While the ductility of tensile strain-hardening UHPFRC is critical for load-bearing capacity at the ultimate limit state and crack control under service conditions, recent studies reveal that conventional UHPFRC with 2–4% fiber volume often fails to achieve the recommended 5‰ tensile strain for tension-critical concrete structures. This paradox arises because increased ductility is frequently linked to larger microcrack widths, necessitating a carefully optimized solution. Building on advances in UHPFRC with hybrid stiff steel and flexible Ultra-High Molecular Weight Polyethylene (UHMW-PE) fibers, this work uniquely addresses both crack width reduction under service conditions and enhanced ductility. Significant portions of cement were replaced with recycled waste granite and limestone powders to promote sustainability.Several UHPFRC mix designs were developed, incorporating variations in fiber type (steel and UHMW-PE), length (6 mm and 13 mm), dosage (0–2% by volume), and hybrid configurations. For steel fibers, two distinct casting methods were employed. Tensile properties were assessed through bending tests combined with inverse analysis in accordance with Swiss SIA 2052 standards, while post-peak behavior was modeled using non-linear finite element analysis (NLFEA). Crack widths were measured using digital image correlation (DIC). Results showed that hybrid UHPFRC, combining stiff steel and ductile UHMW-PE fibers, demonstrated superior strain-hardening, reduced microcrack widths, enhanced ductility, and increased fracture energy while lowering the embodied carbon footprint. Microcracks were kept below 30 μm to ensure impermeability, and hardening strains exceeded 5‰ in tensile-controlled sections. The developed UHPFRC with hybrid fibers and mineral fillers offers a promising solution for advanced structural applications, balancing durability, cost-efficiency, and sustainability.
Although robotic-arm-based and spray-based 3D printing approaches have extended concrete printing toward complex geometries, limitations in deposition accuracy, material utilization, and process stability remain. Meanwhile, conventional extrusion-based 3D printing concrete (3DPC) is still primarily restricted to vertical stacking on horizontal substrates. To address these limitations, this study proposes a 3D lateral printing concrete (3DLPC) method. Material performance tests, printing tests, and computational fluid dynamics (CFD) simulations were conducted to investigate its filament forming mechanism and parameter matching strategy. A printing mixture satisfying the requirements of extrudability, adhesion ability, and sagging resistance was selected based on fluidity and sagging deformation. A filament cross-section parametrization method was then used to analyze the effects of printing thickness, nozzle angle, and nozzle shape on cross-sectional shape and offset ratio. The results show that printing thickness affects offset behavior by regulating the balance between the self-weight effect of the filament and interface constraint, and the lowest offset ratio is obtained at a printing thickness of 8 mm. Nozzle angle affects deposition stability by changing the normal and tangential distribution of extrusion momentum. Increasing the nozzle angle can reduce the offset ratio, but it also increases the flow direction change and extrusion resistance inside the nozzle. The rectangular nozzle can provide a more stable outlet boundary and interface constraint, and its overall forming performance is better than that of the circular nozzle. Based on these results, this study establishes a hierarchical parameter matching framework for 3DLPC. The results can provide a reference for the in-situ forming, repair, and protection applications of 3DPC on complex vertical interfaces.
Weak interlayer and interfilament interfaces remain major limitations for the mechanical reliability of 3D-printed cement-based materials. In this study, a carbonation-regulated algal-bacterial interfacial filling treatment incorporating Spirulina maxima and Bacillus pseudofirmus was investigated for 3D-printed mortar. The effects of microbial component configuration and carbonation curing on culturable BP recovery, interfacial filling, mechanical anisotropy, ultrasonic pulse velocity, and carbonate-containing products were investigated. At 28 d, the CAB group exhibited the highest presumptive culturable BP recovery, reaching 2.16 × 1010 CFU/g interfacial powder. The CAB group achieved the highest interlayer and interfilament bond strengths of 6.112 and 4.857 MPa, respectively, together with the lowest compressive and flexural anisotropy coefficients of 1.145 and 1.117 among the tested groups. These results highlight the simultaneous strengthening of both printed interfaces and identify the proposed treatment as a process-compatible strategy for reducing mechanical anisotropy. Image analysis showed a marked reduction in the projected area of visible open interlayer defects for the CAB group within the selected two-dimensional ROIs, while UPV results showed improved internal structural continuity, with a Z-direction increase rate of 34.7%. Multiscale characterization showed that the interface-near products were dominated by calcite-type CaCO3. Differences in biological suspension configuration and curing condition were associated with the observed variations in carbonate-containing product accumulation and interface-related performance. Overall, the carbonation-regulated algal-bacterial treatment provides a process-compatible strategy for strengthening weak interfaces in 3D-printed cement-based materials.
