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Engineered Cementitious Composites also known as Strain‐hardening cementitious composites (SHCCs) has unique cracking patterns like cracks that have tiny widths and showcase high density. All of this makes it difficult and laborious to compute crack parameters from crack patterns. Unfortunately, this is an essential part of assessing durability and micromechanical modeling. SHSnet is developed to perform end‐to‐end semantic segmentation of SHCC cracks. SHSnet is efficient, attention based deep encoder‐decoder network with large receptive field. Loss function based on Tversky function were used for training the model. SHSnet with loss function shows promising result with mPrecision, mF1Score and mIoU of 0.87, 0.84 and 0.83 respectively for complex SHCC cracks while requiring at least an order of fewer computational parameters than those in the literature. An image processing unit is then used to estimate the width, number, and length of the cracks from the segmentation mask. Test results show that the computed crack parameters with SHSnet are exactly the same as that computed with an optical microscope but require ~100× less time. Results demonstrate that SHSnet works equally well in SHCCs with different surface textures, crack density, and widths; the final result was far superior to a conventional technique. This technique also shows promising results in an automatic evaluation of crack parameters relevant to durability and visualizing crack patterns even in the presence of artifacts during progressive testing. The results also demonstrate the necessity to accurately and densely calculate crack length and maximum crack width; else the durability results are expected to be significantly more conservative than the actual value. [ABSTRACT FROM AUTHOR]

Composite concrete structures are designed to integrate various concrete types at different levels, thereby improving their shear properties. In this paper, the effects of the interfacial keyway, reinforcement ratio, and pouring sequence on the shear strength of concrete-coal gangue concrete interface are studied by experiments and analyses. A total of 10 specimens were made, and the push-off test was carried out. Nonlinear finite element simulation was carried out using ABAQUS, and the influence of keyway angle on crack development was studied based on the extended finite element method (XFEM). It is found that the remarkable tensile and crack stability of engineered cementitious composites (ECC) has a positive effect on the shear strength of the ECC-coal gangue concrete interface. The ultimate shear strength of the interface and the ductility of the interface under shear load are significantly improved by interfacial shear reinforcement. The introduction of an interfacial keyway improves the shear strength of the concrete interface, and the number of keyways has the most significant effect on the interfacial shear strength. The angle between the crack propagation direction and interface will increase with the increase of keyway angle, the simulation results are in good agreement with the experiments. [ABSTRACT FROM AUTHOR]

Engineered cementitious composites (ECCs) have garnered significant attention within the construction industry, owing to their exceptional mechanical properties and durability. This thorough review presents a meticulous analysis of the progress and prospects in ECC research. It begins by introducing the background and rationale for investigating ECCs, while outlining the objectives of the review. The review provides an encompassing overview of ECCs, encompassing their definition, characteristics, historical development, composition and constituent materials. Emphasis is placed on the examination of ECCs' mechanical properties, specifically their flexural behaviour, tensile behaviour, compressive strength and resistance to environmental factors. Furthermore, the rheological properties of ECCs, including workability, flowability, self-healing, crack mitigation, viscosity and thixotropy, are discussed in detail. The review delves into the influence of fibre reinforcement on ECCs, encompassing the types of fibres utilised and their impact on mechanical and structural properties, as well as fibre dispersion and orientation. Additionally, it explores the diverse applications of ECCs across various fields, such as structural applications and sustainable building practices. The challenges and limitations associated with ECCs, such as cost and availability, are addressed, alongside an exploration of future trends and research directions. [ABSTRACT FROM AUTHOR]

The presentation of a constitutive model could help researchers to predict the mechanical behavior of a material, which also contributes to the further generalization of the material. This paper is to explore the tensile constitutive model of engineered cementitious composites (ECCs) reinforced by high-strength steel wire mesh based on experiments and numerical simulations. DIANA was used to simulate the tensile process of the specimens, and experiments were carried out to validate the numerical model. The effect of the ECCs' tensile strength, reinforcement ratio and specimen size were considered during the specimen design process. The results showed that most of the errors of the simulated values compared to the experimental results were within 5%, which proved that the numerical model was quite accurate. The proposed constitutive model revealed the different roles played by ECCs and high-strength steel wires at different stress stages, and the calculation results were in high agreement with the simulation results, indicating the effectiveness of the constitutive model. The study in this paper could provide an important reference for the popularization and application of ECCs reinforced by high-strength steel wire mesh. [ABSTRACT FROM AUTHOR]

