Tensile Strain Capacity Prediction of Engineered Cementitious Composites (ECC) Using Soft Computing Techniques

Plain concrete is strong in compression but brittle in tension,having a low tensile strain capacity that can significantly degrade the long-term performance of concrete structures,even when steel reinforcing is present.In order to address these challenges,short polymer fibers are randomly dispersed in a cement-based matrix to forma highly ductile engineered cementitious composite(ECC).Thismaterial exhibits high ductility under tensile forces,with its tensile strain being several hundred times greater than conventional concrete.Since concrete is inherently weak in tension,the tensile strain capacity(TSC)has become one of the most extensively researched properties.As a result,developing a model to predict the TSC of the ECC and to optimize the mixture proportions becomes challenging.Meanwhile,the effort required for laboratory trial batches to determine the TSC is reduced.To achieve the research objectives,five distinct models,artificial neural network(ANN),nonlinear model(NLR),linear relationship model(LR),multi-logistic model(MLR),and M5P-tree model(M5P),are investigated and employed to predict the TSCof ECCmixtures containing fly ash.Data from115 mixtures are gathered and analyzed to develop a new model.The input variables include mixture proportions,fiber length and diameter,and the time required for curing the various mixtures.The model’s effectiveness is evaluated and verified based on statistical parameters such as R2,mean absolute error(MAE),scatter index(SI),root mean squared error(RMSE),and objective function(OBJ)value.Consequently,the ANN model outperforms the others in predicting the TSC of the ECC,with RMSE,MAE,OBJ,SI,and R2 values of 0.42%,0.3%,0.33%,0.135%,and 0.98,respectively.

High Temperature Flexural Deformation Properties of Engineered Cementitious Composites (ECC) with Hybrid Fiber Reinforcement

Engineered Cementitious Composites(ECC)is a class of high-performance fiber reinforced composites with ultra-ductility designed based on micromechanics,and it has been developed for increasing application in the construction industry during recent decades.The properties of ECC at room temperature have been tested and studied in depth,however,few studies focus on its performance after high temperature that is one of the worst conditions to ECC.To investigate the change tendency and mechanism for the high temperature flexural properties of hybrid fiber reinforced ECC and the feasibility of calcium carbonate whisker to reduce the cost of ECC materials,polyvinyl alcohol fiber(PVA)reinforced strain hardening cementitious composites(PVA-ECC),steel fiber+PVA fiber reinforced ECC(defined as HyFRECC-A)and steel fiber+PVA fiber+CaCO3 whisker reinforced ECC(defined as HyFRECC-B)subject to room temperature and 200℃,400℃,600℃,800℃elevated temperature exposure were experimentally compared.The results indicate that equally replacing PVA fibers by steel fibers degraded the flexural hardening ability of PVA-ECC at room temperature,while the addition of appropriate amount of CaCO3 whisker improved the flexural strength,toughness and flexural hardening behavior.The elevated temperature posed a significant effect on the flexural strength and toughness of the three types of ECCs.Flexural deflection hardening behavior of the three types of ECCs was eliminated after high temperature exposure.Flexural strength and toughness of PVA-ECC presented an exponential decay along with the increase of temperature.The addition of steel fiber slowed down the decay rate.Although the use of CaCO3 whisker increased the post-temperature flexural strength and toughness of HyFRECC-B,the decay rate was not further decreased.

Impact Properties of Engineered Cementitious Composites with High Volume Fly Ash Using SHPB Test

The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete （RPC） and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.

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.

Influence of Thickeners on Cement Paste Structure and Performance of Engineered Cementitious Composites

Hydroxypropyl methylcellulose （HPMC） and amphoteric polyacrylamide （ACPAM） were respectively used to prepare engineered cementitious composite （ECC） which exhibits strain-hardening behavior under uniaxial tension. The connections between cement paste structure and the performance of the composite in fresh and hardened state were investigated, aiming at achieving the desirable workability at a given solids concentration. The experimental results of viscosity and miCrostructure of cement pastes show that the intimate connections between flocculation groups lead to the growing increase in viscosity. The results of deformability and fiber dispersion demonstrate that fiber dispersion coefficient is a comprehensive index which can reflect the performance of deformability as well as uniformity. And the desirable fresh mixture can be achieved by optimizing the viscosity of cement paste. At last, the ductile strain-hardening performance of the ECC prepared with HPMC or ACPAM was investigated through uniaxial tensile test.

