Experimental and numerical study on flexural behaviors of steel reinforced engineered cementitious composite beams

To investigate the flexural behaviors of steel reinforced engineered cementitious composite （ECC） beams, the behaviors of the steel reinforced ECC beam and the conventional steel reinforced concrete beam subjected to flexural load are experimentally compared. The experimental results show that the flexural strength and ductility of the steel reinforced ECC beam are 24.8% and 187.67% times larger than those of the steel reinforced concrete beam, and the substitution of concrete with ECC can significantly delay the propagation of cracks. Additionally, a simplified constitutive model of the ECC material is used to simulate the flexural behaviors of beams by the finite element analysis （FEA）. The results show a good agreement between the simulation and test results. The crack width of the steel reinforced ECC beam can be limited to 0.4 mm under the service load conditions. The application of ductile ECC can significantly increase the flexural performance in terms of flexural strength, deformation capacity and ductility of the beams.

Development of engineered cementitious composites with local ingredients

In order to reduce the cost of high performance polyvinyl alcohol（PVA） fiber reinforced cementitious material（called engineered cementitious composites,ECC）,a ductile ECC material is developed using domestic PVA fibers along with other local ingredients,such as fly ash,cement and sand.In addition to the economic analysis of ECC,the four-point bending test and the optical microscope are employed to investigate the deflection capacity of ECC,its crack width and the occurrence of the self-healing phenomenon.The experimental results suggest that ECC made with domestic ingredients exhibits larger deformability and the average crack width is controlled around 60 μm.Furthermore,the self-healing behavior is observed in cracks of the specimens after cycles of wet and dry curing.The economic analysis shows that the cost of ECC can be greatly reduced via employing domestic PVA fibers.It is,therefore,feasible to produce low cost ECC material employing domestic PVA fibers,while simultaneously retaining high material ductility.

Flexural behavior of steel reinforced engineered cementitious composite beams

In order to enhance the durability of steel encased concrete beams, a new type of steel reinforced engineered cementitious composite(SRECC) beam composed of steel shapes, steel bars and ECC is proposed. The theoretical analyses of the SRECC beam including crack propagation and stress-strain distributions along the depth of the composite beam in different loading stages are conducted. A theoretical model and simplified design method are proposed to calculate the load carrying capacity. Based on the proposed theoretical model, the relationship between the moment and corresponding curvature is derived. The theoretical results are verified with the finite element analysis. Finally, an extensive parametric study is performed to study the effect of the matrix type, steel shape ratio, reinforced bar ratio, ECC compressive strength and ECC tensile ductility on the mechanical behavior of SRECC beams. The results show that substitution concrete with ECC can effectively improve the bearing capacity and ductility of composite beams. The steel shape and longitudinal reinforcement can enhance the loading carrying capacity, while the ductility decreases with the increase of steel shape ratio. ECC compressive strength has significant effects on both load carrying capacity and ductility, and changing the ultimate strain of ECC results in a very limited variation in the mechanical behavior of SRECC beams.

Effects of Water/Binder Ratio on the Properties of Engineered Cementitious Composites

The effects of water/binder ratio （w/b） on the toughness behavior, compressive strength and flexural strength of engineered cementitious composites （ECC） were investigated. The w/b ratios of 0.25, 0.31, 0.33 and 0.37 were selected and the specimens were tested at the ages of 7 d and 28 d. The experimental results showed that there was a corresponding increase in first cracking strength, modulus of rupture, compressive strength and flexural strength with the decrease of w/b. Within the w/b range of 0.25-0.37, higher w/b was found to have improved effects on deflection, strain hardening index and toughness index of ECC. In the permission of meeting the requirement of compressive strength grade, selecting higher w/b in mix design will help to obtain robust ECC.

Flexural behaviors of steel reinforced ECC/concrete composite beams

An engineered cementitious composite （ECC） is introduced to partially substitute concrete in the tension zone of a reinforced concrete beam to form an ECC/reinforced concrete （RC） composite beam, which can increase the ductility and crack resisting ability of the beam. Based on the assumption of the plane remaining plane and the simplified constitutive models of materials, the stress and strain distributions along the depth of the composite beam in different loading stages are comprehensively investigated to obtain calculation methods of the load-carrying capacities for different stages. Also, a simplified formula for the ultimate load carrying capacity is proposed according to the Chinese code for the design of concrete structures. The relationship between the moment and curvature for the composite beam is also proposed together with a simplified calculation method for ductility of the ECC/RC composite beam. Finally, the calculation method is demonstrated with the test results of a composite beam. Comparison results show that the calculation results have good consistency with the test results, proving that the proposed calculation methods are reliable with a certain theoretical significance and reference value.

