DETERMINATION OF THE OPTIMAL AMOUNT OF BASALT AND STEEL FIBERS FOR FIBER-REINFORCED CONCRETE

ABSTRACT

This study investigates the determination of the optimal content of basalt and steel fibers in fiber-reinforced concrete. The main objective of the research is to enhance the mechanical properties of concrete by improving its strength, ductility, and crack resistance. For this purpose, concrete specimens incorporating different proportions (0–0.5%) of basalt and steel fibers were prepared and tested in the laboratory under compressive, flexural, and tensile loading conditions. The obtained results were compared with those of conventional concrete to evaluate the influence of fiber content on the structural behavior of the material. The findings reveal that the combined addition of basalt and steel fibers in specific ratios significantly increases the load-bearing capacity of concrete. However, an excessive amount of fibers was observed to have a negative impact on the homogeneity of the mixture. Based on the results, the most effective-economically and technically optimal-fiber content was identified. The outcomes of this research have practical significance for the design of structural concrete types and the development of durable, long-lasting engineering structures.

АННОТАЦИЯ

В данной научной работе рассматривается вопрос определения оптимального содержания базальтовых и стальных волокон в составе фибробетона. Цель исследования заключается в повышении механических свойств бетона за счёт улучшения его прочности, пластичности и трещиностойкости. Для этого были изготовлены бетонные образцы с различным процентным содержанием (0–0,5%) базальтовых и стальных волокон, которые прошли лабораторные испытания на сжатие, изгиб и растяжение. Полученные результаты были сопоставлены с характеристиками обычного бетона с целью выявления влияния количества волокон на структурное поведение материала. Результаты исследования показали, что совместное введение базальтовых и стальных волокон в определённых пропорциях значительно повышает несущую способность бетона. В то же время было отмечено, что избыточное количество волокон оказывает отрицательное влияние на однородность смеси. На основе проведённого анализа определено наиболее рациональное-экономически и технически эффективное-содержание волокон. Результаты исследования имеют практическое значение при проектировании конструкционных видов бетона и создании прочных, долговечных строительных сооружений.

Keywords: Main properties of basalt and steel fibers, fiber-reinforced concrete, Portland cement, fine and coarse aggregates, fiber elastic modulus, concrete mixture, fiber shape, fiber length.

Ключевые слова: основные свойства базальтовых и стальных волокон, фибробетон, портландцемент, мелкий и крупный заполнитель, модуль упругости волокон, бетонная смесь, форма волокон, длина волокон.

Introduction

One of the promising directions in the study of basalt fiber concrete technology is the justification of using basalt and steel fibers as dispersed reinforcement. It is well known that basalt and steel fibers are distinguished not only by their high physical and mechanical properties but also by their excellent chemical resistance, durability against heat, radiation, and weathering, as well as by the simplicity and cost-effectiveness of their production technology.

1. Objectives of Experimental Research

An analysis of previous scientific studies shows that several investigations have been conducted to study the mechanical properties of fiber-reinforced concrete dispersed with basalt and steel fibers. However, there has been insufficient research on determining the optimal amount of basalt and steel fibers for concrete. Therefore, under the conditions of Uzbekistan, identifying the optimal content of basalt and steel fibers is both necessary and relevant.

A comprehensive study of the mechanical properties of steel- and basalt-fiber-reinforced concrete in the context of Uzbekistan is of great theoretical and practical importance. This is because the optimal fiber content directly influences the strength, deformability, and long-term durability of concrete. Moreover, these parameters serve as the basis for assessing how effectively the concrete can perform under real working conditions.

The main objectives of the experimental research are as follows:

To determine the effect of basalt and steel fibers on the mechanical properties of concrete. For this purpose, cube specimens of plain concrete and fiber-reinforced concrete (with steel and basalt fibers) are prepared and tested under laboratory conditions. The obtained results are comparatively analyzed, and corresponding scientific conclusions are developed.

To determine the optimal content of basalt and steel fibers. This allows for a thorough study of their influence on the strength characteristics of concrete.

To investigate beams reinforced with the identified optimal fiber parameters. These beams are tested experimentally to study their strength and deformation behavior.

In these experiments, Portland cement of grade PS400D20, produced by “Namangancement” LLC, was used [1]. The physical and mechanical properties of the cement were determined as follows: true density – 3.1 g/cm³, bulk density – 1.33 g/cm³, standard consistency – 14%, and fineness – 8.2%. Moreover, the 28-day compressive and flexural strength limits were found to be 34.4 MPa and 7.1 MPa, respectively. The specific surface area of the cement ranged from 3000 to 3500 cm²/g [1, 2].

In the research, fine aggregate was obtained from the “Namangan” quarry located in the Turaqo‘rg‘on district of Namangan region. The sand had a density of 1025 kg/m³, with particle sizes ranging from 0 to 6 mm and a moisture content of 3.1%. As the coarse aggregate, crushed granite (gravel) with a density of 815 kg/m³ and particle sizes ranging from 5 to 24 mm was used. The appearance of the fine and coarse aggregates used in the preparation of cubic samples is shown in Figure 1.

Figure 1. Fine and coarse aggregates used in the experimental study

The steel fibers used in the research had an elastic modulus of 200×10³ MPa, a length of 30 mm, a diameter of 1.2 mm, and a length-to-diameter ratio of 25. Their density was approximately 7.8 g/cm³ (ρ ≈ 7.8 g/cm³). The main properties of the steel fibers are presented in Table 1.

Table 1.

