Flexural Strength Research Articles

Upcycling waste polypropylene with basalt fibre reinforcement enhancing additive manufacturing feedstock for advanced mechanical performance

This research seeks to overcome the printing and processing challenges of using waste polypropylene (PP) reinforced with short basalt fibres, transforming them into upcycled feedstock for additive manufacturing. It introduces an optimised method for producing filaments and 3D printing with these materials, addressing common issues such as adhesion and warpage through innovative techniques while achieving maximum mechanical performance in the resulting composites. Basalt fibre weight fractions of 0 %, 2 %, 5 %, 8 %, 15 %, 30 %, and 50 % were used to reinforce the recycled polypropylene, improving both printability and mechanical properties. The tensile strength reached 53.58 MPa at 15 % fibre content, while the flexural strength peaked at 34.06 MPa with 30 % fibre content, revealing distinct interactions between the fibres and polymer under tensile and flexural loading that were not previously observed. Microstructure, voids, debonding, and dispersion were examined using optical and scanning electron microscopy. Differential Scanning Calorimetry (DSC) was performed to assess the thermal behaviour and crystallinity of the recycled polymer during filament production and printing, revealing slight matrix degradation during these processes. The findings highlight the potential of waste basalt fibre-reinforced PP as a valuable filament feedstock for 3D printing, supporting a circular economy approach to composite manufacturing.

Flexural Strength of Modern CAD/CAM Restoratives After Artificial Aging.

Before clinical trials are initiated, studying the mechanical performance of modern CAD/CAM restorative materials exposed to aging conditions would provide insights on their performance in service. This study evaluated the impact of thermomechanical aging on various resin composite, ceramic, hybrid, and nano-filled resin composite materials after two polymerization modes. Specimens (3 × 4 × 14 mm3) were fabricated using (n = 12 per group) a universal composite (Filtek Supreme XTE photo-polymerized for either 40 s or 120 s per layer), hybrid ceramics (BRILLIANT Crios, GC Cerasmart, Lava Ultimate, VITA ENAMIC), glass ceramics (IPS e.max CAD, VITA Suprinity PC, Straumann n!ce), or feldspar ceramics (VITABLOCS Mark II, GC Initial LRF). In each group, half of the specimens underwent thermomechanical aging. A three-point bending test was applied to all specimens and the results were statistically analyzed (α = 0.05). Glass ceramics and hybrid ceramics presented higher flexural strength values than feldspar ceramics and the universal composite before and after aging (p < 0.05). Thermomechanical cycling affected the flexural strength of all materials (p < 0.05) except Lava Ultimate, Straumann n!ce, and GC Initial (p > 0.05). The highest decrease in flexural strength after aging was found in the universal composite (40 s polymerization) (p < 0.001) and Vita Enamic (p < 0.001), while the lowest decrease was in the hybrid ceramics, Cerasmart and Lava Ultimate (p < 0.05). Extending polymerization duration reduced the aging effect on the universal composite tested. Thermomechanical aging affected the flexural strength of most materials tested. Universal composites and feldspar ceramics presented similar flexural strength values.

Effect of GBFS ratio and recycled steel tire wire on the mechanical and microstructural properties of geopolymer concrete under ambient and oven curing conditions

In this study, the effects of waste steel wire ratios, granulated blast furnace slag (GBFS) ratios, and different curing methods on geopolymer concrete (GPC) were investigated. For this purpose, 12 mixtures were produced and eight of them were cured under ambient conditions and the remaining four were cured in an oven. Steel wire ratios and GBFS ratios were added to GPC as 0–1–2–3 % and 0–10–20 % by volume and weight, respectively. As a result of the mixtures, cubes, cylinders, and beams were obtained and these elements were subjected to compression, tensile, and flexural tests. As a result of the tests, the compressive strengths of the specimens were obtained as 8.5 %, 19.7 %, and 24.9 % for ambient curing and 10.4 %, 23.2 %, and 32.2 % for oven curing, respectively, as the steel wire fiber increased from 0 % to 3 %. The maximum compressive strength of the oven-cured specimen with 3 % steel wire fiber was measured as 42.56 MPa. The tensile strength of GPC also increased as the steel wire increased. The highest tensile strength was obtained with 3 % steel wire. In addition, oven curing conditions increased the tensile strength more than ambient curing. The flexural strength (FS) increased by 21.3 %, 29.4 %, and 33.8 % with increasing steel wire ratios of 1 %, 2 %, and 3 %, respectively. The FS was further increased by oven curing conditions and the maximum FS was achieved with 3 % steel wire. In ambient curing conditions, a successful geopolymerization was achieved due to the high calcium content in the samples containing 20 % GBFS. This allowed to obtain similar strengths between ambient curing and oven curing. Although the oven curing values were higher, similar results were obtained for the samples cured in an ambient containing 20 % GBFS. As a result of the study, mixtures containing 3 % steel wire and 20 % GBFS provided sufficient strength without oven curing and increased the usability of GPC under ambient conditions.

