Steel Microfibers Research Articles

Stiffness degradation and mechanical behavior of microfiber-modified high-toughness recycled aggregate concrete under constant load cycling

The mechanical properties of High-Toughness Recycled Aggregate Concrete (HTRAC) were investigated in this study as an innovative and environmentally friendly construction material, along with its potential applications in structural stability. Small-scale specimens with six levels of micro-steel fiber content were made, and a series of cyclic tests with constant loads were carried out. Using In-Situ 4D CT technology, the damage characteristics of the microstructure of HTRAC and the reinforcing effects of fibers on key mechanical parameters (peak stress, peak strain, ultimate strain, post-peak modulus, and toughness indicators) were analyzed. A comprehensive fiber reinforcing factor calculation model was proposed to assess its contribution to strength, deformability, and toughness, and the correlation between the number of cyclic loadings and stiffness degradation was also quantified. it is confirmed that HTRAC exhibits a significant advantage in toughness compared to traditional recycled aggregate concrete (RAC). The findings of this study provide crucial technical support for the further development and application of HTRAC, indicating its promising prospects in the field of sustainable construction materials

Enhanced Impact Strength of Ultra-High-Performance Concrete Using Steel Fiber and Polyurethane Grout Materials: A Comparative Study

This study examined the impact properties of ultra-high-performance concrete (UHPC) mixtures with steel fiber (SF) and retrofitted with polyurethane (PU) grouting using repeated drop-weight tests. Micro-steel fiber was added to UHPC mixes from 0 to 3% Vf, and PU grouting overlays of 5 mm, 10 mm, and 15 mm were applied. Digital image correlation (DIC) was used to analyze failure modes. The results showed significant impact durability and energy absorption improvements with increased SF content and thicker PU overlays. UHPC-15PU exhibited 363% and 449% higher first crack and failure strengths than UHPC-5PU. DIC analysis confirmed the failure patterns of the U-shaped UHPC specimen under impact load conditions.

Enhancing the pull-out behavior of ribbed steel bars in CNT-modified UHPFRC using recycled steel fibers from waste tires: a multiscale finite element study

In the current investigation, the effect of recycled steel fibers recovered from waste tires on the pull-out response of ribbed steel bars from carbon nanotube (CNT)-modified ultrahigh performance fiber reinforced concrete (UHPFRC) was considered using the multiscale finite element method (MSFEM). The MSFEM is based on three phases to simulate CNT-modified UHPC, recycled steel fibers (RSFs), and ribbed steel bars. For the first time, a bar ribbed has been simulated to make more realistic assumptions, and RSFs have been distributed in the form of curved cylinders of different lengths and with a random distribution within a concrete matrix. The interaction of the steel bar and the RSFs with the concrete is applied by the cohesive zone model (CZM). After confirming the simulation outcomes with the experimental results, the steel bar pull-out response is investigated using load-slip curves. The impact of the CNT content, RSFs and their aspect ratio on the bond strength of steel bars and CNT-modified UHPFRC was assessed. The results show that using RSFs with a lower aspect ratio (steel microfibers) significantly improves the pull-out characteristics of steel bars from concrete. Accordingly, the proposed MSFEM is considered for simulating the effects of different parameters on the pull-out response of ribbed steel bars from concrete without causing complex, time-consuming, or costly experiments. The results indicated that waste fiber or RSF can be used as a toughening component in CNT-modified ultrahigh-performance concrete and as a replacement for industrial steel fibers.

Study on the mesoscopic mechanical behavior and damage constitutive model of micro-steel fiber reinforced recycled aggregate concrete

This study employs in-situ 4D CT experimental techniques to investigate the mesostructured changes and mechanical behavior of micro steel fiber-reinforced recycled aggregate concrete (MSF-RAC) under uniaxial compression and cyclic loading conditions. The research aims to address the scientific problem of limited understanding of how micro steel fibers affect the mesoscopic mechanical behavior and structural damage characteristics of recycled aggregate concrete. High-resolution CT scanning technology was utilized for real-time observation of crack initiation and propagation, revealing the micro-mechanisms by which micro steel fibers enhance RAC. The study found that incorporating micro-steel fibers significantly improves the density of the interfacial transition zone (ITZ), inhibits crack development, and enhances the mechanical properties of the concrete. Based on these observations, an improved stiffness degradation damage constitutive model was proposed, which comprehensively considers the distribution orientation of micro steel fibers and ITZ characteristics. The model effectively predicts the stress-strain relationship of MSF-RAC under various conditions, demonstrating high accuracy and practicality. These findings provide important theoretical support and experimental evidence for the optimal design of RAC, showcasing significant engineering application value by promoting the sustainable use of recycled materials in construction.

