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There is a need to investigate the flexural behavior and mechanical properties of super high-performance concrete (SHPC) for a better understanding of its response to compression, tension, and bending. Super-high-performance concrete (SHPC) lies between high-performance concrete (HPC) and ultra-high-performance concrete (UHPC) in strength, durability, and workability and is suitable for sustainable buildings. This paper presents an extensive experimental and analytical study to investigate the effect of the hybridization of micro-polypropylene and macro-steel fibers on the flexural behavior and mechanical properties of super-high-performance concrete (SHPC). The hybridization of both micro-PP fibers and macro-hooked-end ST fibers gathers the benefits of their advantages and offsets their disadvantages. Three types of fibers (micro polypropylene fibers (PP), macro hooked-end steel fiber (ST), and hybrid fiber (PP + ST)) with different fiber content up to 2% were tested to study their effect on the following: (a) the workability of fresh concrete, (b) concrete compressive strength, (c) splitting tensile strength, (d) flexural behavior, including flexural tensile strength and toughness, and (e) the optimum percentage of each of the two fibers, PP and ST, in the hybrid to get the maximum structural and economic benefits of hybridization. Based upon the experimental results and using a statistical program, formulae to calculate both the tensile splitting strength ( f s p ) and the flexural tensile strength in the form of the modulus of rupture ( f c t r ) were obtained. These formulae were able to predict accurately both the splitting tensile strength and modulus of rupture for SHPC with each of the three types of fibers used in this research. Also, they were in very good agreement with the values corresponding to different experimental results of other research, which means the ability to use these equations more generally. In addition, the prediction of the additional ultimate moment provided for all fibers was investigated. This research confirms the structural and the economical efficiency of hybridization in the behavior of SHPC. It was found that the optimum percentage of the fiber volume content for the hybrid of ST and PP is 1%; 0.5% for each of the two kinds. [ABSTRACT FROM AUTHOR]

Many studies have suggested that engineered cementitious composite (ECC) could be a highly efficient and cost‐effective material for enhancing the flexural strength of reinforced concrete (RC) beams. Recently two effective retrofitting configurations using steel and polyvinyl‐alcohol hybrid fiber reinforced engineered cementitious composite (SPH‐ECC) were proposed (Qasim et al., Eng Struct, 2023, 284, p. 115992) and their high effectiveness for enhancing the flexural strength of RC beam was verified experimentally. However, to examine the performance of these strengthening configurations thoroughly by conducting experiments to cover practical ranges of design parameters is deemed to be too expensive and time consuming. In this study, a numerical parametric study of SPH‐ECC strengthened RC beams was conducted by employing a validated finite element (FE) modeling procedure developed by the authors. The effects of four key design parameters including the compressive strength of concrete and SPH‐ECC, the thickness of SPH‐ECC strengthening layer and the area of reinforcement bars embedded in SPH‐ECC layers on the flexural performance of the strengthened beams were studied. Parametric study results showed that the area of reinforcement bars in the SPH‐ECC layers could significantly affect the flexural strength of the strengthened beams. Furthermore, in order to allow engineers to predict the flexural strength of the strengthened beams quickly, two simple but accurate analytical models were also developed for the two strengthening configurations considered. Their reliability and accuracy were then verified and confirmed by comparing with the parametric study results. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) is an advanced cement-based material with excellent mechanical properties and durability. However, with the improvement of UHPC's compressive properties, its insufficient tensile properties have gradually attracted attention. This paper reviews the tensile properties of steel fibers in UHPC. The purpose is to summarize the existing research and to provide guidance for future research. The relevant papers were retrieved through three commonly used experimental methods for UHPC tensile properties (the direct tensile test, flexural test, and splitting test), and classified according to the content, length, type, and combination of the steel fibers. The results show that the direct tensile test can better reflect the true tensile strength of UHPC materials. The tensile properties of UHPC are not only related to the content, shape, length, and hybrids of the steel fibers, but also to the composition of the UHPC matrix, the orientation of the fibers, and the geometric dimensions of the specimen. The improvement of the tensile properties of the steel fiber combinations depends on the effectiveness of the synergy between the fibers. Additionally, digital image correlation (DIC) technology is mainly used for crack propagation in UHPC. The analysis of the post-crack phase of UHPC is facilitated. Theoretical models and empirical formulas for tensile properties can further deepen the understanding of UHPC tensile properties and provide suggestions for future research. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to improve the performance of desert sand concrete, polypropylene fiber (PF) and glass fiber (GF) were used to prepare desert sand concrete (DSC) with different fiber and volume content, and the basic mechanical properties, such as cube compressive, tensile and flexural strengths, were tested and studied. Based on the mercury injection method (MIP) and scanning electron microscopy (SEM), the evolution of pore structure and interface structure was analyzed. The mechanism of fiber toughening was revealed at the microscopic level. The results show that the slump of DSC decreases with the increase in fiber content. The slump of glass-fiber-reinforced DSC (GFRDSC) is smaller than that of polypropylene-fiber-reinforced DSC (PFRDSC). The strength enhancement of DSC by fibers is in the order of flexural strength > split tensile strength > compressive strength. The flexural strength of hybrid-fiber-reinforced DSC (HyFRDSC) (0.1% PF + 0.1% GF) is increased by 40.7%. Meanwhile, fibers can improve the toughness of DSC. The MIP results show that the porosity of HyFRDSC decreased by 50.01%, and the addition of fiber can effectively refine the large pore size. The SEM results show that the incorporation of PF and GF causes the formation of a uniform and dense structure between the fibers, cement and aggregate. The two can give full play to the crack-resisting and toughening effect in different loading stages, thus improving the macromechanical properties of DSC. [ABSTRACT FROM AUTHOR]

