Flexural Strength and Behavior of Polypropylene Fiber Reinforced Concrete Beams

The strength and deformation characteristics of polypropylene fiber reinforced concrete ( PFRC) beams were investigated by four-point bending procedures in this paper. Two kinds of polypropylene fibers with different fiber contents (0.2% , 0.5% , 1.0% and 1.5% ) by volume were used in, the beam, which measured 100 × 100 mm with a span of 300 mm. It was found that the strength of the reinforced concrete beams was significantly decreased, whereas the flexural toughness was improved, compared to those unreinforced concrete beams. Geometry properties and volume contents of polypropylene fiber were considered to be important factors for improving the flexural toughness. Moreover, the composite mechanism between polypropylene fiber and concrete was analyzed and discussed.

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.

Mechanical Properties of Polypropylene Fiber Reinforced Concrete under Elevated Temperature

Apart from many advantages,High Strength Concrete(HSC)has disadvantages in terms of brittleness and poor resistance to fire.Various studies suggest that when polypropylene(PP)fibers are uniformly distributed within concrete,they play an active role in improving spalling resistance of concrete when exposed to elevated temperature while having no adverse effect on its mechanical properties.Therefore,there is a necessity to quantify the effect of the addition of polypropylene fibers in terms of the fiber dosage,the strength of the concrete,and the residual mechanical properties of fiber-reinforced concrete under exposure to high temperature from fire.The study was carried out on three water/cement(w/c)ratios(0.47,0.36&0.20)using granite aggregate for determining short term mechanical properties of Polypropylene fiber reinforced concrete in comparison to control mix.The experimental program includes 100×200 mm&150 x 300 mm cylinders with fiber volume of 0.5%,that were subjected to temperatures exposures of 400°C and 600°C for durations of 1 hour.From the results,it was observed that no significant enhancement in mechanical properties such as modulus of elasticity,Poisson’s ratio,split tensile strength,flexural strength,and compressive strength was observed at room temperature and at elevated temperatures.

Experimental study on behaviors of polypropylene fibrous concrete beams

Synthetic fibers made from nylon or polypropylene have gained application when loose and woven into geo textile form although no information on the matrix’s mechanical performance is obtained so that more understanding of their structural contribution to resist cracking can be determined. This paper presents the results of an experimental investigation to determine the performance characteristics of concrete reinforced with a polypropylene structural fiber. In this investigation “Fiber mesh” brand of fibers manufactured by SL Concrete System, Tennessee, USA and marketed by M/S Millennium Building System, Inc., Ban-galore, India are used. The lengths of the fibers used were 24 mm. Fiber dosages used were 0.9, 1.8, 2.7 kg/m3. A total of three mixtures, one for each fiber dosage were made. A standard slump cone test was conducted on the fresh concrete mix with and without fibers to determine the workability of the mix. The test program included the evaluation of hardened concrete properties such as compressive, split tensile, modulus of rupture and flexural strengths. The increase in compressive strength is about 36.25%, 26.20%, and 23.75% respectively that of plain concrete. This increase in strength was directly proportional to amount of fibers present in the mix. The increase in flexural strength for Mixes I^III is about 21%, 16.6%, and 23% respectively that of plain concrete specimens. An experimental investigation was also made to study the behaviors of reinforced fibers concrete beams (with longitudinal reinforcements) under two-point loading. The deflection and crack patterns were also studied. The improvements in strength and ductility characteristics were discussed.

