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In this study, biodegradable biocomposites based on polylactide with basalt fibres (BFs) or wood fibres (WFs) of 7.5 or 15 wt% were prepared by injection moulding. Various tests, including tensile test, bending test and impact test, were carried out to investigate the mechanical properties of the composites. Additionally, the samples were tested at different temperatures. Depending on the type of fibre, differences were noted in their mechanical properties; the addition of WF caused a decrease in strength and the higher the fibre content, the higher the decrease was noted from 18% up 25% in the case of tensile strength. However, the Young modulus was improved by 45% for composites with 15 wt% of WF. The addition of BF improved all the properties, especially Young modulus was improved by over 45%. Despite the low strength observed in neat polylactide at high temperatures-394 MPa, the addition of WF or BF improved the flexural strength more than twofold up to 1684 MPa (PLA/15BF). Moreover, the addition of natural fibres caused an increase in dimensional stability as shown by the decrease of the coefficient of thermal expansion which dropped over 50% for composites with 15 wt% of BF, which significantly expands the areas of use of materials. After 4 weeks of biodegradation, only a slight decrease approximately 5% was observed in the mechanical properties together with an increase in crystallinity. Overall, the results confirm that the prepared composites can be successfully used in engineering applications with long-term operation.

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.

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.

Additive manufacturing methods can constitute a valuable alternative to conventional production techniques for components used in the heavy industry, particularly in foundry applications. This innovative manufacturing approach enables an expanded product portfolio as well as higher precision and geometrical complexity of ceramic components. One additive technology applicable to ceramic processing is robocasting, classified within the direct ink writing (DIW) family. In this method, a semi-fluid ceramic paste is extruded to build the part layer by layer; the shaped green body is subsequently fired (sintered) to attain its final functional properties. This study presents the results of materials characterization of printed ceramic filters, encompassing phase composition analysis, density measurements, three-point bending strength testing, hardness, and microstructural examination. The investigations demonstrated that the oxide ceramic Al2O3 processed by the modern robocasting method exhibits mechanical performance at a comparably high level relative to classical manufacturing routes (slip casting, ceramic injection molding, dry pressing). Moreover, the porosity results indicate that 3D printing technology enables lower post-sintering porosity.

Three-dimensional concrete printing (3DCP) is an emerging additive manufacturing technology with increasing application potential in the construction industry, offering advantages such as reduced labor requirements, shortened construction time, and material efficiency. However, structural integrity remains a challenge, particularly due to weak interlayer bonding resulting from the layered manufacturing process. This study investigates the mechanical performance and anisotropy of 3D-printed mineral-based composites with respect to the time interval between successive layers. Specimens were printed with varying interlayer intervals (0, 25, and 50 min) and tested in different loading directions. Flexural, compressive, and tensile strengths (direct and splitting methods) were measured both parallel and perpendicular to the layer orientation. Results showed a clear degradation in mechanical properties with increasing interlayer time, particularly in the direction perpendicular to the layers. Flexural strength decreased by over 25% and direct tensile strength by up to 40% with a 25 min interval. Compressive strength also declined, though less dramatically. Compared to cast specimens, printed elements showed 3–4 times lower compressive strength, highlighting the significant impact of interlayer cohesion. This study confirms that both the time between layers and the loading direction strongly influence mechanical behavior, underlining the anisotropic nature of 3DCP elements and the need for process optimization to ensure structural reliability.

This study investigates the influence of various reinforcing fibers, including coconut, basalt, glass, merino wool, and polypropylene, on the properties and processability of cementitious mixtures, with a particular emphasis on their application in 3D printing. The incorporation of fibers at a concentration of 1 wt.% was found to significantly hinder the printing process. Specifically, certain fibers, such as polypropylene, rendered extrusion impractical due to nozzle clogging. However, reducing the fiber content to 0.5 wt.% improved material flowability and minimized structural defects during printing. Fiber selection, in addition to its impact on mechanical properties, plays a crucial role in determining overall process efficiency. Mixtures incorporating coal slag as a dense filler, combined with stiff fibers such as basalt or glass, exhibited the highest flexural strength. Moreover, the inclusion of merino wool fibers enhanced the flexural performance of fly ash-based mixtures, achieving strength levels comparable to or exceeding those of stiffer fibers. These findings contribute to the advancement of sustainable construction practices. Notably, samples produced via 3D printing consistently demonstrated higher flexural strength than those fabricated using traditional molding techniques. This enhancement is attributed to microstructural modifications induced by the layer-by-layer deposition process. Depending on the sample composition and the type of reinforcing fiber, water absorption behavior varied significantly. Merino wool and coconut fibers exhibited the highest water absorption due to their hydrophilic nature and capillary action, particularly in 3D-printed samples with open-pore structures. In contrast, glass and basalt fibers, characterized by their higher density and hydrophobicity, exhibited lower water absorption levels. These results underscore the importance of optimizing fiber type, concentration, and processing methodologies to achieve tailored performance in fiber-reinforced cementitious mixtures. Such optimizations align with the principles of sustainable development and hold significant potential for advancing 3D-printed construction applications

