Behavior Of Ultra-high Performance Fiber Research Articles

Flexural fatigue behavior of ultra-high performance fiber reinforced concrete

Even though UHPFRC has been extensively utilized in infrastructures owing to its excellent mechanical properties, its fatigue behavior remains unclear because related research is very limited. In this study, the fatigue characteristics of UHPFRC were investigated using a four-point bending experiment. In this study, the fatigue characteristics of UHPFRC were investigated using a four-point bending experiment. To determine the fatigue load conditions, static tests were conducted at different loading speeds and ages before, during, and after the fatigue tests. The obtained mechanical properties exhibited a clear dependence on loading rate and age duration. Consequently, a loading frequency of 3 Hz, which is close to that experienced in real infrastructures, was employed in the fatigue tests. A linear S-N relation with a 0.87 fatigue endurance limit was obtained on a semi-logarithmic scale. Additionally, the fatigue life showed a close relationship with the initial cycle deformation. Correspondingly, threshold values of deformation indicators were proposed for predicting the occurrence of fatigue failure. Furthermore, a linear positive relationship was found between the density of multiple fine cracks and fatigue life, based on post-fatigue crack measurements using a microscope. The relatively narrow crack width compared to other cementitious composites demonstrated UHPFRC's superior resistance to corrosion factors. Consistent with the linear S-N relation, the structural degradation appears to be governed by a fiber slippage-to-pull mechanism, as no fiber rupture was observed.

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.

An experimentally validated numerical analysis of UHP-FRC subjected to blast loading

This paper presents a new material constitutive model for simulating the uniaxial material behavior of ultra-high performance fiber reinforced concrete (UHP-FRC). The model accounts for the contribution of the steel fiber content to the tensile behavior. The model variables are the fracture energy, the characteristic length, and the crack bandwidth. Thus, it guarantees a mesh size independent numerical modeling of UHP-FRC. The model is developed based on the reported results of a state-of-the-art and highly accurate experimental investigation for the uniaxial behavior of UHP-FRC. This paper also adopts the concrete damage plasticity model (CDP) as a multi-axial yield surface criterion and presents the applicability of the material constitutive model and CDP for modeling UHP-FRC under unconfined non-contact blast loading. The results of the numerical models are validated against the experimental data of shock tube testing conducted by the authors at the University of Ottawa shock tube in collaboration with Ryerson University. The results revealed that the developed material constitutive model accurately represented the uniaxial behavior of UHP-FRC. The CDP model combined with the material constitutive model developed in this study can accurately model UHP-FRC structures under unconfined non-contact blast loading.

A review on autogenous self-healing behavior of ultra-high performance fiber reinforced concrete (UHPFRC)

A review on autogenous self-healing behavior of ultra-high performance fiber reinforced concrete (UHPFRC)

Effect of steel fiber-volume fraction and distribution on flexural behavior of Ultra-high performance fiber reinforced concrete by digital image correlation technique

This paper investigated the effect of steel fiber-volume fraction (0.5%, 1.0%, 1.5%, and 2.0%) and distribution on the flexural behavior of ultra-high performance fiber reinforced concrete (UHPFRC). Digital image correlation (DIC) was used to obtain the crack propagation behavior of UHPFRC under bending load. With increasing fiber-volume fraction, the crack-propagation path becomes more zigzagged. Based on the flexural response of UHPFRC and fiber distribution on the crack plane, a correlation between fiber distribution characteristics and flexural behavior was discussed. The fibers number per unit area for S0.5, S1.0, S1.5, and S2.0 were 7, 14, 21, and 31, respectively. The fiber pull-out length in cracked zone with different fiber-volume fractions was about 3.56 mm. The fiber orientation factor (ηθ) of S0.5, S1.0, S1.5, and S2.0 were 0.80, 0.79, 0.69 and 0.61 respectively. A quadratic relationship between the ηθ and the fiber pull-out number is proposed. The flexural-tensile strength ratio (β) is about 2.52 for UHPFRC exhibiting deflection hardening behavior. Finally, the post-cracking tensile behavior of UHPFRC was analyzed based on the matrix softening and fiber bridging curve models by the inverse analysis method. The tension softening curves obtained from the tri-linear softening curve analysis exhibited good agreement with the experimental results.

