Search Results (431)

3D concrete printing (3DP) enables automated construction with reduced material waste and enhanced geometric flexibility. However, its structural performance remains sensitive to anisotropy, mix design, and printing parameters, thereby complicating quality control. Self-sensing cementitious materials provide a promising approach by enabling intrinsic strain monitoring during fabrication and service. In this study, a hybrid multi-material printing strategy was developed using a conductive cement-based mix incorporating graphite (G), milled carbon microfibers (MCMF), and chopped carbon microfibers (CCMF), alongside a plain cement-based matrix. Based on percolation analysis, an optimal composition of 2 wt.% G, 0.25 wt.% MCMF, and 0.0625 wt.% CCMF was selected. Reinforced beam specimens were fabricated with the conductive material embedded in either the tensile (bottom) or compressive (top) region, combined with two internal architectures: diagonal infill and solid-base configuration. Four configurations were defined: Pattern 1 (bottom/diagonal), Pattern 2 (bottom/solid-base), Pattern 3 (top/diagonal), and Pattern 4 (top/solid-base). Cyclic three-point bending tests with spatially distributed electrical measurements were conducted to evaluate the electromechanical response in the elastic range. Specimens with the conductive layer located in the tensile region (Patterns 1 and 2) consistently exhibited higher gauge factors than those in the compressive region (Patterns 3 and 4). Pattern 2 exhibited the best sensing performance, with an average gauge factor of 556 and SNR of 31. Across all configurations, SNR decreased with increasing electrode spacing, with reductions of up to 31.0%, demonstrating the effect of current path length on sensing performance. Full article

This paper examines the integration of three-dimensional (3D) printing and robotic fabrication in contemporary architectural design, with a focus on overcoming the technical limitations that constrain large-scale adoption. While additive manufacturing enables the production of complex geometries and customized structures, its standalone application remains limited by fixed build volumes, planar deposition, lack of tensile reinforcement, open-loop process control, and single-process extrusion. To address these constraints, the paper proposes a functional integration framework that systematically maps robotic fabrication capabilities onto these five critical limitations. Evidence from recent studies demonstrates that such integration has already led to measurable advances, including up to a 90-fold increase in printable volume through mobile robotic systems, robotically fabricated reinforcement systems (e.g., Mesh Mold) achieving post-crack behavior comparable to conventional reinforced concrete, and the implementation of closed-loop sensor-based process control to enhance interlayer bonding. Despite these achievements, interdisciplinary collaboration across architecture, structural engineering, materials science, and robotics remains largely fragmented and is predominantly confined to academic and pilot-scale projects, such as the ETH Zurich DFAB House. Regulatory progress is also limited, with only isolated code-compliant implementations under frameworks such as ICC-ES AC509 and ISO/ASTM 52939. Persistent barriers including high capital costs, loss of information in BIM-to-fabrication workflows, anisotropic material behavior, and the absence of long-term durability standards continue to restrict widespread adoption. These findings suggest that advancing robotic additive manufacturing in architecture requires not only technological innovation but also coordinated cross-disciplinary integration, standardized testing protocols, and harmonized regulatory frameworks. Full article

Three-dimensional concrete printing (3DCP) offers an accurate, formwork-free, and resource-efficient construction process; however, the absence of vibration and compaction often results in increased porosity and reduced durability. This study investigates the influence of nano-calcium carbonate (NC), acting as a nano pore-filler, on the durability and other physical properties of 3DCP. NC was incorporated at dosages of 0–3% by weight of cement, and specimens were fabricated using a laboratory-scale 3D printing machine. Durability performance was evaluated after 120 days under plastic-wrapped curing, sulfuric acid exposure, and magnesium sulfate immersion. In addition, thermal conductivity and sound absorption were measured to identify the effect of pore structure modification by NC. The results show that NC enhances matrix densification and mechanical performance up to an optimal dosage of approximately 2%, beyond which its effectiveness decreases. Under magnesium sulfate immersion, the strength decreased slightly but improved with increasing NC content up to about 2%. In the case of sulfuric acid exposure, the strength decreased significantly after 120 days; however, it still increased with increasing NC content. Incorporating NC into 3DCP appears to provide improved resistance to both magnesium sulfate and sulfuric acid exposure. Thermal conductivity increased with NC addition, indicating improved solid-phase continuity, whereas sound absorption decreased due to the reduction in porosity. These findings demonstrate that nano-calcium carbonate can effectively refine pore structure and improve durability-related performance, contributing to extended service life and more sustainable 3D-printed cementitious materials in the built environment. Full article

