Bond-Slip Behavior of Steel Bar and Recycled Steel Fibre-Reinforced Concrete

Recycled steel fiber reinforced concrete is an innovative construction material that offers exceptional mechanical properties and durability.It is considered a sustainable material due to its low carbon footprint and environmental friendly characteristics.This study examines the key influencing factors that affect the behavior of this material,such as the steel fiber volume ratio,recycled aggregate replacement rate,concrete strength grade,anchorage length,and stirrup constraint.The study investigates the bond failure morphology,bond-slip,and bond strength constitutive relationship of steel fiber recycled concrete.The results show that the addition of steel fibers at 0.5%,1.0%,and 1.5%volume ratios can improve the ultimate bond strength of pull-out specimens by 9.05%,6.94%,and 5.52%,respectively.The replacement rate of recycled aggregate has minimal effect on the typical bond strength of pull-out specimens.However,the ultimate bond strengths of pull-out specimens with concrete strength grades C45 and C60 have improved compared to those with C30 grade.The specimens with longer anchorage lengths exhibit lower ultimate bond strength,with a reduction of 33.19%and 46.37%for anchorage lengths of 5D and 7D,respectively,compared to those without stirrups.Stirrup restraint of 1φ8 and 2φ8 improves the ultimate bond strength by 5.29%and 6.90%,respectively.Steel fibers have a significant effect on the behavior of concrete after it cracks,especially during the stable expansion stage,crack instability expansion stage,and failure stage.

Experimental and Numerical Analysis of High-Strength Concrete Beams Including Steel Fibers and Large-Particle Recycled Coarse Aggregates

In order to study the performances of high-strength concrete beams including steel fibers and large-particle recycled aggregates,four different beams have been designed,tested experimentally and simulated numerically.As varying parameters,the replacement rates of recycled coarse aggregates and CFRP(carbon fiber reinforced polymer)sheets have been considered.The failure mode of these beams,related load deflection curves,stirrup strain and shear capacity have been determined through monotonic loading tests.The simulations have been conducted using the ABAQUS finite element software.The results show that the shear failure mode of recycled concrete beams is similar to that of ordinary concrete beams.The shear carrying capacity of high-strength concrete beams including steel fibers and large-particle recycled coarse aggregates grows with an increase in the replacement rate of recycled coarse aggregates.Reinforcement with CFRP sheets can significantly improve the beam’s shear carrying capacity and overall resistance to deformation.

Punching shear behavior of steel fiber reinforced recycled coarse aggregate concrete two-way slab without shear reinforcement

In this paper,the punching shear performance of 8 steel fiber reinforced recycled coarse aggregate concrete(SFRCAC)two-way slabs with a size of 1800 mm×1800 mm×150 mm was studied under local concentric load.The effects of RCA replacement ratio(rg)and SF volume fraction(Vf)on the punching shear performance of SFRCAC two-way slabs were investigated.Digital Image Correlation(DIC)measurement and Acoustic Emission(AE)technique were introduced to collect pictures and relevant data during the punching shear test.The test results show that the SFRCAC two-way slab mainly exhibits punching shear failure and flexure failure under local concentric load.The punching shear failure space area of SFRCAC two-way slab has no obvious change with increasing rg,however,show a gradual increase trend with increasing Vf.Both of the punching shear ultimate bearing capacity(Pu)and its deflection of SFRCAC two-way slab decrease with increasing rg and increase with increasing Vf,respectively.Finally,through the regression analysis of the results from this study and the data collected from related literature,the influence of rg and Vf on the Pu of two-way slabs were obtained,and the equations in GB 50010-2010,ACI 318-19,and Eurocode 2 Codes were amended,respectively.Furthermore,the amended equations were all applicable to predicted the ultimate bearing capacity of the ordinary concrete two-way slab,RCAC two-way slab,SFRC two-way slab,and SFRCAC two-way slab.

