Master in Construction Materials, Products and Structures

Yeltayev Askhat Talgatuli

L.N.Gumilyov Eurasian National University, Kazakhstan

The production technology of construction ceramics

Abstract. In modern economic conditions, the construction of facilities and the production of building materials tend to unite into a single construction complex. Among all the variety of wall building materials facing ceramic bricks which differ in architectural expressiveness and durability are still in demand and in the future will retain their positions in the market. Obtaining facial ceramic products at brick factories in Kazakhstan is associated with a whole complex of problems. One of the first places in the importance is the lack of any significant reserves for high-quality clay raw materials. Very important for the improvement of technology is reliable information about properties of clay. Meanwhile, even with the construction of modern plants in the period preceding the design and procurement of equipment, careful scientific studies of clay raw materials and the development of optimal technology parameters are not always conducted.

Key words: brick, resource-saving, energy-saving, loam, coal, granulated slag.

Actuality of work. The issue of improving the quality of ceramic materials remains an important task for not only because of worn out equipment, but more often because of insufficient knowledge of many factories in the country. Old factories often produce poor quality products and raw materials and weak development of the main technological regimes. The issues of technology are not given proper attention, and they are often based on scientific possibilities of a century ago.

Even with the construction of modern plants in the period preceding the design and procurement of equipment, careful scientific studies of clay raw materials and the development of optimal technology parameters are not always conducted. This occurs either by the inertia of thinking, or, based on the opinion that there would be good equipment, and the quality of the products itself will come, or for some other reasons. The same can be said about the reconstruction of existing plants.

In the former Soviet Union, it was customary to conduct laboratory and semi-plant trials of clay raw materials. But often laboratory studies reduced to a formal minimum, which did not allow to identify and use all the potentialities of clay raw materials. Accordingly, the quality of products manufactured in the future was relatively low.

In industrially developed countries, the problem of detailed research of raw materials has traditionally been paid much attention, which often makes it possible not to conduct semi-plant tests and debug the technology directly at the start-up of the plant, relying on careful and complete laboratory studies of clay raw materials. The total cost of such research can reach several tens of thousands of dollars, but these costs pay off with high quality products.

The purpose of the article is to develop a resource and energy-saving technology and to study the properties of semi-dry wall ceramics on the basis of loess loams using mechanically activated composite additives.

To achieve this goal, it was necessary to solve the following tasks:

- establish patterns of structure and phase formation in ceramic masses with mechanically activated compositional additives depending on the firing temperature;

- to investigate and develop rational technological modes of production of wall ceramics with mechanically activated composite additives;

- carry out pilot-industrial tests and development of semi-dry pressing technology using loess loam and mechanically activated composite additives.

In connection with the deficit of high-quality clays, one of the most important tasks is the possibility of using a low-grade, widely distributed clay raw material in all regions of the country without sacrificing the quality of the cobalt product. The solution of this problem requires modification by additives and use of various types of activation of raw materials, which to a certain extent contribute to quality improvement. In the process of mechanical activation, mineral raw materials are subjected to intensive mechanical action in grinders-activators, where mineral particles are not only crushed, but also undergo complex structural changes. As a result of these changes, raw materials accumulate a significant part of the applied mechanical energy and become more reactive in various technological processes. The choice from the point of view of rational use, grinders as mechanoactivators is of great importance.

There are many ways of mechanical activation by finely grinding clay raw materials, for example, grinding in ball and vibrational millstones. In batch ball mills, it is possible to grind the materials in dry and wet ways. In our opinion, the mechanical activation of raw materials on these milling equipment has a positive perspective from the point of view of their practical implementation directly in production conditions, since this equipment has proved itself in the technology of cement production, lime-bricks, and in the production of various types without firing binders substances. Proceeding from objective analytical studies, the ball mill was chosen as the most widespread and accessible type of mechanoactivator for carrying out experimental work.

To solve the problems of complex use of mineral raw materials and industrial wastes in ceramic technology, the method of plastic molding is not acceptable. The production of semi-dry pressing products, which includes, as a rule, the initial preparation and dosage of raw materials, drying, grinding, sieving, dampening and mixing of the powder press, pressing, drying and firing products on the kiln car, is characterized by a number of disadvantages and advantages. Proceeding from this, for today the following ways of obtaining high-quality ceramic products of equidistant structure from the widespread poly-mineral clay raw materials by the method of semi-dry pressing are outlined. It:

- development of special technological methods for processing raw materials, depending on its structural and mechanical properties;

- obtaining more dense press powders of the specified granulometric composition and fraktsionnoy humidity;

- selection of the optimal composition of the charge, ensuring the production of caked high quality crust;

- Pressing of products from press powders with moisture below critical, ensuring the integrity of compacts at high-speed drying and firing regimes;

- selection and development of pressing devices, pressing modes.

The limited availability of high quality clay raw materials in the Republic of Kazakhstan requires a scientifically grounded approach to the rational use of these raw materials in compositions with mechanically activated composite additives that include industrial wastes for the production of quality and competitive products.

Investigated materials and methods for evaluating their properties.

As the main raw material for the development of a mechanically activated composite additive, a blast-furnace granular slag of the Karaganda metallurgical plant was used as JSC "ARSELOR MITTAL Temirtau" (Temirtau city). Blast-furnace granular slag is a granular material of gray color. The size module is 3.9 - 4.1.The granular composition of the slag is characterized by the ratio of the fractions shown in Table 1.

