Tensile Strain Capacity Research Articles

Reusing waste glass fines to substitute cement and sand for recycled ultra-high performance strain-hardening cementitious composites (UHP-SHCC)

Using waste glass fines (WGF) as cement and silica sand replacement for recycled ultra-high performance strain-hardening cementitious composites (UHP-SHCC) provides an effective method for the high-value utilization of waste glass while reducing its carbon emissions and preparation cost. This study investigated the feasibility of preparing recycled UHP-SHCC by simultaneously substituting both cement and silica sand with WGF. WGF, abundant in amorphous components, exhibited favorable pozzolanic activity and filling effect. Substituting high-volume cement with WGF negatively impacted the hydration reaction and micro-properties of UHP-SHCC matrix, while replacing silica sand with WGF improved hydration reaction and micro-structure. Generally, substituting WGF for both silica sand and cement decreased the maximum cumulative hydration heat of UHP-SHCC. The drying shrinkage resistance of UHP-SHCC is improved with WGF replacing an appropriate dosage of cement and silica sand. The compressive and flexural strengths of UHP-SHCC declined as the high-volume replacement of cement with WGF, but improved with an increase in the proportion of silica sand substituted. Simultaneously substituting cement and silica sand with WGF can yield recycled UHP-SHCC with mechanical strengths comparable to those of reference UHP-SHCC. The ductility of UHP-SHCC exhibits a trend of first increasing and then decreasing as the proportion of cement substituted by WGF increases, while it decreases with the addition of WGF as silica sand replacement. Simultaneously substituting both cement and silica sand with WGF can obtain more sustainable UHP-SHCC with high strength and ductility. The tensile strength and tensile strain capacity of recycled UHP-SHCC containing WGF substituting 100 % silica sand and 75 % cement are 10.3 MPa and 7.2 %, respectively.

Microstructure and mechanical properties of engineered cementitious composites (ECC) with recycling extracted titanium tailing slag (ETTS)

Generally, engineered cementitious composites (ECC) have a high proportion of cement, resulting in substantial carbon dioxide emissions that detrimentally affect their environmental sustainability. In this paper, the industrial waste, extracted titanium tailing slag (ETTS), was employed as a partial replacement for cement in the preparation of high-strength ECC. The experimental results show that recycling ETTS to partially replace cement reduced the generation of portlandite (CH), hydrate calcium silicate (C-S-H) and ettringite (AFt) in the ECC matrix, moreover, the microstructures of ECC matrix was also coarsened, both of the above likely against the gaining of strength of ECC, such as the compressive and tensile strength of ECC were decreased from 88.9 MPa to 10.54 MPa in reference ECC (T0) to 75.6 MPa and 9.25 MPa as the replacement ratio up to 30 %, respectively. In addition, the X-ray diffraction analysis revealed that the ETTS-ECC mixture exhibits diffraction peaks of Friedel's salt, indicating that the hydration products in the matrix have a chemical adsorption effect on chloride ions. Moreover, the tensile strain capacity of ECC was significantly improved to 5.69–6.65 % from 2.81 % in T0 upon the ETTS incorporating, meanwhile, the average width of cracks in ECC was narrowed from 92.8 μm to 74.6 μm. The present findings are anticipated to increase the utilization of this industrial waste and mitigate the environmental impact associated with cement production.

Limestone calcined clay-based engineered cementitious composites (LC3-ECC) with recycled sand: Macro performance and micro mechanism

Limestone calcined clay cement (LC3) contributes to the development of sustainable cement-based materials. In this study, LC3 was combined with fly ash (FA) and recycled sands (RS) to develop engineered cementitious composites (ECC). Three FA/LC3 ratios (1, 1.5, and 2) and three RS particle sizes (0.15–1.18 mm, 0.15–2.36 mm, and 0.15–4.75 mm) were studied. Compared to ordinary Portland cement (OPC)-based paste, the LC3 substitution resulted in higher hydration heat and hydration degree, forming more hydration products. Although LC3 substitution produced a slightly lower compressive strength, a more robust tensile strain-hardening behavior than OPC-based ECC was achieved. The increasing FA/LC3 ratios gradually reduced compressive strength, tensile strength, and crack width. The multiple cracking behavior with controlled widths of LC3-based ECC was found to be more stable, which could be traced to the superior properties of fiber/matrix interfacial transition zone. In addition, utilizing RS as fine aggregates with various particle sizes could achieve an ultra-high tensile strain capacity exceeding 8 % for LC3-based ECC, thereby enhancing its utilization efficiency. Furthermore, the utilization of LC3 resulted in 28.6–47.1 % and 6.6–22.0 % reductions in carbon emission and embodied energy, respectively. The combination of LC3 and RS holds a promising approach to developing sustainable ECC with desirable mechanical performance.