Wood Polymer Composites Based on the Recycled Polyethylene Blends from Municipal Waste and Ethiopian Indigenous Bamboo (Oxytenanthera abyssinica) Fibrous Particles Through Chemical Coupling Crosslinking.

Valorization of potential thermoplastic waste is an effective strategy to address resource scarcity and reduce valuable thermoplastic waste. In this study, new ecofriendly biomass-derived wood polymer composites (WPCs) were produced from three different types of recycled polyethylene (PE) municipal waste, namely linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), or high-density polyethylene (HDPE), and their blend with equal composition (33/33/33 by wt.%). Bamboo particle reinforcement derived from indigenous Ethiopian lowland bamboo (LLB), which had never been utilized before in a WPC formulation, was used as the dispersed phase. Before utilization, recycled LLDPE, MDPE, and HDPE were carefully characterized to determine their chemical compositions, residual metals, polycyclic aromatic hydrocarbons, and thermal properties. Similarly, the fundamental mechanical properties of the WPCs, such as tensile strength, modulus of elasticity, flexural strength, modulus of rupture, and unnotched impact strength, were evaluated. Finally, the thermal stability and interphase coupling efficiency of maleic-anhydride-grafted polypropylene (MAPP) were carefully investigated. WPCs formulated by melt-blending either of the recycled PEs or the blend of recycled PE with bamboo particles showed significant improvement due to MAPP enhancing interfacial adhesion and thermally induced crosslinking, despite inherent immiscibility. These results were confirmed using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The formulated WPCs may promote PE waste cascading valorization, offering sustainable alternatives and maximizing LLB utilization. Furthermore, comparison with well-known standards for polyolefin-based WPCs indicated that the prepared WPCs can be used as alternative sustainable building materials and related applications.

Evaluation of the incorporation of artisanal lime into the composition of stabilized earth blocks

This study evaluates the incorporation of artisanal lime into the composition of Stabilized Earth Blocks (SEB) to enhance local materials and minimize the use of cement. The objective is to develop a sustainable approach that utilizes available resources while meeting construction needs. The physico-mechanical behavior of the SEB was examined through a mixed chemical stabilization method (cement/lime), gradually replacing cement with artisanal lime. The main parameters analyzed include the replacement rate and the nature of the stabilizer, allowing for an in-depth understanding of the effects of this integration. The results indicate that replacing 12.5% of the cement with artisanal lime improves the long-term physico-mechanical properties of the SEB, particularly in terms of density, absorption, porosity, as well as compressive and flexural strength. Furthermore, this approach supports the transition towards more environmentally friendly construction practices. Additionally, the study includes a comparison of the results obtained using industrial lime, thus reinforcing the relevance of using lime in construction.

Influence of Utilization of Natural Waste Fibers Pyrolysis on Mechanical Properties and Microstructure of Concrete

ABSTRACT The main purpose of this paper is to investigate the impact of the thermal processing of natural fibers on the strength of what is considered fiber-reinforced concrete. Natural fibers extracted from palm trees and bamboo residues were collected and pyrolyzed. The investigation of the morphological alterations that occur during the pyrolysis of natural fibers at a temperature of 200°C showed the impact of the cementitious environment on this process. In addition, the mechanical characteristics of fiber-reinforced concrete were conducted on different dosages (1, 1.5, 2, and 5% wt.) of treated and untreated palm oil, date kernel, and bamboo fibers. The results demonstrated that the inclusion of fibers up to 1.5% wt. enhanced the concrete mixes mechanical properties, which included pyrolyzed fibers. Analyzes of the concrete microstructure revealed that the treated fibers were not damaged. The 1.5% wt. addition of fibers after pyrolysis process can effectively improve their adhesion to the matrix and reduce the width and number of cracks. The analysis of variance results for flexural strength indicated that all sources had no significant impact on the flexural strength of untreated or pyrolysis treated natural fiber reinforced concrete.

