Mechanical Properties of Layered Steel Fiber and Hybrid Fiber Reinforced Concrete

To explore a new structure form of fiber reinforced concrete, namely, the layered steel fiber and layered hybrid fiber reinforced concrete （LSFRC and LHFRC）, the mechanical properties of LSFRC and LHFRC, such as compressive strength, tensile strength, flexural strength, fatigue and durability were focused on. The experimental results show that LSFRC and LHFRC can improve the flexural strength of concrete by 20%-50%. In the aspect of improving the flexural strength of concrete, adulterant rate has more obvious effect than length/diameter ratio. Double logarithmic fatigue equation considered liveability was founded. The impermeability of LHFRC is superior to LSFRC and plain concrete （C）. However, the porosity of LHFRC is lower than LSFRC and C. The shrinkage of LHFRC at every age is obviously lower than C. The antifreeze durability of LHFRC is also better than C.

Mechanical Properties of Layered Hybrid Fiber Reinforced Concrete

To improve the mechanical properties of concrete,Layered Hybrid Fiber Reinforced Concrete (LHFRC) was developed in this paper.Through comparative tests,the effects of layered hybrid fibers on a series of mechanical properties of concrete were discussed.The mechanical properties include compressive strength,tensile strength,flexural strength,compressive stress-strain relationship,flexural toughness and cracking resistance of concrete.The testing results and analysis demonstrate that layered hybrid fibers can significantly improve the flexural strength,toughness and cracking resistance of concrete while the cost of concrete increases slightly.

Bond Behavior between BFRP Bars and Hybrid Fiber Recycled Aggregate Concrete after High Temperature

The aim of this study is to improve the bond performance of basalt fiber reinforced polymer(BFRP)bars and recycled aggregate concrete(RAC)after being exposed to high temperatures.The bond behavior(failure modes,bond strength,bond stress-slip curves)between BFRP bars and hybrid fiber recycled aggregate concrete(HFRAC)after being exposed to temperatures ranging from 20℃up to 500℃was studied by using pull-out tests.The effect of high temperatures on mechanical properties of concrete(compressive strength,splitting tensile strength)and tensile strength of BFRP bars was also investigated.The bond strength decreased as the temperature increased and the drop of bond strength between RAC and BFRP bar was larger than that between HFRAC and BFRP bar.As the temperature rises,the key factor affecting the bond strength was gradually transformed from concrete strength to BFRP bar strength.The relationship between bond stress and slip in the dimensionless bond stress-slip ascending section was established,which was in good agreement with the experimental results.

Flexural Fatigue Behavior of Layered Hybrid Fiber Reinforced Concrete

In order to obtain the fatigue life of layered hybrid fiber reinforced concrete （LHFRC） at different stress levels, flexural fatigue tests were carried out on specimens. The relation between fatigue lives and stress levels was simulated using the two-parameter Weibull distribution. Furthermore, both single- logarithmic and double-logarithmic regressive equations of various reliabilities were derived. It is evident that LHFRC gets the advantage of longer fatigue life over common concrete.

Mechanical and Microstructural Analysis of Waste Ceramic Optimal Concrete Reinforced by Hybrid Fibers Materials: A Comprehensive Study

Combining different types of fibers inside a concrete mixture was revealed to improve the strength properties of cementitious matrices by monitoring crack initiation and propagation.The contribution of hybrid fibers needs to be thoroughly investigated,considering various parameters such as fibers type and content.The present study aims to carry out some mechanical and microstructural characteristics of Waste Ceramic Optimal Concrete(WOC)reinforced by hybrid fibers.Reinforcement materials consist of three dif­ferent fiber types:hook-ended steel fiber(HK),crimped steel fiber(CR)and polyvinyl alcohol(PVA)fibers and the effect of their addition on the waste ceramic composites’mechanical behaviour.Furthermore,a micro­structural analysis was carried out to understand the waste ceramic matrix composition and its bonding to hybrid fibers.Results showed that the ad­dition of hybrid fibers improved the strength characteristics of the ceramic waste composites.For instance,the existence of PVA-CR increased the tensile and flexural strength of the waste ceramic composite by 85.44%and 70.37%,respectively,with respect to the control sample(WOC).As well as hybrid fiber exhibits improved morphological properties as a result of in­creased pore filling with dense and compact structure,as well as increased C-H crystals and denser structure in pastes as a result of the incorporation of hybrid fibers into the concrete mix.The present experimental research shows the choice of using steel fiber with PVA as a reinforcement material.The idea of adding hybrid fiber is to prepare the economic,environmental,and technological concrete.Moreover,it offers a possibility for improving concrete’s durability,which is vital.Finally,it was concluded that steel fiber is more durable,and stiffer and provides adequate first crack strength and ultimate strength.In contrast,the PVA fiber is relatively flexible and improves the post-crack zone’s toughness and strain capacity.

