# Strengthening Polymer Concrete with Carbon and Basalt Fibres
## 3 Results and Discussion
### Analysis of the Fracture Surface of the Tested Samples
A similar picture is that of the fibre clusters. Figure 14: Compressive strength for the samples of polymer concrete reinforced with carbon fibres of different lengths. Figure 13: Bending strength for the samples of polymer concrete reinforced with carbon fibres of different lengths. is observed when reinforcing with basalt fibres. But when reinforcing with basalt fibres, the maximum bending strength is achieved at a fibre length of 10 mm, and the maximum compressive strength at a fibre length of 20 mm. The difference in the optimum fibre length in terms of improving properties for basalt and carbon fibres can be explained by the different properties of these fibres. Also, basalt fibres and carbon fibres have different diameters. Basalt fibres have a larger diameter and this also influences the results obtained. Further research in this area will improve the strength properties of the composite material and optimise its structure for better use in relevant industries. The following conclusions can be drawn as a result of the conducted experiments:  
1. Bending test strength for reinforced polymer concrete samples:  
For the elements with the percentage of the carbon fibre reinforcement of 2.0%, the increase in bending strength compared to that of unreinforced samples is 73.6% (the length of fibres is 10 mm). For the elements with the basalt fibre reinforcement percentage of 1.5%, the increase in bending strength compared to that of unreinforced samples is 35.6% (the length of fibres is 20 mm). 2. Tensile strength during the compression test for reinforced polymer concrete samples:  
For the elements with the percentage of the carbon fibre reinforcement of 1.0%, the increase in bending strength compared to that of unreinforced samples is 10.1%. For the elements with the basalt fibre reinforcement percentage of 1.5%, the increase in bending strength compared to that of unreinforced samples is 15.4%. In general, the mechanical properties of flexural elements with the fibre reinforcement are superior to those of similar elements without the reinforcement [30]. This is due to the higher anchorage value of the reinforcement in fibre-reinforced concrete structures, which ensures a reliable coordination between the reinforcement and polymer concrete, preventing the abrupt development of plastic deformations in the reinforcement. The fibre reinforcement also helps to increase the duration of joint operation between the reinforcement and polymer concrete in the tensile zone, which allows a more efficient redistribution of stresses over the reinforcement bar even when cracks are formed. Studies show that fibres continue to work and retain cracks at the moment of polymer concrete delamination, which significantly increases the overall mechanical performance of the structure, guaranteeing its durability and resistance to loads [29; 30]. The use of the fibre reinforcement throughout the entire section height contributes to the improvement of stiffness of bending elements, which is associated with a uniform distribution of stresses throughout the entire section height and a reduction in the probability of sudden failure [31; 32; 33]. The fibre reinforcement makes it possible to create more reliable and durable structures and engineering products capable of withstanding high loads in harsh operating conditions. The load-bearing capacity of reinforced polymer concrete flexural elements is superior to that of the elements made of conventional concrete and polymer concrete. This can be explained by a number of key factors:  
1. Resistance to deformation in the tensile zone. Polymer concrete in the tensile zone contributes to the strengthening of normal sections, so that even in the event of initial fractures in the material, its ability to absorb stresses is maintained. 2. High adhesion between the reinforcement and structural material. Improved adhesion between reinforcement bars and polymer concrete slows down the development of plastic deformations in the reinforcement, which increases the stability of flexural elements. 3.