Conventional concrete significantly affects the environment due to high CO2 emission into the atmosphere during the production process. In order to improve concrete performance and arrest the incidence of global warming, the use of additive materials for cement replacement has been promoted worldwide. This study was designed to investigate the mechanical properties of high-performance fiber-reinforced concrete (HFRC) produced using rice husk ash (RHA) and hybrid fiber (HF) in accordance with the densified mixture design algorithm (DMDA) mix design method. Samples were produced using RHA as a direct replacement for cement at 10%, 20%, and 30%. HF, comprising steel and polypropylene fibers, was added (by volume) to the 20% RHA group mixture to improve the HFRC sample properties. Based on the experimental results, higher RHA contents had a generally negative effect on the fresh properties of the HFRC mixtures. Compressive strength values ranged from 53 to 72 MPa with various RHA and HF content. RHA replacement levels up to 20% had an insignificant effect on the strength development and dynamic modulus of the HFRC samples. However, the addition of HF improved splitting tensile strength, flexural strength, and dynamic modulus remarkably at all curing ages. Furthermore, the 91-day drying shrinkage was in the ranges of 0.032%–0.039% and 0.023%–0.034% using different RHA and HF levels, respectively. Increasing both RHA and HF contents significantly reduced drying shrinkage in the samples. Multivariable regression was also performed, clarifying that all tested results were consistent and had good correlations. The results of this study also provide a potentially effective use for abundantly available industrial waste products such as fly ash (FA) and RHA to promote the production of greener and more sustainable concrete. [ABSTRACT FROM AUTHOR]

In this study, the macro‐synthetic polypropylene fibers Forta and Barchip are used. The fibers are added at 0.5%, 1%, 1.5%, and 2% by weight of cement. Additionally, various fiber combinations with varying percentages are employed to create the concrete. Cubic specimens, bending beams, and impact specimens are all prepared on a percentage basis of fiber. The findings indicated that utilizing 1.5% fibrillated Forta fibers raised the compressive strength of the concrete by 18% and the flexural strength of the concrete by 58%. By increasing the usage of Barchip single‐strand fibers by 1.5%, the compressive strength increased by 36%, and the flexural strength increased by 89%. The highest ductility rate refers to the specimen containing 1.5% Forta fiber, with an energy capacity of 672 J. All the hybrid samples also possess a high ductility ratio. Forta fibrillated fibers are more effective in ductility, while Barchip monofilament fiber types can impressively increase the flexural strength of concrete. The hybrid usage of fibers improved compressive strength by 32% and flexural strength by 85%. Additionally, by combining fibers in hybrid form, energy absorption, ductility, impact resistance, and residual flexural strength are increased by 22, 2.3, 3.6, and 5.6 times, respectively, over the control sample. [ABSTRACT FROM AUTHOR]

