Mechanical Properties Of Ultra-high Performance Fibre Reinforced Concrete Research Articles

Influence of Type and Volume Content of Steel Fiber on the Compressive Strength of Ultra-High Performance Fiber Reinforced Concrete

The paper presents the results of determining the compressive strength of various compositions of Ultra-High Performance Fiber Reinforced concrete (UHPFRC) with fiber volume content from 1 to 3%. Four types of fibers were used: corrugated fiber of 15/0.3 mm and 22/0.3 mm, straight fiber of 13/0.3 mm and hooked-end fiber of 30/0.5 mm. It was found that corrugated and hooked-end fiber leads to an increase in compressive strength by 10–30 MPa when its content is increased from 1 to 3%. Straight fiber has no noticeable effect on the mechanical properties of UHPFRC. Empirical equations for predicting the compressive strength of UHPFRC depending on the strength of concrete matrix, geometric dimensions and content of dispersed reinforcement for compositions with corrugated and hooked-end fibers have been obtained. It is found that increasing the volume content of aggregate in the concrete matrix composition from 0.2 to 0.4 m3/m3 leads to an increase in the strength of UHPFRC. The strength of specimens with corrugated fiber increased by 5.3–13.3 MPa, with hooked-end fiber – by 14–19.3 MPa, with straight fiber – 5–7 MPa. It is also noted that the most intensive growth of mechanical characteristics due to the increase in the aggregate volume content in the composition is observed at a higher percentage of fiber volume fraction.

The effect of silane surface treatment on the mechanical properties of UHPFRC

Ultra-high performance fiber reinforced concrete (UHPFRC) is a new kind of cement-based composite material with high mechanical properties and excellent durability. However, the poor bonding properties between fiber and matrix in UHPFRC give rise to a weak fiber reinforcement effect. Therein, the surface of steel fiber was treated with γ-aminopropyl triethoxy silane to improve the interfacial bonding property of steel fiber. Optimal treatment of steel fibers with a silane coupling agent was determined through an orthogonal experiment. The mechanical properties, bending toughness, and energy absorption capacity of UHPFRC are investigated. The study found that bending toughness and energy absorption capacity of UHPFRC are increased by 47.6% and 78.0% with 2 vol% of treated steel fibers. The interface microstructure of steel fibers and matrix was characterized using advanced techniques, such as Fourier transforms infrared spectroscopy (FT-IR), X-ray spectroscopy (EDS), and electron microscopy (SEM). The mechanism of fiber treatment improving the interface bonding performance was revealed. This work provides a feasible method for the combination of reinforced steel fibers and the UHPFRC matrix.

Effects of Steel Fiber Percentage and Aspect Ratios on Fresh and Harden Properties of Ultra-High Performance Fiber Reinforced Concrete

Steel fibers and their aspect ratios are important parameters that have significant influence on the mechanical properties of ultrahigh-performance fiber-reinforced concrete (UHPFRC). Steel fiber dosage also significantly contributes to the initial manufacturing cost of UHPFRC. This study presents a comprehensive literature review of the effects of steel fiber percentages and aspect ratios on the setting time, workability, and mechanical properties of UHPFRC. It was evident that (1) an increase in steel fiber dosage and aspect ratio negatively impacted workability, owing to the interlocking between fibers; (2) compressive strength was positively influenced by the steel fiber dosage and aspect ratio; and (3) a faster loading rate significantly improved the mechanical properties. There were also some shortcomings in the measurement method for setting time. Lastly, this research highlights current issues for future research. The findings of the study are useful for practicing engineers to understand the distinctive characteristics of UHPFRC.

Fibre Distribution Characterization of Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) Plates Using Magnetic Probes

Ultra-high performance fibre reinforced concrete (UHPFRC) is an innovative cement-based engineering material. The mechanical properties of UHPFRC not only depend on the properties of the concrete matrix and fibres, but also depend on the interaction between these two components. The fibre distribution is affected by many factors and previous researchers had developed different approaches to test the fibre distribution. This research adopted the non-destructive C-shape ferromagnetic probe inductive test and investigated the straight steel fibre distribution of the UHPFRC plate. A simplified characterization equation is introduced with an attenuation factor to consider the different plate thicknesses. The effective testing depth of this probe was tested to be 24 mm. By applying this method, fibre volume content and the fibre orientation angle can be calibrated for the entire plate. The fibre volume content generally fulfilled the design requirement. The fibre orientation angle followed a normal distribution, with a mean value of 45.60°. By testing small flexural specimens cut from the plates, it was found out that the mechanical performance (peak flexural strength) correlates with the product of fibre volume content and cosine fibre orientation angle.

