Engineered Cementitious Composite Beams Research Articles

Torsional strength design method and cost analysis of FRP bars reinforced ECC beams without stirrups

Fiber reinforced plastic (FRP) bars reinforced engineered cementitious composites (ECC) beams without stirrups own excellent torsional performance and good application prospect. However, the corresponding torsional strength design method is not available. In order to predict the torsional strength of the ECC beams, a theoretical design method is established in this research. The proposed design method is based on the variable-angle space truss (VAST) model, and the tensile resistance supplied by fibers is carefully considered. The established design method is verified through the experimental results. It can be found that the predicted values agree well with the experimental values. A parametric analysis is carried out. Ultimate torque (i.e., torsional strength) increases significantly with the increment of ECC strength grade or longitudinal reinforcement ratio. However, at the same cross-section area, ultimate torque decreases slightly with the increment of height/width ratio. In addition, the cost effectiveness of the ECC beams without stirrups is discussed. Compared with mortar beam with a stirrup reinforcement ratio of 0.7%, FRP bars reinforced ECC beams without stirrups have small cost/ultimate torque ratio (a reduction ratio of 39.14%–60.86%), indicating that the ECC beams without stirrups own satisfactory cost effectiveness. This study will provide a torsional strength design guideline for FRP bars reinforced ECC beams without stirrups.

Shear behavior of low-cost and sustainable bio-fiber based engineered cementitious composite beams –experimental and theoretical studies

The design of reinforced concrete (RC) members subjected to shear dominant loading is complex due to their quasi-brittle failure nature. Hence, a highly ductile material as a replacement for conventional concrete is essential to perform well under shear loading. Engineered Cementitious Composite (ECC) is one such material designed based on micromechanical theory for achieving a high strain capacity of about 3%. The objective of the proposed research work is to develop a cost-effective ECC using bio-based natural fibers such as flax, hemp, kenaf, and pineapple for achieving a large strain levels under shear dominant loading. The test program consists of different ECC specimens with (a) 2.0% flax fiber, (b) 2.0% hemp fiber, (c) 2.0% kenaf fiber, and (d) 2.0% pineapple fiber. In addition, the ultimate shear capacity of natural fiber-based ECC beams are estimated theoretically using the AIJ method and the results are compared with the tests and FE predictions. Test results revealed that the use of flax fibers in ECC beams was highly effective in enhancing the ultimate load through an excellent crack-bridging mechanism when compared to the other natural fiber types. Also, the ultimate load predictions from analytical calculations matched well with the test results.

Self-healing and rebar corrosion performance of cracked engineered cementitious composites exposed to wet coral sand environment

Wet coral sand environment on islands and reefs features high humidity and abundance in aggressive fluids and gases, thus posing a great threat to the durability of reinforced concrete structures. In this study, engineered cementitious composites (ECCs) with strain-hardening and self-healing characteristics are proposed as a potential cover material in wet coral sand exposure. The autogenous self-healing capability of cracked ECCs was evaluated by the visual crack morphology as well as water permeability, and their rebar corrosion performance over a period of one and a half years was investigated based on electrochemical tests. The results show that cracks with initial width up to 70 μm are able to completely close within one day, probably due to the efficient precipitation of calcium carbonate and further hydration of cement. Compared with the uncracked control, the 0.4 %, 1.0 % and 1.6 % strained ECCs can be healed up to 100 %, 93.4 % and 60.5 % at 30 days, respectively. The water permeability coefficient of the strained ECC decreases rapidly in the first 30 days, and then stabilizes in the later stages. Moreover, the load-carrying capacity of preloaded ECC beams is recovered, exhibiting comparable performance to the uncracked controls after the same exposure periods. The corrosion current densities of steel bars suggest an active corrosion conditions. Both of the corrosion current densities and mass losses of rebar show lower values at decreased strain level, which is closely related to the width and number of cracks that reach the reinforcement.

Reliability-based design method for shear capacity of steel reinforced engineered cementitious composites (ECC) beams

Engineered cementitious composites (ECC) is famous for its excellent tensile deformability and crack width control ability. Steel reinforced ECC beams under shear loading exhibit brittle behaviors, which leads to a lack of structural safety. The reliability-based shear capacity model of steel reinforced ECC beams needs to be established for ensuring the structural shear safety. In this research, a test database of steel reinforced ECC beams under shear loading was constructed based on the given selecting principles. Through considering the shear resistance provided by fibers, the shear capacity model of steel reinforced ECC beams was preliminary established. The statistical characteristics of random variables were described and determined, and reliability index was calculated through Monte Carlo simulation. It is found that reliability index increases with increasing ECC strength, while decreases with increasing stirrup strength or stirrup ratio, especially at the high partial factor of ECC. For different target reliability indexes, the recommended partial factors of ECC are obtained through calibration. This research supplies a useful reference for the shear design of steel reinforced ECC beams in the actual engineering.

