This study investigates the effect of aluminosilicate nanotubes (ANTs) on the fresh, mechanical, durability, and microstructural properties of thermally cured geopolymer concrete (GPC) synthesised using Class F fly ash (FA) and metakaolin (MK). ANTs were incorporated at dosages of 0-3.0% by binder weight, and the specimens were cured at 80 degrees C to replicate geothermal conditions. The experimental program included tests for slump flow, compressive and tensile strength (from 3 h to 28 days), water absorption, drying shrinkage, and pore size distribution. To elucidate the geopolymerization process and the role of ANTs in gel evolution and matrix densification, microstructural analyses were performed using X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and derivative thermogravimetry (DTG). Furthermore, a one-way Analysis of Variance (ANOVA) and Tukey's HSD analysis were conducted to evaluate the statistical significance of the findings. The inclusion of ANTs reduced workability, with slump decreasing from 122 mm at 1.0% ANT to 89 mm at 3.0%, due to enhanced internal friction and water adsorption. Compressive strength at 1 day peaked at 55.95 MPa with 2.0% ANTs, 32.77% higher than the control. Likewise, splitting tensile strength improved by up to 191% at early ages with 2.0% ANTs but declined at 3.0% due to agglomeration. Drying shrinkage was minimised in the GPC-ANT_2 mix (3967 & micro;m/m), while maximum porosity refinement was observed in GPC-ANT_3. Mercury intrusion porosimetry confirmed significant pore structure densification, and capillary absorption dropped by over 35% with optimal ANT content. TGA/DTG and XRD results revealed enhanced geopolymer gel formation and thermal stability in ANT-modified GPC, while FTIR and SEM confirmed improved bonding and microstructural compactness at 2.0% ANTs. These findings highlight that an optimum ANT dosage of 2.0% enhances early-age strength, durability, and structural integrity of heat-cured geopolymer concrete.

This study investigates the feasibility of using rice husk ash (RHA) as a sustainable silica source for synthesizing sodium waterglass which serves as an activator in geopolymer composites based on municipal solid waste incineration fly ash (MFA). Six different mixes were prepared using RHA-derived activators and without activators. The activation moduli (Ms) ranged from 0.0 to 1.10. The mixes were evaluated for compressive strength, density, water absorption, porosity, capillary water absorption, and microstructural characteristics using scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). To compare the mechanical strength, total porosity, and water absorption of mixes, a one-way analysis of variance (ANOVA) was conducted at a significance level of 5

This study investigates the effects and mechanisms of three mineral admixtures-fly ash (FA), silica fume (SF), and metakaolin (MK)-on the fresh, mechanical, and microstructural properties of Yellow River sediment (YRS)-based shotcrete. A comprehensive experimental program was conducted, including setting time determination, workability assessment, and mechanical strength evaluation, complemented by microstructural characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results indicate that the incorporation of FA prolonged initial and final setting times and improved pumpability but reduced build-up thickness and compressive strength; splitting tensile strength at later ages remained comparable to the control. SF shortened the final setting time and reduced flowability but enhanced shootability, layer build-up, and medium- to later-age compressive and tensile strengths, with an optimal dosage of 5%. MK accelerated the final setting time, slightly reduced early-age compressive strength, but improved early-age splitting tensile strength and achieved 28-day compressive strength comparable to the control. Microstructural analyses revealed that FA participates in pozzolanic reactions forming C-(A)-S-H gel, while SF and MK promote the formation of dense C-S-H and carboalumination phases, enhancing matrix densification. Based on performance evaluation, the recommended dosages are FA ≤ 20%, SF ≤ 15%, and MK ≤ 15%. These results establish clear links between macroscopic performance and microstructural evolution, providing experimental guidance for the sustainable development of YRS-based shotcrete.

