Mechanical Properties Of Fibers Research Articles

Improving the mechanical performance of railway concrete sleepers using recycled materials: An experimental and numerical study

This paper explores the use of three waste materials available in vast quantities, including waste tires, glass bottles and bamboo furniture, in the manufacture of railway sleepers. Mechanical properties of recycled concrete have been studied to establish an optimal mix suitable for concrete railway sleeper manufacturing. Thus, 5%, 10%, 15% and 20% recycled rubber sands (RRS) by volume of fine aggregate are used instead of 30# and 60# mesh sizes of fine aggregate. Moreover, 20%, 40%, 60%, 80% and 100% of aggregate volume are replaced by recycled glass aggregate (RGA) particles. Furthermore, different percentages of recycled bamboo fibers (RBF) have been used as 1%, 2% and 3% by volume of concrete. According to the optimal concrete mixtures of RRS, RGA and RBF, twelve concrete railway sleepers are manufactured and tested for middle and rail seat bending strengths. Results show that ref. sleeper has almost 16% and 24% lower strengths than RGA sleeper in middle and rail seat, respectively, while ref. sleeper have higher strengths by 16% and 13%, and 18% and 7% than RRS sleeper (M60-R5) and RBF sleeper (B2) in middle and rail seat, respectively. The FEM results show that the ([Formula: see text]) of the RGA sleeper is the minimum ratio by 1.11 and 1.13 for rail seat and middle of sleeper, respectively, which is the best performance. In RBF sleeper FEM model, Bamboo fiber can only bear 5% and 8% of total stress in middle and rail seat, respectively, due to low mechanical properties of fibers.

Pulp and Paper Characteristics of Five Lesser-known Species in Kalimantan: Effects of Re-beating

Five lesser-known species from natural forests in Central Kalimantan, viz., cempaka (Michelia champaca Linn), mentawa (Artocarpus rigidus Blume), menjalin (Xanthophyllum excelsum Miq.), kempili (Lithocarpus elegans (Blume) Hatus. Ex Soepadmo), and sempori (Dillenia sp.) were evaluated in the laboratory for their specific gravity, fiber morphology, pulping and papermaking properties. In addition, their properties after three-phase beating were also evaluated from a recycled paper point of view. The specific gravity and fiber length range were 0.58~0.68 and 1239~2479 μm, respectively. The highest value in specific gravity was observed in menjalin wood, while the longest fiber was observed in sempori. Kraft pulping with 14% active alkali (as Na2O), 23% sulfidity, 2 h at the maximum temperature showed that the highest screened yield was determined in cempaka wood (44.29%) with a kappa number of 17.6. The freeness ranges of unbeaten pulp were 675~780m mL CSF. The freeness ranges of 1st, 2nd, and 3rd beating were 539~630 mL, 235~275 mL, and 220~230 mL CSF, respectively. The 1st beating exhibited the best mechanical properties.  Among the species, cempaka, kempili, and mentawa showed comparatively high tensile (57~60 Nm/g) and burst index (2.6~3.4 KPa m2/g), whereas the highest value for tear index (5.02 mNm2/g) was observed in sempori. A considerable decrease in fiber length, slenderness ratio, and mechanical properties of the paper was observed with an increased beating number. These findings suggest that cutting the fibers or decreasing the slenderness ratio was the main factor causing the strength to decrease.

Machine learning assisted mechanical properties prediction of fine denier polyester fiber

