Ultra High Performance Fiber Reinforced Concrete Mixtures Research Articles

The Influence of UHPFRC Jacket Steel Fiber Content on Strengthening Damaged Columns

Steel fiber is a commonly used material to repair damaged concrete, caused by environmental or design issues. This study used various Micro-copper-coated Steel Fiber (MSF) content (0.0, 0.5, 2.0, and 2.5%) with varying aspect ratios (28, 37, and 45) as part of Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) mixtures to repair damaged concrete columns using a 30 mm layer jacketing. Twelve columns were prepared and tested at first by loading them with roughly 90% of their ultimate axial load capacity. Damage was caused and the columns were subsequently strengthened and rebuilt using UHPFRC mixtures in 30-mm layer jacketing for a second test, to determine the effect of UHPFRC and MSF content on damaged and reinforced columns. The test results showed that the concrete properties improved as the MSF content increased to 2.0% of the volume fraction, beyond which there was a slight reduction. Additionally, the UHPFRC-strengthened columns with and without MSFs experienced higher load capacities than the corresponding unstrengthened. On the contrary, using 2.5% MSF in the UHPFRC decreased the loading capacity by 14% compared to the UHPFRC with 2.0% MSF. The strengthened column with 2.0% MSF content showed the highest load efficiency (165.7% compared to unstrengthened), along with substantial displacement and ductility.

Flexural strength and toughness of self-leveling UHPFRC

Acquiring higher performance at both fresh and hardened states is critical in the practical design of ultra-high performance concrete (UHPC)/ultra-high performance fiber reinforced concrete (UHPFRC). Herein, a total of 12 self-leveling UHPC and UHPFRC mixtures were developed and evaluated for their flexural performance by three-point bending tests, together with their workability and mechanical properties. From load-deflection curves, the first cracking flexural strength, post cracking flexural strength, flexural deflection capacity, and flexural toughness were determined. By corelating the flexural responses to fiber factor and matrix strength, the flexural strengths were found to be positively affected by fiber factor and matrix strength, while the flexural deflection capacity and toughness indices were less influenced by matrix strength but can be substantially enhanced by increasing steel fiber volume. Design equations were derived by physics-informed data-fitting for flexural strengths and toughness with high accuracy, allowing for quantification of synergistic effect between fiber factor and matrix strength in resilient design.

Effect of calcined diatomaceous earth, polypropylene fiber, and glass fiber on the mechanical properties of ultra-high-performance fiber-reinforced concrete

Abstract In this study, the effects of calcined diatomaceous earth (CDE), polypropylene fiber (PF), and glass fiber (GF) on the mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC) were observed, and a total of 33 UHPFRC mixtures, consisting of 3 mixtures without fiber, 15 mixtures with PF, and 15 mixtures with GF were prepared. Subsequently, the fresh concrete mixtures were tested for flow, while the hardened concrete specimen’s mechanical properties were analyzed. These tests include compression, splitting tensile, and flexural tests. The test results showed that the use of 5 and 10% CDE as a binder for cement replacement improved the compressive strength, splitting tensile strength, and flexural strength of the UHPFRC. Furthermore, the addition of PF and GF contents of up to 1% of the concrete volume increased the compressive strength of the UHPFRC, while their contents of up to 1.5% improved their splitting tensile strength and flexural strength. It is also important to note that the workability of the UHPFRC reduced as the fiber and CDE contents increased. Finally, based on the experimental data tested in this study, the relationship between splitting tensile strength, flexural strength, and compressive strength of the UHPFRC containing PF and GF were proposed. Moreover, the reduction in flow value, which is a function of the volumetric content of both PF and GF, with the CDE contents was also proposed.

