Search Results (426)

The layer-wise deposition process of three-dimensional concrete printing (3DPC) induces anisotropic behaviour, while cementitious materials exhibit pronounced tension–compression strength asymmetry. This study develops a concurrent topology and printing-direction optimisation framework for plain 3DPC under Drucker–Prager (D–P) strength constraints. Within a solid isotropic material with penalisation (SIMP) formulation, material density and printing orientation are updated simultaneously using the Method of Moving Asymptotes (MMA). A double-angle vector-field mapping regularises the π-periodic orientation field, while element-wise D–P failure indices are aggregated into a differentiable global constraint through P-norm aggregation with adaptive scale correction. Numerical studies on a four-corner pinned plate, a T-shaped bracket and a perforated deep beam show that the strength constraint reshapes load paths, suppresses local strength violations and increases ultimate load capacity by approximately 200%, 176% and 42%, respectively, relative to compliance-based optimisation. The optimised deep-beam layouts are reconstructed, converted into continuous printing paths, fabricated and tested under three-point bending. Experimentally, the mean ultimate load increases from 8.13 to 9.54 kN, corresponding to an increase of 17.39%, while the mean displacement at peak load and pre-peak energy are 20.58% and 41.16% higher, respectively. The experimental and finite element comparisons show closely similar ultimate-load increases of 17.39% and 17.43%, respectively. The framework provides a strength-aware route from concurrent numerical optimisation to the fabrication and structural assessment of plain 3DPC components. Full article

Flexural strength (FS) governs the structural performance of 3D-printed concrete (3DPC) under bending loads yet remains difficult to predict owing to the coupled influence of binder composition, supplementary cementitious materials, water-to-binder ratio, and fiber reinforcement geometry on interlayer fracture behavior. Much of this compositional diversity stems from supplementary cementitious materials, industrial by-products whose reuse as partial cement replacement lowers the embodied carbon of printable mixes. A machine learning framework was trained on 209 FS records covering OPC- and SAC-based systems (FS: 3.65–45.0 MPa; W/B: 0.15–0.65). Six composite features were constructed from physical principles, two of them specific to bending: Fiber_Pullout_Index encoding post-crack pullout energy and Binder_Efficiency capturing cement quality per unit water content at the fiber–matrix interface; Lasso regularization with the one-standard-error rule reduced the 19-variable space to 14 active predictors. Twenty regression algorithms spanning eight families were benchmarked under 30 independent partitions; the Friedman test rejected equal performance (${\chi }^2=337.02$, $p=4.88\times {10}^{-60}$) and all 19 pairwise Wilcoxon comparisons against CatBoost were Holm-significant. CatBoost ranked first (mean rank of 18.17/20; 30-run $R^2=0.9302\pm 0.0722$; seed-42 partition: $R^2=0.9557$; RMSE = 1.761 MPa; MAPE = 11.20%). n(W/B) emerged as the primary driver across SHAP, ALE and LIME, with a monotonic ALE profile spanning 8.99 MPa and no inflection over the full printable window; Binder_Efficiency ranked second (PDP range: 5.21 MPa), isolating cement grade and paste dilution as independent strength levers. Cross-conformal prediction provided finite-sample coverage guarantees without distributional assumptions (empirical coverage: 95.24%; conformity quantile: 3.83 MPa); bootstrap analysis put the epistemic component at a mean predictive SD of 0.946 MPa, a quarter of that quantile. External validation yielded $R^2=0.769$ (Pearson $R=0.923$, RMSE = 1.91 MPa), with 19 of 20 predictions (95.0%) within Bland–Altman 95% limits of agreement, confirming transfer to a source study withheld from model training. A graphical user interface packaging the 14-feature CatBoost pipeline supports mix design queries without programming. Full article