At present, engineered cementitious composites (ECC) are rapidly replacing ordinary concrete in the building production due to its superior durability and mechanical qualities. Enormous researches have been done on ECC incorporating various fibers, industrial wastes, supplementary cementitious materials and super plasticizers. As far as fiber is concerned, poly vinyl alcohol fiber was widely explored. In this study, attempt has been made to involve alkali resistant glass fiber as a replacement for poly vinyl alcohol fiber. In addition, the high rate related with ECC as a result of the utilization of micro‐sized silica sand has restricted its extensive pertinences. Thus, this study recommends utilization of quarry dust to replace fine silica sand in the ECC at amounts ranging from 0% to 100% in order to establish a green, sustainable and cost‐effective ECC. The flowability and mechanical demeanor of the ECC mixtures in terms of the tensile, compressive and flexural properties were evaluated. It is arrived that 2% of volume fraction would be the optimum dosage by which better mechanical properties can be achieved. As a result of the present research findings, it is found that the quarry dust could be a better substitute for silica sand up to 75% without any compromise in compressive and flexural strengths. To attain higher tensile qualities, however, it might not be appropriate to replace more than 50% of the silica sand with quarry dust. Cost analysis of the ECC mixtures show that using quarry dust as aggregate is both cost‐effective and sustainable. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study that investigates the mechanisms of shear resistance in reinforced concrete (RC) beams that are shear-strengthened with engineered cementitious composites (ECCs) and fiber-reinforced polymer (FRP). The ECC FRP utilizes ECC as the bonding agent between the FRP and concrete and the FRP as the high-strength reinforcement. The test program was divided into three groups: (1) 15 dog-bone shaped ECC FRP coupons; (2) 27 ECC FRP push-off blocks; and (3) two ECC FRP shear-strengthened RC beams 125 mm wide, 300 mm high, and 2,640 mm long. Groups 1 and 2 aimed at investigating the uniaxial tension and push-off behavior, respectively, by simulating the crack separation and sliding mechanisms. These mechanisms are fundamental to understanding the shear resistance of the ECC FRP and are characterized by the applicable tensile stress–strain and shear stress–sliding laws. The embedded FRP mesh in the ECC FRP composites significantly enhances the crack sliding that is required for shear strength development, with a minimal impact on the tensile and shear strengths. In addition, the precrack width reduced the shear strength of the ECC FRP. Group 3 aimed to investigate the shear behavior of the ECC FRP beams. The crack width and sliding were monitored during loading, which provides insights into the shear contributions from the concrete, steel stirrups, and ECC FRP. The results reveal a major shift in the shear capacity contribution from the concrete to the ECC FRP in the strengthened beams, which led to a substantial shear improvement. The contributions of the ECC FRP to shear resistance by crack separation and sliding were comparable throughout the loading process. The FRP meshes in the ECC FRP composites effectively limited deformation, maintained structural integrity, and redistributed the shear capacity from the ECC FRP to concrete. [ABSTRACT FROM AUTHOR]

Abstract The present study introduces a novel approach utilizing machine learning techniques to predict the crucial mechanical properties of engineered cementitious composites (ECCs), spanning from typical to exceptionally high strength levels. These properties, including compressive strength, flexural strength, tensile strength, and tensile strain capacity, can not only be predicted but also precisely estimated. The investigation encompassed a meticulous compilation and examination of 1532 datasets sourced from pertinent research. Four machine learning algorithms, linear regression (LR), K nearest neighbors (KNN), random forest (RF), and extreme gradient boosting (XGB), were used to establish the prediction model of ECC mechanical properties and determine the optimal model. The optimal model was utilized to employ SHapley Additive exPlanations (SHAP) for scrutinizing feature importance and conducting an in-depth parametric analysis. Subsequently, a comprehensive control strategy was devised for ECC mechanical properties. This strategy can provide actionable guidance for ECC design, equipping engineers and professionals in civil engineering and material science to make informed decisions throughout their design endeavors. The results show that the RF model demonstrated the highest prediction accuracy for compressive strength and flexural strength, with R2 values of 0.92 and 0.91 on the test set. The XGB model outperformed in predicting tensile strength and tensile strain capacity, with R2 values of 0.87 and 0.80 on the test set, respectively. The prediction of tensile strain capacity was the least accurate. Meanwhile, the MAE of the tensile strain capacity was a mere 0.84%, smaller than the variability (1.77%) of the test results in previous research. Compressive strength and tensile strength demonstrated high sensitivity to variations in both water-cement ratio (W) and water reducer (WR). In contrast, flexural strength exhibited high sensitivity solely to changes in W. Conversely, the sensitivity of tensile strain capacity to input features was moderate and consistent. The mechanical attributes of ECC emerged from the combined effects of multiple positive and negative features. Notably, WR exerted the most significant influence on compressive strength among all features, whereas polyethylene (PE) fiber emerged as the primary driver affecting flexural strength, tensile strength, and tensile strain capacity.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In coastal regions, the deterioration of structures and bridges due to environmental conditions and corrosion is a significant concern. To combat these issues, the use of corrosion-resistant materials like fiber-reinforced polymers (FRPs) materials, engineered cementitious composites (ECCs), and rubberized ECCs (RECC) shows promise as normal concrete (NC) alternatives by providing increased ductility and energy absorption properties. The effectiveness of confining concrete columns using GFRP tubes with ECC/RECC was assessed in this research by evaluating their performance through compression and push-out tests. The study explored key parameters such as GFRP tube thickness and the presence of shear connectors along the tube height, as well as examining various types of concrete. Additionally, a comprehensive parametric investigation utilizing finite element analysis (FEA) was conducted to analyze how different factors influence the behavior of confined concrete columns. These factors included the effect of GFRP tube thickness and diameter on the overall behavior of different types of confined concretes. The results demonstrate that GFRP tubes significantly enhance column capacity, while the presence of ECC/RECC exhibits even greater improvements in capacity, stiffness, and toughness compared to NC. This approach shows promise in reinforcing coastal infrastructure and addressing corrosion-related concerns effectively. [ABSTRACT FROM AUTHOR]

