钢纤维类型和分布形式对混凝土抗压性能的影响

以几种不同类型钢纤维增强混凝土的抗压性能试验研究为基础,讨论了钢纤维掺量、分布形式以及钢纤维类型对混凝土抗压性能的影响.试验结果表明,随钢纤维掺量的提高, 钢纤维增强混凝土的抗压性能有不同程度的提高;因钢纤维类型不同,对混凝土的增强效果各异,其中弓形钢纤维对抗压强度的增强效果较好,哑铃形钢纤维对延性比提高率的影响较大;钢纤维分布形式的不同对混凝土抗压强度也有一定影响.     

钢纤维类型对混凝土动态力学性能影响试验研究

利用SHPB试验系统对4种不同类型钢纤维混凝土进行了动态力学性能测试,探讨了钢纤维类型和各正交因素对钢纤维混凝土动态抗压强度的影响,并进行了最优化分析。结果表明,波纹形钢纤维更适合在低、中应变率的冲击压缩情况下使用;弓形、压棱形钢纤维的增强效果在高应变率时更为显著;平直形钢纤维的增强效果随应变率提高而减弱。4种钢纤维中,弓形钢纤维对混凝土破坏形态的改善效果最好。     

钢纤维对高强混凝土弯曲性能影响的试验研究

选用工程中常用的铣削型、切断弓型、剪切波纹型钢纤维,以不超过2.0%的体积分数掺入高强混凝土中,通过2种尺寸小梁试件的弯曲强度和韧性试验,研究了钢纤维类型及掺量对高强混凝土弯曲强度及变形性能的影响.结果表明:当3种类型钢纤维分别以2.0%的体积分数掺入高强混凝土中时,可使高强混凝土抗裂能力分别提高72%,41%和42%,弯曲极限强度分别提高90%,84%和57%.钢纤维对高强混凝土试件的尺寸效应系数影响显著,试验时应考虑试件尺寸对试验结果的影响.钢纤维高强混凝土弯曲韧度指数及承载力变化系数均随钢纤维体积分数的增大而增大,并大于理想弹塑性材料的相应值.不同类型钢纤维对高强混凝土弯曲强度及弯曲韧性的改善效果不同,可通过改进钢纤维的加工工艺、表面形状等来提高钢纤维对高强混凝土的增强增韧效果.     

不同纤维形状SFRC抗压强度的正交试验研究

选取水胶比、砂率、钢纤维体积产量和钢纤维形状共4个因素分4个水平,通过正交试验方法研究了不同钢纤维形状的钢纤维混凝土（SFRC）静态抗压强度的差异,并进行最优化分析。结果表明,试验范围内,掺量越高越好,水胶比和砂率两种因素均存在最优水平;不同类型的钢纤维对混凝土抗压强度的影响各异,其中以弓形钢纤维的增强效果最好,其次是平直形钢纤维,压棱形和波纹形对抗压强度的提高效果均不太明显。     

钢纤维掺量和类型对混凝土性能的影响

比较了不同形状钢纤维对不同强度等级混凝土力学性能的影响，分析了钢纤维掺量与混凝土强度之间的关系。结果表明，随钢纤维掺量的提高，钢纤维增强混凝土的各项力学性能都有不同程度的提高；纤维类型不同，对混凝土的增强效果各异，其中弓形和哑铃形钢纤维的增强效果优于平直形和波浪形纤维，并以哑铃形钢纤维为最佳。     

不同几何尺寸纤维对混凝土力学性能的影响

选用不同几何尺寸的微细钢纤维、普通钢纤维、碳纤维,研究了它们对混凝土力学性能的影响。结果表明,增强作用按微细钢纤维、普通钢纤维、碳纤维次序递减;增韧作用按普通钢纤维、微细钢纤维、碳纤维次序递减。荷载与挠度曲线表明,碳纤维裂前增强与增韧作用优于微细钢纤维和普通钢纤维。     

