Increasing Fiber Content Research Articles

3D Printing Technology for Short-continuous Carbon Fiber Synchronous Reinforced Thermoplastic Composites: A Comparison between Towpreg Extrusion and In Situ Impregnation Processes

Three-dimensional (3D) printing of carbon fiber-reinforced thermoplastic composites (CFRTPs) provides an effective method for manufacturing the CFRTPs parts with complex structures. To increase the mechanical performance of these parts, a 3D printing technology for short-continuous carbon fiber synchronous-reinforced thermoplastic composites (S/C-CFRTPs) has been proposed. However, the synchronous reinforcement that existed only at particular positions led to a limited improvement in the mechanical performance of the 3D-printed S/C-CFRTP part, which made it challenging to meet the engineering requirements. To solve this problem, two methods for achieving synchronous reinforcement at all the positions of the 3D-printed S/C-CFRTP part are proposed. To determine a suitable printing process for the S/C-CFRTP part, a comprehensive comparison between the two methods was conducted through theoretical analysis and experimental verification, involving the printing mechanism, fiber content, impregnation percentage, and mechanical performance. The results indicated that the towpreg extrusion process was suitable for manufacturing the 3D-printed S/C-CFRTP part. Compared with the in situ impregnation process, the towpreg extrusion process led to a fiber content increase of approximately 7% and void rate reduction of approximately 6%, resulting in 19% and 20% increases in the tensile and flexural strengths of the 3D-printed S/C-CFRTPs, respectively. Additionally, an optimized process parameter setting for fabricating an S/C-CFRTP prepreg filament with excellent mechanical performance was proposed. The findings of this study can provide a new approach for further improving the mechanical performance of the 3D-printed advanced composites.

The Properties of Modified Bagasse Fiber/Nano-TiO2 Composite Asphalt in a High-Temperature and High-Humidity Salt Environment.

The southern tropical coastal areas of China are high-temperature and high-humidity salt environments, which hinder the durability and service life of ordinary asphalt pavement. To enhance the durability of asphalt pavement in these areas, modified bagasse fiber combined with nano-TiO2 was used to improve the corrosion resistance of asphalt pavement in high-temperature and high-humidity salt environments. The micro-morphology, high-temperature oil absorption, high-temperature heat resistance, and hygroscopicity of bagasse fiber modified using three silane coupling agents combined with NaOH were compared, and the best silane coupling agent/NaOH modification scheme for bagasse fiber was found. Based on conventional physical tests (penetration, softening point, ductility), rheological property tests (rotational viscosity, dynamic shear rheological test, multi-stress creep recovery test, linear amplitude scanning test), and a four-point bending fatigue test of the asphalt mixture, the properties of modified bagasse fiber asphalt binder and mixture after cyclic dry-wet erosion under pure water and salt solution (NaCl, Na2SO4) were determined, and the effects of the erosion environment and fiber ratio on the basic physical and rheological properties of the asphalt were clarified. Compared with the silane coupling agents KH550 and KH590, the bagasse fiber modified with KH570/NaOH had a better high-temperature oil absorption capacity, heat stability capacity, and matrix asphalt compatibility. The worst erosion environment was Na2SO4, but the increase in test temperature and fiber content weakened the sensitivity of the asphalt binder performance in different erosion environments. The erosion capacity order was as follows: Na2SO4 > NaCl > pure water. In the worst erosion environment, 0.5% modified bagasse fiber/Nano-TiO2 asphalt binder (Bn-570-0.5) had the best corrosion resistance in a high-temperature and high-humidity salt environment. The penetration, softening point, creep recovery rate R3.2, non-recoverable creep compliance Jnr3.2, and fatigue life after long-term aging (with 5% strain) of Bn-570-0.5 were, respectively, increased by -16.9%, 37.5%, 37.95%, -27.86%, and 38.30% compared with unblended base asphalt binder (B). In addition, the four-point flexural fatigue life of Bn-570-0.5 was 169.2% higher than that of the unblended base mixture.