3D printed concrete technology has demonstrated great potential in transforming construction methods, improving efficiency, and reducing environmental impacts. However, the current quality control and identification of 3D printed concrete mainly rely on manual experience and traditional non-real-time measurements, enabling the printed quality to face major challenges. Although an increasing number of studies have investigated automated quality monitoring and defect detection in 3D printed concrete, a dedicated review that systematically synthesizes these methods is still lacking. This paper provides a comprehensive review of automated quality monitoring methods for 3D printed concrete, focusing on current techniques, challenges, and future applications. Optical image processing and machine learning have been successfully used to detect defects in 3D printed concrete, although these methods have limitations in real-time performance, automation, and data quality. Further, deep learning-based methods have shown great potential in improving the accuracy and automation of defect detection, although data annotation, model generalization, large-scale construction projects, and real-time integration still face challenges. Finally, the integration of quality monitoring with building information modeling and further developments in multi-source data fusion, data augmentation, real-time adaptive control, and active quality control are recommended to address current challenges. Full article

3D printing is evolving at a fast pace in both the manufacturing and construction sectors. These advancements can greatly benefit these industries. However, the 3D printing of concrete structures presents some challenges due to defects in the 3D concrete printed elements. Hence, this study systematically reviews Artificial Intelligence (AI)-driven techniques, such as Computer Vision and Machine Learning, to identify surface defects that can occur in 3D-printed cementitious material structures. The adopted methodology was the PRISMA statement with the aim of reporting the systematic review and meta-analysis. Two well-known databases, Web of Science and Scopus, were utilised for data extraction of articles published during the past 10 years, between 2014 and May 2025. The initial search provided 110 articles, both conference and journal papers; after screening, only 11 were left for the final review assessment. The smaller number of the final articles shows that much work is still needed in this area. It has been observed that various computer vision and machine learning-based methodologies were employed to classify defects in 3D concrete printed structures. Deep learning algorithms, such as YOLO and RT-DETR, were featured as the most efficient in real-time defect detection and quality monitoring. It was also observed that real-time monitoring systems attached to 3D printers help in reducing the material wastage, which is essential to meet the sustainable goals. However, more work is still required to underline the defects of 3D-printed cementitious material, probably with the involvement of AI image processing tools and techniques. This can help to automate the defects in 3D-printed structures, and by this, the productivity could be enhanced. Full article

The global construction industry urgently requires sustainable alternatives to ordinary Portland cement (OPC) to mitigate its immense carbon footprint. Red mud (RM), a highly alkaline bauxite residue, presents tremendous but challenging potential as a supplementary cementitious material. This review systematically bridges the gap between atomic-level interfacial bonding mechanisms and macroscopic engineering performance, highlighting how these properties are significantly dictated by specific RM sources (e.g., Bayer vs. Sintering processes). We first elucidate advanced pretreatment strategies, notably CO₂ mineralization, which synergistically mitigates extreme alkalinity and sequesters carbon. Crucially, the fundamental bonding mechanisms are decoded: beyond physical filling, RM integration induces significant micro-morphological densification via intense aluminosilicate depolymerization—evidenced by the Al[VI] to Al[IV] coordination shift—and the quantitative integration of approximately 40% reactive iron phases into stable Fe-S-H networks. By clearly distinguishing between traditional hydration and clinker-free alkali-activation pathways, we evaluate holistic structural parameters beyond mere 28-day compressive strength (40–67 MPa), explicitly addressing flexural capacity, modulus of elasticity, and volume stability. Environmental assessments confirm exceptional heavy metal immobilization (>95% efficiency, leaching < 0.010 mg/L) and a substantial 50–80% reduction in Global Warming Potential (GWP), provided the environmental burden of alkaline activators is rigorously accounted for. Furthermore, the long-term risk of Alkali–Silica Reaction (ASR) is evaluated as a primary durability concern. Finally, to overcome persistent rheological bottlenecks, this paper highlights transformative future trajectories, particularly data-driven Machine Learning (ML) for complex mix optimization and 3D concrete printing for advanced infrastructure. Ultimately, this review provides a robust theoretical foundation and a pragmatic roadmap for upcycling RM into safe, high-performance, and ultra-low-carbon building materials. Full article

