Fiber Reinforced Concrete Structures Research Articles

Experimental Study on Impact Behavior of Concrete Panel with and without Polypropylene Macrofibers

Macrofibers have often been used to increase the tensile strength, durability, crack resistance, spalling, impact resistance, and toughness of concrete. However, the impact behavior of fiber-reinforced concrete (FRC) structures is quite different from their static behavior, and the effectiveness of macrofibers in improving impact resistance should be carefully evaluated. In this study, the impact behavior of FRC with polypropylene (PP) macrofibers was studied through a series of drop-weight impact tests. First, the material characteristics of the FRC with PP fibers under static conditions were evaluated. Test specimens were constructed and drop-weight impact tests were performed. The main parameters were the presence or absence of PP fibers and the drop height, which is related to the magnitude of the impact energy. From the results, it can be found that the crack width of the FRC specimen was smaller than the normal concrete specimen for a similar residual deflection after the impact test due to the bridging effect of the macrofibers. However, the effect of PP fibers on the impact resistance was not significant, even though there was a considerable increase in tensile and flexural performance under static conditions, since the hardening effect after the sharp reduction in strength shown in the static test of FRC is not effective in the impact test.

Tensile behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) structure with cold joints

Ultra-high-performance fiber-reinforced concrete (UHPFRC) structures comprise connection joints, which are typically the weakest part. Appropriate joint construction can improve the force-transfer performance of UHPFRC structures. In this study, the effects of the interfacial roughening method, steel fiber content and length, interfacial reinforcement ratio, and embedment length on the tensile behavior of UHPFRC cold joints are investigated via direct tension tests. The test results indicate that the roughening methods using high-pressure water jet and uneven plastic formwork significantly improve the bond performance of UHPFRC cold joints. Moreover, the steel fibers in the cold-joint interface enhance the tensile strength and toughness of these joints. The typical failure mode of the unreinforced UHPFRC cold joint is found to be brittle failure. By contrast, the cracking and failure surfaces shift from the cold joints to the UHPFRC matrix when the UHPFRC cold joint is well-reinforced. Furthermore, an increase in the interfacial reinforcement ratio and embedment length improves the ultimate tensile strength of the reinforced UHPFRC cold-joint specimens, whereas the minimum embedment length decreases with the interfacial reinforcement ratio (should be at least 40 mm). In addition, an equation for the minimum embedment length of reinforcing steel rebars is proposed. The proposed method can be applied to determine the effects of the parameters, tensile strengths of the UHPFRC matrix and cold joint interface, reinforcement ratio, and rebar diameter on the tensile behavior of UHPFRC cold joints.

Microstructure, Shrinkage, and Mechanical Properties of Concrete with Fibers and Experiments of Reinforced Concrete Beams without Shear Reinforcement.

The current findings on concrete with fibers show that research has focused primarily on individual aspects, especially in terms of mechanical properties and structural uses. However, no broader view of the problems solved has been provided. In this study, we present a conceptual overview of a new, comprehensive experimental program for the assessment of fiber-reinforced concrete, which includes the analysis of microstructural and structural elements, as well as specific features such as shrinkage and resistance to pressurized water. The proposed experimental program included several variants of schemes for the dosing of fibers into concrete, using steel fibers that were short and straight. Fiber dosing was performed up to 110 kg/m3. The basic tests performed included tests of the compressive strength of concrete, and of the split and flexural tensile strength for different dosing amounts. Within the structural tests of reinforced concrete beams without shear reinforcement, two variants of spans with different degrees of reinforcement were implemented. Herein, the test results are evaluated graphically with a detailed analysis of the positive effect of fibers, and we also provide general recommendations for the structural uses of the fibers used and the design of fiber-reinforced concrete structures. Among the important results of this experimental program was the observation of a significant increase (of the order of tens) of the percentage of the split tensile strength and an increase of the overall load-bearing capacity of the reinforced concrete beams without shear reinforcement. Among the important aspects of our findings is the fact that a fine-grained concrete mixture was used, which increased resistance to pressure water seepage, and therefore, the effect of shrinkage can be influenced by the method of production and the treatment of the concrete used. We also provide detailed figures of the microstructure.

