Fiber-reinforced Mechanism and Mechanical Performance of Composite Fibers Reinforced Concrete

To understand the enhancing effect and fiber-reinforced mechanism of composite fibers reinforced cement concrete, the influences of composite fibers on micro-cracks and the distribution of composite fibers were evaluated by optical electron micrometer(OEM) and scanning electron microscope(SEM). Three kinds of fiber, such as polyacrylonitrile-based carbon fiber, basalt fiber, and glass fiber, were used in the composite fibers reinforced cement concrete. The composite fibers could form a stable structure in concrete after the liquid-phase coupling treatment, gas-liquid double-effect treatment, and inert atmosphere drying. The mechanical properties of composite fibers reinforced concrete(CFRC) were studied by universal test machine(UTM). Moreover, the effect of composite fibers on concrete was analyzed based on the toughness index and residual strength index. The results demonstrated that the composite fibers could improve the mechanical properties of concrete, while the excessive amount of composite fibers had an adverse effect on the mechanical properties of concrete. The composite fibers could significantly improve the toughness index of CFRC, and the increment rate is more than 30%. The composite fibers could form a mesh structure, which could promote the stability of concrete and guarantee the excellent mechanical properties.

Compressive Strength Estimation for the Fiber-Reinforced Polymer (FRP)-Confined Concrete Columns with Different Shapes Using Artificial Neural Networks

An evaluation of existing strength of concrete columns confined with fiber-reinforced polymer( FRP) was presented with extensive collection of experimental data. According to the evaluation results, artificial neural networks( ANNs) model to predict the ultimate strength of FRP confined column with different shapes was proposed. The models had seven inputs including the column length,the tensile strength of the FRP in the hoop direction,the total thickness of FRP,the diameter of the concrete specimen,the elastic modulus of FRP,the corner radius and the concrete compressive strength. The compressive strength of the confined concrete was the output data. The results reveal that the proposed models have good prediction and generalization capacity with acceptable errors.

Anti-cracking Property of EVA-modified Polypropylene Fiber-reinforced Concrete Under Thermal-cooling Cycling Curing

In order to investigate the synergistic effect of re-dispersible powder-ethylene-vinyl acetate copolymer(EVA) and polypropylene fiber on the crack resistance of concrete under thermal fatigue loading, the compressive strength, ultimate tensile strength, ultimate tensile strain and tensile modulus of elasticity were tested. In addition, ultrasonic method and scanning electron microscope analysis were used to explain the microstructure mechanism. The results show that polypropylene fiberreinforced concrete presents a better performance on crack resistance than ordinary concrete, and the synergism of EVA and polypropylene fiber can improve the anti-cracking ability of concrete further.

Peridynamic Modeling and Simulation of Fracture Process in Fiber-Reinforced Concrete

In this study,a peridynamic fiber-reinforced concrete model is developed based on the bond-based peridynamic model with rotation effect(BBPDR).The fibers are modelled by a semi-discrete method and distributed with random locations and angles in the concrete specimen,since the fiber content is low,and its scale is smaller than the concrete matrix.The interactions between fibers and concrete matrix are investigated by the improvement of the bond’s strength and stiffness.Also,the frictional effect between the fibers and the concrete matrix is considered,which is divided into static friction and slip friction.To validate the proposed model,several examples are simulated,including the tensile test and the three-point bending beam test.And the numerical results of the proposed model are compared with the experiments and other numerical models.The comparisons show that the proposed model is capable of simulating the fracture behavior of the fiber-reinforced concrete.After adding the fibers,the tensile strength,bending strength,and toughness of the fiber-reinforced concrete specimens are improved.Besides,the fibers distribution has an impact on the crack path,especially in the three-point bending beam test.