In this work, to estimate the compressive, splitting tensile, and flexural strength of self‐compacting concrete (SCC) having single fiber and binary, ternary, and quaternary fiber hybridization, the deep‐learning (DL) and support vector regression (SVR) models were devised. The fiber content and coarse aggregate/total aggregate ratio (CA/TA) were the variables for 24 designed mixtures. Four different fibers, which were a macro steel fiber, two types of micro steel fibers with different aspect ratio, and polyvinyl alcohol (PVA) fiber, were used in SCC mixtures. The specimens of each mixture were tested to measure the engineering properties for 7, 28, and 90 days. The amount of cement, fly ash, fine aggregate, CA, high‐range water‐reducing admixture, water, macro steel fiber, PVA fiber, two types of micro steel fibers, and curing time were selected as input layers while the output layers were strength results. The experimental results were compared with the estimation results. The engineering properties were estimated using the SVR model with 95.25%, 87.81%, and 93.89% accuracy, respectively. Furthermore, the DL model estimated compressive strength, tensile strength, and flexural strength with 99.27%, 98.59%, and 99.15% accuracy, respectively. It was found that the DL estimated the engineering properties of hybrid fiber–reinforced SCC with higher accuracy than SVR. [ABSTRACT FROM AUTHOR]

Rigid pavements have high compressive strength and low flexural strength due to the brittleness of concrete. This leads to the formation of cracks easily under the applied loads of vehicles; therefore, the design of concrete pavements usually leads to an increase in the high thicknesses. Hybrid steel fibers are used in concrete to increase flexural strength and minimize crack formation. Using concrete with steel fibers in pavements reduces the required concrete thickness. In recent decades, the application of the finite element method to predict the behavior of rigid pavements has increased. This study investigates the influence of hybrid steel fiber on the behavior of rigid pavements; a finite element modeling approach is used to simulate the case study. Several parameters are entered and investigated in this study, including the proportion mix of hybrid fiber concrete (HFC), which contains 0.2% macro synthetic fibers and 0.68, 0.8, and 0.96% of steel fibers, compressive strengths of 25, 35, and 45 MPa, slab thicknesses of 150, 200, and 250 mm, and the load of the tandem axle at the edge of mid slab on the Winkler foundation. The ATENA software package is used to perform a nonlinear finite element analysis. Thirty-six rigid specimen pavements with dimensions of 3600 × 3600 mm were modeled in this investigation. The results showed that the addition ratio (0.68 + 0.2)% of hybrid fibers is more effective in improving the load bearing capacity with a slab thickness of 150 mm and 25 MPa compressive strength. [ABSTRACT FROM AUTHOR]

To create cost-effective structures, the modern construction industry has sought to reduce the dead load of buildings. Lightweight concrete is a quick way to reduce dead load. The current study is primarily concerned with identifying modern substitutes for coarse aggregate likely to aid in waste management and offer potential alternatives to the most exploited natural resources. According to ACI C 39-M, this study developed a novel lightweight hybrid fiber-reinforced concrete (LWHFRC) with a density of less than 1825 kg/m3 and compressive strength of 50 to 75 MPa. Ordinary Portland cement (53 Grade) was mixed with fly ash, silica fume, and GGBS. Sintered fly ash aggregate (SFA) and palm oil shell aggregate (POS) were used as coarse aggregates. Hooked steel fibers and polyvinyl alcohol fibers were combined in a hybrid form to improve crack propagation properties at the initial and subsequent stages. The water-to-binder ratio was kept constant at 0.30 to 0.35 with a 1% superplasticizer. Four volume fractions of hybrid fibers (both steel and PVA with Vf = 0%, 1%, 1.5%, and 2%) were added. In addition, XRD, SEM, EDS, and EDS mapping tests were performed to finalize the material's chemical composition and crystalline structure. Furthermore, beams and cylinders were tested to determine the modulus of rupture, which was determined to be between 9.5 and 14 MPa by ACI code C 1609-M, and indirect tensile strength, achieved as 10 to 14 MPa by ACI code C 496-M. The researcher altered the modulus of elasticity (Ec) formula for lightweight concrete and discovered a relationship between fc' and fcb, fc' and fspt, and fcb and fspt. Finally, ANOVA and regression tests were run to check the significance of the experiment. The cost analysis revealed that the cost of LWHFRC increased by approximately 16.46%, while the strength increased by 55.98% compared to regular concrete. [ABSTRACT FROM AUTHOR]

