This study examines the pore structure and distribution in 3D printed and cast foamed concrete using protein-based and synthetic foaming agents alongside various stabilizing additives. In 3D printed samples, pores are irregular and flattened due to mechanical forces during printing, whereas cast samples display uniform, spherical pores from homogeneous foam distribution. Samples containing the CA stabilizer show higher apparent densities (up to 2.05 g/cm³ for printed samples), correlating with lower water absorption. Protein-based foaming agents (PS) produce smaller, more evenly distributed pores, while synthetic agents (AS) result in larger, less uniform pores. Stabilizers significantly influence pore characteristics: commercial stabilizers yield smaller, more uniform pores, while recycled industrial oil (UO) leads to larger, more variable pores. Protein-based agents improve structural stability and reduce water absorption through uniform pore distributions, while synthetic agents lower density and increase water absorption. The highest sorption values were observed in samples with AS without stabilizer (1.7 kg/m²h¹/²) and AS and UO (1.6 kg/m²h¹/²) in a vertical orientation, with the horizontal orientation of sample AS and UO achieving a peak value of 2.0 kg/m²h¹/². Moreover, stabilization using UO resulted in higher sorption coefficients than stabilization with CA. High porosity in M1 resulted in low strength (0.2 MPa bending, 0.1 MPa perpendicular compression), while M5 showed superior performance (11.5 MPa perpendicular compression). PS-foamed samples (M4, M6) with uniform pores had the highest strengths, with M6 achieving 3.8 MPa bending and 10.3 MPa perpendicular compression. Perpendicular compression (M5: 11.5 MPa) was up to three times stronger than parallel compression due to weak interlayer bonds in 3D printing.

This paper presents the modification results and effects of reinforcing green polyethylene terephthalate matrix composites (bioPET ECOZEN^® T120) with basalt fibers of two different lengths. Five types of composites with two filling levels of 7.5 and 15 wt% of each fiber were produced by injection molding. Basic mechanical and processing properties, microstructure photographs, and reinforcement effects were analyzed and low- and high-cycle fatigue tests were performed. A significant increase in strength and stiffness was observed (especially for short fibers) proportional to the amount of fibers; longer fibers would also increase the deformation capacity of the composite. Furthermore, longer fibers would reduce relaxation processes (creep) but would not increase the dissipation capacity and mechanical energy. Predictability of fatigue effects enables optimal environmentally friendly materials to be designed.

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.

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.

This article presents the results of a study investigating the influence of surface-modified montmorillonite nanoclay and environmental exposure on the mechanical and surface properties of composites based on orthophthalic unsaturated polyester resin. A series of samples containing 0.02 to 0.1 wt.% of nanoclay, as well as a reference sample, were prepared. Following synthesis, the samples were incubated for one week in aqueous solutions with pH values of 4, 7, and 9. Mechanical testing included tensile strength, flexural strength, impact resistance, and surface roughness (Ra). Additionally, fracture surface analysis was performed using scanning electron microscopy (SEM) and digital optical microscopy. The effect of the additive on hardness was also assessed, and Fourier transform infrared (FT-IR) spectroscopy was carried out. The results indicated that nanoclay addition increased the material’s stiffness (Young’s modulus), although higher filler concentrations led to decreased impact strength and flexural performance, likely due to particle agglomeration. Incubation in chemically aggressive environments caused mechanical degradation and significant increases in surface roughness, especially after exposure to neutral and alkaline media. Microscopic observations confirmed the presence of microstructural changes and nanoclay agglomerates in selected samples. The findings confirm that the effectiveness of nanoclay modification depends not only on concentration but also on dispersion quality and the environmental conditions to which the material is exposed.

This study presents the development and characterization of novel hybrid composites based on a bio-based polyethylene terephthalate (bioPET) matrix reinforced with natural and waste-derived fillers—mollusc and eggshell particles, basalt fibres, and titanium dioxide (TiO₂). The composite specimens were produced using the injection moulding technique. The incorporation of these eco-friendly additives aims to enhance the mechanical performance, sustainability, and functionality of the composites. Mechanical tests including tensile, bending, Charpy impact, and low-cycle fatigue experiments were conducted. The addition of basalt fibres significantly improved tensile and flexural moduli, as well as impact resistance. Organic fillers contributed to increased stiffness but often led to brittleness due to weak interfacial bonding. SEM analysis confirmed heterogeneous fracture morphology with varied filler dispersion. Hybrid composites combining waste particles, basalt fibres, and TiO₂ demonstrated synergistic reinforcement effects and stable mechanical behavior under cyclic loading. These findings highlight the potential of bioPET-based hybrid systems for sustainable engineering applications, indicating a promising route toward eco-functional composite materials with potentially enhanced antimicrobial performance due to the presence of TiO₂.