Study on the polymerization shrinkage and mechanical-physical properties of dental resin composite modified by polyurethane dimechacrylate and glass flake fillers

ObjectivesWe intend to explore the polymerization shrinkage and mechanical-physical properties of the dental resin composite modified by polyurethane oligomer PU-MA and glass flakes fillers, and provide some experimental information for developing new dental materials. MethodsBased on Bis-GMA/TEGDMA, the new dental resin composite was hand fabricated by combining PU-MA with different content (65 wt% ∼ 75 wt%) of glass flakes/Si-Al-borosilicate glass mixed fillers. The kinetics of polymerization shrinkage was investigated by using an experimental set-up based on laser triangulation. The mechanical-physical properties of specimens after 60 days water immersion and 5000 times thermo-cycles were measured by three-point bending test and micro vickers hardness tester. Data were submitted to one-way ANOVA/LSD-test (α = 0.05). Independent sample T test was used to analyze the data before and after aging. Two-way ANOVA was adopted to analyze the effect of composition and aging condition on the mechanical-physical properties (α = 0.05). ResultsPU-PG-75 % performs lower volume shrinkage (1.35%). As the increase of filler content, the water sorption and solubility increased and the depth of cure decreased significantly (P < 0.05). After aging, the flexural strength, elasticity modulus and vickers hardness of commercial products dropped obviously and PU-PG-75wt% was relatively stable. Conclusions20 wt% PU-MA could decrease the volume shrinkage of dental resin composite effectively. 60 days water immersion and 5000 times thermal cycles simultaneously resulted in a significant reduction in the flexural properties for experimental materials. PU-PG-75 % may have the potential to be taken as a low shrinkage dental resin composite with good mechanical properties. Clinical SignificanceThis new synthesized composite could perform low polymerization shrinkage and better mechanical resistance, which may provide a new idea for improving the lifespan of direct restoration.

The Influence of Polymer Impregnating Materials on Structural Strengthening of 3D Printed Sand Molds Produced by Binder Jetting Method.

Additive manufacturing offers great potential for various industrial solutions; in particular, the binder jetting method enables the production of components from various materials, including sand molds for casting. This work presents the results of an extensive set of experiments aimed at enhancing the structural strengthening of 3D-printed sand molds. Structural strengthening was achieved by impregnating the sand-printed structures with two polymer materials: epoxy resin and silicone varnish. Impregnation was performed with variable parameters, such as temperature, pressure, and time. Structural strengthening using polymers was investigated by analyzing the flexural strength and impact resistance of the impregnated products and comparing these obtained values with the reference material in terms of impregnation parameters and the polymer used. Microstructural observations and an analysis of the pore filling were also performed. This approach allowed for a full assessment of the influence of processing parameters and the type of polymer used for impregnation on the properties of sand-printed structures, which allowed for identifying the most optimal method to be used to strengthen the sand molds for casting the components for electrical devices. As a direct proof of concept, it was shown that impregnation with polymeric materials could effectively strengthen the sand mold, increasing its flexural strength and impact resistance by over 20 times and 5 times, respectively. A full-scale mold was printed using binder jetting, impregnated with epoxy resin at 65 °C, and used to successfully fabricate a fully functional electrification device.

Toughening effect and mechanisms of AlN whiskers on a low‐temperature sintered AlNw/AlN ceramics

AbstractConventional aluminum nitride (AlN) ceramics exhibited insufficient mechanical properties expected from their potential applications in the presence of dynamic loads and intensive stresses caused by thermal shock. In this study, the mechanical properties of AlN ceramics were enhanced by toughening them using AlN whiskers (AlNw) via gel casting followed by low‐temperature sintering at 1650°C. The addition of AlNw simultaneously increased the bending strength, toughness and thermal conductivity of the AlN ceramics. The maximum values of the bending strength, toughness, and thermal conductivity of 9.0 wt% AlNw/AlN were 303.92 MPa, 3.92 MPa·m1/2 and 186.53 W·m−1·K−1, respectively, which were higher than those of the AlN ceramics by 39.93%, 61.31% and, 15.61%, respectively. The AlNw in AlNw/AlN ceramics tightly bonded with the ceramic matrix, leading to two characteristic toughening mechanisms in the ceramics: crack pinning and deflection at irregular grain boundaries caused by doped whiskers, as well as bridging and stress relaxation caused by whiskers incorporated with the grains. Moreover, the one‐dimensional morphology of AlNw can provide a channel for quick photon transport, thereby enhancing the thermal conductivity of AlNw/AlN.