To investigate the influence mechanism of Yellow River silt powder on the hydration process, microstructure, and strength development of shotcrete, and to promote the resource utilization of Yellow River sediment, this study systematically investigated the effects of different silt powder replacement levels (0%, 10%, 30%, and 50%) on a cement-accelerator system. A combination of setting time tests, isothermal calorimetry, and mechanical strength measurements was employed, together with microstructural characterization techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis (DTA), and scanning electron microscopy (SEM). The results indicate that the silt powder content exerts a two-stage effect on the setting behavior of shotcrete. At low replacement levels (0-30%), both initial and final setting times are significantly prolonged, whereas at higher replacement levels (>30%), the setting time is anomalously shortened, approaching that of the reference mixture. The incorporation of silt powder delays the onset of the pre-induction period, prolongs the induction stage, and reduces the cumulative heat release, with the reduction exhibiting a staged trend characterized by gradual, pronounced, and then moderate changes as the replacement level increases. With increasing silt powder content, both compressive strength and splitting tensile strength decrease continuously. At a 50% replacement level, the 28-day compressive strength loss reaches 48.35%, while the splitting tensile strength loss reaches 43.30%, with more pronounced deterioration observed at early ages. The tensile-to-compressive strength ratio increases with silt powder content at early ages, while converging to similar values among all mixtures at later ages. Microstructural analysis indicates that silt powder primarily affects hydration through physical dilution and ion adsorption. At low dosages, nucleation effects slightly promote early hydration, whereas at high dosages, the hydration of calcium silicate phases is inhibited, resulting in reduced C-S-H gel formation and increased porosity. Additionally, AFt morphology transitions from dense prismatic crystals to loosely distributed needle-like structures. This study provides a systematic understanding of the role of silt powder in shotcrete and offers theoretical guidance for mix design optimization and the sustainable utilization of Yellow River sediment.

Segmental bridges, consisting of interconnected segments linked by prestressed tendons, are vital for modern infrastructure but face significant durability challenges due to fatigue from cyclic loading, environmental conditions, and material degradation. Although design and construction have advanced, current standards lack comprehensive methods to assess fatigue under these complex conditions, leading to potential performance and safety concerns. A 3% traffic growth can cut fatigue life from 80 to 44 years, cracking may shorten it by 68 years, and corrosion can reduce reliability from 100 to 44 years, underscoring the need for durability-focused design. This review synthesizes research on fatigue mechanisms, design guidelines, and material innovations in segmental bridges. The paper highlights key findings, such as improvement in fatigue resistance through high-performance concrete and posttensioning techniques, but also identifies gaps in current fatigue life assessment methods. The study emphasizes the need for real-time monitoring systems, advanced predictive models, and innovative retrofitting strategies to enhance long-term bridge resilience. Future research should refine fatigue assessment techniques, integrate real-time data for maintenance, and explore sustainable materials and retrofit solutions to ensure the safety and durability of segmental bridges under increasing traffic and environmental stresses.

The growing demand for sustainable concrete has encouraged the use of recycled aggregates and ceramic waste powder (CWP) as partial cement replacements. However, the low reactivity of CWP limits early-age strength development. This study investigates the effect of carbonation curing on the mechanical properties and material characteristics of ceramic waste powder-based recycled aggregate concrete (CRAC). Eight concrete mixes, including recycled aggregate concrete (RAC) and CRAC variants, were exposed to CO2 curing for 0, 1, 2, and 7 days. Mechanical testing, durability evaluation, and microstructural analyses (SEM, XRD, and NMR) were performed. Statistical analysis was performed using one-way ANOVA and Tukey's HSD post-hoc test to examine the significance of results. The results showed that CO2 curing markedly enhances early-age performance. The compressive strength of RAC increased by 27.8 % after 1 day of CO2 curing compared to the control mix without CO2 curing, while CRAC reached a comparable strength level of 33.85 MPa after only 2 days of CO2 curing, matching RAC under conventional curing. The maximum drying shrinkage was reduced from 5520 mu m/m (for CRAC-0d mix) to 3956 mu m/m (for RAC-7d mix) by indicating improved dimensional stability. Carbonation depth reached 10.63 mm in CRAC after 7 days of CO2 curing, substantially higher than RAC due to greater porosity and nucleation sites provided by CWP. Water absorption of CRAC decreased from 4.74 % under standard curing to 4.26 % after 1 day of CO2 curing which reflected a reduced permeability. Microstructural analysis confirmed pore refinement and abundant calcite formation, while ANOVA tests verified statistically significant strength gains (p < 0.05). CO2 curing not only offsets the early-age strength limitations of CWP-based RAC but also improves its durability and carbon sequestration potential and offers a cost-effective and eco-efficient solution for sustainable construction.

