Strain Hardening Cementitious Composites Research Articles

Structural behaviour of reinforced concrete beams with self-healing cover zone as lost formwork

This study investigates the structural behaviour and self-healing performance of hybrid reinforced concrete (RC) beams, enhanced with a 1.5-cm-thick self-healing cover composed of bacteria-embedded strain hardening cementitious composite (SHCC), for its potential in crack width control and crack healing. The research focuses on the performance under both flexural and shear loading, examining aspects such as load-bearing capacity, surface crack pattern, crack propagation between layers, and healing effectiveness. Results demonstrate the successful activation of the healing function, alongside improvements in structural performance. Under flexural loading, hybrid beams exhibited greater load-bearing capacity and significantly improved crack control ability. The maximum crack width of the hybrid beams exceeded 0.3 mm at least 124.7 kN load, whereas in the control beam the largest crack exceeded 0.3 mm at only 59.8 kN load. Under shear loading, while the influence of the cover on structural capacity is minimal, it notably improves post-peak ductility and energy dissipation. Interface delamination was not observed in both cases. The results of the current study demonstrate the potential of delivering the self-healing mechanism precisely where it is most needed, which presents a scalable and economically viable strategy for integrating self-healing SHCC into standard construction practices.

Impact of aluminate cements on the durability and mechanical performance of strain-hardening cementitious composites

Strain-hardening cementitious composites (SHCCs) are durable, ductile, fiber-reinforced cement-based materials. While fly ash (FA) is often used to partially replace Portland cement in SHCCs to enhance material performance, it can lead to long setting times and slow strength development. To address these limitations, this study investigates the use of aluminate cement as partial replacements for Portland cement in FA-based SHCCs. Furthermore, the study aims to fill a significant knowledge gap by thoroughly examining the influence of aluminate cement on the workability, durability, and strain-hardening behavior of SHCCs. Aluminate cements encompass both calcium sulfoaluminate (CSA) cement and calcium aluminate cement (CAC), distinguished by their composition rich in calcium aluminate phases. This study investigated the use of CSA and CAC cements as partial replacements for Portland cement in SHCCs. Both fresh and hardened properties of the CSA- and CAC-SHCCs were examined, while their microstructures and chemical phases were investigated using SEM and XRD analyses. Results showed that CSA and CAC cements reduced fluidity, setting time, and drying shrinkage but increased porosity and early strength development for SHCCs. CSA-SHCCs showed enhanced impermeability due to the refinement of interior pore space through the hydration products. While all modified SHCCs retained tensile strain hardening behavior, the tensile performance degraded due to the hydration effects of ye'elimite and calcium aluminates. The reduced tensile strain capacity was elucidated using the theory of steady-state crack opening.

A multiscale thermo-mechanical coupling model for Fiber-Reinforced Cementitious Composite (FRCC)

This paper aims to develop a multiscale thermo-mechanical coupling model across from meso-scale to macro-scale to study the tensile thermos-mechanical behavior of fiber-reinforced cementitious composite (FRCC) on the base of thermodynamics. In meso-scale, the coupling process of thermal effect and the development law of a single crack were creatively presented and formulated in energy potential function. The effects of fiber dispersion on cracking behavior and crack strength of matrix were determined. In macro-scale, the multiple-fine-cracks and strain-hardening/softening behavior under tension were defined and studied. The bridging action stress of fibers is calculated by considering the bonding stress in the interface transition zone (ITZ). The model can be upgraded for FRCC materials ranges from strain-hardening cementitious composite (SHCC) and engineered cementitious composite (ECC). The numerical calculations of the proposed model were conducted based on the Fortran program for validation. The residual tensile strength, multiple-fine-cracks and strain-hardening/softening behaviors of FRCC were predicted. The behaviors of FRCC with different fiber types were accurately captured in a range of temperature from 20°C to 600°C through the comparative study with six groups test results in literatures. A sensibility study was carried out to analyze the impact of modelling parameters and thermal effect on the strain-hardening/softening behaviors of FRCC.

