲击冲量对试件变形的影响程度增大.在钢管混凝土固简试件中内置CFRP型材可使冲击位置处峰值位移下降9%,且降低程度随着支座约束能力的下降而增加.

CFRP-不锈钢夹层管混凝土柱轴压试验及承载力计算方法

为了提升薄壁不锈钢结构的承载性能和耐久性,在不锈钢管内外壁粘贴碳纤维增强复合材料(Carbon Fiber-Reinforced Polymer,CFRP)复合约束海水海砂混凝土,制得一种CFRP-不锈钢夹层管海水海砂混凝土结构。以CFRP粘贴层数和方式为变化参数,对18个短柱试件进行了单调轴心受压试验,观察了试件的受力破坏过程及形态,获取了荷载-位移曲线和材料应变分布数据,分析了试件轴压力学性能的变化规律。结果表明:内外贴CFRP能有效地提高结构的承载能力和变形能力;无CFRP和内贴CFRP试件的破坏形态均为剪切破坏,但破坏形态会随着外贴CFRP层数的增加向腰鼓破坏转变;在相同粘贴方式下,试件的承载能力、变形能力和耗能能力随着CFRP层数的增加呈非线性提高;在相同粘贴层数下,内贴CFRP的力学性能提升效果优于外贴CFRP,粘贴1层和2层CFRP时,内贴试件的极限承载力相较于外贴试件能再提高5.6%和6.7%,同时内贴1层CFRP的试件的耗能能力与外贴2层CFRP的相当;应变分析显示,在试件破坏前,CFRP与不锈钢协同工作良好。文中最后基于极限平衡法,考虑不锈钢的应变硬化效应,提出了CFRP-不锈钢夹层管混凝土柱极限轴压承载力的计算公式,并收集了73个样本的数据进行验证,发现计算值与试验值较为吻合。

碳纤维增强水泥基复合材料(CFRC)的电学特性

综述了碳纤维增强水泥基复合材料(CFRC)电学特性的研究进展,探讨了CFRC的电磁屏蔽性能和导电性能研究中的相关问题,阐述了原材料、配合比和表面处理对CFRC电磁屏蔽性能的影响,明确了碳纤维分散性和试验方法对CFRC导电性能的影响规律以及CFRC在工程结构中的应用状况,展望了CFRC的发展方向,指出碳纤维分散性、测试方法、温度和应力等多因素条件是CFRC电学特性将来的研究重点。

碳纤维增强水泥基复合材料(CFRC)的压敏特性

论述了碳纤维增强水泥基复合材料(CFRC)压敏特性的研究进展,阐析了CFRC具有压敏特性的机理,明确了组成材料、成型工艺和加载方式等对CFRC压敏特性的影响规律,分析了应力条件下CFRC的压敏特性及其在结构健康监测中的应用,展望了CFRC压敏特性的发展与应用方向,提出了CFRC压敏特性的研究重点.

利用CFRC的导电性评估混凝土结构修补质量

研究了利用碳纤维增强混凝土(CFRC)的导电性对混凝土结构修补质量进行在线评估的可行性,根据敷在服役混凝土结构上CFRC导电性能的变化,判断新旧混凝土界面的粘结质量,并通过CFRC导热性能的差异进行了验证。文中的研究在对修补混凝土结构的同时,为混凝土结构修补质量的监测和在线评估提供了新的方法。

CFRP-铝合金复合管高强混凝土短柱轴压性能研究

为研究CFRP-铝合金复合管混凝土构件的轴压性能,进行了12根短柱试件的轴向压缩试验,主要研究参数为CFRP层数。试验结果表明:复合管混凝土试件出现了多处外凸鼓曲以及对应位置混凝土被压溃的破坏形态,而空复合管试件发生了局部内凹屈曲破坏;试件轴压承载力随CFRP层数的增加而增大,且复合管混凝土试件的承载力提高幅度高于相应的空复合管试件的提高幅度。对各部分的承载力贡献比例进行分析,发现复合管混凝土试件中混凝土的承载力贡献比例超过70%,且承载力贡献度随CFRP层数的增加而提高。提出了CFRP-铝合金复合管混凝土构件的轴压承载力计算公式。

机器人化复合材料自动铺层技术综述

碳纤维增强复合材料(Carbon fiber-reinforced composite,CFRC)因具有轻质高强、耐腐蚀、耐冲击等优越性能,在生产生活中的应用已越来越广泛,然而复材产品的生产制造仍是劳动密集性产业,主要依靠人工.机械臂自上世纪50年代进入工业生产中以来,极大提高了生产效率和质量,然而目前机械臂在复材产品制造中的应用是少见的,主要集中在机械臂形式的自动铺丝(Automated fiber placement,AFP)中.复材产品制造工艺繁琐,将复合材料铺放在模具上是复材产品制造过程中的一个重要环节,本文称之为“铺层”,使用机械臂完成复合材料自动铺层将是未来复材产品制造自动化、智能化发展的一个关键方向.本文将机械臂进行复合材料自动铺层操作分为两种主要形式:铺片和铺带(丝),通过案例调研和分析,归纳总结现有的设计理念和技术方法,提出未来发展趋势,以期对机械臂的应用和研究、复材产品的智能化制造和工业4.0的发展形成参考.

CFRC抗弯试件的灵敏度

对CFRC抗弯试件进行了试验分析,探讨了不同载荷工况下CFRC抗弯试件的电阻变化规律。结果表明:CFRC抗弯试件上层电阻随载荷的增加先减小后增大,下层电阻随载荷的增加而增大;在重复载荷作用下,CFRC抗弯试件受拉区电阻不断增大,受压区电阻先减小后增大,残余电阻的存在反映了试件内部存在损伤和损伤积累;在交变载荷作用下,碳纤维混凝土试件的电阻随着载荷周期次数的增加而增大,直至破坏;试件电极形式不同,电阻变化规律也不同。