Performance Evaluation of One-Way Concrete Slabs Reinforced with New Developed GFRP Bars

The incorporation of fiber-reinforced-polymer (FRP) bars in construction as a replacement to steel bars provides a superior material which is capable to overcome corrosion problems. However, serviceability requirements are important issues to be considered in the design of concrete elements reinforced with glass-FRP (GFRP) bars which are known to have larger deflections and wider crack widths as well as weaker bond compared with steel reinforced concrete. As a solution to this problem, square GFRP bars are proposed. This paper presents the results of an experimental investigation that was performed, in which newly developed square and circular GFRP bars were fabricated in the lab. Also, the GFRP bars were tested and used to reinforce concrete slabs. A total of nine full-scale GFRP-reinforced concrete (RC) one-way slabs were constructed, tested and analyzed, considering the most influencing parameters such as the cross sectional shape of GFRP bars, reinforcement ratio, the concrete characteristics strength, and adding polypropylene fibers to the concrete mixture. The test results were showed that, the tested slabs with GFRP square bars improved the deflection and cracking behavior as well as the ultimate load.

多尺度聚丙烯纤维混凝土弯曲疲劳寿命试验及数值模拟

为研究多尺度聚丙烯纤维混凝土的弯曲疲劳性能,开展基准混凝土、聚丙烯粗纤维混凝土及多尺度聚丙烯纤维混凝土的静载试验及不同应力水平(0.75、0.80、0.85)下的弯曲疲劳试验,建立弯曲疲劳寿命方程,并结合ABAQUS与FE-SAFE软件建立纤维混凝土梁的三点弯曲疲劳有限元模型。结果表明:聚丙烯纤维的掺入,尤其是多尺度聚丙烯纤维混掺显著增强了混凝土基体的抗折、抗疲劳性能。双对数lgS-lgN疲劳方程能够较好地描述多尺度聚丙烯纤维混凝土的应力水平与疲劳寿命的相关性,使用lgS-lgN疲劳方程计算得到200万次循环荷载作用下多尺度聚丙烯纤维混凝土的疲劳强度最高,为3.91 MPa。三组试件疲劳寿命的数值模型预测值均介于实测疲劳寿命的最大值与最小值之间,并接近于疲劳寿命平均值,该模型为多尺度聚丙烯纤维混凝土的疲劳寿命预测提供了理论依据。

聚丙烯纤维增强陶粒混凝土基本力学性能试验研究

为改善陶粒混凝土的强度和脆性,本研究将聚丙烯纤维加入陶粒混凝土,共制备了180个聚丙烯纤维增强陶粒混凝土试件,并进行了立方体抗压试验、劈裂抗拉试验、轴心抗压试验和弹性模量试验。结果表明,聚丙烯纤维能有效提升陶粒混凝土的劈裂抗拉强度和拉压比,对抗压强度和弹性模量的影响相对较小。基于试验结果,本研究提出了聚丙烯纤维增强陶粒混凝土的劈裂抗拉强度与立方体抗压强度、轴心抗压强度与立方体抗压强度的换算关系模型以及弹性模量的数值模型。

高低温循环作用下纤维增强面板混凝土力学性能研究

防止抽水蓄能电站堆石坝面板混凝土的开裂是电站长期安全运行的重要保障,在电站运行过程中,温差循环对面板混凝土耐久性的影响通常容易被忽视。在面板混凝土中掺入聚丙烯纤维,采用环境试验箱模拟5~85℃高低温循环作用,研究该高低温循环作用对纤维增强面板混凝土力学性能的影响。结果表明:450次高低温循环作用后,普通混凝土和聚丙烯纤维增强混凝土抗压强度较90次高低温循环时分别下降了29.1%、26.3%,极限拉伸应力分别下降了43.1%、32.5%;聚丙烯纤维的掺入可以明显降低混凝土的力学性能损失,且对混凝土拉伸性能的改善程度是抗压强度的5倍左右;聚丙烯纤维在抵抗大温差循环作用下混凝土的拉伸破坏中起到了良好的阻裂和桥架作用,纤维增强混凝土表现为延性破坏特征。

The damage evolution behavior of polypropylene fiber reinforced concrete subjected to sulfate attack based on acoustic emission