Experimental investigations on mechanical performance, synergy assessment, and microstructure of pozzolanic and non‐pozzolanic hybrid steel fiber reinforced concrete

AbstractThis paper investigates the effects of pozzolanic substitutions for ordinary Portland cement (OPC) with silica fume (SF) and metakaolin (MK) on the mechanical and toughness performances of steel fiber reinforced concrete (SFRC). Initially, a reference concrete mix with a water‐to‐binder ratio of 0.4 is blended with different volume fractions of steel fibers with varying geometry: crimped steel (CS) and straight steel (SS), both individually and in combination, to examine their mechanical properties. In the subsequent phase, the study investigates the impact of combining macro‐ and microsteel fibers on flexural toughness, to determine potential synergy for suitable combinations. Also, the possible influence of pozzolans in the variation of flexural toughness of hybrid steel fiber reinforced concrete (Hy‐SFRC) was evaluated. Hybridization of steel fibers was found effective in improving the workability of the concrete mix up to 11%. SFRC mixes containing pozzolans exhibited a significant enhancement in compressive strength, modulus of rupture, and modulus of elasticity compared to non‐pozzolanic SFRC. The hybrid combination of CS 1.5% and SS 0.5% was considered the best in terms of mechanical properties. Additionally, the results of synergy assessment showed that hybridization of steel fibers in the pozzolanic concrete mix was particularly effective in the post‐cracking stages with a positive 14% compared to a negative 8% in the pre‐cracking stage. The pozzolanic addition improved the flexural toughness of Hy‐SFRC to about 10%–20%. Blending of SF and MK in Hy‐SFRC was found effective in enhancing the toughness mechanism of concrete compared to Hy‐SFRC mixes containing binary SF and MK, indicating a stronger bond between the fibers and the matrix resulting from the pore refinement and hydration products developed at the interface. Hy‐SFRC containing a ternary pozzolanic mix of SF 10% and MK 10% gave the best results in flexural toughness, and the corresponding synergy values were found to be the maximum. The results were consistent with the morphology analysis, which revealed an increase in hydration products at the interface between the aggregate and concrete matrix, as well as between the steel fiber and concrete matrix, due to the ternary blending of SF and MK.

Assessment of Methods to Derive Tensile Properties of Ultra-High-Performance Fiber-Reinforced Cementitious Composites.

There is no unified method for deriving the tensile properties of fiber-reinforced ultra-high-performance cementitious composites (UHPCC). This study compares the most common material tests based on a large series of laboratory tests performed on a self-developed UHPCC mixture. The cementitious matrix, with a compressive strength of over 150 MPa and a matrix tensile strength of 8-10 MPa, was reinforced with 2% by volume of 15 mm long and 0.2 mm diameter straight high-strength steel microfibers. Over 100 uniaxial tensile tests were performed on three test configurations using cylindrical cores drilled out from larger prismatic specimens in three perpendicular directions. In addition to uniaxial tests, flexural tests on prismatic elements and flexural tests on thin plates were conducted, and the tensile properties were derived through digital image correlation (DIC) measurements and inverse analysis. Furthermore, splitting tensile tests on cylindrical specimens were employed to ascertain the tensile properties of the matrix. The outcomes of the diverse laboratory tests are presented and discussed in detail. The relationships between crack width and deflection in the context of flexural tests were developed and presented. In conjunction with compression tests and modulus of elasticity tests, the constitutive law is presented for the investigated materials.

