钢筋与结构型合成纤维对混凝土抗冲击性能混杂效应的分析

为了研究钢筋与结构型合成纤维混杂后对混凝土抗冲击性能的影响,采用改进的自由落球冲击试验装置,对素混凝土、钢筋混凝土、结构型合成纤维增强混凝土以及钢筋-结构型合成纤维混杂增强的混凝土试件的抗冲击性能进行了试验研究,分析了钢筋、结构型合成纤维以及钢筋与结构型合成纤维混杂后对混凝土抗冲击性能的影响及其增强机理。同时,利用Weibull分布理论分析了试件初裂冲击次数和破坏冲击次数的分布规律。研究表明:结构型合成纤维可以提高混凝土抗冲击性能;对于提高混凝土的抗冲击性能,钢筋与结构型合成纤维表现出显著的正混杂效应;两参数Weibull分布能较好的描述钢筋-结构型合成纤维混凝土抗冲击次数的分布特征。     

钢纤维-聚丙烯纤维混杂对再生混凝土抗冲击性能的影响

为研究钢纤维(SF)与聚丙烯纤维(PPF)混杂后对再生混凝土(RAC)抗冲击性能的影响,采用落锤弯曲冲击试验装置对素RAC、SF/RAC、PPF/RAC和SF-PPF/RAC进行抗冲击试验;分析了不同纤维掺量和掺入方式对RAC抗冲击性能的影响;采用数理统计模型对冲击试验结果进行拟合和失效概率预测,并对SF-PPF/RAC抗冲击性能的阻裂增强机制进行深入分析。结果表明:单掺或混杂纤维均可提高RAC的抗冲击性能;其中混合掺入体积分数为1.5vol%的SF和体积分数为0.9vol%的PPF时,RAC抗冲击耗能的提高幅度最大,RAC基体的延性和韧性最佳。SF-PPF/RAC的抗冲击次数很好地服从两参数Weibull分布。SF与PPF混杂对改善RAC的抗冲击性能呈现出优异的混杂增强效应。      

高延性混凝土板抗落石冲击性能试验研究

为了研究落石冲击荷载作用下高延性混凝土(HDC)板的抗冲击性能,对纤维掺量为0.5%、1.0%、2.0%的6块HDC板和2块普通钢筋混凝土(RC)板进行14 m高度下的落锤冲击试验,对比分析了HDC板和普通钢筋混凝土板抗冲击性能的差异以及不同纤维掺量对HDC板抗冲击性能的影响。采用高速摄像机记录了各试件的试验过程,详细分析了试件的破坏形态,冲击中心最大位移及落锤最大冲击力和冲量。结果表明:在相同的冲击荷载下,普通钢筋混凝土板被击穿,板底喷出大量混凝土碎块,破坏面整齐光滑,裂缝宽且呈十字形,钢筋未屈服,属于局部贯通破坏;HDC板产生数条由中心向四周逐步开展的裂缝,呈放射状分布,板底有少量混凝土碎块剥落,由于HDC与钢筋之间具有很好的粘结能力,钢筋屈服甚至拉断,但是整体裂而不散。落锤直接冲击RC板最小瞬时加速度为933.01g,最大冲击力914.35 kN,最大冲击时间0.021 8 s,大应变率数量级达到10~(11) s~(-1)。反观HDC板落锤直接冲击板的最小瞬时加速度较RC减小28.1%,最大冲击力减小28.1%,最大冲击时间延长0.006 s,大应变率数量级减小10~6 s~(-1)。HDC的各项参数对比均明显优于RC。表明HDC板具有良好的抗冲击性能,且纤维体积掺量为1.0%的HDC抗冲击能力最强。     

UHMWPE纤维混凝土动态压缩力学性能研究

试验研究了一种捻制超高分子量聚乙烯(UHMWPE)纤维增强的新型纤维混凝土动态压缩力学性能。研制了4种纤维体积掺量(0.3%、0.5%、0.7%、1.0%)的C70等级纤维混凝土,采用Φ100 mm分离式霍普金森压杆进行冲击压缩试验,研究了纤维混凝土在140~255 s~(-1)应变率下的动态压缩力学性能。试验结果表明:UHMWPE纤维混凝土抗压强度、峰值应变和弹性模量具有明显的应变率敏感性;纤维混凝土抗压强度应变率敏感性弱于素混凝土,但其弹性模量应变率敏感性强于素混凝土;动态强度增长因子与应变率对数呈线性关系,具体关系与纤维掺量相关。     