Extrusion-based three-dimensional concrete printing enables automated construction without formwork, yet its structural application is restricted by the brittle behavior and limited tensile capacity of printable cementitious materials. In particular, reconciling fresh-state printability with tensile strain-hardening remains a key challenge for engineered cementitious composites (ECC). This study develops and optimizes a shape memory alloy fiber-reinforced engineered cementitious composite (SMAF-ECC) for extrusion-based 3D printing using an integrated material process performance framework. An orthogonal experimental design was employed to optimize ECC mix proportions by jointly evaluating setting time, fluidity, rheology, extrudability, buildability, and hydration heat evolution. An optimal printable ECC mixture was identified and subsequently reinforced with NiTi SMAF of 26 and 32 mm length at 0.35-1.0 vol%. Results show that a 0.60% attapulgite dosage provides balanced early-age hydration and rheological build-up, enabling stable extrusion and high buildability (tan theta approximate to 0.019) without excessive flow resistance. SMAF incorporation slightly reduces flowability but significantly enhances tensile performance. The optimal SMAF-ECC (32 mm, 1.0%) achieved peak tensile stresses of 5.72 MPa cast and 5.40 MPa 3D-printed, representing an improvement of approximately 45% over fiber-free ECC. Ultimate tensile strain increased to 6.8% and 6.35%, respectively, while preserving stable strain-hardening behavior after printing. Microstructural and porosity analyses confirmed a dense C-S-H-dominated matrix, refined pore structure, and predominantly mechanical fiber-matrix interaction. The findings demonstrate that SMAF-ECC enables high-ductility, damage-tolerant, and printable smart cementitious composites, offering a promising solution for advanced structural applications in digital construction.

This research explores the innovative resilience and self-healing properties of engineered cementitious composites (ECC) reinforced with shape memory alloy (SMA) fibers, tailored for environments susceptible to saltinduced freeze-thaw damage from deicing salts, seawater, and saline soils. The study examines ECC composites enhanced with varying SMA fiber volumes 0 %, 0.5 %, 0.75 %, and 1 % and three fiber shapes linear, indented, and hook-shaped, with an additional sandblasting surface treatment. Systematic analyses of monotonic and cyclic flexural behavior, as well as self-healing efficacy, were performed across four distinct freeze-thaw cycles (0, 50, 100, and 150) within environments of fresh water and a 3.5 % NaCl solution. Digital Image Correlation (DIC) was employed to precisely monitor the self-healing performance. The results highlight substantial enhancements in SMA-ECC, particularly improved flexural strength by up to 35 %, 30 %, and 17 % for hook, indented, and linear fibers respectively in freshwater. These gains were slightly reduced under saltwater conditions to 32 %, 26 %, and 15 % respectively. Additionally, crack-closure efficiencies in significant self-healing with improvements of 45 %, 38 %, and 27 % for hook, indented, and linear fibers respectively. The Weibull probability distribution model was used to establish the damage evolution equation of the SMA-ECC in two freeze-thaw environments. The results of this study can serve as a reference for the development of freeze-thawresistant designs for SMA-ECC structures in future applications.

This study investigates enhancing mechanical and microstructural properties in phosphate-activated geopolymer composites with glass fibers (GF) having different lengths (6-9 mm). Calcined kaolinitic clay (CKC) activated with 8 mol/L phosphoric acid serves as the precursor. Results show that flowability increases by 14.7 % with 3 mm fibers at higher dosages but decreases by 41.4 % and 32.8 % with 6 mm and 9 mm fibers due to entanglement. Compressive strength peaks at 43.2 MPa and 39.6 MPa with 6 mm and 9 mm GF at 1 % dosage, improvements of 12.8 % and 19.3 % versus control, before porosity rises with higher dosages. SEM (scanning electron microscopy) with EDX (energy-dispersive X-ray spectroscopy) confirms enhanced crack bridging and interlocking mechanisms without fiber degradation. Future research should focus on optimizing fiber lengths and dosages to further enhance both the strength and ductility of phosphate-activated geopolymer composites.

This study investigates the mechanical and structural performance of synthetic steel fiber-reinforced geopolymer concrete (GP) through rheological, compressive, flexural, and ductility tests. The effect of fiber inclusion (0

In this study, carbon nanotubes (CNTs) are added to improve the mechanical properties of concrete in different percentages from 0 to 2.0%. The mechanical performance of concrete was evaluated through compressive strength at different days of curing. The findings indicate that the compressive capacity of concrete improved with CNT. However, their complex structure and variation in properties present challenges that restrict their application. Therefore, the machine learning approach was used to develop a prediction model for the compressive strength of complex CNT composites. A comprehensive database of 295 points was created from the literature. Numerous models were developed using different hyper-parameters to get an optimized prediction. The evaluation of all the models was done using statistical parameters, sensitivity analysis and parametric. The experimental results of this study were used for validation of predicted results. The results indicate that the proposed prediction model is highly reliable. Additionally, the accuracy of the proposed model was tested with the experimental investigation and the strength of the prediction equation was checked by the comparison with the previously proposed equation. Lastly, a simple, accurate and efficient prediction is proposed for estimating the compressive strength of CNT composites.