Seismic behavior of large-scale FRP–recycled aggregate concrete–steel columns with shear connectors

The application of fi ber-reinforced polymer (FRP) composites for the development of high-performance composite structural systems has received signifi cant recent research attention. A composite of FRP–recycled aggregate concrete (RAC)–steel column (FRSC), consisting of an outer FRP tube, an inner steel tube and annular RAC fi lled between two tubes, is proposed herein to facilitate green disposal of demolished concrete and to improve the ductility of concrete columns for earthquake resistance. To better understand the seismic behavior of FRSCs, quasi-static tests of large-scale basalt FRSCs with shear connectors were conducted. The infl uence of the recycled coarse aggregate (RCA) replacement percentage, shear connectors and axial loading method on the lateral load and deformation capacity, energy dissipation and cumulative damage were analyzed to evaluate the seismic behavior of FRSCs. The test results show that FRSCs have good seismic behavior, which was evidenced by high lateral loads, excellent ductility and energy dissipation capacity, indicating RAC is applicable in FRSCs. Shear connectors can signifi cantly postpone the steel buckling and increase the lateral loads of FRSCs, but weaken the deformation capacity and energy dissipation performance.

BFRP筋回收轮胎钢纤维混凝土黏结性能分析

对玄武岩纤维增强复合材料(BFRP)筋在回收轮胎钢纤维(RTSF)混凝土中的黏结性能进行了试验和分析研究.对不同RTSF体积掺量、BFRP筋直径和嵌入长度的试件进行了拉拔试验,研究其对黏结破坏模式、黏结滑移响应和黏结强度的影响,并提出了BFRP筋RTSF混凝土的黏结滑移理论模型.结果表明:BFRP筋RTSF混凝土黏结破坏类型包括拔出破坏、劈裂破坏以及拔出且劈裂破坏;BFRP筋直径对黏结破坏模式无显著影响,而RTSF体积掺量、BFRP筋直径和嵌入长度均对黏结强度有较大影响,且RTSF体积掺量与极限黏结强度呈正相关,BFRP筋直径和嵌入长度对其影响与之相反;当RTSF体积掺量从0增大至1.5%时,其极限黏结强度最大可提高约23.87%.与已有模型相比,所提出的黏结滑移理论模型对BFRP筋RTSF混凝土的黏结滑移曲线具有更高的拟合精度.

钢纤维对细再生混凝土力学性能的影响研究

为研究细再生集料(FRAP)替代天然细集料(NFA)的可能性。配置1%钢纤维掺量下不同FRAP含量(0%、25%、50%、75%、100%)的水泥混凝土,并测定成型后试件的抗压强度、拉伸特性、应力-应变特性和耐久性能。研究结果表明:以FRAP替代NFA会导致细再生集料水泥混凝的土力学强度降低;加入1%钢纤维,可以显著提高细再生集料水泥混凝土劈裂抗拉强度和抗弯强度,峰值应力增加约15%,峰值应变增加50%,韧性及延展性提高约5倍;以FRAP替代NFA的最佳含量为50%左右。

Punching shear behavior of recycled aggregate concrete slabs with and without steel fibres

A study on the punching shear behavior of 8 slabs with recycled aggregate concrete(RAC)was carried out.The two main factors considered were the recycled coarse aggregate(RCA)replacement percentage and the steel fibre volumetric ratio.The failure pattern,load-displacement curves,energy consumption,and the punching shear capacity of the slabs were intensively investigated.It was concluded that the punching shear capacity,ductility and energy consumption decreased with the increase of RCA replacement percentage.Research findings indicated that the incorporation of steel fibres could not only improve the energy dissipation capacity and the punching shear capacity of the slab,but also effectively improve the integrity of the slab tension surface and thereby changing the trend from typical punching failure pattern to bending-punching failure pattern.On the basis of the test,the punching shear capacity formula of RAC slabs with and without steel fibres was proposed and discussed.

