PHYSICO-MECHANICAL PROPERTIES AND MORPHOLOGICAL ANALYSIS OF POLYMER-BITUMEN COMPOSITES MODIFIED WITH RUBBER-BASED ELASTOMERS

ABSTRACT

This article presents polymer-bitumen compositions obtained by modifying BN 50/70 grade bitumen with rubber crumb, elastomer, and antioxidants in the form of four different samples. The influence of changes in the composition of components on the main properties of polymer-bitumen was studied. According to the obtained results, at a temperature of 25 °C, the needle penetration depth changed from 75 to 59 mm, the softening point (ring-and-ball method) increased from 51 to 70 °C, the brittleness temperature decreased from –16 to –24 °C, and the elongation increased from 45 to 68 cm. Morphological analysis of the obtained polymer-bitumen compositions using SEM microscopy showed that the components of the dispersed phase are evenly distributed, forming a homogeneous dispersed system with clearly defined interfacial boundaries.

АННОТАЦИЯ

В данной статье представлены полимерно-битумные композиции, полученные путём модификации битума марки БН 50/70 резиновой крошкой, эластомером и антиоксидантами в виде четырёх различных образцов. Исследовано влияние изменения состава компонентов на основные свойства полимерного битума. Согласно полученным результатам, при температуре 25 °C глубина проникновения иглы изменилась с 75 до 59 мм, температура размягчения по методу кольца и шара — с 51 до 70 °C, температура хрупкости — от –16 до –24 °C, а удлинение — с 45 до 68 см. Морфологический анализ полученных полимерно-битумных композиций методом СЭМ-микроскопии показал, что компоненты дисперсной фазы равномерно распределены, образуя гомогенную дисперсную систему с чётко выраженными межфазными интерфейсами.

Keywords: polymer-bitumen, elastomer, polymer, plastomer, stabilizer, plasticizer, rubber powder, modification, morphology.

Ключевые слова: полимер-битум, эластомер, полимер, пластомер, стабилизатор, пластификатор, резиновый порошок, модификация, морфология.

Introduction. The sharp increase in the number of light and heavy vehicles, along with aggressive temperature fluctuations, leads to increased deformation loads on road pavements [1]. This, in turn, necessitates a significant improvement in the quality of road surfaces and, first and foremost, the enhancement of the quality of the organic binder material (bitumen), which is the most critical component of asphalt concrete mixtures [2]. Due to the low quality of bitumen produced in the Republic of Uzbekistan, continuous research is being conducted to find ways to improve it []. In Western countries, the SUPERPAVE system has been developed and implemented for the design of asphalt concrete mixtures [3]. One of its main stages is the selection of a binder with high plasticity properties that match the climatic conditions of the area of use. However, without modifying the organic binder materials, the implementation of the SUPERPAVE system is considered complex [4].

Materials and Methods. During the research, four different types of polymer-bitumen composites were obtained using a two-stage method based on hybrid elastomers containing rubber.

Table 1.

The composition of polymer-bitumen composites based on hybrid elastomers containing rubber

Bitumen – GOST 33133 grade 50/70

Rubber powder – Recycled automobile tire, particle size 3–5 mm

Thermoplastic elastomers (polymers) – Styrene-butadiene-styrene (SBS) and polystyrene

Stabilizers – Tetraethoxysilane, kaolin (Al₂Si₂O₅(OH)₄), tetramethylthiuram disulfide, and dithiocarbamate

Plasticizer – Petroleum sludge

In this method, bitumen, recycled rubber powder, and elastomeric polymers were simultaneously loaded into a preheated reactor. The bitumen was typically heated to a temperature of 160–180 °C, after which 5–10% rubber powder and 3–7% elastomer and stabilizers were added and mixed for 1.5–3 hours. During the process, the rubber partially swelled and dispersed within the bitumen, and the physicochemical properties of the resulting composites were studied. The modifying components (rubber powder and elastomers) were pre-prepared: in the first stage, rubber and elastomers, stabilizers (3–7%), and special solvents such as petroleum-based plasticizer (8–10%) were mixed to obtain a concentrated rubber-bitumen suspension. In the second stage, the resulting elastomer–rubber concentrate was added to the base bitumen and mixed at 160–170 °C for 1.5–2 hours until a homogeneous system was formed. As a result of this method, the rubber fully swelled and formed a well-integrated composite with the bitumen, characterized by high elasticity, good thermal stability, and resistance to aging processes [5].

