Ultra-high-performance Fiber-reinforced Concrete Material Research Articles

Detecting Multiple Damages in UHPFRC Beams through Modal Curvature Analysis

Curvature-based damage detection has been previously applied to identify damage in concrete structures, but little attention has been given to the capacity of this method to identify distributed damage in multiple damage zones. This study aims to apply for the first time an enhanced existing method based on modal curvature analysis combined with wavelet transform curvature (WTC) to identify zones and highlight the damage zones of a beam made of ultra-high-performance fiber-reinforced concrete (UHPFRC), a construction material that is emerging worldwide for its outstanding performance and durability. First, three beams with a 2 m span of UHPFRC material were cast, and damaged zones were created by sawing. A reference beam without cracks was also cast. The free vibration responses were measured by 12 accelerometers and calculated by operational modal analysis. Moreover, for the sake of comparison, a finite element model (FEM) was also applied to two identical beams to generate numerical acceleration without noise. Second, the modal curvature was calculated for different modes for both experimental and FEM-simulated acceleration after applying cubic spline interpolation. Finally, two damage identification methods were considered: (i) the damage index (DI), based on averaging the quadratic difference of the local curvature with respect to the reference beam, and (ii) the WTC method, applied to the quadratic difference of the local curvature with respect the reference beam. The results indicate that the developed coupled modal curvature WTC method can better identify the damaged zones of UHPFRC beams.

Composition-strength relationship study of ultrahigh performance fiber reinforced concrete (UHPFRC) using an interpretable data-driven approach

To study the relationship between composition and compressive strength of ultrahigh performance fiber reinforced concrete (UHPFRC), an interpretable data-driven approach is proposed. This approach addresses the high cost, complexity, time consumption and difficulty in studying the multivariate dependence effects of design parameters with traditional experimental methods. To construct the prediction model, 400 experimental data points are leveraged to compose the dataset, and five GridSearchCV (GSCV)-tuned ensemble machine learning (ML) approaches are evaluated. The GSCV-CatBoost model, with its higher prediction accuracy and lower error, i.e., R2 = 0.945, RMSE = 8.567 and MAE = 5.084, is proposed as a robust tool for predicting the compressive strength. Furthermore, the results of the SHAP analysis reveal that concrete age and steel fiber content are the most important features for predicting the compressive strength and those of the multivariate dependence effects analysis show that an increase in FRC will reduce the positive effect of the L/B on the compressive strength when the L/B exceeds 1. The feature importance and size effect of the specimen are noteworthy for material designers in the selection of suitable raw materials to achieve the desired strength properties. Finally, a reverse design method based on the abovementioned approach is proposed for the development of new UHPFRC materials. To maximize the effect of the model, the application range of the model is limited to the target compressive strength of 50–232 MPa and includes basic material parameters such as cement strength and silica fume, sand, steel fiber, water, and superplasticizer content.

Modeling of Ultra-high Performance Fiber Reinforced Concrete Filled Steel Tube Columns under Eccentric Loading

Recently, ultra-high performance fiber reinforced concrete (UHPFRC) has been commonly used as a structural material. In this study, finite element (FE) model is constructed to investigate the behavior of ultra-high performance fiber reinforced concrete filled steel tube columns (UHPFRCFSTs) under axial or eccentric loading. The analysis included three-dimensional FE model using solid elements. The novelty of the suggested FE model is the consideration of the confinement of the UHPFRC in-filled material. Furthermore addition, the numerical model includes initial local and overall geometric imperfections, as well as the inelastic response of both UHPFRC and steel materials. The interaction between the steel tube and UHPFRC in-filled is modelled using surface to surface contact. Experimental results from the literature are used to validate the FE model. It is proved that the FE model can predict the ultimate capacities, failure modes, and post-cracking behavior accurately for both short and long UHPFRCFSTs. The FE interaction diagram agreed very well with the experimental results. Using the verified FE model, a parametric study on UHPFRCFSTs is carried out. Several parameters, including concrete strength material, steel yield strength, and aspect ratio of the columns (column diameter/tube thickness), are investigated. Eventually, comparisons are conducted between the results obtained from FE simulation and the existing design codes for predicting load-moment interaction diagram of UHPFRCFSTs. It has been found that the Eurocode 4 predictions in most analyzed cases are conservative for UHPFRCFSTs.

