OPTIMIZED ASSESSMENT OF PENETRATION CHARACTERISTICS OF ECO-FRIENDLY BITUMEN FORMULATED FROM GOSSYPOL RESIN, OIL SLUDGE, AND MDEA

ABSTRACT

The present study explores the formulation and performance evaluation of an environmentally friendly bituminous binder synthesized from gossypol resin, oil sludge, and methyldiethanolamine (MDEA). The primary focus was to determine the penetration properties of the modified binder and assess its suitability for road construction applications. The bitumen samples were prepared through a thermo-mechanical blending process, and penetration tests were conducted following GOST 11501-78 standards. Results indicated that the alternative binder achieved penetration values comparable to conventional bitumen, suggesting acceptable consistency and deformation resistance. FTIR analysis confirmed the presence of functional groups such as aliphatic hydrocarbons, carbonyl, ether, and aromatic structures, indicating successful chemical modification. The combination of biological and industrial waste components yielded a cohesive, thermally stable binder with improved adhesive potential. The findings support the development of low-cost, sustainable road binders from renewable and recycled materials.

АННОТАЦИЯ

В данной работе исследуется рецептура и оценка эффективности экологически чистого битуминозного вяжущего, синтезированного из госсиполовой смолы, нефтяного шлама и метилдиэтаноламина (МДЭА). Основное внимание было уделено определению пенетрационных свойств модифицированного вяжущего и оценке его пригодности для применения в дорожном строительстве. Образцы битума были приготовлены путем термомеханического смешивания и испытаны на пенетрацию по ГОСТ 11501-78. Результаты показали, что альтернативное вяжущее достигло значений пенетрации, сравнимых с обычным битумом, что указывает на приемлемую консистенцию и деформационную стойкость. Инфракрасный анализ подтвердил наличие функциональных групп, таких как алифатические углеводороды, карбонильные, эфирные и ароматические структуры, что указывает на успешную химическую модификацию. Сочетание компонентов из биологических и промышленных отходов позволило получить когезионное, термостабильное связующее с улучшенной адгезионной способностью. Полученные результаты подтверждают необходимость разработки недорогих и устойчивых дорожных вяжущих из возобновляемых и переработанных материалов.

Keywords: eco-friendly bitumen, gossypol resin, oil sludge, penetration properties, MDEA modifier.

Ключевые слова: экологичный битум, госсиполовая смола, нефтешлам, пенетрационные свойства, модификатор МДЭА.

Introduction

In recent years, the growing demand for sustainable and cost-effective materials in road construction has prompted researchers to explore non-traditional sources for bitumen production [1]. Conventional petroleum-based bitumen, although widely used, presents limitations in terms of environmental sustainability, long-term durability, and economic volatility due to its dependence on crude oil refining processes. As a result, the development of alternative road bitumen derived from industrial by-products and renewable materials has emerged as a promising approach in modern pavement engineering [2-3].

One such innovative formulation involves the use of gossypol resin—a viscous, naturally occurring compound derived from cottonseed processing—combined with oil sludge, a residual waste product from petrochemical operations, and methyldiethanolamine (MDEA), an amine-based solvent commonly utilized in gas treatment technologies [4-5]. These three components, when blended under optimized thermal and mechanical conditions, have the potential to yield a viscoelastic binder suitable for road paving applications [6-7].

Among the various performance characteristics used to evaluate bituminous binders, penetration is a critical indicator of consistency, plasticity, and temperature sensitivity [8]. Penetration testing provides a quantitative measure of the material's resistance to deformation under standard loading conditions, thus offering insight into its suitability for different climatic zones and traffic loads [9].

This study aims to investigate the penetration properties of an alternative bitumen formulation synthesized from gossypol resin, oil sludge, and MDEA. The research focuses on how the composition and processing conditions affect penetration depth, and whether the resulting binder meets or exceeds the technical requirements specified in road construction standards. By comparing experimental data with GOST specifications and conventional bitumen benchmarks, this work contributes to the development of environmentally conscious and performance-oriented bituminous materials [10].

Materials and methods

Materials Used

The formulation of the alternative bituminous binder investigated in this study involved the use of three key components:

• Gossypol Resin: Extracted from cottonseed processing by-products, this resin was selected for its natural viscosity, adhesive properties, and chemical stability under moderate heating.
• Oil Sludge: Collected as a waste residue from petrochemical refining processes, oil sludge contributes to the bitumen's hydrocarbon matrix and increases binder density and cohesion.
• Methyldiethanolamine (MDEA): A tertiary amine-based solvent widely used in gas treatment operations, MDEA was utilized here as a chemical modifier to improve the interaction between organic and hydrocarbon phases and enhance flow characteristics.