Peridynamic study of fatigue failure of engineered cementitious composites

Fatigue crack propagation is crucial in studying fatigue in engineered cementitious composites (ECC). This paper established a peridynamics (PD)-based fatigue crack propagation model for ECC, incorporating the “cycle broken bonds number” to enhance calculation efficiency. First, the PD fatigue crack propagation model was constructed, and the validity of the model was verified by simulating the fatigue crack propagation path of an inclined edge crack in the plate. Secondly, an improved PMB model considering the strain softening stage was used to model the ECC cement matrix, and the fibers were modeled as one-dimensional cyclic dynamic rods to establish a PD fully discrete model of ECC. At the same time, an interface exponential friction attenuation model was introduced. Then, the effectiveness and validness of the fully discrete model were verified by simulating single fiber pull-out tests and uniaxial tensile tests of ECC specimens. Finally, the fatigue crack propagation forms of ECC beams with mid span Type I cracks under three-point bending fatigue loads were studied, and the effects of fiber volume fraction, stress level, and fiber length on the crack propagation forms and structural deflection of ECC beams under four-point bending fatigue loads were investigated.

Size effect on flexural and fracture behaviors of 3D printed engineered cementitious composites: Experimental and numerical studies

One of major problems in 3D concrete printing (3DCP) is the integration of steel reinforcement. Engineered cementitious composites (ECC) with superior tensile properties have the potential to remove steel reinforcement in 3DCP. Interlayer interfaces may affect the size effect and fracture behaviors of printed ECC, which are important for structural design. Nevertheless, the related study is lacking. To fill the research gap, three-point bending test and finite element modeling (FEM) were conducted on printed ECC notched beams with depths from 60 mm to 500 mm. Results reveal that the printed ECC beams exhibit multiple fine cracks and display a branched critical crack. Size effect behavior is found in flexural strength, which decreases from 16.92 MPa to 10.89 MPa with the increase of depth from 60 mm to 500 mm. The fracture toughness ranges from 3.71 MPa·m1/2 to 6.38 MPa·m1/2, comparable to natural timber materials. Parametric analysis reveals that the flexural strength and fracture toughness of FEM model with a depth of 100 mm and bond strength higher than 2.5 MPa are similar to that of mold-cast ECC. The fracture toughness indicates the possibility to construct structural components with ECC in 3DCP, and the findings on size effect can facilitate the structural design.

Investigation on bond behavior of steel-FRP composite bars in engineered cementitious composites by spliced beam tests

The collaborative utilization of steel-FRP composite bar (SFCB) and engineered cementitious composites (ECC) represents a favorable choice for engineering structures exposed to aggressive environments, offering benefits involving both mechanical behavior and durability. This paper primarily studies the bond performance of SFCB embedded in ECC through spliced beam tests coupled with finite element analysis. The findings demonstrate that with an appropriate cover thickness or transverse confinement, spliced ECC beams exhibit failure modes characterized by splitting and pull-out. Under such conditions, the bond-slip response demonstrates limited sensitivity to changes in cover thickness and transverse confinement. Conversely, increasing the cover thickness or introducing transverse confinement in spliced concrete beams, which exhibit splitting failure, significantly enhances the bond strength. Furthermore, in contrast to spliced concrete beams, spliced ECC beams are observed to demonstrate a bond toughness that is 3.85–12.10 times greater. The discrepancy in bond toughness between ECC and concrete diminishes as the cover thickness and transverse confinement increase. Notably, the uniform distribution of bond stress in the splice region of ECC beams remains unaffected by variations in splice length. To incorporate the impact of bond stress distribution when calculating the splice length of SFCB in ECC beams, a coefficient of 0.85 is introduced.