The present study introduces a novel approach utilizing machine learning techniques to predict the crucial mechanical properties of engineered cementitious composites (ECCs), spanning from typical to exceptionally high strength levels. These properties, including compressive strength, flexural strength, tensile strength, and tensile strain capacity, can not only be predicted but also precisely estimated. The investigation encompassed a meticulous compilation and examination of 1532 datasets sourced from pertinent research. Four machine learning algorithms, linear regression (LR), K nearest neighbors (KNN), random forest (RF), and extreme gradient boosting (XGB), were used to establish the prediction model of ECC mechanical properties and determine the optimal model. The optimal model was utilized to employ SHapley Additive exPlanations (SHAP) for scrutinizing feature importance and conducting an in-depth parametric analysis. Subsequently, a comprehensive control strategy was devised for ECC mechanical properties. This strategy can provide actionable guidance for ECC design, equipping engineers and professionals in civil engineering and material science to make informed decisions throughout their design endeavors. The results show that the RF model demonstrated the highest prediction accuracy for compressive strength and flexural strength, with R2 values of 0.92 and 0.91 on the test set. The XGB model outperformed in predicting tensile strength and tensile strain capacity, with R2 values of 0.87 and 0.80 on the test set, respectively. The prediction of tensile strain capacity was the least accurate. Meanwhile, the MAE of the tensile strain capacity was a mere 0.84%, smaller than the variability (1.77%) of the test results in previous research. Compressive strength and tensile strength demonstrated high sensitivity to variations in both water-cement ratio (W) and water reducer (WR). In contrast, flexural strength exhibited high sensitivity solely to changes in W. Conversely, the sensitivity of tensile strain capacity to input features was moderate and consistent. The mechanical attributes of ECC emerged from the combined effects of multiple positive and negative features. Notably, WR exerted the most significant influence on compressive strength among all features, whereas polyethylene (PE) fiber emerged as the primary driver affecting flexural strength, tensile strength, and tensile strain capacity. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Engineered Cementitious Composites are a type of advanced building materials, which have excellent ductility and can significantly enhance structural resistance. However, the expensive material cost of ECC limits its engineering applications. This study investigated the potential of replacing commonly used silica (river) sand and imported PVA fibers with the local desert sand and PVA fibers, aiming at reducing the preparation cost of ECC and improving its economic benefits and sustainability. The mixture proportion was first optimized to obtain favorable strength and ductile enhancement, using a combination of single-factor test and theoretical calculation which mentioned the slurry coating thickness of fibers and desert sand. The potential of desert sand in preparing ECC was experimentally evaluated by comparing the uniaxial tension (compression) properties and microstructures of desert sand-based ECC (DS-ECC) and those of ordinary ECC. The results indicate that optimized DS-ECC can achieve satisfactory performance even when 100% fine aggregates are replaced by desert sand. It has comparable uniaxial tensile (compression) strengths to ordinary ECC but a significantly improved tensile ductility, with the ultimate tensile strain of about 5–8% and 3% at 7d and 28d curing ages, respectively. Meanwhile, the utilization of desert sand and local PVA fibers alone in ECC can substantially deliver a reduction of about 20–30% in material cost and an improvement in environmental impact. [ABSTRACT FROM AUTHOR]

Due to their excellent ductility and crack-control ability, engineered cementitious composites (ECCs) combined with shaped steel can produce steel-reinforced engineering cementitious composite (SRECC) structures which exhibit significant advantages in prefabricated buildings. The interface bond behavior is the base for the cooperative working performance of the shaped steel and ECC. This study included push-out tests of one ordinary concrete control specimen and ten ECC specimens. The various parameters were the ECC compressive strength, fiber volume content, cover thickness, and the embedded length of shaped steel. The bond stress–slip curves at the loading and free end were obtained, and the effects of various parameters on the characteristic points of curves were analyzed. The results indicated that the ordinary concrete specimen failed in brittle splitting, with the cracks completely penetrating the surface of the specimen. Due to the fiber-bridging effect in ECCs effectively preventing the development and extension of cracks, the shaped steel at the free end was obviously pushed out, and the surrounding matrix maintained good integrity after testing finished. For ECC specimens, bond or splitting-bond failure occurred, exhibiting outstanding ductility. Compared with the ordinary concrete specimen, the standard ultimate and residual bond strength of ECC specimens improved by 37.9% and 27.4%, respectively. Besides the increase in ECC compressive strength, the fiber volume content and cover thickness had a significant positive influence on the ultimate and residual bond strength, whereas the effect of the embedded length was the opposite. Finally, the calculation equations of characteristic bond strength were proposed, and the calculated values matched well with the experimental values. [ABSTRACT FROM AUTHOR]