钢-PVA混杂纤维高性能混凝土高温后残余力学性能试验研究

为探究3种因素钢纤维、聚乙烯醇(polyvinyl alcohol,PVA)纤维和矿粉对钢-PVA混杂纤维高性能混凝土(hybrid fiber high performance concrete,HFHPC)高温后残余力学性能的影响。对钢纤维、PVA纤维和矿粉3种因素各取3个水平,采用L_(9)(3^(3))方案进行正交设计,测试HFHPC遭受高温作用后的立方体抗压强度、劈裂抗拉强度和抗折强度,并进行极差与方差分析。结果表明:钢纤维体积分数为2.0%时可以有效提高HFHPC的各项强度。PVA纤维能够抑制混凝土爆裂,与钢纤维混杂可体现优势互补。800℃时,当钢纤维体积分数为2.0%、PVA纤维体积分数为0.3%、矿粉掺量为10%时,HFHPC的抗压强度残余率与劈拉强度残余率达到最高,分别为60.23%和74.5%。当矿粉掺量大于10%时,HFHPC抗压强度可显著提高,而劈拉强度与抗折强度略有下降。最后分别建立了HFHPC立方体抗压强度、劈裂抗拉强度和抗折强度的预测模型。

钢-PVA纤维混凝土预制连梁抗震性能试验研究

为研究钢-聚乙烯醇混杂纤维混凝土(Steel-Polyvinyl Alcohol Hybird Fiber Concrete,简称SPHFC)预制连梁的抗震性能,对1个普通混凝土(RC)预制连梁试件和3个SPHFC预制连梁试件进行低周往复加载试验,分析预制连梁的破坏过程、破坏形态、滞回性能、刚度及耗能能力等抗震指标,研究连梁基体材料和截面宽度对其抗震性能的影响,阐明了SPHFC预制连梁的破坏机理.结果表明:RC预制连梁破坏时混凝土剥落现象严重,最终表现为剪切型破坏;SPHFC预制连梁破坏时几乎无混凝土剥落现象,充分发挥了纤维混凝土多裂缝开展的特点,最终发生弯剪型破坏;SPHFC预制连梁的承载力、延性、刚度和耗能能力均远高于RC预制连梁;分别增大SPHFC预制连梁基体强度或截面宽度,连梁承载力提高,延性和耗能能力略有降低.本文提出的新型SPHFC预制连梁各项抗震指标均显著优于普通RC预制连梁,且制作简便,轻质高强,便于预制吊装,可在装配式结构中推广应用.

PVA纤维增强珊瑚混凝土静动态力学性能试验研究

为增强珊瑚混凝土的力学性能,对其进行了5种聚乙烯醇纤维体积分数(0、0.5%、1%、1.5%和2%)条件下的静态力学试验,并采用直径为100 mm的分离式霍普金森杆研究其在4种应变率下的冲击压缩性能。结果表明:掺入适量纤维能明显提高混凝土静态抗压强度与劈裂抗拉强度;动态力学试验表明珊瑚混凝土具有明显的应变率效应,加入纤维后能提高动态增强因子对应变率的敏感性,增强效果在纤维掺量为1.5%时趋于饱和;纤维在混凝土中起到了阻裂与耗能的作用,能明显地改善混凝土的破坏形态与冲击韧性。

PVA-铁尾矿砂混凝土抗折性能研究

为实现固废再生利用,将铁尾矿砂部分替代细骨料并掺入PVA纤维,制备出具有良好和易性的PVA-铁尾矿砂混凝土,通过标准抗折试验研究了不同铁尾矿砂替代率与PVA纤维掺量对混凝土抗折性能的影响。研究表明,PVA纤维掺量为0%和0.1%(质量分数,下同)时试件发生贯通型开裂脆性破坏,而PVA纤维掺量为0.2%和0.3%的试件破坏时裂缝宽度明显减小且未贯通。当铁尾矿砂替代率为30%、PVA纤维掺量为0.3%时,试件跨中挠度和抗折强度均达到最大值,较普通混凝土分别提高了22.04%和6.57%。当铁尾矿砂替代率超过30%时试件抗折强度和跨中挠度会显著下降。与单掺PVA纤维相比,混掺PVA纤维与铁尾矿砂的试件变形能力增强更明显。由XRD谱可知,30%铁尾矿砂替代率下试件中C-S-H凝胶与钙矾石生成量最多,能显著提高材料强度。