不同纤维掺量再生混凝土骨料轻质混凝土性能研究

为了研究聚丙烯(PP)纤维增强再生混凝土骨料轻质混凝土的性能,以普通硅酸盐水泥、再生废弃混凝土粗骨料、聚丙烯纤维、泡沫为主要材料,选取PP纤维掺量为变量,对试样进行室内试验研究。结果表明:随PP纤维掺量增加,浆体流动度呈下降趋势;当采用再生粗骨料级配(即粒径为9.5~16 mm、16~19 mm、19~26.5 mm、26.5~31.5 mm、31.5~37.5 mm的5类骨料的质量比)为2∶4∶8∶3∶3和30%体积率时,建议浆体流动度大于210 mm;试件抗压强度和劈裂抗拉强度随PP纤维掺量的增加均呈先增大后减小趋势,说明PP纤维对再生混凝土骨料轻质混凝土性能提升效果有限;PP纤维的掺入会使再生混凝土骨料轻质混凝土材料早期抗压强度和劈裂抗拉强度形成速度降低;当纤维掺量由0增大为0.2%时,增加了孔隙率,降低了平均孔径。

高温后纤维增强全再生粗骨料混凝土力学性能试验研究

为研究高温后纤维增强全再生粗骨料混凝土力学性能,以历经最高温度、混杂纤维类型、纤维掺量为变化参数,设计并完成了44个试件的轴压试验,观察了高温后试件的表观变化及受力破坏形态,获取了荷载-位移曲线,分析了各变化参数对试件破坏形态、质量烧失率、峰值荷载和峰值变形的影响规律。结果表明:随历经最高温度升高,纤维全再生粗骨料混凝土表观由青灰色变淡红色,最后呈淡褐色,其质量烧失率近似呈线性增长;随温度的升高,试件破坏开裂时间越早,表观损伤越严重,而随钢纤维、玄武岩纤维掺量增加,试件裂缝发展减缓,整体性更好;试验范围内,掺钢-玄武岩纤维试件的峰值荷载随钢纤维掺量增加而减小,随玄武岩纤维掺量增加而增大,其峰值变形随两类纤维掺量的增加均表现为先增后减;对掺钢-聚丙烯纤维试件,随钢纤维掺量增加,峰值荷载先减后增,峰值变形增大,随聚丙烯纤维掺量增加,峰值荷载减小,峰值变形先减后增。

钢纤维增强碱矿渣再生混凝土的力学性能及碳排放评价

使用工业副产品矿渣和再生骨料制备碱矿渣再生混凝土(AARAC),符合中国“双碳”和“可持续发展”战略目标的要求.通过13组试件的基本力学性能试验,研究了再生骨料取代率和钢纤维掺量对AARAC基本力学性能的影响,并从原材料端对其进行了碳排放评价.结果表明:当再生骨料取代率为75%时,AARAC的力学性能指标与普通水泥混凝土相当;掺加钢纤维有效缓解了再生骨料对AARAC力学性能的负面影响;当再生骨料取代率为50%、钢纤维掺量为0.5%时,AARAC的力学性能优良,可持续性强;基于本文及相关文献的试验数据,建立了AARAC力学强度和弹性模量的计算公式,计算结果与试验结果吻合良好.

再生粗细骨料混凝土受拉力学性能研究

我国城镇化迅速发展的过程中产生了大量建筑垃圾,其处理和有效利用是当前亟需解决的关键问题。为推广再生混凝土在建筑结构中有效利用,通过对国内外大量文献进行研究总结,对再生混凝土受拉强度性能开展了深入研究。首先,研究了不同再生粗骨料、再生细骨料取代率下再生混凝土抗拉强度变化规律;其次,研究了再生粗骨料、再生细骨料抗拉强度与抗压强度关系,建立了再生粗、细骨料混凝土抗拉强度预测模型,最后,研究总结了钢纤维掺量与长径比对再生粗骨料混凝土抗拉强度的影响。

外粘碳纤维布加固混凝土的粘接性能研究

为了提升外粘碳纤维布加固混凝土的粘接性能,对比分析了未掺加钢纤维和掺加不同含量钢纤维的外粘碳纤维布加固混凝土的粘接性能。结果表明,掺加钢纤维可以提升混凝土试件的抗压强度、劈拉强度、极限荷载、峰值扰度和最大应变,从而对混凝土起到加固作用;掺加钢纤维试件的极限荷载要高于未掺加钢纤维的试件,且钢纤维掺加量越大则极限荷载越大,界面滑移也越大;都使用再生骨料混凝土的情况下,掺加钢纤维试件的有效粘接长度大于未掺加钢纤维的试件,且当钢纤维掺加量较大时试件有效粘接长度要高于未使用再生粗骨料的试件。