The carbon-nylon hybrid fibers were employed to modify the silica sol shell for investment casting, and these shells were sintered in vacuum. An optimized mixing process was applied to improve the dispersion of hybrid fibers in slurry, then resulting in the excellent slurry uniformity. The modified shell fabricated by slurry with 4 g/L hybrid fiber displays a higher sintered strength of 5.46 MPa, which is derived from the increased crack propagation path and the dissipated more loading energy through interfacial debonding and friction of the remained carbon fiber pull-out. In addition, the permeabilities of silica sol shells are obviously improved due to the existence of holes in matrix resulted from the melting of nylon fibers during the sintering process. Also importantly, the hybrid fibers modified shell exhibit a good heat transfer efficiency, which is related to the formed heat transfer channels caused by the remained carbon fibers in sintered shell. • An effective mixing process was applied to achieve the uniform distribution of hybrid fibers. • The carbon-nylon hybrid fibers modified ceramic shells were sintered in vacuum. • The 4 g/L hybrid fibers modified shell exhibits an enhanced green strength of 4.2 MPa and sintered strength of 5.46 MPa. • The shell showed a strengthening heat transfer with the addition of hybrid fibers. [ABSTRACT FROM AUTHOR]

"Concrete with numerous short irregular separate low and high modulus fiber is one amongst the distinctive and elite exhibition concrete. Advancement of such substantial builds the wide use of fiber designed up concrete in several framework applications. during this beta review, low modulus and high modulus filaments are used to foster the crossover fiber supported cement. Steel fiber is taken as high modulus fiber and plastic, reused polythene terephthalate fiber is taken as an occasional modulus fiber. completely 10 blends were used for examination together with ancient cement. Three mono fiber blends created utilizing steel, polypropene and reused polythene terephthalate strands with 0.5% volume half. Six crossover fiber utilizing steel fiber and polypropene fiber with 3 distinct volume division and steel fiber and reused polythene terephthalate fiber with 3 distinctive volume portion was utilised being scrutinized. mix in with 0.25% volume portion steel fiber and 0.25% volume division polypropene fiber show higher compared to totally different blends.". [ABSTRACT FROM AUTHOR]

Fiber concretes, as a new generations of concrete, have considerably attracted the attention of researchers and engineers for a couple of decades. Fibers play a very important role for improving the weaknesses of concrete, including the tensile and flexural strengths of concrete. In this paper, the effect of length and percentage of steel fibers on the tensile and compressive strengths of concrete is investigated. For this propose, three concrete samples including plain concrete and fiber concretes with steel fibers with lengths of 3 and 5 cm each with different volume ratios (i.e., 0.5, 1, and 1.5%) have been tested. In addition, the samples of the plain concrete are made to determine the effect of fibers on the strength of the concrete. Afterward, using the hydrulic jack machine, both tension and compression strength tests are performed on the concrete specimens. Based on the obtained results, it is observed that with increasing the length and percentage of steel fibers, the tensile and compressive strengths of the concrete specimens are increased. Furtheromre, the samples containing a combination of 3 and 5 cm steel fibers in concrete have lower strength than samples with only 5 cm fibers and more strength than samples with only 3 cm fibers. According to experiments, in order to increase the tensile and compressive strength of concrete, the use of 5 cm steel fibers with different percentages is preferable to 3 cm steel fibers. [ABSTRACT FROM AUTHOR]

In this paper, basalt fiber (BF) and polyethylene fiber (PE) were mixed into cement matrix to prepare a new hybrid fiber Engineered Cementitious Composite. The Box-Behnken experimental design method within the Response Surface Methodology (RSM) was employed, the effects of water-binder ratio, sand-binder ratio and fiber content on compressive strength, flexural strength and equivalent bending toughness of hybrid fiber ECC were studied. Analysis of variance (ANOVA) was used to verify and optimize the model equation, and the ratio of water-binder ratio 0.2, sand-binder ratio 0.35, BF content 1.25%, PE content 1% was obtained. The results show that the synergistic effect of PE and BF has a favorable effect on the mechanical properties of hybrid fiber ECC. PE can achieve high energy absorption and maintain high strain capacity of matrix. BF increases the strength of the specimen. When the BF content increases from 0.9% to 1.2%, the compressive strength increases by 9.6%. The fiber content is highly sensitive to flexural strength and equivalent bending toughness, and the significance level of each factor is more than 95%. The significance level of each factor is BF content > sand-binder ratio > water-binder ratio. The experiment verified that the established prediction model has high accuracy, and the relative error between the optimized RSM value and the experimental value is less than 5%. To provide a certain reference for the design of ECC mix proportions for preparing multi strength and multi toughness series. • Using RSM to predict and optimize the ratio of ECC based on performance orientation. • The significance of BF in flexural strength and bending toughness exceeds 95%. • The RSM prediction model has high accuracy and an error of less than 5%. [ABSTRACT FROM AUTHOR]