In response to escalating environmental concerns, the construction industry is under growing pressure to adopt sustainable practices. As a major consumer of natural resources and a significant emitter of greenhouse gases, it paradoxically holds the potential to become a leader in green transformation. This study investigates the development of innovative, fire-resistant, and alkali-activated hybrid binder foams incorporating recycled materials: fly ash, coal slag, and ground brick waste, as sustainable alternatives to traditional building materials. The fire resistance performance at a technical scale and the thermal behavior of fiber-reinforced, alkali-activated hybrid binder foams synthesized from recycled aluminosilicate precursors were determined. The properties of unreinforced composite were compared with the composites reinforced with merino wool, basalt fibers, polypropylene fibers, and coconut fiber. Small-scale fire-resistance tests revealed that merino wool-reinforced composites exhibited the best thermal insulation performance, maintaining structural integrity, that is, retaining shape and continuity without delamination or collapse for 83 min under fire exposure. Analyses combining chemical characterization (X-ray fluorescence) with microstructural methods (computed tomography and colorimetry) confirmed that fire performance is strongly influenced not only by fiber type but also by pore distribution, phase composition, and oxide migration under thermal loading. These findings demonstrate the potential of fiber-reinforced foamed, alkali-activated hybrid binder as eco-efficient, printable materials for fire-safe and thermally demanding construction applications.

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.

In the face of accelerating urbanization and the growing demand for environmentally responsible materials and designs, this study presents the development and implementation of a modular parklet demonstrator fabricated using dual-material 3D printing. The structure integrates polylactic acid (PLA) and wood-filled PLA (wood/PLA), combining the mechanical robustness of pure PLA in the core with the tactile and aesthetic appeal of wood-based biocomposite on the surface. The newly developed dual-nozzle 3D printing approach enabled precise spatial control over material distribution, optimizing both structural integrity and sustainability. A comprehensive evaluation was conducted for developed filaments and printed materials, including optical microscopy, coupled thermogravimetry analysis and Fourier Transform Infrared Spectroscopy (TG/FTIR), differential scanning calorimetry (DSC), and chemical and mechanical resistance testing. Results revealed distinct thermal behaviors and degradation pathways between filaments and printed parts composed of PLA and PLA/wood. The biocomposite exhibited slightly increased sensitivity to aggressive chemical environments and mechanical wear, dual-material prints maintained high thermal stability and interlayer adhesion. The 3D-printed demonstrator bench and stools were successfully deployed in public spaces as a functional urban intervention. This work demonstrates the feasibility and advantages of using biocomposite materials and dual-head 3D printing for the rapid, local, and sustainable fabrication of small-scale urban infrastructure.

The study investigates the potential of using Vietnam fly ash (FA) as a substitute for traditional Portland cement to reduce both the volume of landfilled waste and the carbon footprint of concrete mixtures, while maintaining adequate mechanical performance of the produced elements. Additionally, the incorporation of construction and demolition waste, recycled brick aggregate (BR), as a partial aggregate substitute was investigated to enhance the sustainability and resource efficiency of composite formulations. Five mixes, including a reference, were produced by casting and three-dimensional concrete printing (3DCP). Printability (flow table), water absorption (gravimetry and infrared thermography), and flexural/compressive behavior were assessed; printed specimens were tested parallel and perpendicular to the layer plane. Recycled additions reduced flow by 15–22%, yet all mixes remained printable. Printed specimens showed higher capillary uptake than cast ones. In flexure, modified mixtures composition exhibited 50% lower peak stress than the reference. Cast elements outperformed printed ones: the printed reference was 33% weaker than its cast counterpart, and other mixes were 10–15% lower. In compression, printed specimens loaded perpendicular to layers reached 6–7 MPa (35% below cast), whereas parallel loading yielded up to 3.5 MPa with larger scatter. The findings confirm the feasibility of utilizing secondary raw materials in 3DCP formulations to support resource efficiency and carbon footprint reduction in the construction industry.