钢纤维和碳纤维的混合效应对高性能混凝土力学性能的影响

通过在混凝土基体中加入一种纤维和混合纤维,制备了高性能混凝土试件和混合纤维高性能混凝土试件.通过劈裂抗拉强度试验和落锤冲击试验,研究了单掺钢纤维、单掺碳纤维和混合纤维对高性能混凝土试件劈裂抗拉强度和抗冲击性能的影响,分析了混合效应对试件力学性能的增强作用.劈裂抗拉强度试验结果表明,只掺入碳纤维,且碳纤维掺入量为1％时,...     

高温后钢管混凝土短柱落锤动态冲击试验研究

采用落锤冲击实验机进行了高温作用后钢管混凝土短柱抗冲击性能试验研究,通过试验研究试件所经历的最高温度、升降温全过程中轴压力水平、冲击速度、冲击能量和含钢率等参数对高温后钢管混凝土抗冲击性能的影响。试验量测了钢管混凝土应变、冲击力和压缩变形时程曲线,试验结果表明,试件所经历的最高温度、冲击速度、冲击能量和含钢率均对高温作用后钢管混凝土的动态力学性能有显著的影响,而升降温全过程中轴压力水平的影响较小。试件的轴向和径向残余变形随着试件所经历的最高温度、冲击能量、轴压比的增大而增大,随着含钢率的增大而减小。高温后钢管混凝土在冲击作用下产生了较大的压缩变形,延性有所下降,但仍能够保持很好的完整性,说明钢管混凝土在高温作用后有良好的抗冲击能力。     

钢纤维对再生混凝土抗冲击性能的影响

为研究不同再生骨料取代率、钢纤维掺量和纤维类型对再生混凝土(RAC)抗冲击性能的影响,采用自由落锤冲击试验装置,对其进行抗冲击试验.利用两参数Weibull分布函数模型对试件抗冲击初裂次数和破坏冲击次数的概率分布规律,进行了拟合检验和失效概率预测分析;并以抗冲击延性比、抗裂性能定量评价了钢纤维再生混凝土(SFRAC)的...     

基于SHPB试验的多尺寸聚丙烯纤维混凝土动态力学性能研究

选用两种聚丙烯细纤维及一种聚丙烯粗纤维,制备了9组纤维掺量比不同的混凝土试件。采用变截面大尺寸分离式霍普金森压杆(SHPB)进行了冲击压缩试验,研究了在0.4 MPa冲击气压作用下,不同纤维掺量比对混凝土抗冲击性能的影响,基于引入损伤的Z-W-T本构模型对试验结果进行拟合分析。结果表明,单掺粗纤维可提高混凝土的整体性,且能显著提高混凝土破坏前的抗冲击性能,单掺细纤维主要是提高混凝土破坏后的抗冲击性能,而混掺纤维混凝土各个时期的抗冲击性能均得到提高,其中多尺寸纤维混掺的效果最好。     

考虑混杂效应时纤维混杂缠绕筒三维等效弹性模量的理论估算和试验研究

给出了多种纤维混杂多向缠绕筒三维等效弹性模量的理论估算方法, 应用该方法计算了玻璃-碳纤维混杂缠绕筒的三维等效弹性模量。计及混杂效应的影响, 考虑了碳纤维体积分数、 铺层方式、 纤维分散度等因素, 对玻璃-碳纤维混杂缠绕结构, 引入混杂效应系数对该方法进行修正。试验结果表明, 该方法预测的三维等效弹性模量的精度较高。采用该方法可将复杂的纤维混杂缠绕结构等效为具有各向异性性质的均质单一材料, 极大降低了应力分析的工作量。     

太阳能光谱选择性吸收涂层研究进展

采用高速研磨搅拌加水掺法,制备出含不同质量分数的纳米SiO2混杂纤维（NSPF）混凝土,通过力学试验测得立方体抗压强度、劈裂抗拉强度、变形性能及冲击韧性。通过与钢纤维／聚丙烯二元混杂纤维（SPF）混凝土进行比较,NSPF混凝土的立方体抗压强度、劈裂抗拉强度、疲劳次数、弹性模量、初裂抗冲击次数和破坏抗冲击次数分别提高10...     