Fiber reinforced concrete (FRC) is presently being replaced with plain concrete for its superior performance. In most cases, FRC contains just a single kind of fiber. The utilization of at least two kinds of fibers in an appropriate mix can possibly improve the mechanical properties of concrete and result in performance synergy. This paper explores the effect of using steel fiber and polypropylene fiber for reinforcing the concrete to quantify the mechanical properties of the concrete composite. The purpose of this research was to analyze the flexural strength, tensile strength, sorptivity and elasticity modulus of steel, and polypropylene hybrid fiber composite. Crimped steel fibers in conjunction with polypropylene fiber at different volume fractions were utilized. A nondestructive methodology in light of ultrasonic pulse velocity measurements was utilized to evaluate the dynamic elastic modulus. The scanning electron microscope was used to assess the properties of the concrete mixtures, the interfacial bond between fiber and the concrete matrix. The results were analyzed to evaluate fiber synergy if any associated with different volume fractions of fiber. The paper identifies the volume fraction of hybrid fiber that demonstrates maximum synergy under the essential mechanical properties of steel‐polypropylene hybrid fiber reinforced concrete. [ABSTRACT FROM AUTHOR]

The main purpose of this research is to assess the influence of different design parameters on the mechanical performance of high-performance fiber-reinforced concrete (HPFRC) mixtures. Special attention is also paid to achieving deflection-hardening behavior in the presence of a large amount of coarse aggregates. Different mixture design parameters were the initial curing ages (3, 7, 28, and 90 days), ratios of Class F fly ash (FA) to portland cement (PC) (0.0, 0.2, and 0.4), addition/type of nanomaterials [nanosilica (NS), nanoalumina (NA), and nanocalcite (NC)], and combinations of fibers [polyvinyl-alcohol + steel (P, S) or brass-coated microsteel + steel (B, S)]. The experimental program included the evaluation of compressive strength, flexural strength, and midspan deflection results in addition to test parameters recorded under biaxial flexural loading via a series of square panel tests, including peak load and energy absorption capacities. Test results revealed that deflection-hardening response coupled with multiple microcracks can be obtained when large amounts of coarse aggregates are available for all HPFRC mixtures. As expected, experimental results change depending on the different curing ages and FA/PC ratios. The most distinctive parameters affecting the results are addition/type of nanomaterials and the presence of different fiber combinations. In the presence of nanomaterials, all results from the different tests improved, especially for NA and NS inclusions. With slight concessions in flexural deflection results, B fiber is shown to be a successful candidate to fully replace costly P fibers because most properties of B, S fiber-reinforced HPFRC mixtures outperformed those with P, S fibers, both under four-point bending and biaxial flexural loading. [ABSTRACT FROM AUTHOR]

Currently, fiber-reinforced thermoplastic composites are widely applied in structural applications. It has great potential to replace metal structures and provides advantages in weight reduction. In this study, the pretensioned unidirectional carbon fiber was overmolded by Polyamide 6 contained 30%wt of glass fibers (PA 6-30GF). Process parameters such as injection pressure, melting temperature, duration of carbon fiber cryogenic treatment, and fiber pretension were optimized to maximize the flexural strength, impact strength, and interlaminar properties of the hybrid composite. The relationship between factors and responses was analyzed using Box–Behnken design (BBD) from response surface methodology (RSM) and analysis of variance (ANOVA). Three levels were assigned for each factor. There were 27 experimental trials carried out, and a significant regression for the coefficient between the factors was derived. The BBD and ANOVA analysis demonstrate that the predicted values from the model are in satisfactory correlation with the experimental results. The optimum responses found were achieved by setting the following injection molding parameters: melting temperature of 278 °C and injection pressure of 122 bar. Carbon fiber, as a unidirectional reinforcement, should be immersed in liquid nitrogen for 10 min and mounted on the mold in a pretensioned state with a force of 100 N. The combination of these parameters can produce an optimum flexural strength of 248.6 Mpa, impact strength of 173.4 kJ/m2 and an ILSS of 30.4 Mpa.

