Engineered Cementitious Composites Material Research Articles

Hybrid strengthening of RC beams with externally bonded carbon fiber reinforced polymer laminate and engineered cementitious composites transition layer

This paper presents the experimental study on the reinforced concrete (RC) beam strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) laminate and engineered cementitious composites (ECC) material. A total of six beams were tested under the four-point bending test to investigate the influence of strengthening scheme, type of CFRP laminate and the width of CFRP plate on the flexural response. The results revealed that hybrid strengthened beam with the technical of EB-CFRP and ECC transition layer significantly enhanced the crack load (29.0%–133.3%), yield load (50.9%–96.5%) and ultimate load (50.0%–81.9%) of the beams relative to the control beam. The employment of ECC material was an ideal transition layer for delaying the interfacial debonding of CFRP laminate, where the ultimate tensile strain of CFRP plate in hybrid strengthened beams was 13.2%–33.33% higher than that of beam merely strengthened with EB-CFRP plate. Beams strengthened with CFRP sheet had the greater flexural performance and higher utilization of CFRP than its counterparts strengthened with CFRP plate. Moreover, the predicted model associated with ultimate bearing capacity of the hybrid beams was provided based on ACI 440.2R-08, which was relatively conservative with a margin for the ultimate load of the hybrid strengthened beams.

Anisotropic size effect of 3D printed LC3-based engineered cementitious composites (LC3-ECC)

One of the critical factors affecting the development of 3D concrete printing (3DCP) is the challenging issue of in-situ reinforcement. Engineered Cementitious Composites (ECC) are printable self-reinforced materials, and their application in 3DCP technology can facilitate de-steelisation. However, traditional ECC materials pose certain concerns for sustainable environmental development. The integration of Limestone Calcined Clay Cement (LC3) suitable for 3DCP into ECC (LC3-ECC) presents an ideal solution to the aforementioned challenges. Moreover, conducting comprehensive research into its size effects is an essential step from experimentation to engineering application. A thorough exploration of the size effects of 3D printed LC3-ECC in compression, shear, and flexural fracture aspects is conducted to derive size effect laws. The relationship between the anisotropic mechanical properties and size effects has been established. The mold-cast LC3-ECC precisely follows the Bažant size effect law (SEL). The fiber orientation effect enhances bridging efficiency, leading to the fact that the mechanical properties of certain printed LC3-ECC are hardly affected by the size effect. The mechanical performance of some printed LC3-ECC depends on interlayer strength, making its primary reason for size effect not in the Fracture Process Zone (FPZ) energy release, hence closer to the Multifractal Scaling Law (MFSL). LC3-ECC exhibits weak anisotropy in mechanical properties, showing satisfactory stability. However, under flexural fracture behavior, the anisotropic size effect is higher, necessitating careful consideration in structural design.

Tension-shear characteristics, cost and environmental impact of polyethylene fiber reinforced engineered cementitious composites: The role of fiber content

Engineered cementitious composites (ECC) tailored with fibers is famous for distinguished tensile ductility and tight crack width control capacity. The ECC material of the structural members may be in the state of tension-shear stress, e.g. ECC in the shear span of beams. Accordingly, this research focuses on the characteristics of ECC with diverse polyethylene (PE) fiber contents (0.5%, 1.0%, 1.5% and 2.0%) under tension-shear loading. The basic characteristics of PE-ECC subjected to uniaxial tension, uniaxial compression and pure shear were tested. The tension-shear behaviors of PE-ECC subjected to various loading angles were investigated by an elaborately designed test fixture. PE-ECC with the fiber content of over 1% exhibited obvious multiple-cracking phenomenon when subjected to tension-shear loading, and crack number decreased as loading angle continued to raise. The tension-shear strength for PE-ECC was enhanced by increasing fiber content. The failure criteria stemmed from the octahedral stress space (linear function) or stress invariant can be applied for depicting the failure laws of PE-ECC. Additionally, cost comparison and environmental impact evaluation indicated that fiber cost accounted for a significant higher proportion of the total cost (over 36%), while the proportion of fiber carbon footprint to the entire carbon footprint was low (less than 12%). This research will provide a useful assistance in understanding the tension-shear behaviors of PE-ECC and further facilitating its structural applications.