In recent years, more and more attention has been attracted by fine denier polyester fibers in electronic information industry due to their unique structural and excellent mechanical properties. As known, the mechanical properties of fine denier polyester fibers have a close relationship with their melt-spinning process parameters, thus, it is worth further exploring the influence of process parameters on fiber mechanical properties (namely breaking strength, elongation at break and CV of breaking strength). This study aims to develop a novel prediction model based on the artificial neural network (ANN) to predict the key mechanical properties of fine denier polyester fibers. For this purpose, firstly, different specifications of fine denier polyester fibers with different mechanical properties are produced by adjusting the key melt-spinning parameters, namely spinning temperature, take-roll speed and metering pump speed. Then the experimental data is collected, analyzed and augmented with effect to be used for modeling. Next, a novel prediction model based on ANN is developed by importing the two-streams structure and two attention matrices to improve the feature abstraction for mechanical properties prediction. Lastly, different predictive performance indicators, namely root mean square error (RMSE), mean absolute percent error (MAPE) and the coefficient of determination (R2) are imported to evaluate the proposed model. For the total of three mechanical properties, the predicted results of the proposed model in terms of RMSE, MAPE and R2 are respectively 0.3499, 0.0906 and 2.9516.

Remnant polarization and structural arrangement in P(VDF-TrFE) electrospun fiber meshes affect osteogenic differentiation of human mesenchymal stromal cells

Many tissues and cells are influenced by mechano-electric stimulation, thus the application of piezoelectric materials has recently received considerable attention in tissue engineering. This report investigated electrospun fiber meshes based on poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)] as instructive biomaterials for osteogenic differentiation of human mesenchymal stromal cells (hMSCs). The influence played by methyl ethyl ketone (MEK), used as a solvent in place of dimethylformamide (DMF)/acetone mixture, and the effect of rotating velocity of the electrospinning collector on fiber morphology, mechanical and piezoelectric properties were studied. The solvent had noticeable effects on morphology and piezoelectric properties of electrospun fibers, with MEK outperforming DMF/acetone. By increasing the collector velocity up to 4000 rpm, the fiber diameter reduced and the mutual alignment of the fibers increased, corresponding to enhanced mechanical properties and piezo-active β-phase content. However, as a consequence of the diverse mechanical properties of random and aligned fibrous architectures, which ultimately affected the piezoelectric properties, randomly-oriented fibers exhibited higher remnant piezoelectric properties (Vout and d31 piezoelectric coefficient) than aligned ones. On these scaffolds, hMSCs showed an excellent capability of early osteogenic differentiation, leading to high calcium production. Fiber surface topology, fiber mesh morphology and remnant piezoelectric properties played a determinant role on hMSC osteogenic commitment.

Random modeling of hemp fibers mechanical properties

The growing interest in vegetal fiber-based composite materials for reinforcing structural elements is prompting researchers to consider the inherent randomness, arising from various factors which are complex to model. For this reason a general probabilistic approach seems more appropriate to model all uncertainties regardless where they come from. In this paper, factory produced hemp ropes, and their components, are tested to obtain their tensile mechanical properties. In particular, 120 fibers with four different lengths, 55 yarns, 33 strands and 64 ropes are used to obtain a first statistical characterization of tensile strength, strain and Young modulus. These results are used to calibrate two commonly used random models such as Gaussian and three-parameters Weibull distributions and to give both qualitative and quantitative complete random characterization of the tensile properties of each hemp rope components. The obtained results are crucial to estimate vegetal fiber-based composite materials structural response.

Modulating Polyalanine Motifs of Synthetic Spidroin for Controllable Preassembly and Strong Fiber Formation.

Spider dragline (major ampullate) silk is one of the toughest known fibers in nature and exhibits an excellent combination of high tensile strength and elasticity. Increasing evidence has indicated that preassembly plays a crucial role in facilitating the proper assembly of silk fibers by bridging the mesoscale gap between spidroin molecules and the final strong fibers. However, it remains challenging to control the preassembly of spidroins and investigate its influence on fiber structural and mechanical properties. In this study, we explored to bridge this gap by modulating the polyalanine (polyA) motifs in repetitive region of spidroins to tune their preassemblies in aqueous dope solutions. Three biomimetic silk proteins with varying numbers of alanine residues in polyA motif and comparable molecular weights were designed and biosynthesized, termed as N16C-5A, N15C-8A, and N13C-12A, respectively. It was found that all three proteins could form nanofibril assemblies in the concentrated aqueous dopes, but the size and structural stability of the fibrils were distinct from each other. The silk protein N15C-8A with 8 alanine residues in polyA motif allowed for the formation of stable nanofibril assemblies with a length of approximately 200 nm, which were not prone to disassemble or aggregate as that of N16C-5A and N13C-12A. More interestingly, the stable fibril assembly of N15C-8A enabled spinning of simultaneously strong (623.3 MPa) and tough (107.1 MJ m-3) synthetic fibers with fine molecular orientation and close interface packing of fibril bundles. This work highlights that modulation of polyA motifs is a feasible way to tune the morphology and stability of the spidroin preassemblies in dope solutions, thus controlling the structural and mechanical properties of the resulting fibers.