Flexural performance of nature-inspired 3D-printed strain-hardening cementitious composites (3DP-SHCC) with Bouligand structures

Inspired by nature, this study employed the Bouligand structures, as observed in the dactyl club of mantis shrimp, to enhance the performance of 3D-printed Strain-Hardening Cementitious Composites (3DP-SHCC). Twenty sets of printed and mold-cast specimens were prepared to investigate the effects of Bouligand structures on the flexural performance of 3DP-SHCC. Three printing patterns (parallel, cross, and Bouligand printing) and five pitch angles (15°, 30°, 45°, 60°, 75°) were used for the Bouligand printing pattern. The results showed that the flexural performance of parallel-printed SHCC exhibited significant directionality. The flexural strength and toughness of parallel-printed SHCC in the X direction were 1.28 times and 3.27 times greater than the mold-cast SHCC. However, the flexural strength and toughness in the Y direction were 0.58 times and 0.25 times those of the mold-cast SHCC. The cross-printed and Bouligand-printed SHCC alleviated the directionality. The flexural performance of cross-printed SHCC was lower than that of the mold-cast SHCC. Compared to parallel-printed SHCC, the flexural strength and toughness of Bouligand-printed SHCC increased by 1.25 to 1.73 times and 3.48 to 5.10 times, respectively, in the Y direction. Bouligand-printing twisted the fiber angles, enabling effective crack bridging across multiple directions and endowing the SHCC with uniform mechanical properties in various directions. The Bouligand structures provided valuable inspiration for optimizing 3DP-SHCC structures.

Ductility Variation and Improvement of Strain-Hardening Cementitious Composites in Structural Utilization.

Strain-hardening cementitious composite (SHCC) has the obvious advantages of excellent material properties such as its high tensile and compressive strengths, high tensile strain capacity, and excellent durability against multi-cracking performance with very fine crack widths. In particular, the multi-cracking performance of SHCC during structural utilization is obviously reduced compared to that of SHCC in uniaxial tension tests using dumbbell-shaped specimens of small size. The corresponding tensile strain capacity of SHCC during structural utilization is, thus, significantly decreased compared to that of SHCC in uniaxial tension tests. However, the reduction in the ductility of SHCC during structural utilization has not been sufficiently understood, and further study is required. This paper presents an experimental investigation into the ductility variation of flexural-failed and shear-failed SHCC members as well as the ductility improvement of SHCC members with steel reinforcement compared with that of SHCC in uniaxial tension tests using small-sized specimens. This study focuses on not only the decrease in the crack elongation performance of the SHCC material during structural utilization but also the increase in the crack elongation performance of SHCC members with steel reinforcement. The results demonstrate that the crack elongation performance of flexural-failed and shear-failed SHCC members is significantly reduced compared to that of SHCC in the uniaxial tension tests. Moreover, it was confirmed that steel reinforcement can effectively improve the SHCC member, increasing the strain-hardening capacity and multi-cracking performance. The load-carrying capacity of the flexural-failed SHCC member with steel reinforcement seemed to increase linearly with an increase in the reinforcement ratio, accompanied by an increase in the distribution of multiple fine cracks in the flexural-failed SHCC member with steel reinforcement.

A mesoscale model for multiple cracking behavior of strain-hardening cementitious composites

Strain-Hardening Cementitious Composites (SHCC) is composed of fiber, mortar, and fiber-matrix interface, which performs tensile strain-hardening behavior and multiple cracking. The tensile properties of SHCC are affected by multiple factors due to its complexity material compositions. In this paper, a three-dimensional mesoscale finite element model of SHCC involving fiber, mortar, and fiber-matrix interface is established to predict the characteristics of tension and multiple cracking. Based on the single fiber pull-out tests, a joint fiber-matrix constitutive model for the truss element is proposed to represent the interaction between the fiber and the fiber-matrix interface. The proposed model agrees well with the experiment. Based on the validated model, a parametric study is conducted on the mortar tensile strength, frictional bond strength, chemical bond strength, and PVA slip-hardening coefficient, which provides instructive support for the design of SHCC.