A quantitative investigation on the fragmentation performance of SCDA in cracking steel fiber reinforced concrete

A better application of Soundless Chemical Demolition Agents (SCDAs) in fragmentation is based on our knowledge on their expansive characteristics. In this study, an integration of experimental and modeling approaches was developed to investigate SCDA expansion and corresponding cracking processes of Steel Fiber Reinforced Concrete (SFRC). The expansive properties of the selected SCDA were first estimated by free volume expansion (FVE) tests and expansion pressure (EP) tests. Then, cracking experiments were performed on 150 mm cubic SFRC blocks with a predrilled hole, and the cracking process was monitored by using Acoustic Emission (AE) and Digital Image Correlation (DIC) techniques. Generally, the cracking process can be divided into three phases, termed micro-cracking phase, macro-cracking phase, and failure phase. It was observed the hole diameter and fiber content exert significant influences on the cracking process. The crack initiation time was shortened as the hole diameter increases, while it was prolonged with increasing fiber content. The cracked area ratio was further proposed and measured to assess the cracking performance of SCDA. The ratio increases from 2.73% to 8.293% as the hole diameter increases from 16 mm to 26 mm, while it decays from 9.75% to 1.823% as the fiber content increases from 0 to 2.4%. After verified with the experimental data, a modified Concrete Damaged Plasticity (CDP) model was adopted to extend the fragmentation of SFRC from the centimeter scale to the meter scale. The simulations were conducted on SFRC models with various hole diameters, spacings, and fiber contents. The simulated results show the fragmentation performance is related to both hole parameters (e.g., hole diameter, spacing, etc.) and SFRC properties (including elastic modulus, fiber content, etc.). In particular, the cracked area (DamageT > 0.9) varies directly with hole spacing, diameter, and fiber content. Built on the simulated results, an empirical equation was formulated to quantitatively evaluate the fragmentation ability of individual holes. In addition, extra simulations were conducted to assess the efficiency of SCDA in cracking PC/SFRC beams of various sizes. The obtained cracked area tends to decrease first and then approach a constant value with increasing beam sizes, indicating the existence of a size effect, which is primarily due to variations in concrete restraints provided by beams of different sizes. This work quantitatively evaluates expansive properties of SCDA and SCDA-induced cracks, and thus provides a reference for optimizing the field application parameters.

Shear Strength Behaviors of Aeolian Sand Solidified by Microbially Induced Calcite Precipitation and Basalt Fiber Reinforcement.

Aeolian sand flow is identified as the main factor in the formation of sandstorms. However, conventional sand fixation methods cannot meet the current development requirements of environmental protection. In this paper, the method using Microbially Induced Calcite Precipitation (MICP) combined with basalt fiber reinforcement (BFR) was adopted to solidify the aeolian sand. Consolidated undrained triaxial shear tests were carried out to analyze the influence of fiber content, fiber length, confining pressure, and other factors on stress-strain characteristics, peak strength, brittleness index, and shear strength of aeolian sand. A shear strength model of aeolian sand solidification using MICP-BFR and considering the effect of fiber length and fiber content is established according to the test results. The results show that the peak strength of aeolian sand solidified by MICP-BFR is remarkably higher than that of aeolian sand solidified by MICP alone, and the peak strength rises with the increasing fiber length, fiber content, and confining pressure. The application of fiber can effectively reduce the brittleness index of aeolian sand solidified by MICP and improve the sample ductility. As fiber content and fiber length increase, the cohesion of solidified aeolian sand increases while the internal friction angle changes relatively little. In the limited range set by the test, the fiber length of 12 mm and the fiber content of 1.0% constitute the optimum reinforcement condition. The test results coincide with the model prediction results, indicating that the new model is fitting for predicting the shear strength of aeolian sand solidified by MICP-BFR. The research results provide an important reference value for guiding the practice of wind prevention and sand fixation in desert areas.