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.

Experimental relationships between steel fiber volume fraction and mechanical properties of ultra-high performance fiber-reinforced concrete

Adding steel fibers with a suitable dosage to the mix design of ultra-high performance concrete both impressively forms the concrete ductility, and improves the mechanical strength. In this study, an ultra-high performance fiber reinforced concrete (UHPFRC) mixture was designed with different percentages of steel fiber. Then, the effect of fiber percentage in this mix design was compared to the results of the other researches. Furthermore, Mechanical properties of UHPFRC were assessed, including compressive, splitting tensile, and flexural strength. The relationship of these mechanical properties to each other and also to the fiber percentage content were derived. Moreover, a conversion factor between the compressive strength of cubical to cylindrical samples was derived for different fiber percentages. According to the results, the inclusion of 3% straight steel fibers resulted in a maximum increase of 81%, 228% and 180% for compressive, splitting tensile, and flexural strength, respectively which yielded more significant results than other studies.

Impact Resistance and Mechanical Properties of UHPFRC

Ultra-high-performance fibre-reinforced concrete (UHPFRC) is a comparatively new generation of fibre-reinforced composites that have been developed to give outstanding material performance than other types of concrete. Such superior properties have been achieved through the use of an optimized combination of its ingredients like cement, fine sand, microsilica, high range water reducing agent, low w/c ratio and fibres. A detailed study on the mechanical properties of UHPFRC, considering various important factors, is authoritative in order to obtain necessary information for its practical application. Therefore, present paper reviewed the mechanical properties and impact resistance of UHPFRC. It is examined whether (1) UHPFRC is able to absorb sufficient mechanical energy under impact loading than that of normal strength concrete with and without fibres; (2) the use of hybrid steel fibre (long + short) is effective in improving the impact resistance of UHPFRC compared to containing single type of fibres.

Flexural strengthening of RC beams using UHPFRC laminates: Bonding techniques and rebar addition

Ultra-high performance fiber-reinforced concrete (UHPFRC) is a cementitious composite with outstanding mechanical and durability properties. Accordingly, this study focuses on the behavior of reinforced concrete (RC) beams that were strengthened with UHPFRC laminates. Firstly, a preliminary study was carried out at material scale to evaluate the effect of fiber volume on the mechanical properties of UHPFRC, and to select suitable fiber reinforcement ratio for laminate production. In the second step, real-sized laminates were tested to define the bare properties of full-scaled laminate and observe the size effect according to material tests before applying them as a strengthening material. Thereafter, in the final step, flexurally deficient RC beams were strengthened with 30mm thick UHPFRC laminates using two different bonding methods: gluing with epoxy and mechanical anchoring. In addition, longitudinal reinforcing bars were added into the laminates and their effectiveness was evaluated to improve the success of the applied methods. The results showed that UHPFRC laminate usage, especially in the case of anchorage, is an effective technique to improve the load carrying capacity of RC beams. Moreover, it was observed that adding reinforcing bars into the laminates could improve the efficiency of the applied method remarkably.

Influence of flowability, casting time and formwork geometry on fiber orientation and mechanical properties of UHPFRC

In this study, fiber orientation in ultra-high-performance fiber-reinforced-concrete (UHPFRC) with different formwork geometry was evaluated using visualization model concrete and via analysis involving 3D visualization based on X-ray computed tomography (CT). Differences in fiber orientation in the height direction were first reviewed. Furthermore, the influence of flowability and casting time on the fiber orientation and mechanical properties of UHPFRC were examined. The results indicated that flowability dictates eventual fiber orientation in parts close to the surfaces of formwork. The use of UHPFRC with superior flowability results in more fibers being oriented parallel to the longitudinal direction of slabs in comparison to UHPFRC with inferior flowability. It was also found that flowability and casting time can have strong influences on the mechanical properties of UHPFRC. Residual flexural strength after initial cracking exhibited perfect linear dependence on the effective number of fibers at fracture planes.