Fiber-reinforced Concrete Mixes Research Articles

An Investigation of Mechanical Properties of Recycled Carbon Fiber Reinforced Ultra-High-Performance Concrete.

Carbon fiber-reinforced concrete as a structural material is attractive for civil infrastructure because of its light weight, high strength, and resistance to corrosion. Ultra-high performance concrete, possessing excellent mechanical properties, utilizes randomly oriented one-inch long steel fibers that are 200 microns in diameter, increasing the concrete's strength and durability, where steel fibers carry the tensile stress within the concrete similar to traditional rebar reinforcement and provide ductility. Virgin carbon fiber remains a market entry barrier for the high-volume production of fiber-reinforced concrete mix designs. In this research, the use of recycled carbon fiber to produce ultra-high-performance concrete is demonstrated for the first time. Recycled carbon fibers are a promising solution to mitigate costs and increase sustainability while retaining attractive mechanical properties as a reinforcement for concrete. A comprehensive study of process structure-properties relationships is conducted in this study for the use of recycled carbon fibers in ultra-high performance concrete. Factors such as pore formation and poor fiber distribution that can significantly affect its mechanical properties are evaluated. A mix design consisting of recycled carbon fiber and ultra-high-performance concrete was evaluated for mechanical properties and compared to an aerospace-grade and low-cost commercial carbon fiber with the same mix design. Additionally, the microstructure of concrete samples is evaluated non-destructively using high-resolution micro X-ray computed tomography to obtain 3D quantitative spatial pore size distribution information and fiber clumping. This study examines the compression, tension, and flexural properties of recycled carbon fibers reinforced concrete considering the microstructure of the concrete resulting from fiber dispersion.

Research on fiber reinforced concrete and its performance prediction method and mix design method

To better solve the problems of performance prediction and mix design of fiber reinforced concrete (FRC), this paper carried out relevant research based on different kinds of fibers. First, according to the existing results and experimental research, fibers of various scales are selected preliminarily. Then, based on the mechanical property test, the fiber selection, fiber content and fiber hybrid mode are studied, and the fiber action mechanism is revealed through the failure process analysis and microscopic observation. Then, based on the newly constructed fiber reinforcement factor (S), a FRC strength prediction model was established. Finally, by combining S with hybrid fiber effect coefficient (RH) based on comprehensive properties, a method for FRC mix design is formed. The research results and conclusions are as follows: Steel fiber (SF), Short macroscopic polyvinyl alcohol fiber (SMP), fine polyvinyl alcohol fiber (PVA) and Calcium carbonate whisker (CW) have better performance improvement effects in their respective scales, and the content of SF, SMP, PVA and CW with the highest cost performance ratio is 2%, 0.75%, 0.5% and 1% respectively. Micro observation shows that CW not only has the effect of “micro filler” and “microfiber”, but also has the effect of friction resistance at the interface between reinforcement fiber and substrate. According to the mechanical property data and RH value, the best sample group is the sample containing 1.5% SF, 0.5% SMP and 1% CW. In addition, 1.5% SF and 0.5% SMP can also produce good performance when mixed with 1% CW respectively. The regression analysis results show that the FRC strength prediction model established in this paper has good regression coefficients. The mix design method of FRC based on S and RH can provide reference for the research and production of FRC.

Study on Early-Age Elastic Modulus of FRC Using Electrical Resistivity and Resonance Frequency

The correlation between surface electrical resistivity and modulus of elasticity of fiber-reinforced concrete (FRC) was studied within early ages in this study as a novel nondestructive method for predicting the modulus of elasticity of FRC. In addition to the relationship of the two quantities, the influence of various discrete fibers such as glass, nylon, polypropylene, and steel on the early age properties of FRC was investigated. Twenty-one FRC mixes were designed and tested; including four fiber types, three different fiber volume fractions for each fiber type, and three different water-to-cement ratios for all the different mixes. The surface electrical resistivity meter and resonance testing gauge were used to measure each specimen’s surface electrical resistivity and modulus of elasticity. Early-age dynamic modulus of FRC may be predicted using the mechanical properties and dimension of the fiber, according to proposed mathematical calculations. Statistical analysis was performed on the experimental results and the results acquired by the proposed equations, to examine and proof the accuracy of the proposed equations. The acceptable coefficient of variation of 5–9 percent confirmed the good agreement between the measured and predicted values.

