Steel Fiber Dosage Research Articles

Impact Resistance and Strength Reliability of Novel Two-Stage Fibre-Reinforced Concrete

Two-stage fibre-reinforced concrete (TSFRC) is a novel fibrous concrete that differs from the conventional fibre-reinforced concrete (FRC) in several aspects including its placement technique, implementation, fabrication methodology, and high coarse aggregate content. Consequently, the available data from the open literature on the behaviour of the conventional FRC exposed to falling weight collision may not be applicable to TSFRC. For instance, the impact strength performance of the conventional FRC is well documented; however, for TSFRC this has not been duly examined. For the first time, this study pioneers the concept of impact strength of TSFRC under falling weight collision. For this purpose, short crimped fibres and long hooked end steel fibres at 1.5, 3.0, and 5.0% dosage were used in two-stage concrete (TSC). To this end, seven different mixes were prepared and tested under falling weight collision as per ACI committee 544. In addition, a statistical analysis has been performed to analyse the scattered test results by Weibull distribution. For determining Weibull parameters, 20 probability estimators have been used, and the best estimators are taken for the reliability analysis. Based on the obtained Weibull parameters, the impact strength of TSFRC has been reported in terms of reliability. The results revealed that the ability of using higher fibre dosages allows achieving greater impact resistance properties for novel manufacturing TSFRC. Indeed, the TSC with steel fibre dosages exceeding 5%, can be produced easily thus making this innovative, yet simple to produce concrete, a strong contender in many construction applications. The two-parameter Weibull theory has been found to be adequately suitable for analysing the variations in the number of impacts that induces first crack and failure of all group of TSFRC specimens.

Efficiency of steel and macro-synthetic structural fibers on the flexure-shear behaviour of prestressed concrete beams

The efficiency of steel and structural synthetic fibers on the performance improvement of prestressed concrete (PSC) beams under combined flexure-shear is studied. Results of eleven PSC beams tested at a shear span (a) to depth (d) ratio of five are presented. Discrete steel and macro synthetic structural polyolefin fibers of varying dosages of 0.35%, 0.7% and 1.0% by volume of concrete were used. The effect of fiber addition on overall load – displacement, load- strain, and strain energy absorption capacity of PSC beams is analysed. Other parameters such as shear span to depth ratio (a/d), compressive strength of concrete, prestressing reinforcement ratio were kept constant. The test results portray that the addition of steel fibers stiffens the post cracking response, increases the strain energy absorption capacity more efficiently when compared to macro synthetic fibers (Polyolefin). The failure mode changed from less ductile flexure-shear to more ductile flexure dominant mode at 0.35% and 0.70% volumetric dosage of steel and synthetic fibers, respectively. The strain energy absorption capacity increased by more than 100% at 1.0% fiber addition for both steel and macro-synthetic fibers.

Numerical simulation of blast responses of ultra-high performance fibre reinforced concrete panels with strain-rate effect

Ultra-high performance fibre reinforced concrete (UHPFRC) is a promising construction material for protective structures due to its superior material characteristics. In this study, a finite element model is developed for the simulation of structural responses of UHPFRC panels subjected to blast loads. Based on the available experimental data, the procedures for the material model calibration are presented. The effect of strain rate on the dynamic material properties is reviewed, and the formula of dynamic increase factor is selected and proposed based on the steel fibre dosage and matrix strength. The developed finite element model is validated by comparing the numerical predictions with the test results from literature. In addition, a parametric study is carried out to investigate the effects of steel reinforcement ratios and the blast scenarios on the resistance of UHPFRC panels, and the advantages of using UHPFRC in protective structures are demonstrated by the comparison against high strength reinforced concrete panels.

