钢-聚丙烯混杂纤维混凝土轴心受拉应力-应变关系研究

既有研究表明,在混凝土基体中同时加入钢(S)纤维和聚乙烯醇(PVA)纤维,形成S-PVA混杂纤维混凝土,可以显著提升混凝土的综合性能。在此基础上,依据钢纤维、PVA纤维长度和掺量的不同,设计了17组试验组,完成了单轴受力全过程试验。根据试验结果,定量分析了钢纤维、PVA纤维对于改善混凝土弹性模量、材料韧性、抗拉抗压强度及其峰值应变的影响;提出了实用的S-PVA混杂纤维混凝土单轴受拉和受压应力-应变曲线数学表达式。提出的计算公式与试验结果吻合较好,可以为混杂纤维混凝土结构的设计和非线性分析提供理论基础。     

Tensile behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete

The effects of blending fibers on the tensile behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete (UHP-HFRC) are investigated. Four types of steel macro-fibers (of differing length or geometry) and one type of steel micro-fiber are considered. In producing the specimens, the volume content of the macro-fiber was held at 1.0%, whereas the volume content of the micro-fiber varied from 0.0% to 1.5%. The overall shape of tensile stress-strain curves of UHP-HFRC is primarily dependent upon the type of macro-fiber, although the addition of micro-fibers favorably affects the strain hardening and multiple cracking behaviors. UHP-HFRC produced from macro-fibers with twisted geometry provides the best performance with respect to post cracking strength, strain capacity and multiple micro-cracking behavior, whereas UHP-HFRC produced with long, smooth macro-fibers exhibits the worst performance.     

Tensile fracture properties of an Ultra High Performance Fiber Reinforced Concrete (UHPFRC) with steel fiber

This paper presents a study of the tensile fracture properties of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) considering the effects of the fiber content. To investigate the impact of fiber content, notched 3-point bending tests were executed, where the fiber volume ratio was varied from 0% to 5%. From the bending tests, it was found that the flexural tensile strength of UHPFRC linearly increases with increasing fiber volume ratio and the rule of mixture can be applied to UHPFRC. Furthermore, an inverse analysis was performed to determine the tensile fracture model of UHPFRC and a tri-linear tensile softening model is suggested. The suggested model successfully represents the increase of the stress-constant bridging zone and the decrease of the stress-resisting zone with increasing fiber content. The proposed model for various fiber content levels is simple and versatile and can be readily applied to structural design or numerical analysis of UHPFRC.     

钢-聚丙烯混杂纤维混凝土的抗盐冻性能

研究了盐冻循环作用对锂渣混凝土(LiC)和钢-聚丙烯混杂纤维锂渣混凝土(HFC)的质量损失、抗压强度、动弹性模量、基振频率以及溶液吸入量的影响。结果表明:随盐冻循环次数的增加,LiC和HFC均呈现质量损失率逐渐增大、抗压强度先增加后减小、动弹性模量前期稳定后期逐渐减小、溶液吸入量(Ws)先减小后增加的变化规律。将二者对比可以发现,钢-聚丙烯混杂纤维掺入混凝土可以减小盐冻作用对混凝土的内部损伤,显著提高混凝土的抗盐冻性能。     

Shear Strength Evaluation of Concrete Beams Reinforced with BFRP Bars and Steel fibers without Stirrups

This paper presents experimental and analytical investigations on concrete beams reinforced with basalt fiber reinforced polymer (BFRP) and steel fibers without stirrups. Independent behaviour of BFRP reinforced beams and steel fiber reinforced beams were evaluated and the effect of combining BFRP bars and steel fiber was investigated in detail. It is found that combining steel fibers with BFRP could change the shear failure of BFRP reinforced beam to flexural failure. Further, the existing analytical models were reviewed and compared to predict the shear strength of both FRP reinforced and steel fiber reinforced beams. Based on the review, the appropriate model was chosen and modified to predict the shear strength of BFRP reinforced beam along with steel fibers.     

绿色路用纤维增强水泥基复合材料制备及其韧性表征

为提高传统混凝土的路面抗变形能力,采用橡胶粉和玄武岩束制备绿色路用纤维增强水泥基复合材料(FRCC)。对材料的力学特性、韧性指标以及微观结构进行分析,结果表明:单掺橡胶粉时,材料的强度随橡胶粉掺量增加整体呈下降趋势,但其折压比随橡胶粉掺量增加有所提高,试件破坏过程中表现出一定的延性。复掺0.6%、0.8%和1.0%玄武岩纤维束时,材料的强度和折压比均有很大程度的提高,其荷载-挠度曲线具有明显的弯曲硬化特征,峰值荷载所对应的挠度比单掺10%橡胶粉的试验组提高了30%~110%,全曲线所包围面积为单掺10%橡胶粉试验组的14.4~30.3倍。采用初始弯曲韧性比进行弯曲韧性表征结果与折压比之间具有良好的线性相关性。     

Double Punch Test to control the energy dissipation in tension of FRC (Barcelona test)

Current testing methods used to measure tensile properties of Fiber Reinforced Concrete (FRC) are mainly based on bending test of beam specimens. They normally show a considerable scatter that makes difficult the quality control, as in particular when such properties are intended to estimate the strength of structural members. In order to improve the material assessment procedure, the Double Punch Test (DPT) has been recovered for the quality control of the tension behaviour of FRC. Former experimental research showed the feasibility of the test and a reduction of the scatter in the values of the tensile strength and of the toughness. This paper describes the results of an experimental program carried out using both DPT and bending test on FRC with different type of fibers, concretes and fiber contents. In addition, a correlation between both tests is proposed. Its application to steel and polyolefin FRC specimens shows very good results.     