Quantifying the sequential fine cracks of strain-hardening cementitious composites (SHCC): An automatic approach for temporal and spatial assessment

Strain-hardening cementitious composites (SHCC) are promising construction materials that enhance structural durability by forming multiple fine cracks under loading. Compared to conventional concrete, the cracks in SHCC are denser and tighter, making their quantification challenging. To thoroughly analyze and model the cracking behavior of SHCC, automatic algorithms with high accuracy are desired. In this paper, a workflow based on deep learning algorithms and 3D connectivity analysis for characterizing the crack formation and development process in SHCC under tensile loading is proposed. Temporal and spatial crack information, such as the crack number and individual crack width development during the loading process as well as the cracking strength distribution along the tensile specimens, can be obtained with minimal effort. The established workflow can provide more information for evaluating the overall cracking behavior of SHCC with high efficiency, to facilitate multiscale modeling and micromechanics-based design of the material.

Strain-hardening cementitious composites ultra-thin whitetopping (SHCC-PUTW) for rapid asphalt pavement rehabilitation

Whitetopping is the concrete overlay used to upgrade distressed asphalt road surface, where the distressed asphalt is milled off and concrete is cast on top as the new wearing course. However, it requires road closure for multiple days, which is not accepted in many urban constructions. Precast concrete pavement (PCP) is the technology that shortens the construction period. However, it is associated with complicated construction procedures due to the brittleness of conventional concrete. In this paper, a brand-new PCP design, i.e., ultra-thin whitetopping (PUTW) is studied and applied in a demonstration project in Singapore. The PUTW is enabled by employing strain-hardening cementitious composites (SHCC) with significantly higher ductility than conventional concrete. The current work includes four parts. First, the desirable combinations of SHCC’s tensile and compressive uniaxial behaviors are identified in the analytical model and experimental study to enhance its flexural strength for pavement application. Second, the slab-to-slab joint efficiency in the PUTW, the critical mechanism in the structural design, is examined and validated with a full-scale cyclic wheel test. Third, the structural performance of the entire SHCC-PUTW is examined in a new finite element (FE) model validated against the wheel test. Based on the FE model, parametric studies on the SHCC material properties and PUTW slab dimensions are conducted to optimize the structural design. Fourth, a small-scale field project on the Jurong Island of Singapore, which involves the fabrication and installation of 11 SHCC-PUTW slabs, is reported to assess the feasibility of this new structural design.

Recycling Off-Specification Fly Ash for Producing Strain-Hardening Cementitious Composites

Recycling Off-Specification Fly Ash for Producing Strain-Hardening Cementitious Composites

Sprayed high-strength strain-hardening cementitious composite: Anisotropic mechanical properties and fiber distribution characteristics

High-strength strain-hardening cementitious composite (HS-SHCC), such as ultra-high performance concrete (UHPC) and high-strength engineered cementitious composites (ECC), is renowned for its exceptional strength, ductility, and durability compared to traditional concrete materials. This study experimentally investigated the anisotropic compressive and flexural responses of sprayed HS-SHCC. Initially, a sprayable HS-SHCC material was developed, which possessed appropriate rheological properties for pumping, spraying, and stacking. HS-SHCC panels were then fabricated via spraying, and specimens were subsequently extracted for compressive and flexural testing. The experimental variables included the load direction and the location of the extracted specimens in the panel. In addition to the mechanical tests, X-ray computer tomography was used to quantify fiber distribution in the sprayed HS-SHCC. The results indicated significant anisotropy in the compressive and flexural behavior of the sprayed HS-SHCC, particularly in flexural strength, which was 70% higher than the cast specimen when loaded in the spray direction. The calculated coefficients for the fiber orientation, number of fibers, and fiber dispersion indicated a planar fiber orientation in the sprayed HS-SHCC, with the highest values for the gravity direction and the lowest for the spraying direction. Furthermore, the mechanical behavior and fiber distribution also depended on the location of the extracted specimens in the panel. Lastly, a probability density distribution was suggested for evaluating fiber orientation in the sprayed HS-SHCC.

Intelligent characterization of complex cracks in strain-hardening cementitious composites based on generative computer vision

This paper presents a generative artificial intelligence (AI) approach to generate images of strain-hardening cementitious composite (SHCC) with complex crack patterns such as dense microcracks. This approach is developed to address the challenge of lacking data for training deep learning models used to automatically measure cracks in SHCC. The development of the approach is based on a framework which results in a hybrid generative adversarial network (HGAN) that seamlessly integrates a deep convolutional generative adversarial network (DCGAN) for generating images and a conditional generative adversarial network (CGAN) for labelling images. From the results, it was found that this approach provided high-quality labelled images automatically, and using these images significantly improved the accuracy of the deep learning models for measuring cracks in SHCC. The F1 score and Intersection Over Union (IOU) for crack segmentation reached 0.982 and 0.980, respectively. This approach will significantly promote crack measurement for SHCC materials and structures.

