Ultra-High Performance Fibre Reinforced Research Articles

3D printability of recycled steel fibre-reinforced ultra-high performance concrete

3D printability of recycled steel fibre-reinforced ultra-high performance concrete

Mechanical properties and flexural toughness evaluation method of mono/hybrid fiber-reinforced ultra-high performance seawater sea sand concrete

Mechanical properties and flexural toughness evaluation method of mono/hybrid fiber-reinforced ultra-high performance seawater sea sand concrete

Triaxial compressive behavior of 3D printed PE fiber-reinforced ultra-high performance concrete

The layered deposition process of 3D concrete printing can lead to reduced mechanical properties at the interfaces between filaments. To address this limitation, external confinement devices, such as fiber-reinforced polymer (FRP) wrapping, have been proposed to enhance the strength of 3D-printed concrete concrete. Achieving this requires a solid understanding of the triaxial mechanical performance of 3D-printed concrete. This study presents an experimental investigation of the triaxial compressive behavior of 3D-printed PE fiber-reinforced ultra-high performance concrete (3DP-PEUHPC). A total of 16 pairs of concrete cubes were prepared, including mold-cast and 3D-printed specimens, and subjected to uniaxial and triaxial compression tests. The results revealed that the 3D-printed specimens exhibited either column-type or diagonal shear failures under triaxial compression. Weak bonding was observed at both filament-fusion and layer-fusion interfaces, with these weaker bonding interfaces, particularly when aligned parallel to the axial load, showing susceptibility to stress concentration and crack initiation. This led to a reduction in load-bearing capacity of the 3D-printed specimens compared to the mold-cast specimens. Importantly, as confining stresses increase, the difference in compressive strength between 3D-printed and mold-cast specimens decreases, highlighting the effectiveness of confinement in mitigating the directional weaknesses inherent in 3D-printed concrete. This paper also presents a modified model for predicting the axial stress-strain relationship of 3DP-PEUHPC under confinement, providing insights into the mechanism of FRP confinement on the compressive strength of 3D-printed concrete structures.

Split Hopkinson bar and flash X-ray characterization of ultra high performance concrete reinforced by steel fibers subjected to dynamic compression

AbstractExcellent mechanical properties of ultra high performance concrete make it suitable for use in special applications, where the material is subjected to dynamic phenomena such as impacts, explosions, or earthquakes. This paper presents a novel experimental approach that integrates a Split Hopkinson Pressure Bar with a flash X-ray system and high-speed optical imaging to investigate the dynamic behavior of steel fiber reinforced UHPC under high strain rate uni-axial compression. In-situ Flash X-ray radiography emerges as a particularly effective tool, providing clear visualization of deformation response and overcoming challenges associated with flying debris encountered in optical inspection. Moreover, computed tomography and scanning electron microscopy appear as a vital technique for analyzing micro-structure and fiber distribution and orientation. The combined approach offers a promising method to study the dynamic behavior of steel fiber reinforced ultra high performance concrete and also holds promise for analyzing more complex modes of deformation and material interactions, providing valuable insights for enhancing the design and performance of critical infrastructure subjected to dynamic loading events.

Microstructure and radiation shielding characteristics of PVA fiber-reinforced ultra-high performance concrete

The application of nuclear technologies simulates the development of radiation shielding materials. Traditional heavy-weight concrete used for radiation shielding is limited in practical construction due to the poor mechanical properties and durability. This study developed a PVA fiber-reinforced ultra-high performance concrete (UHPFRC) with magnetite as heavy aggregates used for radiation shielding. Due to the scientific skeleton design, UHPFRC exhibits superior mechanical properties, with compressive strength and flexural strength reaching up to 121.9 MPa and 23.2 MPa, respectively. The microstructure of UHPFRC was investigated in detail and the results revealed that the incorporation of PVA fibers refined the pore structure of UHPFRC. The interfacial transition zone between magnetite aggregates and cementitious matrix in UHPFRC was much denser than that in traditional concrete due to the low water to binder ratio. The gamma and neutron radiations shielding capacity of UHPFRC were evaluated by the combination of actual measurement and simulation. By introducing light nuclei and refining the pore structure, the incorporation of PVA fibers improved the neutron radiation shielding capabilities of UHPFRC by 5.1%.