Recent progress in thermal and acoustic properties of natural fiber reinforced polymer composites: Preparation, characterization, and data analysis

AbstractNatural fiber reinforced polymer composites (NFRPCs) have emerged as promising eco‐friendly alternatives over conventional synthetic fiber composites due to their inherent biodegradability, renewability, low environmental impact, and lightweight properties. It has been seen a significant growth in both invention and innovation in the field of NFRPCs. Natural fibers (NFs) reduce the cost of the material by 5%, the weight of the composite by 10%, and the energy required for production by 80%. In terms of thermal, and acoustic properties, NFs can successfully compete with synthetic fibers. As a result, the development of NFRPCs for industrial use has increased significantly in the past decade to meet the growing demands of industrial sectors. To improve the thermal and acoustic properties of NFRPCs, researchers have done a lot of investigation. The aim of the current review is to provide a comprehensive analysis of the existing literature on the thermal and acoustic properties of natural fiber reinforced polymer composites. Thermal properties such as thermal conductivity, TGA, DSC, DMA, and acoustic properties of natural fiber reinforced composites with several parameters, such as different fiber types, different matrix types, fiber weight ratio, fiber to matrix ratio, chemical treatment of fiber have been summarized and analyzed very concisely. This review also emphasizes a summary of different natural fibers, their chemical compositions, composite preparation, characterizations, and future research directions. This article enables the readers, researchers, and manufacturers to realize several opportunities about the latest developments in NFRPCs for the application of thermal and acoustic purposes.Highlights Natural fibers can successfully compete with synthetic fibers, in terms of thermal and acoustic properties. Thermal properties of natural fiber reinforced composites including thermal conductivity, TGA, DSC, and DMA are summarized. Acoustic properties of natural fiber reinforced polymer composites are discussed. Composite materials made of treated fibers result better thermal stability than untreated fiber composites. Sound absorption coefficient generally increases as fiber content increases.

CONTRIBUTORY IMPACT OF SEWAGE ON POLLUTED OGUN AND LAGOS FISHING WATERS: INFLUENCE ON ANTIOXIDANT PROFILE AND PROXIMATE COMPOSITION OF SILVER CATFISH (Chrysichthys nigrodigitatus)

Water pollution, a recurring phenomenon in fishing waters of industrial cities in Nigeria, inadvertently constitute hazards to the host biotic communities and the ecosystem. To continuously delineate the impacts of pollution via sewage outlets on aquatic life, this rainy season study investigated Chrysichthys nigrodigitatus, an aquatic food from Ogun River and Epe Lagoon, Nigeria, both of which are locally channeled for sewage release. Sixty (60) samples of C. nigrodigitatus were collected from six sites each representing a group (n=10), with mean weight and length of 762.20 ± 11.05 g and 42.21 ± 0.30 cm respectively. Ajegunle (control), Alaapa and Quarry (test sites) along the Ogun River course in Abeokuta; Ebute-Alashe (control), Oluwo and Marina (test sites) along the Epe Lagoon. Analysis of Biochemical Oxygen Demand and Chemical Oxygen Demand showed elevated variations at the sampled test sites than the control sites and above WHO safe limits. Significant (p < 0.05) increases in concentrations of heavy metals (lead, arsenic and cadmium) in the fishing waters from the sampled test locations particularly the Quarry and Marina sites, as well as in blood samples of fish, were observed when compared with their respective controls. Antioxidants profiling showed significant increases (p < 0.05) in superoxide dismutase and catalase activities in fishes from Alaapa (14- and 3- folds), Quarry (8- and 4- folds), Oluwo (9- and 3- folds) and Marina (8- and 3- folds) sites, while significant increases in glutathione-S-transferase activity were observed only in fishes from Quarry (5- fold) and Marina (4- fold) sites respectively. The glutathione concentration significantly decreased in fishes from all the test sites while malondialdehyde concentrations significantly increased in fishes from all the test sites compared with the respective controls. Proximate analysis of the fish samples showed significant increases (p < 0.05) in moisture and fiber contents, but significant decrease in fat, ash and protein contents compared with the respective controls. The results of the study showed that sewage pollution of fishing waters is hazardous to aquatic life as it induces oxidative stress and significantly reduces the nutritional value of the fishes obtained from such water bodies.

