# A Method for the Design of Concrete with Combined Steel and Basalt Fiber
## 1 Introduction  
Steel fiber reinforced high-strength concrete (SFRHSC) became a widely used material for structural engineering applications. Many studies were carried out to investigate its properties. New design methods were proposed for providing its ductile behavior and limit its crack development [1]. The studies in fiber reinforced concrete are mainly focused on investigating its mechanical properties such as compressive strength, split tensile strength, toughness, modulus of rupture, post-cracking performance, modulus of elasticity, Poisson's ratio and strain at peak compressive stress [2; 3; 4]. Experimental results from these studies show that fiber reinforced concrete has better post-cracking behavior and more ductility for different fiber types. [PERSON] and [PERSON] investigated the influence of steel fiber's tensile strength on the mechanical properties of fiber reinforced concrete [5]. Fiber with tensile strengths of 1100 and 2000 MPa was used. Steel fiber contents of 0.33%, 0.67% and 1% were used. The concrete mix water/cement ratios were 0.35, 0.45 and 0.55. The results showed the significant effect of the matrix and fiber strength on the fracture energy and characteristic length. Hence the authors recommended taking these parameters into account as criteria in addition to other parameters such as volume fraction and aspect ratio. [PERSON] [6] studied the influence of steel, basalt and other types of fiber on the modulus of elasticity of concrete and cement composites. The results showed that fiber has negligible influence on the modulus of elasticity if the coarse-to-fine aggregate ratio is higher than 1; otherwise discrete fiber reduces the modulus of elasticity. A new equation was proposed for estimating fiber reinforced concrete's modulus of elasticity. The equation is valid for a maximum fiber content of 10% by volume. It was demonstrated that the equationallows accurate prediction of fiber reinforced concrete and cement composites modulus of elasticity values. Due to its considerable advantages, SFRHSC has different application prospects. For instance, replacing normal-strength concrete with SFRHSC results in effective and cheaper solutions suitable for new structures and retrofitting existing ones [7,8]. For instance, two-layer beams, consisting of SFRHSC in the compression zone and normal strength concrete in the tension zone, are effective bending elements [7,8]. Using such beams is logical because as their span becomes longer and the service load increases, a higher concrete strength is required in the compression zone to withstand rather large bending moments. Steel fibers are prone to corrosion and their higher density can be a limitation on their use. Fibers such as basalt fiber (BF) can be a better alternative in such cases. Basalt fiber (BF) production could be arranged at low costs for any business needs [9]. Following the obtained data, even low contents of BF yield an increase in flexural strength of the tested specimens. It was also reported that using BF reinforced concrete is less costly compared to steel, s-glass or carbon fibers. [PERSON] et al. investigated the influences of adding 1, 2 and 3% of BF in high-performance concrete (HPC) [10]. One mix was prepared by using 100% cement, and the other two mixes by replacing 10% cement content with silica fume and metkaolin. It was concluded that adding 2% of BF by volume together with mineral admixtures improved the concrete compressive strength. Additionally, improved strains at maximum compressive strength and splitting tensile strength were observed. [PERSON] et al. investigated compressive stress-strain behavior of fiber reinforced HSC with compressive strengths of 70-85 MPa, and BF content of 1-3% [11]. Based on the experimental data, an analytical model of such concrete stress-strain behavior was proposed. The model has demonstrated good agreement with the experimental data. Comparative effect of basalt and steel fiber on compressive, flexural and splitting tensile strength of concrete class C30/37 was studied [12].