Search Results (343)

In this study, the effects of waste steel fiber and high volume blast furnace slag (BFS) substitution on rheological properties, thixotropic behavior and carbon emission were investigated in order to increase the sustainability of three-dimensional (3D) printable concrete (3DPC). Cement was replaced with BFS at 0%, 25%, 50% and 75% by volume, while waste steel fibers were added to the mixtures at three different lengths (5, 10, 15 mm) and volumetric ratios (0.5% and 1.0%). A total of 39 mixtures were optimized with respect to extrudability, buildability and shape stability criteria, and their rheological and thixotropic properties were characterized by a modified rheometer procedure. Results showed that 50% BFS substitution reduced dynamic yield stress and viscosity by 69% and 52%, respectively, and eliminated the need for a water-reducing admixture. 75% BFS substitution improved structural build-up (A_thix) but required 6% silica fume. The fiber effect interacted with length and BFS content, with short fibers increasing rheological resistance, while the effect of long fibers decreased in mixtures with high BFS. The carbon emission assessment revealed that 75% BFS substitution provided an outstanding CO₂ reduction of up to 71% compared to the control mix. These findings prove that high-volume BFS and waste fibers are an effective strategy to optimize rheological performance and environmental impact for sustainable 3D concrete printing. Full article

Three-dimensional concrete printing (3DCP), an innovative fabrication technique, has emerged as an environmentally friendly digital manufacturing process for using recycled waste materials in the construction industry. The aim of this review paper is to critically evaluate the current state of research on the use of recycled materials such as aggregates and powders in 3DCP, correlating the environmental, economic, and performance parameter effects. This review comprehensively evaluates the potential benefits of incorporating recycled waste materials in 3D printing by critically reviewing the existing peer-reviewed articles through a scientometric review. The resulting bibliometric analysis identified 73 relevant papers published between 2018 and 2024. Through the critical review, five main research categories were identified: recycled materials in 3DCP arising mainly from construction demolition in powder and aggregate forms, which investigates the types of recycled materials used, their extraction methods, morphology and physical and chemical properties. The morphology properties of the materials used displayed high irregularities in terms of shape and percentage of adhered mortar. In the second category, printability and performance, the buildability, rheological properties and the mechanical performance of 3DCP with recycled materials were investigated. Category 3 assessed the latest developments in terms of 3D-printed techniques, including Neural Networks, in predicting performance. Category 4 analysed the environmental and economic impact of 3DCP. The results indicated anisotropic behaviour for the printed samples influencing mechanical performance, with the parallel printing direction showing improved performance. The environmental performance findings indicated higher global warming potential when comparing 3DCP to cast-in situ methods. This impact was reduced by 2.47% when recycled aggregates and binder replacements other than cement were used (fly ash, ground slag, etc.). The photochemical pollution impact of 3DPC was found to be less than that of cast-in situ, 0.16 to 0.18 C2H4-eq. This environmental impact category was further reduced up to 0.10 C2H4-eq following 100% replacement. Lastly, category 5 explored some of the challenges and barriers for the implementation of 3DCP with recycled materials. The findings highlighted the main issues, namely inconsistency in material properties, which can lead to a lack of regulation in the industry. Full article

The automation of concrete constructions through 3D printing (3DP) has been increasingly developed and adopted in civil engineering due to its promising advantages over traditional construction methods. However, widespread implementation is hindered by uncertainties in quality control, homogeneity, and interlayer bonding, as well as the uniqueness of each printed component. Building upon our prior work in developing 3D-printable self-sensing cementitious materials by incorporating graphite powder and carbon microfibers into a cementitious matrix to enhance its piezoresistive properties, this study aims at enabling condition assessment of cementitious 3DP by integrating the self-sensing materials as sensing nodes within conventional components. Three different 3D-printed strip patterns, consisting of one, two, and three strip lines that mimic the pattern used in fabricating foil strain gauges were investigated as conductive electrode designs to impart strain sensing capabilities, and characterized from a series of quasi-static and dynamic tests. Results demonstrate that the three-strip design yielded the highest sensitivity (${\lambda }_{\mathrm{stat}}$ of 669, ${\lambda }_{\mathrm{dyn}}$ of 630), whereas the two-strip design produced the highest signal quality (SNR_stat = 9.5 dB, SNR_dyn = 10.8 dB). These findings confirm the feasibility of integrating 3D-printed self-sensing cementitious materials through hybrid manufacturing, enabling monitoring of print quality, detection of load path changes, and identification of potential defects. Full article