Effect of ceramic fiber on mechanical properties of concrete with different strength grades and its strengthening and toughening behaviors under impact load

The mechanical properties of ceramic fiber reinforced concrete (CRFRC) with different strength grades (C30, C50 and C80) under impact load were studied, and the strengthening and toughening behaviors of ceramic fiber on plain concrete were analyzed and compared with that of carbon fiber. The results show that ceramic fiber can improve the mechanical properties of concrete with different strength grades under impact load, and the optimal content of ceramic fiber is 0.2%. Ceramic fiber has strengthening and toughening effect on concrete, and the strengthening and toughening behaviors of ceramic fiber are better than that of carbon fiber. Ceramic fiber has the best strengthening effect on C50 concrete and the best toughening effect on C80 concrete. The dynamic compressive strength (fcd), energy dissipation density (Edd) and dynamic increase factor (DIF) of CRFRC all have strain rate effect. As the ceramic fiber content increases, the strain rate sensitivities of fcd and Edd of CRFRC increase first and then decrease. As the strength grade increases, the strain rate sensitivities of fcd and Edd decrease. The strain rate effect of DIF of CRFRC has a transition strain rate. The transition strain rate of DIF of CRFRC decreases with strength grade and it decreases compared with plain concrete.

Determination of optimum blast furnace slag ash and hemp fiber ratio in cement mortars

This study aims to investigate the effect of incorporating hemp fibers into cement mortars to enhance their mechanical properties. Additionally, the study examines the use of blast furnace slag (YFC) as a substitute for cement to reduce costs. The findings demonstrate that adding 1%, 2%, and 4% hemp fibers to cement mortars yields the best results in terms of density, water absorption, compressive strength, bending strength, compressive strength after bending, and flexural strength. In conclusion, the study reveals that incorporating hemp fibers enhances the workability of YFC-blended mixtures while reducing the spreading diameter as the hemp fiber content increases. Additionally, an increase in YFC substitution leads to a decrease in compressive strength; however, the addition of 1% hemp fiber to the Y15 mixture results in a approximately 12% increase in compressive strength, indicating improved matrix strength and reduced crack formation. Moreover, the study shows that the flexural strength increases with the addition of hemp fibers, with the highest flexural strength observed in the mixture containing 4% hemp fiber and 10% YFC substitution. The results highlight that the combination of YFC and hemp fibers can produce strong, durable, and environmentally friendly composite materials. These materials offer a lower environmental impact and cost-effectiveness compared to traditional construction materials.

Circular Production, Designing, and Mechanical Testing of Polypropylene-Based Reinforced Composite Materials: Statistical Analysis for Potential Automotive and Nuclear Applications.

The circularity of polymer waste is an emerging field of research in Europe. In the present research, the thermal, surface, mechanical, and tribological properties of polypropylene (PP)-based composite produced by injection molding were studied. The pure PP matrix was reinforced with 10, 30, and 40% wt. of pure cotton, synthetic polyester, and polyethylene terephthalate post-consumer fibers using a combination of direct extrusion and injection molding techniques. Results indicate that PP-PCPESF-10% wt. exhibits the highest value of tensile strength (29 MPa). However, the values of tensile and flexural strain were lowered with an increase in fiber content due to the presence of micro-defects. Similarly, the values of modulus of elasticity, flexural modulus, flexural strength, and impact energy were enhanced due to an increase in the amount of fiber. The PP-PCCF-40% wt. shows the highest values of flexural constant (2780 MPa) and strength (57 MPa). Additionally, the increase in fiber loadings is directly proportional to the creation of micro-defects, surface roughness, abrasive wear, coefficient of friction, and erosive wear. The lowest average absolute arithmetic surface roughness value (Ra) of PP and PP-PCCF, 10% wt., were 0.19 µm and 0.28 µm. The lowest abrasive wear value of 3.09 × 10-6 mm3/Nm was found for pure PP. The erosive wear value (35 mm3/kg) of PP-PCCF 40% wt. composite material was 2 to 17 times higher than all other composite materials. Finally, the single-step analysis of variance predicts reasonable results in terms of the p-values of each composite material for commercial applications.