Main properties of steel fiber

In the research, the basalt fibers used had an elastic modulus of (0.89 – 1.10) × 10⁵ MPa, a length of 30 mm, a diameter of 1.2 mm, and a length-to-diameter ratio (l/d) of 18. The density of the basalt fiber was ρ ≈ 2.6 g/cm³. The main properties of basalt fiber are presented in Table 2 below.

Table 2.

Main properties of basalt fiber

Figure 2. Appearance of steel (a) and basalt (b) fibers

Figure 3. View of the measurement process of steel fibers

In measuring the quantity of steel fibers, a high-precision “AOTE 777” model balance was used.The measurement process for both steel and basalt fibers is illustrated in Figures 3 and 4.For these experiments, steel fibers manufactured by “BVV Constructions and Metal Works” LLC, located in Bukhara region, Uzbekistan, were used, as shown in Figure 3.The main characteristics of the steel fibers are presented in Table 1.

Figure 4. View of the basalt fiber measurement process

In the experimental study, a combination of steel and basalt fibers was added to the concrete mixture in order to produce B25-grade concrete according to design specifications. The experimental and testing procedures were carried out in compliance with the interstate standard GOST 27006-2019 requirements.

Table 3.

 Materials required for producing B25-grade concrete

2. Preparation and Testing of Experimental Specimens

Experimental specimens were prepared in the construction testing laboratory of “Jiydakapa Industry” LLC. A total of 26 series of concrete cube specimens with dimensions of 100×100×100 mm were produced for testing purposes.

In this study, the effectiveness of fibers was investigated by introducing varying proportions of steel and basalt fibers relative to the total concrete volume through dispersed reinforcement. Specifically, steel and basalt fibers with a length of 30 mm were added to the concrete mixture in different volume fractions of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%.

For the 0.1% fiber volume fraction, five separate series of fiber-reinforced concrete specimens were prepared to analyze the effect of different steel-to-basalt fiber ratios:

• Series 1: 100% steel fibers (0.1% of total volume).
• Series 2: 75% steel fibers and 25% basalt fibers.
• Series 3: 50% steel fibers and 50% basalt fibers.
• Series 4: 25% steel fibers and 75% basalt fibers.
• Series 5: 100% basalt fibers (without steel fibers).

This experimental approach allowed for a comprehensive evaluation of the mechanical performance of hybrid fiber-reinforced concrete and the identification of the optimal proportion of steel and basalt fibers to achieve improved strength and durability characteristics. [4]

Figure 5. 0.1% bazalt in the amount of steel fiber added a cubic betonni its consistency and indicators

The best compressive strength result among the fiber-reinforced concrete cube specimens containing 0.1% basalt and steel fibers was achieved in the 100P0B series samples. The compressive strength of the 100P0B series specimens reached 49.5 MPa, while that of the control specimens without fibers was 39.95 MPa. Compared to ordinary concrete, the addition of 0.1% steel fibers in the mix increased the compressive strength by 23.9%.

Figure 6. Compressive strength of concrete cubes containing 0.2% basalt and steel fibers.

The best compressive strength result among the fiber-reinforced concrete cube specimens with 0.2% basalt and steel fibers was obtained in the 100P0B series samples. The compressive strength of the 100P0B series specimens reached 51.4 MPa, while that of the control specimens without fibers was 39.95 MPa. Compared to ordinary concrete, the addition of 0.2% steel fibers to the mix increased the compressive strength by 29%. [5]

Conclusion

During the construction and operation of reinforced concrete structures, cracks, deformations, or failures may occur due to impact and vibration-related dynamic loads, reinforcement errors, variations in the strength, elasticity, and stiffness of the materials used, and other similar influencing factors. The causes of crack formation in concrete and their negative effects on the material properties can be mitigated through the application of dispersed reinforcement in concrete.

In the future, one of the modern construction materials to be widely adopted will be dispersed reinforced concrete (fiber-reinforced concrete). Dispersed reinforcement is achieved by uniformly distributing fibers throughout the volume of the concrete matrix.

The properties of fiber-reinforced concrete depend on the type of fibers and concrete used, as well as their quantitative ratio, and are primarily determined by the bond conditions at the phase interfaces.

Compared to conventional concrete, the composite material exhibits a significant increase in strength characteristics due to the presence of fibers that are chemically stable relative to the matrix. When concrete is dispersedly reinforced with steel fibers of 30 mm in length, the compressive strength increased by up to 30% compared to plain concrete. Moreover, when the fiber content exceeded this level, no noticeable decrease in compressive strength was observed.

References:

1. Abbass W., Khan M. I., Mourad S. Evaluation of mechanical properties of steel fiber reinforced concrete with different strengths of concrete //Construction and building materials. – 2018. – Т. 168. – С. 556-569
2. Abdulhadi M. A comparative Study of Basalt and Polypropylene Fibers Reinforced Concrete on Compressive and Tensile Behavior // International Journal of Engineering Trends and Technology – Vol. 9. – 2014., pp. 295–300.
3. Abdujabbarovich X. S., Rustamovich A. A., Rustam o'g'li O. A. Fibrobeton and prospects to be applied in the construction //Web of Scientist: International Scientific Research Journal. – 2022. – Т. 3. – №. 6. – С. 1479-1486.
4. X.S. Abdujabbarovich, A.A.Rustamovich,. Optimization of Cement Stone //Composition With Basalt Fiber Miasto Przyszłości 53, 760-763
5. A.To‘xtaboyev A.Jo‘rayeva A.Axmedov. CURRENT STATUS OF FIBROCONCRETE //Modern Science and Research. – 2024. – Т. 3. – №. 9. – С. 131-134.