This paper deals with the description, measurement, and use of electromagnetic properties of ferromagnetic fibres used as dispersed fibre reinforcement in composite mixtures. Firstly, the fibres’ magnetic properties are shown, and a method of measuring the hysteresis loop of fibres is proposed. The results from the measurements are presented and a discussion of the influence of measured parameters on the fibres’ orientation in a magnetic field is performed. Furthermore, methods of non-destructive estimation, of their amount and orientation in the composite specimens, are discussed. The main experimental goal of this paper is to show the relationship between this non-destructive method’s results and the destructive flexural strength measurements. The method is sensitive enough to provide information related to fibre reinforcement.

Ultra-high-performance steel-fibre-reinforced concrete (UHP-SFRC) is a technologically advanced composite with a high ability to absorb and dissipate mechanical energy. This work investigates the possibility of increasing ballistic resistance by adding different percentages of corundum and basalt aggregate into this type of concrete. The most common type of ammunition, a 7.62 mm × 39 mm calibre with a full-metal jacket and a mild-steel core (FMJ-MSC), was used to test all samples. The size of the damage and the mode of failure were determined using a 3D scanner operating on the principle of photogrammetry. The experimental campaign showed that the addition of basalt and, especially, corundum aggregate has a positive effect on ballistic resistance. In particular, the increase in compressive strength and the slight decrease in depth of penetration (DOP) was observed in the case of the usage of the corundum aggregate.

The efficiency of fibre reinforcement in concrete can be drastically increased by orienting the fibres using a magnetic field. This orientation occurs immediately after pouring fresh concrete when the fibres can still move. The technique is most relevant for manufacturing prefabricated elements such as beams or columns. However, the parameters of such a field are not immediately apparent, as they depend on the specific fibre reaction to the magnetic field. In this study, a numerical model was created in ANSYS Maxwell to examine the mechanical torque acting on fibres placed in a magnetic field with varying parameters. The model consists of a single fibre placed between two Helmholtz coils. The simulations were verified with an experimental setup as well as theoretical relationships. Ten different fibre types, both straight and hook-ended, were examined. The developed model can be successfully used to study the behaviour of fibres in a magnetic field. The fibre size plays the most important role together with the magnetic saturation of the fibre material. Multiple fibres show significant interactions.

This paper focuses on high-performance fibre-reinforced concrete and its flexural strength concerning fibre orientation. The orientation is provided by a fully controlled special device. This device can align the fibres in fresh concrete using a magnetic field. The specimens are inserted into the device at different angles to ensure different fibre orientations concerning the longer side of the sample, which corresponds to the direction of the main tensile stresses. Specifically, angles of 0 °, 30 #x00B0;, 60 ° and 90 ° are tested and compared with each other and with reference specimens that are not exposed to a magnetic field. All samples are measured by a non-destructive method. This method was developed in our previous research and is based on measuring the quality factor Q of a measuring coil using an impedance meter. The samples are inserted into a measuring coil connected to an impedance meter. Flexural strength is obtained from the results of a three-point bending test. All samples are tested until complete failure.

The mechanical performance of fiber-reinforced concrete is critically dependent on the orientation and concentration of its reinforcing fibers. This paper presents a non-destructive method for diagnosing ferromagnetic (steel) fiber parameters especially suited for large planar specimens. The proposed technique utilizes an electromagnetic measurement system using electrical coils with commercial LCR meters, but also a novel custom-made meter suitable for factory environments, offering a practical solution for quality control in the prefabrication of high-performance structural elements. This study details the theoretical background, experimental setup, methodology and provides an evaluation of the diagnostic system’s effectiveness and accuracy. The experiments were performed using steel fiber specimens with cardboard as a carrier. This allows for the exact placement and orientation of the fibers in a matrix that has negligible influence on the magnetic field, similar to plain concrete. The results demonstrate a strong correlation between the electromagnetic measurements and the actual fiber parameters, confirming the method’s reliability.