Mechanical behaviors of steel reinforced ECC / concrete composite columns under combined vertical and horizontal loading

In order to improve the load capacity, seismic performance and performance-cost ratio of the columns, the concrete at the base of reinforced concrete （RC） columns is substituted with engineered cementitious composites （ECC） to form ECC/RC composite columns. Based on the existing material properties, the mechanical behaviors of the ECC columns, ECC/RC composite columns and RC columns were numerically studied under combined vertical and horizontal loading with the software of ATENA. Then, the failure mechanism of ECC columns and ECC/RC composite columns were comprehensively studied and compared with that of the RC columns. Then, the effects of the height of the ECC, the axial compression ratio, and the transverse reinforcement ratio on the mechanical behaviors of the composite or the ECC column are studied. The calculation results show that the ultimate load capacity, ductility and crack resistance of the ECC or ECC/RC composite columns are superior to those of the RC columns. The ECC/RC composite column with a height of the ECC layer of 1.2h （ h is the height of the cross section） can achieve similar mechanical properties of a full ECC column. With high shear strength, ECC can undertake the shear force and significantly reduce the amount of stirrups, avoiding construction issues and promoting its engineering application.

ECC疲劳损伤规律及微观结构研究

为研究工程水泥基复合材料(ECC,engineered cementitious composites)的疲劳规律并探究其损伤原因,利用疲劳试验机对ECC试件进行单轴拉伸循环加载试验,分析其疲劳规律及损伤界面微观形态。研究结果表明:ECC试件破坏规律与其累积轴向应变速率有关,在加载初始阶段,累积轴向应变会随着循环荷载作用次数增加而明显增大,随后进入稳定变形阶段;进一步加载将导致累积轴向应变快速增长,并最终导致试件断裂破坏;ECC的裂纹宽度发展呈现出中间低、两端高的趋势;ECC试件在循环荷载过程中初次开裂后,不会迅速进入破坏阶段,是因为纤维仍然具有抗拉能力,可继续承受循环荷载加载;通过对纤维-基体界面的微观分析发现,纤维与基体结合较好,可整体耗散能量,为ECC具有高疲劳性能的主要原因。

Seismic behaviors of steel reinforced ECC/RC composite columns under low-cyclic loading

To improve the seismic performance of columns, engineered cementitious composite （ECC） is introduced to partially substitute concrete at the base of the columns to form ECC,/reinforced concrete （ RC） composite columns. The mechanical behaviors of the ECC/RC composite columns are numerically studied under low-cyclic loading with the finite element analysis softwareof MSC. MARC. It is found that the ECC/RC composite columns can significantly enhance the load capacity, the ductility ad energy dissipation of columns. Then, the effects of the height of the ECC, the axial compression ratio and the longitudinal reinforcement ratio on the seismic behaviors of the composite columns are parametrically studied. The results show that the ECC/RC composite column with a height of the ECC layer of 0. Sh（h is the height to the cross-section） can achieve similar seismic performance of a full ECC column. The peak load of the composite column increases significantly while the ductility decreases with the increase of the axial compression ratio. Increasing the longitudinal reinforcement ratio within a certain range can improve the ductility and energy dissipation capacity and almost has no effect on load capacity. The aalysis results ae instructive and valuable for reference in designing ECC structures.

ECC全包裹普通混凝土复合试件的力学性能

为综合利用工程用水泥基复合材料(ECC)在力学性能上和普通混凝土在成本上的优势,本工作提出了一种制备ECC全包裹普通混凝土复合试件的方法,通过进行抗压、抗拉及抗弯等试验系统研究了其基本力学性能,并采用数值分析方法对配筋复合梁进行了正截面受弯性能研究。结果表明:在复合试件受力破坏时,ECC和混凝土界面未出现滑移,两种材料黏结可靠实现了协同受力;相对普通混凝土试件而言,复合试件的抗压强度、抗拉强度及抗弯强度均有所提升,尤其是抗弯强度的提升最为显著,对于截面尺寸为100 mm×100 mm的梁,当ECC厚度分别为10 mm和15 mm时,抗弯强度可提高27.4%和57.1%;复合试件具有良好的延性变形能力,破坏后可保持一定的完整性,整体具备高韧性特征;与普通钢筋混凝土梁相比,配筋复合梁有效利用了ECC材料的性能优势,显著提升了配筋梁的承载和变形能力。