Theoretical and finite element analysis of engineered cementitious composite (ECC) link slab in hollow slab beam bridge base on different load conditions

In order to reveal the feasibility of engineering cementitious composite (ECC) link slab applied to hollow slab beam bridge, the construction process of ECC link slab was simulated based on the birth-death element method and tracking element. Nonlinear analyses of ECC link slab under six load conditions were carried out based on Chinese bridge code. The theoretical formulas are derived and calculated for three of the unfavourable conditions. Finally, the effects of five support conditions on ECC link slab were analysed. The results show that the maximum tensile stresses of the ECC link slab under the overall cooling and negative temperature gradient are 3.569 MPa and 3.440 MPa, and the ECC material has entered plasticity. Theoretical calculations and finite element (linear) results are similar and conclude that temperature-induced axial deformation is the main cause of ECC link slab damage, especially the overall cooling and negative temperature gradient. At the same time different support conditions do not change this result, but rubber bearings can well improve the force behaviour of ECC link slab due to its good deformation coordination ability.

Reinforced ECC-UHPC-SCC composite modular framed shear wall systems under lateral cyclic loading

The shear strength and deformability of high performance reinforced composite framed shear wall systems made of Engineered Cementitious Composite (ECC), Ultra-High-Performance Concrete (UHPC) and Self-Consolidating Concrete (SCC) subjected to lateral cyclic shear loading to failure were investigated. A total of seven framed shear wall specimens were constructed using combinations of ECC or SCC wall, SCC frame and ECC or UHPC frame joints. The performance of such novel modular forms of walling systems were compared based on experimental results in terms of cracking, failure mode, hysteretic shear load-deformation response, shear load capacity, ductility, bearing capacity degradation, stiffness degradation, dissipated energy, viscous damping capacity, induced wall shear stresses and strain development characteristics. ECC walling system exhibited better structural performance compared to their SCC counterparts showing up to 40% higher load capacity forming significantly higher number of closely spaced diagonal cracks with up to 72% lower crack shear stress, 14% to 21% higher ductility, up to 2 times higher energy dissipation capacity and lower rate of stiffness/bearing capacity degradation through both hysteretic and damping actions. The incorporation of ECC and ECC or UHPC joint in frame significantly improved shear strength capacity of infill wall and overall framed shear wall system. ECC incorporated framed shear walls even with frames made of SCC and UHPC joints also exhibited superior performance. This study confirmed the superior performance of ECC material for the construction of reinforced framed shear wall with boundary frame made of ECC/SCC/UHPC combinations for better seismic resistance.

Structural Behavior of Precast Monolithic Composite Beams with ECC Prefabricated Shells

Engineered Cementitious Composite (ECC) was used in the prefabricated shell of a precast composite beam, and the validity of the ECC in the precast monolithic composite beam’s flexural performance was studied. Flexural performance tests were conducted on six specimens to analyze their failure state, failure mechanism, bearing capacity, and deformation capacity. Compared with the Reinforced Concrete (RC) prefabricated shell composite beam, the ECC prefabricated shell composite beam showed a higher bearing capacity and lower damage degree. The yielding load of specimen PSMCB−1 increased by 5.6%. The maximum load of specimen PSMCB−1 reached 256.6 kN, having increased by 8.1%. When the tests stopped, the maximum crack width of specimen PSMCB−1 was 4.1mm, while the maximum crack width of specimen PSMCB−6 reached 9.0 mm. The ECC material in the prefabricated shell also delayed the yielding of the steel bars in the shell.

Investigation on effect of ECC coverage condition on seismic behavior of beam-column joint

There is a renewed interest around the world to do fundamental research on novel materials to enhance the overall response of structures under seismic loading. Engineered cementitious composite (ECC) is a special class of concrete with good ductility, which is widely adopted in engineering structures. In this paper, the seismic behavior of beam-column joints incorporated with ECC materials is numerically and experimentally investigated. A database containing available related test results in literature is collected and analyzed to investigate the relations between ECC coverage area and failure characteristics. An interior and an exterior beam-column joint with ECC adopted in the joint region are prepared and tested in this study. The effect of ECC coverage area on the overall joint seismic response is analyzed through a validated finite element model. A modified strength hierarchy analysis is proposed and conducted to consider the application of ECC on the joint. Based on the analytical investigation, the weakest structural element in the joint region is found. The strength hierarchy analysis results have a good correlation with the experimental failure pattern, which shows a potential application as a preliminary analysis to evaluate ECC joint failure mechanisms under seismic loading.