Influence of splitting load on transport properties of ultra-high performance concrete

This paper presents an experimental investigation on the influence of splitting load on transport properties (air permeability and sorptivity) of UHPC incorporating different dosages of steel fibers (0%, 1%, 2% and 3%). ϕ100 mm × 50 mm specimens were subjected to splitting loads with stress levels varying from 50% to 80% of the ultimate splitting tensile strength. The splitting load induced damage was characterized by the crack pattern, crack opening displacement (COD) and penetrable porosity. Gas permeability and water sorptivity tests were carried out to evaluate the transport property of UHPC specimens after exposure to different levels of splitting load. The correlation among splitting tensile stress level, COD and transport property degradation of UHPC was analyzed. The results indicate that gas permeability and sorptivity of UHPC before loading are much better than that of normal concrete. The splitting tensile strength of UHPC is almost doubled by the addition of 1 ∼ 3% steel fibers in volume and the peak lateral deformation is increased by more than 10 times. Both the maximum value of COD (CODmax) under loading and the residual COD (CODres) after unloading of UHPC specimen increase with the more addition of steel fibers when exposed to the same stress level of splitting load. Both gas permeability and sorptivity of UHPC increase with the splitting load induced CODres. The higher dosage of steel fibers plays a positive effect on improving the transport properties of UHPC with the same CODres value. The sorptivity is more sensitive under a low deformation damage and the gas permeability is a better indicator to describe the durability degradation of UHPC under a high level of deformation.

Fire resistance of steel fiber reinforced concrete beams after low-velocity impact loading

Engineering structures in the city environment surrounded with combustible materials are prone to be in the danger of combined effects of blast-induced impact loading and fire. Four steel-fiber reinforced concrete (SFRC) beams were tested after pre-impact loading (impact velocity = 5.4 m/s) to explore their fire-resistance. The beams were first subjected to impact loadings and then exposed to fire with a constant load. The failure patterns of beams were observed, and the time histories of mid-span deflections, temperature field as well as rebar strains were recorded. Moreover, the fire resistance of these beams were discussed. A three-dimensional finite element numerical model considering the effects of strain rate and high temperature were established. In the simulations, a two-step analysis method was utilized. In the first-step, the impact loading process was simulated. While, in the second-step, and the failure behavior of the SFRC beams subjected to both fire and constant mechanical loading was modeled with a sequentially coupled thermal-stress analysis method, in which the simulation results obtained in the first-step were taken as the initial state. Good agreement between the simulation results and the test results illustrates the validation of the simulation method. It is found that the failure patterns of SFRC under the low-velocity impact load is altered from shear type to bending type with the increase of steel fiber dosage. When the impact energy is relative lower, though weakened by the pre-impact, the beam still work in an elastic stage and shows good fire resistance. Moreover, limited to the low-energy impact conditions, the influence of steel fiber content on the thermal and mechanical behaviors of damaged beam can be ignored.

Experimental and finite element analysis of creep behaviour of steel fibre reinforced high strength concrete beams

The present study is focused on experimental investigations and numerical analyses of compressive and tensile total creep at long-term of high-strength concrete (HSC) beams. Reinforced concrete (RC) beams with and without steel fibres were investigated for their long-term creep behaviour. These beams are under sustained uniformly distributed load (SUDL) in bending containing steel fibres (SF) with two aspect ratios (55 and 80) and two steel fibre dosages (0.5% and 1%). The objective of this work is to evaluate the influence of steel fibres, their dosage and their aspect ratio on compressive and tensile total creep. Experimental results show that the long-term total creep is influenced by the volume fractions of steel fibres. Moreover, steel fibres decrease the tensile total creep more than the compressive one. A non-linear finite element method (FEM) is performed to simulate the long-term total creep strain rate included thanks to the time hardening model called generalized Garofalo creep which is based on Bailey-Norton law called power law creep. It was found a good agreement between the experimental and numerical results.

