Investigation of the Physical and Mechanical Properties of Optimized Polymer-Concrete Compositions Based on Basalt and Silicon Carbide for the Bedways of Precision Machine Tools

Abstract

This article focuses on the research and development of innovative polymer-concrete composites for the manufacture of precision machine tool frames and critical mechanical engineering components. The relevance of this work stems from the need to replace traditional cast iron and cement concrete with materials with superior damping properties and thermal stability. The polymer matrix used in this study was ED-20 epoxy-diane resin, modified with (FAM) furan resin and cured with polyethylenepolyamine (PEPA), which together ensured minimal linear shrinkage (less than 0.5–1%) during polymerization. The focus was on the effect of multimodal filler distribution, including quartz sand, gabbro, and basalt, as well as reinforcing additives such as silicon carbide and fiberglass, on the final performance characteristics of the material. Experimental studies determined the key physical and mechanical parameters of the obtained samples. The results showed that the optimized composition (Smp_001) exhibited compressive strength up to 92.3 MPa, significantly exceeding that of standard high-strength concrete. It was established that the use of silicon carbide and glass fiber promotes the formation of a dense heterogeneous microstructure characterized by extremely low porosity (1.2–2.5%) and record-low water absorption (less than 0.05%). These characteristics guarantee high dimensional stability of the frames during prolonged contact with process fluids and cutting fluids. The scanning electron microscopy (SEM) and (EDS) energy dispersive X-ray spectroscopy methods confirmed the dense packing and high degree of interaction of the polymer matrix with the crystalline phases of the filler. This condition of the interfacial boundaries guarantees stable stress transfer throughout the entire volume of the material, which minimizes the risk of local damage during operation. The study confirmed that the developed material has vibration damping properties 6–10 times more effective than gray cast iron, a critical factor in improving machining accuracy on modern metal-cutting machines. The scientific novelty of the study lies in its substantiation of the synergistic effect of the combined use of basalt fillers and silicon carbide to achieve the precision properties of a structural material. Its practical significance is confirmed by the possibility of producing large-scale parts by casting without the need for complex finishing, opening up new prospects for modernizing the machine tool industry.

1. Introduction

Modern machine tool industry places extremely stringent requirements on the stability of load-bearing systems, where the positioning accuracy of the actuators must be maintained within the micron range [1]. Despite their widespread use, traditional gray cast iron frames and welded steel structures are increasingly unable to cope with the tasks of high-speed and ultra-precision machining. The main critical drawback of these materials is their high thermal conductivity [2,3], which causes significant thermal deformations: up to 70% of the total positioning error on computer numerical control (CNC) machines is due to localized heating of spindle assemblies and guides [4,5]. In addition, the low damping capacity of metals leads to the occurrence of resonant vibrations under intensive cutting conditions [6,7]. These vibrations cause serious errors in the processing of parts, expressed in increased surface roughness and reduced dimensional accuracy, which ultimately limits the capabilities of the equipment for nano-level machining and accelerates the wear of the cutting tool [8,9,10]. Particular attention should be paid to the mechanics of the occurrence of temperature errors, which are nonlinear in nature and difficult to compensate for by software [11,12,13]. During machine operation, heat flows from motors, bearings, and the cutting zone are distributed unevenly across the bed, causing a temperature gradient and subsequent warping of the basic structural elements [14,15,16]. Such thermal expansion leads to axial displacement of the spindle and skewing of the guides, which critically distorts the geometry of the part, especially during long processing cycles [17,18]. In parallel with this, the lack of internal friction in the crystal lattice of cast iron and steel does not allow for the effective absorption of dynamic loads [19]. As a result, forced vibrations arising from contact between the tool and the workpiece propagate unhindered throughout the bed, forming microdeviations in the trajectory of the working elements and making it impossible to achieve stable surface quality under high-performance production conditions [20,21,22].

Traditionally, gray cast iron (GCI) and welded steel have been the dominant materials for machine tool beds due to their established manufacturing processes and structural rigidity [23]. However, over the past decade, the limitations of GCI—such as high thermal expansion, susceptibility to corrosion, and relatively low vibration damping—have driven a significant shift toward alternative materials for machine tool statics [24].

Recent advances in materials science have prioritized the development of mineral castings, polymer concretes (PC), and hybrid composite structures. Mineral castings, often referred to as “synthetic granite”, have transitioned from niche applications to mainstream use in precision grinding and high-speed milling centers [25]. Research indicates that modern polymer concretes, characterized by an epoxy or vinylester resin matrix combined with high-density mineral aggregates, offer vibration damping ratios 6 to 10 times higher than those of traditional cast iron [26]. This characteristic is vital for achieving superior surface finishes and extending tool life by mitigating the regenerative chatter common in high-speed machining.

The selection of fillers has evolved beyond traditional granite or quartz to include diverse reinforcements that address specific mechanical and thermal requirements [27].

Carbon-based fillers (carbon fiber/graphene) are utilized to enhance the elastic modulus and thermal conductivity of the composite. Beyond silicon carbide (SiC), researchers have investigated the use of fly ash, blast furnace slag, and alumina to improve compressive strength while reducing the environmental footprint and cost of the PC [28].

While basalt remains a focus due to its high chemical resistance and mechanical strength, comparative trials with diabase and gabbro-diabase have shown that the grain morphology and surface energy of the filler significantly influence the interfacial bonding with the polymer matrix [29].

Critical to the performance of these materials is the investigation into vibration damping mechanisms. In composite structures, damping is primarily achieved through three channels: interfacial friction between the filler particles and the polymer matrix, the viscoelastic behavior of the resin itself, and the dissipation of energy through micro-cracks or engineered hollow inclusions (such as glass microspheres) [30]. Recent studies emphasize that the interphase—the thin layer where the resin interacts with the filler—is the most influential factor. Optimizing the packing density through multimodal particle distribution (e.g., combining millimeter-scale basalt with micrometer-scale SiC) maximizes these energy-dissipation interfaces, leading to unprecedented structural stability [31].