• The purpose of this study is to establish a suitable fiber combination for high strength high volume fly ash (HVFA) concrete. • Use of eco-friendly, nontoxic, lightweight and low cost silane coated basalt fiber. • Establish the prediction equations for compressive and flexural strength of HVFA mortar. • Determine the mechanical and durability performance of hybrid fiber reinforced HVFA concrete. High volume fly ash (HVFA) is used as cement substitute in many cementitious materials. In recent years, hybrid fibers such as steel and polypropylene have been added to improve the mechanical characteristics. The usage of three fibers combinations is relatively a new concept in HVFA concrete. In this paper, silane coated basalt fiber has been combined with steel and polypropylene due its availability and low costs. Varied hybrid fiber combinations (both two types and three types) were tested on cement mortar specimens to identify the optimal fiber percentages. Based on the experimental results, equations to predict the compressive and flexural strength were developed. Optimal percentages identified from the experimental data were then used to test concrete specimens. It was found that the compressive strengths of three types hybrid fiber concrete showed appreciable increase by 5.44% and the splitting tensile strength increase was 6.77% in comparison with two type hybrid. Furthermore, the long-term durability issue of the selected basalt fiber was examined using the Scanning Electron Microscopy (SEM) and Computed Tomography (CT) X-ray scan. These two techniques confirmed the reduction in porosity and hence the durability of concrete, suggesting the benefit of the added silane coated basalt fiber. [ABSTRACT FROM AUTHOR]

Summary: Fire safety should consider not only the performance of the structure after the fire but also the behavior during the fire. The structural fire reliability performance of hybrid PVA fiber reinforced ferrocement (HFF) panels is experimentally determined based on its flexural characteristics and damage during the exposure to elevated temperatures. The residual compressive strength of 60 cubs was also tested after exposed to temperatures. In addition, 30 HFF panels were tested to evaluate their structural capacity by conducting an in‐situ binding test during the heating of up to 200°C, 400°C, 600°C, and 800°C, and compared with control samples tested at ambient (24°C) temperature condition. The main parameters investigated were the specimen thickness and the effect of using mineral admixtures (fly ash and silica fume) in the mortar mixtures. The results show a strength decline of both flexural and compressive strengths as temperature increases. The bending capacity at 800°C is reduced to about 90% of the ambient capacity only. In between the 2 temperatures, the reduction rate is found to be almost linear. A theoretical prediction of the moment capacity reduction shows a good agreement with the test results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of hybrid fibers on properties of DGCCMs were discussed. • The enhancement mechanism of BF and PVAF was revealed. • The effects of hybrid fibers were quantified by orthogonal test results. Basalt fiber (BF) and polyvinyl alcohol fiber (PVAF) were mixed into desulfurized gypsum-based composite cementitious material (DGCCM) by an orthogonal test to prepare hybrid fiber-reinforced DGCCM, whose mechanical properties, water resistance, and durability were studied using visual, range, variance, and microstructure analyses. The results show that combining the two fibers improved the mechanical properties, water resistance, and durability of DGCCM. In terms of mechanical properties, the maximum absolute dry flexural strength and compressive strength increased by 70.05% and 64.52%, respectively, compared with the blank group. PVAF played a better role than BF in crack resistance and toughening, hence contributing more. When the content of PVFA and BF increased to 0.5% and 0.75%, respectively, the water resistance of hybrid fiber-reinforced DGCCM was better. The enhancement showed that BF had a more significant effect on the softening coefficient of DGCCM than PVAF. The incorporation of fibers inhibits the generation of a large number of cracks during the dry-wet and freeze–thaw cycles of DGCCM, which greatly improves its durability. When the content of PVAF and BF were both increased to 0.5%, the durability of hybrid fiber-reinforced DGCCM was better. [ABSTRACT FROM AUTHOR]