Rapid population growth and accelerating urbanization are intensifying the demand for construction materials, particularly concrete, which is predominantly produced with Portland cement and natural aggregates. This reliance imposes substantial environmental burdens through resource depletion and greenhouse gas emissions. Within the framework of sustainable construction, recycled aggregates and industrial by-products such as fly ash, slags, crushed glass, and other secondary raw materials have emerged as viable substitutes in concrete production. At the same time, three-dimensional concrete printing (3DCP) offers opportunities to optimize material use and minimize waste, yet it requires tailored mix designs with controlled rheological and mechanical performance. This review synthesizes current knowledge on the use of recycled construction and demolition waste, industrial by-products, and geopolymers in concrete mixtures for 3D printing applications. Particular attention is given to pozzolanic activity, particle size effects, mechanical strength, rheology, thermal conductivity, and fire resistance of recycled-based composites. The environmental assessment is considered through life-cycle analysis (LCA), emphasizing carbon footprint reduction strategies enabled by recycled constituents and low-clinker formulations. The analysis demonstrates that recycled-based 3D printable concretes can maintain or enhance structural performance while mix-level (cradle-to-gate, A1–A3) LCAs of printable mixes report CO₂ reductions typically in the range of ~20–50% depending on clinker substitution and recycled constituents—with up to ~48% for fine recycled aggregates when accompanied by cement reduction and up to ~62% for mixes with recycled concrete powder, subject to preserved printability. This work highlights both opportunities and challenges, outlining pathways for advancing durable, energy-efficient, and environmentally responsible 3D-printed construction materials. Full article

Fiber-reinforced foamed composites have recently attracted growing interest due to their potential in sustainable construction and advanced additive manufacturing. However, their performance strongly depends on the type of matrix and fiber system used. The aim of this study was to perform a comparative analysis of matrix type and fiber composition on the porosity, thermal behavior, and mechanical performance of 3D-printed fiber-reinforced foamed composites. To this end, cementitious mixtures (M1–M3) were compared with alkali-activated hybrid binder systems (M4–M6). The results revealed marked differences in mechanical strength, dimensional stability, moisture transport, and interlayer cohesion. Alkali-activated specimens, particularly M5 and M6, exhibited superior compressive, flexural, and shear strength; reduced water penetration; and improved fiber–matrix bonding, associated with a denser and more homogeneous pore structure. In contrast, cementitious composites showed greater dimensional stability and easier process control, indicating practical advantages for large-scale on-site applications. The results highlight that while alkali activation and hybrid fiber reinforcement enhance structural performance, non-activated foamed concretes remain promising for applications prioritizing simplicity, reproducibility, and thermal insulation. Full article

Three-dimensional concrete printing (3DCP) is rapidly emerging as a transformative construction technology, enabling formwork-free fabrication, geometric flexibility, and reduced labour. However, the lack of conventional reinforcement and the strict requirements for fresh and hardened properties present significant challenges. Fibre reinforcement and supplementary cementitious materials (SCMs), such as ground granulated blast furnace slag (GGBS), offer pathways to enhance printability while mitigating environmental impact. This study investigates the combined effect of natural cellulose microfibres and silica fume on the rheological, mechanical, and sustainability performance of 3D-printable mortars. Six mixes were prepared with 50% GGBS, 45% cement, and 5% silica fume, incorporating fibre dosages from 0% to 1%. Results showed that a 0.5% fibre dosage provided the most favourable balance. At this dosage, static yield stress increased to 9.35 Pa and thixotropy reached 8623 mPa·s, enhancing structuration for shape retention. Plastic viscosity remained stable at 4–5 Pa·s, ensuring adequate extrusion performance. Higher fibre dosages (≥0.75%) caused a significant increase in rheological resistance, with static yield stress reaching 208 Pa and thixotropy 135,342 mPa·s. This resulted in excessive structuration, fibre clustering, and poor extrudability. Compressive strength was achieved at 109.10 MPa (92% of silica fume-only mix) with 0.5% fibre. In comparison, flexural strength was 13.20 MPa at 0.5% fibre content and reduced gradually to 12.29 MPa at 1% fibre due to weak fibre–matrix bonding and porosity. Sustainability analysis confirmed that using 50% GGBS and 5% silica fume reduced embodied carbon compared to a 100% cement mix. This study also demonstrated that cellulose microfibres at 0.25–0.5% are optimal for balancing fresh properties, mechanical strength, and sustainability in 3D-printed mortars. Full article