Experimental Study on Improved Engineered Cementitious Composite Using Local Material

Engineered Cementitious Composite (ECC) is a cement based material with ultra-high ductility and strength in tension. This material is a kind of highperformance fiber-reinforced cementitious composite materials (HPFRCCs) reinforced with short fibers and characterized by tight multiple cracking. These characteristics of ECC make it applicable to increase the capacity and the ductility of structural elements so that structural design is economic and sustainable. This paper presents an extended evaluation of Improved Engineered Cementitious Composites (IECC) for the use in the strengthening of masonry in filled reinforced concrete frames. IECC is a mixture of cement, fly ash, water, sand, quartz powder and poly-vinyl alcohol fibers with a better quality of tensile strain rather than common ECC. Two types of fine sand and quartz powder used in this study as filler to improve ECC behavior. Also, to show the effect of fly ash on IECC properties, five different mixtures were considered with various fly ash ratios. Different mixtures of IECC using fine aggregates produced in Iran were selected to find out how the aggregates and fly ash would affect IECC performance. The results show that the optimized mixture has the best characteristics including tensile strength and strain. Also, three-dimensional diagrams were used to compare the properties of different mixtures of IECC more effectively and to represent the influence of the range of fly ash ratios so that it can be opted based on design objectives such as ECC properties, costs and structural parameters and demands. These diagrams show the behavior of IECC which its fly ash content ratio in the binder is 50% to 67%.

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.

Deformation behavior of high performance fiber reinforced cementitious composite prepared with asphalt emulsion

A novel engineered cementitious composite(ECC) was prepared with the complex binder of Portland cement and asphalt emulsion.By adjusting the amount of asphalt emulsion,different mixture proportions were adopted in experiments,including four-point bending test,compressive test,and scanning electric microscopy(SEM).The SEM observation was conducted to evaluate the contribution of polyvinyl alcohol(PVA) fiber and asphalt emulsion to the composite toughening mechanism.The tests results show that the most remarkable deflection-hardening behavior and saturated multiple cracking are achieved when the content of asphalt emulsion is 10%.However,excessive content of asphalt emulsion causes severe damages on the deformation behavior as well as loss in compressive strength of the mixture.SEM observation indicates that the influence of asphalt emulsion on the fiber/matrix interfacial property changes the dominant fiber failure type from rupture into pull-out mode,and thus causes beneficial effects for strain-hardening behavior.

盐冻耦合环境下再生砖粉ECC的耐久性研究

利用再生砖粉取代工程水泥基复合材料(ECC)中的石英砂,制备再生砖粉ECC,采用混凝土快速冻融试验,研究了氯盐、硫酸盐及复合盐(氯盐+硫酸盐)溶液侵蚀作用下再生砖粉ECC的质量损失率和相对动弹性模量变化规律,建立了ECC在盐冻侵蚀环境下的损伤模型,并对其耐久性进行评价。结果表明:冻融循环300次后,再生砖粉ECC在清水、氯盐、硫酸盐及复合盐四种介质中的质量损失率分别为2.884%、4.984%、1.955%和6.891%,相对动弹性模量分别下降了6.468%、16.300%、24.303%和39.861%;再生砖粉ECC在单一盐冻情况下的抗冻等级大于F300,在复合盐冻情况下的抗冻等级大于F250,具有良好的抗盐冻性能;建立的冻融损伤模型可较好地反映ECC在不同冻融介质下的损伤度Dn与冻融循环次数的关系,可以为严寒地区的结构耐久性设计提供有效参考。

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。

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。

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。

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。

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 distributions and crack propagation of the composite columns in different states of eccentric compressive loading are analyzed. 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, compressive 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 loadcarrying capacity of the composite column with small eccentricity.

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。

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.