The increasing demand for rapid and sustainable construction methods has accelerated the adoption of 3D-printed concrete (3DPC) technologies. However, integrating conventional steel reinforcement into layer-by-layer printing processes remains a significant challenge. This study investigates the influence of shape memory alloy (SMA) fibers on the rheological behaviour, extrudability, mechanical performance, and self-recovery capacity of 3D-printed engineered cementitious composites (3DP-ECC). SMA fibers with a 0.4 mm diameter, lengths of 26 mm and 32 mm, and volume fractions of 0.35 %, 0.70 %, and 1.0 % were incorporated into the mix design to evaluate their effects on material performance. Results indicate that fiber length and content significantly affect rheology and extrudability, with static yield stress increasing by up to 50.64 % and dynamic yield stress reaching 253 Pa at 1.0 % fiber content. SMA-reinforced ECC exhibits superior strain-hardening behaviour, with cast specimens achieving peak stress up to 5.78 MPa, ultimate strain up to 7.67 %, and strain recovery rates exceeding 53.9 % compared to 3D-printed counterparts. Digital Image Correlation (DIC) analysis confirmed enhanced crack closure and improved recovery in SMA-reinforced mixtures. SEM analysis confirms enhanced fiber-matrix bonding and denser C-S-H gel formation, while EDS analyze the elemental composition of matrix. Additionally, the finite element model (FEM) validated stress redistribution and interfacial bonding mechanisms, with the calculated values closely aligning with the experimental results. These findings demonstrate that the developed SMA-reinforced 3DP-ECC mixtures offer improved strength, ductility, and self-healing capability, making them promising for use in 3D-printed structural elements requiring high durability and damage resilience.

Incorporating recycled coarse aggregate into concrete development not only meets landfill requirements but also promotes environmentally friendly and sustainable infrastructures. Among various methods for reinforcing and repairing concrete structural elements, ferrocement confinement (FC) stands out as highly adaptable. Its key advantages include affordability, widespread availability, and ease of production by ordinary labor. This research aims to assess the effectiveness of FC in construction practices in emerging nations. A detailed investigation examined the impact of FC wrapping on square-reinforced recycled aggregate concrete columns of different cross-sectional areas. Twenty-four concrete column specimens with varying diameters underwent axial compressive loading. Twelve samples were made with recycled aggregate concrete and FC confinement, while twelve served as control samples with natural aggregate concrete without FC confinement. The specimens were grouped into four categories, each maintaining a consistent slenderness ratio (1:6), to evaluate how column diameter affects the benefits of ferrocement confinement. Results showed that increasing the cross-sectional dimensions of the columns improved the stiffness of FC-confined samples. However, it slightly reduced the strength enhancement factor. Specifically, the strength enhancement factor for confined samples decreased from 2.33 Ks for 100 × 100 mm columns to 2.14, 2.05, and 1.95 Ks for column sizes of 125 mm, 150 mm, and 175 mm side lengths, respectively. Additionally, a cost–benefit analysis underscores the immediate feasibility and urgency for the construction sector to adopt this technique.

This study explores the synergistic influence of hybrid fiber reinforcement (combining natural coconut fibers and synthetic carbon fibers) and varying levels of silica fume (SF) on the mechanical and durability properties of recycled aggregate concrete (RAC). A constant total fiber content of 1.5 % was maintained across all mixtures, while SF was incorporated at 5 %, 10 %, and 15 % as a partial cement replacement. Mechanical performance was evaluated through compressive, flexural, and splitting tensile strength tests, while durability was assessed via water absorption, mercury intrusion porosimetry (MIP), and acid resistance testing. Microstructural and mineralogical characterizations were performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). One-way analysis of variance (ANOVA) test was also performed to examine the statistical significance of the results. The results demonstrated significant enhancements in both mechanical and durability performance, particularly in carbon fiber-dominant mixes. Compared to the control, compressive, flexural, and splitting tensile strengths increased by up to 12.89 %, 11.42 %, and 65.17 %, respectively. Durability improvements included a reduction in water absorption by up to 45.06 % and a 63.83 % decrease in acid-induced mass loss after 28 days. SEM images revealed denser interfacial transition zones (ITZ) and a more compact microstructure, attributed to the pozzolanic activity of silica fume and the effective crack-bridging behavior of the fibers. XRD and FTIR analyses confirmed increased formation of calcium silicate hydrate (C–S–H) and a marked reduction in calcium hydroxide (Ca(OH)₂), indicating improved long-term durability. The findings demonstrate that the optimal combination of carbon-coconut hybrid fibers and 15 % silica fume significantly enhances mechanical strength, acid resistance, and matrix densification. These results highlight a sustainable pathway for improving the durability and structural integrity of recycled aggregate concrete.