Experimental study on impact toughness of multi-combination hybrid fiber-reinforced magnesium phosphate cement-based materials

In order to improve the brittleness of magnesium phosphate cement-based materials (MPC) and overcome the limitations of single fiber-reinforced cement-based materials, this study investigated the mechanical properties of hybrid fiber-reinforced magnesium phosphate cement-based composite materials (HFRMPC) by incorporating four types of fibers: hooked-end steel fiber (HSF), micro steel fiber (MSF), polyvinyl alcohol fiber (PVAF), and basalt fiber (BF). Cylindrical specimens were prepared by single and double hybridization of the fibers and subjected to drop hammer impact tests to analyze the effects of different fiber hybridization methods on the impact resistance of these materials. The two-parameter Weibull distribution was used to analyze the test results to predict failure probabilities and to investigate the fiber reinforcement and toughening mechanisms in MPC through microscopic structural analysis. The results showed that the impact resistance of the fiber hybridization group was much better than that of the single fiber group, and the impact resistance increased continuously with increasing fiber content. The fibers' impact resistance enhancement effects were in the following order: MSF > PVAF > BF. The fiber combination methods were ranked as follows from best to worst: HSF + PVAF > HSF + BF > HSF + MSF > PVAF + BF. The 1.5% HSF+0.6% PVAF hybridization had the best impact resistance performance, with an increase in initial cracking and impact energy dissipation at the failure of 7748.6% and 8921.2%, respectively, compared to the M0. The probability distribution of impact number of initial cracking (N1) and failure (N2) of the specimens followed the double-parameter Weibull distribution well. The multiscale strengthening and toughening zone composed of fibers with different geometric dimensions and elastic modulus was crucial to the material's performance, as the fibers acted in progressive briding under external impact loads, dissipating impact energy through the failure morphology of pull-out and breaking, significantly improving the HFRMPC's impact toughness. A comprehensive evaluation of the four indicators of impact resistance and manufacturing costs for various hybrid fiber compositions found that the combination of 1.5% HSF and 0.6% PVAF exhibits the most outstanding overall performance.

Assessment of flexural behavior of compressed earth blocks using digital image correlation technique: effect of different types of date palm fibers

The present paper provides an experimental investigation to study the effect of the date palm waste fiber (DPW) type and compaction pressure on the flexural behavior of compressed earth blocks (CEBs). The digital image correlation technique (DIC) was used to determine full-field strains of compressed earth blocks. In this context, quicklime as a stabilizer and three different kinds of DPW were added to the CEB composites: Date Palm Waste Aggregate (DPWA), Date Palm Mesh (DPM), and Date Palm Spikelet (DPS). By applying different compacting stresses with static loading, three contents were incorporated into the pressurized mixtures by weight of the waste (0, 0.2, and 0.5%). The results indicate that the flexural strength values were higher for the mixtures with DPWA than those with DPM or DPS. Adding 0.5%DPS increases the ductility of the bricks, resulting in some residual strength and increasing the deflection at failure. As a result of the increase in the compaction pressure, from 2 to 10 MPa, the flexural strength improved by about 262.73 and 371.68% for the control block (samples without DPW) and the block containing 0.5% DPW, respectively. When the compaction pressure increases from 2 to 10 MPa, the apparent modulus of elasticity increases from 393.31 to 809.37 MPa for a block without DPWA and from 214.22 to 321.52 MPa for a block containing 0.5% DPWA. After analyzing the images obtained during the flexural test using the DIC technique, the results of εxx revealed extremely high localized strains in the center of the block at the bottom of the samples under tension. The strain concentration increases as the fiber content increases. In addition, when the compaction pressures of CEBs are increased, the values of εxx are increased.