哑铃形钢纤维增强超高性能混凝土力学模型研究

为研究异形钢纤维对混凝土的增强增韧作用机理,依据Victor Li提出的裂纹面纤维桥联应力公式,考虑钢纤维在基体中的埋置深度、埋置角度以及纤维与基体界面相互作用,提出了单根纤维拔出模型,通过异形钢纤维混凝土梁正截面平衡关系建立了裂纹面纤维桥联应力与截面力的关系。对哑铃形钢纤维在1%、2%、3%三种体积掺量下混凝土梁的弯曲试验数据进行拟合,得到钢纤维混凝土受拉本构关系,应用到截面非线性分析程序后得到的弯矩—曲率关系与试验结果吻和良好。     

BFRP筋部分增强钢纤维混凝土梁受弯性能研究

以不同钢纤维掺入率（0、0.5%、1%、1.5%）、受压区钢纤维混凝土不同厚度为试验变量,设计了7根玄武岩纤维增强塑料筋（BFRP筋）部分增强钢纤维混凝土梁进行受弯性能试验,研究不同钢纤维体积率以及钢纤维在混凝土中的不同厚度对BFRP筋部分增强钢纤维混凝土梁受弯性能的提升效果。试验结果表明：在受压区掺入钢纤维,其极限承载力约可提高8%～35%,开裂荷载约可提高10%～30%,跨中挠度约可减小25%;同一钢纤维体积率下,部分截面掺加钢纤维的混凝土梁的极限承载力与全截面掺加钢纤维的混凝土梁的极限承载力相近。仅在梁受压区掺入钢纤维,可高效利用BFRP筋与钢纤维的增强增韧作用,进而提高梁的受弯性能。基于修正的钢纤维混凝土受压应力-应变模型和结构设计原理,建立了BFRP筋部分增强钢纤维混凝土梁的受弯承载力计算式,计算结果与试验结果吻合较好。     

钢纤维混凝土增韧效果研究北大核心

利用MTS810材料试验机,对钢纤维含量为0、1.5%、3.0%,长径比为34、65的钢纤维混凝土开展了单轴压缩试验,得到纤维含量和长径比对混凝土材料韧性的影响,试验结果表明:增韧效果随着钢纤维含量的增加而增强,长径比为34的钢纤维混凝土明显比长径比为65的增韧效果要好,混合钢纤维的增韧效果不会优于单一钢纤维混凝土。通过对Carreira和Chu提出的混凝土准静态单轴压缩下的本构模型中的参数β进行修正,使得该本构模型能够很好的描述钢纤维混凝土的应力-应变关系,并分别得到了参数β和韧度R关于纤维含量的具体表达式。     

钢纤维混凝土增韧效果研究

利用MTS810材料试验机,对钢纤维含量为0、1.5%、3.0%,长径比为34、65的钢纤维混凝土开展了单轴压缩试验,得到纤维含量和长径比对混凝土材料韧性的影响,试验结果表明:增韧效果随着钢纤维含量的增加而增强,长径比为34的钢纤维混凝土明显比长径比为65的增韧效果要好,混合钢纤维的增韧效果不会优于单一钢纤维混凝土。通过对Carreira和Chu提出的混凝土准静态单轴压缩下的本构模型中的参数β进行修正,使得该本构模型能够很好的描述钢纤维混凝土的应力-应变关系,并分别得到了参数β和韧度R关于纤维含量的具体表达式。     

钢纤维形状对超高性能纤维混凝土力学性能的影响

钢纤维通常加工成端部扁平(简称"端平")或端部弯起(简称"端弯")形状以增强纤维与混凝土的粘结锚固,不同纤维形状对超高性能纤维混凝土力学性能影响差异有待试验验证。对纤维体积率分别为1%、2%、2.5%和3%,端平或端弯两种钢纤维制成的超高性能纤维混凝土的性能差异进行了试验研究。试验结果表明:纤维体积率为2%时,端平纤维超高性能混凝土的工作和力学性能最佳;体积率在2%～2.5%时,端平钢纤维混凝土的抗弯强度和断裂能都优于端弯纤维混凝土;由于端弯纤维的端部锚固效果好,端弯纤维混凝土梁在超过峰值荷载后的延性好于端平纤维梁。     