In order to evaluate the effect of hybrid fibers on the flexural performance of tunnel segment at room temperature, twelve reinforced self-consolidating concrete (SCC) symmetric inclination beams containing steel fiber, macro polypropylene fiber, micro polypropylene fiber, and their hybridizations were studied under combined loading of flexure and axial compression. The results indicate that the addition of mono steel fiber and hybrid fibers can enhance the ultimate bearing capacity and cracking behavior of tested beams. These improvements can be further enhanced along with increasing the content of steel fiber and macro PP fiber, but reduced with the increase of the reinforcement ratio of beams. The hybrid effect of steel fiber and macro PP fiber was the most obvious. However, the addition of micro PP fibers led to a degradation to the flexural performance of reinforced beams at room temperature. Meanwhile, the hybrid use of steel fiber and micro polypropylene fiber didn't present an obvious improvement to SCC beams. Compared to micro polypropylene fiber, the macro polypropylene fiber plays a more prominent role on affecting the structural behavior of SCC beams. A calculation method for ultimate bearing capacity of flexural SCC symmetric inclination beams at room temperature by taking appropriate effect of hybrid fibers into consideration was proposed. The prediction results using the proposed model are compared with the experimental data in this study and other literature. The results indicate that the proposed model can estimate the ultimate bearing capacity of SCC symmetric inclination beams containing hybrid fibers subjected to combined action of flexure and axial compression at room temperature. [ABSTRACT FROM AUTHOR]

Copyright of Tikrit Journal of Engineering Sciences is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper investigated the mechanical properties and elevated temperature resistance of sisal fibers and steel fibers hybridization reinforced ultra-high performance concrete (UHPC). The compressive strength, flexural strength, and toughness of UHPC before and after exposure to elevated temperature were measured. Moreover, the spalling behavior, gas permeability, and sorptivity of hybrid fiber reinforced UHPC after the elevated temperature exposure was also studied. The spalling resistance mechanism was elucidated by thermal analysis and microstructure observation. The result shows that hybridization of sisal fibers and steel fibers exhibits an excellent synergy effect on improving the mechanical properties of UHPC before and after elevated temperature exposure. The addition of sisal fibers significantly increases the gas permeability of UHPC, hence the spalling of UHPC at elevated temperatures was prevented efficiently. A sisal fiber content of 0.6 vol% was most favorable in terms of improving the residual mechanical properties. Sisal fibers can increase the porosity of UHPC after elevated temperature exposure as indicated by sorptivity results, therefore excessive sisal fibers impaired the residual mechanical properties. This study provides new insights into the utilization of natural sisal fibers to produce sustainable and cost-effective UHPC with high spalling resistance characteristics at elevated temperatures. [ABSTRACT FROM AUTHOR]

Injection overmolding was used to produce hybrid unidirectional continuous-short carbon fiber reinforced polypropylene. Polypropylene pellets containing short carbon fibers were melted and overmolded on unidirectional carbon fibers, which act as the core of the composite structure. Four factors were varied in this study: fiber pretension applied to unidirectional fibers, injection pressure, melting temperature, and backpressure used for melting and injecting the composite pellet. This study aimed to evaluate the effect of these factors on fiber volume fraction, flexural strength, and impact strength of the hybrid composite. The relationship between factors and responses was analyzed using Box–Behnken Response Surface Methodology (RSM) and analysis of variance (ANOVA). Each aspect was divided into three levels. There were 27 experimental runs carried out, with three replicated center points. The results showed that the injection molding process parameters had no significant effect on the fiber's volume fraction. On the other hand, melting temperature and fiber pretension significantly affected impact strength and flexural strength. [ABSTRACT FROM AUTHOR]

Currently, fiber-reinforced thermoplastic composites are widely applied in structural applications. It has great potential to replace metal structures and provides advantages in weight reduction. In this study, the pretensioned unidirectional carbon fiber was overmolded by Polyamide 6 contained 30%wt of glass fibers (PA 6-30GF). Process parameters such as injection pressure, melting temperature, duration of carbon fiber cryogenic treatment, and fiber pretension were optimized to maximize the flexural strength, impact strength, and interlaminar properties of the hybrid composite. The relationship between factors and responses was analyzed using Box–Behnken design (BBD) from response surface methodology (RSM) and analysis of variance (ANOVA). Three levels were assigned for each factor. There were 27 experimental trials carried out, and a significant regression for the coefficient between the factors was derived. The BBD and ANOVA analysis demonstrate that the predicted values from the model are in satisfactory correlation with the experimental results. The optimum responses found were achieved by setting the following injection molding parameters: melting temperature of 278 °C and injection pressure of 122 bar. Carbon fiber, as a unidirectional reinforcement, should be immersed in liquid nitrogen for 10 min and mounted on the mold in a pretensioned state with a force of 100 N. The combination of these parameters can produce an optimum flexural strength of 248.6 Mpa, impact strength of 173.4 kJ/m2 and an ILSS of 30.4 Mpa. [ABSTRACT FROM AUTHOR]