Physically explicable mathematical model for strength prediction of UHPFRC

This paper presents a quantitative analysis of the mechanical performance of ultra-high performance fiber-reinforced concrete (UHPFRC). UHPFRC shows great potential in the construction of the cities of tomorrow. However, establishing empirical formulas by incorporating existing data for the practical engineering design of UHPFRC remains a problem. To advance the understanding of UHPFRC, this paper qualitatively and quantitatively studied UHPFRC with an emphasis on its strength. Utilizing abundant data consisting of 111 different UHPFRC mixtures in literature, the key factors governing the strength of UHPFRC, e.g., the volumetric ratios and types of paste, aggregate, fibers and filler, were identified. Based on the key factors, a robust mathematical model for the strength prediction of UHPFRC was established. In addition, an artificial neural network model was constructed. This study shall provide useful guidelines for the mix design of sustainable and resilient UHPFRC.

Estimating the Tensile Strength of Ultrahigh-Performance Fiber-Reinforced Concrete Beams

The tensile behavior of ultrahigh-performance fiber-reinforced concrete (UHPFRC) depends on the dispersion and orientation of steel fibers within the concrete matrix. The uneven dispersion of randomly oriented steel fibers in concrete may cause differences in the tensile behavior between material testing specimens and beams. Therefore, in this study, the tensile behavior was investigated by fitting the analysis result of the moment-curvature curve to the experimental result of a UHPFRC beam. To this end, three UHPFRC mixtures with different compressive strengths were fabricated to test the material properties and flexural behavior of UHPFRC beams. Both a single type of steel fiber and a combination of steel fiber types were used with volume fractions of 1.0% and 1.5%, respectively, in the three mixtures. Based on the design recommendations, the material properties of UHPFRC were modeled. The results ultimately show that by fitting the analysis results to the experimental results of the moment-curvature curves, the tensile strength of UHPFRC beams can be reasonably estimated.

An Octet-Truss Engineered Concrete (OTEC) for lightweight structures

Recent advances in the development of Ultra-High Performance Fiber-Reinforced Concrete (UHP-FRC) with very high compressive strength has inspired the development of a lightweight structure by engineering the void spaces in the material, thus taking advantage of porous concrete’s thermal insulating properties while maintaining strength and stiffness. This paper refers to this engineered material as Octet-Truss Engineered Concrete (OTEC). To make OTEC structures, UHP-FRC and “green” UHP-FRC (G-UHP-FRC) mixtures were developed. 50.8-mm side-length OTEC unit cell specimens with various element diameters as well as 5 × 1 × 1-cell OTEC flexural specimens with 8 mm-diameter elements were cast and tested under uniaxial compression and four-point bending, respectively. The compressive strength of the OTEC unit cell specimens with various element diameters is mainly stretching-dominated, and hence considerably surpasses that of the control foam Green Ultra-High Performance Concrete specimens with random pore orientations. These results indicate a promising application of UHP-FRC and G-UHP-FRC OTECs for lightweight structures.

EXPERIMENTAL STUDY OF ULTRA-HIGH PERFORMANCE FIBER REINFORCED CONCRETE DOSAGES WITH ULTRA FAST SETTING TIME

The overall objective of the work is the development of ultra high performance fiber reinforced concrete (UHPFRC) dosages that can be used for shotcrete. In this study, a number of UHPFRC mixtures with different amount of admixtures (plasticizers and accelerating) and different mixing time were tested, to increase either the rate of stiffening or setting of the concrete or the rate of hardening and early-strength development. Workability, consistency and mechanical properties of UHPFRC including compressive and flexural strengths at different ages were assessed. Results showed mixtures than begin their first setting in less than 1 minute, with very good mechanical properties in 24 hours, and without reducing the compressive strength at 28 days. From the results obtained, various uses of these mixtures are proposed taking into account, the new context of the Construction field, with the appearance of new placing concrete techniques.