Performance enhancement of engineered cementitious composite through tailoring recycled iron sand

Engineered cementitious composite (ECC) possesses predominant tensile properties while a relatively low modulus of elasticity (MOE) due to the low sand-to-binder ratio and fine quartz sand (QS, QS-ECC). Further, the excessive consumption of QS in concrete industry has imposed a serious challenge to natural resource preservation. Iron sand (IS), a by-product of the iron industry with high particle modulus, could be a potential alternative in developing ECC (IS-ECC). This research focused on recycling IS as fine aggregate to develop a sustainable ECC with high mechanical performance, especially high MOE. The influences of water-to-binder ratio, sand-to-binder ratio, and IS particle size were systematically investigated. The results indicated that all the IS-ECC demonstrated robust tensile performance with the tensile strength and strain capacity over 5 MPa and 5%, respectively. Compared with the QS-ECC, a comparable or even superior compressive strength was achieved by all the IS-ECC. Impressively, the MOE of IS-ECC with 20–40 and 40–80 mesh of IS particles exhibited 68% and 60% higher than that of QS-ECC, respectively. SEM observations well reflected the macroscopic tensile performances. The cost and environmental effect analysis revealed the sustainability of IS-ECC. This research provides the groundwork for promoting the utilization of IS in developing high performance ECC material.

Seismic performance analysis of long-span continuous rigid frame bridge with Engineered Cementitious Composite at expansion joints

In this paper, OpenSees software is used to establish a numerical simulation analysis model of a long-span continuous rigid frame bridge with Engineered Cementitious Composite (ECC) expansion joint reinforcement scheme. The seismic response characteristics and laws of structures with ordinary concrete and ECC concrete at expansion joints are compared and analyzed, and their seismic performance is evaluated. The results show that the use of ECC material at the beam end position can effectively reduce the peak response of the structure under earthquake action and reduce the number of collisions. ECC material has a strong energy dissipation capacity and can reduce the collision damage of the beam section near the bridge expansion joint under earthquake action.

Enhancement in performance of RC beam-column joint under cyclic loading by using various grades of engineered cementitious composites in the joint zone-a sustainable numerical study

In this research, the response of the RC Beam-Column Joint under the cyclic loads was analyzed with a FEM solver (Abaqus) by using various grades of Engineered Cementitious Composite (ECC) in the joint zone. The concrete damage plasticity model for concrete and ECC material under cyclic loading was proposed. Accordingly, the Finite Element Analysis (FEA) model was established with the consideration of different constitutive material models for concrete and Engineered Cementitious Composites. The accuracy of the proposed FEA model was validated with the experimental results. Failure mechanism, crack propagation, moment rotation relationship, and energy absorption under cyclic loading were investigated. Under controlled deformation, cyclic loads were applied to the samples at the end of the beam up to the failure point. It was found that the use of various grades of Engineered Cementitious Composites in the joint zone was effective in enhancing the ultimate moment capacity upto 38.50%, ductility upto 13.72%, and siffniness degradation upto 28.57% respectively of the joint up to the failure stage alongwith significant reduction in crack propagation.

Numerical and experimental analysis in seismic performance of post-earthquake reinforced concrete frame retrofitted with ECC

In order to further demonstrate the effectiveness of engineered cementitious composites (ECC) in repairing and strengthening the post-earthquake damaged structure, at the overall structural level, experimental and numerical comparative analysis of structural seismic performance before and after “retrofitted with ECC” is conducted in this paper. A 1:2-scale reinforced concrete frame is tested under cyclic reversed loading and a new ECC material’s constitutive model is proposed in this paper for improving the accuracy and feasibility of numerical modelling. The modelling method and newly proposed constitutive model of ECC has been demonstrated to be workable and accurate. Based on numerical and experimental data, the increase of the average yielding displacement after the installation of ECC is relatively significant (80.4% to 156.4%), and the repairing method using ECC in post-earthquake damaged RC frame can restore and even exceed the original frame’s load bearing capacity. Comparing the ultimate inter-story drift ratio, the ratio with ECC is about 31.0% higher, indicating that ECC has good deformation capacity and the usage of ECC is indeed an effective method to improve deformation capacity in repairing and strengthening post-earthquake damaged structures. The results confirm the effectiveness and superiority of retrofitting ECC in post-earthquake damaged structures for the reason that the repaired structure can reach the same level of seismic performance as the original structure. The “repairable” characteristic can be used in the design of earthquake resilient structures.