Three-dimensional concrete printing (3DCP) is advancing rapidly, yet its sustainable adoption requires alignment with circular-economy principles. This study evaluates the substitution of natural aggregates with recycled constituents, 3DCP waste, brick debris, glass cullet, mixed rubble, fly ash, and slag, and the use of lightweight fillers (expanded perlite, lightweight expanded clay aggregate (LECA), and expanded polystyrene (EPS)) to reduce density and improve insulation. Key properties, such as particle-size distribution, printability, mechanical performance, thermal conductivity, and water absorption, were determined. Results indicate that grading strongly affected mixture behavior. Narrow distributions (fly ash, milled 3DCP waste) enhanced extrudability, while broader gradings (glass, rubble, slag) increased water demand and extrusion risks. Despite these differences, all systems remained within the printable window: flow spread decreased with most recycled additions (lowest for brick) and increased with glass. Mechanical responses were composition-dependent. Flexural strength typically decreased. Compressive strength benefited from broader gradings, with replacement levels up to ~6% enhancing strength due to improved packing. Loading anisotropy typical of 3DCP was observed, with perpendicular compressive strength reaching up to 13% higher values than parallel loading. Lightweight fillers significantly reduced thermal conductivity. LECA provided the best compromise between strength and insulation, perlite showed intermediate behavior, and EPS achieved the lowest thermal conductivity but induced significant strength penalties due to weak matrix-EPS interfaces. Water absorption decreased in recycled-aggregate mixes, whereas lightweight systems, particularly with perlite, retained higher uptake. The results demonstrate that non-reactive recycled aggregates and lightweight insulating fillers can be successfully integrated into extrusion-based 3DCP without compromising printability. Full article

3D-printable concretes often require high binder content. This study evaluates the use of industrial gypsum by-products, phosphogypsum (PG) and borogypsum (BG), as partial cement replacements to enhance sustainability without compromising printability. PG and BG were incorporated at 2.5–10 wt% to replace the gypsum fraction in cement-based mortars containing fly ash (FA) or ground granulated blast-furnace slag (GGBS), with and without fibers. The fresh properties (spread flow diameter, open time, air content, density, and pH) and compressive strength were measured. At 28 days, the highest strength was achieved with a 7.5% PG addition to the GGBS system (~51 MPa), which exceeded the strength of the GGBS control C1 (~47.6 MPa). In the FA system, 2.5% PG reached 42.5 MPa, comparable to the FA control C2 (41.2 MPa). BG caused pronounced strength penalties at ≥7.5% across both binder systems, indicating a practical BG ceiling of ≤5%. Open time increased from ~0.75 h in the controls to ~2–2.5 h in BG-FA mixes with fibers, whereas PG mixes generally maintained a stable, printable window close to control levels. Overall, adding 5–7.5% PG, particularly in the presence of GGBS, improved mechanical performance without compromising workability. However, BG should be limited to ≤5% unless extended open time is the primary objective. These findings provide quantitative guidance on selecting PG/BG dosages and FA/GGBS systems to balance strength and printability in cement-based, 3D-printable concretes. Full article