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This study aims to investigate the influence of different surface treatments, including smooth interface, rough interface, anchor bolt connection, and epoxy bonding agent, on the shear resistance of Engineered Cementitious Composites (ECC)-concrete interface through bi-surface shear testing. The experimental results show that the interfacial shear strength between ECC and concrete is significantly enhanced by the implementation of the three interface treatment methods, as opposed to the smooth interface. Among these methods, the anchor bolt connection exhibits the greatest improvement in interfacial bonding performance. Notably, cohesive failure is observed in the anchor bolt connection method, while the other three methods result in adhesive failure, with only the anchor bolt connection method displaying ductile failure behavior. Following a comprehensive review of relevant studies and the outcomes of this experiment, three distinct interface bonding mechanisms were identified and the forces contributing to the bond were analyzed. Results indicated that the interfacial bond strength is notably influenced by the surface roughness. These research findings substantiate the viability of utilizing the anchor bolt connection method, particularly in applications where ductility requirements in the repair layer are essential for structural integrity. [ABSTRACT FROM AUTHOR]

This research examined the development of modified engineered cementitious composites (MECC) using manufactured sand (M-sand) and a high content of raw agricultural by-products, such as bagasse ash (BA) and rice husk ash (RHA), instead of conventional silica sand and fly ash. Fourteen different types of MECC mixtures were developed using raw BA and RHA blended with M-sand to reduce the cost of MECC. The fresh and hardened properties of all mixtures were examined using various types of testing methods. In addition, microstructure analysis were conducted for both the control and optimal mixtures to identify the bonding of fibres in cementitious composites. The correlation between conventional and MECC was also evaluated based on the hardened properties and cost analysis. The results revealed that workability steadily dwindled with increasing percentages of BA and RHA, from 10 to 55. Optimal mechanical properties were attained with the incorporation of BA and RHA at 10% cement replacement. In contrast, 30% BA and 40% RHA exhibited maximum impact strength compared to the respective control mixes. Similarly, ECC with 20% BA and RHA exhibited optimal durability properties. Moreover, compared to conventional ECC, the cost of the newly developed MECC was slightly lesser due to the incorporation of agricultural by-products and M-sand. [ABSTRACT FROM AUTHOR]

The use of carbon fiber–reinforced polymer (CFRP) grid-reinforced engineered cementitious composite (CFGRE) systems to strengthen concrete-filled steel tubes (CFSTs) offers potential to improve the structural response as well as the resistance to high temperatures and corrosion. This study consists of an experimental investigation on the behavior of eccentrically loaded square CFSTs strengthened with CFGRE systems. Nineteen specimens were tested using a compression-testing machine with loads, deformations, and recorded test observations. The investigated parameters included the number of CFRP grid layers, width-to-thickness ratio of a steel tube, concrete strength grade, and eccentric ratio. The strengthened columns exhibited ductile failure. Due to stress concentrations, the CFGRE systems ruptured at the corners on the compression side. After strengthening, the yielding and ultimate loads of the CFST columns increased from 21.8% to 53.5% and 21.1% to 34.9%, respectively. Although an increase in the number of CFRP grid layers did not significantly affect the bearing capacities of the square specimens, it significantly enhanced the ductility of the columns. An increase in the eccentric ratio weakened the confining effect. An average decrease of 9.7%, 27.6%, and 41.4% was observed in the ultimate loads of the strengthened columns when the eccentric ratio increased from 0 to 0.1, 0.25, and 0.4, respectively. A five-point N–M interaction model was developed based on the principles of force equilibrium and deformation compatibility to predict the eccentric bearing capacities of strengthened columns. The prediction results exhibited high accuracy. [ABSTRACT FROM AUTHOR]

Hybrid double-skin tubular columns (DSTCs), which consist of an outer fiber-reinforced polymer (FRP) tube, an inner steel tube, and a concrete annular layer between the two tubes, possess many advantages, such as high load resistance and large deformation capacity and excellent durability. The use of ultrahigh-performance concrete (UHPC) or engineered cementitious composites (ECCs) instead of normal strength concrete (NSC) in the annular layer, given the advantages such as the ultrahigh strength of UHPC and strain hardening and high toughness feature of ECC, endows the DSTCs with additional high performance, such as an enhanced load-carrying capacity (with UHPC) and an improved cracking resistance (with ECC). The behavior of such DSTC specimens with UHPC or ECC that are subjected to eccentric loading was investigated for the first time, to the best of the authors' knowledge, and the results are reported in this paper. The DSTC specimens with NSC and ECC under eccentric compression exhibited similar great ductility with a bilinear shape for the axial load–deformation curves. In addition, the initial cracking of the FRP tube at the tension side of DSTC specimens with ECC or NSC occurred later than that of DSTC specimens with UHPC, which might imply the better durability performance of DSTC specimens with ECC or NSC during the serviceability state. [ABSTRACT FROM AUTHOR]