Study on the physicochemical properties of Chinese PVA fibers: Toward low-cost cement-based composites

Engineered Cementitious Composites (ECC) reinforced by Japanese Polyvinyl Alcohol (PVA) fiber showed excellent tensile ductility, which attracted much attention in the field of civil engineering in recent years, but the application was still limited by cost. There were quite a few kinds of low-priced PVA fibers in China, with a tremendous difference in physical and chemical properties. In this paper, a variety of typical PVA fibers produced in different regions in China were compared with the products imported from Japan to analyze the performance differences, especially the dispersion and enhancement effect in fiber reinforced cement matrix composites. Combining with the physical and chemical characteristics of each fiber, the relationship between the characteristics of fibers and the properties of composites was summarized. The experimental results illustrated the strength and interface characteristics of PVA fibers were the dominating influencing factors to the bending and tensile properties of PVA-ECC, while hardly affected the compressive strength. Insufficient intrinsic strength of fibers significantly decreased bending resistance and tensile strength. Excessive oil agent treated PVA fibers performed lower interfacial reaction with the cement matrix, meanwhile original PVA fiber with high hydrophilicity was not conducive to the dispersion and bridging function. The appropriate interface treatment approach could guarantee the fibers to achieve the sliding pull out bridge connection, and also meet the high slip strengthening effect, leading to the multi-seam cracking and strain hardening characteristics of ECC material. This work provided the preparation of low-cost cement-based composites, guiding the selection of fiber raw materials in ECC.

Engineered cementitious composites design framework for pavement applications

Engineered cementitious composites (ECCs) have gained attention as a potential material alternative for extending the lifespan of pavements and overlays due to their exceptional mechanical strength and ductility. This study presents a novel thickness design framework that incorporates the elastic and plastic regimes of ECCs, along with a wide range of mechanical properties, to develop general thickness design equations for the fatigue failure mode of ECC pavements. The pavement thickness design framework proposed in this study integrates three components: (1) experimental models characterizing the beam flexural fatigue performance of ECC materials; (2) Finite Element (FE) analysis to quantify the stress response of ECC pavements under vehicular loading; and (3) empirical stress equivalency functions to combine the FE analysis results with the beam flexural fatigue models and predict the fatigue life of ECC pavements during the plastic regime. Using the proposed framework, two general thickness design equations predicting the service life of ECC pavements were developed, one for the elastic regime and one for the plastic regime of ECCs. The thickness design equations developed are in terms of ECC material properties and empirical coefficients, which can be determined through experimentation and modeling. The analysis of the results indicates that the proposed framework provides a more accurate representation of the service life of ECC pavements, particularly during the plastic deformation regime, compared to previous design frameworks discussed in the literature.

Generative AI for performance-based design of engineered cementitious composite

Engineered cementitious composite (ECC) has been intensively studied due to its excellent tensile performance. However, classical micro-mechanical design theory of ECC is qualitative and fails to give detailed ECC mixtures at specific tensile parameters. This study aims to develop a performance-based mixture design model to generate ECC mixtures using generative AI method. An experimental database consisting of 129 polyethylene fiber reinforced ECC (PE-ECC) records has been built. The database was used to train one invertible neural network model and two artificial neural network models. A series of PE-ECC mixtures were generated by the proposed model based on desired mechanical performance and sustainable requirements. Based on the experimental results, the developed model was proven to compose PE-ECC mixtures that satisfy the target requirements with a maximum deviation of less than 16%. The neural network-based model can be used in various application scenarios (e.g., low-cost ECC and low-carbon ECC), thus promoting the development of ECC materials in the area of research and engineering application.