3D Concrete Printing (3DCP) has emerged as a transformative construction technology, offering enhanced design flexibility, reduced material waste, improved construction efficiency, and safer working environments. Despite these advantages, the absence of standardised design provisions for structural 3DCP elements remains a major obstacle to its widespread adoption. This study develops statistical and machine learning models to predict the design strengths of hardened 3D-printed concrete. A comprehensive database of experimental results published between 2012 and 2025 was compiled and analysed, encompassing the compressive, flexural, and shear strengths of hardened 3DCP materials. Regression-based statistical modelling was employed to derive design strength equations and assess their consistency with conventional concrete design approaches. In parallel, several machine learning algorithms were developed using the same dataset to benchmark predictive performance and evaluate the robustness of the proposed statistical models. The statistical models achieved good predictive accuracy for compressive and flexural strengths, with coefficients of determination (R²) of 0.83 and 0.67, respectively. By contrast, the shear strength model exhibited greater variability (R² = 0.39), reflecting the limited availability and considerable scatter of published experimental data. Benchmarking against the optimised machine learning model demonstrated excellent agreement with the proposed statistical equations, yielding coefficients of determination of 0.93 and 0.94 for compressive and flexural strengths, respectively. The proposed modelling framework provides preliminary design strength predictions for hardened 3D-printed concrete, contributing to the development of robust structural design guidelines and facilitating the wider adoption of 3DCP in construction practice. Full article

3D-printed geopolymer mortars (3DPGPMs) are emerging as low-carbon construction materials that combine digital fabrication with alkali-activated binder technology. However, their hardened performance remains difficult to assess because it is controlled not only by geopolymer chemistry but also by printing parameters, rheological evolution, curing conditions, interlayer bonding, pore structure, and loading direction. This review critically examines the current literature on extrusion-based 3DPGPMs, with emphasis on mechanical properties, durability, sustainability, standardization, and practical implementation. The reviewed studies show that precursor type, activator system, aggregate/binder ratio, additives, printing conditions, and curing regime strongly influence compressive, tensile, flexural, interlayer bond, and anisotropic mechanical responses. Durability performance is also governed by the coupled effects of matrix chemistry and printing-induced features, including interlayer voids, directional pore networks, weak interfaces, and transport pathways that may affect shrinkage, water absorption, chloride penetration, carbonation, acid and sulphate resistance, freeze–thaw response, and elevated-temperature behavior. From a sustainability perspective, the environmental benefits of 3DPGPMs are conditional and depend on activator production, precursor availability, curing demand, transport distance, life-cycle assessment boundaries, and field-scale implementation conditions. The review identifies that the main knowledge gap is the limited availability of integrated datasets linking fresh-state rheology, interlayer quality, multi-scale porosity, mechanical anisotropy, durability indicators, and structural-scale validation. Future research should therefore prioritize standardized reporting, performance-based acceptance criteria, long-term exposure testing, field-scale validation, and predictive material–process–durability models. Overall, this review provides a hardened-performance-oriented synthesis to support the development of reliable, durable, and sustainable 3DPGPMs for construction applications. Full article

Three-dimensional concrete printing (3DCP) is an emerging additive manufacturing technology that has attracted significant international interest as a potential alternative to conventional construction methods. Existing research has largely focused on isolated technical domains, resulting in fragmented assessments of the technology and inconsistencies between the construction systems evaluated. This review addresses that gap through a holistic review from technical, architectural, environmental, and economic perspectives, with particular emphasis on its applicability within the New Zealand context. The review found that the multifunctional benefits of 3DCP often cause interdependencies between performance domains, which creates evaluation challenges for individual discipline assessments. Several key barriers to adoption within New Zealand were identified, such as limited evidence of the seismic performance of 3DCP structures, a lack of specific regulatory acceptance pathways, and economic scalability. Nevertheless, 3DCP construction was found to demonstrate suitable technical performance to comply with the New Zealand Building Code (NZBC), though this often involved supplementary construction that failed to fully capitalise on the benefits of 3DCP. Economic, regulatory, and social pressures may be driving re-standardisation in built residential projects, reducing the technology’s architectural differentiation from conventional construction and relinquishing one of the technology’s principal value propositions. Life-cycle assessments suggest environmental performance may be comparable with conventional light timber framing (LTF) where low-carbon strategies are adopted, though this should be re-evaluated as seismically resilient wall typologies are developed. Economic viability remains strongly dependent on deployment scale, with breakeven occurring at approximately eleven dwellings, suggesting the technology will be best suited for large-scale developments and prefabrication facilities. Full article