Predicting density-related mechanical properties of amorphous silicon nitride using molecular dynamics simulations

Silicon nitride fiber is among the most popular candidates for high-temperature wave-transparent ceramic matrix composites (CMC) in aerospace engineering, and the measurement of its mechanical properties has always been the focus of researchers. In this paper, a simple and effective molecular dynamics method is used to generate molecular dynamics models of amorphous silicon nitride (a-Si3N4) materials with different densities, and it is verified that the developed models reflect the microstructure of the fiber. Based on analyzing the effects of size on the results, tensile and shear simulations are carried out to obtain the mechanical properties of the models with different densities. According to the research data obtained, the empirical equation between mechanical properties (Young's modulus, shear modulus, tensile strength, and shear strength) and density of fiber is established, and validated by the published experimental results. The empirical equation can not only predict the mechanical properties of fibers directly from the density but also provide a new way to measure the mechanical properties of fibers nondestructively.

The surface treatment of PVA fibres to enhance fibre distribution and mechanical properties of foam concrete

Fibres are often used to improve the mechanical properties of foam concrete. However, the poor dispersion of PVA fibres in foam concrete significantly restricts their reinforcement efficiency. Limited studies have been conducted on improving the distribution of PVA fibres in a cementitious matrix, particularly in relation to foam concrete. This is noteworthy because pore structure, which can be significantly influenced by the fibres and fibre treatment agents, is a critical parameter that affects the mechanical properties of foam concrete. Therefore, this study employed polar agents (non-ionic surfactants) to treat the fibre surface, aiming to enhance the distribution and reinforcement efficiency of PVA fibres in foam concrete. In view of safety and feasibility, two non-hazardous polar agents, namely PEG-PPG-PEG (designated as PA A) and Polyoxyethylene (20) cetyl ether (designated as PA B), were used to treat the PVA fibres. The impact of fibre treatments on fibre dispersion and pore structure was investigated, and the compressive strength and flexural behaviour of foam concrete were measured before and after the treatments. PA A was found to be unsuitable for fibre treatment due to its poor bonding with the fibre surface. On the other hand, PA B exhibited good bonding with PVA fibres, resulting in enhanced fibre dispersion and pore structure in the foam concrete. Compared to plain foam concrete, the fibres treated with PA B increased the compressive and flexural strength by 47.4 % and 190.3 %, respectively. Moreover, the treated fibres (by PA B) were observed to improve the 0.8 mm toughness of foam concrete by 27.2 %.

Investigation of chemical, physical and morpho-mechanical properties of banana-plantain stalk fibers for ropes and woven fabrics used in composite and limited-lifespan geotextile