Mechanical Behavior of Rectangular Steel-Reinforced ECC/Concrete Composite Column under Eccentric Compression

In order to improve the seismic performance, deformation ability and ultimate load-carrying capacity of columns with rectangular cross section, engineered cementitious composite （ECC） is introduced to partially substitute concrete in the edge zone of reinforced concrete columns and form reinforced ECC/concrete composite columns. Firstly, based on the assumption of plane remaining plane and the simplified constitutive models, the calculation method of the load-carrying capacity of reinforced ECC/concrete columns is proposed. The stress and strain distribu- tions and crack propagation of the composite columns in different states of eccentric compressive loading are ana- lyzed. Then, nonlinear finite element analysis is conducted to study the mechanical performance of reinforced ECC/concrete composite columns with rectangular cross section. It is found that the simulation results are in good agreement with the theoretical results, indicating that the proposed method for calculating the load-carrying capacity of concrete/ECC composite columns is valid. Finally, based on the proposed method, the effects of ECC thickness, com- pressive strength of concrete and longitudinal reinforcement ratio on the mechanical performance of reinforced ECC/ concrete composite columns are analyzed. Calculation results indicate that increasing the thickness of ECC layer or longitudinal reinforcement ratio can effectively increase the ultimate load-carrying capacity of the composite column with both small and large eccentricity, but increasing the strength of concrete can only increase the ultimate Ioad- carrying capacity of the composite column with small eccentricity.

Shrinkage Reducing Measures for Engineering Cementitious Composites

Inhibition measurement of shrinkage of engineering cementitious composites （ECC） was investigated due to typical ECC with higher free drying shrinkage.The effects of expanded admixture （EA）,shrinkage reducing admixture （SRA）,coarse sand＋stone powder （CS＋SP） and superabsorbent polymer （SAP） on drying shrinkage and mechanical properties were studied.The experimental results show that ECC incorporating EA,SRA and coarse sand can retain around 60% of the typical ECC＇s free drying shrinkage.Superabsorbent polymerl（SAP） can delay the development of free drying shrinkage of ECC at different ages,and the effect of SAP is not distinct like the actions of EA,superabsorbent polymer（SRA） and coarse sand.Significantly,SAP may act as artificial flaw to form a more homogeneous defect system that increases the potential of saturated multiple cracking,hence the ductility of ECC will be improved greatly.

Study on time-varying seismic vulnerability and analysis of ECC-RC composite piers using high strength reinforcement bars in offshore environment

As the main seismic component of a bridge,seismic damage to the bridge pier has a greater effect on its subsequent service.In the offshore chloride environment,the issues(e.g.,reinforcement bar corrosion and attenuation of concrete strength)of piers caused by chloride ion seriously curtail the normal service life and deteriorate the anti-seismic property of bridge structures.The engineered cementitious composite(ECC)-reinforced concrete(RC)composite pier with high strength reinforcement bars(HSRB)is expected to solve the above problems.This study aims to clarify the time-varying seismic vulnerability(SV)of the HSRBECC-RC composite pier during its full life cycle(FLC).Based on OpenSees,the refined finite element analysis models of RC pier,ECC-RC composite pier,and HSRBECC-RC composite pier have been established.Moreover,using the nonlinear time-path dynamic analysis method,the influence of chloride ion erosion on the time-dependent seismic vulnerability(SV)of these different piers in different service life and different peak ground acceleration(PGA)were analyzed from a dynamic point of view.The research shows that the exceeding probability(EP)of the same damage level increases with the enhancement of service time and PGA and with the increase of destruction,the exceeding probability(EP)of slight damage(DL-1),moderate damage(DL-2),serious damage(DL-3),and complete collapse(DL-4)decreases in turn;the corrosion degree of chloride ion to piers is small during the early service period,the time-varying vulnerability curve of the bridge piers is almost the same as that of a new bridge,and during later service,as the extent of chloride ion corrosion deepens,exceeding probability(EP)under severe damage(DL-3)and complete collapse(DL-4)is increased,and the seismic performance is significantly enhanced.

