In the process of coal mining, a lot of waste rock is extracted, which eventually accumulates in the form of large mounds reaching tens of meters in height. Such dumps stored on the territory of coal basins are called landfills. Due to coal residues, they can self-ignite and burn for years, releasing large concentrations of carbon monoxide, hydrogen sulfide and other toxic substances into the atmosphere. On average, 4-5 tons of carbon oxides and from 600 to 1100 kilograms of sulfur dioxide are released into the air from one burning dump per day. Such emissions enhance the greenhouse effect, pollute the air and water environment of the region, and harm human health. The use of coal mining waste as a raw material for the production of building materials can be an effective solution to the problem of their disposal. Perm Polytechnic University scientists have studied the possibility of using thermonics as mineral additives for cement and cement-based materials. The proposed approach is capable of increasing the strength of the mortar by 21% compared to the composition without additives.
The negative impact of terricons on the environment is reduced by leveling artificial hills, landscaping and land reclamation, which requires high financial costs – the reclamation of just one terricon can cost tens of millions of rubles. This depends on a number of complex technical, environmental and logistical factors, from artificial improvement of toxic land and control of spontaneous combustion, to the delivery of soil, water and machinery to remote mining areas. Also, it is not possible to implement such methods on all man-made landfills due to poor plant survival.
Another solution is to use coal mining waste in industry. They are a mixture of clay with a small inclusion of coal, aluminum, silicon and iron. Therefore, their secondary use with the separation of useful compounds and application in alloys, carbon fertilizers, asphalt and various building materials is promising.
Perm Polytechnic University scientists have proposed a previously unexplored approach to the use of thermonics as a mineral additive for Portland cements and materials based on them, in particular, concrete.
Experts tested this solution using the example of the territory of the Kizelovsky coal basin, where the volume of man-made waste is estimated at 13 million cubic meters.
Mineral additives in the composition of Portland cement and cement concretes give materials special properties – they increase their strength, water resistance, corrosion resistance, and others. They also allow you to save natural raw materials and increase production by diluting the basic composition. The use of thermonics as mineral additives will solve two issues at once: the environmental problem in coal basins and the problem of resource and energy conservation in cement production.
The polytechnics took samples of burnt and non-burnt terricones, studied their chemical and mineralogical composition, and then conducted an experiment to replace the Portland cement solution with a terricone in the amount of 10, 20 and 30%.
– We determined the chemical composition of the terricones using the fluorescence X–ray spectral method, and the mineralogical composition using the express X-ray quantitative phase analysis method. The results showed that the burnt ceramic consists mainly of quartz, and not the burnt one of kaolinite and quartz with inclusions of coal. The presence of kaolinite in the latter indicates the possibility of its use as an active mineral additive after pre–firing, since this shows a high pozzolanic activity of the material – the ability to react with highly soluble alkalis formed during the hardening of Portland cement, followed by the formation of poorly soluble low-base calcium hydrosilicates, explains Stepan Leontiev, Associate Professor of the Department of Civil Engineering and Materials Science” PNRPU, Candidate of Technical Sciences.
To obtain the mineral supplement, the experts ground the particles to 0.08 mm. The non-burnt ceramic was then fired in a laboratory muffle furnace at a temperature of 700 ° C for 2 hours.
– To evaluate the effectiveness of using the terriconic additive, we prepared a cement mortar consisting of one part of CEM I 42.5N type Portland cement and 3 parts of monofractive quartz sand. As a result, we got 1 control composition without a terricon and 3 compositions each with burnt and non-burnt terricon, which we replaced with 10, 20 and 30% Portland cement. Beam samples were formed from these compounds, which then hardened for 28 days under normal conditions, as well as under conditions of heat and humidity treatment. After hardening, the samples were tested for bending and compression,” says Stepan Leontiev.
Comparing the strength of different polytechnic samples, we determined the effectiveness of using terricon as a mineral additive, as well as its optimal dosage.
– The results showed that replacing up to 30% of cement with burnt grout has very little effect on its strength. While replacing 20% of cement with non-burnt grout increases the strength of the solution by 21% compared to the additive-free composition. This indicates the fundamental possibility of using coal mining waste as mineral additives for cement and cement–based materials,” comments Stepan Leontiev.
The solution proposed by Perm Polytechnic scientists will significantly reduce the number of man-made landfills in coal basins, which will reduce the burden on the environment.
The article is published in the collection “Chemistry. Ecology. Urban Studies”, volume 1, 2025. The research was carried out within the framework of the strategic academic leadership program “Priority 2030”.