C/C-(Hf0.5Zr0.3Ti0.2)C–W–Cu composites: Long-term ablation resistance based on active-passive protection at 2600 °C

Compared with the traditional C/C composites modified by ultra-high-temperature ceramics (C/C-UHTCs), those modified by metal/medium-entropy ceramics have excellent mechanical properties, thermophysical properties, and long-term ablation resistance. These composites have great potential towards improving the high-temperature resistance and service life of thermal protection systems for spacecraft. In this study, a new type of (Hf0.5Zr0.3Ti0.2)C–W–Cu cermet-modified C/C composites (C/C-(Hf0.5Zr0.3Ti0.2)C–W–Cu) was prepared at 1500 °C. Compared with C/C-UHTCs, the bending strength and fracture toughness of C/C-(Hf0.5Zr0.3Ti0.2)C–W–Cu increased by 70 % and 110 % to 364.25 MPa and 14.64 MPa m1/2, respectively. Due to the high thermal conductivity of Cu and W, the thermal conductivity of this new composite was 106 % higher than that of C/C-(Hf0.5Zr0.3Ti0.2)C (44.26 versus 21.53 W/m·K). Under a high heat flow of 4.18 MW/m2, this material exhibited very low mass and linear ablation rates (−0.163 mg/s and −0.193 μm/s, respectively). Active and passive protection occur during ablation due to the evaporative cooling of Cu, CuO, and WO3 as well as a dense outer oxide layer that inhibits oxygen diffusion. The internal oxide layer forms a Hf-Zr-Ti-C-O framework mingled with Ti-rich Ti-Hf-Zr-C-O and an unoxidised W–Cu structure, effectively reducing the osmotic oxygen content. This work provides a new direction for developing thermal protection materials capable of long-term service in ultra-high-temperature environments.

Technological characterization of tropical woods from the genus Eperua (Fabaceae)

ABSTRACT In the Amazon basin, effective forest management plans are essential for sustainability, as they promote the exploration of new species. The Fabaceae family, which is abundant in tropical forests, includes tree species with timber potential, but gaps remain in understanding their properties. This study investigated the chemical and physicomechanical properties of Eperua from the Brazilian Amazon. Trees were randomly collected from native forests in Amazonas/Brazil. The samples were analyzed to determine their chemical and physicomechanical traits. The results revealed that Eperua falcata had high concentrations of extractives and lignin (15% and 27%, respectively), whereas Eperua leucantha and Eperua purpurea presented relatively high holocellulose contents, reaching up to 66%. The physicomechanical properties indicated a low moisture content (dry matter > 90%) and densities ranging from 620 to 900 kg m−3. All the samples had anisotropy values <1.8%. E. falcata and E. schomburgkiana presented the highest values for higher heating value, modulus of elasticity, rupture, and hardness. The analysis of the chemical composition, along with the physical and mechanical properties of the woods from the genus Eperua, reveals significant potential for applications in sustainable construction and high added-value products, particularly in sectors requiring durability and resistance, such as civil construction and furniture manufacturing.

Surrogated modelling for structural reliability and safety assessments of high-strength concrete beams with industrial and recycled steel fibers