河砂粒径与纤维类型对ECC力学性能的影响

研究了河砂粒径(0~0.30、0~0.60、0~1.18、0~2.36 mm)与纤维类型(PVA、PE、PP、BF纤维)对工程水泥基复合材料(ECC)力学性能的影响,并进行了SEM分析。结果表明:随着河砂粒径的增大,试件的28 d极限拉应变、峰值应力和抗折强度基本均降低,多缝开裂特征逐渐减弱;4种纤维中,PVA纤维对ECC单轴拉伸性能和抗折性能的提高效果最好;PVA纤维与各粒级的河砂均具有良好的匹配性,在基体中分散较均匀。

碳纤维与玄武岩纤维网格增强ECC复合板的单轴抗拉性能研究

传统纤维网格增强水泥基复合材料以脆性材料为基体,开裂后裂缝宽度较大导致FRP网格强度无法充分发挥。为解决该问题,使用高延性水泥基复合材料(ECC)作为水泥基替代脆性材料,与FRP网格结合制备出适用于新土木的新型轻质高强材料纤维网格增强水泥基复合材料(FRCM),并通过对FRCM复合板进行单轴拉伸试验研究FRP类型及层数对纤维网格增强水泥基复合材料力学性能影响机制及其与ECC材料协同受力变形的能力。设计2种不同类型纤维网格(碳纤维CFRP与玄武岩纤维BFRP)增强的ECC复合材料拉伸试验,2种试验均考虑FRP网格层数和基体厚度对复合材料性能的影响。基于FRP网格和ECC材料本身的变形特点,探究FRP类型、层数和基体厚度对复合材料破坏模式、初始弹性模量、应变硬化模量、开裂应力、峰值应力和应变的影响规律。结果表明:1)在试验工况下,随着网格层数从1层增加到6层,试件的抗拉强度均表现出先增大后减小的特性,在配置5层网格时强度最高;2)基体厚度对试件弹性阶段的力学行为影响较小,但对应变硬化阶段的模量和峰值强度影响较大;3)2种FRP网格的强度和伸长率不同,且与短纤维的协同工作性能也存在差异,导致CFRP-ECC和BFRP-ECC复合材料的拉伸性能存在较大差异。

ECC全包裹混凝土的抗硫酸盐侵蚀和抗冻性能

工程用水泥基复合材料(ECC)和混凝土组合构件在力学性能上体现出一定的优势,但目前缺乏对此类组合构件耐久性能的定性和定量评价。为研究该类组合构件的抗硫酸盐侵蚀和抗冻性能,采用二次浇筑方式制备出ECC全包裹混凝土组合试件,随后对混凝土、ECC和ECC全包裹混凝土试件进行了硫酸盐干湿循环和冻融循环试验,建立了耐久性损伤模型,并预测了服役寿命。结果表明,从抗压强度、表观状态和质量损失的变化规律来看,ECC全包裹混凝土试件相比普通混凝土试件抗硫酸盐侵蚀和抗冻性能均有显著提升,提升效果随包裹厚度的增大而提高。另外,ECC全包裹混凝土试件在受环境侵蚀后仍能维持良好的表观状态,预测的服役寿命更长,其中尤以在硫酸盐侵蚀环境中表现突出。

高应变率荷载作用下钢筋与ECC的黏结滑移关系研究

采用水泥基复合材料(engineering cementitious composite,ECC)替代混凝土可以提高结构在偶然荷载作用下的抗连续倒塌性能,但在悬链线大变形阶段钢筋与ECC间可能会出现黏结滑移破坏。基于分离式霍普金森压杆(SHPB)试验装置,进行了钢筋与ECC的动态黏结滑移性能试验,分析了ECC强度等级、应变率、钢筋直径对极限黏结强度、刚度和滑移量的影响规律,获得了高应变率下钢筋与ECC的平均黏结滑移曲线,得到其黏结滑移破坏模式。并与静态黏结滑移试验进行对比,得到了动态黏结强度增强因子。进一步,通过钢筋开槽内贴应变片法,获得不同锚固位置的黏结应力及相对滑移的分布规律,提出黏结位置函数。最后,根据试验结果得到钢筋与ECC平均黏结滑移本构,进而乘以黏结位置函数得到考虑锚固位置影响的动态黏结滑移本构,为ECC结构构件设计及有限元分析提供试验依据和理论参考。

