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31RAW MATERIALS AND OPTIMAL COMPOSITIONS FOR NEW GENERATION CELLULAR CONCRETE
Bakhromjon Adhamovich Dilfuza Tillavoldiyevna Madinakhon Tolib qizi Otakulov Sobirova Yokubova
Fergana Polytechnic Institute
ABSTRACT
This article is devoted to the issues of raw materials and the optimal composition of aerated concrete such as aerated concrete and aerated concrete. In addition, information on strength, thermal conductivity, porosity, conditions of hardening, bearing capacity, frost resistance, water absorption, fire resistance, environmental friendliness and durability of the material are given.
Keywords: improving the energy efficiency of buildings and structures, energy resources, thermal insulation, energy efficiency in the design of buildings, increasing the thermal insulation of wall structures.
Aerated concretes are artificial stone materials consisting of a hardened binder with air cells (pores) evenly distributed in it. According to the method of production, cellular concrete is divided into foam concrete, aerated concrete and foam gas concrete. By the type of binding agent, cellular concretes are divided into the following types:
- on cement (foam concrete and aerated concrete);
-On lime binder (foam silicate and gas silicate);
- on gypsum binder (foamed gypsum and gas gypsum).
In addition, when receiving aerated concrete, gypsum-cement-pozzolanic binder and a mixed binder consisting of Portland cement and lime can be used. (Table 1)
Table 1
Characteristics and material requirements
Material Parameter Requirement of regulatory documents Name of normative documentation
Cement. (CEM I 42.5 N.B) Setting time beginning end NG False gripping C3A C3S > 60 min - 29% No <8% GOST 31108-2016 8
Ground quicklime CaO + MgO Quenching >80% >67°C GOST 9179-77
(II grade temperature Blanking time Sieve passage 0.09 Overburn 6-13 min <5%
Lump lime (II grade CaO + MgO Quenching temperature Blanking time >80% >67°C 6-13 min GOST 9179-77
Quartz sand (class II, fine, very fine) SiO2 Size module Humidity PGI >85% 1,0-2,0 <5% GOST 8736-2014
Ground gypsum Ca2SO4 Sieve residue 0.2 Humidity 64-76% GOST 23789-79
A porous structure in the production of foam concrete is created by mixing solutions with previously prepared foam or by introducing a foaming agent directly into the solution, which contributes to the entrainment of air bubbles inside the solution during its intensive movement with or without vibration treatment. To obtain stable foam in industry, the following main types of foaming agents are used: -Glue rosin;
- resinaponin;
- aluminosulfonaphthenic;
-KISK, consisting of rosin, lime, casein glue and SSB.
Aerated concrete is represented by a complex multicomponent system with a large number of influencing input and output parameters. almost all properties are functionally dependent.
The main operational characteristics of the developed formulations:
Sizes - the sizes of aerated concrete blocks (gas and foam concrete) differ markedly. Depending on the purpose, their dimensions can be as follows:
- smooth base unit: width - 200-500 mm, height - 200 mm, length - 600 mm;
- blocks for partitions: width - 75-150 mm with the same length and height;
- blocks for lintels: width 250-400 mm, with a height of 200 mm and a length of 500 mm.
In addition, a variety of complex shaped blocks are available.
It should be noted that the highest requirements are imposed on the geometric dimensions of the heat-insulating blocks: deviations of no more than 1.5 mm are allowed. This is due to the way of laying - on a special adhesive to prevent the
appearance of cold bridges.It is not difficult to make blocks of a different size from standard modules: cellular concrete is just as docile in processing as wood and is perfectly connected with ordinary nails.