ДЕФОРМИРОВАНИЕ ФИБРОБЕТОНА ПРИ ОДНОКРАТНОМ ДИНАМИЧЕСКОМ ВОЗДЕЙСТВИИ С УЧЕТОМ ВЛИЯНИЯ НАЧАЛЬНЫХ НАПРЯЖЕНИЙ ОТ СТАТИЧЕСКОЙ НАГРУЗКИ

An analysis of the experimental studies presented in the scientific literature indicates that the strength and deformability of fiber-reinforced concrete under dynamic additional loading may depend on the initial level of stresses caused by a preliminarily applied static load. In this regard, the purpose of this study was to build improved models of fiber-reinforced concrete deformation of operated fiber-reinforced concrete structures of bearing systems of buildings and structures during their dynamic additional loading, taking into account the nonlinearly elastic law of material deformation at the stage of loading with a static load, as well as changes in the parameters of viscous resistance during loading. As a model of the force resistance of fiber-reinforced concrete of loaded fiber-reinforced concrete structures during their dynamic additional loading caused by an emergency situation, the Kelvin-Voigt model for an elastic-viscous body was adopted. On the basis of the adopted model, an analytical solution of the differential equation of uniaxial compression of fiber-reinforced concrete was obtained under its single dynamic additional loading from an arbitrary level of initial stresses acting in it from a previously applied static load. A step-iterative approach to determining the parameters of state diagrams of fiber-reinforced concrete under static-dynamic loading conditions is proposed. An analysis of the obtained dependences between stresses and strains shows that an increase in the level of initial stresses acting in a compressed concrete element at the moment a dynamic load is applied to it leads to a decrease in the dynamic strength of concrete with the same impact parameters.

Experimental Investigation of Ultrasonic Pulse Velocity (UPV) Test Specimen in Assessing the Strength of Steel Fiber Reinforced Concrete Structure

This study aims to conduct the Ultrasonic Pulse Velocity (UPV) test and compressive strength test of Steel Fiber Reinforced Concrete (SFRC). This paper also examines the correlation of UPV test data and compressive strength test data for SFRC specimens. The experiments were carried out with the same value of the water-cement ratio, superplasticizer but different fiber volumes of steel fiber. Twelve prism sizes 100mm x 100mm x 500mm were casted and 0.5%, 1.0%, and 1.5% of steel fiber reinforced concrete were added and the prisms undergone curing for 7, 14 and 28 days. The highest value of the UPV test at the x-axis is SFRC-0.5%, 6.26 km/s at seven days and 6.8377 km/s at 14 days. The highest value of the UPV test at the y-axis is SFR-0.5%, 6.68 km/s at seven days and 6.34 km/s at 28 days. Nevertheless, the grading is still considered excellent concrete quality based on BS1881. The highest value of compressive strength is SFRC-1.0%, 193.2 MPa at 14 days. The R-squared value for the correlation coefficient between UPV result and the compressive strength result at the x-axis and y-axis is 0.9963 and 0.9966 respectively. The non-linear models show high regression coefficient of R-squared close to 1.00, which means the parameters are strongly correlated. The correlation equation obtained can be used to predict compressive strength based on UPV data for steel fiber volume fraction up to 1.5%. Thus, it can be concluded that percentage of steel fiber added, affect the strength of the tested concrete specimens and the optimized value of steel fiber added is at 1% in this study.

