Steel Fiber Matrix Research Articles

Steel Fiber–Matrix Interfacial Bond in Ultra-High Performance Concrete: A Review

Ultra-high performance concrete (UHPC) is a relatively new cementitious concrete composite with significant application potential in infrastructure construction because of its excellent mechanical strength and durability. The steel fiber–matrix interfacial bond is the main factor that governs other mechanical properties of UHPC, including tensile, flexural, and compressive strengths and failure mode (fracture behavior). This paper presents a comprehensive review on the research progress of fiber–matrix bond behaviors of UHPC by discussing and comparing a range of fiber pullout testing methods and analytical models. The parameters of the fiber–matrix bond, including the geometry and orientation of fibers, surface treatment, and composition and strength of the matrix, are identified and discussed in detail. Lastly, recommendations for future research related to UHPC strengthening methods and testing details are provided based on recent progress.

Contribution of fiber–matrix interface enhancement on flexural properties of Ultra–high–performance concrete

Herein, the effect of steel fiber–matrix interface reinforcement on the macromechanical properties of ultra–high–performance concrete (UHPC) is studied. Two types of nano–SiO2–coated steel fibers are prepared using the sol–gel method. Single–fiber pull–out tests are conducted, and flexural and compression tests of UHPC with fiber contents of 1 vol%, 2 vol%, and 3 vol% are performed. The results reveal that the enhancement of interfacial adhesion significantly influences the macromechanical properties of UHPC. However, the granular nano–SiO2 on the surface of the modified steel fibers increases the roughness of the steel fiber and reduces the fluidity of fresh UHPC mixture. Analysis of the images of crack section reveals that appropriate vibration can reduce the influence of the steel fiber surface roughness on the distribution of fibers in UHPC. A flexural load–deflection response model for UHPC that considers steel fiber–matrix interface bond strength and fiber orientation is established.

Flexural performance and patterns identification of UHPC subjected to alternating elevated and cryogenic attacks with acoustic emission characterization

This paper investigates the flexural performance of ultra-high-performance concrete (UHPC) subjected to a simulated lunar ground temperature environment between 200 °C and −170 °C termed as alternating elevated and cryogenic attack (AECA). Additionally, the cracking behavior during the failure process was characterized by acoustic emission (AE) technique. Compared with unexposed UHPC specimens, those exposed to AECA up to five cycles still exhibit superior flexural performance. The AE results imply that tensile cracks are mainly generated by the failure of cement matrix, and shear cracks are mainly attributed to the steel fiber–matrix debonding and steel fiber pull-out behaviour. AECA exhibits the dual effect of enhancement and deterioration on the flexural performance of UHPCs, and there is even a competitive relationship between the two effects. Due to the dual effect, cement matrix strength and bond strength between cement and steel fiber show different responses to AECA. Finally, four prediction equations that matched excellently with the experimental results are proposed to estimate the residual flexural load and compute the flexural toughness directly according to Newton-Leibniz law instead of integrating the area under the load–deflection curve.

Mesoscopic Modeling Approach and Application for Steel Fiber Reinforced Concrete under Dynamic Loading: A Review

Steel fiber reinforced concrete (SFRC) has drawn extensive attention in recent years for its superior mechanical response to dynamic and impact loadings. Based on the existing test results, the high-strength steel fibers embedded in a concrete matrix usually play a strong bridging effect to enhance the bonding force between fiber and the matrix, and directly contribute to the improvement of the post-cracking behavior and residual strength of SFRC. To gain a better understanding of the action behavior of steel fibers in matrix and further capture the failure mechanism of SFRC under dynamic loads, the mesoscopic modeling approach that assumes SFRC to be composed of different mesoscale phases (i.e., steel fibers, coarse aggregates, mortar matrix, and interfacial transition zone (ITZ)) has been widely employed to simulate the dynamic responses of SFRC material and structural members. This paper presents a comprehensive review of the state-of-the-art mesoscopic models and simulations for SFRC under dynamic loading. Generation approaches for the SFRC mesoscale model in the simulation works, including steel fiber, coarse aggregate, and the ITZ between them, are reviewed and compared systematically. The material models for different phases and the interaction relationship between fiber and concrete matrix are summarized comprehensively. Additionally, some example applications for SFRC under dynamic loads (i.e., compression, tension, and contact blast) simulated using the general mesoscale models are given. Finally, some critical analysis on the current shortcomings of the mesoscale modeling of SFRC is highlighted, which is of great significance for the future investigation and development of SFRC.