New insights into the mechanical behavior and enhancement mechanism of micro-steel-fiber-reinforced recycled aggregate concrete through in-situ 4D CT analysis

Micro-steel-fiber-reinforced recycled aggregate concrete (MSFR-RAC), an innovative and environmentally friendly construction material, is gaining traction in civil engineering due to its superior performance and sustainability. This study utilized in-situ CT tests to investigate the strength and deformation variations in MSFR-RAC influenced by micro-steel fibers. Calculation models for the fiber influence factor (FIF) on peak stress, peak strain, and ultimate strain were proposed, and the optimal volume fraction threshold for steel fibers was determined. Using CT scanning and 3D reconstruction, the internal pore structure, crack evolution, and spatial distribution of steel fibers were analyzed. The interaction mechanism between steel fibers and the concrete matrix was established based on crack evolution patterns. The results demonstrate that steel fibers significantly enhance the microscopic structure and mechanical performance of MSFR-RAC. This study provides essential technical and theoretical support for the design and application of MSFR-RAC in construction.

Behavior of Modified Reactive Powder Concrete Containing Sustainable Materials and Reinforced with Micro-Steel Fibers

Behavior of Modified Reactive Powder Concrete Containing Sustainable Materials and Reinforced with Micro-Steel Fibers

Ballistic behavior of bioinspired layered-and-staggered concrete

Inspired by the structure of abalone shells, a layered-and-staggered concrete system composed of concrete tiles joined with rubber mortar was proposed for ballistic protection. Ballistic tests demonstrated that, when subjected to Type 53 API bullet impact at velocities ranging from 780 to 815 m/s, the layered-and-staggered concrete outperformed both steel fiber reinforced bulk concrete and simple layered concrete with comparable compressive strengths in terms of reducing bullet penetration depth. Furthermore, damage in the layered-and-staggered concrete was primarily confined to areas surrounding directly impacted tiles or joints; cracks on the impact face did not propagate radially as observed in bulk concrete but instead deflected along weak interfaces between adjacent tiles. Additionally, crack deflection and bullet yawing were observed in the thickness direction of the layered-and-staggered concrete targets, aligning with expectations for bionic design effects. Incorporating steel micro-fibers into the layered-and-staggered system enhanced individual tile's impact resistance but did not reduce bullet penetration depth. The proposed layered-and-staggered concrete exhibits promising potential for practical applications, particularly in scenarios requiring prompt repair of damaged components.

Durability of green rubberized 3D printed lightweight cement composites reinforced with micro attapulgite and micro steel fibers: Printability and environmental perspective

The increasing amount of tires manufactured annually worldwide has made waste tire management a major environmental concern. The goal of this work is to investigate the potential applications of waste tire aggregates (WTA) in a novel class of affordable, recycled composite materials. This study assesses the material behavior of rubberized 3D printed lightweight cement composites (3DLC) reinforced with raw micro attapulgite (ATP) and micro steel fibers (MSF) using WTA as a 100 % replacement for fine aggregate manufactured through 3D printing. The paper takes advantage of 3D concrete printing's advantages and addresses the environmental issues associated with waste tires. The extrudability and buildability properties of 3DLC are determined in the fresh state. Physical and thermal properties of 3DLC were determined. Mechanical properties of 3DLC including compressive, flexural, shear strength and flexural toughness were assessed. 3D printed samples were exposed to high temperature and sulfate (MgSO4), and their durability properties were determined. The microstructures of the mixes was analyzed. The CO2 emissions and costs of the blends were also assessed. The outcomes revealed that, the 3DLC mixture with 10 % ATP and 2 % MSF showed the greatest compressive strength performance, with increases of 17.82 and 29.51 % at 28 and 90 days, respectively relative to the mixture without ATP. Regardless of MSF level, at 28 and 90 days, all mixes with 10%ATP content showed the largest flexural strengths. The 3DLC mixture with 10 % ATP and 2 % MSF had the highest measured thermal conductivity. The blends with 20 % ATP and 0 % MSF showed the lowest thermal conductivity. The mixture containing 10 % ATP and 2 % MSF demonstrated the greatest high temperature performance, demonstrating strength enhancement of 21.85, 6.72 and 3.36 % at 200,400 and 600°C respectively. Replacing cement with 10 and 20%ATP greatly increased the sulfate resistance of 3DLC mixtures and the mixture with 20%ATP and 2%MSF exhibited the best sulfate performance. The lowest CO2 emission and cost were determined for the mixture containing 20%ATP and 0%MSF (A20S0).