Effect of Curing Regimes and Fiber Contents on Flexural Behaviors of Milling Steel Fiber-Reinforced Ultrahigh-Performance Concrete: Experimental and Data-Driven Studies

Effect of Curing Regimes and Fiber Contents on Flexural Behaviors of Milling Steel Fiber-Reinforced Ultrahigh-Performance Concrete: Experimental and Data-Driven Studies

The Effect of Cross Sectional Properties of Concrete Column on the Repair Material: A Review

The utilization of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) as a material for repairing concrete structures holds immense promise and potential. UHPFRC usage in concrete has been a significant rise in the interest surrounding the enhancement and renovation of concrete structures, particularly focusing on columns. UHPFRC has showcased remarkable bonding potency with concrete, along with an impressive capacity to renew the load-bearing capability of compromised reinforced concrete columns. However, the limited application of UHPRFC as a repair material for concrete columns is primarily attributable to a lack of comprehension regarding the influence of shape and size effects, particularly as they pertain to square and rectangular columns. In this paper, the factors behind the impact of cross-sectional properties on the effectiveness of UHPFRC as a repair material is presented. Therefore, it can be adopted by researchers to explore the UHPFRC potential in structural rehabilitation applications especially for concrete columns. It is believed that the relationship between the cross-sectional area, aspect ratio, and corner radius ratio of the column and repair material is a vital parameter affecting the performance of repaired columns.

Strengthening of bridges with iron-based shape memory alloy bars embedded in UHPFRC

Bridges are designed for a service life of up to 100 years. A significant number of structures still in use lack the required levels of structural safety, either due to deterioration or because older design codes are partly obsolete. With the increasing focus of the construction industry towards sustainability and circularity, there is a trend to develop innovative and efficient strengthening methods that enable the rehabilitation of under-designed or damaged structural components rather than rebuilding new structures. To this end, this paper presents a research project aiming at developing a new method for flexural strengthening of bridge decks, which consists in applying a layer of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) reinforced with Iron-based Shape Memory Alloy (Fe-SMA) ribbed bars on top of the existing Reinforced Concrete (RC) structure. The Fe-SMA bars are activated through heating, ultimately leading to the development of prestressing forces.To analyse this novel technology, a case study is developed. The performance of the new system is compared to a strengthening using B500B steel reinforcing bars embedded in UHPFRC, highlighting the main advantages of the new method. Furthermore, the bond behaviour of Fe-SMA bars embedded in UHPFRC is characterised in detail through short pull-out tests. Design parameters such as the temperature of activation of Fe-SMA and concrete cover thickness are studied. The bond shear stress-slip relationships show very high bond strengths for all tested covers, even after a slight deterioration of the bond properties resulting from the heating.

The Dynamic Compressive Behavior of Waved Fiber-Reinforced Ultrahigh-Performance Cementitious Composites Containing Fly Ash and Ground Granulated Blast-Furnace Slag

The Dynamic Compressive Behavior of Waved Fiber-Reinforced Ultrahigh-Performance Cementitious Composites Containing Fly Ash and Ground Granulated Blast-Furnace Slag

Flexural Performance of Hybrid Fiber-Reinforced Ultrahigh-Performance Concrete with Locally Available Materials

Flexural Performance of Hybrid Fiber-Reinforced Ultrahigh-Performance Concrete with Locally Available Materials

Influence of steel fiber types on residual mechanical properties and explosive spalling of hybrid fiber reinforced ultra-high performance concrete: Optimization and evaluations

To investigate the influence of steel fiber on improving the high-temperature resistance of hybrid fiber-reinforced ultra-high performance concrete (UHPC), four types of UHPC specimens were prepared. The residual strength and fracture energy of all UHPCs were determined after exposure to varying high temperatures, and internal temperature in the specimens were also measured. Additionally, explosive spalling tests were performed on specimens with different moisture contents. The results indicate that the residual mechanical properties of UHPC initially increase and subsequently decrease as the target temperature increases. Notable differences in thermal conductivity were observed among the tested UHPC specimens. As the moisture content of the specimens increased, the likelihood and severity of explosive spalling in the specimens increased. Corrugated high-strength steel fibers, measuring 35 mm in length and 1 mm in diameter, are highly effective at preventing explosive spalling of UHPC, and high-temperature treated recycled steel fiber from tires also exhibits better performance than other two types of steel fiber. High tensile strength of steel fiber and its distinctive corrugated appearance can be the primary contributing factors. Furthermore, two established computational models which demonstrated a significant level of congruence were employed for evaluating explosive spalling and anti-spalling properties of UHPC specimens. This suggests that cracking resistance provided by steel fiber plays an important role in preventing the explosive spalling of UHPC, emphasizing the importance of exploring specific steel fiber based on its appearance and tensile strength.