Effects of brass coating and nano-SiO2 coating on steel fiber–matrix interfacial properties of cement-based composite

This study focused on the effects of steel fiber coatings on the interfacial properties of a fiber-reinforced cement-based composite. The impact of a brass coating on the interface between the steel fibers and cement matrix was examined, and the improvement effects of a nano-SiO2 coating and nano-SiO2 powder on both the microstructure and interfacial bond properties were compared. A chemical simulation experiment was designed to analyze the brass coating state in a cement hydration environment. The backscattered electron image analysis (BSE-IA) method was used to conduct quantitative analyses of the calcium hydroxide (CH), porosity, and unhydrated cement (UHC) to investigate the microstructure of the fiber–matrix interfacial transition zone (ITZ). Pull-out tests were conducted to determine the interfacial bond performance, and scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for micro-observation and element analyses. The results indicated that because of the destruction of the coating structure and the aggregation of CH caused by the dezincification of the brass in a cement hydration environment, the brass coating did not improve (but weakened) the interfacial microstructure and bond performance. Adding the nano-SiO2 powder directly was a useful method for achieving microstructure densification and defect reduction in both the ITZ and bulk paste, while the nano-SiO2 coating provided a more targeted improvement in the fiber–matrix ITZ, particularly near the fibers, leading to a more effective enhancement of the bond performance.

Strength Characteristics of Slag Based Steel Fiber Reinforced Concrete with Partial Replacement of Steel Slag in Coarse Aggregate

The current research work represents the various test results from an experimental program for the influence of mineral admixture, stone dust, steel slags and rapid hardening (accelerator) type of chemical admixtures along with the inclusion of steel fibers for various mixture proportions on the mechanical properties of concrete. The different strength properties considered the cubical size for compressive strength, prism for flexural rigidity and monitored the ultrasonic pulse velocity test including water absorption (sorptivity) test for different curing days was evaluated. The outcome results for concrete shows that when the percentage of steel slag is increased then there will be a good workability in fresh concrete than normal aggregates. In overall 100% of stone dust, if the portion of steel slag is more than 40% with replacement of coarse aggregate and binding material as slag will lead to minimum workability, there is no change in the proceding workability area in the further addition of super plasticizer. Also, the study indicates that the crimped steel fiber matrix interaction gives considerable results to enhance the bending stress in flexural rigidity caused by the introducing of steel fibers.

Investigation on microstructure and tensile behaviour of stir cast LM13 aluminium alloy reinforced with copper coated short steel fibers using response surface methodology

Copper coated steel fibers reinforced LM13 aluminium alloy composites have been prepared using stir casting process. Experiments have been designed using response surface methodology by varying wt% of reinforcement (0–10), stirrer speed (350–800 rpm) and pouring temperature (700–800 °C). Microstructure, tensile strength and fracture surface of composites have been investigated. Analysis of variance, significance test and confirmation tests have been performed and regressions models have been developed to predict the tensile strength of composites. Response surface plots reveal that tensile strength of composites increases with increasing wt% of copper coated steel fibers reinforcement up to 6 wt%. Further increase in wt% of steel fibers decreases the tensile strength of composites. However tensile strength of composites increases with increasing stirrer speed due to the uniform and homogeneous dispersion of steel fibers in matrix. Optimum stir cast process parameters for obtaining higher tensile strength are found to be 5.9 wt% of reinforcement, 753 °C pouring temperature and stirrer speed of 633 rpm. Fracture mechanism is dominated by steel fiber pullouts in composites with higher wt% of reinforcement and dimples are observed in the surface of composites containing lower levels of wt% of reinforcement.

Effects of different deformed steel-fibers on preparation and fundamental properties of self-compacting SFRC

Effects of different deformed steel fibers on the preparation and fundamental properties of self-compacting SFRC were experimentally studied. Four types and three volume fractions of steel fiber were considered as the influence parameters. Evaluation method of static segregation resistance of steel fibers is presented using the distribution uniformity of steel fibers in matrix. Several suggestions are proposed to improve the test methods for characterizing workability and to evaluate the efficiency of steel fiber in enhancing strengths of self-compacting SFRC. The predictive models for axial compressive and splitting tensile strengths are proposed in relation with the effective distribution of steel fiber.