Influence of Magnetized Water on Mechanical Properties and Durability of Recycled Aggregate Concrete

The main objective of this study was to investigate the influence of using magnetized water on the mechanical properties and durability behavior in terms of freeze-thaw resistance of recycled aggregate concrete. In addition to the effect of different numbers of water rounds in the magnetic field, other variables including steel fibers, super-plasticizers and silica-fume were considered in the concrete production in order to achieve the ideal possible performance for recycled aggregate concrete made with 100% coarse aggregates replacements. For this purpose, a total of 11 concrete mixes were prepared and tested. At the first step, the effects of the mentioned variables on the basic properties, including workability, water absorption, compressive strength, splitting tensile strength, flexural strength and freeze-thaw durability test were investigated. Additionally, flexural toughness was evaluated in accordance with the post-crack strength (PCS) method and the microstructure of concrete specimens was also observed by using scanning electron microscope (SEM). The results of most experiments indicated that magnetized water, although highly effective on the mechanical properties of concrete, should not be solely utilized as a compensating factor for the defects caused by recycled coarse aggregates. The optimum toughness and durability results regarding the fiber-reinforced concrete mixes produced with recycled coarse aggregates, were related to samples containing silica-fume and 10-rounds magnetized water. Furthermore, the existence of cement replaced by 10% of silica-fume and 10-rounds magnetized water in the concrete mix MW-SF2, increased the durability of the recycled aggregate concrete by an average of approximately 63%.

МЕХАНИЧЕСКАЯ ТЕХНОЛОГИЯ СОЗДАНИЯ ПЛИТНЫХ ФИБРОБЕТОННЫХ И ФИБРОЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ С НАПРАВЛЕННОЙ ОРИЕНТАЦИЕЙ ФИБР В ДВУХ НАПРАВЛЕНИЯХ

A modified mobile installation has been developed for creating slab fiber-reinforced concrete and fiber-reinforced concrete elements with a directional orientation of the fibers in two directions according to the proposed mechanical technology. The presented mechanical technology for creating slab fiber-reinforced concrete and fiber-reinforced concrete elements will make it possible to provide a mutually perpendicular orientation of the fibers in various layers of the structure, which will allow for the most complete inclusion of each fiber fiber into the work of the element. Also, due to the use of a mobile installation for laying fiber-reinforced concrete mix, specially designed and modified to work with slab elements, a uniform distribution of fibers in the body of concrete will be mechanically ensured.

The Applicability of TOPSIS- and Fuzzy TOPSIS-Based Taguchi Optimization Approaches in Obtaining Optimal Fiber-Reinforced Concrete Mix Proportions

This research aims to illustrate and express the impact of analytical techniques such as TOPSIS- and FTOPSIS-based Taguchi models on obtaining the optimum design of fiber-reinforced concrete (FRC).Three levels of silica fume content, fly ash content, water-to-cementitious (W/C) ratio, and superplasticizer content were examined in the present work. However, the steel fiber content (1%) and the maximum aggregate size of 14 mm were kept constant for all mixes. Once the experimental results were obtained following Taguchi’s method, it was used as input data to the TOPSIS and FTOPSIS models. The optimum set of mixture factor levels was determined by identifying the two modules. The optimal FRC mix proportions obtained from the TOPSIS- and FTOPSIS-based Taguchi model were 5% silica fume content, 0% fly ash content, 0.27 W/C ratio, and 0.5% superplasticizer. Multi-response optimization approaches are essential to optimize the concrete mix proportions to achieve the required strengths, workability, and production cost. ANOVA was used to analyze the experimental results to find the contribution of each independent variable to the compressive strength and splitting tensile strength of FRC. ANOVA showed that the most predominant factor that affects the FRC mix proportions was the W/C ratio, followed by the fly ash, silica fume, and superplasticizer contents, respectively, in descending order.