Mechanism of rate dependent behaviour of ultra-high performance fibre reinforced concrete containing coarse aggregates under flexural loading

Coarse aggregates are often eliminated in ultra-high performance fibre reinforced concrete (UHPFRC) for the sake of homogeneity, however, this causes an impairment on impact resistance. The flexural performance of UHPFRC with coarse aggregates under different loading rates (0.2, 20 and 200 mm/min) is investigated here to clarify the flexure and energy absorption mechanism. The flexural behavior and crack propagation are measured, meanwhile, the fracture of coarse aggregates and the surface morphology of steel fiber are analysed. The results show the energy absorption tends to be more rate dependent than the first crack stress and flexural strength. An increase of crack propagation speed and multiple cracks are observed at higher loading rates. The percentage of fracture across coarse aggregate is 23%, 32% and 58% at loading rates of 0.2, 20 and 200 mm/min, respectively. Further, a rate-dependent model for predicting the fracture of coarse aggregates is proposed. The present results contribute to designing UHPFRC with enhanced flexural performance under different loading rates.

Mechanical properties and ductility behavior of ultra-high performance fiber reinforced concretes: Effect of low water-to-binder ratios and micro glass fibers

This experimental work investigates the mechanical performance and ductility behavior of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) containing high volume of micro-glass fibers (MGF). The influence of various volume fractions of MGF and two water-to-binder ratios (w/b) are investigated. These w/b ratios are 0.12 and 0.14. Based on these ratios, two groups of UHPFRC mixes were prepared and each group include seven mixes made with 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, and 3% MGF volume dosages. In total fourteen mixes were examined for the mechanical properties such as compressive strength, splitting tensile strength, modulus of elasticity, flexural strength; and the ductility behavior. It was concluded that lower w/b resulted in better mechanical performance. Also, the mixes containing 1.5% to 3% of MGF, resulted in the highest compressive strength reaching up to 160 MPa. Furthermore, the results indicated that no more strength enhancement can be achieved beyond 1.5% MGF.

Synergistic effect of steel fibres and coarse aggregates on impact properties of ultra-high performance fibre reinforced concrete

This study investigates the synergistic effect of steel fibres and coarse aggregates on impact behaviour of ultra-high performance fibre reinforced concrete (UHPFRC). UHPFRC matrices with a low cement content and maximum aggregate sizes of 8 mm and 25 mm are designed by using a particle packing model. Three types of steel fibres (13 mm short straight, 30 mm medium hook-ended and 60 mm long 5D) are studied in terms of the utilization efficiencies. The results show that UHPFRC with coarser aggregates tends to have a lower cement consumption but slightly weaker mechanical strength, and the largest aggregate size is suggested to be no more than 25 mm considering the reduction on flexural toughness and impact resistance. The medium and long fibres contribute to an excellent deflection/strain hardening behaviour instead of short ones. A preferential synergistic effect on impact and flexural properties is observed between the medium fibres and the finer aggregates, while the longer fibres are more compatible to the coarser aggregates. The length of steel fibre is recommended between 2 and 5 times the maximum aggregate size. The flexural strength controls the impact resistance under low-energy impact loadings, and flexural toughness determines it under relatively high-energy (beyond energy threshold) impact loadings.

Improvement on Flexural Performance of UHPFRC with Hybrid Steel Fiber

This study investigates the flexural behavior of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) with hybrid steel fiber referencing the ASTM standard C 1609. Two types of end-hooked fibers in macro fiber concretes and one type short straight fiber in micro fiber concretes were used in mono and hybrid forms. In order to determine the flexural response of UHPFRC, a series of prismatic beam specimens with a dimension of 100 x 100 x 400 mm were tested under the four-point loading and following parameters were compared and discussed in terms of the first cracking load and pattern, flexural strength, deflection capacity, toughness and residual strength capacity under bending loads. The test results showed that as the fiber amount of specimens with the mono fiber increases, in general, better flexural behavior may be ensured. It should be also noted that the hybrid use enhanced the flexural behavior compared to the macro fiber usage.