The Increasing еhe Efficiency of Fiber Reinforced High-Strength Self-Compacting and Carcass Concretes

The results of experimental and theoretical studies of fiber reinforced concretes are presented. The purpose of the research was to establish physical and mechanical properties of self-compacting, carcass concrete and fiber reinforced concrete. When performing the research, white cement was used as a binder. As a reactive additive was used white carbon black BS-100. Plasticizing of the system was carried out by polycarboxylate SP. To increase the volume of dispersed phase, the combined filler from rheologically active fine ground rocks was used, namely: quartz flour R-6, and microcalcite RM-5. To form the filled structure of the composite we also used fine sand PB-150, and at the first stage steel microfiber “BMZ” and glass fiber

Eco-Innovative UHPC-Enhancing Sustainability, Workability, and Ductility with Recycled Glass Cullet Powder and Plastic Bottle Hybrid Fibers.

Utilizing waste materials in producing ultra-high-performance concrete (UHPC) represents a highly effective approach to creating environmentally sustainable concrete using renewable resources. This study focused on incorporating ground glass cullet (GP) at various replacement levels in UHPC production. Additionally, plastic bottle fibers (PBFs) were derived from discarded plastic bottles and employed in the mix. The replacement levels for GP spanned from 0% to 40%. Single-use plastic bottles were transformed into strip fibers, both with and without the inclusion of microsteel fibers, at varying contents of 1.1% and 2.2% (volume-based). A single-fiber test was conducted on PBFs under different strain rates. The introduction of optimal GP content had a profound positive iMPact on compressive strength. Incorporating 2.2% plastic strips induced strain hardening behavior, while further inclusion of microsteel fibers resulted in substantial enhancements in mechanical properties. Two types of microsteel fibers were employed, characterized by different aspect ratios of 65 and 100. The optimum GP content was identified as 10%. Moreover, the UHPC mix achieved superior compressive strength, exceeding 140 MPa when composed of 1.3% (volume-based) microsteel fibers with an aspect ratio of 65 and 2.2% PBF (volume-based). Notably, mixtures featuring microsteel fibers with a higher aspect ratio demonstrated the highest flexural strength, exceeding 8000 N in the presence of 2.2% PBF. Longer microsteel fibers exhibited adequate slip properties, facilitating strain transfer and achieving a strain-hardening response in conjunction with plastic bottle fibers. These findings illuminate the potential for harnessing hazardous waste materials to improve the performance and sustainability of UHPC formulations.

Flexural Residual Strength of Lightweight Concrete Reinforced with Micro-Steel Fibers

Flexural Residual Strength of Lightweight Concrete Reinforced with Micro-Steel Fibers

Properties of High-Content Micro-Steel Fiber Self-Compacting Concrete Incorporating Fly Ash and Slag Powder Performance Study

The addition or substitution of various gel materials in cement-based composites has been proven to be an effective approach in enhancing the performance of concrete. Current research focuses mainly on enhancing the toughness of concrete, but lacks discussion on the performance of alternative gel materials. Therefore, this study aims to explore the effects of partially substituting cement with fly ash and slag powder as gel materials, while incorporating a high volume fraction of micro-steel fibers (6%), on the workability and mechanical properties of self-compacting concrete. By means of rigorous experimental investigation and meticulous analysis, we comprehensively assessed the workability characteristics of self-compacting concrete, encompassing critical aspects such as filling ability, cohesion, and permeability. Additionally, we conducted an extensive evaluation of the mechanical attributes of self-compacting concrete, encompassing vital parameters, such as compressive strength, axial compressive strength, splitting tensile strength, and flexural strength. Last but not least, through a holistic integration of workability and mechanical properties, we conducted a comprehensive performance evaluation of self-compacting concrete incorporating a synergistic blend of fly ash, slag powder, and micro steel fibers. The experimental results indicate that the composite addition of fly ash and slag powder in self-compacting concrete, while compatible with up to 6% micro-steel fibers, leads to a decrease in concrete workability and an increase in cohesiveness due to the addition of micro-steel fibers. Moreover, fly ash predominantly influences the tensile properties of concrete, while the addition of slag powder significantly affects the compressive and flexural properties of concrete. Additionally, the addition of micro-steel fibers significantly improves the overall mechanical properties of concrete.

