ИССЛЕДОВAНИЕ СВОЙСТВ ВСПУЧЕННОГО ВЕРМИКУЛИТA ДЛЯ ПРОИЗВОДСТВA ВЕРМИКУЛИТОВЫХ ТЕПЛОИЗОЛЯЦИОННЫХ ПЛИТ

УДК 721

ABSTRACT

This article presents the physical properties of expanded vermiculite from the Tebinbulak deposit in the Republic of Karakalpakstan, which serves as the primary raw material for manufacturing eco-friendly, energy-efficient, and fire-resistant vermiculite boards with high thermal insulation properties, were investigated. During the research, the grain composition and bulk density of the vermiculite were determined and analysed in laboratory conditions, and their impact on the thermal conductivity coefficient of the finished product was analysed. Based on the research results, the possibilities of producing environmentally friendly, energy-efficient, fire-resistant, and lightweight construction boards with high thermal insulation properties has been demonstrated.

АННОТАЦИЯ

В данной статье исследуются физические свойства вспученного вермикулита месторождения Тебинбулак (Республика Каракалпакстан), который является основным сырьем для производства экологически чистых, энергоэффективных и огнестойких теплоизоляционных вермикулитовых плит. В ходе исследования в лабораторных условиях были определены гранулометрический состав и насыпная плотность вермикулита, а также проанализировано их влияние на коэффициент теплопроводности готовой продукции. На основе результатов исследований обоснованы возможности производства экологически чистых, энергосберегающих, огнестойких и легких строительных плит с высокими теплозащитными свойствами.

Keywords: Expanded vermiculite, vermiculite concentrate, thermal insulation, insulation board, thermal conductivity, bulk density, fire resistance, granularity, expansion coefficient

Ключевые слова: вспученный вермикулит, вермикулитовый концентрат, тепловая защита, изоляционная плита, теплопроводность, насыпная плотность, огнестойкость, зернистость, коэффициент вспучивания.

Introduction. In recent years, comprehensive measures aimed at energy conservation, ensuring environmental safety, and improving fire resistance have been implemented in Uzbekistan. In particular, Decree of the President of the Republic of Uzbekistan No. PQ-57, dated  February 16, 2023, is focused on promoting the use of renewable energy sources and the widespread introduction of energy-efficient technologies; The Decree No. PQ-100, dated March 11, 2025 provides for the fundamental reform of the system for supplying residential and commercial buildings with thermal energy, as well as the implementation of measures to increase the energy efficiency of buildings. In addition, the “Strategy for the Modernisation and Innovative Development of the Construction Industry (2021–2025)”, approved by the Decree of the President of the Republic of Uzbekistan No. PF-6119 of 27 November 2020, is also aimed at promoting the introduction of energy-efficient materials. Moreover, the Decree No. PF-5863, dated October 30, 2019, on the approval of the “Concept for Environmental Protection of the Republic of Uzbekistan until 2030,” as well as Resolution of the Cabinet of Ministers No. 327, dated May 27, 2021, provide for the expansion of the raw material base through the deep processing of natural and mineral resources of the Republic of Karakalpakstan, as well as the improvement of activities related to the protection, reproduction, and rational use of natural resources. Within the framework of these regulatory documents, it is envisaged to improve the efficiency of vermiculite raw material extraction and its deep processing, including increasing the efficiency of extracting the required vermiculite concentrate from raw materials, improving product quality, and developing and implementing investment projects and targeted measures aimed at introducing environmentally friendly and energy-efficient new types of construction materials [1].

It is well known that in the modern construction industry a wide variety of thermal insulation materials are currently in widespread use. To ensure large-scale production of such functional modern construction materials and to meet the growing demand, it is essential to utilize low-cost natural raw materials with sufficient long-term reserves. In this regard, vermiculite-based boards, which are widely used in the construction industry, are considered one of the most effective and environmentally friendly materials providing thermal insulation and fire safety. Therefore, the global demand for this material is increasing, along with stricter regulatory requirements for their quality indicators in terms of energy efficiency and fire safety standards.

The technological process of industrial-scale production of vermiculite boards first requires the separation of vermiculite concentrate from the raw vermiculite ore extracted from deposits. In this process, the mined coarse-grained vermiculite-containing natural raw material is crushed in special crushers and separated into vermiculite concentrate of a specific size, as well as iron compounds, sand, and other inorganic mineral impurities.