FIBER-REINFORCED CONCRETE FOR RIGID ROAD PAVEMENTS MODIFIED WITH POLYCARBOXYLATE ADMIXTURE AND METAKAOLIN

Increasing the strength and durability of road surfaces is crucial. Therefore, the concrete compressive strength, flexural strength, frost, and abrasion resistance of fiber-reinforced concrete for rigid pavements are investigated in this study an experiment is performed based on an optimal plan, in which four factors of concrete composition are varied: the amounts of Portland cement, polypropylene fiber, metakaolin, and polycarboxylate type admixture. Experimental statistical models for investigating the effects of composition factors on concrete properties are established. It is discovered that owing to the use of metakaolin and a superplasticizer, the concrete compressive strength increases. Furthermore, the use of modifiers and fiber reinforcement increases the flexural strength, frost resistance, and wear resistance of concrete. X-ray phase analysis of the fiber-reinforced concrete structure confirm the effectiveness of the modifier effect, in particular the positive role of metakaolin as an active pozzolana. The developed fiber-reinforced concrete for rigid pavements with rational modifiers, depending on the Portland cement content, exhibits compressive strengths from 55 to 70 MPa, flexural strengths from 8 to 9.5 MPa, frost resistances from F350 to F450, and abrasion resistances from 0.3 to 0.4 g/cm2. Such properties ensure the high durability of fiber-reinforced concrete and allow it to be used on road pavements that support heavy loads and traffic.

Effects of fiber material in concrete manufactured with electric arc furnace slag: Experimental and numerical study

Over recent years, Electric Arc Furnace Slag (EAFS), a by-product of the steel-making industry, has been used as a replacement of natural aggregates to produce high-performance concrete. In EAFS concrete, fibers are normally added to improve post-cracking behavior, thereby prolonging the durability and range of applications of the composite. Despite the rise in its production, the mechanical performance of fiber-reinforced EAFS concrete is still poorly understood, posing important barriers to its daily use.This paper aims to study the effect of fiber materials (steel and synthetic) on EAFS concrete performance. To do so, the paper proposes, firstly, an experimental campaign and, secondly, a numerical simulation to model the effect of fibers both in the pre-cracking and post-cracking stages. Importantly, for the numerical study, an in-house Finite Element (FE) code is developed using interface elements to capture crack propagation. The FE code uses, as input, data obtained in the experimental campaign and is validated against previously unseen experimental results. The overall framework gives important insights on how fibers improve the post-cracking behavior of EAFS concrete and the relevance of fiber material in the overall performance. The validated numerical tool can be used in the future to design EAFS fiber-reinforced concrete structures and therefore increase the applicability of such composite material.

Cyclic Behavior of Damage-controllable Steel Fiber-reinforced High-strength Concrete Frame-shear Wall Structures

ABSTRACT Quasi-static tests of two 2-story structures reinforced with HRB 600 MPa reinforcement and ultrahigh-strength (UHS) reinforcement were conducted. These two structures showed an evident post-yield stiffness, which can be repaired before a large drift ratio of 2%. The structure with the UHS reinforcement had stable floor stiffness ratio, which can avoid the deformation and energy consumption concentration in the lower floors. The reinforcement diagonal bracing can effectively limit the inclined crack development, and reduce the shear strength degradation of the shear wall under large lateral deformation. According to the structure failure mechanism, an ideal load-deformation response was proposed.

Reliability-based assessment of the partial factor for shear design of fibre reinforced concrete members without shear reinforcement

Fibre reinforced concrete (FRC) is increasingly used for structural purposes owing to its many benefits, especially in terms of improved overall sustainability of FRC structures relative to traditional reinforced concrete (RC). Such increased structural use of FRC requires safe and reliable models for its design in ultimate limit states (ULS). Particularly important are models for shear strength of FRC members without shear resistance due to the potential of brittle failure. The fib Model Code 2010 contains a model for the shear strength of FRC members without shear reinforcement and the same partial factor accepted for RC structures is accepted for FRC elements. This approach, however, is potentially on the unsafe side since the uncertainties of some design-determining mechanical properties of FRC (i.e., residual flexural strength) are larger than those for RC. Therefore, in this study, a comprehensive reliability-based calibration of the partial factor γc for the shear design of FRC members without shear reinforcement according to the fib Model Code 2010 model is performed. As a first step, the model error δ is assessed on 332 experimental results. Then, a parametric analysis of 700 cases is performed and a relationship between the target failure probability βR and γc is established. The results demonstrate that the current model together with the prescribed value of γc = 1.50 does not comply with the failure probabilities accepted for the different consequences of failure of FRC members over a 50-year service life. Therefore, changes to the shear resistance model are proposed in order to achieve the target failure probabilities.