Projectile Impact Resistance of UHPFRC Structures for Various Methods of Fresh Mixture Placement

This paper present results of an experimental investigation of the projectile impact resistance of ultra-high-performance fibre-reinforced concrete (UHPFRC) slabs. The paper also investigates transparent viscous liquid, based on the ultrasound gel, as an effective suitable tool to replace fresh mixture of ultra-high-performance concrete. The description of the viscous behaviour of both materials and optimisation of the ultrasound gel is shown. An arrangement of fibres in the UHPFRC mixture was demonstrated by the ultrasound gel with an addition of steel fibres. The influence of horizontal and vertical casting of thin slabs against penetration by a projectile was tested and described. The resistance to the penetration was investigated using full-metal jacket projectile with soft-lead core. The results indicated various penetration depths and crater diameters in the target specimens for both methods of casting. Various methods of casting resulted in various arrangement of fibres for both horizontally and vertically casted slabs. However, the protective capacity was guaranteed for both placement methods. The desired outcome was determination of the UHPFRC mechanical properties and projectile impact resistance, depending on the orientation of fibres which depended on the method of placement of the fresh mixture into the formwork. The direction of mixture placement into the formworks had a significant impact on achieved mechanical properties of the hardened concrete. Based on the present findings it was found that slabs from ultra-high-performance fibre-reinforced concrete casted horizontally appear to be more efficient in protection against projectile impact.

Energy absorption capacity of a sustainable Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) in quasi-static mode and under high velocity projectile impact

This paper investigates the energy absorption capacity of a sustainable Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) in quasi-static mode and under high velocity projectile impact. The design of the sustainable concrete mixtures aims on achieving a densely compacted cementitious matrix with a relatively low binder amount, employing the modified Andreasen & Andersen particle packing model. The experiments on UHPFRC are performed using a 4-point bending test and high velocity projectile impact tests. The obtained results show that although the utilization of hybrid steel fibre enhances the mechanical properties of the developed UHPFRC, the application of fibres with hooked ends is crucial in improving the energy absorption capacity of the sustainable UHPFRC in quasi-static mode. However, under high velocity projectile impact, the UHPFRC mixture with hybrid fibres shows a much better energy absorption capacity than the one with hooked steel fibres only, particularly in resisting the scabbing at the rear surface. The intrinsic mechanisms for the energy absorption capacity of the sustainable UHPFRC in quasi-static mode and under high velocity projectile impact are studied and analysed.

Effects of curing type, silica fume fineness, and fiber length on the mechanical properties and impact resistance of UHPFRC

The effects of silica fume fineness and fiber aspect ratio on the compressive strength and impact resistance of ultra high-performance fiber-reinforced concrete (UHPFRC) are investigated experimentally. To this end, UHPFRC mixtures are manufactured by combining silica fumes with different fineness (specific surface areas: 17,200, 20,000, and 27,600m2/kg) and hooked-end steel fibers with various aspect ratios (lengths: 8, 13, and 16mm). The samples are subjected to standard curing, steam curing, and hot-water curing. Compressive strength tests are conducted after 7-, 28-, 56-, and 90-day curing periods, and an impact resistance experiment is performed after the 90th day. A steam-cured mixture of silica fumes with a specific surface area of 27,600m2/kg and 16-mm-long fibers produce better results than the other mixtures in terms of mechanical properties. Moreover, impact resistance increases with the fiber aspect ratio.