高温下掺再生骨料及纤维混凝土物理力学性能研究

目前关于可再生纤维混凝土的性能研究较为充分,但对其高温处理后性能变化认识不足。为此,针对超高性能混凝土(UHPC)、50%粗骨料替代超高性能混凝土(50%R-UHPC)以及50%粗骨料替代-1.0%钢纤维超高性能混凝土(50%R-1.0%S-UHPC)进行高温处理(200℃、400℃、600℃、800℃),研究高温对它们力学性能(单轴抗压强度、弹性模量、劈裂抗拉强度以及抗弯强度等)、抗渗性能以及导热性能的影响,并建立了各项性能指标与孔隙率之间的经验预测模型。研究结果表明:再生粗骨料的添加会弱化UHPC的力学性能、抗渗性能和导热性能,导致抗压强度、抗拉强度和抗弯强度降低,提高UHPC的孔隙率和渗透率;钢纤维的添加会提升UHPC力学性能和导热性能,但会弱化UHPC的抗渗性能。高温处理后UHPC的力学性能、抗渗性能和导热性能会逐渐减弱,并呈现出明显的温度门槛值效应,即400℃之前UHPC力学性能、抗渗性能和导热性能的弱化效应不明显,一旦超过温度门槛值后它们会迅速减弱;对于UHPC和50%R-UHPC来说,随着处理温度的升高,它们的力学性能和导热性能之间的差距会逐渐减小。

回收轮胎钢纤维对超高性能混凝土性能影响的研究

为研究回收轮胎钢纤维(RTSF)对超高性能混凝土(UHPC)各项性能的影响,分别设计了RTSF体积掺量为0%、0.25%、0.5%、0.75%和1%的UHPC,对新拌混凝土的坍落扩展度和含气量,硬化混凝土的抗压强度、弹性模量、抗折强度和吸水量进行了测试。结果表明,RTSF掺量越高,新拌UHPC的坍落度扩展越低,含气量越高。随着RTSF掺量的提高,UHPC的抗压强度先提高后降低,弹性模量和抗折强度呈增高趋势。掺入RTSF能够提高UHPC的吸水量,但不同RTSF掺量对吸水量的影响规律不明确。综合来看,0.5%的RTSF掺量能够在不大幅牺牲UHPC工作性能和抗渗性的前提下,提高各项力学性能。

圆钢管约束型钢再生混凝土短柱抗震性能

针对圆钢管约束型钢再生混凝土短柱的抗震性能进行研究,在验证了分析模型合理性的前提下,考虑了圆钢管径厚比、再生粗骨料取代率和轴压比等设计参数对试件力学性能的影响规律,获取了试件滞回曲线、骨架曲线、延性系数、等效黏滞阻尼系数等抗震性能指标和试件的峰值承载力,并与已有试验进行了对比分析。结果表明:在再生混凝土取代率、轴压比、含钢率等参数基本相同时,圆钢管约束型钢再生混凝土短柱比型钢再生混凝土柱和圆钢管型钢再生混凝土柱表现出更好的变形和耗能能力;再生粗骨料取代率对滞回曲线等抗震性能指标影响不大,可基本满足工程抗震要求,并可广泛应用于工程的承重结构中;在取代率和轴压比相同时,随着径厚比的增大,试件弹性阶段初始刚度、峰值承载力和耗能能力逐渐下降,但延性会有一定幅度的提升,延性变形能力可提高30%~40%;在取代率和径厚比相同时,随着轴压比的增大,试件的峰值承载力和耗能能力变化不大,延性越来越差。

Stress-strain relationship of recycled self-compacting concrete filled steel tubular column subjected to eccentric compression

