Strain Hardening Cementitious Composites Research Articles

Bio-inspired 3D printing of strain-hardening cementitious composites reticulated shell roofs

Inspired by the diving bell structure of the water spider, this study presents an innovative 3D printed strain-hardening cementitious composite (3DP-SHCC) reticulated shell roof. The compressive behavior of the 3DP-SHCC reticulated shell roof is evaluated using a combination of experimental tests and numerical simulation approaches. The 3DP-SHCC reticulated shell roof features excellent mechanical properties and an aesthetically pleasing appearance. The specific energy absorption and ductility index of this structure are 0.065 J/g and 0.078, respectively. The feasibility of this concept is validated by constructing a complete building structure within just 16 min. This printing process has the potential to create complex designs with minimal labor, making it suitable for rapid construction in extreme environments.

A multi-scale modeling method for tensile properties of strain-hardening cementitious composites

The synergistic design of components of Strain-Hardening Cementitious Composites (SHCC) based on micromechanics is the critical to realize its high strength and ductility. We have developed a mesoscale model for revealing effects of mesoscopic parameter of SHCC on its multiple cracking behavior. However, the heterogeneity of mortar in SHCC, which may influence the saturated multiple cracking, was usually absent in the existing mesoscale model. In this paper, a sub-mesoscale model of mortar considering the fine aggregates, hydrated cement paste, and interfacial transition zones (ITZ) are introduced into the previous SHCC mesoscale model. A parameter transfer method linking these two scales is proposed. By linking them, the parameter design of SHCC of different scales can be considered comprehensively. The proposed model is validated by the three-point bending test and uniaxial tensile test of SHCC. The effects of fine aggregate volume, tensile strength of hydrated cement paste and tensile strength of interfacial transition zone on the mechanical behavior are parametrically analyzed via the validated model. The results show that the increase of the volume content of fine aggregate will reduce the tensile strength and elastic modulus of SHCC mortar matrix, while the strength of hydrated cement paste has a significant increase in the first crack stress of SHCC, and the ITZ strength mainly affects the elastic modulus of SHCC mortar. The developed model provides a reference for the material optimization design of SHCC.

Nature-inspired approach for enhancing the fracture performance of 3D printed strain-hardening cementitious composites (3DP-SHCC)

3D printing technology enhances design flexibility, enables the creation of complex geometrical structures, facilitates rapid prototyping, and allows the fabrication of micro- and macroscopic structures. This study investigates the use of 3D concrete printing to create Bouligand structures inspired by mantis shrimp. Bouligand-printed strain-hardening cementitious composites (SHCC) with different pitch angles (15°, 30°, 45°, 60°, 75°, and 90°) are fabricated and compared with traditional parallel-printed and mold-cast SHCC. The fracture behavior of these specimens is investigated through three-point bending tests on notched beams. The results reveal that Bouligand-printed specimens exhibit enhanced flexural strength, fracture energy, and fracture toughness, ranging from 0.97 to 1.29 times, 0.99 to 1.63 times and 0.87 to 1.47 times that of the mold-cast specimens, respectively. Bouligand-printed specimens with a pitch angle of 30° exhibits the highest flexural strength, fracture energy, and fracture toughness. The Bouligand-printed SHCC enhance toughness through the synergistic effects of crack twisting and bridging. A finite element model integrating cohesive elements with the concrete plastic damage model is developed to numerically replicate the experimental process. This study highlights the potential of 3D concrete printing for the fabrication of biomimetic concrete structures with superior fracture performance.

Sustainable and mechanical properties of Engineered Cementitious Composites with biochar: Integrating Micro- and Macro-Mechanical Insight