局部采用PVA-ECC的铁路重力式桥墩抗震性能研究

为探究通过在桥墩墩底局部采用聚乙烯醇纤维增强混凝土(PVA-ECC)来提高铁路重力式桥墩的抗震性能的可行性,设计并制作2个配筋率为1%的桥墩缩尺模型,其中1个桥墩模型在墩底局部采用300 mm高度的PVA-ECC材料,另外1个普通混凝土桥墩模型为对比模型。通过对桥墩模型进行低周往复荷载试验,研究桥墩的破坏形态,并分析对比桥墩模型的滞回曲线、骨架曲线、累积耗能能力、位移延性以及刚度退化规律等抗震性能指标。研究结果表明:在桥墩墩底局部采用PVA-ECC材料,桥墩模型的承载能力、累积耗能能力、刚度以及位移延性系数均得到一定程度提高。研究结果验证了墩底局部采用PVA-ECC材料能够有效提高桥墩的抗震性能。

钢-PVA混杂纤维高性能混凝土隧道衬砌管片抗弯性能试验

为研究钢纤维、聚乙烯醇(PVA)纤维、矿粉3种因素对混杂纤维高性能混凝土隧道衬砌管片受力性能的影响,针对不同体积分数的钢纤维(0.5%,1.0%,1.5%)、PVA纤维(0.1%,0.2%,0.3%)和不同掺量的矿粉(10%,20%,30%)设计了L_(9)(3^(3))的正交试验,并制作1块钢筋混凝土(RC)衬砌管片和9块钢-PVA混杂纤维高性能混凝土衬砌管片进行抗弯性能试验。研究结果表明:与RC衬砌管片相比,钢-PVA混杂纤维能显著提升衬砌管片开裂弯矩、裂缝宽度0.2 mm对应的弯矩、屈服弯矩、极限弯矩和控制裂缝开展的能力,其中钢纤维对管片极限弯矩提升最为显著,最大提升幅度达64.0%,其次是矿粉和PVA纤维;3种因素的最佳掺量组合为:1.5%钢纤维,0.3%PVA纤维和20%矿粉。对钢-PVA混杂纤维混凝土的选用原则和在衬砌管片的应用提供理论及试验依据。

塑性铰区采用PVA纤维高强混凝土柱抗震性能

为了明确局部PVA纤维高强混凝土柱中轴压比、剪跨比和PVA纤维掺量对抗震性能的影响,对不同轴压比(0.2、0.3和0.4)、剪跨比(3.23、4.15和5.07)和PVA纤维体积分数(0、0.3%、0.5%和0.7%)的8根高强钢筋混凝土柱足尺试件进行了抗震性能试验,分析了PVA纤维掺量、轴压比和剪跨比等参数对于高强钢筋混凝土柱耗能能力、自复位能力、强度退化性能、刚度退化性能以及弯矩曲率关系的影响规律.以有限元模拟软件OpenSees为平台建立试件模型,对轴压比和剪跨比进行扩展分析.研究结果表明,PVA纤维混凝土柱的延性、耗能能力明显更优,抗震性能更好;同时,轴压比和剪跨比对抗震性能影响显著,PVA纤维掺量对其影响较大;建立的有限元模型具有较高的准确性.

Experimental study on ductility improvement of reinforced concrete rectangular Columns retrofitted with a new fiber reinforced plastics method

Reinforced concrete （RC） columns lacking adequately detailed transverse reinforcement do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation. In this paper, a new retrofit method, which utilized fiber-reinforced plastics （FRP） confinement mechanism and anchorage of embedded bars, was developed aiming to retrofit non-ductile large RC rectangular columns to prevent the damage of the plastic hinges. Carbon FRP （CFRP） sheets and glass FRP （GFRP） bars were used in this test, and five scaled RC columns were tested to examine the function of this new method for improving the ductility of columns. Responses of columns were examined before and after being retrofitted. Test results indicate that this new composite method can be very effective to improve the anti-seismic behavior of non-ductile RC columns compared with normal CFRP sheets retrofitted column.