This study aimed to assess the potential of banana-plantain stalk fibers (BPSF) as a raw material for ropes and fabrics used in composites and geotextiles. Fibers were obtained by Biological retting and ropes used for geotextile weaving were obtained by three-strand twisting in order to optimize the mechanical properties of geostalk. The thermal, physical, chemical and mechanical characteristics of the fibers were studied in order to assess the impact of the extraction process on fiber performance. In addition, the microstructure of fibers and ropes was analyzed using Scanning Electron Microscopy (SEM) and the results highlighted the presence of cellulose microfibrils parallel to fiber axis and hemicellulose linked by lignin matrix. These constituents are organized in three concentric layers around the lumen. Elementary chemical analyses using X-ray energy dispersion (EDS), Fourier Transform Infrared (FTIR) and chemical deconstruction using Jayme-Wise protocol were carried out to determine the chemical composition of BPSF, which consists of 51.5% Carbon, 47.07% Oxygen and mineral salts that can be highly contribute to soil fertilization after degradation. These chemical constituents represent 40% cellulose, 21.5% hemicellulose, 24% lignin, 0.34% pectin, 7.2% lip soluble extractable and 7.36% water-soluble sugars present in BPSF. Thermal properties of BPSF have been investigated showing the initial degradation around 200°C. Physical analysis and uniaxial tensile testing were performed to determine the multi-scale physical and mechanical properties of geostalk. Statistical evaluation using Weibull distribution established an increasing rate of physical and mechanical properties from the finest scale to the macroscopic scale. Thus, from the BPSF to the ropes, titer increases from 42.5 ± 4.5 g /km to 7983.4 ± 132 g/km and elongation at break increases from 0.75 ± 0.29 mm for the fibers to 52.42 ± 18.91 mm for geostalk. With mass per unit area of 1869 g/m2, the tensile stress of 1281.05 ± 273 MPa and maximum strength of 15.4 ± 1.74 kN/m, geostalk is a sustainable woven fabric alternative to geosynthetics for soil reinforcement as other limited lifespan geotextiles (geojute, geocoir and geosisal). In addition, the thermal stability and high mechanical properties of fibers and ropes suggest their potential application as reinforced phases in composite materials.

Interfacial blending in co-axially electrospun polymer core-shell fibers and their interaction with cells via focal adhesion point analysis

Electrospun polymer scaffolds have gained prominence in biomedical applications, including tissue engineering, drug delivery, and wound dressings, due to their customizable properties. As the interplay between cells and materials assumes fundamental significance in biomaterials research, understanding the relationship between fiber properties and cell behaviour is imperative. Nevertheless, altering fiber properties introduces complexity by intertwining mechanical and surface chemistry effects, challenging the differentiation of their individual impacts on cell behaviour. Core-shell fibers present an appealing solution, enabling the control of mechanical properties of scaffolds, flexibility in material and drug selection, efficient encapsulation, strong protection of bioactive drugs against harsh environments, and controlled, prolonged drug release. This study addresses a key challenge in core-shell fiber design related to the blending effect between core and shell polymers. Two types of fibers, PMMA and core-shell PC-PMMA, were electrospun, and thorough analyses confirmed the desired core-shell structure in PC-PMMA fibers. Surface chemistry analysis revealed PC diffusion to the PMMA shell of the core-shell fiber during electrospinning, subsequently prompting an investigation of the fiber’s surface potential. Conducting cellular studies on osteoblasts by super-resolution confocal microscopy provided insights into the direct influence of interfacial polymer blending and, consequently, altered fiber surface and mechanical properties on cell focal adhesion points, bridging the gap between material attributes and cell responses in core-shell fibers.

Effects of chemical treatment on natural (rice straw/neem saw dust) fiber morphology and mechanical properties of its composite material

Recent years have seen an increase in the use of natural fibers. Rice straw/natural fiber hybrid composites can recycle agricultural waste easily and eliminate fine silica ash pollution. Composite specimens are created by hand lay-up as per ASTM standards. Unsaturated polyester resins and rice straws are studied using scanning electron microscopy. Hybrid composites reinforced with rice straw and neem powder perform better. The optimal fiber content for impact and flexural strength is 50 % by volume fraction. RSNWP6 fibers with hybrid properties have more significant impact strength, hardness, and flexural strength than other fibers at 516.86 J/m, 45 BIU, and 80.03 MPa.