纤维对开裂后混凝土渗透性及裂缝恢复的影响

通过劈裂试验和渗透试验,研究了结构型钢纤维、聚丙烯粗纤维和聚丙烯细纤维对开裂后混凝土的裂缝恢复率、劈裂韧性和渗透系数的影响。研究结果表明:钢纤维和聚丙烯粗纤维的掺入可限制裂缝扩展,使混凝土由脆性破坏转为韧性破坏,提高开裂混凝土在卸载后裂缝的恢复作用,显著减小开裂后混凝土的渗透系数。钢纤维掺量越高,裂缝恢复和渗透性降低越明显,钢纤维掺量由25kg/m~3增加至55kg/m3时,渗透系数减小了87%。钢纤维和聚丙烯粗纤维的掺入具有较好的正混杂效应,当裂缝宽度为150μm时卸载,单掺25kg/m~3钢纤维和4kg/m~3聚丙烯粗纤维与单掺35kg/m~3钢纤维相比,渗透系数减小了60%。而聚丙烯细纤维对开裂混凝土的裂缝恢复和渗透性影响较小。     

钢纤维对玄武岩纤维编织网增强混凝土板双向弯曲性能的影响

为了研究钢纤维对玄武岩纤维网格布增强混凝土方板双向受弯性能的影响,借鉴欧洲EFNARC标准,利用四边简支方板试验,分别对素混凝土方板、玄武岩纤维网格布增强混凝土方板、钢纤维增强混凝土方板及钢纤维与玄武岩纤维网格布混杂增强混凝土方板的弯曲性能进行研究,同时与传统钢筋网混凝土方板的弯曲性能进行对比,分析了网格布对混凝土方板的双向增强效果,探讨了钢纤维与玄武岩纤维网格布混杂使用代替传统钢筋网的可行性。结果表明:玄武岩纤维网格布可以改善方板的内力重分布,显著提高其承载力,但是破坏时脆性特征明显;钢纤维与玄武岩纤维网格布混杂使用表现出显著的正混杂效应,方板的韧性明显提高;在正常使用极限状态下,30 kg/m3的钢纤维与玄武岩纤维网格布混杂方板的弯曲性能高于传统钢筋网混凝土方板,说明钢纤维与玄武岩纤维编织网混杂使用可以代替传统钢筋网。      

Comparative impact behavior of four long carbon fiber reinforced concretes

The addition of long carbon fibers (fibers more than 10 mm in length) to traditional reinforced concrete is proposed as a method to improve the impact spalling resistance of concrete. A series of experimental tests were conducted to compare the impact resistance of plain concrete (PC), steel reinforced concrete, and four different types of long carbon fiber reinforced concrete (LCFRC) panels. The plain and conventional steel reinforced concrete panels served as control specimens. Of the four types of long carbon fibers tested in this study, the first fiber type consisted of an epoxy-impregnated, bidirectional weave (Type A), while the remaining types consisted of fiber tow with three different variations of a polypropylene support system (Type B). To determine the properties and performance of the LCFRC, experimental testing included a drop weight impact test of the panels as well as a standard ASTM test method for flexural performance of fiber-reinforced concrete. The results from each test in terms of impact energy, time histories of impact load and deflection, strain energy, failure crack pattern, and flexural properties were then compared to one another. This comparison indicated that adding long carbon fibers to concrete increases the post-cracking behavior of the concrete and decreases fragmentation during an impact test. Of the four fibers tested, Fiber Type B3 exhibited the highest performance, absorbing more energy during impact. This result is most likely related to the unique shape of this type of fiber in comparison to the others, which allowed more extensive wetting of the fiber with cement paste and thus improved bond to the cementitious matrix.     