This study introduces a novel approach by integrating microencapsulated phase change (MPC) materials into engineered geopolymer composites (EGCs), aiming to enhance thermal energy storage capabilities. This investigation highlights optimized MPC content for improved mechanical strength and reduced water absorption and shrinkage. Natural zeolite and quicklime served as binders, and the effects of MPC on mechanical, thermal, and physical properties were assessed using standardized tests alongside differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX). Results showed that 20

As sustainability gains prominence, the demand for eco-friendly materials is increasing, particularly those with minimal carbon footprints. Geopolymer concrete (GC), utilizing waste materials and by-products, is emerging as a promising low-carbon alternative to traditional Portland cement concrete. Despite its potential, GC’s long-term compressive strength (CS) remains relatively low, necessitating ongoing research to enhance its mechanical properties. While substantial research has explored the mechanical behavior of unconfined GC, there is a notable gap in understanding the structural performance of carbon fiber reinforced polymer (CFRP)-confined GC, crucial for material selection and application. This study addresses this gap by investigating the impact of CFRP sheet confinement on the axial performance of activated red mud-based geopolymer concrete composite (RMGCC). A total of 36 cylindrical RMGCC samples, with strengths of 15 MPa and 30 MPa, were tested, using either one or two layers of CFRP sheets. Finite element analysis (FEA) was employed to predict the structural behavior of CFRP-confined RMGCC samples under axial compression, utilizing an enhanced concrete damaged plasticity model. A detailed parametric study was also performed using proposed FEA model to investigate the effect of various parameters of confined concrete. The study also included a theoretical assessment of compressive strength using various existing models and proposed a new theoretical equation for more accurate prediction of axial strength in CFRP-confined RMGCC. The results demonstrated significant improvements in strength with CFRP confinement. For 15 MPa RMGCC, single and double CFRP layers increased compressive strength by 90.96

The journal retracts the article titled “Mechanical, Durability, and Microstructural Evaluation of Coal Ash Incorporated Recycled Aggregate Concrete: An Application of Waste Effluents for Sustainable Construction” [...]

Shape Memory Alloys (SMAs) have emerged as promising functional materials for enhancing the resilience of civil infrastructure. This review compiles and evaluates recent experimental and numerical studies on SMA-based reinforcement and retrofitting in concrete and masonry structures. The analysis covers the two principal mechanisms of SMAs superelasticity and the shape memory effect, and their applications in beams, columns, joints, shear walls, and isolation systems. Reported performance improvements include up to 60–90 % reduction in residual drift, 20–40 % increase in ductility, and 15–30 % enhancement in energy dissipation compared with conventional steel-reinforced systems. NiTi alloys exhibit excellent cyclic recovery and stability, whereas Fe-SMAs provide comparable functional performance at lower cost, enabling scalable implementation. Documented field applications such as the seismic retrofit of the San Giorgio Church bell tower in Italy and several Fe-SMA strengthening projects in Switzerland validate the engineering feasibility of SMA technologies. The findings highlight SMAs as a key enabler for smart, self-healing, and sustainable infrastructure, while identifying cost reduction, design standardisation, and long-term durability as essential priorities for future development.

This research investigates the axial tensile behavior and self-healing properties of Shape Memory Alloy (SMA) fiber-reinforced Engineered Cementitious Composite (ECC) for enhanced crack recovery and strain performance. The study addresses the limitations of conventional ECC through the integration of SMA fibers, optimizing strain improvement and mechanical recovery under monotonic and cyclic loading. SMA fiber volume fractions of 0 %, 0.5 %, 0.75 %, and 1.0 %, geometries straight, indented, hooked, and surface treatments sandblasting and abrasive paper were systematically explored to assess their effects on crack closure, strain capacity, and self- healing behavior. Experimental findings show that the use of sandblasted hooked fibers significantly improves the strain capacity, achieving up to 15 %, while enhancing crack recovery and tensile strength. Notably, hooked fibers demonstrated a 40 % improvement in self-healing capacity compared to the control mix. The indented fibers showed a 30 % improvement, and linear fibers showed a 15 % improvement in self-healing capacity. Digital Image Correlation (DIC) was employed to monitor crack propagation and recovery during cyclic loading. The optimal performance was observed at a 0.75 % fiber volume fraction, balancing mechanical strength and ductility. A constitutive model was created to predict the tensile behavior of SMAF-ECC, using key parameters like initial crack stress, peak stress, ultimate strain, and damage factor. SHAP (Shapley Additive Explanations) analysis was employed to understand how fiber geometry, surface treatment, and volume fraction influence tensile behavior, offering data-driven insights into the model's accuracy.