The influence of various supplementary cementitious materials (SCMs) and fibres on the fire resistance of composite systems that combine engineered cementitious composites (ECCs) in tension with self-compacting concrete (SCC) in compression was examined. The study was designed to determine the ideal ECC formulation for optimising mechanical properties and bonding performance at ambient and elevated temperatures. The SCC and ECC were hot-joined without vibration or surface preparation, using a fresh-to-fresh casting method. Modifications to the chemical composition of the ECCs included the addition of class F fly ash (FAF), class C fly ash (FAC) or slag, as well as polyvinyl alcohol (PVA) fibres or steel fibres. The samples were exposed to temperatures of 200°C, 400°C, 600°C and 800°C, followed by comprehensive testing to evaluate their flexural strength, tensile strength and interfacial properties. The results indicate that the incorporation of an ECC layer within the SCC system significantly improved mechanical strength and thermal stability, both at ambient temperatures and under high-temperature conditions. Notably, the addition of FAF (rather than FAC or slag) in the ECC layer offered superior thermal stability and ensured the retention of desirable residual mechanical properties. Moreover, steel fibre reinforcement greatly improved the SCC/ECC bonding, outperforming PVA reinforcement at elevated temperatures. [ABSTRACT FROM AUTHOR]

Inclusion of nanomaterials is an effective method for enhancing the mechanical and durability characteristics of cement-based materials. Among various graphene-based nanomaterials, graphene nanoplatelets (GNPs) are cost-effective nanoparticles that possess graphene's key properties. Since limited information is available regarding their influence on the fresh, mechanical, nondestructive, and self-healing behavior of Engineered Cementitious Composites (ECC), this research focuses on GNP inclusion on these properties of ECC in a comprehensive way. In this research, the changes in material properties of ECC were monitored with several mechanical and nondestructive test methods. According to the results, GNP inclusion significantly enhanced flexural behavior and also promoted self-healing of ECC, with preloaded specimens exhibiting substantial or complete crack closure and similar performance to virgin specimens. Non-destructive tests and microstructural analyses also confirmed the promoting effects of GNP. A noticeable increase was observed in compressive strength when GNP was included. In conclusion, this study provides compelling evidence about the positive impact of GNP inclusion on improving the properties of ECC. The findings demonstrate the potential of GNPs to enhance the performance of cementitious materials and offer valuable insights for future research and practical applications. [ABSTRACT FROM AUTHOR]

The existing Reinforced Concrete (RC) School buildings are often characterized by low-rise, very long beams, and relatively large-valued uniformly distributed loads. Beams present a large amount of longitudinal reinforcement so that they exert huge shear stresses, on the joint panels into which they frame, during a seismic event. For this reason, the main cause of seismic inadequacy of these buildings is often the premature shear failure of the joints. These latter can result either (a) completely devoid of reinforcing stirrups, or (b) not suitably reinforced, or (c) under-dimensioned. In some cases, due to either the results of the feasibility study or to instructions given by the Contracting Authority, the seismic rehabilitation of such buildings must be obtained by local interventions. To rehabilitate an existing RC building with under-dimensioned joints, by means of local interventions, the availability of pourable and self-compacting High-Performance Fiber Reinforced Cementitious Composites (HP-FRCC) renders the RC jacketing the ideal solution. In cases in which an aggressive environment is concomitant with the susceptibility to earthquakes, an Engineered Cementitious Composite designed ad hoc could be an even better option. The RC jacketing of the joint allows to enlarge it, thus making it work in un-cracked regime. However, when the joint panel is enlarged, the appropriate hierarchy of resistances must be restored throughout the length of the column, to guarantee the activation of the desired global dissipative mechanism. In this article a calculation strategy to follow in these cases, in compliance with the Building Regulations, is proposed and described by referring to a case-study. Finally, a discussion is provided on some aspects, which are still susceptible to improvement, to refine the intervention technique. [ABSTRACT FROM AUTHOR]

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). This material 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 TSC of ECC mixtures 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. [ABSTRACT FROM AUTHOR]

By collecting engineered cementitious composite (ECC) uniaxial tensile experimental research data, aiming at the multiple cracking characteristics of the strain hardening stage of the ECC stress–strain curve, a theoretical model describing the constitutive relationship of the ECC uniaxial tensile stress–strain – the multiple cracking sawtooth model – is proposed. Several model parameters were obtained with the fitting analysis of many ECC uniaxial tensile stress–strain curves. The application conditions and influencing factors of the three-order multi-crack “sawtooth” model of polyvinyl alcohol (PVA)-ECC and polyethylene (PE)-ECC and the four-order multi-crack “sawtooth” model of PVA-ECC are studied. The result shows that the higher the fiber reinforcement index, the better the tensile properties of ECC. The fiber reinforcement index is linearly correlated with the initial crack stress and ultimate tensile stress of PVA-ECC and with the ultimate tensile stress and ultimate tensile strain of PE-ECC. The characteristic points of PVA-ECC in the multi-crack cracking stage are as follows: the greater the initial cracking strain, the smaller the ultimate tensile strain, showing an exponential correlation; The greater the initial cracking stress is, the greater the ultimate tensile stress is, and the two are linearly correlated.