As a typical compression member,the concrete-filled steel tube has been widely used in civil engineering structures.However,little research on recycled self-compacting concrete flled circular steel tubular(RSCCFCST)columns subjected to eccentric load was reported.In this study,21 specimens were designed and experimental studies on the stress-strain relationship of were carried out to study the mechanical behaviors.Recycled coarse aggregate replacement ratio,concrete strength grade,length to diameter ratio and eccentric distance of specimens were considered as the main experimental parameters to carry out eccentric compression tests.The corresponding stress-strain relationship curves were used to analyze the influence of concerned parameters on ecentric load-bearing capacity of RSCCFCST columns.The experimental results show that the strain of the eccentric compression stress-strain curves increase with the increase of recycled coarse aggregate replacement ratio and concrete strength grade.With increase of eccentric distance,the ductility of specimens increases while the bearing capacity decreases.Moreover,a phenomenological model of RSCCFCST columns is proposed,which exhibits versatile ability to capture the process during loading.The present study is expected to further understanding the behaviors and to provide guidance of RSCCFCST columns in design and engineering applications.

钢-剑麻混杂纤维再生混凝土断裂性能研究

为改善再生混凝土(RAC)的断裂性能,通过三点弯曲断裂试验,研究了钢纤维、剑麻纤维及钢-剑麻混杂纤维对RAC试件断裂性能的影响。同时,采用数字图像相关(DIC)技术测得RAC试件的裂缝扩展全过程。结果表明:未掺纤维的RAC试件断裂性能较差,而掺入纤维后的RAC试件断裂性能明显提升;单掺钢纤维时,试件的起裂韧度与纤维掺量无关;单掺剑麻纤维时,最佳体积掺量为0.15%,其试件的起裂荷载较未掺纤维RAC试件提高了67%。单掺纤维和混掺纤维均可提高失稳韧度和断裂能,但混掺纤维效果更佳。当体积掺量为1.0%的钢纤维和体积掺量为0.30%的剑麻纤维混杂时,其起裂韧度、失稳韧度和断裂能较未掺纤维的RAC试件分别提高了83.92%、575.86%和1244.05%。

废弃混凝土再利用综述

废弃混凝土的有效利用可以大大降低天然资源的损耗以及由此带来的环境问题。因此,综述了再生粗骨料、再生细骨料对再生混凝土工作性能的影响,并且通过相应的技术手段改良工作性能或者在天然骨料中掺入一定比例的再生骨料,使其在经济性与实用性上找到平衡点。

配筋对方钢管再生混凝土短柱轴压性能的影响

为了明确再生粗骨料100%替代率下配筋对方钢管再生混凝土短柱(recycled aggregate concrete-filled tube,RACFST)轴压性能的提高作用,进行了试验研究。以5种配筋率为变化参数设计了5组配筋方钢管再生混凝土(reinforcement and recycled aggregate concrete-filled steel tube,R-RACFST)试件,同时设计相应的钢管混凝土(concrete-filled steel tube,CFST)与钢管再生混凝土(RACFST)试件作为对照组。通过分析配筋率对破坏模式、受力性能、延性、刚度退化和屈强比等关键力学特性的影响规律,发现钢筋笼对核心混凝土产生二次套箍效应,因而明显改善核心再生混凝土的脆性;在一定配筋率范围内,配筋对提高构件极限承载力和延性等力学性能有显著贡献,并在一定程度上延缓再生混凝土的刚度退化。结果表明:配置适量钢筋可将再生粗骨料替代率提高到100%并能保证R-RACFST具有较好的结构适用性;推荐配筋率合理范围为1.34%~3.02%;现行规程可计算再生粗骨料100%取代率下的R-RACFST承载力,但计算结果过于保守;修正得到R-RACFST承载力计算公式,其结果与试验值更吻合,结果稳定可靠。

碱激发再生骨料纤维混凝土的工作性和力学性能研究

研究了碱激发剂浓度(2%、5%、8%)和再生粗骨料取代率(0、25%、50%、75%、100%)对PVA纤维混凝土坍落度、抗压强度、劈裂抗拉强度和轴心抗压强度的影响,建立了碱激发再生骨料纤维混凝土的力学指标换算式。结果表明:随着再生粗骨料取代率和碱激发剂浓度的增加,混凝土拌合物的坍落度降低;试件的抗压强度、劈裂抗拉强度和轴心抗压强度均随着再生粗骨料取代率的增加而减小,随着碱激发剂浓度的增加而增大;建立的抗压强度分别与劈裂抗拉强度和轴心抗压强度的换算式具有较高的拟合精度。