Blending fibres to enhance the flexural properties of UHPFRC beams

In this paper, the flexural behaviour of ultra-high performance fibre reinforced concrete (UHPFRC) beams reinforced with macro-, micro- and a blend of macro- and micro-fibres is investigated at all limit states. The goal of this study is to investigate whether the benefits of fibre blending that are observed at a material scale translate to the structural scale. To this end, six UHPFRC beams with two different cross-sections and three different mix designs were tested. Standard codified approaches as well as a segmental analysis technique are then applied to predict the measured load-deflection and load-crack width behaviour of the beams and it is shown that while standard approaches can predict serviceability deflections, the segmental analysis is more accurate when predicting crack width, member ductility and ultimate deformations. Following validation for beams with blended fibres, it is then used as the basis for a parametric study to further investigate the influence of beam geometry and reinforcing details.

Hybrid fiber use on flexural behavior of ultra high performance fiber reinforced concrete beams

In this study, the flexural behavior of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) beams produced in mono and hybrid forms were investigated experimentally and numerically. Twelve doubly reinforced concrete beams were casted with four different reinforcement ratios representing low to excessive levels. The beams were produced in three groups to study the effects of mono and hybrid steel fiber usages. The first group beams of four are non-fiber beams while the second group contains only short-straight fiber of 13 mm. The last group is composed of hybrid form where the short-straight fiber of 13 mm and the long-hooked fiber of 60 mm were blended together. The beams were subjected to four-point loading, and the parameters of deflection and curvature ductilities, flexural stiffness, flexural moment capacity, cracking behavior and compressive strain were discussed. The test results indicated that the UHPFRC beams with high reinforcement ratios above the limits in current design codes provide remarkable benefits through the fibers’ contribution. It can be deduced that the hybrid fiber usage showed better flexural performance, in general, comparing to the mono form. In addition, two numerical approaches were proposed to predict nominal moment capacity of the UHPFRC beams in the mono or hybrid form.

Research on eccentric compression of ultra-high performancefiber reinforced concrete columns

To study the eccentric compression behavior of ultra-high performance fiber reinforced concrete (UHPFRC) columns, six UHPFRC columns and one high-strength concrete (HSC) column were tested. Variation parameters include load eccentricity, volume of steel fibers and stirrup ratio. The crack pattern, failure mode, bearing capacity, and deformation of the specimens were studied. The results showed that the UHPFRC columns had different failure modes. The large eccentric compression failure mode was the longitudinal tensile reinforcements yielded and many horizontal cracks appeared in the tension zone. The small eccentric compression failure mode was the longitudinal compressive reinforcements yielded and vertical cracks appeared in the compressive zone. Because of the bridging effect of steel fibers, the number of cracks significantly increased, and the width of cracks decreased. The load-deflection curves of the UHPFRC columns showed gradually descending without sudden dropping, indicating that the specimens had better deformation. The finite element (FE) analysis was performed to stimulate the damage process of the specimens with monotonic loading. The concrete damaged plasticity (CDP) model was adopted to characterize the behaviour of UHPFRC. The contribution of the UHPFRC tensile strength was considered in the bearing capacity, and the theoretical calculation formulas were derived. The theoretical calculation results were consistent with the test results. This research can provide the experimental and theoretical basis for UHPFRC columns in engineering applications.