Engineered cementitious composites (ECC), which are a kind of novel composite building material with high ductility and high toughness, can be utilized in areas susceptible to salt-freezing damage, such as that caused by snowmelt agents, seawater, and saline soils. In this paper, engineered cementitious composites reinforced with polyethylene fibers (PE) are analyzed to study the changes in the flexural static load properties, and flexural fatigue life of PE-ECC specimens after four different freeze-thaw cycles (0, 50, 100 and 150) in fresh water and a 3.5 % mass fraction NaCl solution. The results show that upon reaching 150 freeze-thaw cycles, there was a notable disparity in the relative equivalent flexural strength between specimens subjected to chloride salt freeze-thaw and freshwater freeze-thaw environments, with the former exhibiting a 1.07-fold increase in damage compared to the latter specimens. Using the relative dynamic elastic modulus as the damage variable, a relationship model was made between the relative equivalent flexural strength and the freeze-thaw damage degree of PE-ECC in two freeze-thaw environments. The flexural fatigue life of PE-ECC after freeze-thaw obeyed a two-parameter Weibull distribution, and the P-S-N curves at various reliability probabilities correlated well with the test results. The safety coefficient of PE-ECC varied with changes in freeze-thaw conditions, necessitating an increase in the safety coefficient to assure structural safety in locations with more severe freeze-thaw damage. The results of this study can serve as a reference for the development of freeze-thaw-resistant designs for PE-ECC structures in future applications.

Shield tunnel segmental joints are traditionally vulnerable, limited by their tensile capacity and susceptibility to cracking. Engineered Cementitious Composites (ECC) offer a promising solution due to their superior tensile strength, exceptional crack resistance, and remarkable toughness. However, the application of ECC in tunnel segment joints remains unexplored. To address this gap, this paper conducted comprehensive full-scale tests of ECC segmental joints versus ordinary reinforced concrete (RC) segmental joints. It investigated mechanical responses including material behavior, deflection, joint action, bolt strain, crack development, and failure modes. Results revealed that: (1) ECC joints provided a 33.97 % higher stable bearing capacity and a 50 % increase in initial cracking strength compared to RC joints. (2) ECC joints excelled in crack control, maintaining crack widths below 0.2 mm, while RC joints experienced significant cracking with widths exceeding 1 mm. (3) In terms of toughness, ECC joints surpassed RC by 66 % in the elastic stage and 123 % in the normal serviceability stage, with 96 % higher ductility. (4) ECC joints significantly outperformed RC joints in bolt stress uniformity and concentration, achieving a 43.21 % reduction in average bolt stress. (5) Regarding multi-scale mechanical effects, ECC joints increased the toughness and strength advantage over RC by more than 45 % in the elastic phase. These results reveal the potential of ECC in significantly enhancing the durability and resilience of shield tunnels, particularly in harsh environments subjected to high ground stress or seismic activities.

Unreinforced masonry (URM) structure consisting of bricks and mortar suffers severe damage under impact loading, owing to its poor ductility and brittle failure modes. However, natural nacre with a similar structure to that of masonry exhibits superior mechanical properties through the well-designed assembly process. Therefore, a nacre-inspired design method, which hierarchically assembled bricks and engineered cementitious composites (ECC) into novel masonry walls at the macro-scale, was proposed in present study. The variations of the bionic measurements were experimentally explored. Test results demonstrated that the ductility and toughness of the novel masonry structure were dramatically improved by replacing mortar with ECC as horizontal joint and setting artificial local separations. The energy absorption of masonry wall and masonry beam were improved 5.66 times and 8.05 times, respectively. A theoretical frame model for hierarchically-assembled masonry was established, which considered the randomness of masonry and simulated the crack propagation. Finally, a numerical verification was conducted based on the frame model. This study lays the groundwork for applying the nacre-inspired design method in masonry structure to improve its shear properties in terms of ductility and toughness.

Due to the advantageous tensile ductility and multi-slit cracking characteristics, ECC material has attracted great from scholars. It has demonstrated promising potential in various fields including spray construction, additive manufacturing, building repair, and structural reinforcement. However, it is of note that ECC materials typically contain a substantial amount of low-activity mineral admixtures, which can cause lower initial mechanical properties. To address the existing issue, a hydrated calcium silicate (CSH) suspension was synthesized and added to the ECC material as an accelerating admixture. In this study, mechanical properties and hydration products of the ECC material were explored. The results suggest that CSH effectively enhances the early compressive, flexural, and tensile strength of ECC materials, and makes a positive impact on the later mechanical properties. However, it is of importance to note that CSH increases the fracture toughness of the ECC matrix, which may generate a negative effect on the tensile ductility of ECC. Microscopic analysis indicated that CSH promotes the formation of hydration products such as hydrated calcium silicate, ettringite, and Ca(OH)2, leading to improved hydration of cement clinker. In addition, CSH enhances the bond between the fiber and ECC matrix. In general, the research findings indicate that CSH can serve as a promising accelerating admixture for preparing early-strength ECC materials. The current research is highly significant for the advancement of early-strength ECC materials and expanding the range of applications for CSH accelerating admixture.