Effects of TiO2 on fiber spinnability, structure, and mechanical properties of glasses derived from simulated lunar soils

The construction of lunar stations for research and habitation requires high-performance building materials that can adapt to the harsh lunar environment. One of the feasible building materials is fiber-reinforced composites, for which the composition of glass fibers can be designed like lunar soils, i.e., terrestrial basalt, and in turn the “lunar glass” can be drawn into fibers. Because of a wide variation of TiO2 in lunar soils, our study focused on a series investigation on the effect of TiO2 (0.55 wt%-6.14 wt%) on fiber spinnability and strength of the simulated “lunar glass and glass fibers”. The baseline glass composition was derived from a simulated TiO2-lean lunar soil and other glasses were made at different TiO2 doping levels. The addition of TiO2 was found to reduce the thermal stability of the melt, there appears a TiO2 threshold (6.14 wt%), at which fibers cannot be drawn without breakage because of melt devitrification. The fiber tensile strength exhibits a nonlinear characteristic with an apparent maximum at 1.52 wt% TiO2. FTIR and Raman spectroscopic studies were carried out to investigate the glass network structure responses to TiO2 modifications and show TiO2 functions as a network modifier, depolymerizing the silicate network. Statistical structure (FTIR & Raman based)–property modeling was attempted to further elucidate the effect of TiO2-induced structure change on Tg and fiber tensile strength. Good agreements were found between the model predictions and the measured values.

Influence of TEMPO-oxidation on pulp fiber chemistry, morphology and mechanical paper sheet properties

In this contribution, we report on the TEMPO-mediated oxidation of pulp fibers used in the general context of papermaking and for the future design of tailor-made paper in advanced applications. We focus in our studies on properties of TEMPO-oxidized pulp fibers to explain the characteristics of the paper made thereof. 13C solid-state NMR analysis reveals that in particular amorphous regions of the fibers are being chemically oxidized, while at the same time the crystalline regions of the fibers are not significantly affected. Investigation of the fiber morphology before and after oxidation shows that the fiber length is not changed, yet the fibers do exhibit an increase in width if in contact with water, which is attributed to an increase in fiber swelling. In addition, fibrillation decreases due to the oxidative removal of loosely bound fines and fibrils, rendering the surface of the resulting oxidized fibers much smoother in comparison to the original fibers. Finally, we observe that both, dry and wet tensile strengths are also higher for paper made of oxidized fibers, most likely due to cross linkable aldehyde groups formed during oxidation (i.e. hemiacetal bond formation in the sheet during thermal drying). Our results of the oxidation of paper fibers thus offer a systematic study helpful for the design of tailor-made paper useful in several applications where a fiber-modification with fiber-immobilized functional motifs is crucial, such as for example in paper-based microfluidic sensors (µPADs) or lab-on a chip-devices.

Modification of PLA fibers with novel chitosan-based flame retardants by centrifugal melt electrospinning

A novel flame retardant (CSFR) was developed by grafting polylactic acid (PLA) and melamine phosphate ester onto a chitosan framework to enhance the flame retardancy of PLA fibers without compromising their other excellent properties. The PLA/CSFR flame retardant fiber membranes were successfully prepared using a self-designed constant temperature centrifugal melt electrospinning device. Results demonstrated that the synthesized CSFR exhibited a mass residue of 30% at 800°C. Adding a small amount of CSFR effectively improved the fibers' flame retardancy and mechanical properties, while excessive CSFR content resulted in a decline in mechanical performance. The optimal content of CSFR was determined to be 1.0%. The PLA/1.0%CSFR fibers achieved an impressive oxygen index of 42.3% and a mass residue of 7.98% at 800°C. Furthermore, the modified fibers significantly enhanced maximum elongation by 137.5% and tensile strength by 130.27% compared to pure PLA fibers. The molecular weight of the modified fibers decreased by 66.15%, and the mass loss rate was 8.57% after 12 hours of UV irradiation. The synthesized PLA/1.0%CSFR fibers exhibited exceptional flame retardancy, thermal stability, mechanical properties, and UV degradation performance.