Flexural Behavior of Ultra-High Performance Fiber Reinforced Concrete Scale Tunnel Segment

To reduce the weight of precast tunnel segment, ultra-high performance fiber reinforced concrete (UHPFRC) was studied to cast the segment. The flexural performance of UHPFRC scale tunnel segments were tested in this work. The weight of the UHPFRC thinner scale tunnel segment was only 80% of reinforced concrete (RC) segment. The segments were loaded as per CJJ/T 164-2011, and the four-point bending system was used. The results showed that the cracking load increased 50%, and 0.2 mm crack width load increased 22%, and the yield load increased 11%, and the ultimate load only decreased 1%. The stiffness of elastic stage of UHPFRC segment looked the same compared to RC segment. In a word, the UHPFRC thinner segments showed excellent flexural performance beyond the traditional RC segment.

Behaviour of ultra-high performance fibre reinforced concrete beam-column joint under cyclic loading

Ultra-high performance fibre reinforced concrete (UHPFRC) has very high compressive strength up to 200 MPa and exhibits strain hardening effects under flexural loading. The bond strength between UHPFRC and steel reinforcement is much better than the normal strength concrete. Therefore, there is a potential to use UHPFRC material at the beam-column joint region to reduce the congestion of reinforcement as well as to improve the seismic resistance of the structure. In this pilot study, the beam column joints made of normal strength concrete and UHPFRC were tested under lateral cyclic loading up to failure using a 500 tonne capacity computer control servo hydraulic machine. The specimen with normal strength concrete failed at the joint region while the specimen with UHPFRC material failed due to yielding of the rebars in the beam sections near the column face and no obvious cracks were observed at the joint area. The specimens with UHPFRC as joint material exhibited higher initial lateral stiffness and achieved slightly higher ultimate load capacity than the specimen with normal strength concrete.

Influence of fibre orientation on the tensile behaviour of ultra-high performance fibre reinforced cementitious composites

The main objective of this study is to quantify the effect of fibre orientation on the tensile behaviour of Ultra-High Performance Fibre-Reinforced Cementitious Composites (UHPFRC). A strategy to align the steel fibres within the matrix based on the activation of an external magnetic field while casting is adopted to achieve a wide range of fibre orientation profiles. The uniaxial tensile test is used for determining the tensile stress-elongation curves of 22 specimens and the quantitative evaluation of the fibre density and orientation characteristics is performed resorting to an image analysis technique. Based on the obtained results it was possible to validate an analytical formulation for determining the tensile strength of UHPFRC and to quantify the involved parameters. It is also shown that length of the hardening branch of the tensile stress-elongation curve is also very well correlated with the same parameters used in the determination of the tensile strength.

Experimental and numerical study of the flexural behaviour of ultra-high performance fibre reinforced concrete beams

The development of standard analytical procedures and design guidelines for concrete requires extensive tests at material and structural level. For ultra-high performance fibre reinforced concrete (UHPFRC) this task is even more complicated than that of conventional concrete due to the potential range of fibre types and volume fractions. The experimental task of large scale structural members to develop the design procedures can be reduced by adopting an alternative way in which the concrete material model available in finite element packages are validated with the limited number of tests conducted on material and structural members. The validated numerical models can further used to study the effect on the structural behaviour due to change in geometry, loading conditions and reinforcement. Therefore the objective of the present study is to investigate the efficacy of the hybrid approach of validating the existing concrete model to study the behaviour of large-scale structural members made up of UHPFRC. For this four full-scale beams with varied spans and cross-sections were fabricated with the indigenously developed UHPFRC using conventional materials and mixing methods and tested under different loading conditions until failure. Numerical models were developed and validated with the test results of the beams for which the concrete damaged plasticity (CDP) model was adopted to characterize the behaviour of UHPFRC material. The material parameters required to define the constitutive model were identified by conducting direct/uniaxial tension and compression tests. The results obtained from the numerical models shows that the CDP model can accurately predict the load/moment carrying capacities of the UHPFRC beams. The results also show a good capability of the numerical models to predict the overall load deflection behaviour of the UHPFRC beams.