Engineered Cementitious Composites (ECC) are ductile, strain-hardening cementitious composites with a tightly controlled crack opening profile. A significant concern in the development and application of ECC is its high carbon emissions associated with high cement content consumption. As an emerging green additive, biochar can significantly cut down on the carbon emission of concrete products. However, research that integrates micro- and macro-mechanical insights with biochar incorporation is limited. In this study, micro-mechanical tools indicated that a certain amount of substitution biochar could enhance the tensile properties of ECC. The study assessed various properties including compressive strength, porosity, density, tensile performance, crack pattern, sustainability and cost of ECC with different biochar proportions. The findings showed that incorporating 10% to 20% biochar effectively increased the tensile strain capacity and decreased the crack opening width in ECC materials. This improvement can be attributed to the introduction of finer biochar particles (≤75μm) at the fiber/matrix interfacial transition zone, which alters the fiber-bridging force by reducing the chemical and frictional bond strength between the fiber and matrix, as revealed by micro-mechanical tests and microstructural inspection. Moreover, the utilization of biochar contributes to reducing the carbon emission of ECC, enhancing sustainability while maintaining a ∼10% minimal reduction in compressive strength. Overall, this study introduces a novel approach for reusing low-carbon biomass waste in the production of building materials, offering potential advantages in micro- and macro-mechanical performance, cost-effectiveness, and environmental sustainability.

Eco-friendly strain-hardening cementitious composites with recycled PET fine aggregate: Mechanical behavior and environmental benefits

The production of strain-hardening cementitious composites (SHCC) heavily relies on natural fine aggregates. This study employs recycled PET fine aggregates to prepare PET-modified SHCC (P-SHCC). The physical properties and mechanical behavior of P-SHCC with different PET volume replacement ratios (0 %, 25 %, 50 %, 75 %, and 100 %) are experimentally investigated. The microstructures were examined to analyze the impact of additional defects induced by the interfacial transition zone between recycled PET and cementitious matrix. The multiple cracking behavior was discussed based on the crack parameters. The results indicate that the incorporation of PET significantly enhances the ultimate strain and crack control capability of SHCC while reducing the material's density. Furthermore, energy consumption, carbon emission, and comprehensive environmental indexes were employed to analyze the environmental benefits. The findings demonstrate the feasibility of preparing SHCC with recycled PET fine aggregate, particularly in enhancing the strain capacity and environmental benefits.

MXene nanosheets magic: Unveiling the dual effect of strength and ductility enhancement in strain hardening cementitious composites

The aim of this study was to modify strain hardening cementitious composite (SHCC) using MXene nanosheets to further enhance its strength and ductility. The results showed that the addition of 0.03 wt% MXene nanosheets increased the compressive strength and tensile strain of SHCC by 18.04 % and 88.18 %, respectively. The mechanism of MXene nanosheets in improving the mechanical properties of SHCC was revealed by single fiber pullout test, micromechanical analysis, microstructure analysis and finite element analysis. Firstly, MXene nanosheets fill the pores inside the matrix, reduce the porosity of the matrix, disperse the stress, and inhibit the crack propagation, thus improving the compressive properties of SHCC. Secondly, when MXene nanosheets adhered to the fiber surface, they modified the interfacial properties between the fiber and the matrix, preventing fiber pullout and consequently improving the tensile ductility of SHCC.

PET particles modify strain hardening cementitious composites: An approach to introduce defects to enhance deformation capacity

Enhancing deformation capabilities remains a critical direction in the research of Strain-Hardening Cementitious Composites (SHCC). This investigation introduces Polyethylene Terephthalate (PET) particles as a novel method to induce micro-defects within SHCC, aiming to reduce the material's initial crack strength and improve its deformability. Through the exploration of various PET particle volumetric substitutions for traditional aggregates, the development of PET particle-modified SHCC (PMSHCC) was achieved. The paper examines the impact and mechanisms of different PET volumetric substitution rates (0 %, 5 %, 10 %, 15 %, 20 %, and 25 %) on the workability, axial compression strength and tensile properties of PMSHCC. By employing Digital Image Correlation techniques, the progression of crack width and density in PMSHCC under tensile load was documented, facilitating an analysis of the influence mechanisms of varying PET volumetric substitution rates on the tensile strain-hardening behavior of PMSHCC. The findings indicate that the increased Interfacial Transition Zone (ITZ) thickness between PET particles and the cement matrix, combined with the lower elastic modulus of PET particles compared to the cement matrix and quartz sand, collectively contribute to a reduction in tensile initial crack strength and an enhancement in ultimate tensile strain of PMSHCC. Within the examined range, an increase in the PET volumetric substitution rate significantly improves the ultimate tensile strain of PMSHCC by up to 76.0 %, with a minimal reduction in tensile strength of only 3.99 %. Moreover, the study proposes a tensile linear strengthening elasto-plastic model for PMSHCC incorporating the PET substitution rate, enabling accurate prediction of the material's tensile stress-strain behavior. These findings not only offer a novel pathway for the utilization of waste plastics but also provide significant insights for enhancing the deformability of SHCC.