The polymer-concrete composite based on an epoxy binder developed in this study, reinforced with a combination of basalt aggregate and microdispersed silicon carbide (SiC), represents a conceptually new solution to the problem of dynamic stability. The basalt filler forms a rigid mineral skeleton with a low coefficient of thermal expansion, which ensures the geometric immutability of the machine frame [32]. The key innovative component is silicon carbide, which, having a unique thermal conductivity for non-metals, acts as a thermal bridge. This makes it possible to quickly distribute heat flows throughout the entire volume of the bed, eliminating local temperature gradients and the associated misalignments of the guides [33].

It is important to acknowledge that multimodal filler systems for polymer concrete have been previously described in the literature. In particular, Haddad and Al Kobaisi [10] investigated six different aggregates (basalt, spodumene, fly ash, river gravel, sand and chalk) and optimized the composition of polymer concrete for precision machine bases. Their final optimized composition contained basalt, sand, and fly ash with 87% filler and 13% resin. Other studies have explored the addition of silicon carbide to cementitious concrete or the use of glass fiber reinforcement in polymer concrete for various applications.

In addition, the synergistic effect of a viscous polymer matrix and super-hard SiC inclusions provides a damping ability exceeding that of cast iron by 8–10 times. This makes it possible to effectively dampen high-frequency vibrations directly at the site of their occurrence, which is critically important for achieving nano-level surface roughness and extending the life of the cutting tool. Below is a comparative analysis of the operational characteristics, justifying the choice of the developed composition for high-precision equipment [34].

Comparative characteristics of materials used for the frames of metal-cutting machines are given in

Table 1. Comparative characteristics of materials for the frames of metal-cutting machines.

Characteristic	Gray Cast Iron (SCH20)	Standard Concrete	Developed Composition (Basalt + SiC)
Density, kg/m3	7150	2400	2450
Compressive strength, MPa	200–300	30–50	92.3
Modulus of elasticity, GPa	100–120	25–35	38.5
Logarithmic decay decrement	0.012	0.035	0.115
Coefficient of thermal conductivity, W/(m·K)	50	1.1	4.8
Thermal expansion, 10−6/K	11.5	10.5	7.2

.

Furthermore, hybrid structures—combining the high stiffness of steel or aluminum with the superior damping of polymer concrete—have emerged as a leading trend. By utilizing PC as a core filling for hollow metal frames, manufacturers can achieve a synergistic effect that maintains the high natural frequencies of metals while providing the rapid decay of oscillations typical of mineral composites. These developments set the stage for the current investigation into optimized basalt and silicon carbide compositions, aiming to push the boundaries of precision and thermal neutrality in modern machine tool design.

2. Materials and Methods

2.1. Design Philosophy and Formulation Strategy

The experimental program was structured to develop a high-damping, thermally stable composite suitable for the structural frames of precision CNC machinery. Unlike conventional polymer concrete used in mechanical engineering, the formulation in this study was engineered based on the principle of maximum packing density and high-energy vibration compaction. The selection of materials was dictated by the requirement to minimize internal thermal stresses and maximize the logarithmic decrement of damping. The development of the ‘Smp_001’ series involved a multi-stage optimization process. The primary goal was to create a “mineral skeleton” from high-hardness basalt aggregates, which is then reinforced at the micro-level by silicon carbide (SiC) particles. This dual-filler approach is intended to enhance the composite’s elastic modulus while simultaneously providing a network for efficient heat dissipation—a critical factor for maintaining machine tool geometry. Figure 1 shows an algorithm for conducting an experiment to obtain a sample of Smp_001; experimental studies of the composition of Smp_002 were conducted in a similar way.

For the polymer matrix, an ED-20 epoxy-diane resin was selected due to its excellent adhesion to mineral surfaces and low shrinkage characteristics. To ensure optimal flowability during the casting of complex machine bed shapes, the resin was modified with a FAM-type reactive diluent. The curing process was initiated using a polyethylenepolyamine (PEPA) hardener, maintained at a strictly controlled resin-to-hardener ratio to ensure a polymerization degree exceeding 98%, of the same fraction presented in Figure 2 and Figure 3 [19].

This study utilized ED-20 epoxy-diane resin. It exhibits adhesive properties to mineral fillers (basalt, spodumene) and reinforcing components such as silicon carbide and fiberglass. During curing, ED-20 exhibits minimal linear shrinkage (less than 0.5–1%), which is important for maintaining the precision geometry of large machine components and eliminating internal stresses that can lead to cracking. The technical properties of ED-20 resin are presented in Table 1.

2.1.1. Resin

As can be seen from

Table 2. Technical characteristics of ED-20.

Parameter	Value
Density (at 20 °C), kg/m3	1160–1250
Viscosity (dynamic at 25 °C), Pa·s	12–18
Compressive strength, MPa	80–120
Bending strength, MPa	85–140
Tensile modulus of elasticity, GPa	2.7–3.5
Shore D hardness	80–85

, the composition of Smp_001 is an optimized hybrid system reinforced with silicon carbide and fiberglass to achieve maximum damping properties. The composition of Smp_002 is preferred and is characterized by the absence of strengthening micro-additives with a slight increase in the proportion of the polymer matrix to ensure comparable fluidity of the mixture. The comparative formulation of the polymer- concrete samples Smp_001 and Smp_002 is shown in

Table 3. Comparative formulation of the polymer-concrete samples Smp_001 and Smp_002.