钢纤维类型和掺量对高强混凝土力学性能的影响

混凝土加入钢纤维被认为是一种有效增加混凝土韧性,提高力学性能的手段。本文通过掺加不同类型和不同掺量的钢纤维,测试了混凝土的抗压、抗折和劈拉强度,研究了纤维类型和掺量对力学性能的影响。结果表明,混凝土抗压强度随着镀铜微丝型钢纤维掺量的增加而增大,而端钩型、铣削型和熔抽型钢纤维的种类和掺量对混凝土抗压强度的影响并不显著。无论掺加何种类型纤维,纤维的掺入对抗折强度的贡献均大于对抗压强度的贡献。混凝土劈拉强度对纤维的端钩、直径、长度和表面状态等因素敏感,纤维类型对混凝土的劈拉强度影响显著。     

Lateral load response of high performance fiber reinforced concrete beam–column joints

Six beam–column (B–C) joints were constructed according to the existing practice in Jordan and tested under cyclic lateral loading to determine the effect of using high performance steel fiber reinforced concrete (HPFRC) in place of conventional concrete in the joint region. The properties of ultimate strength, ductility, energy dissipation capacity, and joint stiffness of the reference concrete specimens were compared with those containing different amounts of brass-coated (BCSF) or hooked steel fibers (HSF). It was determined that the steel fiber concrete specimens exhibited three times higher load levels, 20 times larger energy dissipation, and two times slower stiffness degradation compared to the reference concrete specimens. Using hooked steel fibers showed a significant increase (three times) in the maximum load carrying capacity and in the initial secant stiffness compared to reference specimens.     

Effect of matrix strength on pullout behavior of steel fiber reinforced very-high strength concrete composites

This paper presents the results of single-fiber pullout tests for deformed and smooth steel fibers embedded in the newly developed very-high strength concrete (VHSC) matrixes. The pullout test program involved four types of steel fibers, eight compressive strengths of VHSC matrixes, and two normal concrete strengths. Test results have shown that pullout behavior of different steel fiber reinforced VHSC composites is influenced by the matrix strength and fiber end condition (smooth, flat end, or hooked). Results reveal that both maximum pull-out load and total pullout energy increases as matrix strength increases for all deformed fibers that did not rupture. The test results also indicated that the increase in total pullout energy is more significant than that in peak load.     

混杂纤维增强钢筋自密实混凝土梁抗剪试验研究

通过对一系列以纤维类型、纤维掺量、配箍率为主要变化参数的混杂纤维自密实混凝土梁斜截面抗剪试验分析,本文研究了在两个对称的集中荷载作用下无箍筋纤维混凝土梁和有箍筋纤维混凝土梁的极限剪力、剪力—加载点位移曲线特性以及破坏形态。结果表明,适量的纤维,尤其是混杂纤维能够显著提高自密实混凝土梁的极限剪力、峰值后承载能力以及韧性,不同纤维共同抗剪时具有明显的正混杂效应。混杂纤维和箍筋的共同作用使按构造配置箍筋的混凝土梁从脆性的剪切破坏转为延性的弯曲破坏。     

Effect of elevated temperature on bond between steel reinforcement and fiber reinforced concrete

The bond behavior between fiber reinforced concrete and 20-mm reinforcing steel rebars was evaluated under elevated temperatures. Fifty modified pullout specimens (100×100×400 mm) were prepared using high strength concrete with basalt aggregate and different volumetric mixtures of three types of fibers, namely brass-coated steel fibers, hooked steel fibers, and high modulus polypropylene fibers, before being cured for 28 days at 40 °C. Specimens, designated for heat-treatment, were then subjected to elevated temperatures, ranging from 350 to 700 °C, whereas unheated (control) ones were left in laboratory air. The overall response of control and heat-damaged specimens, pulled out up to failure, and cracking extent and continuity were described. Standard cubes (100 mm³) were cast, cured, and heat treated under similar conditions, then tested to evaluate compressive and splitting strengths. The results showed marked reductions in residual compressive, splitting and steel–concrete bond under high temperatures with dramatic changes in bond stress–free-end slip trend behavior. Use of fibers minimized the damage in steel–concrete bond under elevated temperatures and hence the reduction in bond strength. Specimens which incorporated hooked steel fibers attained the highest bond resistance against elevated temperatures followed, in sequence, by those prepared with the mixture of hooked and brass-coated steel, the mixture of hooked steel and polypropylene, and brass-coated steel fibers. Statistical models for bond stress versus free-end slip and bond strength versus exposure temperature were developed. These showed excellent agreement with the trend behavior of present experimental data.     