Mechanical properties of multi-scale mono/hybrid non-metallic fiber-reinforced ultra-high performance seawater sea-sand concrete

Ultra-high performance seawater sea-sand concrete (UHP-SSC) is a promising construction material with excellent mechanical and durability properties, addressing the deficiency of materials like fresh water and river sand.Nevertheless, the steel fibers that reinforce UHPC are unsuitable for UHP-SSC, resulting from the corrosion problem. In this regard, this study investigated the impacts of multi-scale (micro and macro) mono and hybrid non-metallic fiber reinforcements on the mechanical properties of UHP-SSC. The experiments, including flowability, compression, and third-point bending, were carried out. The surface morphologies and microstructures of UHP-SSC were characterized by scanning electron microscopy and low-field nuclear magnetic resonance. The mono-fiber comprised three micro-fiber types: polyvinyl alcohol fiber (PVAF), carbon fiber (cF), and basalt fiber (bF); along with two macro-fiber types: polypropylene fiber (PPF) and basalt fiber reinforced polymer fiber (BF), while the hybrid fiber reinforcement was composed of different hybridization of foregoing fibers. The results indicated that the compressive and flexural properties of plain UHP-SSC were enhanced by adding micro- or macro-fiber. The enhancement is positively related to the elastic modulus of fibers. Notably, utilizing macro-fiber can effectively improve the flexural toughness, particularly for BF, which induces strong strain-hardening behavior. Microscopic and microstructure observations confirmed the strength and toughness evolution and illustrated the relevant mechanism. In the case of fiber hybridization, the combination of micro- and macro-fiber has a positive synergy effect, and the mixture with bF and BF exhibits the utmost synergistic influence when the volume of bF is controlled within 0.4 vol%.

Strengthening of the Riddes Viaduct Through UHPFRC-Based Rehabilitation

Built in the mid-1970s, the Riddes viaduct is an important viaduct in the Canton of Valais in Switzerland. Thorough inspection of the viaduct revealed structural deterioration of concrete due to alkali–aggregate reaction, as well as corrosion of the prestressing tendons. In an effort to restore the structural integrity of the viaduct, a retrofit intervention that consists of adding a 50 mm layer of an Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) to the deck was proposed. The layer is characterized by its low permeability and excellent mechanical properties. The contribution of the overlay to the load-carrying capacity and stiffness of the viaduct was investigated through a continuum finite element model. Results of the model revealed that the UHPFRC layer significantly enhances the flexural and torsional strength and stiffness of the box girder and ameliorates tensile cracking. The retrofit intervention was deemed beneficial, and the rehabilitation process was carried out.

Punching shear and flexural performance of ultra-high performance fibre reinforced concrete (UHPFRC) slabs

Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) is a high-performance cementitious composite that is characterised by superior mechanical properties, high energy absorption capacity and enhanced durability. The mechanical characteristics of UHPFRC and more specifically the enhanced tensile strength and the significant energy absorption and crack resistance make it a very popular material, especially for extreme loading conditions or in cases of thin load bearing elements.UHPFRC has been recently introduced in applications such as bridge decks, and thin slabs and for the strengthening of existing elements. However, the punching shear performance and the effect of the fibres on the punching shear strength of UHPFRC have not been sufficiently studied. Also, there is a lack of provisions for the punching shear design of UHPFRC, which limits the extensive application of UHPFRC in thin elements especially when there are concentrated loads.In this study, extensive experimental work has been conducted on slabs with different geometries and various mixes and valuable results are presented for the flexural and the punching shear capacities of UHPFRC. Also, methodologies for the calculation of the punching shear and the flexural capacities of UHPFRC slabs have been examined and important conclusions have been drawn.

Mechanical Properties of Polyethylene Fiber Reinforced Ultra High Performance Concrete (UHPC).

