Steel Microfibers Research Articles

Mechanical and Fracture Parameters of Ultra-High Performance Fiber Reinforcement Concrete Cured via Steam and Water: Optimization of Binder Content.

An investigational study is conducted to examine the effects of different amounts of binders and curing methods on the mechanical behavior and ductility of Ultra-High Performance Fiber Reinforced Concretes (UHPFRCs) that contain 2% of Micro Steel Fiber (MSF). The aim is to find an optimum binder content for the UHPFRC mixes. The same water-to-binder ratio (w/b) of 0.12 was used for both water curing (WC) and steam curing (SC). Based on the curing methods, two series of eight mixes of UHPFRCs containing different binder contents ranging from 850 to 1200 kg/m3 with an increment of 50 kg/m3 were produced. Mechanical properties such as compressive strength, splitting tensile strength, static elastic module, flexural tensile strength and the ductility behavior were investigated. This study revealed that the mixture of 1150 kg/m3 binder content exhibited the highest values of the experimental results such as a compressive strength greater than 190 MPa, a splitting tensile strength greater than 12.5 MPa, and a modulus of elasticity higher than 45 GPa. The results also show that all of the improvements began to slightly decrease at 1200 kg/m3 of the binder content. On the other hand, it was concluded that SC resulted in higher mechanical performance and ductility behavior than WC.

Comparison of extreme learning machine and deep learning model in the estimation of the fresh properties of hybrid fiber-reinforced SCC

This paper studied the estimation of fresh properties of hybrid fiber-reinforced self-compacting concrete (HR-SCC) mixtures with different types and combinations of fibers by using two different prediction method named as the methodologies of extreme learning machine and long short-term memory (LSTM). For this purpose, 48 mixtures, which were designed as single, binary, ternary and quaternary fiber-reinforced SCC with macro-steel fiber, two micro-steel fibers having different aspect ratio, polypropylene (PP) and polyvinylalcohol (PVA), were used. Slump flow, t50 and J-ring tests for designed mixtures were conducted to measure the fresh properties of fiber-reinforced SCC mixtures as per EFNARC. The experimental results were analyzed by Anova method. In the devised prediction model, the amounts of cement, fly ash, silica fume, blast furnace slag, limestone powder, aggregate, water, high-range water-reducer admixture (HRWA) and the fiber ratios were selected as inputs, while the slump flow, t50 and the J-ring were selected as outputs. Based on the Anova analysis’ results, the macro-steel fiber was the most important parameter for the results of slump-flow diameter and t50, while the most important parameter for the results of J-ring was fly ash. Furthermore, it was found that the use of more than 0.20% by volume of 6/0.16 micro-steel fiber positively influenced the fresh properties of SCC mixtures with hybrid fiber. On the other hand, the inclusion of steel fiber instead of synthetic fiber into SCC mixture as micro-fiber was more advantageous in terms of workability of mixtures as result of hydrophobic nature of steel fibers. This study found that extreme learning machine model estimated the slump flow, t50 and J-ring with 99.71%, 81% and 94.21% accuracy, respectively, while deep learning model found the same experimental results with 99.18%, 77.4% and 84.8% accuracy, respectively. It can be emphasized from this study that the extreme learning machine model had a better prediction ability than the deep learning model.

Random forest-based optimization of UHPFRC under ductility requirements for seismic retrofitting applications

UHPFRC is a material that offers several openings within the building industry. One of those applications is the seismic retrofitting of existing non-ductile concrete structures. This paper aims to optimize a UHPFRC to meet ductility needs for seismic retrofitting applications at a lower cost. To achieve this objective, two Random Forest models were created to estimate the energy absorption capacity and the maximum post-cracking strain. Even though random forest models have been reported as one of the most efficient approaches for forecasting the properties of special concretes, with the purpose of demonstrating the efficiency of the proposed methodology, the random-forest-based optimization results were assessed by experimental works. The experimentally validated results showed that the appropriate combination of high-strength steel microfibers and normal-strength steel fibers with hooked ends meet the limit values (g ≥ 50 kJ/m3 and εpc ≥ 0.3%) at a lower cost.

