|Ludmila Voropai||Vologda State University, Lenina Street 15, Vologda, 160000, Russia|
|Olga Kuznetsova||Vologda State University, Lenina Street 15, Vologda, 160000, Russia|
|Anton Sinitsyn||Vologda State University, Lenina Street 15, Vologda, 160000, Russia|
|Olga Yukhtarova||Vologda State University, Lenina Street 15, Vologda, 160000, Russia|
|Irina Akhmetova||Kazan State Power Engineering University, Kazan, Krasnoselskaya Street, 5, 1420066, Russia|
|Irina Atamanyuk||Hamburg University of Technology, Hamburg 21073, Germany|
|Svetlana Ilyashenko||Plekhanov Russian University of Economics, Moscow 117997, Russia|
The relationship between the performance characteristics (e.g., thermal conductivity, specific density, and compressive strength) of a peat heat-insulating composite and its chemical composition has been established. It has also been experimentally proven that high-lying peat and limestone from the Vologda Oblast deposits correspond in chemical composition and structural features to the requirements for producing heat-insulating materials (HIMs). Composite samples with different chemical compositions were obtained under laboratory conditions. To increase the mechanical strength and setting speed when collecting samples, a stage of peat steaming with water vapor and carbon dioxide was provided. HIM testing using modern analytical methods has proven a relationship exists between the content of high-lying peat, quicklime in samples, and their performance characteristics. The optimal chemical composition for obtaining composites was selected. High-lying peat with a moisture content of 30.0% after steaming and quicklime content of 29.0% ensured the production of a composite with the following indicators: thermal conductivity of 0.041 W/m?°C; average density of 259 kg/m3; compressive strength of 3.02 MPa; and toxicity index of less than 0.5. The established dependence enables simulation of the technological process and obtains materials with the desired properties.
Heat insulating; HIM; Thermal conductivity
Various composite heat-insulating materials (HIMs) are used in the modern construction industry to create comfortable conditions while reducing energy and material costs during the construction and operation of buildings and structures (Gudkov et al., 2019; Latief et al., 2019; Ujma and Umnyakova, 2019; Pavlov et al., 2020). The distinctive characteristics of these materials are high porosity, low thermal conductivity, and average density to ensure their secondary use as sound-absorbing materials.
Increased material porosity results in a lower resistance to aggressive environmental factors, higher fragility, and water absorption. These features must be considered when developing new types of heat-insulating materials, which always include heat insulators, i.e. the components with porous surfaces (Abdel-Rehim et al., 2006; Baetens, 2013; Han et al., 2015; Abdulkareem et al., 2016; Abu-Jdayil et al., 2019). To increase mechanical strength and chemical resistance, binders are added, which can also act as heat insulators, fire retardants, antiseptics, and water repellents (Bekbayeva et al., 2020; Voropai et al., 2020; Yukhtarova, 2020). In construction industry, substances of natural, artificial, and synthetic origin are used as heat insulators (e.g., wood, plant raw materials of fibrous structure, liquid and solid synthetic polymers). Gypsum, limestone, tuffs, Portland cement, slaked lime, quicklime, and dust from construction industries can be used as binders. In recent years, polymers (substances of organic origin) have been used instead of mineral binders (Kopanitsa et al., 2006; 2007; 2010).
When choosing a raw material and its amount, it is necessary to consider not only the ability of materials to form a certain number of pores per unit volume, but also the size of the pores, the degree of their openness or closure, and their shape. It is known that a large-pore, concave structure with elongated pores increases the coefficient of thermal conductivity (Ordonez-Miranda and Alvarado-Gil, 2012). Lower thermal conductivity is registered for materials with larger volumes of air trapped in their pores and smaller amounts of solid matter contained in a unit volume of the composite surrounding the pores. Therefore, to obtain an HIM with low thermal conductivity, high mechanical strength, and low specific density, it is necessary to add binders to the composite that will form a single porous structure with HIM after heat treatment and structure formation in air. In our previous work (Yukhtarova, 2020) we developed a new HIM composition based on high-lying peat, sawdust, and binding components—gypsum and a mixture of organosilicon polymers and oligomers (K-9, PVB, MSN-7. After heat treatment, an HIM with useful characteristics (thermal conductivity of 0.049 W/m·°C; compressive strength of 1.59 MPa; average density of 242 kg/m3) was obtained. The aim of this work is to develop a new technology for producing insulating composite with reduced energy, material costs, and product costs, while maintaining the relevant requirements for construction materials, simplifying the technology required for their production, and resolving issues of production waste disposal. Quicklime setting processes occur at lower temperatures than those of gypsum setting processes, so our newly developed technology will use high-lying peat and quicklime as raw materials. The carbonization and hydration processes of quicklime after steaming cause a more porous and solid structure to be formed with a lower specific gravity than a gypsum-based composite.
This paper presents the production stages according to the new technology and establishes the impact of chemical composition on HIM performance characteristics. The course of the work obtained the following: (i) properties and chemical composition of natural raw materials (i.e., high-lying peat and quicklime); (ii) samples of heat insulators using the newly developed technology; (iii) testing of obtained samples to determine the optimal composition of the initial mixture, heat treatment conditions, and obtained composite properties.
The properties of naturally available materials (high-lying peat taken from the Maega deposit of the Vologda region and quicklime obtained from the limestone of the Belo-Rucheysky deposit in the Vytegorsky district of the Vologda region) were studied. The obtained results prove their value in producing thermal insulation materials.
A new type of HIM based on high-lying peat and quicklime was obtained. In contrast to typical technologies, the formation of a solid structure occurred by processing wet peat samples with a mixture of water vapor and carbon dioxide, then carbonizing quicklime. Testing results proved that replacing gypsum with quicklime while excluding sawdust and a three-component polymer from the composite helped simplify the technology for obtaining HIM while improving HIM characteristics. The relationship between the operational properties of the obtained composite samples and their chemical composition was established. Based on this relationship, it is possible to simulate the technology of obtaining composites. The optimal chemical composition for obtaining composites was selected. The content of high-lying peat with a moisture content of 30.0% (after treatment with water and carbon dioxide) and 29.0% quicklime provided a composite with the following indicators: thermal conductivity coefficient is 0.041 W/m·°C; average density is 259 kg/m3; compressive strength is 3.02 MPa; toxicity index is less than 0.5.
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