Table 1 - Granulometric composition of blast-furnace granulated slag

Diameter of sieve holes, mm	2,5	1,25	0,63	0,315	0,14	less 0,14
Sieve residue, %	14-17	35-37	26-30	14-17	2-5	2-4

The chemical composition of blast-furnace granulated slag of the Karaganda Metallurgical Combine is presented in Table 2.

Table 2 - Chemical composition of blast-furnace slag

Name of raw materials	Oxide content, wt.%
	SiO2	Al2O3	Fe2O3	CaO	FеО	MgO	SO3	Na2O	K2O	CO2	TiO2	ShO	п.п.п.
Granulated blast furnace slag from Karaganda Metallurgical Plant	40,62	16,24	0,19-0,52	42,11	0,43	5,33-10,39	1,66	0.36-1,5	0,42-1,32	-	0,62-0,88	0.11-1,37	0,92

According to the classification of clay-sandy rocks, the loams of the Kaskelen deposit belong to the class of silty fraction (0.50-0.01 mm), an average of 62.4%. The content of clay particles with a particle size of less than 0.001 mm averages 14.9%.

Loams are: according to the content of Al2O3 * TiO2 in the calcined state, to the group of acid rocks, since their sum is 12.66 i.e. less than 15, Fe2O3 content - to the raw materials with a high content of coloring oxides (Table 3). On the content of finely dispersed fractions - to coarsely dispersed raw materials.

Table 3 - The chemical composition of the loam of the Kaskelen deposit

Name of raw materials	Oxide content, wt.%
	SiO2	Al2O3	TiO2	CaO	MgO	Fe2O3	P2O5	F	SO3	CO2	Na2O	K2O	p.p.p.
Loam from Kaskelen	55,09	12,00	0,66	11,5	2,24	5,29	0,15	-	0,07	-	1,18	2,33	9,78

The plasticity of the loam is 7-8. As the second component, the coal of the Karaganda coal basin, which is the main in Kazakhstan for the extraction of coking coal, was used to create the composite additive. The color of coal varies from brown to intensely black, shine from matte to glass, hardness on the Mohs scale is from 1 to 5, density is from 0.92 to 1.7 g/cm3. The coal of the Karaganda basin is characterized by the heat of combustion for the fuel mass from 8000 to 8300 kcal/kg.

       To evaluate the properties of samples and conduct detailed studies, standard techniques, modern instruments and equipment were used.

The frost resistance test was carried out in accordance with GOST 7025-91. The strength of the samples was tested in accordance with GOST 530-2012. Firing samples-cylinders with a diameter of 5, a height of 5 cm and beams (4x4x16 cm) was carried out in a special electric muffle furnace. The firing of natural products was carried out in a special electric furnace. The determination of the complex of physic-mechanical properties of the samples was carried out according to standard methods.

Composition, structure and properties of facial ceramic bricks using loess loams and mechanically activated composite additives

One of the effective techniques for producing high-quality ceramic products is the introduction of various thin-milled additives. At the same time, ceramic raw systems containing composite additives are still poorly understood. In this connection, complex investigations of the ceramic masses on the basis of loess loams in a composition with mechanically activated composite additives were made, taking into account the specific properties of specific raw materials and in the interrelation of the dominant factors of each technological transformation (pre-treatment of raw materials, molding, drying, roasting).

The loess loam of the Kaskelen deposit of the Almaty region as the main clay raw material was chosen as the raw materials to be studied, and blast-furnace granular slag and coal were chosen to create a composite mechanically activated additive. To achieve this goal, raw materials were first dosed according to the experimental design matrix, the preparation of the composite additive blast-furnace granulated slag-coal was mechanically activated by co-grinding in a laboratory ball mill to a specific surface of 1500-2000 cm2 / g.

An analysis of the change in the properties of the samples under study from the content of the composite additive made it possible to optimize the compositions of the ceramic mass. For the optimal compositions of the ceramic composition, mixtures having high indices of the investigated properties were adopted. These requirements correspond to compositions of the ceramic mass located in the region limited by the following limiting concentration of components, mass%: loess loam 79.0-84.0; Composition additive 16.0-21.0 As the results of the study show, with an increase in the content of mechanically activated granulated blast furnace slag and coal due to a decrease in the content of loess-like loam, there is an increase in compressive strength and bending strength, and also frost resistance. In this case, the greater the specific surface area of the ground composition, the higher the parameters of the indicated properties under study. For example, the increase in compressive strength and bending with a change in the specific surface from 820 to 2100 cm2 / g is from 10.2 to 17.4 MPa and from 2.6 to 4.0 MPa, respectively. It should be noted that the increase in compressive and flexural strength is generally more than 50%. With an increase in the specific surface area of the composite mixture, a significant increase in frost resistance is observed. Comparative analysis of changes in these properties compared to samples based on pure loam general showed that an increase in compressive strength is 61%, with a bend of 79%, and an increase in frost resistance from 16 cycles to 49 cycles, i.e. an average of 3.5 times.

As for changes in the average density, although the specific surface area of the added composite additive assumes an increase in the average density of the samples due to the increase in the packing density of the raw system as a whole, there is a significant reduction in the average density of heat-treated samples based on the ceramic composition studied. The decrease in the average density in comparison with the average density of samples based on pure loam is from 1840 to 1700 kg / m3, which is about 8%, that is, the mass of 1 m3 of the product on the basis of the test samples is easier compared to 120-140 kg.

Conclusion

The main regularities of the change in physical and mechanical properties at different ratios of ceramic compositions before and after heat treatment are revealed. Before the thermal treatment, the dependencies of the sensitivity coefficient to drying, raw strength, air shrinkage and average density of the molded samples were established. In addition, the influence of humidity and pressing pressure on these properties was investigated.

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