Numerical assessment of fiber distribution effects on strain-hardening cement composites using a rate-dependent Voronoi-Cell-Lattice-Model

Strain-hardening cementitious composites, also known as high-performance fiber-reinforced cementitious composites, display exceptional strength and toughness not only under static conditions but also under high-speed dynamic loading. The mechanical properties of these composites are greatly influenced by the orientation and dispersion of embedded fibers. However, experimental analysis of complex fiber arrangements in real specimens has limitations, necessitating the development of computational models to understand the impact of fiber distribution. This study examines the effect of fiber distribution conditions on composite behavior using a Voronoi-Cell-Lattice-Model that incorporates reinforcing effects into discrete-type quasi-brittle matrix elements. Firstly, virtual fiber distribution models revealed that as the gauge length of specimens increased, weaknesses in fiber distribution were more likely to form, leading to decreased strength and strain capacity. Secondly, the model demonstrated that favorable fiber orientation relative to the loading direction and minimal sectional deviation in fiber dispersion significantly increased strain capacity and toughness. Finally, the study explored the wall-effect that may arise during specimen fabrication due to the boundary of the casting mold.

Investigation of non-uniform carbonation in strain-hardening magnesia composite (SHMC) and its impacts on fiber-matrix interface and fiber-bridging properties

Unlike Portland cement, the reactive magnesia cement (RMC) develops its strength via carbonation. Non-uniform microstructure and properties due to the varied carbonation degree across cross-section depth have thus been observed. However, the existing micromechanics design theory employs uniform material properties (cementitious matrix and fiber-matrix interface characteristics) to design strain-hardening composites. This research investigated such non-uniform carbonation in a strain-hardening magnesia composite (SHMC) and its impacts on fiber-matrix interface and fiber-bridging properties. Results showed that mineral phase composition (of the cementitious matrix) and fiber-matrix interface properties across cross-section depth are highly non-uniform in SHMC due to varied carbonation degrees. The outer layer exhibited a much higher carbonation degree with significantly stronger fiber-matrix friction, while the inner core showed negligible carbonation with distinct fiber-matrix properties. Insights gained from the micro-scale investigation were used to calculate the fiber-bridging constitutive law of SHMC with non-uniform carbonation across cross-section depth and to assess its strain-hardening performance. This investigation highlights the importance and necessity of considering non-uniform carbonation in the modeling and design of SHMC. The study presents a framework for the consideration of non-uniform micromechanical parameters in the design of strain-hardening cementitious composites.

3D printed strain-hardening cementitious composites (3DP-SHCC) reticulated shell roof inspired by the water spider

Inspired by the diving bell of the water spider, this paper designs and fabricates nature-inspired 3D printed strain-hardening cementitious composites (3DP-SHCC) reticulated shell roofs. The compression performance and energy absorption capabilities of 24 specimens with eight different strut angles are evaluated through a combined experimental and simulation approach. The results demonstrate that all specimens exhibit excellent ductility and structural integrity under ultimate load conditions. The 45–45 and 60–60 specimens exhibit the highest energy absorption and efficiency, respectively, while 60–90 specimens exhibit the best ductility. Compared with traditional lightweight concrete structures, reticulated shells have lower average structural density, higher specific energy absorption, and ductility index values. A building with a proposed nature-inspired 3DP-SHCC reticulated shell roof is constructed to verify buildability, demonstrating reduced construction time and enhanced automation. This paper offers valuable insights for highly automated construction projects, especially in extreme environments.