Utilizing porcelain tile polishing residue in eco-efficient high-strength geopolymers with steel microfibers

Geopolymers are an alternative that produces low environmental impact binders with satisfactory mechanical properties. This research evaluated the influence of adding steel microfibers to a binary geopolymer matrix composed of metakaolin and ceramic tile polishing residue. Three mortar compositions (1:2, 1:3 and 1:4 cement:sand mass ratios) were produced with three microfiber concentrations (vf = 0.45, vf = 0.90 and vf = 1.35 % of total volume). The mechanical properties were evaluated by testing compressive strength, dynamic modulus of elasticity, flexural strength, and toughness. For 1:3 mortar, autogenous shrinkage measurements were performed for the 3 microfiber concentrations. Equivalent carbon dioxide emissions and binder intensity were also quantified. The mechanical properties classify the geopolymer concrete as high strength, achieving up to 95 MPa (composition 1:3) of compressive strength at 28 days and low binder consumption (9.82 kg.m−3. MPa−1). An improvement in flexural tensile strength was observed as the concentration of steel microfibers increased, reaching 20 MPa with vf= 1.35 %. For the concentration vf= 0.90 %, there was a reduction of ∼38 % of the autogenous shrinkage measurements about the reference (vf=0.0 %) at 28 days. In addition, regarding the CO2 intensity index, the lowest values were obtained for the 1:3 compositions, being minimum for vf= 0.90 % (9.01 [kg. ECO2-eq /m³ of mortar]/MPa), producing geopolymeric composites with low CO2 emissions, allowing the production of construction materials with low environmental impact.

Investigating the influence of nano-silica incorporation on mechanical characteristics of steel fiber-reinforced concrete to mitigate solid waste and environmental contamination

ABSTRACT Using nano-silica and steel micro-fibers in high-strength concrete has gained attention due to their potential to reduce solid waste and environmental pollution. In this study, the impact of nano-silica inclusions on the mechanical properties of steel fiber-reinforced concrete, referred to as “Micro-Concrete Reinforced with Steel Fibers Embedding Nano-Silica” (MRSFEN), was assessed. MRSFEN mixtures were prepared with 0%, 1%, and 2% nano-silica content and 0.5%, 1%, 2%, and 3% steel micro-fiber content. Tests showed a 17%-32% increase in compressive strength and a 12%-29% increase in tensile strength by adding 1%-2% nano-silica across all fiber contents. Incorporating 1%-3% steel micro-fibers resulted in 18–25 MPa higher compressive strength, 6–12 MPa higher tensile strength, and 10%-35% higher flexural strength relative to non-fiber concrete. However, workability reduced by 15%-30% with 3% fiber content. The combined use of nano-silica and steel micro-fibers enhanced strength and ductility, with the optimum composition identified as 1% nano-silica with 2% steel micro-fibers based on the mechanical performance. The results indicate the potential of tailored MRSFEN mixtures to improve the mechanical properties of steel fiber-reinforced concrete, with benefits in reducing solid waste and mitigating environmental contamination.

A comprehensive study on enhancing of the mechanical properties of steel fiber-reinforced concrete through nano-silica integration

Steel fiber reinforced concrete (SFRC) offers improved toughness, crack resistance, and impact resistance. Nano-silica enhances the strength, durability, and workability of concrete. This study investigated the combined effect of nano-silica and steel microfibers, termed micro-concrete reinforced with steel fibers embedding nano-silica (MRFAIN), on the mechanical properties of concrete. The aim was to determine the influence of different percentages of nano-silica and steel microfibers on fresh state properties, mechanical strength, and mechanical performance of MRFAIN. MRFAIN mixtures were prepared with cement, sand, water, superplasticizer, varying dosages of nano-silica (0–2%), and steel microfibers (0–2% by volume). Mechanical properties evaluated at 28 days included compressive strength, flexural strength, modulus of elasticity, and fracture energy. Incorporating steel microfibers reduced workability but enhanced mechanical properties like strength and ductility. Nano-silica addition showed variable effects on compressive strength but increased tensile strength. Optimal nano-silica content was 1% and steel microfibers 2%, giving compressive strength 122.5 MPa, tensile strength 25.4 MPa, modulus of elasticity 42.7 GPa. Using nano-silica and steel, microfibers enhanced the mechanical performance of steel fiber-reinforced concrete. This shows potential for reducing construction waste and pollution. Further research can optimize the proportions of nano-silica and steel microfibers in MRFAIN.