Experimental Investigation on the Mechanical Properties of Natural Fiber Reinforced Concrete

Recently,addition of various natural fibers to high strength concrete has aroused great interest in the field of building materials.This is because natural fibers are much cheaper and locally available,as compare to synthetic fibers.Keeping in view,this current research conducted mainly focuses on the static properties of hybridized(sisal/coir),sisal and coir fiber-reinforced concrete.Two types of natural fibers sisal and coir were used in the experiment with different lengths of 10,20 and 30 mm and various natural fiber concentrations of 0.5%,1.0%,and 1.5%by mass of cement,to investigate the static properties of sisal fiber reinforced concrete(SFRC),coir fiber reinforced concrete(CFRC)and hybrid fiber reinforced concrete(HFRC).The results indicate that HFRC has increased the compressive strength up to 35.98%with the length of 20 mm and with 0.5%concentration,while the CFRC and SFRC with the length of 10 mm and with 1%concentration have increased the compressive strength up to 33.94%and 24.86%,respectively.On another hand,the split tensile strength was increased by HFRC with the length of 20 mm and with 1%concentration,CFRC with the length of 10 mm and with 1.5%concentration,and SFRC with the length of 30 mm and with 1%concentration have increased up to 25.48%,24.56%and 11.80%,respectively,while the HFRC with the length of 20 mm and with 0.5%concentration has increased the compressive strength of concrete but has decreased the split tensile strength up to 2.28%compared to PC.Overall,using the HFRC with the length of 20 mm and with 1%concentration provide the maximum output in terms of split tensile strength.

BFRP筋与超高性能纤维混凝土黏结性能试验研究

为探究玄武岩纤维增强复合材料(BFRP)筋与超高性能纤维混凝土(UHPFRC)之间的黏结性能,通过中心拉拔试验,对BFRP-UHPFRC试件破坏模式、黏结-滑移曲线进行分析,且探讨了筋材直径、单一纤维及钢-PVA混杂纤维对黏结强度的影响。结果表明,试件破坏模式包括BFRP筋拔出破坏与拉断破坏。BFRP筋直径的增大将导致黏结强度降低。随着单一纤维掺量增加,黏结强度呈先增大后减小的趋势。而相较于单一纤维,钢-PVA混杂纤维显著提高了试件的黏结强度,当掺入1%钢纤维和0.5%PVA纤维时,黏结强度最高(25.35 MPa)。此外,通过灰狼算法优化的支持向量回归模型实现对黏结强度的预测,预测值与实际值拟合较好。

高温后混杂纤维混凝土力学性能

通过高温后抗压强度和劈裂抗拉强度试验研究了温度、纤维种类、单掺玄武岩纤维掺量、混掺玄武岩纤维(BF)及纤维素纤维(CF)对混凝土力学性能的影响。结果表明:单掺BF或CF均可提升高温后混凝土的抗压及劈裂抗拉强度,相同体积掺量时单掺BF提升效果优于CF。各温度下,随着BF体积掺量的增加,抗压强度与劈裂抗拉强度增加。试验中,单掺玄武岩纤维最佳体积掺量为0.20%,混凝土抗压强度增加率为13.1%~32.6%,劈裂抗拉强度增加率为28.0%~62.4%。各温度下适量混掺BF和CF可以提高混凝土的抗压强度和劈裂抗拉强度,二者具有正混杂效应,比单掺纤维增强效果好。混掺BF体积掺量为0.15%和CF体积掺量为0.10%的B2C1组试件抗压强度和劈裂抗拉强度最高,与普通混凝土相比,抗压强度增加率为14.8%~36.2%,劈裂抗拉强度增加率为31.6%~75.3%。引入协同效应系数分析了玄武岩纤维与纤维素纤维的正负混杂效应,并建立了高温后纤维混凝土的抗压强度和劈裂抗拉强度计算模型,可用于纤维混凝土结构设计及灾后性能评估。