高延性水泥基材料(ECC)开裂后渗透性研究综述

高延性水泥基材料(ECC)是突破了传统混凝土脆性及应变软化属性的变革性的工程结构材料,该材料的拉伸延性与裂纹控制功能决定其适用于构件拉应力区带裂纹服役。开裂ECC的裂纹宽度对于工程耐久性至关重要,如何在保留材料延性的同时更有效地降低裂纹宽度是进一步提升ECC耐久性的关键。文章总结了该材料自研发以来取得的多种裂纹调控方法,指出其裂宽自控能力与延性的不匹配问题,分析了裂纹宽度、纤维掺量、纤维混杂等因素对开裂水泥基材料渗透性的影响,综述了ECC材料独特的开裂渗透规律及其理论预测模型,进一步提出混杂高模量纤维协同聚乙烯醇纤维调控微裂纹的方法,以期为ECC开裂抗渗性与延性的匹配设计、ECC结构的耐久性提升提供借鉴。

GFRP约束ECC短柱偏压试验研究

纤维增强复合材料(Fiber Reinforced Polymer,FRP)约束工程纤维增强水泥基复合材料(Engineered Fiber Reinforced Cementitious Composites,ECC)轴压柱可显著提高其承载能力和延性,但偏压作用下FRP约束ECC柱的性能提升程度和作用机理有待研究。基于此,以偏心距(0、10、30、50 mm)和FRP层数(0、2、4层)为试验变量,对玻璃纤维增强复合材料(Glass Fiber Reinforced Polymer,GFRP)约束ECC短柱展开了竖向加载试验,并对试验结果进行了分析。研究结果表明:小偏心破坏时受压侧FRP断裂、混凝土被压碎,大偏心破坏时受拉侧FRP撕裂与混凝土横向裂缝近乎同时出现。轴压作用下,轴向变形和抗压强度显著增大;偏压作用下,抗压承载力随着偏心距的增大而减小,而极限位移无明显变化规律。此外,承载力和延性都随着FRP层数的增加而增大。

模拟地震作用下PP-ECC桥墩抗弯性能试验研究

为研究聚丙烯纤维水泥基复合材料(PP-ECC)桥墩与普通混凝土桥墩在压弯荷载作用下承载力差异,本文通过拟静力试验对6个局部采用PP-ECC桥墩和2个普通混凝土桥墩的抗弯性能进行试验研究。结合PP-ECC桥墩的破坏过程,确定PP-ECC桥墩的压弯破坏的特征点,之后基于PP-ECC材料的简化本构模型推导出PP-ECC桥墩的理论开裂、屈服和极限荷载公式。对PP-ECC材料进行单轴拉伸和单轴压缩试验,得到简化PP-ECC本构模型的特征参数,通过试验结果对计算结果进行验证,并对比不同轴压比和PP-ECC区高度下桥墩的抗弯承载力、最大变形的差异。结果表明:PP-ECC桥墩在开裂之后,受拉区PP-ECC并未退出工作,而是协同受拉钢筋参与截面受力;PP-ECC桥墩在达到极限荷载时,裂缝稳态发展,没有出现普通混凝土桥墩保护层混凝土大面积剥落的情况;局部采用PP-ECC桥墩极限荷载时最大变形较普通混凝土桥墩有较大提升,且增加轴压比会降低桥墩的变形能力;在较高轴压比下增加PP-ECC区高度,桥墩的抗弯承载力提升了8.8%;使用简化本构模型计算PP-ECC桥墩特征点抗弯承载力时计算精度为0.86~1.13,且方差分析值偏小,具备良好的计算精度。

ECC-既有混凝土界面黏结性能研究

利用工程水泥基复合材料(ECC)对混凝土结构进行维修和加固时,新旧材料的界面黏结强度至关重要。研究了不同养护条件(标准养护、20℃水养、-10℃自然养护、40℃自然养护)下,涂刷界面剂[乙酸乙烯酯(VA)、乙酸乙烯酯-乙烯(VAE)、乙酸乙烯酯-叔碳酸乙烯酯(VA/VeoVa)]对ECC-既有混凝土界面黏结性能的影响,并在标准养护条件下,对比分析了涂刷VA/VeoVa、凿毛、凿毛+涂刷VA/VeoVa对ECC-既有混凝土界面黏结性能的影响。结果表明:与VA、EVA相比,VA/VeoVa在各养护条件下均能有效提高试件的拉伸黏结强度;标准养护条件下,凿毛+涂刷VA/VeoVa对试件拉伸黏结强度的提高效果最好,其次是凿毛,最后是涂刷VA/VeoVa。