With the global concept of sustainable development gaining widespread acceptance, the resource utilization of solid waste has become an important research direction in the field of building materials. Geopolymer concrete (GPC), especially solid waste-based geopolymer concrete (SWGPC) prepared using various industrial solid wastes as precursors, has gradually become a frontier in green building material research due to its low carbon footprint, high strength, and excellent durability. However, the rapid expansion of literature calls for a systematic review to quantify the knowledge structure, evolution, and emerging trends in this field. Based on two thousand and thirty-nine (2039) relevant articles indexed in the Web of Science Core Collection database between 2008 and 2025, this study employs bibliometric methods and visualization tools such as VOSviewer and CiteSpace to systematically construct a knowledge map of this field. The research comprehensively reveals the developmental trajectory, research hotspots, and frontier dynamics of SWGPC from multiple dimensions, including publication trends, geographical and institutional distribution, mainstream journals, keyword clustering, and burst word analysis. The results indicate that the field has entered a rapid development stage since 2016, with research hotspots focusing on the synergistic utilization of multi-source solid waste, optimization of alkali-activation systems, enhancement of concrete durability, and environmental impact assessment. In recent years, the introduction of emerging technologies such as machine learning, 3D printing, and nano-modification has been driving a paradigm shift in research. This systematic analysis not only clarifies research development trends but also provides a theoretical basis and decision-making support for future interdisciplinary integration and engineering practice transformation. Full article

High-performance concrete for 3D printing has recently attracted significant attention due to its potential to create structural elements without the need for traditional reinforcement. While various formulations have been proposed by researchers, evaluations are often limited to mechanical performance and printability, while cost and environmental impact are generally overlooked. This study expands the analysis by also considering cost and environmental impact, aiming to identify the optimal mix using a multi-criteria decision-making analysis (MCDMA). In the first phase, several high-strength mortar formulations were developed and assessed based on mechanical strength, printability, environmental impact, and cost. In the second phase, the most promising mix from the initial evaluation was further modified by incorporating different types of fibers, including aramid, carbon, glass, cellulose, and polypropylene. Comprehensive testing—covering mechanical properties and printability—together with cost and a life cycle assessment were conducted to determine the most effective mortar formulations. One of the main findings is that adding 0.05% of 20 mm length cellulose fibers in weight to a mortar containing Cem I 42.5R can increase the compressive strength by more than 9% without affecting the cost or environmental impact, also allowing the obtainment of a mortar apt for 3D printing. This increase in the compression strength is presumably related to a lateral restriction in movements of the mortar, which makes it increase the maximal principal stresses, and thus, its strength. Full article

The traditional construction industry significantly contributes to global resource consumption and climate change. Conventional methods limit the development of complex and multifunctional architectural forms. In contrast, 3D concrete printing (3DCP), an additive manufacturing technique, enables the creation of intricate building envelopes that integrate architectural and energy-efficient functions. Bioinspired design, recognized for its sustainability, has gained traction in this context. This study investigates the thermal and energy performance of various bioinspired and regular 3DCP infill patterns compared to conventional concrete building envelopes in tropical climates. A three-stage methodology was employed. First, bioinspired patterns were identified and evaluated through a literature review. Next, prototype models were developed using Rhino and simulated in ANSYS to assess thermal performance. Finally, energy performance was analyzed using Ladybug and Honeybee tools. The results revealed that honeycomb, spiral, spiderweb, and weaving patterns achieved 35–40% higher thermal and energy efficiency than solid concrete, and about 10% more than the 3DCP sawtooth pattern. The findings highlight the potential of bioinspired spiral infill patterns to enhance the sustainability of 3DCP building envelopes. This opens new avenues for integrating biomimicry into 3DCP construction as a tool for performance optimization and environmental impact reduction. Full article