In the next stage, expanded vermiculite is obtained through thermal treatment of the vermiculite concentrate at high temperatures (800–1000°C) by means of a so-called “thermal shock,” i.e., a rapid increase in temperature. As a result of the abrupt release and evaporation of water contained within the raw material structure, the vermiculite expands significantly, increasing its volume by 10–16 times and forming a new highly porous structure.

Based on expanded vermiculite, vermiculite boards are produced from the prepared concentrate supplied for manufacturing. The main technological processes in the production of vermiculite boards include mixing expanded vermiculite particles with appropriate inorganic or organic binding agents (typically liquid glass or special polymers); forming the prepared mixture into plates of the required size and thickness under relatively low pressure; and drying the shaped plates in special drying chambers to achieve the required mechanical strength. Finally, the quality characteristics of the produced materials are controlled in accordance with standardised testing methods defined by regulatory requirements.

In addition, where necessary, large-sized vermiculite boards may be further processed by cutting them into smaller dimensions according to specific requirements.

Vermiculite boards possess several advantages compared to conventional thermal insulation materials (such as expanded polystyrene or mineral wool), including superior thermal insulation performance, high fire resistance, environmental friendliness, and resistance to various microorganisms. The thermal conductivity coefficient of vermiculite is very low (W/m·K), which significantly contributes to reducing heating and cooling costs in buildings. These boards can withstand temperatures up to 1100°C and, unlike many other materials, do not emit toxic substances during fire exposure. Furthermore, they are resistant to decay, mould growth, insects, and rodents over long-term service life [2-3].

In construction practice, vermiculite boards are widely used for thermal insulation of internal and external walls in multi-storey buildings to reduce heat loss; fire protection of metal and reinforced concrete structures; manufacturing of fire-resistant doors and partitions; lining of high-temperature industrial equipment and household fireplaces; as well as thermal and acoustic insulation of floor structures and cavities in building foundations.

In the Republic of Uzbekistan, the regulatory requirements for vermiculite boards and their applications are defined in QMQ 2.01.04-2018 (“Construction Heat Engineering”) and the updated GOST 12865-2025 (“Expanded Vermiculite. Technical Specifications”).

Materials and Methods. The experimental and laboratory investigations presented in this study were carried out using a sample of vermiculite raw material industrially extracted from the Tebinbulak deposit located in the Republic of Karakalpakstan. The study of the extracted vermiculite concentrate was performed according to a predefined sequence of research tasks [5], as follows:

-sieving of vermiculite concentrates and separation into fine and coarse fractions;

- determination of the bulk density of the vermiculite concentrate;

- determination of the specific gravity of thermally expanded vermiculites;

- determination of the bulk density of expanded vermiculite;

- determination of the granulometric characteristics of expanded vermiculite;

- comparative investigation and analysis of the physico-technical properties of thermally expanded vermiculites [6–7].

Results of Experimental Investigations. Vermiculite is a mineral belonging to the mica group, characterized by its ability to split into thin and flexible lamellar plates. It is classified as a calcium–magnesium layered aluminosilicate. The chemical composition of vermiculite is complex and variable. The presence of adsorbed (bound) water in its structure significantly alters its physicomechanical properties. For this reason, it is classified as a group of hydrated micas, i.e., hydromicas. This hydration property is responsible for the thermal expansion (exfoliation) of the mineral under heat treatment, leading to a significant volumetric increase [8].

When liquid glass is used as a binding agent, it is possible to obtain fire-resistant and thermal-insulating vermiculite boards based on expanded vermiculite that can withstand high temperatures.

Vermiculite is classified into the following fractions according to grain size: 1) fine – 0–0,63 mm; 2) medium – 0,63–5 mm; 3) coarse – 5–10 mm [9].

The experimental studies were conducted using vermiculite raw material industrially extracted from the Tebinbulak deposit located in the Karauzyak district of the Republic of Karakalpakstan. Vermiculite concentrate fractions used in the experiments included coarse fractions of 5,0–10,0 mm; medium fractions of 1,6–2,2 mm, 2,0–3,0 mm, and 3,0–4,0 mm; and fine fractions of 0,8–1,6 mm.

a)                                                                    b)

Figure 1. a) Vermiculite raw material extracted from the Tebinbulak deposit, Republic of Karakalpakstan; b) sample of enriched vermiculite concentrate

In general, the chemical formula of vermiculite can be expressed as Mg⁺², Fe⁺²,Fe⁺³)₃ [(Al,Si)₄O₁₀]·(OH)₂·4H₂O. However, due to the presence of various impurities in its structure, this formula may also appear in modified forms. The chemical composition of vermiculite mineral typically includes SiO₂ (33–36%), TiO₂ (0,47%), Al₂O₃ (6–8%), Fe₂O₃ (5–7%), FeO (0,2–0,29%), and MgO (between 4–25%). In some cases, oxides such as CaO, MnO, NiO, and others may also be present. Table 1 below presents the chemical composition of the vermiculite concentrate from the Tebinbulak deposit used as the raw material in the research:

Table 1.