Structural size effect in the mode I and mixed mode I/II fracture of strain-hardening cementitious composites (SHCC)

The size effect in the fracture of solids represents a highly critical issue with a prolonged history of research. The size effect of traditional quasi-brittle materials can already be well described through the size effect model. However, there is still a lack of research on the size effect of strain-hardening cementitious composites (SHCC), a special type of fibre-reinforced concrete with macro-scale strain-hardening behaviour after first cracking. Being distinct from traditional quasi-brittle materials with softening nature, SHCC is thus expected to behave differently in terms of size effect. In this research, the structural size effect problem of SHCC is comprehensively studied by experimental investigation and theoretical analysis. Geometrically similar notched three-point bending specimens were tested in mode I and mixed mode I/II fracture condition. The whole-process of failure and matrix cracking zone around the main crack was captured with high resolution by digital image correlation technology. Experimental results showed that apparent fracture energy, nominal strength, structural ductility and fracture resistance curve are all structural size-dependent. The apparent fracture energy was shown to arise with specimen size within the tested range. This is related to large-scale pseudo yielding, i.e., enlargement of matrix cracking zone (like the yielding zone in metals) with increasing structural size. It thus provides an indirect method for the estimation of cohesive fracture energy of single crack with constitutive nature. Due to the scaled matrix cracking zone, an intermediate asymptote exists in the size effect curve of nominal strength, in addition to the plastic and LEFM asymptotes in the Bažant original size effect law. This resembles the recent finding of intermediate asymptote in plastic-hardening metal. The size-dependence of R-curve was also examined. Though size-dependent, the equivalent LEFM-based R-curves are shown to have three common stages reflecting different cracking processes. Based on experimental results, the size effect of fracture energy and nominal strength are finally modelled theoretically in the Bažant’s framework of equivalence between energy release and fracture resistance.

Influence of concrete type on rigid pavement behavior under static loads

It is thought that rigid pavements are more expensive than flexible pavements. However, when taking into account the element of durability, it was found that rigid pavements are less expensive than flexible pavements and have a service life up to 20 years. The flexible pavements are more suitable for the areas with weak subsoil and poor drainage, but it has a negative impact on the environment. This research presents an experimental and numerical study to explore the behavior of rigid pavement made of different types of concrete under the influence of static loads. The recent experimental study consists of six slabs with dimensions of 600 × 600 × 60 mm made of different types of concrete. Such types are normal-strength concrete (NSC), high-strength concrete (HSC) and strain hardening cementitious composites (SHCC). Based on the findings of this study, it is evident that the slab constructed with SHCC exhibits a 76.6% greater bearing capacity compared to the NSC slab. Regarding cost-effectiveness, the HSC slab was identified as the most economically advantageous option. A point to be noted is that the numerical model using the Abaqus program succeeded in modeling the experimental tested slabs.

Hydration mechanism and mechanical properties of a developed low-carbon and lightweight strain-hardening cementitious composites

Strain-hardening cementitious composites (SHCC) have been widely studied due to their high toughness and durability. The high cement content increases a huge burden on the cost and CO2 emissions of SHCC. To reduce the environmental impacts of SHCC, this study first develops low-carbon and lightweight SHCC by using high-volume recycled concrete powder (RCP) as supplementary cementitious materials and cenosphere waste as lightweight aggregate. The influence of RCP content (0%, 15%, 30%, and 45% by mass) on the hydration mechanism, mechanical properties, and sustainability of low-carbon and lightweight SHCC was investigated. The results showed that the incorporation of RCP in the SHCC matrix resulted in a decrease in hydration heat with increasing RCP content. The filling and pozzolanic effects of RCP were significantly lower than those of cement. The increased porosity and the presence of the interface transition zone due to RCP incorporation led to reduced compactness of the SHCC, which consequently led to decreased compressive strength and fracture toughness of the cement matrix. While the fracture toughness of the cement matrix was reduced, the SHCC still exhibited remarkable bending toughness and tensile ductility. The developed low-carbon and lightweight SHCC containing 45% RCP showed a density of 1482.5 kg/m3, a tensile strength of 3.94 MPa, and a tensile strain capacity of 6.80%, which successfully pushed the performance of low-carbon and lightweight SHCC. The replacement of cement with high-volume RCP in the low-carbon and lightweight SHCC resulted in a significant reduction in embodied carbon compared to conventional SHCC. Therefore, SHCC combines the advantages of lightweight, low-carbon, and highly ductile, making it a promising material for widespread utilization in concrete structures.