To study the damage evolution behavior of polypropylene fiber reinforced concrete(PFRC)subjected to sulfate attack,a uniaxial compression test was carried out based on acoustic emission(AE).The effect of sulfate attack relative to time and fiber hybridization were analyzed and the compression damage factor was calculated using a mathematical model.The changes to AE ringing counts during the compression could be divided into compaction,elastic,and AE signal hyperactivity stages.In the initial stage of sulfate attack,the concrete micropores and microcracks were compacted gradually under external load and a corrosion products filling effect,and this corresponded with detection of few AE signals and with concrete compression strength enhancement.With increasing sulfate attack time,AE activity decreased.The cumulative AE ringing counts of PFRC at all corrosion ages were much higher than those for plain concrete.PFRC could still produce AE signals after peak load due to drawing effect of polypropylene fiber.After 150 d of sulfate attack,the cumulative AE ringing counts of plain concrete went down by about an order of magnitude,while that for PFRC remained at a high level.The initial damage factor of hybrid PFRC was-0.042 and-0.056 respectively after 150 d of corrosion,indicating that the advantage of hybrid polypropylene fiber was more obvious than plain concrete and single-doped PFRC.Based on a deterioration equation,the corrosion resistance coefficient of hybrid PFRC would be less than 0.75 after 42 drying-wetting sulfate attack cycles,which was 40%longer than that of plain concrete.

玄武岩-聚丙烯纤维混凝土孔隙结构分形维数及力学性能研究

本文基于试验探讨了玄武岩-聚丙烯纤维对混凝土抗压强度和劈裂抗拉强度的影响,并利用光学方法的分形模型计算混凝土孔隙结构的分形维数。试验结果表明:混杂纤维能够提高混凝土的抗压强度和劈裂抗拉强度,当玄武岩纤维(BF)和聚丙烯纤维(PF)含量各为0.05%时,混杂纤维的协同效应最强,抗压强度和劈裂抗拉强度的最大增量分别为5.97%和8.46%,然而当纤维含量过高时,混杂纤维会对试件力学性能产生不利影响。玄武岩-聚丙烯纤维增强混凝土(BPFRC)的孔隙结构表现出明显的分形特征,其分形维数在2.297~2.482范围之间。分形维数与孔隙率和间距系数具有很强的相关性,随着孔隙率的增加而显著降低,随着间距系数的增加而增加。分形维数还与抗压强度和劈裂抗拉强度具有正相关关系。因此,孔隙结构的分形维数可用于评价混凝土的微观孔隙结构,也可以反映孔隙结构的复杂性对混凝土宏观力学性能的影响。

聚丙烯纤维混凝土单轴受压疲劳寿命分析

为研究聚丙烯纤维混凝土(PFRC)单轴受压疲劳寿命,考虑聚丙烯纤维的长径比和体积分数两种因素,共制作180个试块,考察聚丙烯纤维混凝土的疲劳破坏形态,阐明变形规律,建立疲劳强度和疲劳寿命方程.研究表明,聚丙烯纤维混凝土疲劳破坏形态分为劈裂破坏、楔形破坏和剪切破坏三种,试块的破坏断面上可以分为疲劳源区、疲劳裂缝稳定扩展区和瞬时断裂区三个区域;在聚丙烯纤维长径比为280、体积分数为0.2%时疲劳性能提升最明显,疲劳强度相较于素混凝土提高33.83%;建立了含纤维特征参数的疲劳方程,可以较好地描述疲劳应力水平、疲劳寿命、失效概率、纤维特征参数之间的关系,为工程中承受重复动荷载的聚丙烯纤维混凝土结构设计及分析提供相应的依据.

