# Strengthening Polymer Concrete with Carbon and Basalt Fibres
## 4 Conclusions  
The characteristics of polymer concrete, reinforced with carbon and basalt fibres, are determined by the interaction of the fibre content, fibre length and matrix-fibre interactions. The optimum fibre content (up to 2% for carbon and up to 1% for basalt) ensures a good fibre distribution, effective crack bridging and stress transfer. In case of such percentage contents of fibres, for basalt fibre the maximum bending strength is achieved when the length is 10 mm and compressive strength is reached at 20 mm in length. As for carbon fibre, the maximum compressive and bending strengths are achieved when its length is 10-15 mm. Beyond these optimal values, such negative effects as fibre agglomeration and poor adhesion reduce the benefits, resulting in reduced mechanical properties and fractured structural integrity. Understanding these micromechanisms allows fine-tuning the polymer concrete compositions to achieve the desired balance of strength, durability and reliability.  
When the carbon fibre content exceeds 2% or the basalt fibre content exceeds 1.5%, fibre agglomeration occurs. These agglomerates act as weak points in the material. Instead of a uniform distribution of fibres, the agglomerates create localised microregions of high stiffness and low strength, which leads to stress concentration. An excessive fibre content can prevent the fibres from mixing and bonding properly with the matrix. A poor adhesion results in an ineffective stress transfer, which leads to the formation of microcracks under mechanical loads. Over time, these microcracks widen, which compromises the structural integrity and durability of the material.  
In addition, in the case of the excessive fibre content, the combination of components and adhesion between fibres and the matrix deteriorate. This leads to the appearance of microcracks, which increase in the course of time under mechanical loads. This phenomenon significantly influences the durability and reliability of the material.  
The results of the work also showed that the reinforcement with carbon fibre provided a greater increase in bending strength than the reinforcement with basalt fibre did. In case of compressive strength, an opposite situation was observed. At the same time, the cost of basalt fibre is significantly lower, and if maximum strength characteristics under bending are not required, it is more economically feasible to use reinforcement with basalt fibre.  
Therefore, optimisation of the percentage of the fibre content in composites is a key factor for achieving maximum strength and durability of finished products. This fact, in turn, is directly related to the practical aspects of production and allows, based on the experimental data, the development of new materials with specified characteristics to meet the requirements of various industries. In particular, polymer concrete reinforced with basalt or carbon fibres can be used as a material for a number of industrial parts. Examples of such parts include gearbox housings, pump casings and other parts where the strength requirements are not high.  
Conceptualisation, K.Y. and D.B.; methodology, L.A. and D.B.; validation, V.Y.K. and T.A.O.; formal analysis, V.Y.K. and T.A.O.; investigation, I.A.; data curation, K.Y. and I.A.; writing--original draft preparation, K.Y., N.V.M. and V.Y.S.; writing--review and editing, N.V.M. and V.Y.S.; supervision, K.Y.; project administration, N.V.M. and V.Y.S.; funding acquisition, I.A. and D.B. All authors have read and agreed to the published version of the manuscript.  
The work was supported by the Ministry of Science and Higher Education of the Republic of Kazakhstan within the framework of the AP19177970 project. The theme of the project: \"Improvement of the technology for manufacturing a pump part body from fiberglass\", for which the authors express their deep gratitude to them.  
Not applicable.  
Data Availability Statement: The data presented in this study are available from the corresponding authors upon reasonable request.