Preparation and properties of alkali-activated slag/metakaolin incorporated with hybrid PE-modified beta-silicon carbide whiskers

Alkali-activated materials are considered a promising sustainable development cementitious materials. However, the brittleness of alkali-activated materials hinders their application, thus deteriorating durability. This study investigates properties including macroscopic and microscopic tests, and introduces modified alkali-activated slag/metakaolin using polyethylene(PE) and modified beta-silicon carbide whiskers(β-SiCw). Modified β-SiCw were prepared utilizing successful methods. The compressive and flexural tests were used to evaluate the mechanical properties under different curing times. The uniaxial tension and fracture toughness were comprehensively discussed to reveal ductility behavior. Meanwhile, the ductility index of modified specimens was also analyzed. The microstructure and morphology were researched using scanning electron microscopy(SEM), mercury intrusion porosimetry(MIP), fourier transform infrared spectroscopy(FTIR) and x-ray diffraction(XRD). Combined 1.0 wt% PE with 0.45 wt‰ modified β-SiCw, modified alkali-activated slag/metakaolin showed a 63.7 MPa compressive strength and a 7.3 MPa flexural strength. Simultaneously, the tensile strain capacity obtained 5.56 % with a 5.20 MPa tensile stress. The fracture toughness was optimized designed for the foundation of modified alkali-activated slag/metakaolin. Moreover, a new synergism mechanism for hybrid PE-modified β-SiCw was explained.

The Flexural Behavior of Reinforced Ultra-High Performance Engineering Cementitious Composite (UHP-ECC) Beams Fabricated with Polyethylene Fiber (Numerical and Analytical Study)

Ultra-high performance engineered cementitious composite (UHP-ECC), which is a new and ductile version of concrete, has attracted researchers recently due to its exceptional mechanical properties: its very high compressive strength (from 100 to 200 MPa) and very high tensile strain capacity (not less than 3% and up to 8%). However, the available experimental literature is small due to its very high cost. To overcome the high cost of the experiments of UHP-ECC, the finite element modeling package ANSYS was used to create a new modeling technique using the Menetrey–Willam constitutive model, recently added to ANSYS. This technique was validated using previous experimental results for UHP-ECC beams and found to be accurate and effective. The previous FE model was used to conduct a parametric study and the variables—the compressive strength of the concrete, the percentage of the volume content of polyethylene fibers, the tensile reinforcement ratio, and the span-to-depth ratio—were found to be effective upon the flexure behavior of the reinforced UHP-ECC beams. As the analysis and design of UHP-ECC beams fabricated with polyethylene fiber are not available yet through design codes, an analytical model including some equations was deduced to calculate the flexure capacity of such beams. The results of the parametric study were used to investigate the validity and accuracy of the analytical model. The proposed equations demonstrated a good estimation compared with the numerical analysis results.

Review of Recent Developments in Tensile Properties of Engineered Geopolymer Composites