Modified softened membrane model for ultra-high-performance fiber-reinforced concrete solid and hollow beams under pure torsion

Limited research has focused on the development of rational theoretical models for evaluating the pure-torsional behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams. To fill this research gap, this study aimed to develop a modified softened membrane model for torsion (SMMT). Based on the direct tension force transfer model, a UHPFRC tensile constitutive model was derived by considering the fiber pull-out behavior. The proposed constitutive model was implemented in the SMMT, and the modified SMMT was found to be useful in predicting the pure-torsional behavior of UHPFRC beams with solid and hollow cross-sections. Moreover, the theoretical torsional responses were compared with the experimental results, and the experimental data reported in previous studies were used to verify the applicability of the proposed model. The results indicate that the estimated analytical responses matched well with the experimental outcomes, and the modified SMMT considered the influences of both the wall thickness and excellent UHPFRC material properties. The proposed model is expected to be effective for further investigation of the torsional mechanism and design methodology of UHPFRC members under pure torsion.

Mechanics-based formulation for modeling of ultra high-performance fiber reinforced concrete material using bonded discrete elements

Ultra High-Performance Fiber Reinforced Concrete (UHPFRC) possesses high strength and ductility relative to traditional concrete. As a relatively novel material, utilization of UHPFRC generally requires comprehensive studies on feasibility and applicability, where numerical modeling techniques become more convenient and cost-effective as compared to laboratory or field testing. In this study, a numerical model based on the bonded discrete element method is developed to simulate mechanical behaviors of UHPFRC materials. The formulation consists of three major components, which correspond to physical counterparts of fine aggregates, the cementitious matrix, and embedded steel fibers. A mechanics-based derivation is presented that facilitates calibration of the associated constitutive parameters. As validation of the numerical modeling and demonstration of the calibration procedure, results from laboratory experiments conducted on UHPFRC specimens are reproduced via simulation. In addition, parametric studies targeting the effect of particle size and packing are carried out to assess framework robustness.

Flexural behaviour of ultra-high-performance fiber-reinforced concrete at high strain rates

In this study, the flexural resistance of ultra-high-performance fiber-reinforced concrete (UHPFRCs) containing different fiber volume content, under static and dynamic flexural loading was investigated. Thirty-six specimens of UHPFRCs, size 0.5x0.5x210 (mm), reinforced with 0.5%, and 1.5% volume of smooth steel fiber (d=0.2 mm, l=19 mm) were cast and tested by three-point bending test, under the static load (strain rate 1.67x10-5 s-1) and high acceleration load (strain rate up to 210 s-1). Experimental results show that the flexural strength of UHPFRCs increases significantly when the fiber reinforcement content increases. In addition, as the loading speed increases, the flexural resistance of the material also increases. The flexural strength of UHPFRC material reinforced with 0.5 and 1.5% of fiber volume content was 17.7 and 30.0 MPa at static loads, increased to 23.6 and 51.92 MPa at a loading rates of 110 s-1 and 28.86 and 61.04 MPa at loading rate of 210 s-1.

Effect of interfacial surface preparation technique on bond characteristics of both NSC-UHPFRC and NSC-NSC composites

Ultra-high performance fiber reinforced concrete (UHPFRC) reveals superior mechanical properties that make it suitable for the strengthening/rehabilitation of normal strength concrete (NSC) structures. This paper investigates the effects of the interfacial surface preparation's methods on the bond performance for both the NSC-UHPFRC and the NSC-NSC composites. The interfacial bond characteristics of five surface preparation methods were studied, i.e., the fair face, the wire brushed surface, the use of the colloidal glue and the x-wrap epoxy on both the fair face and the wire brushed surfaces in addition to the drilled holes and grooves with different areas by using the slant shear, the splitting tensile and the direct shear bond tests. The results indicated that the overall interfacial performances of the NSC-UHPFRC composites were better than their NSC-NSC counterparts because the viscous UHPFRC material can fill the pores and the concaves on the NSC surface causing shear connectors able to enhance the bond performance. The bond strengths of the fair face composites could not achieve the acceptable minimum requirements specified by the ACI 546-06 in contrast to the wire brushed specimens. The area of the drilled holes and grooves had a significant effect on the bond performance and the failure patterns of the tested composites. The recorded splitting tensile bond strength level of the drilled holes and grooves composites categorized as an “Excellent” bonding. The cohesion and the friction parameters of the all tested composites with the proposed interfacial preparations methods achieved the acceptable limits specified by the AASHTO (2010).