With increasing strain on GGBS supply, waste glass powder (GP) has emerged as a promising candidate for functionalizing alkali-activated binders, particularly for improving acid resistance-a persistent challenge in aggressive environments. Furthermore, the data on the microstructural changes of these systems under acid attack are scarce. This study investigates the degradation mechanism, pore evolution, and crack sealing potential of 50/50 GP-GGBS alkali-activated material (AAWG-S mortar/paste) binder exposed to biogenic acid using multi-scale analytical techniques. It was found that the acid attack partially dissolved the aluminosilicate network, produced gypsum, and led to a 51% loss in gel hardness at the corroded surface, while the inner matrix remained structurally stable due to the formation of Si-rich low-Ca C-(N)-A-S-H gels introduced by GP. XCT and BSE image analysis revealed pronounced porosity coarsening near the surface (41.6%) vs. (15.8% in the intact region) but limited internal damage. Additionally, partially dissolved GGBS particles acted as Ca reservoirs, promoting localized carbonate-based crack sealing. Overall, the synergistic effects of Si-rich hybrid C-(N)-A-S-H gel chemistry, controlled porosity gradients, and localized healing mechanisms collectively contributed to the enhanced durability of GP-GGBS binary AAM binder under acidic conditions.
Extrusion-based 3D concrete printing (3DCP) enables automated, formwork-free fabrication of cementitious components, but its structural use is still limited by quasi-brittle fracture, weak interlayer interfaces, and anisotropic damage evolution. This study develops and assesses an impact-resilient 3D-printed cementitious composite beam system based on two complementary mechanisms: an embedded steel–concrete composite reinforcement beam, where perforated steel plates and welded shear keys provide distributed mechanical interlock across printed layers, and a detachable deformation-triggered elastomeric constraint (EC) designed to engage mainly during the large-deflection stage.Drop-weight impact tests were conducted on 12 specimens using a 265 kg falling mass. Three configurations were examined: foamed benchmark beams, 3D-printed composite beams, and 3D-printed composite beams with EC. Two loading orientations relative to the printing axes and drop heights from 0.4 to 2.0 m were considered. Synchronised measurements of contact force, support reaction, deflection, strain, and damage evolution confirmed a two-stage impact response, consisting of an inertia-dominated force peak followed by a large-deflection damage stage. The EC did not systematically increase the initial peak impact force, but significantly improved post-peak force retention, rebound recovery, and damage tolerance. For matched cases with rebound, maximum and residual deflections were reduced by 16.7%–42.3% and 25.0%–53.2%, respectively. Under the most severe impact case, the baseline 3D-printed beam exhibited collapse-type behaviour, whereas the EC-enhanced beam remained rebound-capable.A validated Abaqus/Explicit model further showed that EC engagement stabilises the steel–concrete load-transfer path and mitigates late-stage interlayer damage, cementitious matrix degradation, and steel-plate instability.
Structural supercapacitors require electrolytes that combine efficient ion transport with adequate mechanical integrity. Unlike previous geopolymer-based structural supercapacitors that mainly rely on externally introduced electrolytes, separator/framework design, electrode engineering, or conductive-filler modification, this study focuses on the internal regulation of metakaolin-based geopolymer structural electrolytes by sodium polyacrylate (PAAS). Without an external electrolyte, the ionic conductivity increased in a threshold manner after the addition of 15% PAAS, reaching 13.11 mS/cm. Symmetric devices assembled with identical carbon-based electrodes exhibit improved electrochemical performance. P20 provides the most balanced electrochemical and mechanical performance. Compared to the control group, P20 delivers an areal capacitance of 507.27 mF·cm-2, representing a 95.1% increase, while retains 91.9% of the compressive strength to 33.15 MPa. Microstructural characterization indicates decreased total porosity but increased average pore diameter, suggesting a redistribution toward more transport-relevant accessible pores. Overall, these results demonstrate the feasibility of a PAAS-regulated geopolymer structural electrolyte strategy for integrated energy-storage applications.