EFFECTS OF STEEL FIBRES ON CONCRETE PROPERTIES AND FLEXURAL BEHAVIOUR OF REINFORCED CONCRETE SLABS

Concrete is a material that is good in compression but weak in tension. Enhancing the tensile properties of concrete will lead to its greater application in construction. It was reported that improvement on the mechanical properties of reinforced concrete structure can be achieved by the inclusion of short fibres. The use of short steel fibres have been reported to increase the toughness, abrasion, impact resistances and allow for decrease in concrete slab thickness. This paper focuses on the study conducted in the laboratory on the effect of steel fibre on concrete properties and behaviour of steel fibre reinforced concrete slabs under flexure with different amount of tensile reinforcements. A number of concrete cubes and prisms with and without steel fibres, 0%, 0.5%, 1.0%, 1.5% and 2.0% together with four reinforced concrete slabs having different amount of tensile reinforcement were cast and tested to failure in flexure. The optimum dosage of steel fibre to be included in concrete slab was 1%. The reinforced concrete slabs manufactured consist of slab with tensile reinforcement bar of R-150 as control slab, slab with tensile reinforcement bar of R-300 and 1% dosage of steel fibres, slab with 1% dosage of steel fibres without tensile reinforcement, and one plain concrete slab without reinforcement. All the slabs cast having the overall dimensions of 100 x 500 x 1000 mm, and tested to failure under four point loading. Cube compressive strength, modified compressive strength, flexural strength, ultrasonic pulse velocity test and rebound hammer test were conducted. The behaviour of the reinforced concrete slabs was studied through their ultimate load, load-deflection characteristic upon loading, cracking history, and mode of failure. The experimental results show that the inclusion of steel fibres was found to improve the compressive strength, slightly lowered the UPV value but no significant effect on the rebound hammer compared to the control sample. It was also found that based on slab SB-R300-1SF the inclusion of steel fibres increased the ultimate load of the slab by 25%, reduce the tensile reinforcement by about 50%, improve the flexural stiffness and ductility of the slab when compared to the control slab, SC-R150.

Assessment of the toughness of fibre-reinforced concrete using the R-curve approach

The fracture response of brittle materials like concrete can be characterised using modified linear elastic fracture mechanics models, such as the rising resistance curve (R-curve). In this study, the R-curve, determined by utilising the experimental response in the notched beam test with mode I fracture, is proposed as a measure of the toughness of fibre-reinforced concretes (FRCs). The unambiguity of the R-curve obtained is assessed by comparing the predicted flexural response of specimens of different geometries with experimental data. The variation in the R-curves with the dosage of steel and polymer fibres is also discussed.

Effect of Hybridization of steel fibers on the mechanical properties of high strength concrete

The hybridization of fibers for arresting the crack in concrete is a key factor and play an important role to improve mechanical properties of high performance concrete with respect to mono fibers. The effect of hybridization of hooked end steel fibers with different length and diameter on mechanical properties of high strength concrete was investigated in this research work. The different percentages of hook ended fibers (60 mm and 40 mm) are hybridized in the concrete mixture while keeping total percentage of fibers by volume equal to 1%. The compressive and flexural properties with complete load verses deflection curves of hybrid steel fiber reinforced high performance concrete were investigated to find the optimized dosage of hybrid steel fibers. The results showed that the hybridization of fiber provided better compressive and flexural performance. It was also observed from the results that combination of 65% of 60 mm and 35% of 40 mm hooked end fibers proved to be best for enhancement in compressive and flexural properties.

Short-term behaviour of reinforced and steel fibre–reinforced concrete composite slabs with steel decking under negative bending moment