3D Concrete Printing (3DCP) is increasingly explored as a digital fabrication technology offering design freedom, automation, and material efficiency. Nevertheless, its application in reinforced and long-life structures remains limited by insufficient understanding and poor comparability of durability performance, as previous reviews have not systematically linked methodologies to transport-related results. This study presents a systematic and critical review of carbonation and chloride ingress in 3DCP cementitious materials, conducted in accordance with the PRISMA methodology. Following a structured database search and two-stage screening process, the selected studies are subjected to qualitative analysis. Experimental methodologies, specimen typologies, exposure conditions, and attack directions are compiled and qualitatively compared. The review highlights pronounced methodological heterogeneity and frequent under-reporting of key parameters, particularly attack direction, sealing conditions, CO₂ concentration, and indicator methods, limiting cross-study comparison. Despite these limitations, consistent qualitative trends are identified. Printed specimens generally exhibit inferior durability performance than cast specimens, while cold joints are associated with increased penetration depth and result dispersion. Directional effects are non-negligible, although they are systematically addressed in only a limited number of studies. Overall, the findings emphasise the critical role of process-induced features and the need for harmonised testing methods to enable reliable durability assessment. Full article

Additive manufacturing of concrete offers reduced waste, faster construction, and design freedom, yet effective reinforcement integration remains a major challenge due to weak interlayer bonding and anisotropy. Most prior studies focus on vertical reinforcement, short fibers, or metallic systems, achieving modest flexural improvements (15–60%). This study evaluates horizontal continuous reinforcement using glass fiber mesh and two carbon fiber meshes (ARMO-mesh 200/200 and 500/500) integrated during 3D printing. The methods include extrusion-based printing of small (four-layer) and beam-like (eight-layer) specimens, both printed and cast, followed by three-point flexural and compression tests at 7 and 28 days under vertical and horizontal loading. The results show that ARMO-mesh 500/500 significantly enhances flexural strength—up to 100% over unreinforced controls (e.g., 24.4 kNm vs. 12.2 kNm in small specimens at 28 days) and ~60% over ARMO-mesh 200/200, while glass mesh provides only marginal gains (~12%). Carbon meshes also improve post-cracking toughness and apparent interlayer cohesion. A pronounced size effect reduces nominal strength in larger specimens. These findings demonstrate that wide-format porous carbon meshes offer a scalable, corrosion-resistant solution for load-bearing 3D-printed concrete elements, advancing automated digital construction. Full article

The urgent need to decarbonize the global cement industry is compounded by the declining availability of conventional supplementary cementitious materials (SCMs). Limestone-calcined clay cement (LC3) emerges as a highly sustainable alternative, enabling up to 50 percent clinker replacement and an approximate 40 percent reduction in carbon dioxide emissions. Unlike existing reviews that focus on basic material properties, this paper critically bridges the gap between fundamental hydration thermodynamics and next-generation sustainable engineering applications. Through a structured bibliographic analysis of 135 contemporary sources published between 2000 and 2026, it traces the evolution of LC3 from a laboratory innovation to a highly promising solution for large-scale industrial implementation and circular economy integration. The discussion highlights the synergistic alumina carbonate reaction. This reaction forms carboaluminate phases. These phases significantly densify the microstructure and enhance long term durability. Key engineering properties are examined, contrasting rheological challenges from high water demand and carbonation susceptibility against its exceptional chloride resistance in aggressive environments. The transition to field application is thoroughly assessed, emphasizing technological advances in flash calcination, environmental footprint reduction through life cycle assessment (LCA), and production scalability. Finally, rather than restating known challenges, this review exposes the limitations of current empirical mitigation strategies. It proposes a targeted research agenda focused on molecular-level green admixture design and field calibrated durability models to support the integration of LC3 into emerging sustainable technologies such as 3D concrete printing. Full article