COMPARISON OF FIBER CONCRETE PROPERTIES FOR INDUSTRIAL FLOORS AND ROAD PAVEMENTS WITH STEEL AND POLYPROPYLENE FIBER

The article presents a comparative analysis of the type of dispersed reinforcement effect with steel fiber produced by «Stalkanat-Silur» (50 mm length, ⌀1 mm) and polypropylene fiber «Baumesh» produced by BAUTECH-Ukraine LLC (36 mm length, ⌀0.68 mm) on physical and mechanical properties and failure mode of fiber-reinforced concrete samples for cement concrete pavements and industrial floors. The indicators of strength and durability as one of the most important concrete properties for pavement structures, that are constantly operate under the influence of high dynamic loads were determined. The possibility of using the studied compositions of concrete with structural fiber of different types is analyzed. All concrete mixtures had equal workability S4. For fiber-reinforced concrete mix preparation, Portland cement ПЦ II/А-Ш-500 (CEM II/A-S 42.5 R), crushed stone 5-20 mm and sand with a fineness modulus of 2.75 were used. Polycarboxylate superplasticizer MC-PowerFlow 3200 was used to achieve the required workability of fiber concrete mixtures. It has been established that the use of dispersed reinforcement increases the concrete compressive strength by 13-16%, flexural strength increases by 30-31%, and the abrasion resistance decreases by 31-39%. The use of dispersed reinforcement with «Baumesh» polypropylene fiber in an amount of up to 3 kg/m3 makes it possible to increase the compressive and flexural concrete strength and also to reduce its abrasion resistance on the same scale as the use of dispersed reinforcement with steel anchor fiber «Stalkanat-Silur» up to 25 kg/m3. In this case, from an economic point of view, the use of polypropylene fiber is more appropriate. The optimal content of dispersed reinforcement to increase the strength and abrasion resistance in the fiber-reinforced concrete composition was determined. The fiber-reinforced concrete compositions with steel and polypropylene fibers of compressive strength grade C25/30, and flexural strength grade Btb 3.6, with an increased abrasion resistance were obtained.

Mechanical Experiments on Concrete with Hybrid Fiber Reinforcement for Structural Rehabilitation.

Reinforced concrete is used in the construction of bridges, buildings, retaining walls, roads, and other engineered structures. Due to seismic activities, a lot of structures develop seismic cracks. The rehabilitation of such structures is necessary for public safety. The overall aim of this research study was to produce a high-performance hybrid fiber-reinforced concrete (HPHFRC) with enhanced properties as compared to plain high-performance concrete and high-performance fiber-reinforced concrete (HPFRC) for the rehabilitation of bridges and buildings. Kevlar fibers (KF) and glass fibers (GF) with lengths of 35 mm and 25 mm, respectively, were added and hybridized to 1.5% by mass of cement to create hybrid fiber-reinforced concrete mixes. Eight mixes were cast in total. The compressive strength (f′c), flexural strength (fr), splitting tensile strength (fs), and other mechanical properties, i.e., energy absorption and toughness index values, were enhanced in HPHFRC as compared to CM and HPFRC. It was found that the concrete hybridized with 0.75% KF and 0.75% GF (HF-G 0.75 K 0.75) had the most enhanced overall mechanical properties, illustrating its potential to be utilized in the rehabilitation of bridges and structures.

Impact response and endurance of unreinforced masonry walls strengthened with cement-based composites

Unreinforced Masonry (URM) walls are construction elements that have been found to resist in-plane forces, which proved beneficial for wind and earthquake resistant design. The out-of-plane resistance of URM walls, however, is very minimal, if any. Strengthening the walls in the out-of-plane direction is an ongoing research topic. This study aims at conducting laboratory experiments on the impact resistance of strengthened and unstrengthened URM walls. Impact tests are carried out to measure the failure resistance of structural members to suddenly applied load. The developed strengthening techniques consist of the application of fiber reinforcement cement-based composites using shotcrete technology. Two types of fibers are considered, polypropylene macro-fibers for FRC (Fiber Reinforced Concrete) and polyethylene micro-fibers for the ECC (Engineered Cementitious Composites). The FRC mixes were prepared with two dosage rates of polypropylene fibers (4.6 and 6 kg/m3) while the ECC, one dosage of polyethylene fibers (16 kg/m3) was used. A total of 12 URM walls were constructed with precast reinforced concrete frame and then infilled with hollow concrete blocks. The walls were strengthened and then tested under drop weight with a mass of 52 kg from a height of 3.8 m resulting in a kinetic energy of about 2000 J. Multiple drops were performed on each wall until failure. Test results revealed that the walls strengthened with the ECC Shotcrete (ECCS) endured ten drops, the largest number, without visible failure. The FRC Shotcrete (FRS) with 6 kg/m3 fibers ranked as the second-best strengthening technique; the FRS-6 walls endured more than six drops without major failure. In addition, the performance of each wall is evaluated in terms of endurance, impact force, energy absorption, flexural stiffness, and impact duration.