Component	Smp_001 (% Mass.)	Smp_002 (% Mass.)	Role of the Component
Epoxy resin ED-20	8.9%	9.4%	The main binder
FAM resin (modifier)	8.9%	9.4%	Reactive diluent
PEPA hardener	3.5%	3.8%	Polymerization agent
Quartz gabbro sand (0.14–1.25 mm)	44.8%	47.6%	Primary filler
Fine filler (0.14 mm)	10.2%	29.9%	Compaction of the structure
Silicon carbide (SiC) (0.1–0.4 mm)	3.6%	–	Thermal stabilization and hardness
Fiberglass (3–12 mm)	2.1%	–	Dispersed reinforcement
Basalt crushed stone (Basalt) (5–20 mm)	18%		The main filler for the supporting frame

.

2.1.2. Selection and Characteristics of the Hardening Agent

To ensure effective polymerization of the epoxy matrix and the formation of a rigid spatial structure of the composite, polyethylene polyamine (PEPA) was used in the work. The choice of this cold curing agent is due to a number of technological advantages that are critically important for creating precision equipment mills.

PEPA is a mixture of aliphatic amines that reacts actively with epoxy groups of ED-20 resin at room temperature. For the purposes of this study, the key advantage of PEP is its ability to provide minimal linear shrinkage (within 0.5–1%), which guarantees high dimensional accuracy of the cast machine components and the absence of internal microcracks [20]. Technical characteristics of polyethylene polyamine are given in

Table 4. Technical characteristics of polyethylenepolyamine (PEPA).

Parameter	Value
Density (at 20 °C), g/cm3	1.00–1.05
Viscosity (dynamic at 25 °C), Pa·s	0.8–1.2
Flash point (in open crucible), °C	110–120
Autoignition temperature, °C	350–370

.

2.1.3. Role and Rationale for the Use of Polymerization Accelerators

To optimize the curing process of the epoxy-amine system and achieve the specified performance characteristics, a polymerization accelerator was introduced into the composite. Its use in this study is due to the need for precision control of the kinetics of chemical reactions, which directly affects the microstructural integrity of the bed. The accelerator reduces the activation energy of the reaction between the epoxy groups and the PEP hardener. Due to the reduction in gelation time (the transition of the mixture from a liquid to a jelly-like state), heavy mineral particles (basalt, silicon carbide) do not have time to settle under the influence of gravity. This helps to maintain the uniformity of the composition over the entire height of the casting. The use of an accelerator makes it possible to standardize the extraction time of finished products from molds, which increases the reproducibility of the experimental results and the technological efficiency of the prototype manufacturing process. The accelerator’s technical characteristics are listed in

Table 5. Technical characteristics of the UP-606/2 accelerator.

Parameter	Value
Density (at 20 °C), g/cm3	0.97–0.99
Viscosity (dynamic at 25 °C), Pa·s	0.15–0.25
Flash point (in open crucible), °C	140–150
Autoignition temperature, °C	335

.

2.2. Methodology for Composite Mixture Preparation

The process of manufacturing polymer concrete requires compliance with time regulations at the preparation stage of the mixture. The mixing time of the components is one of the key factors determining the future physico-mechanical properties of the finished product. Insufficient duration of the process leads to the formation of zones with a non-uniform distribution of filler, and excessive duration can provoke premature polymerization or the involvement of excessive amounts of air. To ensure high reproducibility of the results and achieve the optimal physico-mechanical characteristics of polymer concrete, the sample manufacturing process is strictly regulated by time and temperature parameters. The technology provides for mandatory five-minute mixing of each portion of the mixture, which guarantees complete homogeneity and high-quality coating of filler particles (basalt and silicon carbide) with a polymer matrix. The composition of the composite includes 83% mineral fillers and 17% binder based on epoxy resin ED-20. A special feature of the protocol is the use of the UP-606/2 accelerator in an amount of 1% by weight of the resin (0.17% of the total mass of the mixture), which makes it possible to accurately control the kinetics of chemical reactions and standardize the time for removing products from molds. Rapid gelation initiated by the accelerator effectively prevents sedimentation of heavy mineral fractions, ensuring isotropic properties of the material throughout the volume.

The forming of the samples is accompanied by high-energy vibration sealing (50 Hz with an oscillation amplitude of 0.5 mm), which minimizes the number of explosive inclusions and allows achieving a low porosity in the range of 1.2–2.5%. After extraction from the molds, the samples are kept in controlled laboratory conditions until a predetermined test age is reached, necessary for the uniform development of the polymer structure grids (28 days).

For compressive strength, ultrasonic pulse velocity, and hardness testing, cubic specimens measuring 10 × 20 × 56 mm and 30 × 105 × 65 mm were used. After casting, all specimens were removed from the molds after initial setting and cured under controlled laboratory conditions at room temperature until the specified test age, ensuring uniform development of the polymer matrix (

Table 6. Ratio of mixture components.

Component	Share in the Total Mass of the Mixture (%)	Role and Note
Fillers (basalt, SiC, ash, etc.)	83.00%	Solid phase (beam frame)
Epoxy resin ED-20	15.30%	The main binder
PEPA hardener	1.53%	10% of the resin weight
Accelerator UP-606/2	0.17%	1% of the resin mass

and

Table 7. Types and sizes of samples.

Sample Type	Dimensions (mm)	Purpose of the Test	Standard
Cube (Smp_002)	30 (H) × 105 (L) × 65 (W)	Compressive strength, ultrasonic pulse propagation and hardness	GOST 10180-2012 “Concrete. Determination Methods” [35], GOST 22690-2015 [36], GOST 17624-2021 [37]
Cube (Smp_001)	10 (BH) × 56 (L) × 20 (W)

).

A summary of all tests performed, including specimen dimensions, applicable standards, and the number of replicates, is presented in

Table 8. Summary of test methods, specimen dimensions, standards, and number of replicates.