Building 3D printing technology exhibits remarkable construction advantages, with solid waste-based 3D printing slurry emerging as a research hotspot in the field. Phosphogypsum is compatible with diverse solid wastes for the fabrication of geopolymer, whereas its feasibility as a 3D printing material merits further investigation. In this study, calcium carbide slag (CS), ground granulated blast-furnace slag (GGBS), recycled concrete powder (RCP), and phosphogypsum (PG) underwent co-activation. The mix proportion received optimization via response surface methodology (RSM), and printability assessment proceeded based on the optimized proportion. Key conclusions include the following: PG exerts a role in optimizing the internal structure within the geopolymer matrix. The 28-day compressive strength of the composite geopolymer exceeds 25 MPa. Application as a 3D printing material facilitates enhancement of slurry stability in the later stage. Excessive PG addition elevates the shear stress and viscosity of the 3D printing paste, shortens the paste open time, and impedes paste extrusion and molding. Based on a comprehensive analysis of printability and the performance of printed specimens, the optimal mix proportion of the phosphogypsum-based geopolymer 3D printing paste was determined as follows: CS: 22.5%; GGBS: 45%; RCP: 22.5%; PG: 10%; W/b: 0.4. Full article

This study proposes a novel semi-discrete model of non-ordinary state-based peridynamics. It is used to simulate the tensile failure process of dog bone-shaped specimens of 3D-printed fiber-reinforced concrete with 0%, 1% and 2% fiber volume fractions. The results are compared with the literature laboratory results to verify the feasibility and reliability of the approach. In addition, it is utilized for a 3D-printable engineered cement-based composite (ECC) disk splitting simulation. Effects of different fiber lengths, printing interfaces, and fiber orientations on the failure process of disc specimens are investigated. It is found that ductile failure appears in the loading direction, while brittle failure appears in the other direction. Effect of fiber length on the bearing capacity is feeble. In addition, the non-ordinary state-based peridynamics semi-discrete model is used to simulate the crack propagation of three-point bending. The principal stress contours, damage diagrams, and displacement–load curves of the concrete matrix at different time steps during the crack propagation process are obtained. The simulation is in great agreement with the experimental results. Finally, it is demonstrated that the novel non-ordinary state-based peridynamics approach proposed in this paper is accurate and efficient to simulate fracture behavior of 3D-printed ECC beams. Full article

Interlayer bond strength is critical for ensuring the safety and durability of 3D-printed concrete (3DPC) structures. However, there remains a lack of real-time prediction methods addressing interlayer performance under the combined effects of interval time and environmental factors during the in situ printing process. To address this issue, this study conducted experiments considering various printing interval times and environmental conditions, incorporating monitoring of dielectric constant and water evaporation, alongside interlayer splitting tensile tests. By integrating the SHAP interpretability algorithm with nonlinear regression analysis, the results indicate that the printing interval time is the dominant factor inducing interlayer strength decay (with a contribution rate of 68.6%), while relative humidity emerges as the primary environmental variable (with a contribution rate of 21.3%). Mechanism analysis reveals that prolonged printing intervals intensify the hydration of the lower deposited layer, leading to reduced interfacial moisture content and loss of plasticity. Furthermore, environmental evaporation significantly regulates this process, with high-humidity environments notably mitigating the moisture loss and strength reduction caused by time delays. Based on the correlation mechanism between moisture and strength, a dimensionless general prediction model for 3DPC interlayer strength was established, incorporating printing interval time and an evaporation index (goodness of fit, R² = 0.96). Consequently, a digital twin quality inversion scheme based on companion specimen monitoring and printing timestamps was proposed. This study quantifies the intrinsic relationships among printing interval time, environmental conditions, and interlayer strength, offering a novel approach for determining the construction window and achieving non-destructive quality prediction for 3DPC in complex environments. Full article