Research on Seismic Performance of Fiber Concrete Lining Structure of Urban Shallow-Buried Rectangular Tunnel in Strong Earthquake Area

Due to the space utilization and support requirements of shallow-buried rectangular tunnel in city, special treatment is needed for lining structure. More stable structure should be taken to prevent the influence of strong earthquake on the rectangular section of tunnel. ABAQUS finite element model was established to clarify the influence of fiber-reinforced concrete lining structure on the seismic performance of urban shallow-buried rectangular tunnel. Based on the design and engineering conditions, firstly C25 concrete was applied as lining structural materials. Then, the seismic effects of steel fiber concrete (SFRC) and steel-basalt hybrid fiber concrete (SBHFRC) as the lining structure are compared and analyzed. The influence of internal force is studied and compared by calculating the safety factors of the tunnel lining structure under the above three conditions. The results show that the seismic performance of the lining structure using SFRC is better than that of using SBHFRC. The results have important reference value for the seismic fortification design and related research of urban shallow-buried rectangle tunnels in strong earthquake area.

Development of effective fiber-reinforced concrete compositions used in transportation structures

The possibility of producing fiber-reinforced concrete with high deformation properties by regulating the microstructure and using it in the design of transport structures was considered. It was found that to create high-performance transport structures, it is necessary to modify fiber mixtures with complex additives, i. e. increase the strength of fiber-reinforced concrete at the micro-level. To obtain a denser structure of the concrete matrix, complex additives were used – ultrafine additive (silica fume) and Master Air 200 B air-entraining additive. It was experimentally proved that using such additives reduces the water-cement ratio and further strengthens the concrete matrix structure. The design of the unloading structure on the railway line constructed from the Karadag station (Republic of Azerbaijan) to the SOCAR oil and gas processing and petrochemical complex using fiber-reinforced concrete modified with complex additives was made. The results of designing the fiber-reinforced concrete unloading structure were analyzed and the results of designing the fiber-reinforced concrete unloading structure and the regular concrete unloading structure were compared. As a result of the comparison, it was found that using fiber-reinforced concrete decreases the cross-section diameter of the effective reinforcement of the slab – the cross-section diameter of the effective reinforcement of the pavement slab decreases from Æ2×32 mm to Æ32 mm in the upper and Æ25 mm in the lower row, respectively. Crack resistance is also increased compared to regular concrete. Thus, in order to create structures with high transport and operational parameters, it is necessary to modify fiber-reinforced concrete mixtures with complex additives

Study of Combined Multi-Point Constraint Multi-Scale Modeling Strategy for Ultra-High-Performance Steel Fiber-Reinforced Concrete Structures.

Compared with normal strength concrete (NSC), ultra-high-performance steel fiber-reinforced concrete (UHPFRC) shows superior performance. The concrete damage plasticity (CDP) model in ABAQUS can predict the mechanical properties of UHPFRC components well after calibration. However, the simulation of the whole structure is seriously restricted by the computational capability. In this study, a novel multi-scale modeling strategy for UHPFRC structure was proposed, which used a calibrated CDP model. A novel combined multi-point constraint (CMPC) was established by the simultaneous equations of displacement coordination and energy balance in different degrees of freedom of interface nodes. The advantage is to eliminate the problem of the tangential over-constraint of displacement coordination equation at the interface and to avoid stress iteration of the energy balance equation in the plastic stage. The expressions of CMPC equations of typical multi-scale interface connection were derived. The multi-scale models of UHPFRC components under several load cases were established. The results show that the proposed strategy can well predict the strain distribution and damage distribution of UHPFRC while significantly reducing the number of model elements and improving the computational efficiency. This study provides an accurate and efficient finite element modeling strategy for the design and analysis of UHPFRC structures.

Computational Model for the Evaluation of the Service Life Of Fiber-Reinforced Concrete Structures Under Long-Term Static Loading

We propose a computational model for the evaluation of the service life of fiber-reinforced concrete structural elements subjected to long-term tension. The model is based on the first law of thermodynamics and a proposed idealized tensile stress-strain diagram of fibrous concrete. This model is used for the evaluation of the service life of a fiber-reinforced concrete plate containing a circular hole under the conditions of long-term bilateral tension.