As a secondary material recycled from tyres, Recycled Steel Fibre Reinforced Concrete (RSF) aims to replace industrial steel fibres (ISF) to improve concrete matrix‘s severability, fracture toughness, and residual tensile stress. Despite the increasing attention on the mechanical properties of this material, RSF concrete’s influence on structural component strength is still neglected due to a lack of sufficient and reliable experimental data. This study looks into existing Crack mouth opening displacement (CMOD) experiment results of both types of steel fibre reinforced concrete beams together with nonlinear finite element model (FEM) simulations using the RILEM TC 162-TDF crack damage model(CDP) proposed for ISF in ABAQUS. Meanwhile, an additional parameter analysis of the experimental data related to shear capacity also examines the shear span ratio, fibre content, and fibre type of the two types of fibre reinforced concrete beams. Moreover, Kriging surrogate models (KSM) and Sobol global sensitivity analysis have been conducted. For the reference concrete beams with a fibre content of 0.4 %, the prediction accuracy ratios of ultimate strength, corresponding displacement, and stiffness between the FEM and the experiment results are 98 %, 88 %, and 100 %, respectively. This paper has been proved that the CMOD-based CDP model effectively elucidates the shear contribution of different steel fibres, which can be used in structural analysis of ISF or RSF concrete for structure components. Utilizing FEMs, a series of modified flexural strength prediction formulas based on TR63 standards are proposed to enhance structural applications with ISF and RSF. Moreover, the prediction ability of the proposed formulas is validated using the results of 183 real flexural capacity experiments of ISF reinforced concrete beams, achieving an improved R² value of 0.97.

Self-healable epoxy/graphene oxide vitrimers and their recyclable glass fiber reinforced composites

Glass fiber-reinforced polymers (GFRPs) made from thermoset polymers have been widely used across various industries. However, these composites have significant drawbacks, including poor interfacial adhesion between the fiber and matrix, as well as a substantial contribution to waste and environmental pollution due to the challenges in recycling, reprocessing, and reuse. Herein, firstly graphene oxide (GO) was incorporated in vitrimer matrix to fabricate recyclable vitrimer nanocomposites with improved interfacial interaction, high thermal stability, low dielectric constant, fast stress relaxation as well as rapid self-healing ability. The nanocomposite with 0.2 wt% GO is optimized to achieve excellent remoulding (89% of flexural strength) and self-healing (60 min for a 48 μm scratch) properties due to dynamic disulfide bond exchange mechanism. Furthermore, epoxy/GO matrix was used to develop glass fiber reinforced composites via vacuum assisted resin infusion molding process (VARIM). The developed composites demonstrate tremendous mechanical strength (250 MPa), shape-memory, weldability, and degradable properties. Due to the rapid chemical degradation of epoxy vitrimer under mild conditions in the thiol (2-mercaptoethanol and 1-otanethiol), facilitated by thiol disulfide exchange reaction, glass fibers (GFs) can be effectively recycled. The performance of recycled glass fibers closely matches that of original fibers, exhibiting nearly identical woven structure and mechanical properties. The single yarn of recycled glass fibers can achieve tensile strength of 85% (1-octanethiol) and 72% (2-mercaptoethanol) of the original glass fibers, thus, the recycling of glass fibers would be highly advantageous in terms of achieving the sustainability goals.

Research on the Preparation of Dry Mixed Mortar Using Waste Incineration Fly Ash

This study investigated the effect of water-washed municipal solid waste incineration fly ash (MSWI FA) as an admixture on the performance of dry mixed mortar and used X-ray diffraction (XRD) and scanning electron microscope (SEM) detection methods to conduct microscopic analysis. The experiment investigated the effects of the amount and water content of washed municipal solid waste incineration fly ash, cement, additives, sand and gravel, and curing time on the compressive flexural strength of dry mixed mortar at 28 days. The results show that when the content of water-washed MSWI FA is 9.80%, the content of sand and gravel is 73.50%, the content of ordinary Portland cement (PO42.5) is 16.66%, the content of water-reducing agent is 1.47‰, the content of cellulose is 0.03‰, the content of the expansion agent is 0.49‰, the addition of water is 130–160 mL/kg, the consistency of the sample can reach 91.8 mm, and the water retention rate can reach 93.6%. The flexural strength of the sample at 28 days can reach 7.5 MPa, and the compressive strength at 28 days can reach 28.30 MPa. Metal ions, such as Pb2+ and Gd2+ in MSWI FA, under the combined action of silicate cement in dry mixed mortar and fibers in cellulose, crisscross and form a solidified material, which will not be leached out. This quality meets the requirements of dry mixed mortar for ordinary plastering and masonry mortar (GB-T 25181-2019), and the leaching toxicity of the sample meets the “Identification Standard for Hazardous Waste” (GB5085.3-2007). This work provides a meaningful exploration of the resource utilization of water-washed MSWI FA.