基于响应面回归模型的纤维混凝土力学性能分析

为研究玄武岩纤维和纤维素纤维掺量对混杂纤维轻骨料高强混凝土抗压强度、抗折强度和劈裂抗拉强度的影响,构建响应面回归模型,对比分析其力学试验实测值和预测值,并结合渴求函数获得混凝土优化配合比.结果表明:此回归模型有效且可信度高,可用于分析试验结果;两种纤维交互作用、水灰比与纤维素纤维交互作用对抗压强度、抗折强度、劈裂抗拉强度影响显著;模型预测最优水灰比为0.30,纤维素纤维掺量为0.90 kg/m3,玄武岩纤维掺量为4.00 kg/m3,强度预测值与试验值间相对误差绝对值均小于5%,该回归模型可为混杂纤维轻骨料高强混凝土的配合比多目标优化提供参考.

混杂网格增强超高性能混凝土双向板的弯曲性能

网格增强超高性能混凝土(ultra-high performance concrete,UHPC)具有轻质、高强、耐久性好等特性,已应用于薄壁结构和工程加固领域,但单一网格很难实现高效的增强增韧效应.为研究混杂网格增强UHPC双向板的抗弯性能,对3个钢丝网格与玻璃纤维网格混杂增强UHPC板、3个钢丝网格与玄武岩纤维网格混杂增强UHPC板、6个单一网格增强UHPC板和1个无网格UHPC对照板进行弯曲试验,研究网格种类、总层数及铺层方式对其破坏形态、承载能力和弯曲韧性的影响.结果表明:与单一钢丝网格板和单一玻璃纤维网格板相比,钢-玻璃纤维网格混杂板开裂后表现更显著的硬化现象,在连续网格与混杂短纤维协同效应下,板呈现多裂缝破坏模式,延性较理想.铺设2层网格时,钢-玻璃纤维网格混杂板的承载能力较单一钢丝网格板提升23.7%,且其在20 mm挠度处的残余承载力较单一玻璃纤维网格板提升28.2%;钢-玄武岩纤维网格混杂板峰前阶段的能量吸收值和20 mm挠度处的残余承载力均优于单一玄武岩纤维网格板.网格总层数为3层时,与单一玄武岩纤维网格板相比,2层钢丝网格与1层玄武岩纤维网格混杂增强板在峰前挠度为2 mm时的能量吸收值提高了21.6%,20 mm挠度处的残余承载力提高了42.6%.钢-玻璃纤维网格混杂板的网格强度利用率最理想,其承载能力、能量吸收值及弯曲韧性指标均高于钢-玄武岩纤维网格混杂板.最后,考虑网格强度有效利用率建立了混杂网格增强UHPC双向板抗弯承载力理论公式,适用性良好.

超高性能混凝土中纤维作用效应研究综述

超高性能混凝土(UHPC)是一种具有超高强度、高耐久性的新型水泥基复合材料,其应用仍受到包括造价高、韧性不足、高温抗爆裂性能差等因素的影响,相关研究表明上述因素均与内掺纤维有关。为进一步促进纤维对UHPC性能的优化,推进UHPC在工程领域中的应用,通过梳理国内外近年来相关研究成果,总结钢纤维形状和长径比、不同纤维类型、纤维混杂和纤维取向分布对UHPC相关性能的影响,结果表明:钢纤维具备优异的力学性能且来源广泛,仍为UHPC中主要使用的纤维,异形钢纤维改善UHPC抗拉、抗弯等性能效果更好,但工作性能会相应地降低,建议钢纤维掺量采用2%~3%;不同类型纤维混掺存在最优组合,非钢纤维掺量普遍不超过0.5%;纤维平行于主拉应力方向分布能够提升纤维桥接作用的有效性,随机分布的纤维有效性降到了30%,对于纤维取向控制方法尚不成熟,需要进一步完善方法实现在非实验室条件下纤维定向分布的实际尺寸。

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.

