Single Fiber Type Research Articles

Understanding Toughening Mechanisms and Damage Behavior in Hybrid-Fiber-Modified Mixtures Using Digital Imaging

Pavement cracking is a primary cause of early damage in asphalt pavements, and fiber-reinforcement technology is an effective method for enhancing the anti-cracking performance of pavement mixtures. However, due to the multi-scale dispersed structure of pavement mixtures, it is challenging to address cracking and damage with a single fiber type or fibers of the same scale. To investigate the toughening mechanisms and damage behavior of hybrid-fiber-modified mixtures, we analyzed the fracture process and damage behavior of these mixtures using a combination of basalt fiber and calcium sulfate whisker hybrid fiber modification, along with semicircular bending tests. Additionally, digital imaging was employed to examine the fracture interface characteristics, revealing the toughening mechanisms at play. The results demonstrated that basalt fibers effectively broaden the toughness range of the modified mixture at the same temperature, reduce mixture stiffness, increase residual load at the same displacement, and improve crack resistance in the mixture matrix. While calcium sulfate whiskers enhanced the peak load of the mixture, their high stiffness modulus was found to be detrimental to the mixture’s crack toughness. The fracture interface analysis indicated that the three-dimensionally distributed fibers form a spatial network within the mixture, restricting the relative movement of cement and aggregate, delaying crack propagation, and significantly improving the overall crack resistance of the mixture.

Development and characterization of hybrid polymer composite materials with reinforcement of glass/carbon fibers for enhanced mechanical properties: an experimental and numerical approach

Composite materials, particularly fiber-reinforced plastics (FRP), are used in aerospace and automotive industries due to their desirable properties and surpassing traditional metals in various applications. Researchers are countering the drawbacks of using a single fiber type in FRP by creating hybrid composites that combine different fibers in a single matrix. These hybrids harness the cost-effectiveness and corrosion resistance of glass fibers alongside the strength and stiffness of carbon fibers, resulting in a balanced combination of properties for various applications. Tensile tests were performed according to the ASTM D3039 standard, with a 2 mm/min strain rate. The results showed that increasing the carbon fiber percentage (6.56%, 13.79%, and 21.07%) led to significant improvements in the tensile strength of the hybrid composites (34.18%, 55.44%, and 85.40% higher than glass fiber composites). However, changing the stacking sequence did not significantly affect tensile strength, indicating its insignificance in this regard. Numerical simulations were conducted to validate the experimental results, and the errors between experimental and numerical data were below 10% for various stacking sequences. These discrepancies were attributed to factors such as fiber waviness, which resulted in heterogeneous property distribution within the composites, and the manufacturing process used for creating the hybrid composites. Scanning electron microscope analysis was also performed to study the failure modes on the fracture surface of the tensile-tested specimens.

An investigation of self-sensing and mechanical properties of smart engineered cementitious composites reinforced with functional materials

Abstract In this study, hybrid functional fillers were used to create an electrical network that is used to develop self-damage sensing ability within conventional cementitious mixtures. This electrical network was used to examine the self-sensing properties of cementitious composites under different loading scenarios such as compression, splitting tensile, and cyclic loading for three ages, those are 7, 14, and 28. With the help of a single type of functional filler or fiber, the self-sensing capabilities of the majority of previous works are demonstrated. This study incorporates two types of functional fillers for sustainability and low cost: micro-scale carbon fibers (CF) and waste iron (Ir) powder in the form of microparticles. The purpose of the current work is to fill up the subject’s gap using two different types of functional fillers as a hybrid form. Three hybrid proportions of a micro-scale CF (vol% of mixture) and waste iron powder (Ir) (wt% of cementitious materials) are utilized. These are (0.33, 15), (0.67, 10), and (1.00, 5), respectively. Unlike carbon-based materials, polyvinyl alcohol is used as a mechanical reinforcing fiber 2% by volume of the cementitious mixture. Additionally, a control combination without any fillers has been created. The electrical resistivity of the fabricated samples was monitored during various loading applications for every second to confirm their self-sensing capabilities. Regarding the fractional change in electrical resistivity, the self-sensing behavior was superior for mixes containing high dosages either of waste iron powder or CF in the same hybrid matrix. Quite the contrary to that, the piezoresistivity was modest in the middle hybrid ratio.