This study evaluates the mechanical performance, anisotropy, and spatial variability of 3D-printed cementitious and alkali-activated composites under laboratory, atmospheric, and freeze–thaw conditions. Alkali-activated composites exhibited substantially higher shrinkage than cement-based mixtures, reflecting differences in their reaction mechanisms and pore structure development. Compressive strength was measured in two orthogonal directions representing perpendicular ($⟂$) and parallel ($\parallel$) behaviour. Non-activated mixtures exhibited compressive strength of 11–12 MPa, whereas alkali-activated composites reached 19–20 MPa in the reference condition. Atmospheric exposure increased compressive strength by 10–22%, while freeze–thaw cycles did not significantly affect perpendicular strength. Flexural strength of non-activated mixtures remained low (3.7–5.3 MPa), whereas activated composites showed higher values in the reference state (8.8–15.0 MPa) but decreased after atmospheric exposure to 5.3–5.8 MPa. The degree of anisotropy increased significantly for alkali-activated mixtures (from 0.09 to 0.24) while remaining relatively stable for non-activated materials (0.04–0.11). Glass fibres showed no significant degradation after environmental and freeze–thaw exposure, while merino wool fibres exhibited only minor surface irregularities, confirming the potential of both fibre types for use in sustainable lightweight 3D-printed cementitious and alkali-activated composites. Full article

Three-dimensional concrete printing (3DCP) enables the fabrication of wall sections with internal cavities that are impractical to form with conventional methods. Although individual studies demonstrate that cavity geometry influences thermal resistance, the magnitude of this effect has not been quantified on a common basis across the literature. This paper introduces the Thermal Effectiveness Index (TEI), defined as the ratio of the theoretical U-value of a solid concrete wall (calculated using the material’s actual thermal conductivity) to the reported U-value, in order to isolate the purely geometric contribution to thermal performance. A structured extraction from 24 Scopus-indexed articles yielded an analysis dataset of 255 variants from 23 articles (after the exclusion of one study whose composite mix made the geometric effect inseparable from material substitution), spanning 17 typology categories. Results show that standard rectangular air cavities perform worse than solid printed counterparts of the same material (median TEI $=0.56$ versus $1.00$ for solid walls) due to internal convection and thermal bridging, whereas sinusoidal infills with post-printed insulation reach a median TEI of 8.9 (18 variants from a single study, so the magnitude requires independent replication). These patterns are descriptive; an article-level sensitivity check indicates that the number of independent studies per wall-type group is not yet sufficient for confirmatory statistical inference. A compliance analysis against five building energy codes showed that only 22% of variants meet the $0.30$ $\mathrm{W}$/($\mathrm{m}$² $\mathrm{K}$) threshold, in line with the component-based U-value criteria specified in the Passive House Institute’s EnerPHit Standard for building retrofits and warm-climate classifications, as opposed to the more stringent $\le 0.15 \mathrm{W}/({\mathrm{m}}^2 \mathrm{K})$ requirement applicable to new construction in temperate climates. Full article