Concern about carbon reduction in the construction industry is growing. Engineered cementitious composites (ECC) have been extensively studied for their potential sustainability, continuous efforts are being made for a greener ECC. In this study, a new type of low-carbon supplementary cementitious materials (SCMs), limestone calcined clay (LC2), was blended with fly ash (FA) as the cementitious materials of ECC. A series of experiments were carried out to study the effects of blended LC2/FA on the mechanical properties and drying shrinkage of ECC materials, XRD and MIP were also used to explain the mechanism. The results show that LC2 can accelerate the hydration, improve the mechanical properties of ECC, especially in the early age. The addition of LC2 can improve the flexural bearing capacity, but weaken the bending deformation capacity and affect the flexural toughness. The increase of LC2 content significantly refined the pore size, thus reduced the drying shrinkage. In addition, based on the drying shrinkage model of ordinary concrete, the improved drying shrinkage model proposed in this study can accurately describe the drying shrinkage behavior of ECC.

A new kind of functional gradient material (FGM) based on engineering cementitious composites (ECC) and normal concrete (NC) was proposed in this study. This material offers enhanced crack control while minimizing ECC consumption. Foremost, uniaxial compression tests were carried out on single-layer NC-ECC composites featuring varying ECC volume fractions (0%, 20%, 40%, 60%, 80%, and 100%). These tests yield an elastic modulus formula, E(y), for the NC-ECC composite. Subsequently, based on the E(y) formula, a 5-layer NC-ECC FGM is designed, with each sub-layer having distinct ECC volume fractions. This is contrasted with pure ECC and 2-layer NC-ECC specimens for reference. The study concludes with an analysis of the failure patterns, load-displacement curves, and elastic moduli of the NC-ECC FGM. The results demonstrate consistent performance trends of elastic modulus in single-layer NC-ECC composite specimens, confirming the feasibility of employing a functional gradient between NC and ECC. Utilizing the formula E(y) derived from single-layer NC-ECC, the ECC volume fractions in the 5-layer NC-ECC FGM are computed as 100%, 86.89%, 68.13%, 41.55%, and 0% for each layer. Importantly, the NC-ECC FGM exhibits a failure mode resembling ECC specimens, with primary cracks not extending along interfacial layers. In contrast, 2-layer NC-ECC specimens experience cracking along interfacial boundaries. The compressive strength of NC-ECC FGM surpasses that of ECC specimens by 1.42 times while retaining ECC-like ductility, showcasing a 25.85% improvement over 2-layer NC-ECC. The findings from this study provide valuable insights for the design and subsequent engineering applications of functional gradient materials.

This paper aims to establish an explicit crack bridging model that can link engineered cementitious composites (ECC) behavior from single fiber to single crack scale, which is great of designing ECC featuring pseudo tensile strain hardening and multiple cracks expanding by tailoring microstructure and materials selection. In this study, fiber bridging stress was divided into three parts including fiber bridging stress with no rupture, fiber debonding fracture stress, and fiber pullout fracture stress. Subsequently, the fundamental crack bridging model was emerged when fiber bridging stress with no rupture subtracted from the fiber rupture stress in debonding and pullout stage. Moreover, two-way pullout and Cook-Gordon effect were also considered to establish the complete model. It was found that the two-way pullout situation of polyvinyl alcohol (PVA) fiber has a significant influence on the crack opening width due to its slip hardening property, while the Cook-Gordon effect presents a faint crack width increment for PVA-ECC. However, the Cook-Gordon effect makes a significant contribution to the crack opening width of the composite produced by polyethylene (PE). This building intelligible model presents a better prediction for ECC through the comparison of experimental data or real average crack width in previous models, thus confirming the validity of this model.

The presentation of a constitutive model could help researchers to predict the mechanical behavior of a material, which also contributes to the further generalization of the material. This paper is to explore the tensile constitutive model of engineered cementitious composites (ECCs) reinforced by high-strength steel wire mesh based on experiments and numerical simulations. DIANA was used to simulate the tensile process of the specimens, and experiments were carried out to validate the numerical model. The effect of the ECCs’ tensile strength, reinforcement ratio and specimen size were considered during the specimen design process. The results showed that most of the errors of the simulated values compared to the experimental results were within 5%, which proved that the numerical model was quite accurate. The proposed constitutive model revealed the different roles played by ECCs and high-strength steel wires at different stress stages, and the calculation results were in high agreement with the simulation results, indicating the effectiveness of the constitutive model. The study in this paper could provide an important reference for the popularization and application of ECCs reinforced by high-strength steel wire mesh.

