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This work aims to investigate the effect of a wide range of oblique impacts of the 7.62-mm-caliber projectile on the slim high-performance fiber-reinforced concrete (HPFRC) panels. The trajectory of the projectile, the depth of penetration, and the extent and type of plate damage are discussed in detail. The numerical models developed in commercially available software are also included in this work to support and supplement the experimental data. In the model, each fiber is modeled separately, leading to a more realistic prediction of the material behavior. The analyses identified four basic scenarios for projectile impact: total plate perforation by the projectile core, core penetration combined with or without rear HPFRC material detachment, and ricochet. The results show that the numerical model can effectively and accurately predict the impact response and damage morphologies of the slim HPFRC panel. [ABSTRACT FROM AUTHOR]

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.

This paper presents experimental testing of various types of concrete under impact loading by using a 2.8-second drop shaft. The drop shaft is located in the Josef Underground Laboratory and allows dropping a projectile from 40 meters that results in a maximal velocity of 100 km/h. Three basic types of concrete were used in the framework of this study. This was normal strength concrete, fibre-reinforced concrete, and high-performance fibre-reinforced concrete. The slabs were constructed 1700 mm × 500 mm × 70 mm in size and the clear span of the impacted slab was 1500 mm. Damage of the slab was recorded and the velocity of the projectile was measured with the high-speed camera before and after the impact. It was demonstrated that high-performance fibre-reinforced concrete has a higher ability to absorb and dissipate the kinetic energy of the impact that their lower strength counterparts.

This work aims to demonstrate the effective use of fibre reinforcement in thin plate elements made of UHPFRC under projectile impact loading. The use of fibre reinforcement is very efficient in case of ballistic loading, as fibres are evenly distributed over the entire volume of the material body and possible damage to the plate is thus suppressed in all points of the plate element equally. The aim of this study is therefore to provide data on the residual flexural capacity of plates that have been significantly damaged by the impact of the projectile and to demonstrate the benefits of using fibre reinforcement for localized impact loading.

The aim of the paper is an experimental determination of the longitudinal expansion of autoclaved aerated concrete (AAC) during the freeze-thaw cycle. Longitudinal changes were measured with lasers and the surface temperature was measured using an infrared temperature gauge. The temperature distribution over the sample was verified by a numerical calculation.

This study aims to analyze the performance of laminated glass against ballistic loading and investigates its residual load-bearing capacity. Two groups of specimens were used in quasi-static four-point bending experiments, first without prior ballistic damage and then with it. The main objective was to compare the load-bearing capacity of these two groups to see the effect of ballistic damage. Three different layer compositions were used. The ballistic loading was conducted using an in-service 9 mm bullet fired from a semiautomatic carbine with the glass specimens hanging on steel ropes in a free boundary setup. Numerical simulation and analytical methods were used and validated against the measured response of the undamaged specimens. The simulations were in good agreement with the experimental results. All of the glass specimens were able to withstand the ballistic loading, and the subsequent performance during the quasi-static bending loading was similar to that of the undamaged specimens. The quality of the glass edges seemed to be more important than ballistic damage. The front-plate damage played a negligible role, and the back-plate damage needed to be extensive to influence subsequent performance. Provided that ballistic damage is mainly localized only to the centers of the plates, it did not affect the post-impact loading capacity. [ABSTRACT FROM AUTHOR]

The interaction of ultrahigh-performance concrete (UHPC) and normal-strength concrete (NSC) is one of the main issues for strengthening conventional concrete structures or other applications where NSC and UHPC are interrelated. UHPC stands out for its strength and durability, while NSC is significantly inexpensive and easier to work with. Efficiently designed structures can exploit the advantages of both mixtures. At the interface of these materials in newly designed structures, the formwork can be modified at the interface to give the concrete surface sufficient roughness and thus cohesion as required. This improves both the tensile and shear strength of the contact resulting in the enhanced capacity of the composite structure. In this study, a button foil was inserted into the formwork for the UHPC and then a part of NSC was made. The shear strength of the interface without any stress component in the transverse direction was measured on small-scale samples. It was to justify the possibility of the use of this interface in real constructions such as beams and columns. The main objective of further research is to design a composite beam using a UHPC shell as formwork for NSC and protrusions at the interface. It is expected that the U-shaped shell made of the UHPC could significantly contribute to the load-bearing capacity of the resulting composite NSC–UHPC structure and also to its enhanced durability. In addition, if the NSC is enclosed in a shell of UHPC, it can be made from various secondary materials, therefore it can decrease cement consumption by more than 50%. [ABSTRACT FROM AUTHOR]