Application of HPFRCC in beam–column joints to reduce transverse reinforcements

In this paper, in order to prevent the congestion of transverse reinforcements in beam-column joints of reinforced concrete frames which meet special seismic regulations, high-performance fiber reinforced cement composites (HPFRCC) with a combination of double hooked-end steel fibers and steel microfibers were used.For this purpose, four external beam-column joints were constructed to a scale of 1/2 and the specimens were tested under cyclic loading.The tested specimens include a normal concrete one meeting special seismic regulations as the control specimen and three HPFRCC ones made by reducing the transverse reinforcement in the beam and column. Hysteresis behavior, load-carrying capacity, energy dissipation and cracking patterns were analyzed and compared with the cyclic response of the control specimen for all experimental specimens. The test results indicate that the HPFRCC specimens, in comparison with the control specimen, have higher stiffness, load-carrying capacity and energy dissipation. Moreover, HPFRCC joints show a better damage tolerance capacity than the control specimen at higher drifts. Furthermore, the results of this study indicate that the use of HPFRCC in joint can be a proper strategy for increasing shear capacity and reducing the amount of beam and column transverse reinforcements.

Impact Performance of Steel Fiber-Reinforced Self-Compacting Concrete against Repeated Drop Weight Impact

The self-compacting concrete (SCC) was invented to overcome the compaction problems in deep sections, owing to its perfect workability characteristics. Steel fibers when used with SCC would affect the required fluidity characteristics but improve its impact resistance. In this research, an experimental work was conducted to evaluate the impact response of micro-steel fiber-reinforced SCC, under flexural impact. A 5.47 kg free-falling mass was dropped repeatedly from 100 mm height on the top center of 270 mm-length beam specimens. Eight mixtures with two design grades of 30 and 50 MPa were prepared to distinguish the normal and high-strength SCCs. The distinguishing variable for each design grade was the fiber content, where four volumetric contents of 0%, 0.5%, 0.75%, and 1.0% were used. The test results showed that the impact resistance and ductility were significantly improved due to the incorporation of micro-steel fibers. The percentage improvements were noticeably higher at failure stage than at cracking stage. For the 30 MPa mixtures, the maximum percentage improvements at cracking and failure stages were 543% and 836%, respectively. Weibull’s linear correlations with R2 values of 0.84 to 0.97 were obtained at the failure stage, which meant that the impact failure number followed the Wiebull distribution.

Effect of dispersed micro-fibers on tensile behavior of uncoated carbon textile-reinforced cementitious mortar after high-temperature exposure

The mechanical and structural behavior of infrastructure and buildings under high-temperature environment is one of the major concerns in retrofit technologies. The present study aims to experimentally investigate the effectiveness of dispersed micro-fibers on the tensile behavior of uncoated carbon textile-reinforced mortar (TRM) after exposure to high temperatures. The main experimental parameters include the micro-fiber type, fiber volume fraction, and high-temperature level. Micro-steel fibers and amorphous metallic fibers with lengths of 13 and 15 mm, respectively, were utilized in this study to ameliorate the cementitious mortar matrix with a volume fraction in the range of (0.4–0.8) %. Three investigated temperature levels were 25 °C (ambient condition), 200 °C, and 400 °C. The tensile tests were carried out based on RILEM TC 232-TDT after specimens cooled down to ambient temperature. The experimental results indicate that the inclusion of micro-steel and amorphous metallic fibers within the mortar matrix significantly ameliorated the tensile characteristics of TRM specimens at both ambient and high temperatures. In addition, micro-amorphous metallic fibers exhibited significant advantages compared with steel fibers to improve the crack stress after exposure to 200 °C. Based on the experimental results and material characteristics, this study proposed an analytical model to predict the tensile strength after exposure to high temperatures and the idealized tensile stress-strain curves at the ambient temperature, of TRM composites incorporating dispersed micro-fibers, and the model prediction showed a good correlation with the experimental results.

