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BASIC ISSUES OF THE THEORY OF HYDROPHOBIZATION OF CEMENT SYSTEMS BY ADDITIVES OF PRODUCTS OF PETROCHEMICAL SYNTHESIS
Teshaboeva Nodira Djuraevna teshaboyevanodira 1953 @ gmail.com Senior Lecturer, Department of Buildings and
Structures of Construction Ferghana Polytechnic Institute, Uzbekistan.
Annotation: The flock provides, тhe most important scientific and technical problems of cement-concrete technology include, in particular, an increase in the workability of concrete mixtures with a decrease in the water-cement ratio and a decrease in cement consumption, as well as an increase in frost resistance and durability of concrete products.
Key words: durability, concrete, products.
Аннотация: Флок обеспечивает, к важнейшим научно-техническим задачам цементобетонной технологии относятся, в частности, повышение удобоукладываемости бетонных смесей при снижении водоцементного соотношения и снижении расхода цемента, а также повышение морозостойкости и долговечности бетонных изделий.
Ключевые слова: прочность, бетон, изделия.
Previously, technical surface-active additives in cement-concrete technology were mainly natural products, now in connection with the accelerated development of chemistry in our country, products of petrochemical synthesis - synthetic fatty acids obtained by oxidation of paraffin [10] from bottoms residues, as well as oxidized petrolatum.
The nature of the action of additives - petrochemical products in cement systems largely obeys the general laws established earlier in the study of hydrophobic-plasticizing substances from among natural higher fatty acids and petroleum acids [13].
So, the intensifying effect can be achieved by the use of chemical additives -surfactants, additives for grinding cement clinker is explained not only by the effect of the adsorptive decrease in hardness, established at the time by P.A. sticking them to chalking bodies and mill walls.
INTRODUCTION
DISCUSSION AND RESULTS
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Surface - active additives, as shown by VA Kireev, generally act especially effectively on the finest particles of powders [6]. In addition, the additives reduce the friction between the individual cement grains and thereby contribute to its tighter packing, affecting the increase in the bulk density of the cement in the mill. Therefore, the ratio between the weight of the grinding bodies and the volume of the grinded product changes favorably, which in turn accelerates the grinding.
A decrease in the hygroscopicity of cements containing a hydrophobizing additive occurs due to the fact that a thin chemisorption layer is formed on the cement grains of oriented surfactant molecules, which are converted by hydrocarbon radicals into the external environment. The hydrophobized cement powder becomes practically non-hygroscopic. Therefore, hydrophobic cement is able to retain its activity during long-term storage even in humid conditions.
It is known that ordinary cement of medium grades loses up to 25-30% of its activity within 2-5 months of storage. High-grade cements deteriorate even faster. So, for example, "600" grade fast-setting cement sometimes loses about 25% of its initial activity after a month's storage.Therefore, the high initial activity of finely ground, fast-hardening cements, the production of which in our country is expanding every year, is practically not fully utilized, if the cement has been on the road or in the warehouse even for a relatively short time.
This kind of loss in cement activity is usually not considered, but it causes significant damage, as can be seen in the following example. If from 1 ton of cement grade "500" it is possible to prepare 4.5 m3 of concrete grade "150", then with a loss of cement of 20% activity it will be possible to obtain from 1 ton of ordinary cement only 3.75 m3 of concrete of equal strength. In the case of using hydrophobic cement, such an overconsumption of 20 percent of the cement can be avoided. Water-repellent surfactants visibly plasticize cement systems.
The increase in the mobility of mortar and concrete mixtures when using cement with hydrophobizing additives should be explained mainly by the lubricating effect due to the "layered" structure of thin oriented films. Polarly active groups of hydrofibrating substances tend to associate, there are strong power bonds between them. Hydrocarbon chains, on the other hand, have a weak force field. For these reasons, the planes formed by the methyl groups of hydrocarbon radicals are slip planes;
Slip occurs only when there are external forces tangential to these planes. Such efforts occur when mixing mixtures, when they move through pipes, as well as when laying and compacting freshly cast concrete. During these operations, there is a more
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or less frequent movement of particles between the surfaces of solids (sand, gravel, slag, walls and blades of a mortar mixer, pipeline walls, etc.), is in relative motion.
In this case, the force field of clinker minerals, which is intense with respect to water, as well as aggregates on which calcium ions were adsorbed, is for a certain period of time (until the setting of cement has begun) partially neutralized and replaced by a much weaker field of methyl groups that form the ends of hydrocarbon radicals. Therefore, the friction caused by molecular attraction is reduced.Oriented molecules are capable of sliding over each other, resisting deformation in all other directions.
The plasticizing effect of additives of the hydrophobic type is manifested the sharper, the thinner the cement paste layer, i.e. with the use of such additives, the effect of the actual plasticization is most significant in lean systems, characterized by a developed surface of the filler grains. Therefore, the water demand of hydrophobic cement in concrete (especially lean) and in mortar mixtures is less than that of ordinary cement; the consumption of cement in concrete can sometimes be reduced by 10-12%.Reducing the consumption of cement in concrete entails not only economic benefits, but also an improvement in some properties of concrete structures. So, for example, with a reduction in the specific amount of cement, the exotherm of concrete decreases.
It is known that increased heat generation causes thermal deformations and unevenly distributed stresses in monolithic concrete, which leads to the formation of cracks. With a reduction in cement consumption, shrinkage deformations in concretes and concrete products also decrease. Consequently, the reduction in cement consumption is not only an economic, but also a technical factor. One of the main features of concretes with the addition of hydrophobic substances is the formation of a homogeneous fine-crystalline structure.
As a result of crushing and homogenizing the structure of the cement stone, the gaps between the solid particles are reduced, which, however, does not change the total volume of this system, but only reduces the pore cross section.
By reducing the cross-section of the pores, the orientation of thin layers of water near solid surfaces is of particular importance, which complicates the migration of moisture. Slowing down the penetration and movement of water improves the properties of materials in relation to the action of corrosive liquids and freezing. Thus, hydrophobizing additives have a beneficial effect on reducing capillary absorption, water absorption and water permeability, as well as on increasing frost resistance. In hydrophobized systems, such a material exchange between the cement stone and
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aggressive substances in the environment is hampered. The limitation of harmful acts of interaction of concrete with the environment should help to increase its durability.
These are brief theoretical explanations concerning the essence of the action of petrochemical hydrophobizing additives on cement systems. As technical surfactants, we used oxidized petrolatum, hereinafter referred to as OP, a number of fractions of synthetic fatty acid, hereinafter referred to as FFA, distillation residues of synthetic fatty acids, hereinafter called distillation residues, and a surfactant additive - OKO-2, used in the form of a water-soluble emulsion.
All these additives were introduced during the grinding of the clinker. Sulfite-Alcohol Barda / SSB /, often used in the manufacture of hydro-technical concretes, was used in a number of experiments in the form of a combined additive with OP and FFA. Sulfite - alcohol stillage was introduced directly with mixing water. In a number of experiments, hydrophobic cements based on soap (MN) were used for comparison.
The clinker was ground in laboratory ball mills with a volume of 20 and 100 liters. Preparation, shaping and testing of mortars and concretes were carried out in accordance with the current state standards. Where necessary, detailed descriptions of sample preparation and testing procedures are provided in the appropriate sections.
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CONCLUSION
REFERENCES
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