Test/Property	Specimen Dimensions (mm)	Standard	Number of Specimens per Composition	Total Number of Specimens
Compressive strength	30 × 105 × 65	GOST 10180-2012 [35]	6	12
Elastic modulus	30 × 105 × 65	GOST 10180-2012 [35]	6	12
Poisson’s ratio	30 × 105 × 65	GOST 10180-2012 [35]	6	12
Shore D hardness	10 × 20 × 56 (cube)	GOST 22690-2015 [36]	5 measurements on each of 6 specimens	30 per composition
Ultrasonic pulse velocity (UPV)	30 × 105 × 65	GOST 17624-2021 [37]	6	12
Water absorption	30 × 105 × 65	GOST 10180-2012 [35]	3	6
Estimated from SEM images	30 × 105 × 65	Mercury intrusion porosimetry (or other)	3	6

.

3. Results

3.1. Mechanical Properties

Section 3 evaluates the mechanical performance and internal structure of the developed PCs. We analyzed parameters including compressive resistance, elastic modulus, and water absorption to assess long-term reliability.

While traditional concrete is limited by its brittle nature, our polymer matrix significantly boosts crack resistance, as evidenced by the splitting tensile tests. Furthermore, the ultrasonic pulse velocity (UPV) measurements confirmed a dense, defect-free internal structure. A strong correlation was observed between high pulse velocities and the material’s overall hardness, validating the effectiveness of our vibration-compaction manufacturing process.

To study the structural behavior of polymer concrete, a series of mechanical and durability tests were conducted. These experiments not only quantified key strength characteristics but also determined the material’s stiffness, deformation properties, surface quality, internal density, and permeability—parameters that collectively determine its long-term operational reliability.

Compressive strength testing served as the primary criterion for load-bearing capacity. Given that concrete structures under real-world operating conditions predominantly experience compressive loads (GOST 10180-2012), this type of testing is considered the most significant for assessing the material’s performance. The results obtained were also used as a benchmark when comparing Portland cement with traditional cement concrete.

Tensile strength testing by splitting allowed us to evaluate the material’s ability to resist tensile stresses, which are the primary cause of crack initiation and propagation. Since conventional concrete typically has low tensile strength, a significant improvement in this parameter demonstrates the effectiveness of the polymer matrix in increasing the crack resistance of polymer concrete. The elastic modulus and Poisson’s ratio were determined under axial loading. The elastic modulus characterizes the material’s stiffness and directly influences the magnitude of structural deflections and its vibration behavior. Poisson’s ratio, in turn, describes the transverse deformations under load. Together, these two parameters provide a more complete understanding of the stress–strain relationship in the material under study.

To assess the strength and homogeneity of the surface layer, a non-destructive rebound hardness test was used. In addition to operational quality control, the obtained hardness values demonstrated a good correlation with compressive strength and microstructural density, confirming the validity of the destructive testing results.

For a detailed study of the structural behavior of composites, a set of strength and durability tests was conducted (Figure 4, Figure 5, Figure 6 and Figure 7,

Table 9. Mechanical properties of the developed polymer-concrete compositions (n = 6 for each composition, mean ± SD, 95% confidence interval in brackets).

Property	Sample	Mean ± SD	95% CI	Min–Max
Compressive strength, MPa	Smp_001	92.58 ± 2.53	[89.92, 95.24]	89.5–96.1
	Smp_002	82.52 ± 2.07	[80.35, 84.69]	79.8–85.2
Modulus of elasticity, GPa	Smp_001	36.70 ± 1.00	[35.66, 37.74]	35.5–38.1
	Smp_002	33.55 ± 0.89	[32.62, 34.48]	32.5–34.8
Shore D hardness	Smp_001	87.83 ± 1.47	[86.29, 89.37]	86–90
	Smp_002	78.83 ± 1.47	[77.29, 80.37]	77–81
Poisson’s ratio *	Smp_001	0.19 ± 0.02	[0.17, 0.21]	–
	Smp_002	0.235 ± 0.02	[0.215, 0.255]	–

* Poisson’s ratio data from the same set of specimens; SD derived from the reported range.

). In addition to quantifying strength, stiffness, deformation properties, surface quality, and permeability were determined. The experiment was conducted on the basis of GOST 17624-2021 and GOST 22690-2015 to ensure reliable non-destructive testing of the density and hardness of the structure, as well as in compliance with the manufacturers’ technological regulations on the dosage of hardeners and accelerators to achieve the maximum degree of polymerization and minimal shrinkage of the material.

The main criterion for assessing load-bearing capacity is compressive strength. Since structures are most often subjected to compressive loads in real conditions, this test is the most indicative. Under axial loading, the modulus of elasticity and the Poisson’s ratio were determined. The elasticity module characterizes the rigidity of the material and directly affects the size of the deflections and the vibration behavior of the bed.

To control the uniformity of the surface layer, Shore hardness (rebound method) was determined, which correlates well with the data on the density of the microstructure and the results of destructive tests.

Ultrasonic testing (UCC) showed that the high pulse velocity in the samples indicates a dense packing of particles and a minimum number of internal voids, which is an important indicator of durability.

As shown in Table 9, the Smp_001 composition exhibited a mean compressive strength of 92.6 ± 2.5 MPa (95% CI: 89.9–95.2 MPa), which is 2.2–2.5 times higher than that of high-strength M400 concrete and approaches the characteristics of structural composites. The difference between Smp_001 and Smp_002 was statistically significant (two-sample t-test, t(9.6) = 7.54, p < 0.001).

The average elastic modulus was 36.70 ± 1.00 GPa (95% CI: 35.66–37.74 GPa) for Smp_001 and 33.55 ± 0.89 GPa (95% CI: 32.62–34.48 GPa) for Smp_002. The difference was significant (t(9.9) = 5.76, p < 0.001).

Hardness values were 87.8 ± 1.5 (95% CI: 86.3–89.4) for Smp_001 and 78.8 ± 1.5 (95% CI: 77.3–80.4) for Smp_002 (t(10.0) = 10.61, p < 0.001).

