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STUDY OF THE COMPOSITION OF ALKALI CEMENTS AND CONCRETES BASED ON VOLLASTONITE OF KOYTOSH DEPOSIT
Uktam Samaridinovich Sirojiddinov, Samarkand State Institute of Architecture and Construction. Uzbekistan, [email protected];
Kamoliddin Shodiyev, Samarkand State Institute of Architecture and Construction, Uzbekistan, kamoliddin. [email protected].
Abstract: This article describes the properties of binders with the addition of natural wollastonite, the physicochemical basis of hydration activity, the formation of the solidification structure, the principles of rational use in the production of binding building materials. The results of experimental studies on the use of Koytash deposit wollastonite and wollastonite rocks in cement preparation technologies are presented.
Key words: Active mineral additives, wollastonite, wollastonite rocks, binders, fillers, clinker, alkaline concretes
Аннотация: В статье описаны свойства вяжущих с добавлением природного волластонита, физико-химические основы гидратной активности, формирование структуры затвердевания, принципы рационального использования вяжущих строительных материалов. Приведены результаты экспериментальных исследований по использованию волластонита и волластонитовых пород Койташского месторождения в технологиях приготовления цемента.
Ключевые слова: активные минеральные добавки, волластонит, волластонитовые породы, вяжущие, наполнители, клинкер, щелочные бетоны.
Concrete is currently the most widely used material in construction due to the fact that it is a universal product, can change its physical and chemical properties at the expense of additives and mixtures, is relatively inexpensive and durable. However, the onset of drying, low resistance to elongation is a disadvantage of concrete. These defects can be remedied by applying pre-stressed reinforcement or adding active additives from local raw materials to the concrete mix. The quality of concrete in many respects determines their durability, strength and service life in building structures. In some cases, we observe the collapse of buildings and structures in case of non-compliance with the established requirements. This often indicates that the concrete used has high water resistance and low frost resistance. The most convenient way to increase the strength and frost resistance of concrete products is to enrich the cement composition with chemical and natural mineral additives.
INTRODUCTION
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educational, natural and social sciences (~) ISSN 2181-1784
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DISCUSSION AND RESULTS
One of the most promising ways to improve the quality of concrete without significant changes in production technology is the introduction of various additives that actively affect the formation and properties of the cement stone structure during the hydration of cement. By replacing a portion of the cement with other additives, an improved stable system can be created [1]. In this regard, the use of local raw materials, which are available in large quantities in our country, has been identified as the most effective and inexpensive method. One such active mineral supplement is wollastonite. It is used in the construction industry for ceramics, various paints, pigments, asbestos-cement products, in the cement industry, etc. widely used in obtaining. There are more than ten wollastonite deposits in the country, the most productive of which is the Koytash deposit.
Wollastonite is a yellowish, reddish, white or light gray rock. It also has a colorless, absolutely transparent variety that shines like glass and shines like pearls. For natural wollastonite, the elongated shape of the crystal bonds is characteristic and takes on a needle-like appearance when crushed.
Figure 1. Natural wollastonite.
The needle-shaped shape of wollastonite crystals has led to its widespread use in composite materials as a micro-reinforcing component and as an alternative material to asbestos cement, which is considered harmful [2]. Chemical formula of pure wollastonite CaSiO3=Ca3[SiO3O2] (calcium silicate) in its chemical composition 48,3% CaO (calcium oxide) and 51,7% SiO2 (silicon oxide) have. It was also found to contain up to 9% of other minerals (iron, sodium, magnesium, aluminum oxides and other compounds). Due to the fact that the composition has a separate needle-like
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chain structure, wollastonite crystals do not lose their needle-like structure even when crushed. The high strength of quartz crystals ensures the hardness of this mineral.
The reinforcing property of wollastonite is manifested in the fact that due to the unevenness of the surfaces, it mixes with other elements in the composition of the mixture, keeps them around and reduces their mobility relative to each other [3]. Due to the needle-like structure of wollastonite, it is used as a mineral additive in the production of cement, and mainly as a micro-reinforcing filler in the preparation of concrete. It does not lose its needle-like (fibrous) structure even when crushed. One of the important indicators determining the quality characteristics of wollastonite is determined by the ratio of long fibers to the width of these fibers. The efficiency of micro-reinforcement with fibers is determined by the ratio of the length of the crystal l to its diameter d, the size and the degree of strength of bonding with the material. In general, ensuring the l /d ratio at optimal values improves the strength properties of the material. Microamaturation of composite materials with coniferous rocks increases their resistance to abrasion and increases their resistance to thermosets. In addition, the needle-like structure prevents the formation of cracks and the elongation of their trajectory.