Effect of water/cement ratio on micro-nanomechanical properties of the interface between cementitious matrix and steel microfibers in ultra-high performance cementitious composites

abstract: Ultra-high performance concretes with steel microfibers have been studied in depth with the aim of producing more efficient and durable structures. The performance of these materials depends on the characteristics of the interface between microfibers and cementitious matrix. This research investigates the micro-nanomechanical properties of the interfacial transition zone between the steel microfibers and the matrix of ultra-high performance cementitious composite. The effect of the water/cement ratio and distance from the microfiber were analyzed. The results confirm the formation of high-density calcium-silicate-hydrate (HD C-S-H) matrix at higher concentrations than low-density calcium-silicate-hydrate (LD C-S-H) for w/c ratios of 0.2 and 0.3. The properties in cementitious matrix interface with steel microfibers were very similar to that measured for the cement paste, and no significant difference was observed regarding the distance to the microfibers in relation to the elastic modulus, hardness and chemical composition. Thus, the authors can conclude that the formation of a less resistant region does not occur at the interfacial transition zone cement paste/microfibers.

Mechanical properties of fiber and nano-Al2O3 reinforced magnesium phosphate cement composite

In this paper, the mechanical properties of magnesium phosphate cement (MPC) was enhanced by adding fiber and nano-Al2O3. The effects of fiber and nano-Al2O3 on the workability, compressive strength and flexural toughness of MPC were studied. The variables of the experimental investigation included the types of fiber, fiber volume fraction, nano-Al2O3 substitution rate and curing time. The experimental results showed that the workability and the mechanical properties of the MPC could be improved by adding nano-Al2O3. The workability decreased gradually with increasing fiber content, while the compressive and tensile strength gradually increased. Among different types of fiber, the micro-steel fiber (MSF) had the most significant effect on the improvement of flexural toughness. Based on the analysis of experimental data, empirical formulae for predicting the compressive strength and splitting tensile strength of fiber and nano-Al2O3 reinforced MPC composite (FNRMC) were proposed. In addition, the modification mechanisms of nano-Al2O3 on the MPC were revealed by XRD and SEM for microscopic phase tests.

Investigation and Improvement of Bond Performance of Synthetic Macro-Fibres in Concrete.

Strength and stiffness are the key parameters characterising the bond performance of fibres in concrete. However, a straightforward procedure for estimating the bond parameters of a synthetic macro-fibre does not exist. This study employs pull-out tests to investigate the bond behaviour of synthetic macro-fibres. Two types of macro-fibres available in the market were investigated. A gripping system was developed to protect the fibres from local damage. The experimental campaign consisted of two stages. At the first stage, 32 concrete specimens were manufactured for performing 96 pull-out tests (three fibre samples were embedded in each cube perpendicular to the top surface and two sides). Two types of macro-fibres with either 10 or 20 mm embedment length were tested. The obtained load–displacement diagrams from pull-out tests demonstrate that the bond performance (characterised by the strength and deformation modulus) of the “top” fibres is almost 20% weaker than fibres positioned to the side surfaces. At the second stage, one type of macro-fibre was chosen for further experimentation of the feasibility of improving the bond performance through the use of colloidal silica or steel micro-fibres. This investigation stage employed an additional 36 concrete specimens. The use of steel micro-fibres was found to be an efficient alternative. The success of this solution requires a suitable proportioning of the concrete.

Experimental Tests and Reliability Analysis of the Cracking Impact Resistance of UHPFRC

Ultra-high performance (UHP) concrete is a special type of fibrous cementitious composite that is characterized by high strength and superior ductility, toughness, and durability. This research aimed to investigate the resistance of ultra-high performance fiber-reinforced concrete (UHPFRC) against repeated impacts. An adjusted repeated drop mass impact test was adopted to evaluate the impact performance of 72 UHPFRC disc specimens. The specimens were divided into six mixtures each of 12 discs. The only difference between the mixtures was the types of fibers used, while all other mixture components were the same. Three types of fibers were used: 6 mm micro-steel, 15 mm micro-steel, and polypropylene. All mixtures included 2.5% volumetric content of fibers, however with different combinations of the three fiber types. The test results showed that the mixtures with the 15 mm micro-steel fiber absorbed a higher number of impact blows until cracking compared to other mixtures. The mixture with pure 2.5% of 15 mm micro-steel fiber exhibited the highest impact resistance, with percentage increases over the other mixtures ranging from 25 to 140%. In addition, the Weibull distribution was used to investigate the cracking impact resistance of UHP at different levels of reliability.

