Technology and Specifics of the Large-Sized Ceramic Stones Manufacture from the Opoka Rocks

Introduction. At present one of the pressing issues of the wall ceramics production is manufacturing the large-sized ceramic stones with compressive strength of 10–15 MPa, thermal conductivity less than 0.12 W/(m ·°C) and market price of 5000–6000 rubbles per 1 m3, which would be able to compete with the foam concrete blocks. This task can be solved by developing a modern energy-efficient technology of production and using the opoka rocks as the main raw material and the by-products of coal benefication as the fuel-burning additive.

Materials and Methods. The opoka rocks of the southern Russia deposits Nagolnovskoye, Bakanskoye, Shakhtinskoye, Avilo-Fyodorovskoye and the coal slurry produced at the Pyramida LLC were used for the research. The study of the chemical and mineral composition was carried out on the prepared specimens using the standard methods. The study of the ceramic and technological properties of raw material (plasticity, molding water content, degree of fineness, air and firing shrinkage, compressive strength, water absorption) was carried out according to the common methodology, using the test specimens preground to a certain grain-size composition. This was required because, depending on the opoka type, it might not swell or swell slowly on wetting.

Results. Pre-firing technological properties of the opoka rocks and their differences from the traditional, swelling on wetting, clay raw materials were confirmed: increased molding water content, small air shrinkage, low sensitivity to drying. The dependence of the specimens’ density and strength on opoka degree of fineness, firing temperature and the amount of coal slurry in the raw-material mixture has been established. The optimal amount and influence of the coal benefication by-products on the physical and mechanical properties of the firing specimens have been determined. Adding the coal slurry has made it possible to exclude or minimize the use of gas for firing. On the basis of the obtained results a simplified process flow chart for the minimal prime cost manufacture of the large-sized stones has been developed.

Discussion and Conclusion. The proposed process flow chart comprises two basic units of mixture preparing equipment, the molding of products is carried out by semi-solid extrusion, the drying of products is carried out directly in kiln cars, whereas the coal slurry added into the raw mixture is used for firing. These factors and technological methods allow getting the products with the low thermal conductivity, but with the strength 3–5 times higher than that of the similar density foam concrete blocks. The ceramic stones prime cost will amount to 3000–3500 rubbles per 1 m3 of products. The deposits of the opoka rocks and stock of the unused technogenic coal raw material available in Rostov region can make it a centre of the low cost large-sized ceramic stones manufacture and ensure supply of the high-quality wall materials to the southern and central parts of the country.

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