Effects of citrus pomace on mechanical, sensory, phenolic, antioxidant, and gastrointestinal index properties of corn extrudates

Ready-to-eat snacks are popular among consumers, but these largely carbohydrate-based snacks have high glycemic indexes that pose various health issues, such as increased risk of diabetes, heart disease, high blood pressure, etc. This work aimed to increase the healthfulness (fiber, phenolic content, antioxidant capacity) of corn based extrudates through the addition of citrus pomace as a sustainable dietary fiber source. Extrudates were prepared using twin screw extrusion with citrus pomace concentrations in the range of 0%–15%, incorporated into corn grits. Results show that inclusion of 15% citrus pomace increased fiber content by 58.33% and dietary fiber contents increased 2.12 times compared to corn extrudates used as control samples. Antioxidant activity (DPPH) and mineral (calcium) contents of 5% pomace-containing extrudates significantly increased between 9.36 and 14.32 times respectively compared to the control sample without any supplementation. However, the expansion ratio, porosity, oil binding, and absorption capacities decreased due to the fiber addition. The sensory attributes of extrudates up to 5% pomace addition were acceptable in sensory evaluation. In the range of 0%–5% citrus pomace addition, extrudates may be successfully used for sustainable consumption, food waste management, and nutritional security.

Production of waste carpet fiber-reinforced concrete as sustainable material

Waste materials evolve from various processes in industries that require efficient management for their disposal to ensure a cleaner environment. Disposing of solid waste, such as carpets, to sites has grown challenging since the development and management of sites are very costly. There is a dire need to manage such a vast amount of carpet waste efficiently. This study examines certain mechanical properties and durability characteristics of concrete incorporating discarded carpet threads and silica fume (SF). Initially, six different concrete mixes were produced, with 0.25%–1.0% waste carpet fibers by concrete volume and 10% SF by weight of cement. Then samples were tested for mechanical strength, i.e., compressive strength, tensile strength, and flexural strength. The durability characteristics, such as water absorption, rapid chloride penetration test, drying shrinkage, and freeze-thaw action, were also determined. The study shows that the abandoned carpet waste threads and SF (an industrial waste) in concrete significantly increase tensile and flexural strengths and various other durability characteristics. The further increase in fiber content resulted in a lowering of mechanical strengths and workability. Experimental results show the increase in tensile and flexural strengths of the concrete by waste carpet fibers (0.25%) and SF (10%) by 16.5% and 34%. SF and waste carpet fibers improve other durability characteristics, reducing freeze-thaw, drying shrinkage, and chloride ion permeability coefficient by up to 47%, 79%, and 50%. Additionally, using waste carpet fibers to ameliorate concrete properties instead of fresh fibers helps conserve natural resources. It leads to the conservation of resources, sustainability, recycling of wastes, and a circular economy.

Experimental study on recycled steel fiber-reinforced concrete under repeated impact

Abstract Recycled steel fiber comes from the waste produced by machining. Adding recycled steel fiber into concrete can significantly enhance the toughness of concrete. In order to study the impact toughness of recycled steel fiber-reinforced concrete, the drop weight repeated impact experiment method was used to study the performance of recycled steel fiber-reinforced concrete under repeated impact load. Four kinds of recycled steel fiber-reinforced concrete samples with different volume contents were designed and made, and the loading impact experiments under five working conditions were carried out. Taking the drop weight and drop height as changing parameters, the corresponding blow counts of the first crack and sample failure under the impact of the drop hammer are recorded, and the ductility coefficients of different samples are calculated. The results show that the impact resistance of the sample decreases significantly with the increase of the drop weight and drop height. With the increase of recycled steel fiber content, the impact toughness of the sample increases obviously. The impact toughness of recycled steel fiber-reinforced concrete under standard loading conditions is the best.

A new orientational molding method for ultra-high performance concrete with high content of steel fiber and investigation on its flexure and axial tensile properties

Although ultra-high performance concrete (UHPC) has ultra-high mechanical properties (compressive strength up to 150 MPa), the tensile strength to compressive strength ratio is even lower than that of ordinary concrete (less than0.1). Therefore, improving the flexural and tensile properties of UHPC is an important issue in civil engineering. In this paper, based on the vibration and cement paste flow control, a fiber orientational extrusion nozzle was designed. Then, a new orientational molding method for UHPC was developed. Four groups of UHPC with different steel fiber contents were designed (0 vol%, 2 vol%, 4 vol%, and 6 vol%) and fabricated by the new method. The flexural and axial tensile performance of UHPC were systematically studied. The results indicated that the new orientational molding method was suitable for manufacturing UHPC with high content of steel fibers, which reached even 6 vol%. With the orientational molding method, the flexural strength and axial tensile strength of UHPC with 4 vol% content of steel fiber reach 55.6 MPa and 14.1 MPa, respectively. In addition, the results show that the flexural and tensile strengths of the specimens formed using the oriented technique were maximum at 4 vol%. The flexural strength increases with increasing fiber content as the fiber content increases from 0 vol% to 4 vol%. However, the flexural strength decreases at 6 vol% fiber content. Besides, X-ray micro-computed tomography (CT) was used for the analysis of the orientation of steel fiber. Results indicate that most of the fibers showed parallel to the casting path orientation when using the orientational molding technique. The orientational rates were 72%, 81%, and 75% for fiber contents of 2 vol%, 4 vol%, and 6 vol%, respectively.