Post-Crack Flexural and Joint Performance Behaviors of Fiber-Reinforced Concrete for Pavements

This study investigated the influence of fiber properties on the post-crack flexural and joint performance behaviors of fiber-reinforced concrete (FRC) for thin concrete overlays. The study included a literature review, an online survey, and laboratory testing. It was found that the majority (almost 93%) of the FRC overlays in the United States of America were constructed with synthetic macro fibers. In the laboratory study, a total of 46 different FRC mixes were prepared with 11 different types of fibers. Fiber dosage, stiffness, and geometry significantly influenced the residual strength ratio (RSR) and residual strength (RS). In general, stiffer fibers with geometry like embossed, twisted, and crimped shapes showed higher post-crack flexural strength on average than the low-stiffness straight synthetic fibers. From the joint performance testing, it was found that fibers can improve the load transfer efficiency (LTE). A nomogram was developed so that agencies can select fiber dosage and type based on the target values of RSR, RS, and/or LTE.

Effects of Fibers on Compressive Strength of Concrete

This laboratory analysis was done to scrutinize the compressive strength of nominal mix concrete (NMC) and fiber reinforced concrete (FRC) for M30 grade of concrete. In this study, cubes of NMC prepared by adding fly ash 20% and 30% of the weight of cement. Apart from this, the FRC mix prepared by adding steel and glass fiber in the NMC mixture. The experimental study consists of the construction of 84 cubes, out of which 36 cubes of SFRC and 36 cubes of GFRC cast for different percentages of fiber. Out of 36 cubes of SFRC, 18 cubes cast with 20% fly ash and 18 cubes cast with 30% fly ash and the same as for GFRC and 12 cubes of NMC, 6 cubes cast with 20% fly ash and 6 cubes cast with 30% fly ash. The compressive strength calculated by averaging the strength of three cubes cast for each fiber ratio. These mixes tested for its hardened property like compressive strength in this comparative study. The compressive strength tested on UTM after 7 and 28 days curing, where results show improvement in individual fibers.

Mechanical properties of 3D printed concrete in hot temperatures

Concrete 3D printing is continuously studied as a new construction method. However, the use of concrete for this application is challenging in terms of workability and mechanical performance. Additionally, this technology is still lacking evaluation standards and guidelines. Furthermore, performance of printing concrete in hot temperature conditions is still generic. This study was conducted to assess the mechanical properties of a 3D printed fiber-reinforced concrete mix in two environmental conditions: ambient and hot. Compressive, flexural, and interlayer bond shear strengths were evaluated. A novel test setup was designed for bond strength evaluation at different printing time intervals. Compressive strength was evaluated to be 47 MPa in control cubes. Results from compression and bond tests indicated accelerated water evaporation and surface dehydration in hot conditions, and that the presence of joints in printed parts is detrimental to such parameters. Flexural strength was increased in hot temperatures compared to control and ambient specimens by 21% and 18% respectively. Flexural strength results demonstrated that fibers have a good orientation by the print process, and can be further improved in hot conditions due to lower material viscosities.