The average elastic modulus was 36.8 ± 1.8 GPa, confirming the material’s high rigidity and its ability to minimize elastic deformations under load [38]. Although this value is lower than that of steel, it is significantly higher than that of conventional concrete (25–30 GPa). Combined with the high damping coefficient, it effectively dampens vibrations while maintaining the precision of the equipment.

Poisson’s ratio was recorded at 0.24 ± 0.02, demonstrating the isotropic structure and stable behavior of the material under biaxial loading [39]. These data correlate with values for gray cast iron (0.25–0.27). Taken together, the obtained results confirm that the developed hybrid composition based on an epoxy matrix and mineral fillers possesses a unique combination of high strength and dynamic stability, necessary for the construction of new-generation machine tools.

The material’s hardness was measured using a TKM-359S hardness tester (RPE "Mashproekt", St. Petersburg, Russia) using the Shore D scale, which is the preferred method for dense polymer composites and mineral castings. The hardness of the samples was 88.0 ± 1.5 units (Smp_001) and 79 ± 1.5 units (Smp_002). The minimal standard deviation of the results indicates a high degree of component homogenization and the absence of significant surface defects or air inclusions, which was achieved through the use of rational vibration compaction modes [40]. The obtained hardness values, exceeding 85 units on the Shore D scale, not only guarantee high wear resistance of the future MRS frame during operation, but also confirm the complete polymerization of the binder, ensuring the stability of geometric parameters in the installation areas of precision equipment components. Thus, the achieved level of hardness, combined with the high homogeneity of the material, makes the developed composition optimal for use under the conditions of intense mechanical impacts typical of modern machine tool manufacturing.

Figure 8 shows that the compressive strength (92.3 MPa) of the developed compound was higher than that of standard concrete and approached the requirements of highly loaded structures. The damping capacity was about 9.6 times better than that of gray cast iron SH20. The coefficient of thermal expansion (7.2 × 10⁻⁶ K⁻¹) was the lowest among the compared materials, which ensures better dimensional stability.

3.2. Microstructure Evaluation Using Scanning Electron Microscopy (SEM)

Scanning electron microscope (SEM) images confirmed that the developed compositions possessed a dense, heterogeneous morphology with a uniform distribution of crystalline phases throughout the binder. The microstructure was characterized by the absence of visible macropores and cracks, indicating high-quality degassing and compaction of the mixture during polymerization. The interface between the resin matrix (RM) and the filler particles (FPs), consisting of basalt and silicon carbide, was firmly bonded, ensuring efficient transfer of mechanical stress and minimizing localized deformations of the filler crystal lattice.

Compared to traditional polymer concretes, these compositions exhibited a virtually complete absence of capillary pores, which directly correlates with extremely low water absorption (less than 0.05%) [39]. Micrographs (especially at ×400–×500 magnification) revealed transition zones at the phase boundaries (TZs), which are characterized by high density due to the incorporation of finely dispersed fly ash and SiC microparticles into the intergranular space. The relatively smooth and monolithic surface texture confirms high hardness values and ultrasonic pulse velocity. The integrated relationship between the compacted microstructure and strong adhesion in the TZs is a key factor in ensuring the superior compressive strength and high crack resistance of the upgraded frame.

3.3. Energy-Dispersive X-Ray Spectroscopy (EDS) Analysis

The elemental composition of polymer composites was determined by energy dispersive X-ray spectroscopy (EDS). The spectra are characterized by a predominance of carbon (75–87%) and oxygen due to the structure of the spatially crosslinked epoxy-diane matrix. The high local concentration of the carbon phase confirms the creation of a continuous viscoelastic polymer medium, which is a determining factor in increasing the damping capacity of machine tool bearing systems compared to traditional casting [40].

Special attention was paid to the distribution of silicon (up to 2.3%) and aluminum (up to 1.9%). Unlike building concretes, these elements in the studied compositions are not bound into calcium hydrosilicates, but form a rigid mineral frame and high-hardness inclusions of silicon carbide (SiC). The elemental mapping data confirmed the homogeneous distribution of SiC particles in the matrix volume. In the structure of precision equipment, silicon carbide particles perform the function of dispersed hardening and simultaneously serve as heat-conducting bridges, which helps to stabilize the temperature field of the bed and reduce thermal deformations during intensive cutting conditions.

The presence of sodium (up to 2.1 wt.%) in the composition is explained by the use of alkaline modifiers and the introduction of spodumene, which helps to increase the adhesive strength at the binder–filler interface. The detection of traces of gold (Au) was a consequence of the preparation of samples by magnetron sputtering to ensure the electrical conductivity of the surface during electron bombardment. The complete absence of calcium (Ca) peaks confirms that the material belongs to the class of cementless polymer composites, where the integrity of the structure is ensured solely by the adhesive interaction of the resin with the active surface of crushed basalt and SiC filler particle.

A study of the morphology of the fracture surface by scanning electron microscopy (Figure 9 and Figure 10) revealed a dense structure with a porosity coefficient of less than 2.5%. SiC particles exhibit tight mechanical engagement with the polymer phase without forming micro voids at the interfacial boundaries. A similar mechanism of interaction of solid inclusions of silicon carbide with a polymer matrix determines the achievement of the required indicators of static rigidity and effective vibration damping [41].

The chemical composition and distribution of elements in the polymer-concrete structure were studied by energy dispersive X-ray spectroscopy (EDS) performed in parallel with electron microscopy. The obtained elemental mapping data (Figure 11 and Figure 12) made it possible to visualize the localization of the main components of the matrix and fillers, such as carbon (C), oxygen (O) and silicon (Si). The analysis of the spectra confirmed the presence of calcium (Ca), sodium (Na), and aluminum (Al), which are part of the mineral aggregates, and also identified the following amounts of related elements. The synchronous use of SEM and EDS analysis ensured the verification of the homogeneity of the mixture and confirmed the high-quality adhesion of the polymer binder to the surface of basalt and silicon inclusions.