Synthesis and characterization of ceramic refractories based on industrial wastes

The possibility of reusing ceramic roller waste to produce cordierite and mullite refractories was investigated. Five batches were designed using wastes representing ceramic roller waste, magnesite, and silica sand, shaped and fired at 1300 °C/2 h, and one batch was selected at 1200 °C. The chemical composition and precipitated phases of the used raw materials and the fired batches were analyzed using XRF and XRD techniques, respectively. Densification parameters, morphology, microstructure and electrical properties were also studied to evaluate the effect of the formed phases on the properties of fired materials. Bulk density increases with an increase in mullite and a decrease in cordierite, and it also increases with increasing temperature, whereas porosity and water absorption show a opposite behavior to density (it decreases with an increase in mullite and temperature). The main phases developed after firing at 1300 °C/2 h were cordierite, mullite, corundum, baddeleyite, and spinel. Bending strength increases with increasing mullite percentage and density, and decreasing grain size and porosity. The microstructure develops and becomes finer with increasing mullite percentage and density. The grain size of the crystals was very fine at 1200 °C/2 h and increased at 1300 °C/2 h. Broadband dielectric spectroscopy was employed to study the electrical and dielectric behavior of the investigated samples. The increase in mullite concentration shows a remarkable increase in ε’, especially at lower frequencies, as it is three times higher than that of M10. At f > 103 Hz ε’, frequency independence is accompanied by an increase in mullite concentrations due to the lag of dynamics fluctuations after the alteration of the electric field. The generation of new free ions leads to the enhancement of conductivity as the mullite concentration increases.

Comparison of mechanical and flammability properties of thermoplastic and thermoset matrix glass fibre woven fabric composites

This study aims to examine the mechanical and burning properties of composites made from twill (0°/0° and 0°/90° orientations) and plain fabrics using hybrid yarns produced by combining glass and polypropylene yarns with interwoven and intermingled methods. The properties of interwoven and intermingled hybrid fabric composites were compared with thermoset composites. Each composite (56% glass fibre content) plate is produced by combining eight fabrics with the same parameters using the press moulding technique. The effects of yarn and fabric weaving types on the results were examined in detail. When the results are examined, the breakage of glass fibres in intermingled hybrid yarns negatively affects the strength results. Therefore, composites made with intermingled hybrid yarn types and plain weave types of fabric had the lowest tensile strength value (132 MPa). The composite of twill woven fabrics produced with interwoven yarns arranged in 0°/0° orientation had the highest tensile strength of 315 MPa, and these results were very close to those of thermoset composites. Although the 0°/90° oriented twill composite showed a 2.3 times lower tensile strength value than the 0°/0° oriented twill composite, it had a 7.7 times higher value when bending strength values were taken into account. The main reason for this is that glass fibres contribute to the warp and weft directions. It has been observed that the composite consisting of plain fabrics woven with commingled hybrid yarns had the highest impact resistance. Additionally, when the combustion results were examined, it was concluded that the type of yarn and fabric weaving affected the burning rate. The slower combustion of hybrid commingled yarn composites resulted from fibreglass breakage during yarn production. These findings provide valuable insights into optimizing composite materials for specific applications, considering factors such as weaving pattern, fibre orientation, and mechanical performance.

Al-Doped ZnO/SiO2 Nano-glass Ceramic System: A New Composite System for Improvement in Thermal Stability and Mechanical Properties of Dental Resins

AbstractThis study aims to enhance dental resins' mechanical and thermal properties by reinforcing them with Al-doped ZnO/SiO2 nano-glass ceramic. The synthesis of the nano-glass ceramic involved the addition of Al-doped ZnO nano-powders to a diluted aqueous solution of liquid glass (25 mL) in ethanol (50 mL) at room temperature. The synthesized samples were characterized using TEM, EDS, FE-SEM, and XRD techniques. Various concentrations of the nano-glass ceramic (2, 5, 8, 10, and 15 wt.%) were then integrated with Bis-GMA and TEGDMA. The mechanical properties, including flexural strength (FS), compressive strength (CS), diameter tensile strength (DTS), and flexural modulus (FM), were evaluated. Thermal stability was assessed through TGA analysis, which indicated polymer degradation occurring between 300 and 450 °C. An increase in filler content correlated with enhanced thermal stability. The optimal mechanical properties were observed at a 7.5 wt.% filler content, showing significant improvements in FS (124.652 MPa), FM (9.87GPa), DTS (33.87 MPa), and CS (178.47 MPa).