A Review: Properties of Micro Steel Fibre (MSF) in High-Performance Concrete in Terms of Crack Propagation

A Review: Properties of Micro Steel Fibre (MSF) in High-Performance Concrete in Terms of Crack Propagation

Water Impact-Abrasion Erosion of Hybrid Fiber-Reinforced High Performance Concrete

Aiming to evaluate the resistance of High Performance Concrete (HPC) against the abrasion erosion due to the continual impact of water and water borne materials, six HPC mixtures reinforced with different fibers and fiber combinations were prepared and tested experimentally in this study. All mixtures share the same contents of all materials, while the types and combinations of fibers used were different among the mixtures. All mixtures included a total of 2.5% volumetric content of fibers. The mixture S6 included pure 6 mm micro-steel fiber (S6), S15 mixture included pure 15 mm micro-steel fiber (S15), while the S6-S15 mixture included 1.25% of each of S6 and S15. S6-PP and S15-PP included 2.0% of S6 or S15, respectively, in combination with 0.5% of polypropylene fiber (PP), while the sixth mixture included 1.0% S6, 1.0% S15 and 0.5% PP. The impact abrasion test was conducted on 200×200 mm plat targets with 50 mm thickness that were fixed perpendicular to a water jet with a high speed of 20 m/s. The results revealed that all HPC mixtures exhibited much higher abrasion resistance than normal concrete. The results also showed that the S15 mixture was the one with highest abrasion resistance with an abrasion loss of only approximately 20 grams after 12 hours testing.

Experimental Investigation of Mechanical and Dynamic Impact Properties of High Strength Cementitious Composite Containing Micro Steel and PP Fibers

Cementitious composites are one of the most consumed construction materials in the world. The use of cementitious composites is increasing due to their special characteristics. The behavior of high strength cementitious composites is improved by increasing the fiber percentage. In the present paper, the effects of steel microfibers and polypropylene fibers on mechanical properties and impact resistance of high strength cementitious composites are investigated. The percentage of fibers used in the study was 0, 0.5, and 1.5% in seven separate and three combined mix designs. Experiments were carried out on 120 specimens in 10 mix designs. Compressive strength, tensile strength, flexural strength, and dynamic impact tests were carried out on 10 mix designs manufactured in this research. The dynamic impact strength of the disc specimen was investigated by a drop hammer test machine with a capacity of 7500J. After testing the samples, it was shown that using a high percentage of steel and polypropylene fibers reduces the compressive strength and increases tensile strength, flexural strength, and impact strength. The effects of steel microfibers on the reduction of the crush displacement resulting from the dynamic impact were higher than that of polypropylene fibers.

Experimental study on the effects of the fiber and nano-Fe2O3 on the properties of the magnesium potassium phosphate cement composites

In this study, a new cement-based composite is developed by the combined action of fiber and nano-Fe2O3 (NF) in magnesium potassium phosphate cement (MKPC) mortar. The performances of MKPC composite with fiber and NF are evaluated, including the workability, compressive strength, splitting tensile strength, flexural toughness and flexural ductility. The microscopic mechanism of MKPC with NF is revealed by using the Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The main variables of this study include fiber type, curing time, micro-steel fiber (MSF) volume rate and NF substitution rate, and the micro-steel fiber (MSF), cut hook (CH), milling hook (MH) and macro-polypropylene fiber (MPF) are selected as the reinforcing material. In comparison to other fibers, the MSF has the most significant positive effect on the mechanical properties of FNRMC. The compressive strength, splitting tensile strength, flexural toughness and flexural ductility of FNRMC evidently increase with increasing MSF volume rate, while the workability of FNRMC gradually decreases. The compressive and splitting tensile strengths of FNRMC have a trend of first increasing and then decreasing with increasing NF substitution rate from 0% to 4%.