Evaluation of Factors Affecting the Performance of Fiber-Reinforced Subgrade Soil Characteristics Under Cyclic Loading

This study is focused on evaluating the factors affecting the performance of fiber-reinforced subgrade under cyclic loading. To achieve the objectives of this study, a series of dynamic triaxial (DT) tests was performed, and the following parameters, such as resilient modulus (MR), number of loading cycles (N), cyclic stress (CS), resilient strain (RS), and stress-strain hysteresis response of both the reinforced and unreinforced subgrades were evaluated. Subsequently, a series of scanning electron microscope (SEM) tests was conducted to track the fiber-soil interfacial bonding after the completion of DT test. The results indicated that N and CS triggered an appreciable decrease in MR with significantly high RS deformation for the unreinforced subgrade. However, reversed responses were noted upon the inclusion of sisal fiber due to fiber-soil adhesion and a high ductility response was portrayed by the reinforced subgrades. A reversed response was significant upon 0.25% and 0.5% fiber inclusion, beyond which the CS resistance slightly decreased. The stress-strain hysteresis loop was observed to increase as the axial strain increased proportionally with an increase in fiber contents, thus causing a significant increase in energy absorption in specimens. The SEM micrograph showed tightly knitted fiber-soil adhesion after the DT test. This study indicated that the reinforced subgrade sustained the CS, N, and improved energy absorption capacity, and MRupon fiber inclusion. Doi: 10.28991/CEJ-2023-09-08-015 Full Text: PDF

A comparative study of polylactic acid (PLA)-Based unidirectional green hybrid composites reinforced with natural fibers such as kenaf, bamboo and coir

Plant-based composites are considered as new generation materials that offer sustainability, eco-friendly and green chemistry, utilized by numerous sectors. Composites of green hybrid made from polylactic acid (PLA) and three different plant fibers were prepared using two symmetrical fibers stacking sequences; namely high modulus and brittle (HMB) fibers (kenaf-bamboo-coir/PLA) and low modulus and ductile (LMD) fibers (coir-bamboo-kenaf/PLA) in the outmost layers. The stacking sequence was prepared using a simple slot tool to properly align the fibers and it was dried at 50 °C before being compressed using hot press. It was found that the tensile strength and tensile modulus of both hybrid composites increased linearly up to 158 MPa and 7 GPa respectively. It shows that the stacking sequences had no significant effect on tensile strength, but fracture strain increased by 58% produced by LMD fibres. However, the use of HMB fibres in the outmost layers significantly improved flexural strength up to 49% higher than that of LMD fibres. In contrast, the impact strength of the green hybrid composites using LMD fibres in the outmost layers was 21% higher than that of its counterpart. Like other plant fiber composites, both composites had an increased water absorption capacity of up to 39% due to increased fibre content. These stacking sequence properties are essential to fabricate a specific application to ensure properties suitable for the job's features. High modulus and brittle composites require a high load to deform permanently, as well as low modulus and ductile composites. Both exhibit versatile mechanical characteristic, providing a balance of sealant toughness and the ability to retain overall shape, such as in sound absorption and vibration in transportation.

The Effect of SMA Fiber Content on the Bending and Self-Recovery Performance of ECC Beams.