X-ray diffraction analysis of the first polymer-concrete sample showed that the basis of the crystalline phase is calcium carbonate (CaCO₃). The absence of pronounced impurities or accompanying phases indicates a high degree of homogeneity of the polymer matrix. According to calculations using the Williamson–Hall method, the crystallite sizes range from 640 microns to 4.2 mm, and the values of the microstress of the crystal lattice are 0.05–0.15%, depending on the type of composition under study. The data obtained confirm the formation of an ordered structure, which directly correlates with the high values of compressive strength recorded during mechanical tests.

When studying the microstructure of the Smp_001 composition, the presence of heterogeneous phase boundaries was recorded. Local distortions of the crystal lattice of mineral fillers are caused by internal stresses that occur during the curing of the binder. The integrity of the grain boundaries in the SEM images serves as indirect evidence that the level of microdeformations remains within acceptable values without compromising the stability of the physico-mechanical characteristics of the composite.

During the analysis of the second polymer-concrete composition, it was found that the dominant crystalline phases were calcium carbonate (CaCO₃) and silicon carbide (SiC). The purity of the diffraction spectrum confirms the uniformity of the obtained material. The crystallite sizes for this composition, determined by the Williamson–Hall method, ranged from 5 to 120 microns. Scanning electron micrographs revealed that the polycarbonates had a dense and irregular particle morphology with strong bonds between the matrix and aggregates. A reduction in microcracks and limited void formation were observed on the surfaces, reflecting the low porosity values obtained during durability testing. The microstructure of the polycarbonates was significantly less porous and more compact, consistent with their superior mechanical strength and lower water absorption. The predominant phase is the carbon-containing amorphous phase (polymer). The crystalline component is represented primarily by silicates and aluminosilicates (quartz, basalt components) and oxide compounds, which provide the composite’s frame rigidity. The composition of sample Smp_002 was characterized by a highly uniform filler distribution within the matrix.

The elemental composition of the studied polymer-concrete composites is characterized by the dominance of the carbon phase, accounting for 49.4% to 87.5% by weight, confirming the formation of a dense organic matrix acting as a viscoelastic binder. The high oxygen content (up to 46.7%) combined with silicon (up to 2.33%) and aluminum (up to 0.81%) reflects the presence of a stable mineral framework of silicates and aluminosilicates, typical of basalt filler and fly ash. This chemical composition indicates the creation of a heterogeneous structure, where rigid crystalline inclusions are effectively integrated into the polymer environment, providing the final product with a unique combination of high static rigidity and excellent damping properties necessary for damping vibrations in machine tool beds [42].

The distribution of trace inclusions, such as sodium (up to 2.1%), magnesium, and trace amounts of iron, plays a key role in modifying the microstructure and increasing adhesion strength at the interface. The uniform distribution of these microimpurities throughout the material facilitates the filling of nanoscale defects and pores, significantly reducing internal stresses that arise during thermal shrinkage of the polymer. The presence of sodium compounds may indicate the use of specific alkaline activators or filler surface modifiers, which improve the wettability of basalt grains with resin. Thus, the controlled amount of fine inclusions and their homogeneous distribution prevent localized stress concentration and minimize the risk of microcracks, ensuring the durability and dimensional stability of the upgraded machine tools.

The presence of silicon carbide (SiC) inclusions, which act as a highly hard reinforcing component, plays a key role in the structure of the second composition. Elemental analysis revealed localized concentrations of silicon and carbon in the stoichiometric ratio characteristic of this superhard phase. The introduction of silicon carbide into the polymer-concrete matrix significantly increased the modulus of elasticity and wear resistance of the bed material by creating additional crystallization centers and strengthening the interphase boundaries. Due to their high thermal conductivity, SiC microparticles facilitate more efficient heat dissipation generated during machine operation, minimizing thermal deformations and maintaining the precision of the equipment.

The finely dispersed distribution of silicon carbide inclusions ensures the creation of a rigid internal “skeleton” at the microscopic level. These particles effectively block the propagation of microcracks in the polymer matrix, redistributing mechanical stress from cutting tools and heavy workpieces [43]. When combined with basalt filler, silicon carbide forms a multimodal structure, where particles of varying sizes and hardnesses are packed together in the most densely packed manner. This not only increases the overall rigidity of the upgraded frame, but also significantly improves its damping capacity, converting vibration energy into thermal energy at the interfaces between the solid inclusions and the viscous polymer.

Quantitative analysis using energy-dispersive spectroscopy (EDS) showed that the average elemental content in representative samples was approximately: carbon (C)—78.5%, oxygen (O)—18.2%, silicon (Si)—1.6%, sodium (Na)—1.2%, as well as minor inclusions of aluminum (Al)—0.4% and silicon carbide (SiC). The predominance of the carbon phase confirms the formation of a stable polymer matrix, while the presence of silicon and aluminum clearly reflects the integration of mineral fillers—basalt and fly ash—into the composite structure.

The identified element distribution indicates a high degree of mixture homogeneity, with silicon carbide and aluminosilicate microparticles uniformly dispersed throughout the binder. This ensures the creation of a rigid, finely dispersed framework that minimizes internal stresses and prevents the development of microcracks. The obtained data confirm the calculated material model, demonstrating the effective combination of a lightweight organic base with high-strength crystalline phases, a key factor in increasing the static rigidity and damping capacity of the modernized machine beds. Images obtained by energy dispersive spectroscopy (EDS) from samples Smp_001 and Smp_002 are shown in Figure 13.