机制砂高延性工程水泥基复合材料(ECC)的性能研究

采用双因素方差分析法,研究了水胶比(0.30、0.35、0.40)和砂胶比(0.35、0.45、0.55)对工程水泥基复合材料(ECC)抗压和抗折强度的影响,优选出了最佳水胶比和砂胶比。在此基础上,研究了PVA纤维体积掺量(1.0%、1.5%、2.0%)和机制砂掺量(0、50%、100%)对ECC弯曲韧性的影响,并采用非线性回归法建立了预测模型。结果表明:ECC的最佳水胶比和砂胶比分别为0.30和0.55;掺入适量机制砂能在一定程度上提高ECC的峰值挠度,改善ECC的弯曲韧性;当PVA纤维体积掺量为2.0%、机制砂掺量为50%时,ECC的各项弯曲韧性指标相对最优;建立的机制砂高延性ECC峰值抗弯强度和峰值挠度预测模型的拟合精度较高,具有一定的适用性。

Numerical study on flexural behaviors of steel reinforced engineered cementitious composite(ECC) and ECC/concrete composite beams

Engineered cementitious composite(ECC)is a class of high performance cementitious composites with pseudo strain-hardening behavior and excellent crack control capacity.Substitution of concrete with ECC can largely reduce the cracking and durability problems associated with brittleness of concrete.In this paper,a simplified constitutive model of the ECC material was applied to simulate the flexural behaviors of the steel reinforced ECC and ECC/concrete composite beams with finite element method.The simulation results are found to be in good agreement with test results,indicating that the finite element model is reasonably accurate in simulating the flexural behaviors of the steel reinforced ECC flexural members.The effects of the ECC modulus,ECC tensile ductility,ECC thickness and ECC position on flexural behaviors in terms of ultimate moment,deflection and the maximum crack width of the steel reinforced ECC or ECC/concrete composite beam are hence evaluated.

Seismic behavior of precast concrete coupled shear walls with engineered cementitious composite (ECC) in the critical cast-in-place regions

The seismic performance of precast reinforced concrete(RC) coupled shear walls is significantly influenced by coupling beams and the beam-to-wall joints during large deformations into plastic ranges.This study investigated the use of engineered cementitious composite(ECC) in the cast-in-place beam-to-wall joints and the upper regions of the composite coupling beams as an innovative method to improve the seismic performance of precast RC coupled shear walls.Two 1/2-scale precast coupled shear walls were tested under reversed cyclic loading and seismic behavior in terms of failure characteristic,mechanical characteristic value,load-displacement hysteresis curves,load-displacement envelope relationship,stiffness degradation,ductility and energy dissipation capacity were evaluated.Research results show that the substitution of concrete with ECC in the critical cast-in-place regions proved to be an effective method to improve the seismic performance of the two-story spatial of precast RC coupled shear walls.

纤维编织网增强ECC夹心保温复合墙板抗弯性能

目前,夹心保温墙板已经被广泛使用在建筑保温结构中,但是墙板的饰面层通常采用普通混凝土,使得内部保温材料极易因外饰面开裂脱落而受到腐蚀.因此,选用纤维编织网增强工程水泥基复合材料(Engineered Cementitious Composites,ECC)作为饰面层,通过四点弯曲试验研究夹心保温复合墙板的抗弯性能,影响因素包括保温材料类型、保温层厚度、面层厚度、纤维编织网处理方式、有无连接件和连接件角度.结果表明:增大保温层厚度对墙板抗弯承载力和延性的影响不大,但能够提高墙板的组合程度;发泡聚苯乙烯(Expanded Polysty⁃rene,EPS)保温板与ECC基体的黏结性能更好,墙板的组合程度也更高,但EPS自身的受力性能和刚度较差,使得墙板的承载能力较低;纤维编织网经过浸渍和浸胶黏砂处理会降低墙板的承载能力,但浸胶黏砂处理能提高ECC基体与纤维编织网的黏结从而改善墙板的延性;连接件的存在能够提高墙板的组合性能,并且减小连接件角度或者增大面板厚度有助于提升墙板的抗弯刚度、承载能力和组合性能,但会导致墙板的延性下降.最后,推导了纤维编织网增强ECC(Textile Reinforced ECC,TRE)夹心保温墙板抗弯承载力计算公式,并将计算结果与试验结果进行对比,结果表明提出的计算方法具有一定的可行性.