聚丙烯纤维混凝土纤维增强作用机理研究

为分析混凝土添加聚丙烯纤维后的应用效果,以水泥、粉煤灰等为材料,掺杂0.05%、0.10%、0.15%添加量的网状聚丙烯纤维,制备聚丙烯纤维混凝土试件。试验结果表明,添加聚丙烯纤维后混凝土的抗压、抗折、抗剪强度均得到不同程度的提升;添加0.10%纤维含量的试件在收缩时的裂缝面积、最大缝宽以及失水速率均低于普通混凝土试件;当试件经过拉伸试验后,添加聚丙烯纤维含量为0.10%的混凝土试件拉伸应力最高;在不同高温环境下,聚丙烯纤维混凝土试件的强度、质量损失率均低于普通混凝土试件,0.10%含量混凝土试件抗渗性最高。综合试验各方面分析可知,0.10%聚丙烯纤维含量的混凝土性能最佳。

钢-聚丙烯混杂纤维混凝土单轴受压疲劳寿命研究

考虑钢纤维体积掺量及长径比、聚丙烯纤维体积掺量及长径比、应力水平5个因素,设计制作36组混凝土试件,通过单轴等幅疲劳受压试验研究钢聚丙烯混杂纤维混凝土(HFRC)的疲劳寿命。基于疲劳试验数据,分析HFRC疲劳受压全过程,探讨纤维特征参数对混凝土试件疲劳寿命的影响规律,建立考虑纤维特征参数的P-S-N疲劳方程。研究结果表明,HFRC在疲劳荷载作用下的破坏形态为剪切破坏,呈现出延性特征;HFRC疲劳变形发展可分为三个阶段:快速增长阶段、稳定发展阶段、疲劳破坏阶段;混杂纤维在提高混凝土疲劳寿命方面优于钢纤维或聚丙烯纤维,体现出正混杂效应;文章提出的疲劳方程与文献中试验结果吻合较好,能够真实地预测HFRC的疲劳寿命。研究成果可为今后混杂纤维混凝土结构抗疲劳设计提供参考。

多尺度聚丙烯纤维混凝土二次衬砌受力特性研究

运营隧道出现开裂、渗漏水、腐蚀等严重病害时,对衬砌病害的治理不仅要考虑支护结构的受力状况,还需考虑支护材料的性能。基于某病害隧道二次衬砌置换项目,开展了多尺度聚丙烯纤维混凝土(Multi-scale Polypropylene Fiber Reinforced Concrete,MPFRC)的二次衬砌现场浇筑试验,对衬砌强度、隧道表观、初期支护与二次衬砌接触压力、混凝土应变等进行长期观测与数据采集,研究了纤维混凝土二次衬砌结构的受力特性。结果表明:纤维对混凝土的强度提升明显,抗压、劈裂抗拉和抗折强度分别增长了7.51%、11.45%和26.95%;普通混凝土段与纤维混凝土段初期支护与二次衬砌最大接触压力均在拱脚,分别为282.63 kPa和231.83 kPa;二次衬砌纤维混凝土的应变相比于普通混凝土要小约45.45%,其应变-时间曲线相对平缓、数值更加稳定;MPFRC提高了衬砌强度的安全性,研究成果可为类似工程的病害预防与治理提供参考。

抗裂材料对面板混凝土性能影响试验研究

在常态面板混凝土中分别掺入纤维素纤维、聚丙烯纤维及增强密实(抗裂)剂3种抗裂材料,形成抗裂面板混凝土,对其力学性能、耐久性能、干缩性能以及早期抗裂性能开展试验研究,分析抗裂材料对面板混凝土性能的影响规律。结果表明:3种抗裂材料对混凝土的拉伸、抗渗、抗冻及早期抗裂性能有不同程度地提升作用,可明显减少和抑制混凝土的干缩变形;而对混凝土各龄期抗压强度均无显著影响,对混凝土弹性模量有一定降低作用。纤维素纤维对混凝土的极限拉伸值、轴拉强度、干缩变形和混凝土早期抗裂性能的改善最优,而增强密实(抗裂)剂对混凝土抗渗性能的改善最优。研究结论可为面板混凝土配合比设计提供参考。