An experimental study was conducted on reinforced and steel fibre–reinforced concrete composite slabs with steel decking under negative bending moment to quantify the ultimate behaviour, loading capacity and crack width under short-term loading. Eight full-scale slab specimens were cast with different types and amounts of reinforcement in the concrete (e.g. mesh, steel fibre or normal reinforcing bars) but with the same type of steel decking. Each slab was simply supported and tested in four-point bending under increasing load until failure. The deflections at mid-span and under the applied point loads were monitored together with the end interface slip. The crack widths were obtained for each slab for different levels of applied load. It was found that the end slip was quite negligible and complete interaction on the steel decking–concrete slab interface existed at service loads and ultimate limit states. Compared to the slab with 20 kg/m3 steel fibre, the application of steel fibre in excess of 60 kg/m3 increased the rotational capacity and ultimate load by 60% and 80%, respectively. Moreover, the higher dosage of steel fibres resulted in improved crack control, as for the same level of applied load, the crack width was often reduced by 75%. However, the slabs with conventional high-strength ductile reinforcements had the greatest ultimate load and rotational capacity and exhibited the best degree of crack control with finer and more distributed cracks.

Novel steel fibre-reinforced preplaced aggregate concrete with superior mechanical performance

This study pioneers the concept of fibre-reinforced preplaced aggregate concrete through premixing and preplacing steel fibres with aggregates in the formwork, then injecting a flowable grout. Unlike in conventional steel-fibre reinforced concrete where the fibre dosage, length and aspect ratio are hampered by workability considerations, the influence of fibres on workability, place-ability and consolidation is eliminated. Hence, fibre dosages beyond those conceivable in conventionally mixed concrete can be considered. The compressive, tensile and flexural strengths, load-deflection curves and toughness were appraised for the new steel fibre-reinforced preplaced aggregate concrete incorporating various dosages of steel fibres having different lengths. It is shown that the ability of using higher fibre dosages allows achieving exceptional engineering properties for preplaced aggregate concrete. Indeed, the material can easily be produced with steel fibre dosages exceeding 6%, making this innovative, yet simple to produce concrete, a strong contender in many construction applications.

Effects of mineral admixtures and steel fiber on rheology, strength, and chloride ion penetration resistance characteristics of wet-mix shotcrete mixtures containing crushed aggregates

This study presents the effects of various mineral admixtures such as silica fume, fly ash, ground granulated blast furnace slag (GGBFS), and metakaolin and steel fiber on the rheology, strength, and chloride ion penetration resistance characteristics wet-mix shotcrete (WMS) mixtures made with crushed aggregates. The mixtures tested in this study are mostly ternary mixtures blended with silica fume. Potential implications of measured rheological properties in relation to pumping and shooting performance of WMS mixtures were also analyzed. The results have shown that silica fume may be an effective admixture benefiting both pumpability and shootability of WMS. Fly ash was found to adversely affect the pumpability of WMS mixtures by markedly increasing the torque viscosity. GGBFS had non-significant effects on both pumpability and shootability, whereas it strongly improved the chloride ion penetration resistance and strength of WMS. It was also identified that no more than 5% metakaolin by mass of cement is necessary to enhance the pumpability, shootability, and chloride penetration resistance of WMS. Despite many expected advantages of using steel fibers in WMS, special attention should be paid to prevent excessive degradation of pumpability and chloride ion penetration resistance when a high dosage (>50kg/m3) of steel fibers is used.

Fuzzy inference systems based prediction of engineering properties of two-stage concrete

Two-stage concrete (TSC), also known as pre-placed aggregate concrete, is characterized by its unique placement technique, whereby the coarse aggregate is first placed in the formwork, then injected with a special grout. Despite its superior sustainability and technical features, TSC has remained a basic concrete technology without much use of modern chemical admixtures, new binders, fiber reinforcement or other emerging additions. In the present study, an experimental database for TSC was built. Different types of cementitious binders (single, binary, and ternary) comprising ordinary portland cement, fly ash, silica fume, and metakaolin were used to produce the various TSC mixtures. Different dosages of steel fibres having different lengths were also incorporated to enhance the mechanical properties of TSC. The database thus created was used to develop fuzzy logic models as predictive tools for the grout flowability and mechanical properties of TSC mixtures. The performance of the developed models was evaluated using statistical parameters and error analyses. The results indicate that the fuzzy logic models thus developed can be powerful tools for predicting the TSC grout flowability and mechanical properties and a useful aid for the design of TSC mixtures.