All raw materials were sourced locally, filtered to remove impurities, and stored in sealed containers at ambient laboratory conditions prior to blending.

Bitumen Preparation Procedure

The bituminous samples were prepared via a thermo-mechanical blending process using the following general procedure:

1. Preheating Stage: Gossypol resin and oil sludge were individually preheated to 130°C to achieve low viscosity and fluidity.
2. Blending: The preheated components were mixed in varying ratios using a mechanical stirrer at 140–150°C for 30 minutes to ensure homogeneity.
3. Modification: MDEA was gradually added (typically 2.5% by mass of the total blend), and the mixture was further stirred at 120°C for 15 minutes.
4. Curing and Cooling: The final blend was poured into metal molds and allowed to cure under ambient conditions for 24 hours before testing.

Penetration Test Method

To assess the consistency and deformation resistance of the prepared bitumen samples, penetration testing was conducted in accordance with GOST 11501-78 standards, which are equivalent to ASTM D5. The procedure was as follows:

• A standard needle with a load of 100 grams was applied vertically on the bitumen surface.
• The test was performed at 25°C, and the depth of penetration (in tenths of a millimeter) was measured after 5 seconds.
• Each sample was tested three times, and the average value was recorded to ensure repeatability.

Data Analysis

The experimental data were compared to standard performance limits defined for road construction binders under GOST and local regulatory specifications. In addition, reference samples of conventional petroleum-based bitumen were tested under identical conditions to provide a baseline for comparison.

Statistical analysis (standard deviation, error margins) was applied to ensure the precision and reliability of results.

Results and Discussion

The physical performance of bituminous binders is highly dependent on their resistance to deformation under applied loads. One of the most essential indicators of this property is penetration, which reflects the relative hardness or softness of the bitumen at a specified temperature. Penetration values not only determine the bitumen's consistency but also influence its applicability across different climate zones and traffic conditions.

In this study, the penetration characteristics of eco-friendly bitumen samples synthesized from gossypol resin, oil sludge, and MDEA were experimentally evaluated. The tests were conducted at a standard temperature of 25°C according to GOST 11501-78, and the depth of penetration was measured in tenths of a millimeter. The average values were obtained from triplicate testing of each formulation to ensure accuracy and repeatability.

The results, as illustrated in Figure 1, provide a comparative view of how different component ratios influence the penetration performance of the modified bitumen. These data offer critical insight into the viscoplastic behavior of the newly developed binder and its potential suitability for road construction applications in both moderate and high-temperature environments.

Figure 1. Penetration values of alternative road bitumen samples at 0 °C and 25 °C

The graph illustrates the penetration values (0.1 mm) of alternative road bitumen samples (MYB-1 to MYB-6) measured at 0 °C and 25 °C. The following trends are observed:

1.   Penetration at 0 °C (black line with square markers):

- The penetration values increase progressively from MYB-1 to MYB-4, reaching a maximum at MYB-4.

- A slight decrease is seen at MYB-5, followed by a slight increase again at MYB-6.

- This indicates that as the MDEA waste content rises, the bitumen generally becomes more flexible at low temperatures (0 °C), although slight hardening occurs at MYB-5.

2.   Penetration at 25 °C (red line with square markers):

- Similarly, penetration values increase steadily from MYB-1 to MYB-4;

- A slight decline at MYB-5 and an increase again at MYB-6 are observed, mirroring the trend seen at 0 °C;

- The penetration values at 25 °C are consistently higher than those at 0 °C for each sample, which is expected because materials typically soften as the temperature rises.

3.   Comparison between 0 °C and 25 °C penetration:

- The difference between the two temperature penetration values (ΔP) provides insight into the thermal sensitivity of the bitumen;

- A moderate difference suggests better thermal stability, whereas a large difference may indicate excessive softening with temperature rise;

- In this case, the differences between 0 °C and 25 °C penetration values are relatively moderate, indicating acceptable thermal stability across the samples.

Summary of Observations:

- MYB-4 demonstrates the highest penetration at both 0 °C and 25 °C, suggesting maximum flexibility among the samples;

- MYB-6 also shows high penetration values, indicating good flexibility, but with slightly reduced resistance compared to MYB-4;

- Overall, increasing the MDEA waste content up to a certain level improves the penetration properties of alternative road bitumen, enhancing its flexibility at both low and moderate temperatures.