异形钢纤维对超高性能混凝土增强增韧的影响

以钢纤维掺量、类型和分布方式为变量,测试了掺异形钢纤维超高性能混凝土(UHPC)的直接拉伸性能和弯曲韧性,并采用显微镜对这种钢纤维的拔出通道和拔断截面进行了观测.结果表明:异形钢纤维对UHPC具有较好的增强增韧效果,相应试件的直接拉伸强度、断裂能及裂后承载力均大幅提高,且其掺量越大,提高幅度越显著;当异形钢纤维沿拉应力方向有序分布时,与随机分布相比,更有利于UHPC的增强增韧;相比于端钩型钢纤维,在相同掺量下,波纹型钢纤维的增强增韧效果更佳,其拔出通道更加曲折,还存在被拉直的现象,这主要是由于其与基体间存在更强的机械咬合力所致;此外,在拉拔过程中,2种异形钢纤维的断口邻近截面均出现了明显的颈缩.     

钢纤维增强混凝土动态力学性能及HJC本构模型参数标定

探讨了不同体积掺量钢纤维和镀铜钢纤维对混凝土动态力学性能的影响,以及标定本构模型参数对钢纤维混凝土和镀铜钢纤维混凝土的适用性。在高强混凝土中掺加0.5%、1%、1.5%体积掺量的钢纤维制备7组试件,分别进行静态力学性能试验和分离式霍普金森压杆试验（SHPB）,基于静态、动态力学结果修正Holmquist-Johnson-Cook（HJC）本构模型参数,并利用有限元分析软件验证HJC模型参数的有效性。结果表明,在0.5%、1%、1.5%体积掺量下,混凝土动态峰值抗压强度随纤维掺量的增加而提高。标定的HJC模型对钢纤维混凝土的动态峰值抗压强度预测效果良好,模拟得到的应力-应变曲线与SHPB试验结果大致吻合。以侵蚀准则模拟得到动态冲击试验试件破坏过程,为钢纤维混凝土的抗冲击设计提供参考。     

Flexural behavior of strengthened concrete beams with corroding reinforcement

This paper presents the results of an experimental investigation on a total of 30 under-reinforced concrete beams which were subjected to corrosion after the cover zone was replaced with different high-performance fiber reinforced cementitious composites. A power supply was used to induce different degrees of corrosion into reinforcement. The beams were then tested under four-point bending for their load–deflection relations. The results show significant reductions in flexural strength due to reinforcement corrosion. The beams cast with a cover containing 50/50 blend of brass coated and hooked steel fibers have the best flexural performance. The beams cast with a cover containing glass fiber showed the smallest amount of strength reduction and a reasonable ductile failure after corrosion.     

Fresh and hardened properties of high-performance fiber-reinforced concrete containing fly ash and rice husk ash: Influence of fiber type and content

Although fibers are used only infrequently as an additive in concrete in the construction industry, fiber-enhanced concrete is known to provide a wide range of advantages over conventional concrete. The main objective of this study was to investigate the influences of fiber type and content on the mechanical properties and durability of high-performance fiber-reinforced concrete (HPFRC) designed using a novel densified mixture design algorithm with fly ash and rice husk ash. Three types of fiber, including polypropylene (PP) fiber, steel fiber (SF), and hybrid fiber (HF), were considered. Based on the results, the inclusion of fibers decreased HPFRC flowability, regardless of fiber type. Although the compressive strength of HPFRC with 1.6% PP fiber content was 11.2% below that of the reference HPFRC specimen at 91 d of curing age, the 91-d compressive strengths of both SF and HF-enhanced HPFRC specimens were significantly better than that of the reference HPFRC specimen. Furthermore, the HPFRC specimens incorporating SF and HF both exhibited better splitting tensile and flexural strengths as well as less drying shrinkage than the HPFRC specimens incorporating PP fiber. However, the fiber-enhanced specimens, especially those with added SF, registered less surface electrical resistivity and greater vulnerability to chloride ion penetration than the reference HPFRC specimen.