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。

高温后钢-PVA混杂纤维高性能混凝土与变形钢筋黏结性能试验

为研究高温后钢-聚乙烯醇(polyvinyl alcohols,PVA)混杂纤维高性能混凝土(hybrid fiber high performance concrete,HFHPC)与变形钢筋的黏结性能退化规律,以200、400、600、800℃为目标温度,选取钢纤维体积率、PVA纤维体积率、矿粉掺量为正交试验因素设计并制作25组HFHPC试件,完成了单调荷载下的中心拉拔试验。结果表明:高温后各组HFHPC试件黏结破坏形态均表现为钢筋拔出破坏;试验温度范围内,对HFHPC试件黏结强度的影响程度均为:钢纤维体积率最大、矿粉掺量次之、PVA纤维体积率最小;随着温度的升高,HFHPC试件黏结强度逐渐下降,且在相同温度条件下,HFHPC试件黏结强度和峰值滑移相比于未掺纤维的混凝土试件均有所提升,其中,200℃时HFHPC试件的黏结强度提升最为显著,分别提升了33.69%、35.76%、37.54%和46.03%;混杂纤维能显著提高高温后高性能混凝土与钢筋的峰值界面能,明显改善黏结延性和耗能能力;提出的考虑温度作用后的混杂纤维混凝土与钢筋黏结-滑移模型与试验实测结果吻合较好,可为火灾后混杂纤维高性能混凝土结构损伤评估及加固方案提供参考。

PVA-钢纤维自密实混凝土早期干燥收缩研究

研究了钢纤维、PVA纤维、PVA-钢混杂纤维对自密实混凝土早期干燥收缩的影响。结果表明:纤维的掺入不会改变自密实混凝土干燥收缩的发展趋势;单掺钢纤维或PVA纤维均能抑制自密实混凝土的干燥收缩,其中,PVA纤维较钢纤维对自密实混凝土干燥收缩的抑制效果更好,但纤维体积掺量过高则会导致纤维的抑制效果减弱;PVA-钢混杂纤维对自密实混凝土干燥收缩的改善效果优于单一纤维,其中,0.3%体积掺量的钢纤维与0.06%体积掺量的PVA纤维混杂对自密实混凝土干燥收缩的改善效果相对最好,表现出显著的混杂效应。

混杂纤维混凝土的力学性能及微观分析

通过L9(33)正交试验研究了玄武岩纤维(BF)、聚丙烯纤维(PPF)和粉煤灰的掺量对混凝土力学性能的影响,并进行了微观分析。结果表明:混掺适量PPF和BF,同时掺入适量粉煤灰可有效改善混杂纤维混凝土的力学性能及微观结构;综合考虑,推荐PPF、BF、粉煤灰的掺量分别为0.10%、0.10%、20%。

混杂纤维增强超高性能混凝土的高温性能试验研究

本文对混杂钢纤维(SF)-聚丙烯纤维(PPF)-硫酸钙晶须(CSW)增强超高性能混凝土(UHPC)进行高温试验(200~800℃),研究了混杂纤维增强UHPC高温前后的物理力学性能,并借助光学显微镜和扫描电子显微镜进行微观形貌观测,探讨了基体裂缝发展过程中多尺度纤维的作用机理。结果表明:随着温度升高,UHPC的质量损失率呈增大趋势,而超声波速则呈下降趋势,同时混杂SF-PPF-CSW对基体超声波速的降低有一定减缓作用;当温度小于400℃时,混杂SF-PPF-CSW增强UHPC的弯曲强度变化微弱(<5%),超过400℃后则迅速下降,在800℃下仅为初始强度的19.2%~24.7%;残余抗压强度随温度升高呈先上升后下降趋势,在400℃时达到峰值,较常温时提升了48.9%~62.0%;各温度下,掺加SF-PPF-CSW的UHPC物理力学性能均得到了有效提升,其中混杂1.7%(体积分数)SF、0.3%(体积分数)PPF、1.0%(体积分数)CSW对UHPC力学性能提升效果最佳。