The growing demand for construction materials has intensified concerns regarding natural sand depletion and the accumulation of industrial waste. Among these wastes, oil-contaminated sand (OCS) generated from petroleum-related activities presents environmental challenges while also offering potential for beneficial reuse. Previous studies have reported that low OCS contents can enhance workability and improve mechanical properties, highlighting its potential as a sustainable construction material. This study investigates the feasibility of incorporating OCS as a partial replacement for natural sand in 3D concrete printing (3DCP). Three mixes containing 0%, 0.5%, and 1% OCS were evaluated in terms of flowability, setting behaviour, printability, rheological response, hydration behaviour, mechanical performance, anisotropic response, and microstructural characteristics. The results showed that OCS incorporation had only a limited influence on flowability, while both the initial and final setting times exhibited noticeable delays. The maximum printable layers reached from 19 for the control mixture to 22 and 26 layers for the 0.5% and 1% OCS mixes, respectively, accompanied by reduced settlement and structural deformation. Rheological analysis revealed higher static yield stress and structuration rates for the OCS-modified mixes, contributing to enhanced buildability and geometric stability. Hydration calorimetry showed comparable heat-flow behaviour between the control and OCS-modified mixes, suggesting only a limited influence of OCS on cement hydration kinetics. The incorporation of OCS improved the compressive strength of the printed mixes and reduced compressive anisotropy, while SEM observations revealed a denser and more homogeneous microstructure, particularly for the 0.5% OCS mix. Thus, the findings indicate that low-level incorporation of oil-contaminated sand is a viable strategy for improving the printability and performance of 3D-printed concrete, promoting the sustainable reuse of contaminated industrial waste. Full article

The relationship between rheological properties and printability in 3D-printed recycled concrete incorporating calcined oyster shell powder (COSP) remains insufficiently understood. The unstable rheological behavior and insufficient buildability of 3D-printed recycled concrete limit its application in digital construction. In this study, the COSP, a marine solid waste-derived functional powder, was incorporated into 3D-printed recycled concrete to improve rheological behavior and printability. The effects of different COSP contents on rheological properties and structure build-up were assessed. In addition, MIP, XRD, and SEM analyses were used to clarify the underlying regulation mechanism. The results showed that COSP significantly improved the rheological properties of fresh paste. As the COSP content increased from 0% to 5%, the static yield stress, dynamic yield stress, and thixotropic recovery degree increased from 1703 Pa to 4561 Pa, from 92 Pa to 375 Pa, and from 56% to 87%, respectively. Meanwhile, the structural deformation rate decreased from 12.3% to 6.37%, corresponding to a reduction of approximately 48%. An appropriate COSP content also improved the mechanical properties, with the flexural strengths in the X and Y directions increasing to 5.17 MPa and 4.99 MPa, respectively, and the compressive strengths increasing to 26.04 MPa and 25.48 MPa, respectively. The microscopic performance results indicated that COSP refined the pore structure, promoted the formation of hydration products, and improved compactness. This study offers preliminary evidence for improving the printability of 3D-printed recycled concrete, while addressing the urgent environmental challenge of marine solid waste utilization and enhancing the economic feasibility and production efficiency of 3D-printed concrete. Full article

Three-dimensional printed concrete (3DPC) exhibits anisotropic mechanical behaviour due to layer-wise extrusion, yet a standardised methodology for estimating constitutive model parameters from full-field experimental data remains absent. This study presents a digital image correlation (DIC)-based approach for estimating the elastic modulus and compressive strength of 3DPC from uniaxial compression tests. Six printing groups and one cast control were fabricated, with three groups spanning the nozzle diameter extremes prioritised for complete DIC re-analysis. Full-field surface strain was acquired using a custom interactive Ncorr batch pipeline, with verified region-of-interest selection. The secant elastic modulus, derived from DIC displacement gradients, was 27 ± 3 GPa (15 mm nozzle), 17 GPa (30 mm nozzle), and 22 ± 6 GPa (cast control). Preliminary Poisson ratio estimates of 0.16 and 0.17 were obtained from two specimens. Full-field strain maps revealed greater heterogeneity in the printed specimens than in the cast controls. Results indicate that the choice of nozzle diameter impacts both strength and stiffness, with a 59% increase in each when reducing the nozzle diameter from 30 mm to 15 mm at constant layer height. This approach provides preliminary estimates from a single test, though validation against direct extensometry is recommended before its application to structural simulations. Full article