Glass fiber reinforced polymer (GFRP) concrete beams reinforced by carbon fiber reinforced polymer (CFRP) grid reinforced engineering cementitious composite (ECC) have excellent flexural performance and corrosion resistance in marine environments. However, the lack of a reliable theoretical model for predicting the flexural behavior of the hybrid beams makes it challenging apply them in the practical engineering. To address this issue, a series of numerical models were established to investigate the effects of key parameters on the flexural behavior of the hybrid beams, including the peak load, the neutral axis height, and the sectional stress distribution. Subsequently, based on the influence of the failures of different materials on the flexural performance of the hybrid beam, the loads of four feature points were calculated in the theoretical model to predict the entire load–displacement curve. Finally, the application range of the theoretical model was given based on the neutral axis height. The results showed that the cover thickness of the ECC, the GFRP reinforcement ratio and the cross‐sectional area of the CFRP grid were the key factors affecting the flexural performance of the hybrid beams. The theoretical model established in this study can predict the load–displacement curve accurately and can provide a reference for the subsequent design of the hybrid beams. [ABSTRACT FROM AUTHOR]

As a high-performance composite material, polyvinyl alcohol (PVA) fiber-reinforced engineered cementitious composites (PVA-ECCs) are often used in sub-elevated temperature environments (< 200°C) for long-term service. However, the effect of exposure time in sub-elevated temperature on the performance of PVA-ECCs is not still clear. In this study, the properties of PVA-ECCs in sub-elevated temperature environments were examined, with emphasis on the effect of exposure time (1, 3, 6, and 9 h). Furthermore, the microstructure and tensile behavior of single PVA fibers exposed to a sub-elevated temperature environment was investigated. Results showed that PVA-ECCs have enhanced tensile ductility at different sub-elevated temperature exposure times below 100°C. However, the tensile properties of PVA-ECCs at 150°C showed a strain retraction phenomenon at 6 and 9 h. The strain-hardening characteristics of PVA-ECCs gradually disappeared with the increase of the sub-elevated temperature exposure time at 200°C. The results of thermogravimetric-differential scanning calorimetry (TG-DSC), Fourier transformation infrared spectroscopy (FTIR), and scanning electron microscope (SEM) revealed that the degradation of PVA fibers was accelerated by exposure time in sub-elevated temperature, which caused the reduction of mechanical properties of PVA-ECCs. [ABSTRACT FROM AUTHOR]

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A crucial component of many building projects is concrete. An innovative construction material known as Engineered Cementitious Composites, or Bendable Concrete, is developed by utilizing polyvinyl alcohol and jute fibers to generate a cementitious matrix that is reinforced with highperformance fibers. The characteristics of ECCs include a relatively average fiber content of 2% or less by volume, a narrow fracture width of about 60 µm, and high flexibility in the strain range of 3-7%. Uniaxial pressures cause these composites to exhibit strain-hardening behaviors. In comparison to ordinary and fiber-reinforced concrete, the strain can reach 3-8% higher. In this paper, the background, development, and potential of ECCs are discussed along with a study of the properties of conventional concrete and ECCs. By using a material design based on fracture principles and micromechanics, ECCs have been created to achieve increased tensile ductility with only a moderate amount of fiber reinforcement. Because of its resilience to cracks and ability for self-healing, engineered cementitious composites (ECC) offer the potential to lower the energy and carbon footprints of the built environment. In today's world, sustainability is essential to almost every industry, but none more so than the building and construction sector. Hence, exploring the potential of ECCs as a sustainable building material is necessary. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The mechanical properties of polyethylene fibre reinforced cementitious composites (PE-ECC) and polyethylene fibre-calcium carbonate whisker reinforced cementitious composites (PECW-ECC) were tested after exposure to different temperatures. And the microstructure changes of ECCs were observed by scanning electron microscope. The results showed the compressive and tensile strengths of PE-ECC and PECW-ECC tended to increase and then decrease with the increase of exposure temperature. The incorporation of CW improved the mechanical properties of PE-ECC to a certain extent. At the same exposure temperature, the compressive and tensile strengths of PECW-ECC are better than that of PE-ECC, and the plastic deformation capacity is also better than that of PE-ECC. The reason is that CW can be tightly bonded with the matrix material, and it has a filling effect on matrix defects, a bridging effect on the microscopic cracks, and a deflecting effect on the microscopic cracks.

Due to their excellent ductility and crack-control ability, engineered cementitious composites (ECCs) combined with shaped steel can produce steel-reinforced engineering cementitious composite (SRECC) structures which exhibit significant advantages in prefabricated buildings. The interface bond behavior is the base for the cooperative working performance of the shaped steel and ECC. This study included push-out tests of one ordinary concrete control specimen and ten ECC specimens. The various parameters were the ECC compressive strength, fiber volume content, cover thickness, and the embedded length of shaped steel. The bond stress–slip curves at the loading and free end were obtained, and the effects of various parameters on the characteristic points of curves were analyzed. The results indicated that the ordinary concrete specimen failed in brittle splitting, with the cracks completely penetrating the surface of the specimen. Due to the fiber-bridging effect in ECCs effectively preventing the development and extension of cracks, the shaped steel at the free end was obviously pushed out, and the surrounding matrix maintained good integrity after testing finished. For ECC specimens, bond or splitting-bond failure occurred, exhibiting outstanding ductility. Compared with the ordinary concrete specimen, the standard ultimate and residual bond strength of ECC specimens improved by 37.9% and 27.4%, respectively. Besides the increase in ECC compressive strength, the fiber volume content and cover thickness had a significant positive influence on the ultimate and residual bond strength, whereas the effect of the embedded length was the opposite. Finally, the calculation equations of characteristic bond strength were proposed, and the calculated values matched well with the experimental values.