Engineered Cementitious Composite (ECC) is a type of highly ductile cementitious material. However, due to its characteristics of high energy consumption and high carbon emissions, it is necessary to seek a new type of low-carbon and environmentally friendly substitute. Engineered Geopolymer Composite (EGC), as a promising construction material for replacing ECC, has broad application prospects. Through visual analysis of the relevant literature in Web of Science, it was discovered that the research on EGC mainly concentrates on aspects such as the types of precursors, the chemical composition of the alkali-activated solution, and the related parameters of fibers. This paper mainly combines the relevant experimental research data on the tensile properties of EGC conducted by scholars at home and abroad, and focuses on analyzing the influence of precursor types, the chemical composition of the alkaline activator, and fibers on the tensile properties of EGC. The statistical results indicate that fly ash and ground granulated blast-furnace slag (GGBFS) are the most commonly used precursor materials. Replacing an appropriate amount of fly ash in the precursor with GGBFS can significantly enhance the tensile strength of EGC. The type of alkaline activator and its molarity have a relatively obvious influence on the tensile properties of EGC. An increase in the molarity of NaOH within a certain range can enhance the tensile strength of EGC. Furthermore, the incorporation of fibers, especially synthetic fibers such as polypropylene (PP) and polyvinyl alcohol (PVA) fibers, as well as inorganic fibers such as glass fibers (GF) and carbon fibers (CF), can effectively enhance the tensile strength and tensile strain capacity of EGC. The use of hybrid fibers may further improve the tensile properties.

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 %–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 (≤75 μm) 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.

Machine Learning Modeling for Predicting Tensile Strain Capacity of Pipelines and Identifying Key Factors

Abstract Machine learning (ML) techniques have recently gained great attention across a multitude of engineering domains, including pipeline materials. However, their application to tensile strain capacity (TSC) modeling remains unexplored. To bridge this gap, this study developed and evaluated an ML model to predict the tensile strain capacity of girth-welded pipelines. The model was trained on over 20,000 data points derived from a TSC equation available in the literature. The ML model demonstrated robust performance in predicting tensile strain capacities. Evidence of this lies in the near-zero means, minimal standard deviations, and normal distribution of residuals for both the training and test datasets. These collectively suggest that the model provides a good fit for the data. Furthermore, the model's loss behavior indicates successful convergence and generalization, without signs of overfitting or underfitting. An analysis using the random forest method revealed that the geometry of the flaw, specifically the flaw depth, is the most influential variable in predicting the TSC. This could be attributed to its significant impact on the fracture toughness of materials. In contrast, material properties and fracture toughness exert less influence relatively, despite their contributions to the model. This finding underscores the importance of flaw geometry in TSC prediction models. Overall, the development of a data-driven TSC model has shown efficient TSC modeling. This model leverages ML techniques, allowing for continuous updates with new data via deep learning.

Study on fracture behaviour of pipeline girth welds based on curved wide plate specimens: Experimental and numerical analysis

Understanding the fracture characteristics and strain capacity of pipelines with girth welds under external loads is crucial for evaluating pipeline safety. The use of curved wide plate (CWP) specimens closely resembling full-scale (FS) pipelines in geometry provides a more realistic representation of crack tip constraint states compared to small-size fracture toughness test specimens in laboratory settings. This study aims to investigate the ductile fracture characteristics of center cracks on the outer surface of girth welds in high-grade steel pipelines under external loads through large-scale CWP tensile tests and advanced numerical simulations. Tensile tests were conducted on CWP specimens using a kiloton tensile testing machine, with double crack opening displacement (COD) gauge monitoring crack mouth opening displacement (CMOD), and high-precision displacement sensors and strain gauges tracking deformation and strains at various positions. The study yielded significant experimental results, and a finite element (FE) model of the CWP was developed using the nonlinear finite element method (FEM) to validate the experimental data against simulation results. The FE model was then used to investigate the influence of material properties on crack propagation resistance and driving force curves. A method for determining the ultimate tensile strain capacity (UTSC) of pipelines based on actual material fracture toughness was proposed. This research contributes valuable experimental data for further exploration of fracture behaviour in large-scale pipeline girth welds and offers insights for safety evaluations of such welds.

Crack-healing of cost-effective engineered cementitious composites reinforced by recycled selvage fiber

This paper presents the first experimental investigation of the crack-healing behavior of recycled selvage fiber-reinforced engineered cementitious composites (RSF-ECCs). Fly ash (FA), ground granulated blast-furnace slag (GGBS), and crumb rubber powder were utilized to fabricate greener ECCs. RSF was used as main reinforcement; it contains polyethylene (PE), glass (GS), and PET fibers. For overall mechanical properties, RSF-ECC incorporating GGBS (ECC-S-RSF) obtained a compressive strength of over 80 MPa and a tensile strain capacity of over 10 %, values that are unprecedented in other recycled fiber-reinforced ECCs. Furthermore, the ECC-S-RSF showed the best cost efficiency among representative recycled and PE fiber-reinforced high-performance ECCs. In terms of the crack-healing performance, test results indicated that RSF-ECCs had excellent healing capacity in closing crack openings, and GGBS had a greater contribution to crack-healing than FA did. However, the stiffness and tensile restorations of RSF-ECCs were relatively modest compared to those of conventional ECCs. Calcium carbonate and C-S-H gel were dominant healing materials of RSF-ECCs.