Experimental and multi-scale numerical investigation of ultra-high performance fiber reinforced concrete (UHPFRC) with different coarse aggregate content and fiber volume fraction

This study investigates the influence of the coarse aggregate content and steel fiber volume fraction on the mechanical properties of UHPFRC. On the meso-scale, according to Mori-Tanaka homogenization method and progressive damage theory, the equivalent damage constitutive model of UHPFRC composite is established. On the macro-scale, the mesoscopic equivalent properties of UHPFRC material are input into the finite element model corresponding to the test for numerical simulation, and the mesoscopic material properties are coupled with the macroscopic finite element model to study the influence of mesoscopic components of UHPFRC on its macroscopic mechanical properties. The compression, tension and four-point bending numerical simulation results of UHPFRC show that the predicted results of the multi-scale numerical model are in good agreement with the test results. It is also found that with the increase of fiber volume fraction, the compressive strength, tensile strength and four-point bending strength of UHPFRC increase first and then decrease. The improvement effect of coarse aggregate on the properties of UHPFRC is not as obvious as that of fiber, and the increase of fiber volume fraction has a significant enhancement effect on the ductility and post peak toughness of UHPFRC slab.

Modeling the fracture behavior of Ultra - High Performance Fiber Reinforced Concrete slabs under contact Blast Loading

This paper presents a fracture behavior modeling of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) slabs under contact blast loading using the finite element method. The UHPFRC is supposed to be brittle material and follow the Johnson–Holmquist-II(JH-2) model. The steel rebar is modeled using the elasto-plastic model. The Emulsion Explosive has been used and modeled by the SPH method. UHPFRC slabs with the dimensions 1000mm of length, 800mm of width and 120mm of thickness is considered. The steel fibers with a volume fraction of 2% is used. The UHPFRC material is fabricated in laboratory using the material available in Vietnam. The concrete crater and spall damage of UHPFRC slab under contact blast loading are considered. The numerical results are compared with experiment. These results allow to evaluate the resistance against blast load of UHPFRC fabricated in lab.

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.

Experimental and Analytical Study of Ultrahigh-Performance Fiber-Reinforced Concrete Curved Beams

This paper presents experimental and analytical investigations on the structural behavior of horizontally curved ultrahigh-performance fiber-reinforced concrete (UHPFRC) beams subjected to concentrated loads applied normal to plane of the beam. Four fixed-ends supported UHPFRC beams with curvatures of 0°, 60°, 90°, and 120° were tested. The structural responses, including the deflection, out-of-plane rotation, and reaction forces of UHPFRC curved beams under all stages of loadings, were experimentally studied. A change in failure mechanism of a UHPFRC beam with the change in its curvature was observed, and the load-carrying capacity and ductility of a UHPFRC beam decreased slightly with an increase in the curvature of the beam. The experimental results also indicated that due to the strain-hardening behavior of UHPFRC materials under tension, a UHPFRC curved beam exhibited improved load-carrying capacity and ductility over conventional straight reinforced concrete beams because the ductility index of each of the UHPFRC curved beam tested was over 3. In addition, structural mechanics–based closed-form solutions were developed for horizontally curved UHPFRC beams using Castigliano’s second theorem to predict the values of bending moment, shear force, reaction force, and torsional moment of the beams under linear-elastic material conditions. Influence lines for bending moment, shear force, and torsional moment were also generated using the validated closed-form equations to show the influences of critical factors on the behavior of UHPFRC curved beams.

Research on dynamic constitutive model of ultra-high performance fiber-reinforced concrete

A dynamic constitutive model for ultra-high performance fiber-reinforced concrete (UHPFRC) was investigated in this paper. In view of the particularity of UHPFRC material, two improvements including the modifications of yield surface and the change of strain rate effect due to the adjunction of steel fibers were made based on the Holmquist-Johnson-Cook model (HJC model). Further, on the purpose of model parameter determination, a series of mechanical tests for UHPFRC material, including uniaxial compression test, bending test, uniaxial cyclic compression test and SHPB test were carried out. And the 22 calculation parameters required in the improved HJC model such as strength parameters, damage parameters and pressure parameters were obtained through data analysis and fitting. Finally, the numerical simulation of the SHPB test performed in this study and the drop hammer impact test in the literature were carried out in order to verify the rationality and practicability of the improved HJC model. The numerical simulation results of SHPB test show that the failure morphology and stress-strain curves of UHPFRC specimens are in good agreement with the test results. When the improved HJC model and the appropriate corrosion strain value (1.0% in this work) were selected, the mid-span deflection-time curve obtained by numerical simulation is consistent with the result of the drop hammer impact test.