Concrete canals lining with modern materials: A Review of hybrid fiber reinforced concrete

Water losses in irrigation canals occur during the process of water transportation, with seepage loss being the main contributor to total water loss in irrigation conveyance. Cracks and settlement are the most problematic factors affecting canal lining structures, leading to reduced performance of irrigation canals due to issues such as sediment deposition, waterlogging, and leakage. Seepage losses typically range from 20 % - 30 %, but this can be reduced to 15 % - 20 % with the use of canal lining. However, the concrete lining structure, being a thin plate, is prone to high rates of cracking, which weakens the performance of canals. Therefore, it is crucial to enhance the flexure and splitting-tensile strengths of concrete to control the rate of cracking in the canal lining. The splitting-tensile strength of concrete is particularly important in crack control. Hybridization of fibers, such as combining polypropylene and jute fibers, can efficiently enhance flexural toughness, flexural strength, and fracture energy more than using a single type of fiber. The overall aim of this review is to summarize the literature on the use of modern materials to reduce water losses in concrete canal lining. Initially, hybrid fibers (one natural fiber and one artificial fiber) are selected to explain the behavior of hybrid fiber reinforced concrete (HFRC). The crack arresting mechanism of HFRC can help reduce losses in concrete canal lining. The findings of this review will be valuable as a reference for both industry practitioners and academic researchers interested in the development of hybrid fiber reinforced concrete materials, particularly for canal lining applications.

Experimental study of multiscale hybrid fiber-reinforced ambient-cured LEGC under uniaxial compression

This study proposed the addition of cellulose nanofibers (CNFs) and basalt fibers (BFs) as hybrid fibers (HFs) into lightweight expanded polystyrene (EPS) geopolymer concrete (LEGC) to enhance its mechanical properties from chemical and physical perspectives. First, uniaxial compression tests were performed on LEGC specimens with moderate densities (1120–1920 kg/m3) reinforced with HF prepared with different CNF weight ratios (0.1%, 0.2%, and 0.3%) and fixed BF volume content of 0.6%. The test results demonstrated that the integrity of the specimens under the effect of the suitable dosing of HF was better maintained at final destruction, and the enhancement rates of the compressive strength and elastic modulus of the specimens with HF were superior to those with a single fiber type. The suitable dose of CNF was 0.2% for EPS volume contents of 10% and 20%, while 0.1% was suitable for EPS volume contents of 30% and 40%. Meanwhile, the cracking resistance mechanism of HF specimens was analyzed from chemical and physical perspectives, and the synergistic mechanism was determined quantitatively. In addition, the enhancement rates of the energy absorption capacity of the specimens with a suitable dose of HF were also more effective, which ensured the light weight of the material and improved its energy absorption capacity. Finally, this study developed a nine-parameter damage constitutive model that could better describe the five-stage characteristics of the complete stressstrain curve of the specimens, providing a certain theoretical basis for the structural design and analysis of LEGCs.

Water Sorption in Hybrid Polyester/Glass/Jute Composites Processed via Compression Molding and Vacuum-Assisted Resin Transfer Molding.

The aim of this work is to analyze water sorption in hybrid polyester/glass fabric/jute fabric composites molded via compression and VARTM (Vacuum-Assisted Resin Transfer Molding). The laminates were produced with five different stacking sequences and subjected to water sorption testing at room temperature, 50 °C and 70 °C. This study consisted of two stages: experimental and theoretical stages. The composites had a fiber volume content ranging from 30% to 40%. Water absorption and diffusion coefficient in the hybrid composites were intermediate to those reinforced with a single type of fiber. There were no significant differences in these properties based on fiber arrangement once the composites reached saturation. Diffusion coefficient values were higher for specimens with jute fiber on at least one of the outer surfaces. Water sorption rates increased with higher immersion temperatures. The water sorption at saturation point was not affected by the manufacturing process. Among the hybrid composites, those with jute on the surfaces showed the highest diffusion coefficient, while those with glass on the surface had the lowest values. Higher diffusion coefficient values were observed at temperatures of 50 °C and 70 °C. The main influencing factors on the absorbed moisture content for composites are the presence and content of jute fibers in the system and the immersion temperature. The manufacturing process does not affect the water sorption at saturation point.