Freeze–thaw resistance is a key durability concern for cementitious materials intended for use in cold climates, especially when alternative binders are introduced into extrusion-–thaw resistance is a key durability concern for cementitious materials intended for use in cold climates, especially when alternative binders are introduced into extrusion-based 3D concrete printing (3DCP). This study examines the effect of oil shale ash (OSA), a by-product of oil shale combustion, on the fresh and hardened performance of 3D-printable cementitious mixtures, with particular focus on durability under freeze–thaw exposure. Four mixtures were prepared with 0%, 10%, 20%, and 40% replacement of ordinary Portland cement by OSA. Fresh-state properties, including flowability, density, and buildability, were evaluated alongside hardened properties such as density, water absorption, mechanical properties, microstructure (SEM) and crystalline phase composition (XRD), and ultrasonic pulse velocity. Freeze–thaw resistance was assessed using NaCl-solution cycling with mass loss measurements. The results indicate that moderate OSA replacement (10–20%) contributes to a denser microstructure, resulting in higher compressive strength and reduced permeability. At 28 days, the OSA-10 and OSA-20 mixtures achieved compressive strengths of approximately 54 MPa, compared with 50 MPa for the reference mixture. The OSA-20 mixture also exhibited the best freeze–thaw performance, with mass loss after 56 cycles reduced from 35 g/m² to 26 g/m², corresponding to an improvement of approximately 26%. In addition, 3D-printed specimens exhibited 20–30% lower compressive strength than corresponding cast specimens. These mixtures also showed improved or comparable resistance to freeze–thaw action compared to the reference mix. In contrast, higher replacement levels (40%) increase porosity, weaken the microstructure, and significantly reduce durability. At 40% replacement, freeze–thaw mass loss increased to 77 g/m² after 56 cycles. The findings suggest that controlled incorporation of OSA can improve the sustainability and durability of 3D-printed cementitious materials for cold-region applications. Full article

Process dependence is a defining feature of 3D concrete printing (3DCP), and any pooled inference across laboratories must quantify rather than ignore the laboratory effect. We assembled a harmonized corpus of 80 primary 3DCP studies (465 experiments and 1083 hardened mechanical observations) under PRISMA-style screening, applied controlled vocabularies and unit canonicalization, and estimated the share of variance attributable to the study cluster. The intraclass correlation coefficient is 0.77 (95% CI [0.59, 0.86]; 345 records and 40 studies), so more than three quarters of the dispersion in 28-day compressive strength lies between laboratories rather than between mixtures within the same laboratory. A 7-to-28-day calibration evaluated under leave-one-study-out (LOSO) cross-validation produces $R^2=0.625$, MAE $=8.67$ MPa and RMSE $=11.38$ MPa, with 95% prediction intervals covering 96.9% of held-out observations; the band is wide enough (≈85 MPa at the median) that the calibration is suitable for early-screening of mixture and process candidates rather than for code-compatible structural verification. Most of this between-study scatter traces back to processing variables, curing regimes and loading directions that are inconsistently reported. We propose a three-tier Minimum Reporting Set (MSRS) and demonstrate, through a retrospective audit of the included corpus, that adoption is feasible at the entry tier (63% already comply) while higher tiers identify the metadata that must be added before pooled inference can support structural-design decisions for printed elements. Full article