3.4. The Role of Porosity and Transport Properties

Small filler particle sizes occupy the space between large basalt grains, displacing air and excess polymer. This reduces the overall porosity to less than 1–2%. Low porosity means an absence of stress concentrators. In porous materials, microcracks begin to grow from voids; in this composition, the dense structure blocks this process, increasing the compressive strength (up to 92.3 MPa, as demonstrated by the experiment). Thanks to the polymer matrix, which “seals” the channels between filler particle, the transport properties of the compositions tend to zero. This prevents the absorption of cutting fluids (CWs), which, if introduced into ordinary concrete, can cause swelling or chemical degradation. The presence of isolated micropores can provide additional vibration damping. A sound or mechanical wave, passing through the solid-microcavity boundary, loses energy, improving the damping properties of the frame. The low porosity of the studied compositions, achieved through the multimodal distribution of filler particle, minimizes the material’s transport properties. This prevents the diffusion of aggressive process media into the frame structure, ensuring high corrosion resistance and maintaining the precision of the machine tools during long-term operation.

4. Discussion

4.1. Phase-Interface Transition Zone and Crack Resistance

The images of the samples (especially at ×400 and ×500 magnifications) clearly demonstrate the morphology of the interface between the polymer matrix and the crystalline inclusions (basalt, spodumene, and SiC). Unlike classic cement concretes, where the transition zone is often porous and loose, in the Smp_001 and Smp_002 compositions, the polymer tightly “flows” around the filler. The absence of visible microgaps at the phase interface indicates high wettability of the mineral surface by the resin. The presence of finely dispersed fly ash and silicon carbide particles in close proximity to large basalt grains creates a “gradient” transition zone. This prevents a sharp jump in the elastic modulus at the interface, reducing the risk of filler delamination under dynamic loads on the frame. The images show that the filler has an acute, irregular shape. When a microcrack occurs in a brittle polymer matrix, it encounters a high-strength crystallite (such as SiC or basalt) and is forced to change trajectory. This increases the overall length of the crack path and absorbs a significant portion of the fracture energy.

4.2. Integrated Relationship of Microstructure and Performance

The microstructure of the composites is a densely packed system, where the carbon polymer matrix (up to 87.5%) holds rigid crystalline inclusions of basalt and silicon carbide. The high concentration of silicon (Si) and carbon (C) at the filler points indicates the creation of a rigid internal skeleton. This ensures resistance to static loads. Minimal deformation of the filler crystal lattice allows the machine tool to maintain precision accuracy when loading heavy workpieces.

When vibrations occur during metal cutting, the energy of mechanical vibrations is effectively dissipated at these numerous interfaces due to viscous friction in the polymer interlayer. This allows vibration damping to be achieved 6–10 times faster than in traditional cast iron, directly improving the surface finish of the parts.

The uniform distribution of sodium (Na) and aluminum (Al) may indicate a modification of the filler surface, improving the bond with the polymer.

High crack resistance. Under peak dynamic loads, the fracture energy is expended by the crack bypassing solid inclusions (crack deflection effect), preventing sudden equipment failure.

The low porosity and virtually zero water absorption of the developed compositions provide the upgraded frames with excellent corrosion resistance and stable performance under constant contact with process fluids. This distinguishes this project from traditional solutions, extending the service life of the equipment and reducing maintenance costs.

Very low porosity (<0.5%) and minimal water absorption (~0.05%) are clear indicators of the dense microstructure achieved in Portland cement concrete. These values are significantly lower than those typical for high-strength Portland cement concrete, which often exhibit water absorption of 3–6%. Thus, the use of a multimodal filler distribution (basalt, fly ash, silicon carbide) allowed us to achieve extremely low porosity (1.2–2.5%) and virtually zero water absorption (<0.05%). This ensures the stability of the geometric dimensions of the machine bed when exposed to coolant and moisture. Electron microscopy confirmed the absence of gaps in the matrix-filler transition zone. High adhesion of the polymer binder to the basalt and SiC filler particle ensures effective stress transfer, resulting in a compressive strength of up to 92.3 MPa (sample Smp_001). Due to its heterogeneous structure and the presence of multiple interphase boundaries, the material has a damping capacity 6–10 times greater than that of gray cast iron, which is critical for high-precision machining. The introduction of silicon carbide and fly ash contributed to the refinement of filler particle and the implementation of the Hall–Petch effect, which increased the crack resistance and elastic modulus of the composition.

4.3. Quantitative Correlation Analysis of Mechanical Properties

To provide numerical support for the qualitative statements regarding interrelations between the measured properties, a Pearson correlation analysis was performed on the individual test data for both compositions combined (n = 12 specimens, six from Smp_001 and six from Smp_002). The results are summarized in

Table 10. Pearson correlation coefficients between key mechanical properties.

Variable Pair	r	p-Value
Compressive strength vs. Shore D hardness	0.962	<0.001
Compressive strength vs. elastic modulus	0.947	<0.001

.

All correlations were statistically significant (p < 0.001), indicating strong linear relationships among the properties. The highest correlation (r = 0.962) was observed between compressive strength and Shore D hardness. Figure 14 shows the scatter plot with a linear regression fit for this pair.

Similarly, the compressive strength versus elastic modulus yielded R² = 0.897 (Figure 15). These quantitative correlations validate the excellent homogeneity and structural integrity of the developed polymer-concrete compositions.

All correlations were statistically significant at p < 0.001 (

Table 11. Comparison of the mechanical properties of Smp_001 with selected polymer-concrete compositions from the literature.

Reference	Binder Type	Filler/Reinforcement	Compressive Strength (MPa)	Elastic Modulus (GPa)	Target Application
Present work (Smp_001)	Epoxy ED-20 + furan	Basalt aggregate + quartz sand + SiC (3.6%) + glass fiber (2.1%)	92.6 ± 2.5	36.7 ± 1.0	Precision machine tool bed
[11]	Epoxy	Basalt + sand + fly ash	Not reported (flexural strength ~31)	Not reported	Precision machine base
[44]	Epoxy	Basalt + silica sand + fly ash (25:52.5:17.5)	~94.1	Not reported	General structural
[45]	Polyester	Recycled aggregates	~85.0	Not reported	General construction
[46,47]	Vinyl-ester	Quartz + fly ash	~100.0	Not reported	Polymer-concrete-like composites
[48]	Epoxy	Quartz + fly ash	~90.0	Not reported	–
Typical concrete (M400) [49]	Cement	Sand + gravel	30–50	25–30	General construction
Gray cast iron (SCH20) [50]	Metal	–	200–300	100–120	Machine tool beds (traditional)

). The high coefficients of determination indicate that more than 89% of the variance in hardness and modulus can be predicted from compressive strength, confirming the excellent structural homogeneity of the developed composites.