Non-destructive tests to evaluate the self-healing capacity for a 3D printing ECC material

The conventional construction sector is the one that generates CO2 emissions, as well as waste generation. Faced with this problem, 3D printing has positioned itself as an alternative. Therefore, in recent years, interest in cement-based material for 3D printing has increased in the construction sector as a partial or total replacement for conventional construction methods. However, 3D printing, despite being a novel technique, has some drawbacks, one of the biggest threats being the generation of cracks or microcraks that appears by the transport or the design of the 3D printed figures. These cracks can cause major structural and durability problems in the final application. Numerous materials have been developed to meet the requirements of 3D printing. Nevertheless, there are few publications on materials that are able to be printed in 3D and have an autogenous self-healing capacity. Therefore, in this study, we are working on the development of an Engineered Cementitious Composites (ECC) material, also known as Strain Hardening Cementitious Composites (SHCC) that has the characteristics to achieve structural integrity, durability, reliability, and robustness of 3D printing (ECC-A3D).This paper describes the experimental procedure of an ECC material in two different environments (at room temperature, 34 ± 2% RH and 20 ± 2 °C, and curing chamber 98 ± 2% RH and 20 ± 2 °C). The characterization of the ECC-A3D material is studied by fresh properties, consistency, open time, extrudability and buildability and hardened properties, compressive and flexural strength up to 90 days. A 3D printing material has been achieved that reaches a value of 16.54 MPa and 50.82 MPa in flexural and compression at the hydration age of 28 days at room temperature, and 17.13 MPa and 58.26 MPa in curing chamber. The self-healing behavior of ECC is evaluated by three non-destructive methods: absorption and sorptivity tests, optical microscopy, and micro-computed tomography, confirming a reduction in absorption and crack healing during hydration time.

The Effect of ECC Materials on Seismic Performance of Beam—Column Subassemblies with Slabs

The main objective of this investigation was to study the influence of an Engineered Cementitious Composite (ECC) on the seismic performances of beam–column–slab subassemblies. Tests and simulations were conducted on several models. The bearing capacity of the ECC model was 15% higher than that of the RC member, the deformability increased by 19%, and the energy dissipation capability increased by 34%. The use of an ECC in the slab could reduce the contribution of the reinforced bars in the slab to the flexural strength of the beam. At a drift of 2%, the range of the yielding bars in the slab of the RC models was 5h to 6h. However, the yield range of reinforcement in the slab of the ECC models was nearly 3h. As a result, the ECC subassemblies were prone to reach a “strong column and weak beam” yield mechanism.

Repair of fire-damaged RC square columns with CFRP textile-reinforced ECC matrix

Fiber-reinforced polymer (FRP) textile reinforced engineered cementitious composite (ECC) matrix (TRE for short) is a newly developed composite system with great potential for the strengthening and life extension of damaged reinforced concrete (RC) columns after fire exposure. It combines the advantages of the lightweight and high strength of FRP textile and the ultra-high ductility of ECC material. However, there is a lack of research on the use of the TRE system to strengthen fire-damaged RC columns. This paper presents an experimental study on the axial compressive behavior of fire-damaged square RC columns strengthened with the TRE system. A total of 13 specimens were prepared and tested under axial compression. The test variables included the fire-exposure time (2 h or 3 h) used to produce the initial pre-damage of RC columns, the type of cementitious matrix (ECC or mortar), the number of TRE layers (2 layers or 3 layers), and the thickness of the concrete cover (20 mm or 40 mm). The failure modes, load capacity, secant stiffness, ultimate displacement, load–displacement curves of the specimens and the hoop tensile strains in the outermost layer of the CFRP textiles were investigated and discussed. The typical failure mode of the strengthened specimens was characterized by tensile rupture of the fiber rovings bridging the main crack in the strengthening jacket. The results showed that the use of the TRE system could significantly increase the load capacity, secant stiffness and ultimate displacement of fire-damaged RC columns. Depending on the design parameters, the enhancement percentages in the load capacity varied between 18% and 126%.