基于分子动力学的氧化石墨烯对PVA纤维-CSH界面影响机理研究

纤维增强混凝土的宏观力学性能与纤维/基体的界面结合密切相关。本文通过分子动力学模拟,研究氧化石墨烯(GO)对聚乙烯醇纤维(PVA)/基体界面结合的影响。结果表明,当GO与PVA纤维以共价键连接时,PVA纤维从混凝土中被拉出所需的拉力最大,GO的存在能提升纤维与基体的界面黏结性能。混凝土基体与GO主要以钙氧键和氢键连接,其中钙氧键数量多且化学键强度高。但GO与PVA纤维物理连接时,GO与PVA纤维仅依靠强度较弱的氢键连接,对界面的黏结性能带来负面作用。此外,GO受到更多离子键和氢键的束缚,原子平移运动减少,与基体的界面黏结性能提高。

Punching and Local Damages of Fiber and FRP Reinforced Concrete under Low-Velocity Impact Load

In recent years, the development and application of high performance fiber reinforced concrete or cementitious composites are increasing due to their high ductility and energy absorption characteristics. However, it is difficult to obtain the required properties of the FRCC by simply adding fiber to the concrete matrix. Many researchers are paying attention to fiber reinforced polymers (FRP) for the reinforcement of construction structures because of their significant advantages over high strain rates. However, the actual FRP products are skill-dependent, and the quality may not be uniform. Therefore, in this study, two-way punching tests were carried out to evaluate the performances of FRP strengthened and steel and polyvinyl alcohol (PVA) fiber reinforced concrete specimens for impact and static loads. The FRP reinforced normal concrete (NC), steel fiber reinforced concrete (SFRC), and PVA FRCC specimens showed twice the amount of enhanced dissipated energy (total energy) under impact loadings than the non-retrofitted specimens. In the low-velocity impact test of the two-way NC specimens strengthened by FRPs, the total dissipated energy increased by 4 to 5 times greater than the plain NC series. For the two-way specimens, the total energy increased by 217% between the non-retrofitted SFRC and NC specimens. The total dissipated energy of the CFRP retrofitted SFRC was twice greater than that of the plain SFRC series. The PVA FRCC specimens showed 4 times greater dissipated energy than for the energy of the plain NC specimens. For the penetration of two-way specimens with fibers, the Hughes formula considering the tensile strength of concrete was a better predictor than other empirical formulae.

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.

PVA纤维-纳米SiO2对混凝土抗疲劳性能的影响及机理分析

为研究PVA纤维和纳米SiO2的掺入对混凝土抗疲劳性能的影响,设计了单掺PVA纤维(P组)、单掺纳米SiO2(S组)和混掺PVA纤维与纳米SiO2(SP组)3组试件,对其展开疲劳后的单轴压缩试验,以经历疲劳荷载后混凝土试件的相对动弹性模量和抗压强度,作为分析评价不同掺料方式对混凝土疲劳性能影响的评价指标,并利用SEM电镜扫描试验研究了掺合料的微观作用机理。结果表明:3组混凝土较普通混凝土在抗疲劳性能上都有明显的提升,S组在提高混凝土强度方面表现最为明显;而SP组能够更有效地抑制混凝土内部劣化损伤的发展。从作用机理上来讲,PVA纤维是通过提高混凝土各单元间的抗拉能力,有效降低了混凝土在疲劳荷载作用下的损伤破坏,相当于延长了混凝土的破坏过程;而纳米SiO2则是通过参与反应生成C-S-H(水化硅酸钙)凝胶填充混凝土薄弱区,提高了混凝土的抗压强度,相当于提高了混凝土在疲劳荷载作用下的破坏起点。研究成果对混凝土结构抗疲劳设计有参考价值。