In order to achieve better efficiency of dispersed fiber reinforcement in cementitious composites, manufacturers need to be able to directly control the fiber orientation. The magnetic orientation of fibers is an effective way to align fibers in the desired direction of the main tensile stresses and significantly improve the load-bearing capacity of the composite material. In this study, cementitious composites with different percentages of fiber reinforcement were subjected to the magnetic fiber-orienting process and their resulting mechanical parameters were examined. Also, a nondestructive method was used to evaluate the fiber orientation and volume. The flexural strengths and the capacity to dissipate mechanical energy were improved considerably compared to the reference nonoriented specimens. The nondestructive method was also reasonably accurate to predict these results. [ABSTRACT FROM AUTHOR]

This paper aims to determine the resistance of a wide range of building materials against projectile penetration using the depth-of-penetration (DOP) test and several well-established ballistic factors. Within the DOP test, the residual penetration into a backing aluminum alloy cylinder after passing through a sample with a defined thickness and bulk density was measured. The materials investigated here were plasters, mortars, autoclaved aerated concretes (AAC), normal-strength concretes (NSC), ultrahigh-performance concrete (UHPC), full fired-clay brick (FCB), granite, basalt, laminated glass, and ice. The findings show that the ballistic efficiency factors depend substantially on the material used, allowing one to identify materials with different levels of penetration resistance. Inferences drawn from this study can be used by engineers, architects, and contractors to assess the perforation resistance of various building materials to optimize their use against high-speed projectile impact. In addition, it is demonstrated that the uniaxial compressive strength of the building material might be misleading as the identifier of a material resistance against projectile impact because a significant difference in penetration resistance between materials with comparable compressive strength was found. [ABSTRACT FROM AUTHOR]

The article presents a mobile anti-vehicle barrier created from a high-performance fibre-reinforced concrete, which resembles a historical design of the Czech Hedgehog barrier. The performance of this design when subjected to a moderate velocity vehicle impact was evaluated. A preliminary crash test provided basic data to perform an optimisation of the design using numerical simulations conducted in LS-DYNA. Several key observations were made regarding the crucial role of the barrier-surface interactions and overall barrier behaviour. Based on the simulations, improved geometry of the barrier was proposed and subjected to more full-scale crash tests with various barrier placements. The improved barrier design was able to stop an ordinary road vehicle weighing 1300 kg moving with a velocity of 48 km/h while retaining beneficial characteristics, most importantly low weight. [ABSTRACT FROM AUTHOR]

Featured Application: The ballistic modular system was developed to serve as a mobile protective barrier against projectile impact and also to mitigate the effect of secondary fragments and explosions. The advantage of the system lies in its very fast assembly at the point of intervention, where no heavy machinery is needed. The whole system can be assembled just by manual manipulation into various shapes. The system is based on reasonable mobility and versatility of the whole solution, which is achieved by combining basic elements according to the needs of the situation. The static response of ballistic panels and also its resistance to blast and ballistic impact is investigated in the framework of this study. By connecting individual ballistic panels together, the protective barrier can be constructed. The protective barrier can be featured as a system with high mobility and versatility that is achieved by linking basic interlocking plate elements together. The resulting protective barrier can be shaped according to many possible scenarios in a wall with various possible opening angles and a small post with the tetragonal base or a larger post with the hexagonal ground plan. The material solution of the protective barrier benefits from the application of ultra-high-performance fibre-reinforced cement-based composites (UHPFRCC), which meets the requirements for enhanced resistance against extreme loads such as blast or impact. Besides, by using UHPFRCC, thin and slender design can be adopted, which is advantageous in many ways. Slender design results in a lower weight, allowing for easy manipulation and replacement. To verify the behavior of the panels, the proposed barrier was subjected to various loadings at different strain rates. The experimental campaign demonstrated that the protective barrier has a reasonable load-bearing capacity and also sufficient resistance against projectile impact and blast effects. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]