Mechanical and environmental performance of high-strength strain-hardening cementitious composites with high-dosage ternary supplementary cementitious materials: Fly ash, limestone, and calcined clay

Strain-Hardening/Engineered Cementitious Composites (SHCC/ECC) are emerging as cementitious composites with high deformation capacity and excellent crack control ability. However, the high cement dosage (typically 1000–1500 kg/m3) in conventional high-strength SHCC leads to high environmental impacts, while using high-dosage conventional supplementary cementitious materials (SCM) to replace cement typically leads to low strength. This study aims to solve this conflict by using ternary SCM to develop high-strength SHCC with satisfactory mechanical properties and environmental performance. High dosages of ternary SCM (50–80 % by weight of binder) were explored, with 10–70 % fly ash and 0–40 % limestone calcined clay (LCC). Test results showed that with 30 % Portland cement, 50 % fly ash, and 20 % LCC, SHCC achieved compressive strength of 96.89 MPa, tensile strength of 11.24 MPa, ultimate tensile strain of 6.71 %, and average crack width of 78 µm. Additionally, the embodied carbon and energy per unit tensile strength of the developed SHCC is much lower than that of conventional SHCC. To assess the overall performance of SHCC for sustainable construction, seven key performance indices were comprehensively compared, encompassing mechanical properties, environmental impact and economic viability. This new version of sustainable high-strength SHCC holds great potential for reducing carbon footprint in various practical applications.

Flexural Behavior of Self-Compacting PVA-SHCC Bridge Deck Link Slabs

This paper studied the flexural behavior of bridge deck link slabs made with polyvinyl alcohol–strain-hardening cementitious composites (PVA-SHCC). The tensile and flexural properties of the self-compacting PVA-SHCC with four volume fractions, i.e., 0%, 1%, 1.5%, and 2%, were evaluated first. Next, using the similarity theory, composite models with a geometric similarity ratio of 1:5 were designed to represent the bridge deck with the link slabs. The models considered three materials for link slabs, including concrete, cement mortar, and self-compacting PVA-SHCC, and two different curing ages at 7 and 56 days. Bending tests were performed to investigate the flexural behavior of the models. Based on the fractal theory, the cracking characteristics of the models with different types of link slabs were compared, and the relationship between fractal dimensions and the flexural behavior of the models was studied. Numerical models were built to correlate with the results from the bending tests. It was illustrated that the flexural behavior of the self-compacting PVA-SHCC link slab is better than that of concrete and cement mortar link slabs, where the crack initiation and propagation can be postponed. The results can provide theoretical support and design guidance for the self-compacting PVA-SHCC bridge deck.

Simultaneous enhancement of ductility and sustainability of high-strength Strain-Hardening Cementitious Composites (SHCC) using recycled fine aggregates

In this study, recycled fine aggregates (RA) were successfully adopted to produce strain-hardening cementitious composites with a compressive strength of over 120 MPa. A multiple-scale investigation was conducted to study the tensile performance and cracking mechanism of the developed cement-based composites. Compared to the fine silica sand-based counterpart, significantly higher tensile strain capacity (>5%), more distinguished multiple cracking, and smaller average crack width (<100 μm) were achieved in RA-based strain-hardening cementitious composites. Supported by microscopic and mesoscopic results, the old mortar of RA with loose microstructures and weak RA/matrix interfaces were found to work as “additional flaws” in the matrix, which effectively tailored the distribution of active flaws and promoted multiple cracking behavior. In addition, the developed RA-based composites presented higher sustainability and lower material costs compared to fine silica sand-based ones. This study provides a new avenue for the upcycling of construction wastes in developing greener high-performance fiber-reinforced cementitious composites.

Performance of high-strength green strain-hardening cementitious composites incorporating CSA/CAC cements and GGBS

Strain-hardening cementitious composites (SHCCs) possess crack control and durability properties. In the pursuit of reducing CO2 emissions and addressing potential issues of slow strength development for SHCCs with pozzolans, the objective of this study was to develop high-strength green SHCCs (HSG-SHCCs) that exhibit improved early strength, drying shrinkage, and environmental friendliness. A ternary binder system was proposed, comprising of ground granulated blast furnace slag (GGBS), ordinary Portland cement (OPC), and either calcium sulfoaluminate cement (CSA) or calcium aluminate cement (CAC). The fresh, mechanical, and durability properties of the proposed HSG-SHCCs were experimentally investigated. Additionally, the microstructures and chemical phases of the developed CSA/CAC-GGBS-OPC ternary binder system were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that the developed HSG-SHCCs demonstrated 6-hour and 28-day strengths of up to 11 MPa and 110 MPa, respectively. The CSA/CAC-based ternary binder system also exhibited enhanced durability and improved drying shrinkage. However, the inclusion of CSA and CAC in HSG-SHCCs could lead to a reduction in tensile performance, specifically in strain capacity. The main hydration products of the CSA/CAC-GGBS-OPC ternary binder system were C-S-H, ettringite, gibbsite, and calcium hydrate. In addition to the fresh, mechanical, and durability properties, the environmental impact of the developed HSG-SHCCs was also assessed. The results indicated that a 30 % replacement of OPC with CSA cement in the HSG-SHCC mix notably improved the trade-off among CO2 emissions, compressive strength, and tensile cracking resistance.