VAE乳胶粉/碳纤维复合改性混凝土的力学性能

为探究醋酸乙烯酯-乙烯共聚物(VAE)乳胶粉和碳纤维对混凝土力学性能的混杂改性效果及机理,制备了1种VAE乳胶粉改性混凝土(VAEMC)、3种碳纤维改性混凝土(CFMC)和3种VAE乳胶粉/碳纤维复合改性混凝土(VAE/CFMC),测试了改性混凝土的电阻率和力学性能,并进行了扫描电镜试验和压汞试验.结果表明:VAE乳胶粉可以促进碳纤维的分散,VAE/CFMC的电阻率小于CFMC;与CFMC相比,VAE/CFMC的力学性能更佳;VAE乳胶粉与碳纤维具有“正混杂效应”,复掺VAE乳胶粉与碳纤维时,混凝土的力学性能呈现出“1+1>2”的复合增强效果;VAE乳胶粉可以优化CFMC的孔隙结构,细化其孔径,增强碳纤维/混凝土基体界面的物理结合,使碳纤维的破坏形式由拉滑破坏转变为拉断破坏.

非晶合金纤维和钢纤维单/混掺增强混凝土开裂及断裂性能研究

为探索纤维混凝土抗裂性能,本文研究了不同类型纤维(平直型钢纤维、平直型非晶合金纤维、钢纤维+非晶合金纤维)和不同纤维体积掺量(1.0%,1.5%和2.0%)混凝土的早期开裂性能和硬化后的断裂性能。首先通过平板法试验并借助数字图像对混凝土的早期裂缝特征进行量化分析,评估了纤维混凝土的早期开裂性能;再通过带切口棱柱体试件的三点弯曲试验,基于双K断裂参数,分析并评估了混凝土硬化后的断裂性能。结果表明,钢纤维单掺和混掺纤维混凝土的早期抗裂性能最好;纤维掺量由1.0%增加至2.0%时,钢纤维、合金纤维和混掺纤维混凝土失稳韧度分别增加了58.9%、44.3%和55.5%,且掺量为2.0%的混掺混凝土断裂能是普通混凝土的11.8倍。钢纤维和非晶合金纤维可在混凝土硬化过程的不同时期发挥协同作用,两种纤维混掺不仅能阻止混凝土早期的塑性开裂,还可有效控制硬化后受拉裂缝的形成和发展,达到分阶段抗裂的目的。综合考虑混凝土的早期开裂性能、硬化后受拉性能以及断裂性能,体积掺量相同情况下混掺纤维混凝土整体性能更优。

混杂纤维高强轻骨料混凝土单轴受压试验研究

为了改善高强轻骨料混凝土(HSLC)的脆性破坏特征,采用钢纤维(SF)和聚丙烯纤维(PF)对HSLC进行增强,通过单轴受压试验研究两种纤维对HSLC单轴受压性能的影响。结果表明:SF和PF的体积掺量分别为2.0%和0.2%时具有最优的混杂效应,应力-应变曲线拐点处应力和收敛点处应变较单掺SF时分别提高了10.0%和56.5%,较单掺PF时分别提高了99.1%和150%;混杂纤维使HSLC的峰值应力、峰值应变和弹性模量最高分别提升了19.0%、1.20%和16.9%。最后,基于试验数据,提出了考虑两种纤维混杂效应的峰值应力、峰值应变和弹性模量的计算公式,建立了双参数混杂纤维增强HSLC的单轴受压本构模型,并且其与试验曲线吻合较好。该研究结果可为纤维增强HSLC的结构设计提供理论参考。