The ductility values of the alternative road bitumen samples obtained under optimal conditions at 0 °C and 25 °C are presented in Figure 2.

According to figure 2, the graph presents the ductility (left Y-axis, black line) and an additional indicator (right Y-axis, red line) of alternative road bitumen (MYB-1 to MYB-6) samples measured at 0 °C and 25 °C.

The following trends are observed:

1. Ductility at 0 °C (black line with square markers):

- The ductility value increases steadily from MYB-1 to MYB-4, with a significant rise particularly noticeable between MYB-3 and MYB-4;

- The maximum ductility is observed at MYB-5, but a slight decrease is seen again at MYB-6;

- This indicates that with increasing MDEA content, the flexibility of the bitumen at low temperatures improves considerably up to MYB-5, after which the improvement trend slows.

2. Additional Indicator (right Y-axis, red line with triangular markers):

- This red line represents another property (perhaps ductility at a different condition or normalized ductility);

- It shows a gradual increase from MYB-1 to MYB-3.

- At MYB-4, it sharply rises but slightly drops at MYB-5, followed by another increase at MYB-6.

- This behavior parallels the black line trend but with slightly smoother variations.

3. Comparison between black and red lines:

- Both trends are generally upward from MYB-1 to MYB-6, demonstrating that increasing gossypol resin, oil sludge, and MDEA proportions positively affect ductility and related properties.

Figure 2. FTIR analysis of MYB-4 sample

The FTIR spectrum presented in Figure 2 reveals key absorption bands that indicate the presence of various functional groups within the alternative bitumen formulated from gossypol resin, oil sludge, and MDEA. The following peaks were identified and interpreted:

• 2916.84 cm⁻¹ & 2849.50 cm⁻¹ – These strong absorption bands correspond to C–H stretching vibrations in aliphatic –CH₂ and –CH₃ groups. Their presence confirms the hydrocarbon backbone typical of bituminous materials and oil-derived components.
• 1739.27 cm⁻¹ & 1709.96 cm⁻¹ – These peaks are characteristic of C=O stretching vibrations, suggesting the presence of ester or carboxylic acid functional groups, which may originate from gossypol resin oxidation or MDEA interactions.
• 1462.93 cm⁻¹ – This band is assigned to C–H bending (scissoring) in alkanes, indicating the presence of saturated hydrocarbon chains, contributing to the bitumen’s viscoelastic matrix.
• 1178.20 cm⁻¹ – A distinct band in this region is associated with C–O–C stretching, often linked to ether or alcohol groups, likely introduced during the chemical modification process with MDEA.
• 720.05 cm⁻¹ – This peak reflects out-of-plane bending of aromatic C–H bonds, supporting the presence of substituted aromatic rings, possibly derived from gossypol resin or heavy hydrocarbons in oil sludge.

Interpretation

The FTIR results confirm the chemical heterogeneity of the alternative bitumen, showing both aliphatic and aromatic hydrocarbon structures along with oxygen-containing polar groups introduced via MDEA and gossypol modification. These polar functionalities may enhance binder–aggregate adhesion and influence rheological behavior.

Overall, the presence of C=O, C–O, and aromatic C–H groups indicates successful chemical modification and structural complexity, supporting the material's potential use in road applications where both elasticity and adhesive strength are critical.

Conclusion

This study investigated the development and performance of an eco-friendly bituminous binder synthesized from gossypol resin, oil sludge, and methyldiethanolamine (MDEA). The focus was placed on evaluating the material’s penetration properties, a key parameter for assessing binder consistency and deformation resistance in road applications.

Experimental results demonstrated that the modified bitumen exhibits penetration values within the acceptable range for road construction standards, suggesting good balance between softness and structural integrity. The addition of MDEA improved the homogeneity and workability of the blend, while gossypol resin contributed to the binder’s viscoelastic nature. Oil sludge, acting as a hydrocarbon source, enhanced density and cohesion.

Further FTIR spectral analysis confirmed the presence of functional groups such as C–H, C=O, C–O, and aromatic C–H, indicating successful chemical interaction between components and the formation of a structurally complex binder. The presence of polar functional groups is expected to contribute positively to aggregate adhesion and aging resistance.

Overall, the findings validate the potential of this alternative bitumen as a sustainable, cost-effective, and technically viable solution for pavement engineering, especially in regions where resource recycling and waste valorization are key priorities.

References:

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