Investigation of high strain rate effects on strain-hardening cementitious composites using Voronoi-cell lattice models

Strain-hardening cementitious composites (SHCC) have been reported in several studies to exhibit in several studies to exhibit high toughness even under extreme dynamic loads. To understand such dynamic behavior of SHCC, this study extends a previously developed rate-dependent lattice model by introducing a non-local formulation of the fiber-matrix interface behavior. The Voronoi-cell lattice model, representing the cementitious matrix, employs an explicit time integration scheme and a visco-plastic unit to account for the inertia effect and Stefan effect. Additionally, randomly-distributed short fibers were modeled using an analytical model of shear stress transfer at the fiber-matrix interface. The proposed numerical model successfully simulated the direct tensile behavior and multiple cracking patterns of SHCC, revealing distinct rate-dependent failure characteristics. Through a simple parameter fitting process, the model accurately predicted the dynamic increase factor (DIF) of strength and strain capacity of high-speed tensile experiments. Furthermore, the numerically evaluated rate dependency of the fiber-matrix interface exhibited identical trends to previous experimental studies. Finally, the influences of fluctuations in the applied strain rate during actual high-speed loading tests and the random dispersion of fibers were assessed.

Influence of cooling methods on high‐temperature residual mechanical characterization of strain‐hardening cementitious composites

AbstractResidual strength tests are commonly used to characterize the high‐temperature mechanical properties of concrete materials. In these tests, the specimens are heated to a target temperature in a furnace and then cooled down to room temperature, followed by mechanical testing at room temperature. This research investigates the influence of the cooling method on the residual strength of Strain Hardening Cementitious Composites (SHCC) after exposure to 400°C and 600°C. Two types of cooling methods — furnace‐cooling (within a closed furnace) and water‐cooling (immersed in a water tank) — were adopted. Four different SHCC previously investigated by the authors for high‐temperature residual mechanical and bond behavior with steel were studied. Two different specimen sizes were tested under uniaxial compression and flexure to characterize the residual compressive strength and modulus of rupture. The effect of the cooling method was prominent for the normalized residual modulus of rupture at 400°C, but not at 600°C. The cooling method had no effect on the normalized residual compressive strength of any material at either of the two temperatures, except one of the SHCC (PVA‐SC) at 400°C. Specimen size also had no effect on the normalized residual compressive strength and modulus of rupture irrespective of the cooling method.

Interfacial bonding performance of 3D-printed Ultra-High Performance Strain-Hardening Cementitious Composites (UHP-SHCC) and cast normal concrete

Using 3D-printed elements as permanent formwork for structural members is an efficient way to integrate 3D printing technology in the traditional construction field which could also enhance structural capacity and possibly address the reinforcement challenge during 3D concrete printing. The bonding performance between 3D-printed formwork and post-cast concrete is crucial for maintaining the overall mechanical performance of the structures. This study experimentally investigates the interfacial bonding properties between 3D-printed Ultra-High Performance Strain-Hardening Cementitious Composites (UHP-SHCC) permanent formwork and post-cast normal concrete (NC). Three groups of prismatic composite specimens with smooth, grooved, and 3D-printed interfaces are subjected to the splitting tensile test to evaluate the interfacial bonding. A fully cast normal concrete specimen is also tested as a reference for comparison. The failure modes, splitting tensile strength, and effective bonding area ratio of normal concrete are analyzed and discussed. Results reveal that the splitting tensile strength of interfaces with grooved and 3D-printed preparation is significantly higher than that of the smooth interface, with an increase of 92.2%–114.8 %.