Ultra-high performance concrete (UHPC) is a kind of cement-based material with ultra-high strength, high toughness and excellent durability. However, the tensile strain capacity of UHPC is often below 0.5%, and the mode of single crack failure is the main failure pattern, which limits the development of UHPC. In order to overcome the weakness of the relatively low strain capacity of UHPC, five types of polyethylene (PE) fibers with different geometrical and mechanical parameters (length, diameter and elastic modulus) were added into the matrix, and the corresponding mechanical behavior was investigated. The experimental results showed that the high fiber length and fiber diameter of PE fibers are a benefit for the compressive strength and tensile strength of UHPC. The increase of the fiber diameter and elastic modulus remarkably attributed to the increase in the tensile strain capacity of UHPC. With the increase of the fiber diameter and elastic modulus, the overall energy absorption capacity G and the energy absorption capacity of the substrate prior to the softening section ga of UHPC were both enhanced. The diameter of PE fiber was the main factor affecting the energy consumption of UHPC. Among the five types of PE fiber, PF fiber (PF fiber is PF type polyethylene fiber; Fiber length: 15 mm; Fiber diameter: 27 μm; Elastic Modulus: 117 GPa) is the optimal fiber to increase the tensile mechanical behavior of UHPC.

Behavior of Reinforced Ultra-High Performance Concrete Slabs Under Impact Loading After Exposure to Elevated Temperatures

Steel fiber-reinforced ultra-high performance concrete (UHPC) material is prone to explosive spalling under elevated temperatures. With the addition of polypropylene (PP) fiber, thermal spalling of UHPC can be mitigated and its fire resistance can be improved. This research investigates the impact resistance of steel and PP fiber-reinforced UHPC slabs after exposure to elevated temperatures, and the structural behavior and damage were compared against normal strength concrete (NSC) slabs. Karagozian & Case concrete (KCC) model was adopted to simulate both NSC and UHPC materials. With consideration of thermal hazards, the material damage, equation of state and strain rate sensitivity were adapted. The validity of this numerical model was evaluated against available experimental results. The numerical model was used to investigate the impact resistance of the reinforced UHPC slabs after exposure to fire hazards. The effect of fire exposure time, impact velocity and impact mass on the resistance of the reinforced NSC and UHPC slabs were analyzed. The simulation results revealed that punching shear failure areas in the NSC slabs were 2.5 times, 3.4 times, 3.0 times and 1.2 times larger than the UHPC slabs after exposure to international standardization ISO-834 standard fire for 1[Formula: see text]h, 2[Formula: see text]h, 3[Formula: see text]h and 4[Formula: see text]h, respectively. After exposure to the standard fire ISO-834 for 2 h, the punching shear failure on the bottom side of NSC increased 90.9% with the increase in falling height from 1[Formula: see text]m to 7[Formula: see text]m, while for the UHPC slabs, the increment was around 67.9%. After exposure to the standard fire ISO-834 for 2[Formula: see text]h, the punching shear damage of the NSC slabs increased by 72.9% with the punch weight increased from 100[Formula: see text]kg to 700[Formula: see text]kg, whereas the damage in the UHPC slabs increased by 53.8%.

Uniaxial tension– Compression behaviour of the UHPFRC using GGBS

The purpose of this study was to investigate the mechanical characteristics of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) under compression uniaxial loading conditions, using waste in the mixture. UHPFRC is a class of cementitious material with high durability and strength, limited to a minimum value of compressive strength of 150 MPa. The difference with traditional concrete lies mainly in the post-peak behaviour that occurs due to the presence of fibres, which are responsible for ensuring the ductile behaviour of the material. Uniaxial compression tests on twenty cylindrical specimens were carried out and tested after 28 days of curing, with a percentage of steel fibres of 1% at a displacement loading speed of 0.5 mm/min. The mixture design that was used allowed to manufacture a thixotropic material, characterized by a compressive strength and an average modulus of elasticity of 150.89 MPa and 47.71 GPa respectively. A simple production process was used, including Ground Granulated Blast Furnace Slag (GGBS) as the main sustainable material and as partial substitute for cement. Curves for design and structural analysis were plotted and compared with the average experimental curve and with other research consulted in the literature, including the elastic and inelastic behaviour of the material.