The addition of superelastic shape memory alloy fibers (SMAF) into engineering cementitious composites (ECC) can create a new type of SMAF-ECC composite material with good self-recovery and energy dissipation performance, which is very suitable for seismic structures. In this study, 10 groups of beam specimens with different volume contents of SMAF were fabricated, and the bending performance, deflection recovery and energy dissipation ability of these beams were studied through three-point bending cyclic loading tests. The failure mode, peak load, load-deflection curve, crack width and other indicators of the specimens were analyzed, and the relationship expression between fiber content and bending strength was established by fitting analysis. The results show that adding SMA fibers can significantly improve the peak load of ECC beams, with a maximum increase of 48.31%. The knotted SMA fibers can fully exert their superelasticity, providing the beam specimens with crack self-closing and deflection recovery ability. When the volume content of SMA fibers is 0-0.6%, the bending strength, energy dissipation ability and deflection recovery ability of the composite material beams increase with the increase in fiber content. When the volume content of SMA fibers is 0.6-1.0%, the above indicators decrease with the increase in fiber content. The suggested equations can well reflect the relationship between fiber content and beam bending strength. The research results of this paper provide theoretical support for the engineering application of SMAF-ECC composite materials.

Mechanical Performances Analysis and Prediction of Short Plant Fiber-Reinforced PLA Composites.

Plant fiber-reinforced polylactic acid (PLA) exhibits excellent mechanical properties and environmental friendliness and, therefore, has a wide range of applications. This study investigated the mechanical properties of three short plant fiber-reinforced PLA composites (flax, jute, and ramie) using mechanical testing and material characterization techniques (SEM, FTIR, and DSC). Additionally, we propose a methodology for predicting the mechanical properties of high-content short plant fiber-reinforced composite materials. Results indicate that flax fibers provide the optimal reinforcement effect due to differences in fiber composition and microstructure. Surface pretreatment of the fibers using alkali and silane coupling agents increases the fiber-matrix interface contact area, improves interface performance, and effectively enhances the mechanical properties of the composite. The mechanical properties of the composites increase with increasing fiber content, reaching the highest value at 40%, which is 38.79% higher than pure PLA. However, further increases in content lead to fiber agglomeration and decreased composite properties. When the content is relatively low (10%), the mechanical properties are degraded because of internal defects in the material, which is 40.42% lower than pure PLA. Through Micro-CT technology, the fiber was reconstructed, and it was found that the fiber was distributed mainly along the direction of injection molding, and the twin-screw process changes the shape and length of the fiber. By introducing the fiber agglomeration factor function and correcting the Halpin-Tsai criterion, the mechanical properties of composite materials with different contents were successfully predicted. Considering the complex stress state of composite materials in actual service processes, a numerical simulation method was established based on transversely isotropic material using the finite element method combined with theoretical analysis. The mechanical properties of high-content short plant fiber-reinforced composite materials were successfully predicted, and the simulation results showed strong agreement with the experimental results.

Sourdough Wheat Bread Enriched with Grass Pea and Lupine Seed Flour: Physicochemical and Sensory Properties

Legume seeds, such as grass pea, yellow lupine, and narrow-leaf lupine, are highly nutritious and offer a wide range of health benefits. The objective of this research was to explore the possibility of partially replacing wheat flour (at levels of 10, 15, 20, and 25%) with flour derived from these legume seeds in sourdough wheat bread and examine its impact on the physicochemical and sensory properties of the bread. The physical properties of the dough were also assessed. The substitution of wheat flour with ground legume seeds resulted in increased water absorption (from 54.1 to 63.5%) and prolonged dough development time (from 2.0 to 13.5 min). Ground lupine seeds reduced the volume of the bread and increased its crumb density, consequently making the bread harder. The most significant increase in hardness was observed when narrow-leaf lupine flour was added to the wheat flour (from 8.4 to 22.5 N). Narrow-leaf lupine had the greatest impact on enhancing the protein content in the enriched bread (from 11.5 to 20%), while yellow lupine caused the highest increase in fiber content (from 1.9 to 6.9%). The proposed additives slightly but significantly (p < 0.05) increased the antioxidant activity and phenolic content in the bread samples. Importantly, for all legume seeds, replacing up to 15% of the wheat flour allowed the production of bread with high consumer acceptability.