Flexural strengthening of RC beams using PGFRP bars embedded in strain-hardening cementitious composites (SHCC)

The application of the near surface mounted (NSM) fiber reinforced polymer (FRP) as an additional reinforcement at tension side of flexural members is efficient to upgrade the flexural strength. However, this technique must be applied to concrete beams having hard concrete cover to avoid premature failure induced by concrete cover deterioration. The current research aims to improve and evaluate the flexural behavior of reinforced concrete (RC) beams strengthened with embedded prestressed glass fiber reinforced polymer (PGFRP) bars, based on replacement of weak concrete cover with a layer of strain hardening cementitious composites (SHCC). For this investigation, one reference beam (without strengthening) and nine flexural strengthened beams were tested under a four-point bending scheme. All beams had the same reinforcement and geometry, 150 mm width, 300 mm total depth, a total length of 3000 mm and the effective span was 2700 mm. The test parameters were: (1) the strengthening technique (conventional NSM-PGFRP bars, NSM-PGFRP bars covered with external SHCC layer and PGFRP bars embedded in SHCC replaced cover), (2) the prestressing levels in the GFRP bars (0, 10 % and 20 % of the ultimate bar strength) and (3) the thickness of the SHCC layer (30, 40 and 50 mm). Compared to the conventional NSM strengthened beams, the conjunction of SHCC with PGFRP bars not only prevented the spalling of the concrete cover but also increased the load carrying capacity up to 26.5 % and the ductility up to 16 %. A model for the prediction of flexural capacity of the strengthened beams having SHCC replaced cover was conducted, the predicted ultimate loads have a good consistency with the test results.

Pseudo strain-hardening alkali-activated composites with up to 100 % rubber aggregate: Static mechanical properties analysis and constitutive model development

Strain-hardening alkali-activated materials (SHAAM) provide a sustainable alternative to conventional strain-hardening cementitious composites (SHCC), offering significant environmental and economic benefits. This study examines the effects of various rubber powder (RP) volume replacement ratios (0 %, 25 %, 50 %, 75 %, and 100 %) on the properties of Rubber Powder Modified Strain-Hardening Alkali-Activated Composite Material (R-SHAAM), assessing workability, uniaxial compressive behavior, and uniaxial tensile behavior. The findings reveal that R-SHAAM with 100 % RP aggregate significantly enhances durability, achieving a 50.7 % reduction in crack width. Optimal axial tensile performance is observed at a 25 % replacement ratio, where R-SHAAM shows an 8.1 % increase in tensile strength and a 4.1 % increase in ultimate tensile strain. The robust multi-dimensional performance of R-SHAAM across different RP replacement ratios suggests its potential for diverse applications including pavement, marine structures, and explosive engineering, thereby offering valuable insights into sustainable material design and the effective recycling of waste materials in construction.

Flexural performance of concrete beams via 3D printing stay-in-place formwork followed by casting of normal concrete

In traditional mold-casting for concrete, the process of assembling and demolding formwork is both costly and time-intensive, limiting the design possibilities of complicated shaped and composite applications. Autonomous or semi-autonomous 3D concrete printing presents an innovative solution, allowing for the customization of intricate formwork shapes and facilitating the creation of composite structures. This study develops and manufactures a novel concrete beam that incorporates 3D-printed (3DP) ultra-high performance strain-hardening cementitious composites (UHP-SHCC) U-shaped jackets used as stay-in-place formwork, with normal concrete (NC) as filled concrete. To evaluate the flexural performance of the proposed beam, composite beams with cast-in-place formwork and post-cast NC, fully cast NC beams and fully cast UHP-SHCC beams are also tested. The flexural performance of these beams is assessed through four-point bending tests, including failure modes, load–displacement response, and cracking behavior. Results indicate that concrete beams utilizing 3DP UHP-SHCC stay-in-place formwork demonstrate superior flexural performance, characterized by deflection-hardening behavior, outperforming the other tested configurations.