As a representative digital additive construction material, three-dimensional printed concrete (3DPC) imposes a synergistic rheological requirement on fresh cementitious mixtures, namely “pumpability–extrudability–buildability,” throughout the forming process. Rheological parameters and their temporal evolution not only govern the stability of the material during pumping, nozzle extrusion, and layer-by-layer deposition, but also directly determine interlayer interfacial integrity, geometric fidelity, and the development of macroscopic mechanical performance. This paper provides a systematic review of the regulation strategies and evolutionary characteristics of 3DPC rheology, with particular emphasis on how raw material composition, printing parameters, and multiscale evolution mechanisms influence yield stress, plastic viscosity, and thixotropic behavior. The time-dependent evolution of rheological properties is elucidated across multiple length scales, encompassing microscopic particle interactions and hydration-induced bridging, mesoscopic aggregate force-chain networks and particle migration, and macroscopic shear stimulation coupled with temperature–humidity effects. On this basis, it is further highlighted that existing models and characterization frameworks remain insufficient to capture the time-dependent structural evolution under realistic printing conditions. Therefore, the establishment of unified characterization standards, together with in situ rheological measurements and multiscale simulations, is urgently required to enable the coordinated optimization of material design and printing processes and to facilitate engineering-scale implementation. Full article

The advancement of sustainable construction requires the development of earthen materials compatible with 3D printing (additive manufacturing), along with specified engineering standards. Many existing studies improve workability and early strength using chemical stabilizers such as cement; however, these additives increase embodied carbon and undermine sustainability objectives. Challenges remain in the formulation of an earthen mixture that satisfies both printability and structural requirements for large-scale construction. Previous earth-based mixes have reported excessive shrinkage and inadequate compressive strength. This study presents the systematic optimization of a low-carbon, 3D-printable earthen mixture using locally sourced clay-loam soil from Belén, New Mexico (NM). The soil was modified with graded concrete sand and rice hull fiber to improve printing parameters such as buildability, extrudability, and printability while meeting the NM Earthen Building Code requirements for compressive and flexural strength. Soil characterization tests (particle size distribution, consistency, optimal water content) guided iterative refinement to enhance dimensional stability and mechanical performance. A baseline 2:1 soil-to-sand ratio (max aggregate size No. 4) was established. Incorporating $2\%$ rice hull fiber and reducing max aggregate size to No. 16 (S67F2) early-age shrinkage was reduced from $12.33\%$ to $3.48\%$ ($72\%$ reduction) while maintaining a 28-day compressive strength exceeding 660 psi, more than twice the code minimum. The optimized mixture supported 24 printed layers without deformation, achieved 189 psi flexural strength (three times the code minimum), and produced a stable 2-ft-diameter dome with minimal cracking. Full article

A significant portion of plastic products is not accepted by curbside recycling companies and goes to landfills or incineration, causing an adverse impact on the environment. This study investigated the effects of utilizing post-consumer plastic and e-waste in concrete. A plastic product made of thermoplastic polypropylene (PP) was ground into fine particles and used for 10% volumetric replacement of sand, while bare printed circuit boards (PCBs) were pulverized into powder and used for 10% cement replacement by mass. This study introduces a unique utilization of grounded powder PCBs by partially replacing cement in concrete. Furthermore, reinforced concrete beams with the replacements were constructed and tested under flexure for structural behavior evaluation. The results of this study show an average of 11% reduction in both the compressive strength of concrete and the maximum load capacity of the beams incorporating plastic products. A life cycle assessment study was conducted using a functional unit of 1.0 cubic yard concrete production. The system boundary for the environmental assessment of the concrete in this study includes only the production phase, which is from the cradle to the end gate of the ready-mix concrete plant. The environmental impact estimation of a 10% reduction in constituents of concrete showed a 10% reduction in most LCA measures where cement was replaced compared to a 1% effect for the fine aggregate replacement. Full article