The Performance Evaluation of Circular Flange Bolted Connection in Ultra High Performance Fiber Reinforced Concrete Segmented Communication Tower

This study herein presents investigations about behavior of circular flange bolted connection (CFBC) in ultra high performance fiber reinforced concrete (UHPFRC) hollow segmented communication tower subjected to lateral dynamic load. The CFBC consists of two flanged concrete, cast together with the structural segment tubes and then connected using steel bolts. The paper is illustrated with CFBC joint of 500mm flange thicknesses, and 8M25 high strength steel bolts coming from a typical real design tower. For this purpose, the full scale CFBC joints for communication tower are made from Ultra High Performance Fiber Reinforced Concrete (UHPFRC). The connection was cast and experimentally tested by applying cyclic lateral load using dynamic actuator. The lateral strength and stiffness resistance of the UHPFRC CFB connections were evaluated in this study. Besides, a rigorous FEM analysis was executed in order to evaluate the performance of CFBC in the communication tower by investigating the mechanism of force transfer, load bearing capacity as well as failure behavior of the circular flange bolted connection (CFBC) under lateral cycling loading. The experimental and numerical analysis results showed the ability of UHPFRC circular bolted connection to resist the applied lateral loads. In addition, the considered model revealed that for joints under tension, bolts were seriously not subjected to bending moments which is due to the prying effect. This was made possible by the provision of adequate flange thickness and strength of the UHPFRC material.

Precast Ultra-High-Performance Fiber-Reinforced Concrete (UHP-FRC) for Fast and Sustainable Pavement Repair

This paper presents a new methodology, which enables streets, roads, highways, bridges, and airfields to use an advanced fiber-reinforced concrete material, which can delay or prevent the deterioration of these transportation infrastructure when subjected to traffic and environmental loadings. The major problem of concrete is its considerable deterioration and limited service life due to its brittleness and limited durability. As a result, it requires frequent repair and eventual replacement, which consumes more natural resources. Ultra-high-performance fiber-reinforced concrete (UHP-FRC) introduces significant enhancement in the sustainability of concrete structures due to its dense microstructure and damage-tolerance characteristics. These characteristics can significantly reduce the amount of repair, rehabilitation, and maintenance work, thereby giving the transportation infrastructure a longer service life. This research addresses the strong need to develop fast and sustainable UHP-FRC materials for pavement repair that can be easily cast onsite without special treatments. This avoids any major changes to current concrete production practice and accelerates the use of UHP-FRC materials. This research investigated a new method for concrete repair by combining precast UHP-FRC panels with a small quantity of cast-in-place UHP-FRC for pavement repair without any dowel bars.

Design of 38m Span Post-tensioned Ultra High Performance Fiber-Reinforced Concrete (UHPFRC) Composite Bridge

Although ultra-high-performance fibre reinforced concrete (UHPFRC) has become commercially available in many countries, there are still limited design standards for UHPFRC structures. In 2016, the French Standard Institute has published the world first design standard for UHPFRC structures (NF P18-710) which is read conjunction with the UHPFRC material specification code (NF P18-470). This standard is the national complement to Eurocode 2 for the design of UHPFRC structures. To date, there have several UHPFRC bridges been designed by using this French Standard. The aim of this paper is to demonstrate working example on the design calculation of 38m span post-tensioned UHPFRC composite bridge using DURA® Grade140 which was recently constructed in Kuala Terengganu. The working example mainly focus on (i) the material properties input in the structural analysis software – Midas Civil; (ii) the output results on the design forces at the critical sections (mainly the design moment effect, MEd, and design shear force effect, VEd); (iii) the stresses of the post-tensioned UHPFRC U-girder at transfer, at different construction load history and at service stage (iv) the design moment resistance (MRd) and design shear resistance (VRd) of the composite section.

Effect of Curing Conditions on the Shrinkage of Ultra High-Performance Fiber-Reinforced Concrete

The effect of curing conditions on the early age and long-term shrinkage of ultra high-performance fiber-reinforced concrete (UHPFRC) was systematically studied. The shrinkage of the early age (0–168 h) and long-term age (0–90 d) of UHPFRC material was measured based on three kinds of humidity conditions (dry, sealed, and soaked) and curing temperatures (25°C, 40°C, and 75°C), respectively. In this paper, the hydration degree of different shrinkage stages was studied in combination with chemical-bound water experiment. Meanwhile, the influencing mechanism of curing condition on the shrinkage of UHPFRC was analyzed. The results show that the early shrinkage rate of UHPFRC is accelerated with the increase of temperature, and the rate of shrinkage development at the latter stage is suppressed with the increase of temperature. With the increase of humidity, the early age shrinkage of UHPFRC and its increasing rate gradually decrease, which means drying condition > sealing condition > soaking condition. According to the long-term shrinkage results, increasing temperature has very significant inhibiting effect on the UHPFRC shrinkage in the sealed condition. Due to the majority of the in-site components of UHPFRC cured in the sealed condition, high-temperature curing has evident inhibition of early age shrinkage of UHPFRC. Therefore, promoting curing temperature is fairly effective at inhibiting the early age shrinkage of UHPFRC for the in-site structures.