Direct tensile behavior of ultra high performance fiber reinforced concrete (UHP-FRC) at high strain rates

This experimental study investigates the direct tensile behavior of ultra-high performance fiber reinforced concrete (UHP-FRC) at strain rates ranging from 90 to 146/s. The tests are conducted using a recently developed impact testing system that uses suddenly released strain energy to generate an impact pulse. Three fiber types were considered, a twisted fiber and two other types of straight fibers. Specimen impact response was evaluated in terms of first cracking strength, post-cracking strength, energy absorption capacity and strain capacity. The test results indicate that specimens with twisted fibers generally exhibit somewhat better mechanical properties than specimens with straight fibers for the range of strain rates considered. All UHP-FRC series tested showed exceptional rate sensitivities in energy absorption capacity, generally becoming much more energy dissipative under increasing strain rates. This characteristic highlights the potential of UHP-FRC as a promising cement based material for impact- and blast-resistant applications.

Effect of loading rates on pullout behavior of high strength steel fibers embedded in ultra-high performance concrete

In this paper single fiber pull-out performance of high strength steel fibers embedded in ultra-high performance concrete (UHPC) is investigated. The research emphasis is placed on the experimental performance at various pullout rates to better understand the dynamic tensile behavior of ultra-high performance fiber reinforced concrete (UHP-FRC). Based on the knowledge that crack formation is strain rate sensitive, it is hypothesized that the formation of micro-splitting cracks and the damage of cement-based matrix in the fiber tunnel are mainly attributing to the rate sensitivity. Hereby, different pull-out mechanisms of straight and mechanically bonded fibers will be examined more closely. The experimental investigation considers four types of high strength steel fibers as follows: straight smooth brass-coated with a diameter of 0.2 mm and 0.38 mm, half end hooked with a diameter of 0.38 mm and twisted fibers with an equivalent diameter of 0.3 mm. Four different pull out loading rates were applied ranging from 0.025 mm/s to 25 mm/s. The loading rate effects on maximum fiber tensile stress, use of material, pullout energy, equivalent bond strength, and average bond strength are characterized and analyzed. The test results indicate that half-hooked fibers exhibit highest loading rate sensitivity of all fibers used in this research, which might be attributed to potential matrix split cracking. Furthermore, the effect of fiber embedment angles on the loading rate sensitivity of fiber pullout behavior is investigated. Three fiber embedment angles, 0°, 20°, and 45°, are considered. The results reveal that there is a correlation between fiber embedment angle and loading rate sensitivity of fiber pullout behavior.

Improvement of Torsional Resistance in Ultra-High Performance Fibre Reinforced Concrete Beams

This research highlights the effect of concrete cover on the behavior of ultra-high performance fiber reinforced concrete rectangular solid beams under pure torsion. The main parameter in this research is the thickness of concrete cover which is varying between 21 and 52 mm. For this purpose, four under-reinforced ultra-high performance fibre reinforced concrete rectangular solid beams were cast and they were tested under pure equilibrium torsion. The test results verified that the torsional resistance at peak and crack loads were improved up to 113% and 134%, respectively, of the estimated value based on thin walled tube theory. Moreover, all of the twisting angle at ultimate load and shear strain in concrete were found to decrease up to 64.9%, 40.1%, respectively. In addition, both strain in longitudinal reinforcement and strain in stirrup were reduced up to 50%. The space truss analogy was modified to be compatible with this parameter effect. The modified model showed that it has a good agreement with test results.

Behavior of ultra-high performance fiber reinforced concrete columns under pure axial loading

This paper presents the results of a study examining the axial load performance of ultra-high performance fiber reinforced concrete (UHPFRC) columns. As part of the experimental program six large-scale columns were tested under pure axial loading to examine the effect of UHPFRC and transverse reinforcement detailing on column performance. The results demonstrate that the provision of closely-spaced and well-detailed transverse reinforcement allows for the development of excellent ductility in UHPFRC columns. The results also indicate that spacing and configuration of transverse reinforcement are important factors affecting the axial strength and toughness of UHPFRC columns. The analytical investigation examines the suitability of using existing high-strength concrete and fiber reinforced concrete confinement models to predict the axial response of the columns tested in this research program. The results indicate the need for the development of UHPFRC-specific confinement models.