Assessment of fiber distribution characteristics in the hybrid fiber reinforced concrete – An experimental study

Assessment of fiber distribution characteristics is critical in the determination of the mechanical properties of the Fiber Reinforced Concrete (FRC). In this study an experimental investigation was carried out to ascertain the Fiber distribution characteristics (Fiber dispersion coefficient and Fiber orientation factor) of the M30 grade Mono Glass FRC (MGFRC), Mono Steel FRC (MSFRC), Graded FRC (GrFRC), Hybrid FRC (HyFRC) and Hybrid Graded FRC (HyGrFRC). Two lengths of glass fibers and two lengths of steel fibers were blended into the concrete to obtain MGFRC, MSFRC, GrFRC, HyFRC, and HyGrFRC mixes. An image analysis technique using an optical microscope was used to determine the dispersion coefficient and orientation factor of all the mixes, as mentioned earlier. Effect of fiber length, fiber type and fiber grading on the fiber distribution characteristics of the FRC mixes were discussed. The fiber distribution characteristics were improved by the addition of glass and steel fibers, where glass fibers enhance the dispersion coefficient, and steel fibers enhance the orientation factor. Graded FRC specimens exhibited better fiber distribution than Mono FRC specimens. HyGrFRC specimens showed better fiber distribution characteristics when compared to HyFRC specimens, and this may be due to the more uniform distribution of fibers without clumping in HyGrFRC mixes due to the grading of fibers. From this study, it can be inferred that the blending of graded glass and graded steel fibers in a hybrid form into the concrete have shown a remarkable enhancement in the fiber distribution characteristics.

Stress-Strain Constitutive Material Models for Hybrid Steel Fiber Reinforced Concrete

Recent advancements in fiber reinforced concrete (FRC) technology has led to the development of fibrous concrete composites, comprised of fibers with different material and/or geometry, commonly known as hybrid FRC. In one type of hybrid FRC composites, advantageous behaviors of fibers of the same material but with different geometries are gathered in a single FRC mix. The aim of this paper is to develop and validate stress-strain relationships for hybrid steel FRC composites. Six different steel FRC mixes are produced and characterization tests are conducted. Cube, cylindrical and beam specimens are produced for each characterization test corresponding to each of the Steel FRC (SFRC) composites. In this regard, an experimental program is performed to determine the basic engineering properties of SFRC composites using standard compressive, splitting tensile and three-point bending tests. The prescribed procedure of the RILEM guideline, originally developed for non-hybrid FRC, is followed using the obtained experimental results to develop stress-strain behavior models for the SFRC mixes. To validate results for the hybrid SFRC composites, numerical simulations of the 3-point bending tests were performed and compared to that of corresponding experimental results. The results indicated that the proposed stress-strain relationships yield acceptable results for characterizing the behavior of hybrid SFRC composites.

Experimental study on the out-of-plane strengthening of unreinforced masonry walls using cement-based fiber composites

This paper presents results from an ongoing research that is intended to study the behavior of URM walls for out-of-plane action. The effect of fiber reinforced shotcrete (FRS) as a strengthening method for the URM walls is examined. Eight URM walls were built inside a precast reinforced concrete boundary frame and strengthened with cement-based shotcrete mixes reinforced with different types of fibers. The masonry wall is 1.2x 1.2 m, and the masonry units were hollow concrete blocks (10 x 20 x 40 cm). Conventional fiber reinforced concrete (FRC) and engineered cementitious composite (ECC) were used as the strengthening layers sprayed on the surface of masonry walls. Control walls with plain shotcrete and conventional plastering mortar were also examined. Synthetic macro-fibers at dosage rate of 6 kg/m3 in FRC mix and Polyethylene micro-fibers at a dosage rate of 16 kg/m3 in ECC mix were considered in this study. The walls were placed in a carefully designed set up and tested under static central load using a hydraulic actuator with a capacity of 500 kN. The parameters recorded during testing were the applied load and out-of-plane displacement of the walls. Cracking pattern and failure modes were also monitored. The reported test results demonstrate that FRC and ECC mixes can significantly increase the out of plane strength and ductility of the URM walls.