Critical evaluation of epoxy-hemp-pineapple-palm fiber composites using hybrid AHM-TOPSIS technique for sustainable structural applications

ABSTRACT This study explores the use of hemp, pineapple, and palm in green composites that are ecological substitutes for synthetic fibers in ballistics and architecture. Multi-criteria decision-making (MCDM) methodologies are taken into consideration to select the optimal choice for the configuration or constituent under deliberation. Integrated MCDM approaches like the Attribute Hierarchy Model (AHM) and TOPSIS are used to rank developed composites. Thermogravimetric analysis (TGA) revealed the thermal stability of palm, pineapple, and hemp fibers, with steadiness temperatures of 276°C, 241°C, and 166°C, respectively. The investigation spans various fiber contents, evaluating thermal, mechanical, and water absorption properties. Hybrid epoxy composites with pineapple and palm fibers exhibit exceptional performance, showcasing heightened tensile strength, yield strength, and hardness. In contrast, the hybrid composite with hemp and pineapple had better water absorption (18%) and specific heat capacity (5.6%) compared to the pineapple-only composite. An in-depth AHM-TOPSIS unveiled that the hybrid epoxy composites (FC7; 0.8524) with palm, hemp, and pineapple exhibit the highest quality, and composite incorporating pineapple fiber (FC2; 0.1393) ranks lowest. Scanning electron microscopy (SEM) scrutinizes fiber morphology and interfacial boundaries in composite subjected to stress rupture.

Wet-Spun Chitosan-Sodium Caseinate Fibers for Biomedicine: From Spinning Process to Physical Properties.

We designed and characterized chitosan-caseinate fibers processed through wet spinning for biomedical applications such as drug delivery from knitted medical devices. Sodium caseinate was either incorporated directly into the chitosan dope or allowed to diffuse into the chitosan hydrogel from a coagulation bath containing sodium caseinate and sodium hydroxide (NaOH). The latter route, where caseinate was incorporated in the neutralization bath, produced fibers with better mechanical properties for textile applications than those formed by the chitosan-caseinate mixed collodion route. The latter processing method consists of enriching a pre-formed chitosan hydrogel with caseinate, preserving the structure of the semicrystalline hydrogel without drastically affecting interactions involved in the chitosan self-assembly. Thus, dried fibers, after coagulation in a NaOH/sodium caseinate aqueous bath, exhibited preserved ultimate mechanical properties. The crystallinity ratio of chitosan was not significantly impacted by the presence of caseinate. However, when caseinate was incorporated into the chitosan dope, chitosan-caseinate fibers exhibited lower ultimate mechanical properties, possibly due to a lower entanglement density in the amorphous phase of the chitosan matrix. A standpoint is to optimize the chitosan-caseinate composition ratio and processing route to find a good compromise between the preservation of fiber mechanical properties and appropriate fiber composition for potential application in drug release.

Spatiotemporal Expression Characterization of KRTAP6 Family Genes and Its Effect on Wool Traits.

Keratin-related proteins (KAPs) are structural components of wool fibers and are thought to play a key role in regulating the physical and mechanical properties of fibers. Among all KAP genes (KRTAPs), KRTAP6 gene family (KRTAP6-1, KRTAP6-2, KRTAP6-3, KRTAP6-4, and KRTAP6-5) is a very important member with high polymorphism and notable association with some wool traits. In this study, we used real-time fluorescence quantitative PCR (RT-qPCR) and in situ hybridization to investigate spatiotemporal expression of KRTAP6s. The results revealed that KRTAP6 family genes were significantly expressed during anagen compared to other stages (p < 0.05). And it was found the five genes were expressed predominantly in the dermal papillae, inner and outer root sheaths, and showed a distinct spatiotemporal expression pattern. Also, it was found that KRTAP6-1 and KRTAP6-5 mRNA expression was negatively correlated with wool mean fiber diameter (MFD) and mean staple strength (MSS) (p < 0.05). In summary, the KRTAP6 family genes share a similar spatiotemporal expression pattern. And KRTAP6-1 and KRTAP6-5 may regulate the MFD and MSS of Gansu Alpine fine-wool sheep wool by changing the expression.