Enhanced thermal insulation and structural health monitoring with ultra-lightweight ECC incorporating air entrainment and cenospheres

This study presents an approach to produce multifunctional ultra-lightweight engineered cementitious composites (ULW-ECCs) spanning an air-dried density ranging from 1398 to 572 kg/m³ utilizing air-entraining agents (AEA) and fly ash cenospheres. The multifunctional ULW-ECCs combine exceptional mechanical properties with enhanced thermal insulation, self-sensing and self-healing functions. Variation of the AEA content results in compressive strengths ranging from 65.92 to 2.82 MPa, tensile strengths from 5.75 to 0.84 MPa, tensile strain capacities of 6.67 %–2.92 %, and flexural strengths of 14.41 to 3.64 MPa. Thermal insulation properties, including conductivity (20 °C: 0.73–0.20 W/(mK); 800 °C: 0.289–0.065 W/(mK)) across different temperatures, effusivity and volumetric heat capacity, were systematically tested. The small-scale thermal insulation test confirms the outstanding performance of ULW-ECCs in thermal insulation. Furthermore, ULW-ECC exhibits excellent self-sensing ability under tension and bending. Resonant frequency and impedance testing results affirm the self-healing ability. Microstructural analysis using an optical microscope, scanning electronic microscope (SEM), and mercury intrusion porosimeter (MIP) reveals that high-speed mixing, cenospheres, AEA and long polyethylene fibres are crucial for achieving porous structures, low-density and multifunctionality. This novel ULW-ECC holds promising applications in structural retrofitting, enhancing energy efficiency, thermal insulation, fire resistance and enabling simultaneous structural health monitoring.

Strategies for reusing multiple recycled powders: Evaluating the mechanical performance and sustainability of Engineered Cementitious Composites (ECC)

Engineering Cementitious Composites (ECC) are fibre-reinforced cementitious materials with excellent tensile strain capacity. Recycling powder from building and demolition waste can improve the ecological efficiency of concrete and reduce the cost of raw materials. In this study, recycled glass powder (RGP) was used to partially replace traditional cement. Based on using a 1:1 replacement of recycled brick powder (RBP) and recycled concrete powder (RCP) for fine aggregates, two sets of variables were set: the RGP substitution rate (10 %, 15 %, 20 %, and 25 %) and RGP particle-size range (38–75 μm, 75–150 μm, and 150–300 μm). Comprehensive material testing and mechanical experiments were conducted, including X-ray diffraction analysis, thermogravimetric analysis, shrinkage tests, uniaxial compressive tests, uniaxial tensile tests, and scanning electron microscopy. The results indicated that fully substituting quartz sand with RBP and RCP enhanced the ECC performance. Incorporating RGP significantly improved the ultimate tensile strain and crack-propagation ability of the ECC while reducing the 90-d shrinkage rate. The 28-d compressive strength and tensile strength have some loss, but can meet the strength requirements. SEM showed that incorporating RGP weakened the bonding strength of the fibre matrix, making it easier for the fibres to be pulled out. By evaluating the experimental results, the mix ratio of a 20 % substitution rate and 75–150-μm size was selected. A material-sustainability indicator (MSI) analysis of the raw materials and production process of RGP-ECC was performed. The embodied energy, carbon emissions, and economic indices were reduced to a certain extent, thereby improving the ecological efficiency of concrete.