Resistance of slim UHPFRC targets to projectile impact using in-service bullets

Significant buildings, transportation hubs, protective or defence structures are at exposure risk to extreme load event such as blast loading or direct armed attack. This kind of loading is typical by its rapid increase in release of energy in a very short time. It is believed that emerging cementitious materials such as Engineered Cementitious Composite (ECC) or Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) provide better passive protection to significant buildings compared to High-Strength Concrete (HSC) or conventional Fibre Reinforced Concrete (FRC). In this study, response of several UHPFRC slabs to projectile impact was examined in order to simulate the effects of possible damage by small fire arms or by fragments generated by an explosion. Real ammunition was used with impact velocity in the range of 691–720 m/s and fibre content of the UHPFRC was selected as the main test variable. The optimal fibre content in the UHPFRC mixture was determined using damage parameters such as crater diameter, penetration depth, debris fragment mass and residual penetration potential of the bullet. It was verified experimentally that the optimal fibre content in the UHPFRC mixture is 2% by volume. Using less than 2% of fibre volume fraction might be unsafe in the slim UHPFRC targets due to increased volume of secondary fragments generated from the back side of the slab and also due to the higher residual penetration potential of the bullet exiting the back side of the slab. Using more that 2% of fibre volume fraction could be inefficient. No improvement in all damage parameters was observed when the fibre volume fraction was changed from 2% to 2.5% or 3%.

Low Cost Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) with Flash Metakaolin

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) presents remarkable mechanical and durability properties. Concretes can be considered as UHPFRC when compressive strength and direct tensile strength reach respectively reach 150 MPa and at 7 MPa at 28 days [1]. The UHPFRC matrix is generally composed by a high amount of cement and silica fume as binder, steel fibers, very low Water/Binder (W/B) ratio and high rang water reducer. Special heat treatment is often required in order to achieve compressive strengths over 150-200 MPa. This work focuses on the development of low cost UHPFRC with less energy in production process in order to widespread its use. To reach this objective, some mix criteria have been set up: use of local materials, substitution of silica fume by less expensive and more available flash metakaolin, reduced cement content, without heat treatment. Four UHPFRC mixtures have been fixed. The reference one incorporates silica fume. In the second one, metakaolin substitutes weight by weight silica fume. Two other mixtures have been designed using a wet packing method [2] and a metakaolin water absorption test [3], in order to optimize the metakaolin/cement mass ratio and to reduce cement content. Workability and mechanical tests have been carried out. Results show that the weight by weight substitution of silica fume by flash metakaolin leads to a slight reduction (about 5%) of strengths but a more important reduction of cost (about 10% of UHPFRC material cost per m3). The optimization of metakaolin/cement ratio allows reaching equivalent performances of silica fume reference mix and reducing cement content without significant strengths decrease.

Resistance Of Ultra High PerformanceFibre Reinforced Concrete To Projectile Impact

The aim of this work is to describe the resistance of ultra high performance fibre reinforced concrete (UHPFRC) to projectile impact. The main goal is to find an optimum fibre content in the UHPFRC mixture with respect to the resistance to projectile impact, strength and workability. In addition, the authors describe the formulation process of UHPFRC that was developed without using heat treatment, pressure or a special mixer. Only ordinary materials available commercially in the Czech Republic were utilized throughout the process. The compressive strength of the resulting UHPFRC mixtures exceeded 150 MPa after 28 days and the flexural strength in three point bending was in the range of 40 MPa. Such high strengths were achieved due to the utilization of the high strength fibres and low water-to-binder ratio. The resistance of the UHPFRC to projectile impact is evaluated experimentally. Slabs made of UHPFRC with different fibre content were hit by deformable projectiles. The magnitude of the impact damage induced in the concrete specimens was evaluated from the average crater diameter and penetration depth. It was verified experimentally that an increase of fibre content has no significant effect on penetration depth while decreasing crater diameter. It was found that with respect to the resistance to projectile impact, strength and acceptable workability the optimal fibre content in the UHPFRC mixture is between 2 and 3% by volume.