Performance evaluation of fly ash–copper slag-based geopolymer bricks

This study investigates the production and evaluation of geopolymer bricks made from a blend of fly ash, copper slag, soda ash activator, and sand as fillers. Locally abundant industrial and mining waste materials were selected as the primary components. The bricks were synthesized using two binders: 60% fly ash with 40% copper slag, or 70% fly ash with 30% copper slag. Both were milled with the activator at a 0.2 soda ash-to-precursor ratio. Fine sand was added to the mixes at 1:2 and 1:3 binders-to-sand ratios. The bricks’ physical, mechanical, and durability properties were examined through compressive strength, modulus of rupture, density, water absorption, drying shrinkage, and efflorescence test, and their performance was compared to established industry standards. The experimental findings indicate that bricks made with 60% fly ash, 40% copper slag, and a 1:2 binder-to-sand ratio exhibited optimal compressive strength (9.64 MPa) and water absorption (7.5%) at 28 days of curing age. Conversely, there was only a marginal increase of up to 4.7% in the strength of the formulation with 70% fly ash and 30% copper slag, attaining a compressive strength of 4.9 MPa between the curing ages. Furthermore, the results indicated a positive correlation between the density and compressive strength of the geopolymer bricks at similar curing ages. The bricks’ density showed minimal variation with curing age and the highest modulus of rupture value observed was 2.5 MPa. The optimal bricks also exhibited relatively low linear shrinkage, good resistance to efflorescence, and met the relevant industry standards.

Physico-mechanical properties and decay fungi resistance of Dendrocalamus asper and Bambusa spinosa thermally modified in spent engine oil medium

This study examined the effects of thermal modification (TM) using spent engine oil as the heat transfer medium on the physico-mechanical properties and decay resistance of Bambusa spinosa Roxb. and Dendrocalamus asper (Schult. & Schult.f.) Backer. The TM process was conducted at three temperatures (140, 160 and 180 °C) and three durations (30, 60 and 90 minutes), coded as T1 to T9. The tests followed ASTM D 143–94 and ASTM D 2017–05 standards. The results revealed that thermally modified bamboo samples exhibited noticeable aesthetic colour changes, with a gradual darkening towards brown, and significantly improved dimensional stability, demonstrated by reductions in water absorption (27–75 %), thickness swelling (25–89 %), and equilibrium moisture content (31–64 %) compared with control samples. However, a decrease in flexural strength was observed at the highest temperature and longest duration (T9: 180 °C for 90 min), with reductions of 54–56 %. Despite this decrease in mechanical strength, the decay resistance of the T9-treated samples was comparable to chemically preserved bamboo, classifying them as highly resistant to decay fungi. Overall, the study demonstrated that spent engine oil is an effective medium for the thermal modification of bamboo when conducted in a controlled temperature setting.

3D printing of biodegradable biocomposites based on forest industrial residues by fused deposition modeling

This study investigated the impact of industrial forest residues (IFR) type and proportion on 3D-printed biocomposites (BC). Fused deposition modeling (FDM) produced BC containing up to 20 % Jack pine sawdust, wood ashes, cellulose fibers, and polylactic acid (PLA). The BC thermal stability, surface chemistry, microstructure, and physical and mechanical were investigated. Thermal stability investigations revealed that adding IRF resulted in a decline in the PLA degradation temperature, an increase in the residual mass, a decrease in the glass transition temperature, and an improvement in crystallinity. Add IRF to PLA showed an important reduction in ductility, a consistent reduction of the tensile and flexural strengths with increasing proportion but only a slight or a non-significant reduction the modulus of elasticity. Adding forest waste filler to pure PLA increased the water absorption (WA) and dimensional accuracy (TA) of the biocomposites, which was expected due to the hydrophilic character of fillers. The microstructural analysis demonstrated that a higher filler level resulted in a greater porosity, roughness, and visible filler pull-out on the filament and printed parts surfaces. Surface chemistry analysis suggested poor interactions between the PLA and the fillers and consequently poor interfacial adhesion. Furthermore, the rheological investigations confirmed that the complex viscosity and storage modulus of PLA-Jack pine's sawdust and PLA-cellulose fibers increased with filler. In contrast, the PLA-wood ashes showed opposite results. Using 3D-printed biodegradable biocomposites provided a sustainable option for reducing dependence on non-renewable plastic, valorizing the value chain of forest products, and promoting the circular economy.