Additive manufacturing (AM) is applied in sustainable architecture and Construction 4.0 because it can support design flexibility, mass customization, material efficiency, and reduced reliance on conventional formwork. Prior reviews often addressed either construction applications or broader digital transformation, leaving the intersection of AM, construction sustainability, digital technologies, and lifecycle performance underexplored. This study conducts a systematic and bibliometric review of literature retrieved from Scopus and Web of Science covering the period from January 2016 to January 2026. The review protocol followed SPAR-4-SLR principles and PRISMA 2020 guidelines, with 58 records retained for analysis. Bibliometric and thematic analyses identified a marked rise in publication activity after 2021 with four major research themes: material development and innovation, digital fabrication and process control, lifecycle assessment and circularity, and digital integration and project implementation. Construction 4.0 technologies, including BIM, digital twins, automation, and robotics, were the most frequently represented digital enablers. The review further identifies future research opportunities and outlines a proposed conceptual pathway toward Construction 5.0. This pathway connects materials, robotics, lifecycle performance, and human-centered priorities as a future research agenda. Overall, this study contributes to a more integrated understanding of how AM can advance sustainable, digitally enabled, and human-centered construction practice. Full article

3D concrete printing (3DCP) is an emerging modern method of construction with potential to improve construction efficiency, reduce labour requirements, and support the delivery of sustainable housing. In Ireland, its recent adoption coincides with increasing policy emphasis on modern methods of construction and the introduction of stricter European requirements for assessing the climate impact of buildings. The recast Energy Performance of Buildings Directive (EPBD) introduces progressive requirements for the calculation and reporting of whole-life Global Warming Potential (GWP) for new buildings, creating a need for Life Cycle Assessment (LCA) methodologies aligned with current regulatory requirements and capable of capturing the specific characteristics of emerging construction technologies. This paper reviews the applicability of the EPBD, EN 15978, EN 15804, Level(s), and relevant Irish methodologies to 3DCP buildings. It also examines existing LCA studies on 3DCP and evaluates their methodological scope, system boundaries, functional units, data sources, and alignment with current regulatory requirements. The review shows that most existing 3DCP LCA studies remain focused on materials, components, or limited life-cycle stages, with cradle-to-gate assessments being particularly common. Consequently, many published studies do not fully align with the whole-building, cradle-to-grave assessment framework introduced under the revised EPBD.. The review also identifies a lack of LCA methodologies specifically tailored to 3DCP buildings, particularly in relation to printable material design, construction-process energy consumption, material efficiency, reinforcement strategy, durability, maintenance, and end-of-life scenarios. These gaps limit the comparability and regulatory relevance of current sustainability assessments. The paper concludes that EPBD-compliant whole-life carbon assessments of complete 3DCP buildings are urgently needed, alongside the development of 3DCP-specific methodological guidance and data to support reliable environmental benchmarking and wider adoption of the technology in Ireland and Europe. Full article

Extrusion-based three-dimensional concrete printing (3DCP) has emerged as a promising digital construction technology that requires precise control of material rheology and structural performance. This study investigates the influence of steel fibre dosage on the rheological behaviour, mechanical performance, and potential printability of cement-based materials. Mortar mixtures incorporating straight copper-coated steel fibres at dosages from 0 to 1.0% were evaluated. Rheological properties, including yield stress, plastic viscosity, thixotropy, structuration rate, re-flocculation rate, viscosity recovery, and flow index were characterised using rotational rheometry, while compressive and flexural strength were measured at 14 and 28 days. Results show that steel fibres significantly enhance structural build-up and recovery, with both static and dynamic yield stress increasing markedly with fibre dosage. Plastic viscosity and flow behaviour indicate increased resistance to flow at higher contents. Compressive strength exhibits a non-monotonic trend, reaching a maximum increase of approximately 40% at 0.2%, whereas flexural strength is improved at higher fibre dosages due to crack-bridging effects. A normalisation-based composite index was applied to integrate performance indicators. Based on rheology-derived printability implications, a practical working window was proposed, including static yield stress of approximately 280 to 400 Pa, dynamic yield stress of 70 to 160 Pa, plastic viscosity of 7 to 15 Pa·s, re-flocculation rate of 40 to 55 Pa/min and flow index of 0.6 to 1.0. Although higher fibre dosages produced higher composite index values due to dominant rheological enhancement, excessive rheological resistance may reduce practical processability. Based on the proposed working window, 0.2% steel fibre provides the most balanced performance for potential large-scale 3DCP applications. Full article