Nacre-inspired design of engineered cementitious composite (ECC) beams for enhanced impact resistance and energy absorption

This paper presents an investigation into the flexural behaviour of bio-inspired engineered cementitious composite (ECC) beams under quasi-static and dynamic bending loads. These beams included a monolithic structure and three additional beams inspired by the structure of nacre. Three-point bending tests were conducted on the beams with different loading rates. The force-displacement response, failure modes, and energy absorption characteristics of these ECC beams were studied. The results indicated that the bio-inspired beams were more ductile, sustaining larger deformation, absorbed more energy, and were more resistant to impact than the monolithic beams. Specifically, under quasi-static bending, the bio-inspired beams sustained 150–300% larger maximum deformation and 55–195% higher energy absorption than the monolithic beams. Moreover, under dynamic bending, the layered beam incorporating polyurethane interlayers showed 27% more energy absorption than the monolithic counterpart. When surface asperities and steel wire mesh were incorporated, the energy absorption capacity was more than doubled.

Experimental investigation on seismic performance of plain engineered cementitious composite beams

The authors proposed using plain engineered cementitious composite (ECC) in construction without aligned reinforcement. In this study, ECC with a tensile strain capacity of up to 10% was produced, which has a comparable deformability level to steel reinforcement. To demonstrate the feasibility of plain ECC construction, five plain ECC beams and two steel reinforced concrete reference beams were prepared, and four-point bending reversed cyclic loading tests were conducted on the beam specimens. The experimental tests indicated that the plain ECC beams showed more stable hysteresis loops with improved energy dissipation capacity, deformation restoring capacity, and lower stiffness degradations than normal RC beams. Two categories of failure modes were observed, i.e., flexural failure mode and shear failure mode. With the increase in the shear span ratio, the failure mode of ECC beams changed from shear failure to flexural failure. Additionally, the increase in sectional dimension had a positive influence on the stiffness and energy dissipation capacity of ECC beams. It is experimentally verified that the plain ECC beams have sufficient load-bearing capacity under static and seismic loading.

Numerical investigation of the influence of casting techniques on fiber orientation distribution in ECC

Engineered cementitious composites (ECC), also known as bendable concrete, were developed based on engineering the interactions between fibers and cementitious matrix. The orientation of fibers, in this regard, is one of the major factors influencing the ductile behavior of this material. In this study, fiber orientation distributions in ECC beams influenced by different casting techniques are evaluated via numerical modeling of the casting process. Two casting directions and two casting positions of the funnel outlet with beam specimens are modeled using a particle-based smoothed particle hydrodynamics (SPH) method. In this SPH approach, fresh mortar and fiber are discretized by separated mortar and fiber particles, which smoothly interact in the computational domain of SPH. The movement of fiber particles is monitored during the casting simulation. Then, the fiber orientations at different sections of specimens are determined after the fresh ECC stops flowing in the formwork. The simulation results show a significant impact of the casting direction on fiber orientation distributions along the longitudinal wall of beams, which eventually influence the flexural strength of beams. In addition, casting positions show negligible influences on the orientation distribution of fibers in the short ECC beam, except under the pouring position.

Damage Monitoring of Engineered Cementitious Composite Beams Reinforced with Hybrid Bars Using Piezoceramic-Based Smart Aggregates.

In order to explore the crack development mechanism and damage self-repairing capacity of ECC beams reinforced with hybrid bars, the smart aggregate-based active sensing approach were herein adopted to conduct damage monitoring of ECC beams under cyclic loading. A total of six beams, including five engineered cementitious composite (ECC) beams reinforced with different bars and one reinforcement concrete counterpart, were fabricated and tested under cyclic loading. The ultimate failure modes and hysteresis curves were obtained and discussed herein, demonstrating the multiple crack behavior and excellent ductility of ECC material. The damage of the tested beams was monitored by smart aggregate-based (SA) active sensing method, in which two SAs pasted on both beam ends were used as actuator and sensor, respectively. The time domain analysis, wavelet packet-based energy analysis and wavelet packet-based damage index analysis were performed to quantitatively evaluate the crack development. To evaluate the self-repairing capacity of the beams, a self-repairing index defined by the difference of damage index at loading and unloading peak points was proposed. The results in time domain and wavelet packed analysis were in close agreement with the observed crack development, revealing the feasibility of smart aggregate-based active sensing approach in damage detection for ECC beams. Especially, the proposed damage self-repairing index can describe the same structural re-centering phenomena with the test results, showing the proposed index can be used to evaluate the damage self-repairing capacity.