The 85.0 MPa result indicates that the current composite is a high-performance material. In general engineering terms, high-strength concrete typically ranges between 70–80 MPa; the current study’s composite exceeds these ratings, making it a viable lightweight alternative for heavy-duty structural applications.

4.4. Comparison with Existing Polymer-Concrete Materials

To assess the performance of the developed Smp_001 composition, a quantitative comparison was made with previously reported polymer-concrete materials intended for similar or related applications. The results are summarized in Table 10.

The compressive strength of Smp_001 (92.6 ± 2.5 MPa) was significantly higher than conventional polymer concretes used for general structural purposes, which typically exhibit compressive strength in the range of 70–80 MPa [45]. It is comparable to the quaternary polymer concrete developed by [50] (94.1 MPa), which contained 25% epoxy resin, 52.5% silica sand, 5% fly ash, and 17.5% basalt. However, the composition reported in [50] was optimized for maximum compressive strength without addressing damping performance or the thermal stability requirements specific to machine tool beds.

A direct comparison with the study by Haddad and Al Kobaisi [10,11] is particularly instructive, as it specifically targeted polymer concrete for precision machine bases. Their final optimized composition contained basalt, sand, and fly ash with 13% resin and 87% filler, and exhibited a coefficient of thermal expansion of approximately 22·10⁻⁶/K at 17% resin content. The compressive strength of their composition was not explicitly reported, but the flexural strength was approximately 31 MPa. In the present study, Smp_001 achieved a compressive strength of 92.6 MPa, an elastic modulus of 36.7 GPa, and a thermal expansion coefficient of 7.2·10⁻⁶/K, which were substantially lower than the values reported by Haddad and Al Kobaisi [10]. The superior thermal stability of the present composite can be attributed to the incorporation of silicon carbide, which acts as a heat-conducting bridge within the basalt-based skeleton.

Compared to recent polymer concretes for precision machine tool beds [8], the developed Smp_001 composition offers a favorable balance of compressive strength and damping capacity. The damping ratio of the present composite was 6–10 times higher than that of gray cast iron, which is consistent with the range reported in the literature (1.6–30 times higher) [8]. Table 10 provides a quantitative overview of the performance of Smp_001 alongside selected reference materials.

It should be noted that direct comparisons are complicated by differences in testing standards, specimen geometry, binder types, and filler compositions across studies. Nevertheless, the data in Table 10 show that the Smp_001 composition is competitive with, and in several respects surpasses existing polymer-concrete materials designed for precision machine tool applications. The combination of high compressive strength, low thermal expansion, and excellent damping capacity achieved in this work has not been previously reported for a basalt–SiC–glass fiber system.

5. Conclusions

The results of the study confirm that the developed polymer-concrete composite based on ED-20 epoxy resin, reinforced with basalt filler and microdispersed silicon carbide (SiC), exhibits a range of physical and mechanical properties that significantly exceed those of traditional structural materials, such as SCh20 gray cast iron and standard cement concrete. A key indicator of structural reliability is the achieved compressive strength of the optimized Smp_001 composition, which was 92.3 MPa. Combined with an elastic modulus of 38.5 GPa, this allows the material to effectively withstand significant operational loads in precision machine tool manufacturing. The use of a multimodal distribution of filler fractions (quartz gabbro-sand, basalt) and the introduction of reinforcing additives ensured the formation of a dense heterogeneous microstructure with extremely low porosity (1.2–2.5%) and record-breaking water absorption values of less than 0.05%, preventing frame degradation during prolonged contact with process fluids. The use of a furan resin-modified matrix and PEPA hardener minimized the linear shrinkage to values less than 0.5–1%, ensuring high geometric accuracy of the castings and the absence of internal microstresses. The high adhesion of ED-20 resin to basalt filler particle and silicon carbide particles ensures the effective transfer of mechanical stress throughout the material. The dynamic properties of the material are particularly important: the damping capacity of the composite is 6–10 times higher than that of gray cast iron, which is critical for suppressing resonant vibrations and improving surface finish. Furthermore, the introduction of silicon carbide ensured high thermal stability and a reduction in the coefficient of thermal expansion to 7.2 × 10⁻⁶/K, minimizing thermal deformation and guideway distortion during equipment operation. Microstructural analysis using scanning electron microscopy confirmed the presence of strong adhesive bonds at the polymer–filler interfaces, ensuring efficient stress distribution throughout the material. The data obtained provide scientific substantiation for the feasibility of replacing metal castings with the developed polymer-concrete compositions for the manufacture of critical components of next-generation metal-cutting machines. The study demonstrated that the synergistic effect of basalt and silicon components enables the desired balance between rigidity, thermal stability, and vibration resistance of precision equipment to be achieved.

Unlike previous studies on multimodal filler systems for polymer concrete [10], which focused on the optimization of aggregate composition without introducing silicon carbide or glass fiber, the present work proposes a different concept: the combined use of basalt as a load-bearing skeleton, silicon carbide as a heat-conducting and stiffening additive, and glass fiber as a damping-enhancing component. This three-phase hierarchical architecture, where each component has a distinct functional role, has not been reported previously for precision machine tool beds. The obtained compressive strength of 92.3 MPa, damping capacity 6–10 times higher than that of gray cast iron, and extremely low water absorption below 0.05% confirm the viability of this approach for modern machine tool manufacturing.