钢-聚丙烯混杂纤维超高性能混凝土受压细观数值模拟

为深入研究钢-聚丙烯混杂纤维超高性能混凝土(hybrid fiber reinforced ultra-high performance concrete,HFR-UHPC)受压力学性能及纤维增强机理,本文利用ABAQUS软件建立了HFR-UHPC三维细观数值模型,对其轴心受压过程进行了数值模拟。通过对比轴心受压试验结果,验证了模型的合理性。在此基础上,拓展分析纤维掺量、长径比等参数对超高性能混凝土(ultra-high performance concrete,UHPC)受压特性的影响,进一步分析压力作用下纤维增强机理。结果表明:随着钢纤维体积掺量增加,超高性能混凝土损伤发展变缓,单轴受压峰值强度略有提高,峰后延性明显增加;钢纤维长径比对超高性能混凝土受压应力-应变曲线的影响较小,但是更长的纤维更好地发挥了阻裂作用;在超高性能混凝土单轴受压过程中,钢纤维在峰值点前主要发挥骨架作用,在峰值点后主要发挥阻裂作用。

聚丙烯纤维与纤维素纤维混凝土的防裂抗渗性能

渠道工程施工过程中衬砌混凝土容易出现开裂,导致渗水问题。渗入水分对渠道结构产生影响,并对工程耐久性带来严重负面影响,在混凝土中掺入纤维能够阻止微小裂缝的生成和发展。由此出发,设计对比试验,分析聚丙烯纤维混凝土、纤维素纤维混凝土的纤维掺量对抗渗性能和抗裂性能的影响,并探究纤维混凝土中显微结构改良抗渗性能、抗裂性能的机制,获取适宜纤维掺量。试验结果表明,掺入纤维素纤维、聚丙烯纤维后,混凝土抗渗性能和抗裂性能均有所改善,其中纤维素纤维混凝土的抗渗性能和抗裂性能改良效果均更加明显。

纤维类型和掺量对混凝土抗冲击性能的影响研究

通过自制落球试验装置,进行了端勾型、微丝型、铣削型3种不同尺寸钢纤维和聚丙烯纤维混凝土抗冲击性能试验研究。结果表明,在相同掺量条件下,微丝型钢纤维对混凝土抗冲击性能提升效果最佳,铣削型提升效果最差。在一定掺量范围内微丝型纤维掺量和混凝土抗冲击性能成正相关。掺入聚丙烯纤维降低了钢纤维混凝土抗冲击性能,提高了混凝土的初裂后延性。微丝型钢纤维和端勾型钢纤维产生了正向混杂效应,两种尺寸不同的钢纤维对混凝土的抗冲击性能提升得到了互补。

利用再生轮胎纤维增强混凝土抗剥落特性的统计与分析

废旧轮胎具有很强的抗热、抗生物、抗机械性,自然条件下很难降解。中国每年产生的废旧轮胎数量以9%左右的速度递增,产量巨大,通过掩埋及堆放的处理方式会造成极大的环境污染和资源浪费,若能对废旧轮胎重新加以利用,也能变废为宝。经研究人员反复实验论证,在混凝土中加入聚丙烯纤维(PPF)能有效缓解和防止混凝土剥落,但就可持续性和经济性而言,从废旧轮胎中提取再生聚合物纤维(RTPF)比消耗资源生产聚丙烯纤维(PPF)更具可持续性,且成本相对较低,但就废旧轮胎纤维的存放及加工、纤维增强混凝土构件的耐久性和强度,以及火灾剥落试验的真实场景建立等方面仍需进一步考虑和完善。

超高性能混凝土和聚丙烯纤维混凝土与素混凝土结合情况的实验研究

为修复梁端寻找一种可替代的材料,以恢复受损梁的抗剪能力,延长受损梁的使用寿命。对超高性能混凝土和聚丙烯纤维混凝土与素混凝土粘结的试件进行斜剪试验和劈裂圆筒试验,获得试件破坏时的最大荷载,并进行数据分析,得出超高性能混凝土在粘结强度、抗拉强度和抗压强度以及经济适用性方面具有优秀的表现。超高性能混凝土在梁端修复甚至结构物的修补上将会是很好的一种选择。