Results and Discussion. The increase in the content of components in the polymer-bitumen composites had a significant effect on all performance indicators. Penetration and brittleness temperature decreased, while other parameters — softening point, elongation, viscosity, and elasticity — increased. This scientifically substantiates the superiority of the modified polymer-bitumen composites over conventional bitumen in terms of strength, resistance to heat and cold, flexibility, and service life.

In Figure 1, the penetration value for the RSGEPB-1 sample was 74∙0.1 mm, while in the RSGEPB-4 sample it decreased to 59∙0.1 mm. This trend is explained by the increased content of rubber powder and thermoplastic elastomers (such as SBS) in the composition. Polymers and rubber powder form a denser, more elastic, and highly interconnected network structure within the bitumen matrix. Specifically, the styrene blocks in the SBS polymer act as rigid segments, enhancing the structural stiffness, while the butadiene segments provide elasticity. The rubber powder interacts with the light fractions of bitumen (paraffins, aromatics), swells, and forms a dispersed phase. This swelling phenomenon increases the overall density of the material and makes needle penetration more difficult. The aromatic rings (π-electron system) and saturated hydrocarbon chains present in the rubber form compact and homogeneous networks within the bitumen structure through π–π interactions, dispersion forces, and van der Waals bonds with the aromatic components of the bitumen.

In Figure 2, the increase in softening point observed in polymer-bitumen composites based on rubber-containing hybrid elastomers indicates their improved resistance to high-temperature operation. The softening point determined by the Ring and Ball method was 52 °C for the RSGEPB-1 sample, while for the RSGEPB-4 sample it increased to 70 °C. This is explained by the influence of the components included in the composition — in particular, elastomers, rubber powder, stabilizers, and plasticizers. The presence of the two-phase microstructure of styrene-butadiene-styrene (SBS) polymer (styrene and butadiene blocks) in the polymer-bitumen matrix forms a phase with high thermal and mechanical stability within the bitumen. The styrene segments form a rigid, thermally stable phase that resists bitumen flow, while the butadiene segments provide elasticity. Due to this phase structure, the material withstands high temperatures, resulting in an increased softening point. Furthermore, the rubber powder — derived from automobile tires — interacts with the light fractions in bitumen through its aromatic structures and saturated hydrocarbon chains, adsorbing them and forming a macromolecular network.

Graphical analysis of the elasticity indicators of polymer-bitumen composites at 25 °C (see Figure 3) shows that the elasticity values increase consistently from 62% in the RSGEPB-1 sample to 85% in the RSGEPB-4 sample. This steady upward trend is explained by the increased content of elastomeric components (SBS, recycled rubber powder) and plasticizers in the compositions. Higher elasticity enhances the material’s resistance to crushing, deformation, and thermal cracking caused by hot-cold temperature fluctuations.

The dynamic viscosity values of the obtained samples increased from 0.85 Pa·s in the RSGEPB-1 sample to 1.60 Pa·s in the RSGEPB-4 sample (see Figure 3). This consistent increase is directly related to the higher content of elastomer (SBS) and rubber powder in the composition. The styrene segments of SBS polymers form a rigid phase resistant to high temperatures, while the butadiene segments create a flexible and elastic phase. When this microphase structure, composed of the two segments, is mixed with bitumen, it imparts high viscoelastic properties to the material.

Conclusion. The main physicochemical and rheological properties of the polymer-bitumen composites prepared based on rubber-containing hybrid elastomers were determined. The research results on penetration, softening point, brittleness temperature, elongation, elasticity, and dynamic viscosity are presented in Table 2.

Table 2.

Research results on penetration, softening point, brittleness temperature, elongation, elasticity, and dynamic viscosity

The RSGEPB samples fully meet the requirements of STO 09414893–001–2016 for all key indicators. The modified polymer-bitumen composition ensures high-temperature resistance, brittleness stability, elasticity, aging resistance, and rheological stability simultaneously. Therefore, it is considered optimal for use in climate-contrast zones and heavily loaded highways. This indicates the high quality of the modified polymer-bitumen composites and their potential for successful application in road construction. Moreover, the images obtained using a scanning electron microscope provided comprehensive and precise information about the spatial and morphological structure of the modified polymer-bitumen composites. This analytical method serves as an important tool for scientifically evaluating the technological quality of the composition, optimizing production processes, and predicting the performance of road pavements.

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