High- and ultra-high-performance concrete produced with sulfate-resisting cement and steel microfiber: Autogenous shrinkage, fresh-state, mechanical properties and microstructure characterization

High-performance concrete (HPC) and ultra-high-performance concrete (UHPC) are cement-based composites that present improved mechanical performance and durability. However, their low water/binder ratio and high binder content lead to significant autogenous shrinkage. This work investigated the autogenous shrinkage of HPC and UHPC produced with sulfate-resisting cement and steel microfiber in volumetric fractions (Vf) of 0–1.5%, from the first minutes of hydration. In addition, fresh performance (mini slump flow), hardened properties (dynamic modulus of elasticity – Ed, compressive and flexural strength at 28 days) and microstructure (SEM-EDS) were evaluated. Results showed that steel microfiber incorporation progressively reduced the autogenous shrinkage of both HPC and UHPC (by up to 11% and 22%, respectively) because of the increased resistance to volumetric reduction caused by the capillary pressure. The fresh-state performance of UHPC was not affected by microfiber incorporation (mini slump flow of 305–310 mm), while increasing Vf progressively reduced the mini slump flow of HPC from 305 mm (Vf 0%) to 262 mm (Vf 1.5%); this behavior was associated with the viscosity of the mixes. Furthermore, increasing Vf progressively increased the compressive strength (by up to 8% for HPC and 23% for UHPC) and the flexural strength (by up to 23% for HPC and 47% for UHPC) due the inhibition in propagation and opening of microcracks, while no significant differences were observed in the Ed. In turn, 0.75% microfiber incorporation in UHPC increased the air content by 80%, thus reducing its flexural strength. SEM-EDS analysis indicated the absence of chemical bond between the fiber and the cementitious matrix, suggesting that this interaction was essentially mechanical. Overall, steel microfibers incorporation was effective in reducing the autogenous shrinkage of HPC and UHPC produced with sulfate-resisting cement, in addition to keeping or even improving the mechanical performance of the composites.

Study on mixture design method and mechanical properties of steel fiber reinforced self-compacting lightweight aggregate concrete

A new mixture design method of steel fiber reinforced self-compacting lightweight aggregate concrete (SFSLC) based on paste film thickness theory and combination method was proposed in this study. In order to verify the feasibility of the proposed mixture design method, two types of SFSLC were designed and prepared. The effect of steel fiber content on the workability and mechanical properties including compressive strength, splitting tensile strength and flexural toughness performance of self-compacting lightweight aggregate concrete (SLC) was studied. The results showed that this new mixture method could quantitatively determine the content of raw materials. The addition of fiber reduced the filling ability and passing ability of SLC, but improved the segregation resistance of SLC. The improvement effect of micro-steel fiber on the mechanical properties such as compressive strength, splitting tensile strength and flexural toughness of SLC was significantly better than that of long steel fiber.

Performance of green RPC containing nanoparticles and reinforced with hybrid fibers used for repairing damaged concrete

Recently, there is an increased research awareness towards the use of high strength cementitious matrices like reactive powder concrete (RPC) for rehabilitation and repairing damaged structures in addition to their use in the maintenance of concrete structures. Therefore, this research has been conducted to present some RPC mixes prepared from various percentages of cement replacement, nanoparticles materials, and reinforced with three different types of fibers.The green RPC mixes were prepared with a total 30 % replacement of cement by silica fume, slag powder, and glass powder. Then, the addition of Nanoparticles combination as 2.5 % Nano glass powder (NG) plus 2.5 % Nano Iron slag powder (NS) was performed. Besides, the uses of mono micro steel fibers and hybridization of micro steel fibers (MSF), sisal fibers (SIF), and human hair fibers (HHF) were achieved. The combined systems of substrate concrete and such different green RPC mixes which were proposed here as repair materials besides epoxy were tested in bi-surface shear, oblique shear, flexural bond strength, splitting bond strength, and Pull-out.The results showed that the reinforcing of green RPC with hybrid nanoparticles (2.5 %NG + 2.5 %NS) and hybrid fibers (1.5 %MSF with 0.25 %SIF and 0.25 %HHF) boosted the best performances among green RPC mixes in bi-surface shear, oblique shear and Pull-out tests. Also, the said mix gives higher bond strengths between RPC with substrate concrete than that of epoxy by 2.273 %, 3.663 %, 6.168 % and 10 % through bi-surface shear, oblique shear, splitting strength and flexural strength, respectively.