Improved bleached eucalyptus kraft pulp-based tissue papers incorporating wet-strength resins

Abstract Common tissue paper manufacturing trends aim at partial or total replacement of softwood pulp with hardwood pulp for its production, such as bleached eucalyptus kraft pulp (BEKP), in order to optimize the process and the final product properties such as softness. However, the use of a single type of hardwood fiber results in lower strengths of both wet and dry webs. To maintain necessary strength and desired properties, the incorporation of several additives is often required. In this context, low molecular weight polyethylene glycol (PEG) and different wet strength resins, such as polyamideamine-epichlorohydrin (PAE) and glyoxalated polyacrylamide (GPAM) resins, were combined to achieve an innovated product with improved properties. In particular, wet and dry tensile strength was significantly improved when combining PEG and wet strength resins, especially observed in tissue papers prepared with PAE resin, high-charge cationic agent and bulk applied aqueous PEG solution. Noteworthy that water absorption capacity and softness of tissue paper were not critically affected by PEG incorporation, regardless of application method used (in bulk or by spray).

Low-velocity impact behaviour of biocomposite laminates reinforced by flax, basalt and hybrid fibres at various temperatures: Analytical, numerical and experimental results

In recent years, the non-biodegradable nature of synthetic composite materials has shifted the research focus on natural fibres as possible substitutes for traditional reinforcements. This paper investigates the effects of temperature variation on the impact behaviour of natural fibre laminates from an experimental, analytical, and numerical point of view. Flax, basalt, and hybrid/epoxy resin composites have been characterized through a variegated experimental campaign: from −40 °C to 80 °C. In addition to these studies, two different analytical models available in literature for synthetic materials are, here, combined and validated to reproduce the full loading–unloading trend of natural fibre composites. Since the aim of this study is the investigation of low-velocity impact behaviour as a function of the operating temperature, it is worth noting that no modifications have been made to these models, except for material parameters like Young’s and shear moduli. Subsequently, a finite element numerical investigation has been carried out, using the solver RADIOSS, with the aim of generating, in very reasonable computation times, a first numerical approximation of the experimental impact response. The obtained results show how both the presented procedures can predict well the response of these composites during an impact event. Moreover, the mixed trend observed in the hybrid configuration supports the thesis of hybridization’s importance, as a technique capable of exploiting the synergistic effects arising from the application of different types of reinforcement and reducing the drawbacks connected with the employment of a single type of fibre.

Use of Dietary Fibers in Reducing the Risk of Several Cancer Types: An Umbrella Review.

(1) Background: Numerous meta-analyses have shown that a high intake of dietary fiber plays a protective role in preventing the development of various types of cancer. However, previous studies have been limited by focusing on a single type of dietary fiber and variations in outcome measures, which may not be effectively applied to provide dietary guidance for the general population. (2) Object: We summarized the meta-analysis of dietary fiber and cancer, and provided references for residents to prevent cancer. (3) Methods: Systematic search of relevant meta-analyses on the association between dietary fiber and cancer occurrence in PubMed, Web of Science and other databases was conducted from the time of database construction to February 2023. The method logical and evidence quality assessments were performed by applying the criteria in the "A Measurement Tool to Assess Systematic Reviews-2" (AMSTAR2) scale and the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) Expert Report, respectively. (4) Results: Our analysis included 11 meta-analyses, and the AMSTAR 2 assessment revealed that the overall methodological quality was suboptimal, with two key items lacking sufficient information. Nonetheless, our findings indicate that a high intake of dietary fiber is associated with a reduced risk of several types of cancer, including esophageal, gastric, colon, rectal, colorectal adenoma, breast, endometrial, ovarian, renal cell, prostate, and pancreatic cancers. The majority of these associations were supported by a "probable" level of evidence. (5) Conclusions: Dietary fiber intake has different protective effects on different cancers.