Influence Factors on the Properties of Ultrahigh-Performance Fiber-Reinforced Concrete Cured under the Condition of Room Temperature

Ultrahigh-performance fiber-reinforced concrete (UHPFRC) is a new type of concrete with excellent performance and good application prospects. However, expensive heat curing or high-pressure curing was often adopted to ensure the sufficient compressive strength. This study focuses on improving the compressive strength and workability of UHPFRC by changing the composition materials and the mixture ratios under standard curing conditions. The 0-1 mm and 1∼3 mm sintered bauxite was adopted as coarse aggregate. UHPFRC with high compressive strength and good workability was developed by changing the water-binder ratios, by adding ground-granulated blast furnace slag (GGBFS) or fly ash, and by changing the bauxite content of different particle sizes. When the volume ratio of steel fiber was 3%, the recommend water to binder ratio was 0.194 according to this experiment, the dosage of GGBFS-replaced cement is recommended as 20%, the dosage of fly ash instead of silica fume is recommended as 30%. The recommend ratio of 0-1 mm and 1∼3 mm sintered bauxite was 1.51 : 1. Finally, a kind of UHPFRC material with a compressive strength of 152.4 MPa and a slump of 120 mm was developed under the standard curing conditions.

Size effect of ultra‐high performance fiber reinforced concrete composite beams in shear

In this paper, a finite element model (FEM) based on a concrete damage‐plasticity approach was developed to investigate the size effect of ultra‐high performance fiber reinforced concrete (UHPFRC) and normal‐strength concrete or high‐strength concrete (NSC/HSC) composite beams. The material behavior of UHPFRC was modeled by introducing a suitable tension stiffening model to simulate the behavior of UHPFRC beams in tension. Specimens containing UHPFRC with different fiber volume content that have an overall height between 300 and 1,200 mm, a constant shear span‐effective depth ratio of 3 and no stirrups were investigated. The validity of the proposed model was established through comparisons between the experimental test results and those obtained in other studies. The results revealed that the size effect of UHPFRC members was diminished for fiber volume content higher than 1.5% due to the high ductility of UHPFRC material.

Dynamic identification of damage control characteristics of ultra-high performance fiber reinforced concrete

An experimental investigation has been conducted to assess the damage control properties of ultra-high performance fiber reinforced concrete (UHP-FRC) in comparison to traditional concrete. Five identical reinforced concrete (RC) plates, with the exception of concrete material, are damaged gradually using repeated impact technique. Damage progression has been evaluated stepwise based on the change in dynamic parameters and validated by visual inspection, midpoint residual displacement and successive number of impact tests to each specimen. Test results showed that UHP-FRC exhibits superior damage characteristics. The damage rate of UHP-FRC materials are approximately in the range of 6–15% the damage rate of normal-strength concrete.

High-strength steel reinforced squat UHPFRC shear walls: Cyclic behavior and design implications

Ultra-high performance fiber reinforced concrete (UHPFRC) is characterized by ultra-high compressive strength and ductile tensile strain hardening behavior accompanied by dense fine cracks. This study experimentally investigated the seismic behavior of squat UHPFRC shear walls. For this purpose, four squat shear walls were tested under displacement reversals, with the experimental variables including the strength of steel reinforcement, shear stress demand for the wall, steel fiber, and dowel bar. In particular, the performance of squat UHPFRC shear walls reinforced with high-strength steel rebar with an actual yield strength above 685MPa was explored. The seismic behaviors of the squat walls were evaluated using various performance measures, such as the hysteretic response, steel reinforcement strain, stiffness, strength, energy dissipation capacity, and detailed displacement component. The results revealed that the presence of steel fibers enhanced the strength, confinement, and crack-width control ability of squat UHPFRC shear walls, allowing the walls to exhibit ductile flexural-dominant behavior even when the shear stress demand for the wall was 20% greater than the code-specified maximum allowable value. Furthermore, the proposed novel squat shear wall not only took advantage of the ultra-high mechanical properties of high-strength steel and UHPFRC materials, but also resolved the concern of the potential premature failure modes for high-strength reinforcement and concrete.