Fully recycled engineered geopolymer composite: Mechanical properties and sustainability assessment

Combining the two advantages of mitigation of dependence on cement and natural sand resources and recycling waste concrete material, the utilization of recycled concrete powder (RCP) and recycled fine sand (RFS) to produce geopolymer concrete is of great value. However, the insufficient compressive strength and inherent brittleness of the existing RCP or RFS geopolymer concrete hampered its application. This paper aims to develop a high-performance engineered geopolymer composite (EGC) by maximizing the recycle amount of RCP and RFS. The effects of RCP and RFS on the physical, mechanical, and microscopic properties of EGC were investigated. The results indicated that, the less reactivity of RCP decreased the amount of gel products and compromised the strength development, while favored the multi-cracking behavior and the robust ductility. RFS showed a stronger interfacial bond with paste than quartz sand, compensating the degradation of strength driven by RCP and marginally affecting the tensile strain capacity. The developed EGC incorporating 50% RCP and 100% RFS possessed an 84 MPa compressive strength, 7.4 MPa tensile strength, and 8.1% tensile strain, which are at the highest level among the existing RCP or RFS geopolymer concretes. The main products included the coexistence of calcium aluminosilicate hydrate and alkali aluminosilicate (C(N)-A-S-H) gel and layered double hydroxide (LDH). The energy- and carbon-reduction were 16% and 57%, respectively, compared to the M45-ECC.The current findings prove the feasibility of utilizing high amounts of recycled materials to produce high value-added concrete.

Curing-dependent behaviors of sustainable alkali-activated fiber reinforced composite: Temperature and humidity effects

Despite alkali-activated fiber reinforced composite (AAFRC) attracting increasing attention due to the advantages of low-carbon and superior tensile performance, the curing-dependent behaviors in practical environments are lack of knowledge. This paper aims to fill this gap by comparably investigating the macro-mechanical properties and pore structures of AAFRC under the different temperatures of −5, 20, and 60 °C and humidities of 60 % and 95 % RH. The loss on ignition, scanning electronic microscope (SEM), and fourier transform infrared spectroscopy (FT-IR) tests were performed to decouple the influence mechanisms. The results showed that the high-temperature curing slightly decreased the tensile and compressive strength but increased the tensile strain capacity with the main reason of decreasing the matrix toughness by forming more micro-cracks. The low-temperature curing deteriorated both the strength and tensile strain capacity by hindering its geopolymerization reaction. A decrease in humidity during the curing process was unconducive to the mechanical strength and slightly affect the tensile strain capacity of AAFRC, which resulted from the loss of water impeded its reaction to proceed. The normalized energy consumption and carbon emission of the AAFRC cured under the standard curing decreased by 22.6 % and 70.2 % than the classic engineered cementitious composite (ECC-M45), respectively, showing great sustainability.

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.

Sea/coral sand in marine engineered geopolymer composites: Engineering, mechanical, and microstructure properties

AbstractUtilizing marine waste and resources for eco‐friendly building materials is pivotal in promoting sustainable development in island and coastal construction industries. Among the potential alternatives, coral sand as well as sea sand stands out as a promising material. This research seeks to explore the potential of coral/sea sand as a fine aggregate in the creation of environmentally sustainable marine engineered geopolymer composites. An assessment was conducted on the influence of varying proportions of coral sand, meant as a substitute for sea sand, on the flowability, drying shrinkage, mechanical properties, and microstructure of the marine engineered geopolymer composites. The findings indicate that as coral sand replaces sea sand, flowability and drying shrinkage decrease, while compressive strength experiences an initial rise followed by a decline. Encouragingly, a combination of coral and sea sands enhances tensile ductility. Overall, a 20 wt.% coral sand mixture yields optimal results, with the compressive strength is 54.4 Mpa and the tensile strain capacity is 2.397% after 28 days. Moreover, microscopic tests reveal changes in hydration products and pore structure. Our research delves into the potential of coral/sea sand as a fine aggregate in the creation of environmentally sustainable marine engineered geopolymer composites.