Influence of Ground Granulated Blast Furnace Slag on the compressive strength and ductility of Ultra High-performance fibre reinforced cementitious composites

The mechanical properties of Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRCC) is basically influenced by the type of fibres and reactive binders used. Fibres primarily influence the ductility whereas reactive binders influence the compressive strength of UHPFRCC. Among the commonly used reactive binders, Ground Granulated Blast Furnace Slag (SL) with its vitreous nature has the ability of influencing both the compressive strength and ductility of UHPFRCC. This study discussed the microstructure and mechanical properties of six different mixtures made up of 0%, 20%, 40%, 60% 75% and 90% cement replacement of SL. The XRD results indicated that, increased levels of C-S-H and ettringite retard the hydration process leading to lower compressive strength and vice versa. The SL-cementitious composite can achieve a compressive strength of up to 108.1MPa and ductility of up to 1.67% without the use of fibres. The maximum compressive strength and ductility were achieved with 40% SL replacement of cement whereas the minimum compressive strength and ductility were achieved with 60% and 20% SL contents, respectively. Moreover, the optimum mechanical properties (i.e. compressive strength, tensile strength, flexural strength, and tensile strain) were achieved with a 40% SL replacement of cement in the cementitious composite.

Investigation onmechanical property adjustment of multi-scale hybrid fiber-reinforced concrete

In order to avoid the tunneling disasters in the adverse geology, the ultra-high performance concrete needs to be used for control the deformation. As a random multiphase material, concrete is mostly heterogeneous and heterogeneous, and its characteristics are complex. So the relevant test cycle is long and the cost is high. In order to know the required mechanical properties of the ultra-high performance concrete, the advanced research can be carried out by the finite element method. The fiber-reinforced concrete model was established to study how the multi-scale hybrid fiber-reinforced concrete has been enhanced by the finite element method. The concrete is considered as the elastic-plastic constitutive relationship, but the fibers in the concrete follow the elastic constitutive relationship. Eight-node hexahedral reduced integral elements are adopted for both matrix and fiber. The reliability and validity of the fiber-reinforced ultra-high performance concrete by the finite element method was verified by the experiment. It can be used to predict the mechanical properties of concrete with different fiber characteristics, but unable to be used to predict more complex behaviors such as damage and fracture. The results indicate that the compressive strength and the flexural strength of concrete with a fiber volume content of 1.0% are larger than other 6 different fiber volume content, the beam axially undergoes plastic deformation is the largest of the seven, and the fiber concrete numerical model can better simulate the static mechanical properties and the failure mechanism of fiber fibers when the fiber volume content is 0.1%, and the fiber length is 15 mm. This study can provide a reasonable and effective reference for the actual engineering.

Crack control for repair and strengthening of reinforced concrete structures using the multi-cracking behaviour of Ultra-high Performance Fibre Reinforced Shotcrete (UHPFRSC)

Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) is an innovative material for the repair and/or strengthening of reinforced concrete structures. In the field of traffic infrastructure, the outstanding mechanical properties are used as a protective surface layer and to increase the load capacity of the structure. UHPFRC is characterised by a dense granular structure and correspondingly high resistance against chloride attack. The material is typically applied as cast in-situ concrete. To optimise implementation of the strengthening and repair method, the UHPFRC is applied as sprayed concrete, so-called Ultra-High Performance Fibre Reinforced Shotcrete (UHPFRSC). The research aims to increase the service life of damaged and/or overloaded structures. Crack widths in the UHPFRSC layer must be limited to avoid migration of chlorides. The thin UHPFRSC layer provides crack distribution and control of localised macro cracks in the existing reinforced concrete structure. The fibres in the Ultra-High Performance Shotcrete (UHPSC) allows for limiting the crack width to 50 µm. When the UHPFRSC is applied on cracked reinforced concrete, it can be assumed that multi-cracking in the UHPFRSC surface layer will provide a chloride-dense layer equivalent to a coating. Under load, the two layers - UHPFRC and RC - act as a composite. For structural analysis, a particular focus must be placed on the interaction between cementitious materials. In addition, the pre-damage and pre-loading of the existing structure will influence the structural behaviour and crack formation. The paper presents the results of bending tests of UHPFRC - RC composite elements. The investigation shows the outstanding crack control behaviour of UHPFRSC. Based on this investigation, an analytical model will be provided, and a calculation of the crack widths will be derived. The research presents a central aspect of a large interdisciplinary research project at Munich University of Applied Science, called i-SCUP.