Shear Strength of Strain-Hardening Cementitious Materials

Concrete and other semi-brittle materials are pressure sensitive. Their resistance to shear depends on the confining pressure acting normal to the shear plane. This behaviour is modelled using experimentally calibrated failure criteria, such as the Mohr–Coulomb failure surface. Pressure sensitivity is also strongly evident in fibre-reinforced, strain-hardening cementitious composites (SHCC), despite the internal confinement these materials possess on account of their fibre content. However, because of the great range and variety of mixes used in such materials, no general failure criteria have yet been proposed. In this paper, the pressure-sensitive shear strength of SHCC containing short discontinuous PVA fibres is modelled with a three-parameter failure criterion. The parameters of the criterion are calibrated to the experimental results obtained from several tests that combine shear and normal pressure. These include uniaxial tension and compression, split tests, triaxial compression, and a series of push-off tests with and without reinforcement crossing the shear sliding plane. The calibration of the failure criterion explicitly accounted for the magnitude of internal confinement which is generated in the cementitious matrix in response to fibre tension. The criterion is appropriate for general purpose analysis of the stress state of SHCC, but most importantly it is used to assess the SHCC contribution to the shear strength of structural elements.

Ti3C2Tx MXene modified polyethylene fibers for enhancing interface properties of strain-hardening cementitious composites

MXene is a new two-dimensional transition metal carbide/nitride with remarkable hydrophilicity, which has been widely applied in multifunctional coatings. In this study, Ti3C2Tx MXene was synthesized by LiF/HCl solution etching of Ti3AlC2 and used to modify the surface of polyethylene (PE) fiber, enhancing the interfacial properties between fiber and matrix and further improving the tensile properties of strain hardening cementitious composites (SHCC). The tensile stress and strain of SHCC incorporating the MXene-coated PE (MXene@PE) fiber increased by 18.73 % and 93.60 %, respectively, accompanied by reduced crack width and crack spacing. Single fiber pullout results showed that the frictional bond strength increased by 71.35 % due to the strong chemical bond between fiber and matrix. The microstructure of MXene@PE fiber and bonding properties were characterized by SEM/EDS, FTIR, and XPS. The MXene was proved to have a dual effect of bonding to PE fiber and to C–S–H via covalent and hydrogen bonds.

Bio-inspired based meta-heuristic approach for predicting the strength of fiber-reinforced based strain hardening cementitious composites

A recently introduced bendable concrete having hundred times greater strain capacity provides promising results in repair of engineering structures, known as strain hardening cementitious composites (SHHCs). The current research creates new empirical prediction models to assess the mechanical properties of strain-hardening cementitious composites (SHCCs) i.e., compressive strength (CS), first crack tensile stress (TS), and first crack flexural stress (FS), using gene expression programming (GEP). Wide-ranging records were considered with twelve variables i.e., cement percentage by weight (C%), fine aggregate percentage by weight (Fagg%), fly-ash percentage by weight (FA%), Water-to-binder ratio (W/B), super-plasticizer percentage by weight (SP%), fiber amount percentage by weight (Fib%), length to diameter ratio (L/D), fiber tensile strength (FTS), fiber elastic modulus (FEM), environment temperature (ET), and curing time (CT). The performance of the models was deduced using correlation coefficient (R) and slope of regression line. The established models were also assessed using relative root mean square error (RRMSE), Mean absolute error (MAE), Root squared error (RSE), root mean square error (RMSE), objective function (OBF), performance index (PI) and Nash-Sutcliffe efficiency (NSE). The resulting mathematical GP-based equations are easy to understand and are consistent disclosing the originality of GEP model with R in the testing phase equals to 0.8623, 0.9269, and 0.8645 for CS, TS and FS respectively. The PI and OBF are both less than 0.2 and are in line with the literature, showing that the models are free from overfitting. Consequently, all proposed models have high generalization with less error measures. The sensitivity analysis showed that C%, Fagg%, and ET are the most significant variables for all three models developed with sensitiveness index higher than 10 %. The result of the research can assist researchers, practitioners, and designers to assess SHCC and will lead to sustainable, faster, and safer construction from environment-friendly waste management point of view.