Elucidating the role of recycled concrete aggregate in ductile engineered geopolymer composites: Effects of recycled concrete aggregate content and size

Utilizing recycled fine aggregate (RFA) as silica sand replacement for ductile engineered geopolymer composites (EGC) provides a high value-added approach to recycling concrete waste and reduces the needs for high-cost silica sand. RFA contains abundant active alkaline substances which can promote the secondary geopolymerization of EGC. Substituting RFA for silica sand can improve EGC micro-characteristics, and the micro-structure of RFA-EGC is further refined with the decreased RFA size. The compressive/flexural strength of EGC is elevated as RFA is incorporated, and the decreased RFA size further enhances the compressive/flexural strength of RFA-EGC. Attributed to the micro-pores and micro-cracks in RFA, including RFA benefits the formation and development of crack, leading to an enhancement in the uniaxial tensile behavior of EGC. The tensile strength and tensile strain capacity of 100 % RFA blended EGC are 5.7 % and 8.6 % higher than those of 100 % silica sand blended EGC. The decreased RFA size can enhance the tensile strength, and an appropriate increase in RFA size improves the tensile strain capacity of RFA-EGC. When RFA size is 0.15–0.3 mm and 0.3–0.6 mm, the tensile strain capacity of 100 % RFA blended EGC is 8.6 % and 12.9 % larger than the reference EGC with 100 % silica sand (0.15–0.3 mm). A moderate increase in silicate modulus can further improve the tensile behavior, and the RFA-EGC with 1.5 M shows the best tensile behavior; besides, the longer fiber length results in the higher tensile strength of RFA-EGC. By optimizing the replacement rate and size of RFA, adjusting the silicate modulus and fiber characteristics, one can achieve a sustainable high-ductility RFA-EGC with exceptional mechanical behavior.

Hardening properties and microstructure of 3D printed engineered cementitious composites based on limestone calcined clay cement

Comparison of three-dimensional (3D) printing and cast methods on the mechanical properties of cementitious materials is the basis for intelligent construction development. To achieve this, a series of experiments including the uniaxial tensile, compressive, flexural and interlayer bonding tests of mould-cast and 3D printed (3DP) specimens are conducted to investigate the effects of different preparation technologies on the microstructure and hardening properties of limestone calcined clay cement (LC3) based engineered cementitious composites (ECC). Results indicate that the tensile strength and strain capacity of the printed LC3-ECC decrease by 16.6%–22.7 % and 43.3%–54.6 % compared to the cast specimens, while it still possesses a strain capacity of 2 % and multiple cracking behaviour. The compressive and flexural properties of the printed LC3-ECC both show significant anisotropy, the maximum values of which are observed in the Z- and Y- directions, respectively. The interlayer bonding strength increases by 54.3%–91.9 % at 28 d compared to that at 7 d due to the hydration of LC3. The pore structure of the printed LC3-ECC is denser than that of the cast LC3-ECC, with more regular arrangement and finer size of pores. The macro-micro properties correlation analysis proves the better comprehensive performance of printed LC3-ECC relative to casted LC3-ECC, as well as reveals the relationship between pore structure and anisotropy. In terms of material sustainability, 3DP-LC3-ECC has a significant reduction in energy and carbon emissions compared to typical M45-ECC, contributing to the environmental development.

Strain-hardening magnesium-silicate-hydrate composites (SHMSHC) utilizing reactive magnesia cement (MgO) and calcined clay (metakaolin)

This study demonstrated the feasibility of utilizing calcined clay (metakaolin) as a silica source for the development of polyethylene (PE) fiber-reinforced strain-hardening magnesium-silicate-hydrate composite (SHMSHC). The study also discussed the effects of variation in the Mg/Si ratio of the mixture when pure silica source (silica fume with SiO2 content >90 %) is replaced with metakaolin (SiO2 content ⁓ 51 %) on the mechanical performance of SHMSHC. A comprehensive mechanical characterization of SHMSHC at composite scale and fiber-matrix interaction effects was conducted. The damage characterization was carried out using residual crack width and spacing analysis. The chemical characterization of the MSH matrix (SHMSHC without fibers) was performed using XRD, TGA, and FTIR, and the microstructural investigation was done using FE-SEM. The MgO-metakaolin paste based SHMSHC showed compressive strength of 51.9 MPa, tensile strength of 5.0 MPa, and tensile strain capacity of 4.7 %, demonstrating the feasibility of calcined clay utilization in SHMSHC. The tensile strain capacity was reduced after the addition of aggregates in SHMSHC. The study demonstrated that the variation in the Mg/Si ratio significantly affects the toughness of the MSH matrix and fiber-matrix interaction characteristics, influencing the strain-hardening potential of SHMSHC.

Data-driven prediction on critical mechanical properties of engineered cementitious composites based on machine learning

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.