Fracture and multiple-cracking modelling of strain-hardening cementitious composites

Strain-hardening cementitious composites (SHCC), composed of short fibres embedded within brittle matrix, exhibit distinctive pre-peak strain-hardening characteristics and remarkable tensile ductility. The fracture and failure process of SHCC, involving both hardening and softening stages as a result of matrix multiple micro-cracking and strain localization, is highly complex and poses a significant challenge for numerical modelling. In the present paper, a novel numerical framework, characterized by the bi-layer superposed cohesive zone strategy, is developed for the numerical modelling of fracture and multiple cracking of SHCC, at both the material scale and structural scale. The developed model is based on diffused cohesive interface model, but with adaptions to consider fibre bridging mechanism. The crack interface is simulated by two cohesive elements sharing the same nodes: one for the matrix-cohesion effect and the other for the fibre-bridging effect. Cohesive constitutive relations of matrix cohesion and fibre bridging are carefully assigned. The proposed model is first validated on the material scale through a uniaxial tension test. With the aid of a random material field, multiple-cracking phenomenon and stress fluctuation are successfully predicted by the model. The model is then applied to the structural fracture modelling, where four case studies, including both pure mode I and mixed mode fracture, are performed. The size effect and boundary effect on the fracture behaviour are well captured by the numerical modelling. The model proposed in the current work has the potential to be extended to the multiple cracking modelling of other materials.

Development of strain-hardening cementitious composites (SHCC) as bonding materials to enhance interlayer and flexural performance of 3D printed concrete

3D concrete printing (3DCP) has limitations in weak interlayer bond strength and reinforcement integration. To tackle these challenges, this study aims to develop and deposit strain-hardening cementitious composites (SHCC) as bonding materials between layers for simultaneous enhancement of interlayer bond strength and flexural ductility of 3D-printed concrete. The impact of rheological properties of SHCC materials and configurations of SHCC layers on multi-layer printed structures were investigated experimentally and theoretically. Results show an increase in interlayer bond strength by approximately 80 % compared to the reference without SHCC interlayers. Microstructure characterization reveals that the SHCC bonding material effectively reduces the interfacial porosity by nearly 35 %. Four-point bending was adopted to evaluate flexural strength, ductility, and fracture properties. With SHCC interlayers, flexural hardening behavior was attained with an increase in flexural strength, deflection, and energy absorption capacity by approximately 25 %, 180 %, and 800 %, respectively. Furthermore, a theoretical model was proposed to predict flexural strength with nearly 95 % accuracy. The findings reveal that the newly developed printing scheme has the potential to address both reinforcement and weak interlayer problems in 3DCP.

Experimental and numerical investigations of the shear performance of reinforced concrete deep beams strengthened with hybrid SHCC-mesh

This paper investigates the shear strengthening of simply supported deep beams using welded wire mesh and glass fiber mesh filled with strain-hardening cementitious composites (SHCC) concrete. Nine reinforced concrete (RC) deep beams were tested in this study to investigate different shear-strengthening techniques including the type of mesh (glass fiber mesh and welded steel wire mesh), number of layers (single and double), and the effects of additional anchor using high-strength bolts on the shear performance of RC deep beams. The results showed the SHCC-mesh jackets increased the ultimate load of the deep beams by up to 82 %, cracking load by up to 73 %, elastic stiffness by up to 457 %, and energy absorption by up to 380 % compared to the unstrengthen control beam. Furthermore, the welded wire mesh provided greater enhancements of strength, stiffness, and energy absorption than the glass fiber mesh. In addition, anchoring the jackets further improved the strengthening efficiency. Advanced nonlinear three-dimensional finite element models were also simulated to capture the structural responses of the RC deep beams strengthened using welded wire mesh and glass fiber mesh. It was found that the numerical models accurately predicted the behavior of the beams upon validation against the experimental results.