The growing application of 3D concrete printing (3DCP) in construction has raised important questions regarding its long-term durability under freeze–thaw (F–T) exposure, particularly in cold climates. This review paper presents a comprehensive examination of recent research focused on the F–T performance of 3D-printed concrete (3DPC). Key material and process parameters influencing durability, such as print orientation, admixtures, and layer bonding, are critically evaluated. Experimental findings from mechanical, microstructural, and imaging studies are discussed, highlighting anisotropic vulnerabilities and the potential of advanced additives like nanofillers and air-entraining agents. Notably, air-entraining agents (AEA) reduced the compressive strength loss by 1.4–5.3% after exposure to F–T cycles compared to control samples. Additionally, horizontally cored specimens with AEA incorporated into their mixture design showed a 15% higher dynamic modulus after up to 300 F–T cycles. Furthermore, optimized printing parameters, such as reduced nozzle standoff distance and minimized printing time gap, reduced surface scaling by over 50%. The addition of a nanofiller such as nano zinc oxide in 3DPC can result in compressive strength retention rates exceeding 95% even after aggressive F–T cycling. The lack of standard testing protocols and the geometry dependence of degradation are emphasized as key research gaps. This review provides insights into optimizing mix designs and printing strategies to improve the F–T resistance of 3DPC, aiming to support its reliable implementation in cold-region infrastructure. Full article

Increasing labor costs, labor shortage, high environmental impact, and low productivity levels are the main reasons that have led the construction industry to search for sustainable alternatives to conventional traditional construction techniques, such as Additive Construction. Large-scale concrete 3D printing has emerged as a viable alternative, which can address these major challenges. Through the high material efficiency, design flexibility, and automation levels provided, 3D printing can revolutionize the way buildings are designed and built. The seismic behavior of 3D-printed load bearing elements remains generally underexplored. To that scope, the structural design of a two-story building is investigated. The proposed methodology involves finite element models and stress analysis of critical structural members. The performance of the studied walls is further investigated using 3D solid element models and nonlinear constitutive laws to validate structural adequacy. Different printing patterns and structural details of unreinforced and reinforced 3D-printed concrete walls are analyzed through parametric analyses. The results indicate the acceptable response of 3D-printed load bearing elements, under certain construction configurations, as required by the existing regulatory framework. The proposed methodology could be applied for the design of such structures and for the optimization of printing patterns and reinforcing details. Full article

The article deals with the evaluation of dimensional deformations of a building element manufactured additively from a cement mixture. The study follows up on previous research within the 3DStar project and expands the methodology for monitoring deformations over time. The aim is to contribute to the development of more accurate simulation models for predicting the behaviour of printed structures, especially in the early stages after printing. For the analysis, an experimental ‘L’-shaped element was designed and printed, whose deformations were monitored using repeated 3D scanning and dimensional changes were evaluated for up to 93 days. The results show that the most significant deformations occur in the first hours after printing due to gravitational loading and mixture curing, while later changes are mainly due to shrinkage. The element’s geometry and the walls’ thickness also play a role. The analysis confirms the effectiveness of the ‘Caliper’ measurement method and outlines the potential for future use of photogrammetry as a method for online deformation monitoring. The data obtained will be used to optimise printing parameters and calibrate material parameters in the developed simulation software for non-linear numerical simulations in additive manufacturing using cement mixtures. Full article

Three-dimensional concrete printing (3DCP) is an emerging technology that improves design flexibility and material efficiency in construction. However, widespread adoption of 3DCP requires overcoming key material challenges. These include controlling rheology for pumpability and buildability and achieving sufficient mechanical strength. This paper provides a comprehensive review of the application of nanoclays (NCs) as a key admixture to address these challenges. The effects of three primary NCs (attapulgite (ATT), bentonite (BEN), and sepiolite (SEP)) on the fresh- and hardened-state properties of printable mortars are systematically analyzed. This review summarize findings on how NCs enhanced thixotropy, yield stress, and cohesion, which are critical for shape retention and the successful printing of multilayered structures. Quantitative analysis reveals that optimized dosages of NCs can increase compressive strength by up to 34% and flexural strength by up to 20%. For enhancing rheology and printability, a dosage of approximately 0.5% by binder weight is often suggested for ATT and SEP. In contrast, BEN can be used at higher replacement levels (up to 20%) to also function as a supplementary cementitious material (SCM), though this significantly impacts workability. This review consolidates the current knowledge to provide a clear framework for selecting appropriate NCs and dosages to develop high-performance, reliable, and sustainable materials for 3DCP applications. Full article