Mode I and II interlaminar fracture toughness of glass/carbon inter‐ply hybrid FRP composites: Effects of stacking sequence and testing temperature

AbstractEven though laminated FRP composites show exceptional performance in various modes of loading, they are susceptible to delamination. The ambient temperature and elevated temperature delamination resistance of glass/carbon fiber interply hybrid composites were assessed via mode I and mode II interlaminar fracture toughness tests performed at 30, 50 and 70°C. Interply hybrid composites performed better than composites with single type of fiber. The fracture toughness of inter‐ply hybrid composites varied with the stacking position. At 30°C, mode I fracture toughness value of alternative glass and carbon fiber stacking sequence (G1C1)5 of hybrid composite showed 40% improvement over 10 layered carbon/epoxy (C10) composite. Further, Mode II fracture toughness of C5G5 composite showed 22% enhancement, and C10 exhibited 42% improvement over 10‐layered glass/epoxy composite. Increasing the test temperature of all composites improved their GIC and GIIC values. The increment in the mode I fracture toughness properties of all composite was in the range of 5%–23% at 70°C from its room temperature value. The fractographic images of fractured samples were studied under a scanning electron microscope and failure mechanisms of composites were identified.

Effect of hybrid-fiber- reinforcement on the shear behavior of high-strength-concrete beams

The shear behavior of concrete beams is highly affected by the implementation of better performance concrete. Hybrid fibers addition to concrete mixture has proven to improve the performance compared to just using single type of fiber. Thus, in this current study, the shear behavior of hybrid-fiber-reinforced-high-strength-concrete beams was investigated experimentally. In addition, the effect of the span-to-depth ratio and the transverse reinforcement ratio were examined. Results showed that, when .45% of the cement weight is replaced with polypropylene fiber and 7% of the cement weight is replaced with steel fibers, the shear strength of the beam was enhanced by 18% in comparison to the control beam. The Formation and progression of cracks were also better controlled. The behavior of hybrid-polypropylene-steel-fibers-high-strength-concrete beams was observed to be comparable to that of conventional concrete ones as the shear strength increased with the decrease in span to depth ratio or the increase in transverse reinforcing ratio. A non-linear numerical model was developed and validated using the experimental results. The shear capacities of beams were calculated using ACI, which was compared to experimental and numerical results. The ACI’s calculations were conservative when compared with the experimental or numerical results. The coefficient of variance between the ACI and experimental shear capacity results was 4.8%, while it was 9.2% between the ACI and numerical shear capacity results.

The relationship between single muscle fibre and voluntary rate of force development in young and old males.

It is suggested that the early phase (< 50ms) of force development during a muscle contraction is associated with intrinsic contractile properties, while the late phase (> 50ms) is associated with maximal force. There are no direct investigations of single muscle fibre rate of force development (RFD) as related to joint-level RFD METHODS: Sixteen healthy, young (n = 8; 26.4 ± 1.5 yrs) and old (n = 8; 70.1 ± 2.8 yrs) males performed maximal voluntary isometric contractions (MVC) and electrically evoked twitches of the knee extensors to assess RFD. Then, percutaneous muscle biopsies were taken from the vastus lateralis and chemically permeabilized, to assess single fibre function. At the joint level, older males were ~ 30% weaker and had ~ 43% and ~ 40% lower voluntary RFD values at 0-100 and 0-200ms, respectively, than the younger ones (p ≤ 0.05). MVC torque was related to every voluntary RFD epoch in the young (p ≤ 0.001), but only the 0-200ms epoch in the old (p ≤ 0.005). Twitch RFD was ~ 32% lower in the old compared to young (p < 0.05). There was a strong positive relationship between twitch RFD and voluntary RFD during the earliest time epochs in the young (≤ 100ms; p ≤ 0.01). While single fibre RFD was unrelated to joint-level RFD in the young, older adults trended (p = 0.052-0.055) towards significant relationships between joint-level RTD and Type I single fibre RFD at the 0-30ms (r2 = 0.48) and 0-50ms (r2 = 0.49) time epochs. Electrically evoked twitches are good predictors of early voluntary RFD in young, but not older adults. Only the older adults showed a potential relationship between single fibre (Type I) and joint-level rate of force development.