Pull-out behavior of steel fiber embedded in flowable RPC and ordinary mortar

The aim of this research is to investigate some of the factors which affect the steel fiber–matrix bond characteristics by means of pull-out test. Ordinary mortar (OM) and reactive powder concrete (RPC) were used as main matrices. The effect of parameters such as end condition of fiber (smooth or hooked-end), embedment length, water/binder ratio, paste phase of RPC, steel-micro fiber, and curing conditions on fiber–matrix pull-out behavior were determined. The fiber–matrix bond characteristics improved as the embedment length of fiber increased, especially for smooth fiber. Low W/C ratio, which enhances the bond strength, reduces the importance of embedment length of the hooked-end fiber. Furthermore, the pull-out peak load and debonding toughness increased as the W/C ratio decreased in the all curing conditions. Microstructural investigation revealed that the congestion of hydration products in fiber–matrix interface improves pull-out behavior remarkably.

The effect of metakaolin and end type of steel fiber on fiber-SIFCON matrix bond characteristics

SIFCON (Slurry Infiltrated Fiber Concrete) can be described as a special type of cement based composite produced with fiber volume fraction values between 5 to 30%. As a result of superior mechanical properties such as compressive, tensile, shear and flexural strengths with extraordinary toughness values, SIFCON can be used in in industrial floors, repair and reinforcement works and military applications such as anti-missile hangers. Mechanical properties of fiber reinforced cement based composites are dramatically influenced by steel fiber–matrix bond characteristics. Many parameters such as fiber type and geometry, matrix strength, curing conditions and properties of fiber-matrix interface affect the fibermatrix bond characteristics. The density of this zone can be increased with supplementary cementitious materials such as metakaolin. In this study the effect of metakaolin and end type of steel fiber on bond characteristics has been investigated. The fiber-matrix bond characteristics were determined by applying single-fiber pull-out test. Utilization of metakaolin has improved the compressive strength and fibermatrix bond characteristics. In addition, hooked-end fiber has a better performance compared to the smooth fiber. ©2014 Usak University all rights reserved.

The effect of alkali–silica reaction on steel fiber–matrix bond characteristics of cement based mortars

The effect of ASR on fiber–matrix bond behavior has been investigated in this research. The potentially reactive basaltic aggregate was chosen as a reactive material. Two series of specimens containing different amounts of supplementary cementing materials (SCMs) were prepared. One of them was cured in 1M NaOH solution at 80°C, other series were cured in 80°C water up to 150days to obtain similar maturity. ASR expansion, single fiber pull-out load, debonding toughness, flexural and compressive strength was determined. Test results indicate that the ASR gel congestion in fiber–matrix interface increased the bond strength significantly during alkali exposure. Furthermore, SCMs are effective to reduce ASR expansion and to prevent the mechanical properties loss due to ASR. Micro-structural investigations revealed the reaction products having different morphology (fibrous, rosette type, network appearance, etc.) in alkali exposed specimens.

Gold–palladium supported on porous steel fiber matrix: Structured catalyst for benzyl alcohol oxidation and benzyl amine oxidation

Abstract Au, Pd and Au-Pd alloy are deposited on porous steel fiber matrices via sputtering technique. By this technique the preparation of the heterogeneous catalysts is clean, simple and fast as noble metal complexes, solvents or reducing agents are not needed. The studied Au-Pd catalyst exhibits good activity in the aerobic oxidation of benzyl alcohol and benzyl amines. Especially in the oxidation of benzyl amines, the Au-Pd catalyst shows a great synergistic enhancement in the activity.

Study on Interfacial Properties of Ultra-High Performance Concrete Containing Steel Slag Powder and Fly Ash

The interfacial properties of reactive powder concretes (RPCs), other known as ultra-high performance concrete (UHPC), containing steel slag powder and ultra fine fly ash are studied in this paper. The microstrctural characterization of interfacial transition zones (ITZs), including the aggregate-cement paste interfacial zone and the steel fiber-paste interfacial zone, is investigated by SEM. The microhardness of the aggregate-paste ITZ and the steel slag-paste ITZ is studied and the bond strength of steel fiber in matrix is tested through fiber pullout tests. The results indicate that the microhardness of the steel slag-paste ITZ is slightly higher than that of the aggregate-paste ITZ, which implies the advantage of the substitution of quartz powder with steel slag powder in preparation of RPCs to some degrees. Moreover, the hardness of these two ITZs is higher than that of the hardened paste. A certain amount of hydration products has been observed exsiting on the surface of steel fiber by SEM and the bond strength of steel fiber-martix is up to 9.3MPa. These interfical properties are definitely critical to obtain high performance of UHPCs containing steel slag powder and fly ash.

