# Strengthening Polymer Concrete with Carbon and Basalt Fibres
## 2 Methods and Materials
### Sample Preparation for Tests  
As a result of testing the samples at the previous stage, a rational composition of polymer concrete was selected [5; 23]. This experimental composition was selected taking into account the previous experimental works carried out by the authors. Polymer concretes can be used not only in industry, but also as a possible replacement of some hull parts. In [5; 23; 24], the authors showed that certain compositions of polymer concretes can meet the requirements for the manufacture of housing parts of gearboxes. With minimum consumption of components, samples of polymer concrete of the exhausted composition have high compressive and bending strengths, which guarantees a long-term operation of housing parts under severe working conditions. We used rubble with the size of fractions of 2-3 mm as an aggregate for the polymer concrete mixture. Quartz sand with a fraction size of 0.5-1 mm and mineral flour with a fraction size of 0.05-0.01 mm were used as fillers. For the separation of rubble into fractions, a sieve with a mesh size not exceeding 1.8 mm was used, which allowed sifting out of the largest fraction with a size ranging from 2 mm and separating smaller particles and powdery components. Then, for the selection of fractions of the required size (2-3 mm), a sieve was used. The use of silica sand as a filler also helped to improve the mechanical properties of the material due to its high hardness and stable structure. Mineral flour, due to its fine fraction, contributes to the denser filling of voids in the matrix, which reduces the number of pores and improves the overall quality of the obtained material. The crushed rubble, used to make the samples, was dried. In this case, drying was carried out in the drying SHS-200 SPU (Smolenskoye Sktb, Smolensk, Russia) unit at a temperature of 80 \({}^{\circ}\)C for 120 min. A similar temperature regime was used for drying quartz sand and mineral flour. These measures are necessary to reduce the moisturecontent of the components, thus avoiding undesirable reactions during the mixing and polymerisation process. The composition of the polymer concrete mixture included the following proportions: 50% of rubble of a 2-3 mm fraction, 25% of quartz sand of a 0.5-1 mm fraction and 15% of mineral flour of a 0.05-0.01 mm fraction from the total mass of the sample. To improve the mechanical properties of the mixture, the reinforcing filler (carbon fibre or basalt fibre) was added in an appropriate amount. The dry components were mixed for 3 min. Polyester, which is the main component of polymer concrete, consists of alcohols, acids and anhydrides. In our case, ethylene glycol is used as alcohol; fumaric acid acts as acid, and phthal anhydride is used as anhydride. To achieve the required strength of polymer concrete products, the epoxy resin was heated to a temperature of 60 \({}^{\circ}\)C.  
The analysis of the obtained results [5] showed that achieving a necessary strength requires the rational drying temperature in the range of 120-130 \({}^{\circ}\)C. This temperature range provides consistently high strength of polymer concrete products. A polyester resin hardener was added to the polyester resin heated to a temperature of 120 \({}^{\circ}\)C to act as a catalyst for the chemical curing reaction of the polymer concrete mixture. Its addition and subsequent stirring for 2 min provided a uniform distribution of the catalyst throughout the volume of the resin, which is a critical step for subsequent uniform curing. The polyester resin with the uniformly distributed hardener was then added to the vessel with the pre-prepared dry mix. The obtained mixture was stirred for 6 min to achieve a homogeneous mass. After the thorough mixing, the polymer concrete mixture was evenly distributed into matrices, each of which had 3 cells. A vibration table was used for a denser distribution of the mixture in the matrix cells.