Study of self-healing at large ages for a 3D printable ECC material

The conventional construction sector is the one that generates CO2 emissions, as well as waste generation. Among all new construction techniques, 3D printing has emerged as an alternative since it is capable of mitigating these inconveniences and has a number of advantages, such as speed of construction and design flexibility. As a result, interest in 3D printing has increased in recent years as a total or partial replacement in the construction sector. Nevertheless, 3D printing has some drawbacks; one of the biggest threats is the generation of cracks or microcracks that appears during the transport or the design of the 3D printed figures. These cracks can cause major structural and durability problems in the final applications.Numerous materials have been developed to meet the requirements of 3D printing. One of the possible developing materials is the ECC (Engineered Cementitious Composites) since it has the capacity for autogenous self-healing, that is, the material presents in its composition the capacity to reduce and heal the possible cracks that are generated. The main goal is to evaluate the self-healing behavior of the 3D printed material (ECC-A3D). This material has the characteristics to achieve structural integrity, reliability, and robustness of 3D printing.In previous stages of research, an ECC-A3D material has been developed having the characteristics to achieve the structural integrity, reliability, and robustness of a 3D printed material. This paper describes the experimental procedure of the evaluation of the self-healing behavior of the ECC-A3D in two different curing conditions (at room temperature, 35 ± 2% RH and 20 ± 2 °C, and curing chamber at 98 ± 2% RH and 20 ± 2 °C). Hardened properties are researched via compressive and flexural for up to 90 days. Meanwhile, the self-healing behavior of ECC is investigated by mechanical recovery test, and absorption and sorptivity tests.This study presents the results of the tests in a hardened state and shows the results that confirm the autogenous healing of ECC material in two different environments.

Study on the performances of fire-resistive engineered cementitious composites (ECCs)

The high ductility of fire-resistive engineered cementitious composites (ECC) makes it possess better cohesive performance than the traditional cement-based fireproof material, and improves the cracking and delamination between the fireproof material and the substrate material. In this paper, the tensile and compression properties, dry density, heat insulation properties, and high temperature resistance of the prepared fire-resistive ECC materials were systematically studied, and the heat transfer behavior in the heating process was studied by means of small-scale fire resistance test. The results demonstrate that the prepared fire-resistive ECC materials possess both the favorable thermal insulation properties and adequate mechanical properties. Meanwhile, compared with traditional cementitious fireproof materials, better high temperature stability of prepared fire-resistive ECC avoids the failure due to the deterioration of mechanical properties during heating process. Then the reduction of temperature rising rate and equilibrium temperature shown in small-scale fire resistance experiments verifies that it can effectively improve the fire performance of the structure under actual fire. Finally, with the help of microscopic experiments the action mechanism of the porous fillers on the ductility and fire performance of fire-resistive ECC materials were explored.

Performance of engineered cementitious composite (ECC) monolithic and composite slabs subjected to near-field blast

To improve the performance of reinforced concrete (RC) structural members subjected to blast, especially the spalling due to the brittleness of concrete, engineered cementitious composite (ECC) was applied in monolithic and composite slabs and their responses subjected to near-field blast were experimentally investigated in the present study. First, two different ECC materials were prepared and tested with quasi-static direct tension and flexural tests, whose results showed significantly improved tensile ductility and strength compared to normal concrete. Then a field test was conducted to investigate the response of ECC monolithic and composite slabs under near field blast, with an RC slab as reference. The responses of these slabs were compared in terms of response mode, residual deformation, crack initiation and development, spalling, strain time history, etc. The test observations suggested that in addition to the ductile response and failure of ECC subjected to quasi-static direct tension and flexural tests, ECC still exhibited ductile response at high strain rate when applied in monolithic and composite slabs under near field blast. Compared to the perforation and spalling of RC slab, the ECC monolithic or composite slabs underwent large deformation, until collapse failure with a major crack in the mid-span occurred. Importantly, throughout the whole response process, even the ECC monolithic and composite slabs collapse with a major crack at mid-span, no spalling was observed. Furthermore, no delamination occurred in the interface between the RC and ECC layer of the RC/ECC slabs. Both the ECC monolithic slab and RC/ECC composite slab exhibited favorable performance subjected to near-field blast. These observations implied that the ECC is promising in the potential application of structural protection against blast, not only for replacing certain key components in the newly built structures but also for retrofitting existing RC structures.