Flexural behavior of reinforced concrete (RC) beams retrofitted with hybrid fiber reinforced polymers (FRPs) under sustaining loads

This paper reports experimental studies of reinforced concrete (RC) beams retrofitted with new hybrid fiber reinforced polymer (FRP) system consisting carbon FRP (CFRP) and glass FRP (GFRP). The objective of this study is to examine effect of hybrid FRPs on structural behavior of retrofitted RC beams and to investigate if different sequences of CFRP and GFRP sheets of the hybrid FRPs have influences on improvement of strengthening RC beams. Toward that goal, 14 RC beams are fabricated and retrofitted with hybrid FRPs having different combinations of CFRP and GFRP sheets. The beams are loaded with different magnitudes prior to retrofitting in order to investigate the effect of initial loading on the flexural behavior of the retrofitted beam. The main test variables are sequences of attaching hybrid FRP layers and magnitudes of preloads. Under loaded condition, beams are retrofitted with two or three layers of hybrid FRPs, then the load increases until the beams reach failure. Test results conclude that strengthening effects of hybrid FRPs on ductility and stiffness of RC beams depend on orders of FRP layers.     

纤维对超高性能混凝土残余强度及高温爆裂性能的影响

采用普通原材料制备56 d龄期抗压强度为140~160 MPa的空白组超高性能混凝土、钢纤维超高性能混凝土及混杂纤维超高性能混凝土,测定其遭受高温作用后的残余抗压强度和劈裂抗拉强度,并对100%含湿量的混凝土试块进行高温爆裂试验。此外,测定大小2种加热速率对超高性能混凝土高温爆裂行为的影响。结果表明:所配制混凝土的残余抗压强度均随着目标温度的升高呈现先增大再降低的趋势,800℃高温后的残余抗压强度约为常温强度的30%。钢纤维与混杂纤维混凝土的残余劈裂抗拉强度亦呈现先升高再降低的趋势,800℃高温后的残余劈裂抗拉强度分别为常温强度的15.1%和35.4%。空白组混凝土的残余劈裂抗拉强度随着目标温度的升高而单调下降,800℃高温后的强度值约为常温强度的20.3%。7.5℃/min加热速率下,100%含湿量的3种混凝土试块均发生了严重高温爆裂,单掺钢纤维可以改善超高性能混凝土的高温爆裂,但不能避免爆裂的发生,而混杂纤维对超高性能混凝土高温爆裂的改善效果并未显著优于钢纤维。2.5℃/min加热速率下,混杂纤维可避免部分超高性能混凝土试块发生爆裂。      

碳纤维单丝带对酚醛树脂基复合材料力学性能的增强作用

将连续碳纤维束用空气梳分散成单丝状的长带, 经60 %硝酸进行表面氧化处理后用作酚醛树脂复合材料的增强材料。用红外光谱、扫描电镜等表征复合材料的微观结构, 通过力学性能测定发现, 与连续的碳纤维束增强相比, 单丝带增强复合材料的弯曲强度提高了1 倍, 层间剪切强度( ILSS) 提高了2 倍, 但冲击强度有所降低。结果表明, 碳纤维经过表面氧化和丝束分散的处理后, 能有效地提高其与复合材料中树脂基体的结合性能。      

钢管钢纤维高强混凝土抗冲击压缩性能的试验研究与数值模拟

遮弹层的建成及优化对防护工程的发展尤为重要。钢管钢纤维高强混凝土蜂窝遮弹层是一种具有高强抗力的新型遮弹层,文章对其组成构件钢管钢纤维高强混凝土进行霍普金森压杆(SHPB)动态力学性能试验,并借助动力有限元分析软件LSDYNA进行数值模拟。冲击压缩试验中,试件的钢纤维掺量分别为0%、0.5%、1.0%、1.5%,钢管壁厚分别为2mm、3mm。结果表明钢管钢纤维高强混凝土具有应变率强化效应,应变率越高,试件的动态抗压强度越大。当气压为1.0 MPa时,壁厚3mm、钢纤维掺量1.5%的试件强度达258.3 MPa。与钢纤维高强混凝土相比,钢管钢纤维高强混凝土的抗冲击压缩性能更好,动态抗压强度最大增幅达35.4%,且具备承受多次冲击压缩作用的能力。数值模拟与试验结果吻合度高,表明数值模拟方法具有可行性。     