Predicting myosin heavy chain isoform from postdissection fiber length in human skeletal muscle fibers.

Experimental techniques in single human skeletal muscle cells require manual dissection. Unlike other mammalian species, human skeletal muscle is characterized by a heterogeneous mixture of myosin heavy chain (MHC) isoforms, typically used to define "fiber type," which profoundly influences cellular function. Therefore, it is beneficial to predict MHC isoform at the time of dissection, facilitating a more balanced fiber-type distribution from a potentially imbalanced sample. Although researchers performing single fiber dissection report predicting fiber-type based on mechanical properties of fibers upon dissection, a rigorous examination of this approach has not been performed. Therefore, we measured normalized fiber length (expressed as a % of the length of the bundle from which the fiber was dissected) in single fibers immediately following dissection. Six hundred sixty-eight individual fibers were dissected from muscle tissue samples from healthy, young adults to assess whether this characteristic could differentiate fibers containing MHC I ("slow" fiber type) or not ("fast" fiber type). Using receiver operator characteristic (ROC) curves, we found that differences in normalized fiber length (114 ± 13%, MHC I; 124 ± 17%, MHC IIA, P < 0.01) could be used to predict fiber type with excellent reliability (area under the curve = 0.72). We extended these analyses to include older adults (2 females, 1 male) to demonstrate the durability of this approach in fibers with likely different morphology and mechanical characteristics. We report that MHC isoform expression in human skeletal muscle fibers can be predicted at the time of dissection, regardless of origin.NEW & NOTEWORTHY A priori estimation of myosin heavy chain (MHC) isoform in individual muscle fibers may bias the relative abundance of fiber types in subsequent assessment. Until now, no standardized assessment approach has been proposed to characterize fibers at the time of dissection. We demonstrate an approach based on normalized fiber length that may dramatically bias a sample toward slow twitch (MHC I) or fast twitch (not MHC I) fiber populations.

Application of electrical resistivity for estimating compressive strength of FRC at early-ages

ABSTRACT The addition of fibers improves the ductility and compressive strength of concrete. Utilizing fiber in concrete, on the other hand, alter the electrical conductivity of concrete and that is especially important when concrete is being used in applications that electrical resistivity of concrete has been taken into account in the design process. Electrical resistivity of concrete can be measured using nondestructive testing techniques. Electrical resistivity has been proven to be in relationship with compressive strength of cementitious materials. The link between surface electrical resistivity (ER) and compressive strength (CS) of FRC at early ages has been investigated in the current study. Twenty-one distinct FRC mixtures have been cast using various fiber types, w/c ratios and fiber volume fractions. Test results have shown a strong relationship between electrical resistivity and mechanical properties of fiber reinforced concrete. A novel empirical equation has been proposed to estimate the compressive strength of early-age fiber reinforced concrete. The adequacy of this equation was determined by comparing actual and projected compressive strength values for FRC using a coefficient of variation. The early-age compressive strength of FRC was found to be reliable when the proposed equations were utilized.

Click chemistry modifications for the selective crosslinking of wood pulp fibers - effect on the physical and mechanical properties of paper.

The Cu(i)-catalyzed Huisgen cycloaddition click chemistry reaction is of particular interest in the production of paper sheets or natural fiber composites since it leads to the formation of chemically stable bonds between two fibers. This study focuses on the click chemistry modification of kraft pulp fibers. We based our approach on prior research that treated kraft fibers using click chemistry, including propargylation and tosylation reactions. Our focus was on enhancing these treatments to achieve better final sheet properties. After the azidation of tosylated fibers, the crosslinking is carried out with and without a catalyst using water as a solvent to form enhanced kraft fiber sheets. The chemical characterization and the mechanical properties of fibers obtained at intermediate stages confirmed the presence of various functions on the surface of the modified fibers, with a very high degree of substitution and the inter-fiber cross-linking by click chemistry. The presence of inter-fibers covalent bonds led to significant improvements in the mechanical strength and tensile stiffness of the sheets.