Torsional behavior of BFRP bars reinforced engineered cementitious composites beams without stirrup

Engineered cementitious composites (ECC) is characterized by high tensile strain capacity and tight crack width control. The combination of ECC and fiber reinforced plastic (FRP) bars is expected to have better mechanical performance. This study aims to investigate the torsional behaviors of basalt FRP (BFRP) bars reinforced ECC beams without stirrup. Seven beams with different fiber contents and water to binder ratios were prepared and tested under pure torsion. BFRP bars reinforced ECC beams without stirrup and plain ECC beam exhibit a maximum crack width of less than 0.4 mm at service state, which meets the requirements of the corresponding codes for crack width. The ECC beams possess high ultimate torque and superior ductility performance as compared with reference beam with longitudinal bars and stirrups. It is noteworthy that minimum stirrup ratio may be not necessary in the torsional design of BFRP bars reinforced ECC beams. Moreover, an empirical formula is proposed for predicting the ultimate torque. The predicted values are consistent with the experimental results, indicating the effectiveness of the proposed formula. This study provides a helpful reference for the torsional design of BFRP bars reinforced ECC beams without stirrup.

Experimental and Numerical Investigation on the Shear Behavior of Engineered Cementitious Composite Beams with Hybrid Fibers.

The shear behavior of innovative engineered cementitious composites (ECC) members with a hybrid mix of polyvinyl alcohol (PVA) and polypropylene (PP) fibers is examined. The overall objective of the investigation is to understand the shear behavior of ECC beams with different mono and hybrid fiber combinations without compromising the strength and ductility. Four different configurations of beams were prepared and tested, including 2.0% of PP fibers, 2.0% of PVA fibers, 2.0% of steel fibers and hybrid PVA and PP fibers (i.e., 1% PP and 1% PVA). In addition to the tests, a detailed nonlinear finite element (FE) analysis was accomplished using the commercial ABAQUS software. The validated FE model was used to perform an extensive parametric investigation to optimize the design parameters for the hybrid-fiber-reinforced ECC beams under shear. The results revealed that the use of hybrid PVA and PP fibers improved the performance by enhancing the overall strength and ductility compared to the steel and PP-fiber-based ECC beams. Incorporating hybrid fibers into ECC beams increased the critical shear crack angle, indicating the transition of a failure from a brittle diagonal tension to a ductile bending.

Analytical and Numerical Investigation of the Behavior of Engineered Cementitious Composite Members under Shear Loads.

This research discusses the performance of engineered cementitious composite (ECC) beams with and without transverse reinforcements using thorough analytical and finite element (FE) approaches under shear. The overall goal of this investigation was to assess the impact of various design characteristics, such as (i) shear span-to-effective depth ratio, (ii) transverse reinforcement ratio, etc., on the shear behavior of ECC beams. Nonlinear three-dimensional (3-D) FE analysis was performed with the commercial software ABAQUS to simulate the shear performance of ECC beams by employing the material properties obtained from the damage plasticity model. The correctness of the proposed FE model was validated with the benchmark experiments available in the literature. The developed FE model accurately computed the ECC beam’s overall load–deflection behavior and failure modes. In addition, the provision available in the Architectural Institute of Japan (AIJ) A-method was successfully employed to assess the shear load-carrying capacity of ECC beams. Furthermore, the effects of transverse reinforcement (pw) and shear span-to-depth ratio (a/d) on the behavior of ECC beams were also investigated. From a detailed parametric study, it was understood that a decreased a/d ratio exhibits enhanced load-carrying capacity for beams with and without stirrups for a particular cross-section. It was also observed that for the entire a/d ratio, the amount of stirrups had no substantial effect on the load-carrying capability of ECC beams.

Experimental investigation of flexural behaviours of hybrid engineered cementitious composite beams under static and fatigue loading

Due to its superior flexural performance in both static and fatigue loading, hybrid engineered cementitious composites (ECC) has a high potential for application in structural components subject to repeated loads such as highway bridge link slabs. For such applications, properties of ECC in terms of flexural strength, ductility, cracking behaviour, and especially the fatigue life are key parameters that affect its performance. In this study, four-point bending tests were conducted on 36 hybrid ECC beams subject to static and fatigue loadings. In order to investigate the effects of different fibres contents, three types of hybrid ECCs with different polyethylene fibre (PE) and steel fibre (ST) volume fractions were tested. The experimental work was designed to study the flexural strength, ductility, fatigue life as well as the cracking behaviours of the beams. It is found that by using hybrid fibre, both the static and fatigue performances of ECC could be enhanced when compared with mono-fibre ECC with similar fibre content. Test results also indicated, among the three hybrid ECCs tested, the ECC with 1.25%+0.75% PE-ST fibre showed a balanced performance on ductility, flexural strength, cracking control performance and fatigue life.