Mechanical properties and fracture parameters of ultra high performance steel fiber reinforced concrete composites made with extremely low water per binder ratios

This study examines the effects of high-volume micro-steel fibers (MSF) content on the mechanical properties, fracture parameters, and ductility of ultra-high performance fiber reinforced concrete (UHPFRCs). The MSFs used in this experiment had an aspect ratio of 37.5 with average length of 6 mm. The investigated parameters include very low water/binder (w/b) ratio and fiber content. Sixteen UHPFRC mixes were examined, eight mixes were made with w/b of 0.12 and eight fiber contents (0%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5, 4%) while the other eight mixes were made with the same fiber contents but with w/b of 0.14. The UHPFRC mixes were examined for various strengths (compressive, splitting tensile, flexural), elastic modulus, and fracture parameters. The experimental results showed that the mixture with 4% of MSFs content and 0.12 w/b ratio exhibited a compressive strength of more than 160 MPa, splitting tensile strength higher than 12 MPa, and modulus of elasticity greater than 43 GPa. Moreover, the results also demonstrated that with increasing MSFs content from 0 to 4% the load–displacement behavior, ductility, and all other fracture parameters were improved significantly.

Combined effects of microsilica, steel fibre and artificial lightweight aggregate on the shrinkage and mechanical performance of high strength cementitious composite

In this study, the effects of micro-steel fiber, pelletized fly ash lightweight aggregate and microsilica content on the fresh and hardened properties of high-performance cementitious composite (HPCC) were experimentally investigated. Micro-steel fibers having a length of 6 mm were used in the production of mixtures at the level of 0%, 1% and 2% by total volume. Besides, artificial lightweight aggregate produced by the pelletizing method was employed in the mixture production by 0% and 20% of total aggregate volume. 0% and 25% of the total binder content were designated as microsilica. Thus, a total of 12 different HPCC mixtures were obtained. The water-to-binder ratio of 0.2 was chosen in the design of all HPCC mixtures. A high-rate water-reducing chemical admixture is used to give a suitable flow for the fresh mixtures. The mechanical properties of HPCC mixtures are evaluated in terms of compressive and flexural strengths and elastic modulus. In addition to these, total water absorption and capillary water absorption tests were performed to evaluate the pore structure and permeability. The drying and autogenous shrinkage values were determined during the 60-day drying period. Thus, the effects of fiber content, microsilica addition, and artificial lightweight aggregate content were examined. The results of the experiment showed that the mechanical properties of HPCC and shrinkage behavior have been improved with the increase of steel fiber volume fraction. Furthermore, the negative effects of artificial lightweight aggregate can be eliminated by microsilica.

Flexural Behavior of Reinforced Concrete Beams Reinforced with 3D-Textile Composite Fiber

Normal concrete is weak against tensile strength, has low ductility, and also insignificant resistance to cracking. The addition of diverse types of fibers at specific proportions can enhance the mechanical properties as well as the durability of concrete. Discrete fiber commonly used, has many disadvantages such as balling the fiber, randomly distribution, and limitation of the Vf ratio used. Based on this vision, a new technic was discovered enhancing concrete by textile-fiber to avoid all the problems mentioned above. The main idea of this paper is the investigation of the mechanical properties of SCC, and SCM that cast with 3D AR-glass fabric having two different thicknesses (6, 10 mm), and different layers (1,2 layers). As well as micro-steel fiber with 1.25% volume fraction was used. Sixteen rectangular reinforced concrete beam specimens have been tested to study the behavior of their flexural strength. The results concluded that utilizing 3D-TFs with mortar mixture gave significantly higher enhancement for the load-carrying capacity than the concrete mixture. The utilization of 3D-TFs and micro-steel fiber together in the SCM mix gave better results. The stiffness of the specimens was improved with increasing the thickness and the number of textile fiber layers.