混杂比对碳/芳纶纤维混杂纬编双轴向多层衬纱织物增强复合材料力学性能的影响

利用层内混杂的方式制备碳/芳纶纤维混杂纬编双轴向多层衬纱织物,通过对材料进行拉伸、三点弯曲等实验研究该织物增强复合材料的力学性能及混杂比对其力学性能的影响。结果表明,按照一定的混杂比加入芳纶纤维后复合材料的拉伸性能提高,表现出积极的混杂效应。由于延伸性好的芳纶纤维的加入,使复合材料的拉伸断裂伸长率明显提高,材料破坏模式出现了完全脆性断裂模式(C12材料破坏形式)和“扫帚”形纤维断裂模式(C8A4,C6A6材料破坏形式)。此外,按照一定的混杂比加入芳纶纤维也有效改善了碳纤维增强复合材料的破坏韧性,碳/芳纶纤维混杂MBWK织物增强复合材料的弯曲强度和弯曲模量随混杂比的提高而呈下降趋势,当复合材料中芳纶含量从42%(体积分数,下同)(C6A6)到59.2%(C4A8)的变化过程中,弯曲强度和弯曲模量的降低率较高。0°试样在混杂比为59.2%(C4A8)时,弯曲挠度最大,达到7.49 mm,远高于纯芳纶纤维或纯碳纤维增强的复合材料。所有90°混杂复合材料试样的弯曲挠度均高于纯芳纶纤维或纯碳纤维增强的复合材料,表现出积极的混杂效应。     

Fiber synergy in Hybrid Fiber Reinforced Concrete (HyFRC) in flexure and direct shear

In most cases, fiber reinforced concrete (FRC) contains only one type of fiber. The use of two or more types of fibers in a suitable combination has the potential to improve the mechanical properties of concrete, and result in performance synergy. This combining of fibers, often called hybridization, is investigated in this paper under flexure and direct shear. Along with a reference plain concrete mix, several single-fiber reinforced concrete mixes and two-fiber reinforced hybrid composite mixes were cast using diverse fiber combinations. Two types of macro-steel fibers and a micro-cellulose fiber were examined. Flexural and direct shear tests were performed and the results were analyzed to identify synergy, if any, associated with various fiber combinations. The paper highlights the influence of load configuration on fiber synergy.     

Performance of reinforced concrete beams strengthened by hybrid FRP laminates

In the last two decades, the use of advanced composite materials such as Fiber Reinforced Polymers (FRP) in strengthening reinforced concrete (RC) structural elements has been increasing. Research and design guidelines concluded that externally bonded FRP could increase the capacity of RC elements efficiently. However, the linear stress–strain characteristics of FRP up to failure and lack of yield plateau have a negative impact on the overall ductility of the strengthened RC elements. Use of hybrid FRP laminates, which consist of a combination of either carbon and glass fibers, or glass and aramid fibers, changes the behaviour of the material to a non-linear behaviour. This paper aims to study the performance of reinforced concrete beams strengthened by hybrid FRP laminates.

This paper presents an experimental program conducted to study the behaviour of RC beams strengthened with hybrid fiber reinforced polymer (HFRP) laminates. The program consists of a total of twelve T-beams with overall dimensions equal to 460 × 300 × 3250 mm. The beams were tested under cyclic loading up to failure to examine its flexural behaviour. Different reinforcement ratios, fiber directions, locations and combinations of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) laminates were attached to the beams to determine the best strengthening scheme. Different percentages of steel reinforcement were also used. An analytical model based on the stress–strain characteristics of concrete, steel and FRP was adopted. Recommendations and design guidelines of RC beams strengthened by FRP and HFRP laminates are introduced.