Performance of Reinforced Engineered Cementitious Composite Beams

Performance of Reinforced Engineered Cementitious Composite Beams

Experiment and Research on Calculation Methods on Flexural Mechanical Behaviors of Non-Metallic Reinforced ECC Beams

Engineered cementitious composites (ECC) has high tenacity and the characteristics of strain hardening. In the bending test, ECC beams equipped with carbon fiber reinforced polymer (CFRP) in the tensile region show good deformation ability and bending ability. In this paper, the constitutive models of ECC and CFRP materials are established by uniaxial tensile compression test. Based on the plane section supposition, the analysis theory of bending capacity of cross section for ECC beams with non-metallic reinforcement is proposed. The calculation results are compared with the four-point bending test results. The results show that: (1) ECC beams with non-metallic reinforcement reflect the advantages of the two materials, and have strong deformation capacity before bending failure. (2) The calculation results based on the theory of flexural capacity of normal section are in good agreement with the experimental results, and the maximum error is less than 4%. The research results can provide the basis and reference for the calculation analysis and practical application of non-metallic reinforced high toughness material structure.

Prediction on the flexural deflection of ultra-high strength rebar reinforced ECC beams at service loads

To reduce the amount of reinforcement and control crack width, ultra-high strength rebar reinforced Engineered Cementitious Composites (UHSRRE) beams are considered a promising choice. A model is developed for predicting the flexure deflection of UHSRRE beams in service stage based on internal force equilibrium and the compatibility of deformation. In this model, the bilinear stress–strain model for Engineered Cementitious Composites (ECC) and ultra-high strength rebar is adopted, and the tensile zone of UHSRRE beams is considered. The flexure tests of seven beams with different reinforcing ratios and matrix materials are carried out for verifying the proposed model. It is observed that the experimental results are basically consistent with the predicted results. This model can provide a useful tool for the calculation of deflection. Additionally, parametric analysis is conducted to analyze the influence of reinforcement bars and matrix materials on the bending deformation of UHSRRE beams. Through comparison of the results, it is found that using higher strength grade bars not only reduces the amount of reinforcement but also maintains excellent bending performance.

Mechanical properties of engineered cementitious composites beams fabricated by extrusion-based 3D printing

Engineered cementitious composites (ECC) is emerging as promising candidate cementitious materials for 3D concrete printing (3DCP). This paper experimentally investigated the bending behaviors of 3D printed ECC beams with different geometric configuration. A novel mix design for ECC with ultra-high molecular weight polyethylene (PE) fiber was developed and the PE-ECC beams were casted by two methods, i.e., mold-cast and extrusion-based 3D printing. The four-point bending tests were conducted for plain ECC beams, reinforced concrete (RC) beams as well as cast-in-situ unreinforced ECC beam. The influences of different parameters including fabrication methods, print angles and superposition types were particularly investigated. The anisotropic mechanical properties under bending of printed beams and bending capacity of cast in place reinforced concrete beams were also investigated. Also, the strain distribution of longitudinal steel reinforcement in reinforced concrete as well as printed ECC beam were studied. The results indicated that the printed ECC beam presented a ductile failure mode accompanied with strain hardening behaviors. Also, the ECC beams exposed to z direction loading showed better mechanical anisotropic properties when compared with those exposed to x direction.

Influence of fibre type on the shear behaviour of engineered cementitious composite beams

The shear behaviour of large-scale engineered cementitious composite (ECC) beams reinforced with different types of fibre was evaluated. Four types of fibre were used: 8 and 12 mm long polyvinyl alcohol fibres (PVA8 and PVA12), 19 mm long polypropylene fibres (PP19) and 13 mm long steel fibres (SF13). An additional normal concrete (NC) beam of comparable compressive strength was cast and tested for comparison. The performance of all the test beams was evaluated through their load–deflection curves, cracking behaviour, first crack load, diagonal crack load, ultimate load, ductility and energy absorption capacity. The ultimate capacity and cracking moment of all the test beams were also compared with theoretical values estimated by some design code equations. The results indicated that, compared with the NC beam, all the ECC beams showed better performance in terms of cracking behaviour, shear capacity, ductility and energy absorption. The ECC beam reinforced with PVA8 fibres showed the highest shear strength and ductility of all the ECC beams with other polymeric fibres. Longer PVA fibres appeared to be less efficient than shorter ones. The beam reinforced with PP19 showed the lowest performance, while the use of SF13 proved to be the most effective in improving the first crack load, ultimate load, ductility and energy absorption capacity.