Restrained Shrinkage of High-Performance Ready-Mix Concrete Reinforced with Low Volume Fraction of Hybrid Fibers.

Cracking due to restrained shrinkage is a recurring issue with concrete bridge decks, impacting durability and ultimately service life. Several scholars' research has proven that the incorporation of fibers in concrete mitigates restrained shrinkage cracking when utilizing high (0.5-3%) fiber volumes. This often presents a mixing and placement issue when used for ready-mixed concretes, which discourages their use in bridge decks. This study aims to optimize the incorporation of fibers for their benefits while producing concrete that is conducive to ready-mix, jobsite use. A series of tests were performed on a high-performance concrete (HPC) mix which incorporated blended, multiple fiber types (steel crimped, macro polypropylene, and micro polypropylene) while maintaining low total fiber (0.19-0.37%) volume. These "hybrid" fiber mixes were tested for multiple mechanical properties and durability aspects, with a focus on the AASHTO T334 ring test, to evaluate fiber efficiency under restrained conditions. Promising results indicate the use of a low-volume hybrid fiber addition, incorporating a macro and micro polypropylene fiber (0.35% by volume) blend, reduced the cracking area by 16.6% when compared to HPC incorporating a single fiber type, and 39% when compared to nonfibrous HPC control mixture.

Influence of Hybrid Basalt Fibres’ Length on Fresh and Mechanical Properties of Self-Compacted Ambient-Cured Geopolymer Concrete

Recently, short basalt fibres (BFs) have been gaining considerable attention in the building materials industry because of their excellent mechanical properties and lower production cost than their counterparts. Reinforcing geopolymer composites with small volumes of fibres has been proven an efficient technique to enhance concrete’s mechanical properties and durability. However, to date, no study has investigated the effect of basalt fibers’ various lengths and volume content on self-compacted geopolymer concrete’s fresh and mechanical properties (SCGC). SCGC is prepared by mixing fly ash, slag, and micro fly ash as the binder with a solid alkali-activator compound named anhydrous sodium metasilicate (Na₂SiO₃). In the present study, a hybrid length of long and short basalt fibres with different weight contents were investigated to reap the benefits of multi-scale characteristics of a single fibre type. A total of 10 mixtures were developed incorporating a single length and a hybrid mix of long (30) mm and short (12) mm basalt fibres, with a weight of 1%, 1.5% and 2% of the total binder content, respectively. The fresh and mechanical properties of SCGC incorporating a hybrid mix of long and short basalt fibres were compared to plain SCGC and SCGC containing a single fibres length. The results indicate that the hybridization of long and short fibres in SCGC mixture yields better mechanical properties than single-length BF-reinforced SCGC. A hybrid fibre coefficient equation will be validated against the mechanical properties results obtained from the current experimental investigation on SCGC to assess its applicability for different concrete mixes.

Effects of aggregate type, aggregate pretreatment method, supplementary cementitious materials, and macro fibers on fresh and hardened properties of high‐strength all‐lightweight self‐compacting concrete

AbstractIn this research, a new high‐strength all‐lightweight self‐compacting concrete (HALSCC) was developed with a density less than 1760 kg/m3 and a compressive strength of more than 40 MPa. The effects of different parameters were investigated: pretreatment methods, binders, type of aggregates, and hybrid steel fibers on the properties of HALSCC. The experimental investigation evaluated the properties of fresh, mechanical, and microstructure of several concrete mixtures that incorporate low‐C3A cement, silica fume, metakaolin, and hybrid steel fibers. The results show that HALSCC can be developed. The binder pretreatment method could improve the compressive strength by 14.1% compared with the water pretreatment method through the strengthening of Zone 1 and Zone 2 of interfacial transition zone. Also, the mixes incorporating stalite could improve the compressive strength by 40.8% and 106% compared to the mixes with scoria and leca respectively. Hybrid length steel fibers could increase the mechanical properties when compared to a single type of fiber.