PVA-ECC复合无接缝水泥混凝土路面施工技术研究

为进一步研究并解决传统水泥混凝土路面切缝造成的耐久性和行车舒适性问题,考虑到PVA-ECC材料的优良性能,文章依托河北省某重点高速公路项目,将该新材料应用到服务区水泥混凝土路面施工中。运用ABAQUS软件建立了PVA-ECC罩面型与补丁型两种复合无接缝水泥混凝土路面结构分析模型,进行了温度-荷载耦合作用下的敏感性分析,分析了土基模量、PVA-ECC模量、PVA-ECC厚度、水泥板模量、水泥板厚度等动力响应规律。研究发现,罩面型路面结构的最大耦合弯拉应力受罩面层厚度与PVA-ECC模量的影响较大,补丁型路面结构的最大弯拉应力受模量的影响较大。通过试验段现场实测与理论模拟情况比对分析,验证了ECC混凝土的抗压性能可以满足传统抗压使用要求,同时实际测试和理论模拟得到的拉应变数值都远小于资料显示的PVA纤维混凝土0.5%极限拉应变,最终得出PVA-ECC复合无接缝水泥混凝土路面ECC结构层最佳层厚为7 cm,满足使用要求且能达到消除混凝土接缝的效果,该研究成果可为PVA-ECC材料的推广应用提供参考。

PVA纤维地聚合物再生混凝土轴拉性能研究

通过20组共计60个试件的轴拉试验,研究再生粗骨料质量替代率和PVA纤维体积掺量对地聚合物混凝土破坏形态、弹性模量、峰值应力及峰值应变的影响,结果表明,试件的破坏均由单一横向裂缝引起,裂缝主要经过旧砂浆—骨料及骨料—基体界面过渡区,再生粗骨料替代率的增大导致混凝土弹性模量降低,峰值应变增大,轴心抗拉强度先增大后减小,而掺加适量PVA纤维(1.0%≤VPF≤1.5%)能改善地聚合物再生混凝土的轴拉性能。在GB50010模型的基础上,利用试验数据回归得到适用于PVA纤维地聚合物再生混凝土的轴拉本构模型,模型曲线与试验曲线吻合较好。

双掺剑麻纤维和PVA纤维再生骨料混凝土梁力学性能研究

为研究纤维对高强再生骨料混凝土梁抗弯性能的影响,以粗骨料类型、纤维种类、纤维掺入方式和纤维体积掺量为变化参数完成了3根混凝土梁的四点弯曲试验验,分析了不同参数对再生骨料混凝土梁破坏特征、裂缝宽度、挠度、开裂荷载、抗弯承载力和延性的影响。试验结果表明:掺入纤维的高强再生骨料混凝土梁和未掺入纤维的高强再生骨料混凝土梁破坏特征与高强天然骨料混凝土梁相似,均经历了弹性阶段、带裂缝工作阶段和破坏阶段;高强再生骨料混凝土梁的开裂荷载、刚度和变形性能较高强天然骨料混凝土梁均有所降低,且裂缝较宽,挠度较大;掺入聚乙烯醇/植物纤维有效抑制了裂缝的产生和进一步扩展,提高了开裂荷载,增强了变形性能;利用规程对纤维增强再生骨料混凝土梁进行抗弯承载力计算,计算结果与实测结果吻合较好。

早龄期加载的PVA纤维超高强混凝土徐变性能研究

以混凝土强度、聚乙烯醇(PVA)纤维体积分数、加载龄期三个因素作为控制变量,共成型18组混凝土试件,开展了坍落度试验、抗压强度试验、徐变试验,分析不同强度等级、PVA纤维体积分数、加载龄期对混凝土徐变规律的影响。同时,基于ACI209徐变预测模型和试验结果拟合结果,提出了适应早龄期PVA纤维超高强混凝土的徐变预测模型。试验实测曲线与预测模型计算曲线的对比表明,该徐变预测模型能够用于PVA纤维混凝土早龄期徐变随加载时间、纤维体积分数、混凝土强度因子变化的预测。