Artificial Neural Model based on radial basis function networks used for prediction of compressive strength of fiber-reinforced concrete mixes


 
 
 
 
 
 
 
 
 
 
 Existe una relación compleja y no lineal entre los factores que influyen en la resistencia de diseño y la compresión de hormigones reforzados con fibras de acero. La relación entre las variables de entrada, los factores y la variable de salida, y la resistencia de diseño a la compresión puede ser obtenida por un modelo neuronal artificial, cuyas características sean autoadaptación, autoestudio y mapeo no lineal. En este documento se presenta la elaboración de un modelo neuronal artificial basado en redes neuronales de funciones de base radial. La resistencia de diseño a la compresión en dosificaciones de mezclas de hormigón reforzados con fibras de acero es estimada, predicción que se analiza a partir del coeficiente de correlación R al compararse con los valores reales de la resistencia. Los resultados muestran que los valores estimados usando las redes de base radial coinciden con los valores experimentales, y la capacidad de predicción de la propiedad mecánica del modelo neuronal es mejor que la de otros modelos basados en redes multicapas desarrollados por los autores. El entrenamiento de los modelos neuronales permitió concluir que el uso de relaciones de los materiales es un indicador más adecuado para la comparación entre diferentes dosificaciones de mezclas de hormigón que llevan a similares resistencias a la compresión. Así, se potencia una agenda futura en la generación de nuevos métodos de estudio de la resistencia de diseño a la compresión en hormigones reforzados con fibras metálicas en el campo de la ingeniería.
 
 
 
 
 
 
 
 
 
 

Application of Ordinary Fiber-Reinforced Concrete Layer for In-plane Retrofitting of Unreinforced Masonry Walls: Test and Modeling

The masonry walls should have sucient in-plane strength and sti ness to withstand the seismic loads during strong ground shakings. Di erent retro tting techniques have been proposed for improving in-plane behavior of the unreinforced masonry (URM) walls. This study focuses on experimental evaluation and numerical simulation of a simple practical retro tting technique employing Fiber Reinforced Concrete (FRC) surface layer.The simple FRC mix has conventional and available ber, low ber content, ordinary mix design, and applicable construction procedure. E ects of FRC mix properties, including ber type, ber content, and surface layer thickness, on in-plane behavior of masonry panels made up of conventional solid clay bricks are evaluated through experimental study in accordance with ASTM E-519 diagonal tension strength of masonry panels. In addition, a numerical simulation model for this retro tting technique in ABAQUS software is proposedand validated with test results of bare and retro tted panels.

Rate Effects of Fiber-reinforced Concrete Specimens in Impact Regime

A study of the rate sensitivity of prismatic specimens of steel fiber-reinforced concrete (FRC) is carried out in this contribution. Experimental results are analyzed from impact tests carried out with an instrumented drop weight testing machine. FRC mixes with two types of fibers have been studied, namely short straight fibers and long hook-ended fibers. The experiments have included two amounts of fibers (volumetric fractions of 0.5% and 1.0%), and also companion unreinforced plain concrete specimens are studied. The analysis has focused on the bending properties of the studied mixes, i.e. bending strength and absorbed energy. The study shows that each particular mix of FRC has different rate sensitivity because the dynamic behavior is a consequence of the rate dependence of the mechanisms governing the interaction between fibers and matrix. For the impact strain-rate domain achieved in the tests (1-10 s-1), it is shown that the study has to be done in terms of the energy absorption capacity of FRC. According to the results, the rate sensitivity decreases as the amount of fibers increases and, furthermore, the rate sensitivity of FRC mixes with hook-ended fibers is smaller than that of FRC mixes with straight fibers.

Research on Steel Fiber Reinforced Concrete Mix Proportion Based on the Theory of the Orthogonal Experiment

According to the needs of the quick mending engineering in concrete pavement, the theory of orthogonal experiment and the major indicators that influence the performance of steel fiber reinforced concrete, the influence of the various factors’ change on physical and mechanical properties of the mixed steel fiber reinforced concrete is studied, with water-cement ratio, accelerator, steel fiber content, coarse aggregate gradation as the essential factor. The research shows that flexural strength of steel fiber reinforced concrete increases with the increase of the steel fiber content and decreases with the increase of the water-cement ratio. In addition, the level of grade aggregate also has an important influence on the flexural strength of steel fiber reinforced concrete. The study figures out the optimum mix proportion of steel fiber reinforced concrete and provide a good reference to engineering application.

Research on Steel Fiber Reinforced Concrete Mix Proportion Based on the Theory of the Orthogonal Experiment

Research on Steel Fiber Reinforced Concrete Mix Proportion Based on the Theory of the Orthogonal Experiment