Torsional behavior of ultra-high performance concrete (UHPC) rectangular beams without steel reinforcement: Experimental investigation and theoretical analysis

Steel fiber is the main reinforcing fiber of ultra-high performance concrete (UHPC) and could greatly improve its tensile strength and toughness. As a result, steel fiber has a significant influence on the structural behavior of UHPC beams under pure torsion. However, related research in this regard is severely insufficient. To fill in this research gap, this paper presents an extensive investigation to explore the effect of steel fiber property on the torsional performance of UHPC beams without steel reinforcement. A total of 8 UHPC rectangular specimens (including one control beam without steel fibers) were tested under pure torsion until failure. The variables in the specimens included the volume fraction, type, dimension and hybrid effect of steel fibers. The failure modes, torque versus angle of twist curves, torque versus strain curves and distribution of cracks for all specimens were acquired based on the torsion tests. Results show that the addition of steel fibers significantly increased the cracking and ultimate torques of UHPC beams, with maximum increases of 79 % and 159 %, respectively. The volume content, shape and dimension of steel fibers exhibited significant influence on the torsional performance of UHPC beams, including torsional capacity, ductility and cracking pattern. The shape and dimension of steel fibers both affected the post-cracking load-carrying capacity of UHPC beams. The cracking and ultimate torques of the two UHPC beams with hybrid steel fibers were higher than those containing single type of steel fiber, both exhibiting positive hybrid effects. Based on the experimental results of this study, the hybrid use of 1 % end-hooked and 1 % long straight steel fibers is recommended in UHPC beams by comprehensively considering the torsional performance and the cost. Finally, by fully considering the excellent tensile behavior of UHPC, theoretical formulas were proposed for calculating the cracking and ultimate torques of UHPC beams without steel reinforcement based on the Bredt thin-tube theory. Comparison between the experimental and theoretical results on 36 UHPC torsional beams demonstrated the feasibility of the proposed formulas.

Properties of Slag-Fly Ash Blended Geopolymer Concrete Reinforced with Hybrid Glass Fibers

Geopolymer concrete is typically characterized by a brittle behavior and limited crack resistance. This study evaluates the performance of ambient-cured slag-fly ash blended geopolymer concrete reinforced with glass fibers. Two types of glass fibers were used exclusively or as a hybrid combination. The workability of glass fiber-reinforced geopolymer concrete was assessed using the slump, compaction factor, and vebe time. The compressive strength, splitting tensile strength, and modulus of elasticity were used to characterize the mechanical properties, while water absorption, sorptivity, abrasion resistance, and ultrasonic pulse velocity were employed in evaluating the durability. Experimental results showed that the slump and compaction factor decreased by up to 75% and 18%, respectively, with glass fiber addition but less significantly in mixes reinforced with hybrid fiber combinations. Meanwhile, the vebe time increased by up to 43%. Hybrid glass fibers led to superior mechanical and durability properties compared to plain mixes and those reinforced with a single type of glass fiber, even at higher volume fractions. The compressive strength, splitting tensile strength, and modulus of elasticity increased by up to 77%, 60%, and 85%, respectively. While the water absorption decreased by up to 42%, the sorptivity, abrasion resistance, and ultrasonic pulse velocity increased by up to 67%, 38%, and 280%, respectively. Analytical regression models were established to predict the mechanical and durability characteristics of glass fiber-reinforced slag-fly ash blended geopolymer concrete and were compared to those of design codes.

A Review: “Experimental Study on Steel Fiber Reinforced Concrete Using flat Crimped &amp; Round Crimped Type Steel Fiber.”

