## 1 Introduction  
The proposed protective barrier represents a new protective measure to mitigate the consequences of various extreme load events by providing a lightweight flexible structure that can be built on-site very quickly without the need for heavy machinery. Barriers are based on the utilization of highly resistant and tough ultra-high-performance fibre-reinforced cement-based composite (UHPFRCC), which is well pronounced as a material with increased kinetic energy absorption and dissipation capacity and it is, therefore, well suited as a material for protective structures [1]. Increased energy absorption and dissipation capacity benefit mainly from the usage of disperse fibre reinforcement. The key phenomenon is that the fibres are being pulled out of the matrix when a fracture occurs, which is much more energy-consuming than pulling out a single rupture of the fibre [2]. The resulting structure was designed as a flexible precast system that is based on high mobility and versatility, which is achieved by interlocking the basic panel elements. The shape of the basic element-protective panel is 1.5 m in length and 0.4 m in width. The panels are 40 mm-thick and the weight of the UHPFRCC panel is less than 55 kg, assuring easy manual operation. There is no rebar reinforcement in the panel and steel fibres are uniformly distributed over the material body. The fibre volume content was set to 1.5%, which was derived from previous studies [3, 4] as an optimal trade-off between the price, workability, and resulting performance. The lightweight and protective mobile barrier benefits mainly from using an ultra-high-performance fibre-reinforced cementitious composite that is well-pronounced for its increased strength, toughness, ductility, and energy absorption and dissipation capacity [5, 6, 7, 8]. Besides quasi-static loadings, protective barriers were designed and tested against various extreme load events such as projectile impact and blast. By assembly of individual plates together, several possible structures can be built such as a free-standing wall or closed structure with a tetragonal or hexagonal base. By using locks that are provided at the ends of each plate from both sides, there is no need for any additional fastening material as UHPFRCC plates easily fit together. Moreover, there is no need for a foundation as the system itself is self-bearing. The system of the protective barrier might find its application in the industry in the protection of objects, buildings, and strategic infrastructure; special checkpoints or fortified posts, mobile city barriers, and lightweight barricades for crowd control; protection and support of music and sports events, and safety corridors at shooting ranges and training centres. A previous study of the ballistic resistance of the UHPFRCC was performed on rectangular slabs with dimensions of \(300\times 400\) mm and various thicknesses ranging from 40 to 50 mm [9, 10, 11, 12, 13]. Each impact test was conducted using CZ858 semiautomatic rifle, which is the civilian version of a former Czechoslovak SA-58 military assault rifle [10], and two types of ogive-nosed projectiles were used [11], i.e., a deformable projectile with a full-metal jacket and a soft-lead core (SLC) and a nondeformable projectile with a mild-steel core (MSC) and a smaller lead tip. Both types of projectiles had a mass of 8.04 g with an outer diameter of 7.92 mm, and the inner diameter of the core MSC and SLC was 5.68 mm and 6.32 mm, respectively [9, 10, 11, 12]. After the impact, only the core continued penetration [11]. The average muzzle velocity for MSC and SLC was 710 m/s [14]. According to [PERSON] et al. [9], during the experiment, not all slabs were completely perforated since in some of them the projectile was stuck or the slab was punched but the projectile bounced back. In the cases of MSC projectile impact, an intense shattering and fragmentation occurred; whereas in the SLC projectiles cases, less-intense shattering occurred [11].