One-part alkali-activated materials (AAMs) are increasingly promoted as low-CO2 alternatives to Portland cement, yet their sustainability and commercial viability are constrained by the high energy demand, cost, and embodied carbon of conventional solid activators such as sodium metasilicate. While waste-derived activators have recently been proposed, the mechanistic links between the activator chemistry, dissolution behaviour, reaction kinetics, and the microstructure in one-part systems remain poorly understood. This study addresses this knowledge gap by valorising end-of-life photovoltaic (PV) glass as a source of sodium silicate powders synthesised via low-temperature alkaline fusion (250 °C), with the glass-to-NaOH ratio tuned to achieve silica modulus (Ms) of 1.0–1.5. These PV-glass-derived activators are systematically compared with commercial sodium metasilicate activators in one-part alkali-activated binders, focusing on dissolution behaviour, reaction kinetics, phase assemblage and microstructural evolution. The PV-glass-derived activators generate a higher proportion of depolymerised Q0 silicate species and produce nanocrystalline C–S–H-type phases in the dissolution residues, which could accelerate early-age reactions through both seeding and chemical effects. Increasing Ms reduces the dissolution efficiency and slows early-age reactions, lowering 1-day strength, yet 28-day compressive strengths remain comparable to those obtained with the commercial activator. Phase analysis reveals strätlingite formation in systems with lower-Ms synthetic activators, while higher PV-glass contents (corresponding to higher Ms value) promote denser microstructures and more cross-linked C–(N)–A–S–H networks. This work advances the fundamental understanding of waste-PV glass activation and outlines a scalable pathway to decarbonise one-part AAMs.
Electrodeposition has been proposed as a method to promote mineral precipitation in cracked reinforced concrete, potentially limiting ingress of aggressive agents and delaying corrosion initiation. However, the extent to which electrodeposition-induced crack filling improves corrosion resistance under marine exposure, and the influence of electrolyte composition on the effectiveness and mechanism of electrodeposition, remains overlooked.This study investigated deposition behaviour of electrodeposition in either artificial seawater or Ca-Mg nitrate solution and evaluated corrosion performance of electrodeposition-treated (2x3) and non-electrodeposition-treated (references, 2x2) specimens during artificial seawater exposure.Reinforced concrete cylinders containing tensile-induced transverse cracks underwent three-month electrodeposition treatment, followed by a three-month artificial seawater exposure. Crack filling and deposition patterns were examined using X-ray computed tomography (XCT), optical microscopy, and μXRF elemental mapping, while corrosion behaviour was assessed through half-cell potential monitoring and post-exposure CT. Analytical interpretation was further used to interpret observed electrodeposition behaviour.A difference in Ca2+ and Mg2+ ion concentrations between the Ca-Mg nitrate solution and artificial seawater results in different crack-filling behaviour. Electrodeposition in Ca-Mg nitrate solution resulted in extensive internal crack filling reaching the steel-concrete interface, independent of crack geometry and width (maximum surface crack width 0.75 mm), and no corrosion was observed. In contrast, electrodeposition treatment in artificial seawater resulted in deposits primarily near the crack mouth and an influence of crack geometry. In these specimens, corrosion was prevented in two specimens and reduced in the third. The findings demonstrate that electrodeposition can delay corrosion initiation in cracked concrete when sufficient internal crack filling is achieved.
The incorporation of conductive nanomaterials into cementitious matrices to construct functional percolation networks paves the way for sustainable and energy-resilient infrastructure. Accurately characterizing the three-dimensional dispersion state and connectivity of these nanomaterials is prerequisite for optimizing energy conversion and storage efficiencies. However, due to the inherent opacity, heterogeneity, and high hardness of the cementitious matrix, existing microstructural characterizations remain largely confined to two-dimensional planes. This restriction makes it challenging to authentically resolve the 3D spatial distribution of the carbon phase and hydration products at the mesoscale. To overcome this limitation, this study proposes a 3D chemical imaging framework integrating Broad Ion Beam milling with Serial Section Raman Tomography to achieve high-precision volumetric reconstruction. Applying this methodology to a modified cement paste incorporating 4.5 wt.% nano-carbon black (NCB) not only demonstrates the feasibility of 3D visual reconstruction within an opaque matrix but also intuitively reveals the NCB distribution and its spatial nucleation mechanisms. Furthermore, the intrinsic topological parameters of the conductive network are successfully quantified, including tortuosity, fractal dimension, and average coordination number. Utilizing these parameters, the macroscopic conductivity of the composite was accurately predicted at 0.038 S/m, theoretically elucidating the correlation between the formation of the 3D conductive network and the enhanced energy-storage capacity in cementitious materials. This work provides a novel characterization tool for the 3D mesoscopic analysis of complex multiphase systems and corrects stereological errors inherent in planar evaluations, laying a geometric foundation for establishing quantitative structure-property relationships correlating micro-3D architecture with macroscopic energy transport and electrochemical storage.