Dynamic properties of steel fiber-reinforced potassium magnesium phosphate cement-based materials after high-temperature treatment

Potassium magnesium phosphate cement (MKPC) demonstrates remarkably high-temperature resistance and exhibits ceramic-like characteristics above 1000 °C. When micro steel fibers (MSF) are introduced, the resulting micro steel fiber-reinforced potassium magnesium phosphate cement-based (MSF-MKPC) material displays superior impact resistance even at high temperatures. Besides that, it is non-toxic and environmentally friendly. To investigate the impact resistance of MSF-MKPC at high temperatures, the split Hopkinson pressure bar test was conducted to analyze its dynamic mechanical properties under varying conditions, including MSF content, temperature, and strain rate. Mechanism analyses were carried out using scanning electron microscopy, mercury intrusion porosimetry, and X-ray diffraction testing. The experimental findings revealed the following key points: (1) MSF content has a more significant impact on enhancing the dynamic compressive strength of MSF-MKPC after high-temperature exposure compared to room temperature. Additionally, as the temperature increases, the residual dynamic compressive strength of MSF-MKPC initially decreases and then rises. (2) In contrast to room temperature conditions, the overall dynamic toughness index of MSF-MKPC shows an upward trend with increasing MSF content after high-temperature exposure. As the strain rate increases, the overall dynamic toughness index of MSF-MKPC also increases. (3) A dynamic impact constitutive regression equation is proposed for MSF-MKPC after high temperature, and the predicted results align well with the experimental findings. The analysis of the dynamic performance of MSF-MKPC after high temperatures can serve as a theoretical basis for the design of MSF-MKPC in future engineering applications, as well as for advancing the environmental sustainability and mechanical properties of fiber-reinforced cement-based composite materials.

Phase‐field modeling for failure behavior of reinforced ultra‐high performance concrete at low cycle fatigue

AbstractThe influence of different fiber contents and orientations on the overall material behavior of steel microfiber reinforced UHPC is studied. To analyze the failure behavior of UHPC, the three‐point bending beam tests at low cycle is investigated experimentally and simulated numerically. For that purpose, recently developed phenomenological material model, see our recent works [1] and [2], based on the combination of elasto‐plastic phase‐field model for fracture and transversal isotropic elasto‐plasticity is implemented. For the modeling of distinct behavior of UHPC in tension and in compression, two different continuous stepwise linearly approximated degradation functions are used, cf. [3]. The numerical calibration is done using the measured mechanical properties of UHPC and steel fibers in the experiments. To use the different fiber distributions and orientations of steel fibers, the orientation distribution functions (ODF) are constructed. The prediction capability of the presented numerical model in terms of accuracy of numerical results comparing to the experimental data is discussed.

Experimental Investigation on the Impact of Micro-Steel Fibers on the Flat Slabs' Punching Shear Resistance

This research examined the effects of micro-straight steel fiber percentage and column form on the punching shear of SFRC slabs. Fibers made of micro steel with a diameter of 0.2 mm and a length of 13mm with an aspect ratio equal to 65 were used. The fiber content varied between 0.5%, 1%, and 1.5% by volume. Four different types of concrete mixes were adopted and tested. Experimental results showed that when the percentage of steel fibers in SFRC increased, its compressive strength, flexural strength, splitting tensile strength, and direct tensile strength improved. This investigation applied a monotonic load to eight cast slabs (two each of conventional concrete of square and circular column sections of the equivalent area while the other six slabs were made with steel fiber concrete. The dimensions of each slab were (920 x 920 x 80 ) mm. Each slab specimen had essential, edge-based support with square and round column sections. It has been demonstrated that slabs with square column sections endured a relatively higher ultimate load than slabs with circular column segments when the steel fiber dosage was 0.5% or 1.0%. Still, at a steel fiber dosage of 1.5%, circular column segment slabs approached the ultimate load of square column segment slabs. The heterogeneous behavior in concrete can be attributed to the random and unequal distribution of steel fibers throughout the material. There were only flexural fractures visible on the tensile face of the slab. New fractures emerged in the center of the slab as the load increased.