Fatigue behaviour of transversely restrained precast steel fibre reinforced concrete slabs in a deconstructable composite deck

This study investigates fatigue behaviour and failure of transversely restrained precast reinforced concrete (RC) deck slabs with and without steel fibres (SF) in a novel deconstructable steel-concrete composite deck that takes advantage of bolted shear connectors. In total, seven precast (SF)RC slabs were tested under a static load to establish the peak load capacity of the specimens and the another eight slabs were tested under cyclic loads. The types of lateral restraint (i.e. cross-bracings or ties) provided for the slabs, reinforcing configuration and steel fibre dosage (i.e. 0.25% and 0.5%) were the main variables in this study. The results of experiments showed that increasing the level of service load on accounting of strength enhancement provided by arch action has no negative impact on the fatigue behaviour of transversely restrained (SF)RC deck slabs. Furthermore, it was concluded that adding 0.25% and 0.5% fibres have similar effect on the static load capacity, but significant enhancement in the fatigue life was only observed in the transversely restrained slabs with a fibre dosage of 0.5%.

Explosive spalling of ultra-high performance fibre reinforced concrete beams under fire

Purpose The purpose of the study was to investigate the spalling phenomenon in ultra-high performance fibre reinforced concrete (UHPFRC) beams on exposure to a standard fire curve (ISO 834) under a sustained load. Design/methodology/approach The variables in this study were steel fibre dosage, polypropylene (PP) fibres and loading levels. The research investigated seven beams – three of which contained steel fibres with 2 vol.%, another three had steel fibres with 4 vol.% dosage and the seventh beam had a combination of steel fibres (2 vol.%) and PP fibres (4 kg/m3). The beams were tested for 1 h under three loading levels (20, 40 and 60 per cent) based on the ambient temperature ultimate flexural strength of the beam. Findings Spalling was affected by the loading levels; it exacerbated under the load level of 40 per cent, whereas under the 60 per cent load level, significantly less spalling was recorded. Under similar loading conditions, the beams containing steel fibres with a dosage of 4 vol.% spalled less than the beams with fibre contents of 2 vol.%. This was attributed to the additional tensile strength provided by the excess steel fibres. The presence of PP fibres eliminated spalling completely. Originality/value There is insufficient research into the performance of UHPFRC beams at elevated temperature, as most studies have largely focussed on columns, slabs and smaller elements such as cubes and cylinders. This study provides invaluable information and insights of the influence of parameters such as steel fibre dosage, PP fibres, loading levels on the spalling behaviour and fire endurance of UHPFRC beams.

Influence of steel and/or polypropylene fibres on the behaviour of concrete at high temperature: Spalling, transfer and mechanical properties

In this study different mixtures of high strength concretes (70MPa) were prepared with different natures of aggregates, moisture content, length and dosage of polypropylene fibres (PPF) and steel fibres (SF) and subjected to the standard ISO 834 fire. Concretes with 60kg/m3 of SF show spalling while plain concrete (without fibres) and concrete with 0.75kg/m3 of PPF and 60kg/m3 of SF did not spall. Microstructure, thermal, hydric and mechanical properties of concretes were investigated. PPF increase the porosity and permeability of concretes. Steel fibres control crack development which reduce the stress relaxation phenomenon and the size of new pores.

THE STRAIN RATE EFFECT ON THE FLEXURAL STRENGTH AND COST OF STEEL FIBER REINFORCED CONCRETE BEAMS

The beneficial effect of strain rate upon the ductility and loading capacity of steel fiber reinforced concrete (SFRC) beams subject to quasi-static and dynamic three point bending tests with various amounts of steel fibers and the economical influence on the construction was investigated in this paper. Experimental results revealed that the loading capacity of SFRC beams attained higher values at dynamic strain rates applied in beams with low dosage of steel fibers. In addition, the cost construction of these SFRC beams was mainly affected by concrete class and not fibers dosage to attain SFRC beams the optimum loading capacity.