Behaviour of Different Types of Concrete under Impact and Quasi-Static Loading

This paper describes mixture formulation of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) with 2% of fibres by volume and its response to quasi-static and dynamic impact loading. The UHPFRC mixture was prepared using locally available constituents and no special curing or mixing methods were used for its production. In addition, the mechanical parameters of three other types of concrete, i.e. normal strength concrete (NSC), fibre reinforced concrete (FRC) and high performance concrete (HPC) is compared. The main properties assessed throughout the experimental work are compressive, flexural and direct tensile strength as well as response of tested concretes to impact flexural loading. The impact loading is produced by a vertically falling weight of 24 kg from the height of 1 m on concrete prisms. The strain rate increase corresponds to low-velocity impacts such as vehicle crash or falling rocks. Compressive strength of UHPFRC exceeded 130 MPa and its direct tensile strength was 10.3 MPa. This type of concrete also exhibited strain hardening both in flexure under quasi-static conditions and during impact. Based on the comparison of impact reactions, it was concluded that the resistance of UHPFRC to impact loading is superior compared to the referent types of concretes (NSC, FRC, HPC).

Mix design of UHPFRC and its response to projectile impact

The aim of this paper is to describe mix design of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) and its response to deformable and non-deformable projectile impact. UHPFRC represents a class of cementitious composite in which stress–strain response in tension undergoes strain hardening behaviour accompanied by multiple cracking, leading to a high strain prior to failure. The compressive strength of the resulting UHPFRC mixtures exceeded 130 MPa and direct tensile strength was in the range of 10 MPa. Several UHPFRC mixtures with different content of fibers were subjected to deformable projectile impact. It was found that specimens containing 2% of fibers by volume have optimal resistance against deformable projectile impact. Slabs containing 2% of fibers were further subjected to a non-deformable projectile impact. In addition, response of slabs made of traditional fiber reinforced concrete (FRC) is discussed. The magnitude of the damage was assessed based on the penetration depth, crater diameter and loss of mass.

Experimental Investigation of Ultra-high Performance Fiber Reinforced Concrete Slabs Subjected to Deformable Projectile Impact

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is currently one of the biggest challenging issues in modern concrete technology. The UHPFRC represents a concrete with improved durability and strength, which is significantly higher than in conventional normal strength concrete. This may result in reduced cross-sections and as a consequence smaller dead-load of the structure. The uniaxial compressive cylinder strength of UHPFRC used in this study exceeded 150MPa and the uniaxial direct tensile strength exceeded 10MPa. Several UHPFRC mixtures with different content of fibers were subjected to deformable projectile impact. The ogive-nose projectile weighed 8.04 grams and its average velocity was determined to be 710 m/s. It was shown that plain UHPC specimen failed in the brittle manner which caused that the slab split into several pieces. Further, it was demonstrated that addition of steel micro fibers enhanced the resistance to deformable projectile impact and it was specified that specimens containing 2% of fibers by volume have optimal resistance against impact loading. In addition, response of slabs made of conventional fiber reinforced concrete (FRC) and normal strength concrete (NSC) was studied for comparison. The magnitude of the damage was assessed based on the penetration depth, crater diameter and mass loss. Experimental results clearly showed that implementation of high strength steel micro fibers significantly increased the resistance to projectile impact. It was stated, that UHPFRC has much better resistance to projectile impact in comparison to conventional FRC.

Mechanical and thermal evaluation of Ultra High Performance Fiber Reinforced Concretes for engineering applications

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) is a cement-based material, which behaves like a low-porosity ceramic material with excellent mechanical performance. This work was aimed to study soft cast (flowable at casting time) UHPFRC s and, in particular, the time development of compressive strength, flexural strength and elastic modulus was monitored for UHPFRC prepared by varying the water to cement ratio from 0.20 to 0.32. Silica fume, steel fibers and acrylic-based superplasticizer were employed to prepare the UHPFRC mixtures. Optimum workability and mechanical performance were obtained with a water to cement ratio of 0.24. Thermal conductivity was determined for the same UHPFRC, in the presence and in the absence of steel fibers. The scope was to evaluate the effect of steel fibers on the thermal conductivity coefficient, in order to predict the UHPFRC capacity for heat loss. This information as well as its drilling characteristics, in order to test its suitability to be machined, could be essential for possible fields of application such as in mechanical engineering, where UHPFRC materials can be employed as high abrasion-resistant dies in the molding process of metal and polymer products.