Chemical composition of vermiculite concentrate from the Tebinbulak deposit, (wt.%)

In the production of thermal insulation vermiculite boards, it is necessary to determine the void volume (porosity) between particles of fine and coarse vermiculite concentrate and expanded vermiculite, as well as to calculate the average density of both vermiculite concentrate and expanded vermiculite fractions.

The bulk density of expanded vermiculite and vermiculite concentrate was determined in accordance with the requirements GOST 12865-2025, based on the free-flow filling method using a graduated measuring cylinder.

The vermiculite sample is poured through a special funnel into a pre-weighed measuring cylinder from a height of 10 cm until a conical heap is formed. After the cylinder is completely filled, the excess material is carefully removed without compaction using a steel ruler, leveling the surface by moving from the center of the cone towards both sides along the cylinder rim. The filled cylinder is then weighed on a laboratory balance with an accuracy of 0,1 g to determine the mass of the sample. During the determination of average density, the measuring cylinder containing the sample must not be shaken, as this may lead to compaction of vermiculite particles and result in inaccurate measurements [10, 11].

a)                                                                          b)

Figure 2. a) Vermiculite concentrate; b) determination of the bulk density of expanded vermiculite

Experimental resarch and measurements were repeated at least five times for each sample, and the arithmetic mean value was taken as the final result. The bulk density of free-flowing materials was determined in accordance with GOST 12865-25. The results of bulk density determination for vermiculite concentrate are presented in Table 2:

Table 2.

Results of bulk density determination of vermiculite concentrate (1 L measuring cylinder)

The obtained results (Table 2) indicate a linear relationship between the particle size of vermiculite concentrate and its bulk density. As the particle size increases from 0,8–1,6 mm to 8,0–10,0 mm, the density value increases from 754,6 kg/m³ to 1206,8 kg/m³. This phenomenon is related to the arrangement of the voids between the granules and the material’s granulometric composition. In the following Table 3, the results of bulk density determination for expanded vermiculite are presented:

Table 3.

Results of bulk density determination of expanded vermiculite (in a 1 L measuring cylinder)

The expansion coefficient of expanded vermiculite is one of the most important parameters of the raw material and represents a key factor determining the quality and technical properties of finished construction materials. Table 4 below presents the relationship between the expansion coefficient of expanded vermiculite, particle size, and bulk density.

Table 4.

Expansion of vermiculite concentrate and expansion coefficients of expanded vermiculite

Conclusion. The experimental research carried out made it possible to determine that the granulometric composition of vermiculite concentrate has a significant effect on its physical and thermal-technical properties. In particular, it was found that as the particle size increases from 0,8–1,6 mm to 8–10 mm, the bulk density of the vermiculite concentrate increases from 754,6 kg/m³ to 1206,8 kg/m³. In other words, coarse fractions exhibit higher density compared to fine fractions. . However, after expansion at high temperature, the opposite situation is observed in the vermiculite sample. Specifically, as particle size increases, the bulk density of expanded vermiculite decreases from 293,7 kg/m³ to 106,6 kg/m³. This is linked to the layered structure of vermiculite: during heating, the evaporation of bound water in the crystal lattice generates internal pressure, causing the particles to expand in volume.

In addition, this effect can also be explained by the higher content of heavy impurities such as iron compounds and sand particles in coarse fractions of vermiculite concentrate.

In coarse grains, this process proceeds more intensively, resulting in a more porous, low-density structure. The increase in the expansion coefficient from 2,5 to 11,3 confirms that granulometric composition is the primary factor. The results of the resarch indicate that the granulometric composition of the vermiculite concentrate has a decisive influence on its expansion properties and the density of the final product. This makes it possible to use them as a highly efficient raw material for enhancing thermal insulation properties and for producing vermiculite boards, lightweight concretes and composite materials based on expanded vermiculite.

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