Relationship between Flowability, Entrapped Air Content and Strength of UHPC Mixtures Containing Different Dosage of Steel Fiber

This study investigated the effects of different fiber contents by volume (0%, 1%, 2%, and 3%) on flowability, entrapped air content, and compressive and flexural strength of ultra high performance concrete (UHPC). Four water-to-binder ratios (0.18, 0.20, 0.22, 0.24) were used and four different dosages of superplasticizer were introduced for preparing each water-to-binder ratio mixture. The experimental results reveal that the increased content of fiber decreases the flowability and entrapped air content of fresh UHPC mixtures. The compressive strength of UHPC increased with a greater addition of steel fiber, from 1% to 3%. The flexural strength was increased slightly by the addition of 1% steel fiber and increased remarkably with the addition of 2% and 3% steel fiber. For every water-to-binder ratio mixture, with and without steel fiber, a good linear relationship can be found between compressive strength and entrapped air content. Therefore, it is suggested that lowering the entrapped air provides a significant contribution to increasing compressive strength of UHPC containing higher steel fibers.

Effect of fiber dosage and prestress level on shear behavior of hybrid GFRP-steel reinforced concrete I-shape beams without stirrups

Abstract Corrosion of steel reinforcements embedded in concrete elements is generally known as one of the most common reasons that shorten the service life of the structures. The present study aims to contribute in overcoming this problem by replacing steel stirrups as shear reinforcement of concrete beams using a steel fiber reinforced self-compacting concrete (SFRSCC). In the present research the potential of SFRSCC for improving the shear resistance of the beams without stirrups is explored. In order to further reduce the risk of corrosion in this type of beams, a hybrid system of flexural reinforcement composed of a steel strand and GFRP rebars is applied and properly arranged in order to assure a relatively thick concrete cover for the steel reinforcement. The GFRP bars are placed with the minimum cover thickness for providing the maximum internal arm and, consequently, mobilizing efficiently their relatively high tensile strength. The effectiveness of applying different dosages of steel fibers and varying the prestress force to improve the shear behavior of the designed beam are evaluated. By considering the obtained experimental results, the predictive performance of a constitutive model (plastic-damage multidirectional fixed smeared crack model) implemented in a FEM-based computer program, as well as the one from three analytical formulations for estimating shear resistance of the developed beams were assessed. The FEM-based simulations have provided a good prediction of the deformational response and cracking behavior of the tested beams. All the analytical formulations demonstrated acceptable accuracy for design purposes, but the one proposed by CEB-FIP Modal Code 2010 predicts more conservative shear resistance.

Electrochemical immittance spectroscopy applied to a hybrid PVA/steel fiber engineered cementitious composite

Alternating current (a.c.) electrical property measurements are presented on an Engineered Cementitious Composite (ECC) reinforced with a hybrid mix of polyvinyl alcohol fibers (fixed dosage) and straight steel fibers of varying dosages (0.15–1.0% by volume), with the aim at elucidating the influence of conductive inclusions on the nature of conduction and polarization processes within the composite. Measurements were undertaken over the frequency range 1Hz–10MHz at 7, 14 and 28days after casting and the data presented in a range of formalisms to aid interpretation. When plotted in the frequency domain, the work shows that steel fibers enhance the polarizability of the material, particularly within the frequency range ~10Hz–10kHz. When presented in Nyquist format, this feature manifests itself as an intermediate arc forming between a high frequency arc (>10kHz) and a low frequency arc (<10Hz), the latter resulting from polarization processes at the sample/electrode interface. The prominence of the intermediate arc was found to be dependent upon steel fiber dosage and curing time. It is shown that the bulk electrical conductivity conforms to the equivalent inclusion theory which is a variant on the effective medium theory.