玻璃纤维-铝合金层板(GLARE)的残余应力

对确定纤维金属层板残余应力的几种方法的基本原理进行了介绍，用Ｘ光衍射法，解析法和腐蚀去层法确定了玻璃纤维－铝合金层板（ＧＬＡＲＥ）的残余应力，对以上几种测试方法的优缺点进行了分析，提出了确定纤维金属层板残余应力的建议。     

氯盐干湿环境下TRC与老混凝土的界面特性研究

采用双面剪切的加载方式研究了氯盐干湿循环对纤维编织网增强混凝土(Textile reinforced concrete,TRC)与普通硅酸盐混凝土界面性能的影响,并通过SEM(Scanning electron microscope)技术探究了氯盐干湿循环作用下界面的微观结构。研究发现:氯盐干湿循环下,TRC与老混凝土界面微观结构会损伤劣化;与连续氯盐浸泡相比,氯盐干湿循环对界面粘结性能的影响较大;相同干湿循环次数下,加固界面的粘结强度随着氯盐溶液浓度的增加而降低;相同氯盐溶液浓度下,加固界面的粘结强度随着循环次数的增加而降低。     

Energy absorption capacity of a sustainable Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) in quasi-static mode and under high velocity projectile impact

This paper investigates the energy absorption capacity of a sustainable Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) in quasi-static mode and under high velocity projectile impact. The design of the sustainable concrete mixtures aims on achieving a densely compacted cementitious matrix with a relatively low binder amount, employing the modified Andreasen & Andersen particle packing model. The experiments on UHPFRC are performed using a 4-point bending test and high velocity projectile impact tests. The obtained results show that although the utilization of hybrid steel fibre enhances the mechanical properties of the developed UHPFRC, the application of fibres with hooked ends is crucial in improving the energy absorption capacity of the sustainable UHPFRC in quasi-static mode. However, under high velocity projectile impact, the UHPFRC mixture with hybrid fibres shows a much better energy absorption capacity than the one with hooked steel fibres only, particularly in resisting the scabbing at the rear surface. The intrinsic mechanisms for the energy absorption capacity of the sustainable UHPFRC in quasi-static mode and under high velocity projectile impact are studied and analysed.     

Influence of silica fume content on microstructure development and bond to steel fiber in ultra-high strength cement-based materials (UHSC)

The use of silica fume can significantly enhance mechanical properties of concrete given its beneficial filling and pozzolanic effects. In this study, a simple and effective double-side pullout testing method was adopted to characterize the interfacial bond properties, which include pullout load-slip relationship, bond strength, and pullout energy, of steel fiber-matrix in ultra-high strength cement-based material (UHSC) with 0–25% silica fume by the mass of binder. The effects of silica fume content on flowability, heat of hydration, compressive and flexural strengths, hydration products, and pore structure of matrix at different curing time were evaluated as well. Backscatter scanning electron microscopy (BSEM) and micro-hardness measurement were used to examine the quality of interfacial transition zone (ITZ) around the fiber. In terms of the results, the optimal silica fume content could be in the range of 15%–25%. UHSC mixtures with these dosages of silica fume showed significant improvement in pullout behavior. Its bond strength and pullout energy at 28 d could increase by 170% and 250% compared to the reference samples without any silica fume. The microstructural observation verified the findings on the macro-properties development. Formation of more and higher strength of hydration products and refinement of ITZ around the fiber ensured higher micro-hardness, and thus improved the bond to fiber.     

Interaction between plasticity and damage in the behaviour of [+φ, −φ]n fibre reinforced composite pipes in biaxial loading (internal pressure and tension)

In this paper, we propose a new model which describes the behaviour of [+φ, −φ]_n composite laminates. Tests were performed on glass-epoxy pipes subjected to biaxial tensile and internal pressure loading. Experiments showed that [+55, −55]_n pipes exhibit varying types of damaged elastoplastic behaviour depending on the stress ratio σ_zz/σ_θθ (axial stress/hoop stress). A plastic model is based on the definition of a yield criterion and an associated flow rule. Damaging occurs when transverse microcracks appear in the layer. A micromechanical model defines the anisotropy of the damage. Interaction between plasticity and damage was of major importance in the definition of damage kinetics. This effect was observed on proportional loadings as well as on sequential tests: a preliminary loading in pure internal pressure (σ_zz=0) induced large plastic phenomena which blocked crack propagation in additional internal pressure with closed ends effect (IPCEF) tests (R=σ_zz/σ_θθ=1/2), even though IPCEF caused considerable damage on an unloaded specimen.