Noble metal-modified TiO2 thin film photocatalyst on porous steel fiber support

Through-porous steel fiber matrix with high specific surface area and self-support strength was examined as the support of TiO2 film photocatalyst. TiO2 was uniformly and conformally deposited onto the surface of the metal skeleton of the porous steel fiber matrix via atomic layer deposition method so that the porosity as well as gas permeability of the matrix is maintained. For further improving the photocatalytic activity, noble metals (Au and Pt/Pd alloy) were sputtered onto the surface of TiO2 photocatalyst. The photodegradation of methyl orange was used for evaluating the photocatalytic properties. The results show that compared with TiO2 films deposited on flat Si wafers, TiO2 films on the porous support display higher photocatalytic activities, owing to their higher specific surface areas. The photocatalytic activity of TiO2 on porous support was not enhanced by Au, while it was remarkably improved by Pt/Pd. The TiO2 photocatalysts were also analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy.

Application of nanoindentation testing to study of the interfacial transition zone in steel fiber reinforced mortar

The characteristics of the profiles of elastic modulus and hardness of the steel fiber–matrix and fiber–matrix–aggregate interfacial zones in steel fiber reinforced mortars have been investigated by using nanoindentation and Scanning Electron Microscopy (SEM), where two sets of parameters, i.e. water/binder ratio and content of silica fume were considered. Different interfacial bond conditions in the interfacial transition zones (ITZ) are discussed. For sample without silica fume, efficient interfacial bonds across the steel fiber–matrix and fiber–matrix–aggregate interfaces are shown in low water/binder ratio mortar; while in high water/binder ratio mortar, due to the discontinuous bleeding voids underneath the fiber, the fiber–matrix bond is not very good. On the other hand, for sample with silica fume, the addition of 10% silica fume leads to no distinct presence of weak ITZ in the steel fiber–matrix interface; but the effect of the silica fume on the steel fiber–matrix–aggregate interfacial zone is not obvious due to voids in the vicinity of steel fiber.

Effect of silica fume, steel fiber and ITZ on the strength and fracture behavior of mortar

Two sets of parameters known to affect the quality and thickness of the interfacial transition zone (ITZ), i.e. water/binder ratio and content of silica fume were varied in a series of mortars without and with steel fiber. Compressive and three-point bending tests were performed and the dissipated energies were calculated. Nanoindentation characteristics of the steel fiber–matrix and fiber–matrix-aggregate interfacial zones in the steel fiber reinforced mortars were studied. Influence of water/binder ratio, steel fiber, silica fume and ITZ on the strength and toughness of the mortar was analyzed, respectively. It is found that mortar compressive strength can be increased with low volume addition of steel fiber if the air content is well controlled; the interfacial characteristic and microstructural morphology near the fiber surface play a critical role on the three-point bending strength and the toughness of the steel fiber reinforced mortar.

Mesomechanism of steel fiber reinforcement and toughening of reactive powder concrete

Reactive powder concrete (RPC) is a novel cement-based composite material with ultra-high strength. Embedding a certain amount of short steel fibers in the matrix can improve the RPC’s toughness and overcome the disadvantage of high brittleness. In this paper, a number of direct uniaxial tension tests have been carried out with ‘8-shape’ RPC200 specimens. The bond-slip process, mesoscopic structural variation and mechanical characteristics of a fiber pullout of the matrix have been investigated using the real-time SEM loading system and CCD observation techniques. The influence of the volume of embedded short steel fibers in matrix on the mesoscopic morphology of attachments on the surface of a pulled individual fiber, the initial cracking force, the ultimate pullout force, interfacial bond strength and the pullout rupture energy have been analyzed. A general formulation relating these quantities to the volume of fibers in matrix has been proposed. The components comprising the interfacial bond strength have been outlined. In addition, the contribution that fibers make to enhance and toughen the reactive powder concrete has been discussed. It is shown that there exists an optimal threshold of fiber volume ρ v, opt = 1.5% at which the bond performance of a fiber pullout of RPC behaves best.

Effect of silica fume on steel fiber bond characteristics in reactive powder concrete

In this paper, the effect of silica fume on the bond characteristics of steel fiber in matrix of reactive powder concrete (RPC), including bond strength, pullout energy, etc., are presented. The experimental results on steel fiber pullout test of different conditions are reported. Various silica fume contents ranging from 0% to 40% are used in the mix proportions. Fiber pullout tests are conducted to measure the bond characteristics of steel fiber from RPC matrix. It is found that the incorporation of silica fume can effectively enhance the fiber–matrix interfacial properties, especially in fiber pullout energy. It is also concluded that in terms of the bond characteristics, the optimal silica fume content is between 20% and 30%, given the conditions of the experimental program. The microstructural observation confirms the findings on the interfacial-toughening mechanism drawn from the fiber pullout test results.