Wollastonite is a mineral raw material that is resistant to high temperatures and chemical influences, inert, able to strengthen structures that work to bend and break. According to the requirements for reinforcing fibers, they must have the properties of elongation, bending, compression, stiffness, elasticity and impact resistance. Vollastonite meets all these requirements.
The results of experimental studies on the use of vollastonite in the production of composite cement-based building materials and products showed that its physicochemical composition is similar to other raw materials used in cement production, rheological parameters of concrete - structure formation, strength and deformation properties of solid composites. In modern construction practice, organic (inorganic) fibers are used in order to keep the dimensions uniform, to prevent the formation of cracks, to prevent penetration when drying, to mechanically strengthen various other Portland cement-based products and composite materials. Wollastonite increases the ability of mixtures to retain water, enhances the formation of its structure and completely eliminates its penetration during the solidification process. The main physical and mechanical properties of wollastonite are given in Table 1.
Table 1.
Basic physical and mechanical properties of wollastonite
Identified key indicators
The
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/n results obtained
Actual density,% 2,85
Pile density, kg / m3 1700
Porosity,% 5,02
Humidity,% 0,2-0 ,3
Water demand,% 5,2
Hardness on the Moos scale 4,5
Hydrogen index, rN 8-8,5
Whiteness,% 80-90
Refractive index, Ng 1,631,64
0 Coefficient of thermal expansion 6,51 0-6
1 Harmful additives and components No
2 Attitude to water and alkaline environments Stable
Wollastonite-based concretes have been found to have high resistance to bending and elongation. The geographical location of Uzbekistan, the sharp continental, dry and hot climatic conditions, the use of wollastonite in the production of concrete and reinforced concrete structures made of solid concrete with such properties. In our research, samples from the Koytash deposit were used, and the results of the research obtained confirmed our hypotheses.
Initially, experiments were conducted to determine the possibility of increasing the strength of wollastonite powder by adding it to portland cement. The amount of basic elements in the composition as a filler-supplement CaO - 47%; SiO2 - 51% long fibrous vallastonite 0,08...0,16 fraction was used. During the study, wollastonite powder was replaced with an amount of 10-30% of the cement mass in 400 grade Portland cement, and the following results were obtained (Table 2).
Table 2.
Influence of wollastonite admixture on Portland cement strength
Cement composition Strength limit Relati
/n Portland Portland reached in 28 days, MPa ve amount
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cement, % cement, % (bending / compression)
100 0 5,3/23,0 100/1 00
90 10 5,9/26,0 111/1 13
80 20 5,4/24,0 102/1 04
70 30 4,6/20,0 87/87
The addition of wollastonite increases the water requirement of the cement paste. Experimental results showed that vollastonite had a very low hydraulic activity when mixed with water. Under natural conditions, this mass does not solidify. When vallostonite is mixed with portland cement clinker, the thickening time is accelerated. However, this mixture has low strength and high cold resistance. When the binder content of wollastonite was 10%, its thickening increased from 28% to 34%. When mixed with water, the thickening of the cement paste began after 2 hours and 10 minutes and ended after 4 hours and 10 minutes.
As a result of scientific research, it has been proven that the addition of wollastonite in optimal amounts increases the strength of concrete. It was found that the optimal value that provides the required level of concrete strength is to reduce the amount of portland cement in the mix by 10% and add the same amount of wollastonite instead. This optimal amount also corresponds to the limit of strength for bending and compression.
CONCLUSION
In conclusion, wollastonite powder added to cement clinker as a mineral additive significantly improves its physical and mechanical properties. Such cements have low deformation, resistance to external influences, frost resistance and other technological properties. As a result, the use of fractionated wollastonite sand and gravel as a filler for concrete allows to obtain high-strength concrete. In addition, the use of wollastonite in obtaining concrete with the same strength significantly saves cement consumption in concrete. This shows that wollastonite concretes are also cost effective.
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Uktam, Kamolidin Shodiyev
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