• Development and effects of filler on properties of hybrid/twisted natural FRP composites. • Better mechanical properties with HIRDLLF and THIRDLLF samples at warp direction. • HIRDLBF samples recorded optimum mechanical properties at weft direction. • THIRFSLF samples significantly increased in properties than corresponding THIRFSL at warp direction. • Demonstration of applicability of the innovative twisted hybrid natural FRP composites. This paper focuses on hybrid and twisted hybrid Indian mallow/roselle cellulosic fiber yarn mat reinforced polyester composites and effects of their wood sawdust filler. The composite materials were fabricated usingcompression moldingtechnique. There were four different combinations of hybrid yarn mat composite samples used, while the twisted hybrids were six. An evaluation of the hybrid and twisted hybrid mechanical properties for the single and double layer cases of the yarn mat was done with and without wood sawdust filler effects. The samples were tested at both warp and weft directions. From the results obtained at warp direction, it was observed that for the hybrid double layer case, longitudinal yarn mat with wood sawdust (filler) composite sampleexhibited better tensile, impact and flexural strength properties in comparison with other related composites of hybrid type reported in literature. Moreover, the modified twisted hybrid double layer composites with longitudinal yarn mat andwood sawdust fillersamplerecorded significantly greater improvement on the mechanical properties at warp direction, when compared with the hybrid double layer longitudinal yarn mat composites with wood sawdust filler and other reported similar hybrid composite materials. Scanning electron microscopy (SEM) technique was utilized to evaluate morphological internal damage (cracks) and fractured surfaces of the various tested composite samples. Based on their mechanical performances and for further practical evidence, these two types of eco-composites were used to effectively fabricate tri-wheeler auto-wheel hubs and ceiling fan blades, as applicable to automobile and electronics industries, respectively. [ABSTRACT FROM AUTHOR]

• Recycled steel and coper fibers were used to improve the tensile behaviour of cement mortar. • The tensile behaviour of the mortar was evaluated using direct and indirect tensile strength tests. • The fibers were added using different combinations and ratios. • The direct tensile strength increases with the increase in fibers ratio. • The direct tensile strength is nearly about 55% of the flexural tensile strength as average. This study aims to improve the tensile strength of cement mortar using recycled short copper fibers (CE) from wastes of electrical connection wires and long steel fibers from galvanized binding wires (GB). Therefore, a series of direct tensile tests were performed to investigate the tensile behavior of mono and hybrid fiber reinforced cement mortar in addition to compressive and flexural strengths properties. Different hybrid ratios (CE: GB = 0: 100, 100: 0, 50: 50, 30: 70, and 70: 30) % and fiber volume contents (0.5, 0.75, 1, 1.5 and 2)% were studied to investigate their effects on the tensile behavior. The test results revealed the following: (i) the (GB) fibers improve the flexural strength in all volume fraction ratio when compared with (CE) fibers and the optimum ratio was 1%. While for mixtures with hybrid fibers, the (30%CE to 70%GB) combination gives the highest percentage increase in flexural strength at 1.5% volume content when compared with all other mixtures; (ii) for both types (GB) and (CE) fibers, the direct tensile strength increases with the increase in volume fraction ratio till 1.5%. While, for hybrid fibers, the direct tensile strength increases with the increase in fibers ratio for all volume contents and for all combinations; (iii) the largest increase in direct tensile strength is observed at 1.5% volume content of (GB) fibers and give the highest values in comparison with (CE) fibers and hybrid fibers in all mixes; (iv) the brittleness ratio ranges between (4%-8%), (5%-10%) and (4.5%-9.5%) for (CE), (GB) and hybrid fibers cement mortar, respectively. And the direct tensile strength is nearly about 55% of flexural tensile strength as average for all fibrous cement mortar. [ABSTRACT FROM AUTHOR]