Probabilistic Studies on the Shear Strength of Slender Steel Fiber Reinforced Concrete Structures

Shear failure is a brittle and undesirable mode of failure in reinforced concrete structures. Many of the existing shear design equations for steel fiber reinforced concrete (SFRC) beams include significant uncertainty due to the failure in accurately predicting the true shear capacity. Given these, adequate quantification and description of model uncertainties considering the systematic variation in the model prediction and measured shear capacity is crucial for reliability-based investigation. Reliability analysis must account for model uncertainties in order to predict the probability of failure under prescribed limit states. This study focuses on the quantification and description of model uncertainty related to the current shear resistance predictive models for SFRC beams without shear reinforcement. The German (DAfStB) model displayed the lowest bias and dispersion, whereas the fib Model 2010 and the Bernat et al., model displayed the highest bias and dispersion. The inconsistencies observed in the resistance model uncertainties at the variation of shear span to effective depth ratio are a major cause for concern, and differentiation with respect to this parameter is advised. Finally, in line with the EN 1990 semi-probabilistic approach for reliability-based design, the global partial safety factors related to model uncertainties in the shear resistance prediction of SFRC beams are proposed.

Experimental Studies of Fiber-Reinforced Concrete Prisms Exposed to High Temperatures

Fiber-reinforced concretes are varieties of composite materials. Such materials are commonly used nowadays. Concrete is fiber-reinforced using various fibrous materials, or fibers, which are evenly distributed over the volume of the concrete matrix and simultaneously provide its 3D reinforcement. Fiber-reinforced concrete has better stress-related strength characteristics than ordinary concrete. Since building structures must meet both the strength, rigidity and stability requirements, and the fire safety requirements, then for the extensive use of fiber-reinforced concrete structures, not only the external load design, but also temperature effect design should be conducted in the design phase. The strength and strain characteristics of fiber concrete exposed to high temperatures must be known for this purpose. In view of this, three series of prisms were manufactured and tested: the first series contained no fiber at all (control prisms), the second series contained basalt fiber, and the third series contained steel fiber. The test results showed that adding fibers improves the mechanical characteristics of fiber-reinforced concrete samples under specified conditions.

Failure Analysis of Ultra High-Performance Fiber-Reinforced Concrete Structures Enhanced with Nanomaterials by Using a Diffuse Cohesive Interface Approach.

Recent progresses in nanotechnology have clearly shown that the incorporation of nanomaterials within concrete elements leads to a sensible increase in strength and toughness, especially if used in combination with randomly distributed short fiber reinforcements, as for ultra high-performance fiber-reinforced concrete (UHPFRC). Current damage models often are not able to accurately predict the development of diffuse micro/macro-crack patterns which are typical for such concrete structures. In this work, a diffuse cohesive interface approach is proposed to predict the structural response of UHPFRC structures enhanced with embedded nanomaterials. According to this approach, all the internal mesh boundaries are regarded as potential crack segments, modeled as cohesive interfaces equipped with a mixed-mode traction-separation law suitably calibrated to account for the toughening effect of nano-reinforcements. The proposed fracture model has been firstly validated by comparing the failure simulation results of UHPFRC specimens containing different fractions of graphite nanoplatelets with the available experimental data. Subsequently, such a model, combined with an embedded truss model to simulate the concrete/steel rebars interaction, has been used for predicting the load-carrying capacity of steel bar-reinforced UHPFRC elements enhanced with nanoplatelets. The numerical outcomes have shown the reliability of the proposed model, also highlighting the role of the nano-reinforcement in the crack width control.

