## 1 Introduction  
The growing global population, which was 5 billion in 1987, reached 8 billion in 2024, with a projected 9.7 billion by 2050, is driving an increasing demand for cement, which is essential in the construction process. This contributes to an increase in energy consumption related to cement production. It is estimated that 1 Mg of cement generates as much as 0.73 to 0.99 Mg of CO\({}_{2}\)[1]. Due to increasingly stringent production standards associated with material reuse, reduction of carbon footprints, and limiting temperature growth, optimizing the use of concrete in construction is essential. This can be achieved by reducing the content of clinker in cement, replacing part of the cement with supplementary cementitious materials (SCM), using recycled aggregate, or making effective use of cross-section capacity [2, 3, 4]. These sustainability-driven approaches align with broader trends in material engineering that aim to incorporate renewable and low-impact raw materials into construction products. Similar concepts have been explored, for example, in the development of epoxy-based modifiers for bitumen derived from plant-based feedstocks [5]. To achieve this, concrete mixes must be designed to achieve high-strength parameters while optimizing the use of cement and SCM. Concrete can be reinforced with recycled fibers,such as steel wires obtained by pyrolysis of used tires [6; 7], natural fibers such as coconut fibers [8], or fibers extracted from palm trees [9; 10]. High-rise buildings, long-span bridges, impact-resistant shelters, structures located in seismic zones, and reinforcements for damaged or poorly executed structures are examples of applications requiring high-quality cementitious composites [11; 12; 13; 14; 15; 16; 17; 18]. Normal-strength concrete (up to 55 MPa compressive strength) has significant limitations for such structures. The concept of ultra-high performance concrete (UHPC) was first proposed by [PERSON] and [PERSON] [19], who achieved a 28-day compressive strength of 165 MPa and a splitting tensile strength of 6.6 MPa for fiber-free concrete with a water-to-binder ratio (W/B) of 0.14. It is generally accepted that the compressive strength of this type of concrete should exceed 120 MPa [20]. A key advantage of UHPC with added fibers is its high tensile strength and high energy absorption capacity [21]. Due to its excellent mechanical properties, ultra-high-performance concrete is one of the most promising construction materials dedicated to civil and military infrastructure systems, including long-span bridges, defensive structures, and high-rise buildings [22]. UHPC is characterized by a low water-to-binder ratio, resulting in low permeability and high resistance to chloride and sulfate penetration, significantly reducing the corrosion of reinforcement bars or steel (ST) fibers [23; 24; 25; 26; 27; 28]. UHPC exhibits excellent resistance to carbonation due to its high strength parameters, which delay crack formation and control crack width in the development phase, making it difficult for water to penetrate [29]. Furthermore, it has a high particle packing density, low porosity, and excellent impermeability, resulting in high durability and extended service life of structures [30]. Initially, ultra-high performance concrete without fibers were used, in which the improvement of parameters was achieved by designing mixtures with high-quality cement and aggregates, along with an appropriately low W/B ratio, which for UHPC typically ranges between 0.14 and 0.20 compared to 0.4-0.5 for conventional concrete [31; 32; 33; 34; 35; 36; 37]. However, such UHPCs exhibited a high degree of brittleness [38; 39], leading to the initial use of a single type of steel fiber, allowing for an improvement in properties sufficient to meet material requirements. The addition of a single type of fiber improved the static properties of UHPC, particularly the compressive and tensile strength.