Abstract: Steel Fibre Reinforced Concretes are characterized by high tensile and flexural strengths and high ductility, as well as by a high compressive strength and a very good workability. Ductility and strength of concrete can be improved at lower fiber contents, where fibers are used in combination rather than reinforcement with a single type of fiber. Durability problems concerning one type of fiber may be offset with the presence of a second type of fiber. Steel Fiber is added by 1% volume of concrete. The different concrete mixesalong with control mix proportions as 100% round crimped type fiber, 50% round crimped type fiber -50% flat crimped type fiber and 100% flat crimped type fiber. Two types of crimped steel fiber i.e. round crimped type steel fiber and flat crimped steel fiber are used of length having 50mm. An extensive experimental investigation consisting of 12 specimen of size 50 x 10 x 10cm for determining flexural strength, 12 specimen for compressive strength and 12 specimen for split end test are used.In the experiment, an combination of steel fibre with concrete is used, which improved various mechanical properties and the strength. This review study is a trial of givingsome highlights for inclusion of steel fibers especially in terms of using them with new mix ratio combinations with concrete.

An experimental study of compressive toughness of Steel–Polypropylene hybrid Fibre-Reinforced concrete

The hybridized polypropylene fibre (PF)-macro steel fibre (MSF) can improve the mechanical and ductility characteristics of concrete. PF-MSF hybrid fibers are more effective in arresting cracks macro/micro than a single fiber type. This study aims to examine the effect of the PF-MSF hybrid fibres on the compressive toughness characteristics of fibre-reinforced concrete (FRC) to identify the fibers’ optimized mixture proportion. To this end, the effect of the PF, MSF, and PF-MSF hybrid fibres on the density, water absorption, and voids in concrete hardened, compressive strength, compressive toughness, and toughness index of FRC has been also examined. The conducted comparison of the above-mentioned properties between the prepared specimens with the variables involves different PF ratios, including (0%, 0.1%, 0.175, 0.25%, 1.0%) and MSF (0%, 0.75, 0.825, 0.9%, 1.0%), by volume. The experimental results showed that hybrid FRC achieved more significant improvements in compressive toughness characteristics compared with mono MSFs or PFs inclusion. The reinforced specimen with 0.1% PF-0.9% MSF hybrid FRC has accomplished higher compressive toughness of approximately 0.321 MPa, i.e., 106.5% higher than that of the controlled mix. More importantly, the most significant improvement in compressive strength with increasing density and reducing water absorption and voids has been observed for the hybrid mixture of 0.1% PF-0.9% MSF. This work on hybrid fiber-reinforced concrete is believed to provide useful insights into a more thorough understanding of the influence of hybrid fiber on concrete.

Effect of different fiber combinations and optimisation of an ultra-high performance concrete (UHPC) mix applicable in structural elements

In this study, Ultra-High Performance Concrete (UHPC) mix was optimised to expand its use in large-scale applications. Using alternative curing methods instead of heat treatment, it was aimed that UHPC will meet the required strength and workability criteria and thus be presented applicable solutions for widespread use of UHPC in engineering applications. Therefore, effect of aggregate type, fiber content, curing method, compacting method, cement type, water/cement ratio and aggregate granulometry on mechanical properties of UHPC was investigated. Compressive strength, flexural tensile strength, splitting tensile strength, pull-out behaviour, modulus of elasticity and toughness values of the UHPC series were determined. Standard water curing (compared to wet hessian application) increased the compressive strength by 11.2% and the flexural tensile strength by 19%, while the inclusion of hybrid fibers (compared to the use of a single type of fiber) increased the compressive strength by 16.7% and the flexural tensile strength by 48%. Type of aggregate was found very effective on flexural tensile strength as well, and it provided additional ductility by increasing the matrix strength. In cases where heat treatment is not available, it was observed that the required strength criteria can be met with standard water curing as well. UHPC with a compressive strength of 170 MPa, which has excellent workability, was developed. As a result of the study, optimum solutions were proposed for the widespread use of UHPC in the precast industry.