A study on avalanches of early age basalt fiber reinforced concrete beams during flexure

In this work, stress variations during flexure of early age basalt fiber reinforced concrete beams were studied using high resolution temporal measurements. An experimental system was created to collect stress-time curves at 100 kHz sampling rate so that temporal profiles of stress variations were analyzed in detail. Stress drops were modeled as avalanches resulting from interactions between basalt fibers and cementitious matrices. Four-point bending tests at different loading rates were conducted to investigate avalanches during flexure of beams with different fiber volume fractions. Good agreement was obtained between measured avalanche statistics or dynamics and predictions from the mean field model. Different types of avalanches were detected during the flexure of basal fiber reinforced concrete beams, including avalanches with limited size and durations collapsed onto the scaling regime in the logarithmic scale, avalanches with an incubation period before stress drops beyond the scaling regime and giant avalanches occurred at the fracture of bottom concrete. Observations of different avalanche types disclosed the critical failure evolution during flexure of basalt fiber reinforced beams, which could lead to the creation of durable ecofriendly fiber-reinforced concrete structures.

Impedance-based structural health monitoring applied to steel fiber-reinforced concrete structures

The goal of the present contribution is to test the effectiveness of an impedance-based structural health monitoring (ISHM) methodology to detect damage in steel fiber-reinforced concrete structures. For this aim, a piezoceramic sensor coated with epoxy is used. A prismatic concrete specimen was evaluated for the case in which the damage condition was obtained from compression testing. The impedance signatures were measured both before and after the compression testing for the specimens placed inside an environmental chamber. An optimization procedure was applied to compensate for the temperature effects that appear on the impedance signatures. For illustration purposes, the coated piezoelectric transducer was initially bonded to the surface of an aluminum beam to detect damage induced by a loosening bolt. An impedance analyzer was used to measure impedance signatures in the frequency range of 40–70 kHz for the procedure with the aluminum beam and 50–80 kHz for the prismatic steel fiber concrete specimen. An in-house portable impedance meter (SySHM impedance meter) was used to measure the impedance signatures. The results encourage the use of the ISHM approach for health monitoring of steel fiber-reinforced concrete structures.

Determination of Mechanical Characteristics for Fiber-Reinforced Concrete with Straight and Hooked Fibers

Fiber-reinforced concrete has a wide application in practice, and many fields of research are devoted to it. In most cases, this is a specific problem, i.e., the determination of the mechanical properties or the test method. However, wider knowledge of the effect of fiber in concrete is unavailable or insufficient for selected test series that cannot be compared. This article deals with the processing of a comprehensive test study and the impact of two types of fibers on the quantitative and qualitative parameters of concrete. Testing was performed for fiber dosages of 0, 40, 75, and 110 kg/m3. The fibers were hooked and straight. The influence of the fibers on the mechanical properties in fiber-reinforced concrete was analyzed by functional dependence. The selected mechanical properties were compressive strength, splitting tensile strength, bending tensile strength, and fracture energy. The results also include the resulting load–displacement diagrams and summary recommendations for the structural use and design of fiber-reinforced concrete structures. The shear resistance of reinforced concrete beams with hooked fibers was also verified by tests.

Numerical simulation of ultra-high-performance fiber-reinforced concrete frame structure under fire action

The research activity in progress and the advancements in concrete technology are leading to an increased use of ultra-high-performance fiber-reinforced concrete (UHPFRC) in structural engineering. UHPFRC is characterized by steel fibers, cement, silica fume, fine sand, superplasticizer, and very low water–cement ratio. UHPFRC is defined as a new material, with unique properties (high ductility, low permeability, very high strength capacity in compression, higher toughness) in comparison with conventional concrete (Buttignol et al, Revista IBRACON de Estruturas e Materiais 10(4):957–971, 2017). This makes it possible to make slender constructions because a smaller cross section can transfer the same force as a larger cross section. However, in case of fire safety design a disadvantageous behavior of UHPC compared to normal-strength concrete is well known and documented. The high packing density of the cement matrix is the main reason for explosive spalling behavior when exposed to fire. In this paper, the numerical simulation using finite-element method has been used to evaluate the behavior of UHPFRC frame structure under fire action. According to results, the three-dimensional finite-element model can be used for calculating the mechanical localized of UHPFRC concrete frame structures subjected to nominal fire curves. The results of numerical analysis under fire action are also compared to the other materials for more understanding the fire resistance between UHPFRC material (with PP fiber, without PP fiber) and high-strength concrete.