Properties of materials: Density - the most important property of aerated concrete (including blocks and slabs) is thermal insulation, it depends on the density and on the degree of porosity. The nature of the binder and the conditions of hardening have practically no effect on this factor. Depending on the number and volume of closed pores, the thermal conductivity of aerated concrete blocks will increase or decrease. The strength and thermal conductivity of the material appear to depend on the degree of porosity. (table 2).
table 2
Strength and thermal conductivity of the material depending on the degree of porosity
Porosity,% Density, kg / cubic meter Compressive strength, MPa Thermal conductivity, W / (m.K)
50 1100-1200 10-15 0,33-0,40
60 900-1100 5-12 0,24-0,30
70 700-800 2,5-5 0,17-0,22
80 400-600 1,2-4 0,10-0,14
90 200-300 0,7-1,2 0,06-0,08
95 200 0,4-0,7 0,06
The density of cellular materials is determined in a dry state by compressing a cube with an edge of 20 cm, kept for the prescribed 28 days. Marked with the letter D, the numbers given indicate the density of the material in kg / m3. Aerated concrete includes the following brands: D 200, D 250, D 300, D 350, D 400, D 500, D 600, D 700, D 800, D 900, D 1000, D 1100.
Strength. The grade of a given material or its strength determines the compressive strength of the material. The sample for research is the same concrete cube after hardening. Classes of foam concrete: B 0.35; B 0.5; B 0.75; IN 1; 1.5; IN 2; 2.5; 3.5; AT 5; 7.5; AT 10 O'CLOCK; B 12.5; B 15. The coefficient indicates the ultimate pressure that the material can withstand without destruction. So, for B 0.35 this pressure is 0.5 MPa.
Curing conditions. The strength and, accordingly, the strength class is significantly influenced by the nature of the binder and the conditions of hardening. So, autoclaved concrete exceeds the strength of the same material hardened in natural conditions by almost 6-8 times. An equally important factor is the amount of mixing water. The excess volume does not bind, but forms cavities and interlayers, which, of course, intensively reduces the indicator. Therefore, a compulsory stage in the manufacture of the material is the vibration effect both during the preparation of the solution and during the swelling period.
The load-bearing capacity of a material is determined by its density. So, heat-insulating materials based on cellular concrete cannot be used in the construction of load-bearing walls, supports or floors of any plan, while the structural version with a density of 1100 kg / m3.used for the construction of both walls and panels.
Frost resistance significantly affects the durability of materials, therefore, the number of freezing and thawing cycles when saturated with water is a very important indicator. According to this parameter, the cellular material is inferior to ordinary concrete, since the pores, nevertheless, absorb moisture to a greater extent. To reduce absorption, mixtures are produced with the maximum number of closed pores. The frost resistance classes are as follows: F15, F25, F35, F50, F75. The number means the number of cycles that the material transfers without destruction. Considering that aerated concrete is mainly used for external thermal insulation, the need for a protective or decorative layer is obvious.
The amount of water absorption. The amount of water absorption depends on the type of binder. Thus, aerated concrete based on Portland cement absorbs less water than based on lime or gypsum. If the first option is allowed to be used in rooms with humidity up to 50%, then the gypsum material requires protection in any case. The fire resistance of cellular concrete is higher than usual, which, nevertheless, does not allow the use of materials in conditions where strength is required at a constant high temperature. The thermal stability or heat resistance of foam concrete is low: the material begins to collapse at temperatures above 400 C. However, a brief heating of a product made of aerated concrete is tolerated quite satisfactorily. So, when heating the block of the class. At 0.35, the material deflection by 24 mm with a total thickness of 400 mm was observed only at 151 minutes of exposure. A deflection of 18 mm - at 61 minutes. These are sufficient indicators to consider the material fire resistant.Environmental friendliness. Environmental friendliness, that is, an assessment of the naturalness of raw materials, the energy intensity of the process, the possibility of natural processing, etc., depends on the method of manufacture, but in general it far exceeds not only reinforced concrete, but also clay and silicate bricks. According to the Ministry of Health, foam concrete has an indicator of 2.00. For comparison, the
indicator tree is 1.0, and the environmental friendliness of expanded clay concrete is 20.0. The material is completely harmless to humans and the environment. Durability. The question of the durability of foam concrete remains open, since it has been in operation not so long ago. The service life of a building made of aerated concrete is about 100 years, subject to major repairs after 60 years. However, it is no secret that conditions strongly influence the durability of the material. So, too high humidity will cause destruction much earlier. The characteristics of aerated concrete, blocks of them will allow you to choose the right material for each construction site and for any operating conditions. At large facilities, the material most often serves as a heat insulator, but in low-rise construction it is indispensable due to its lightness.
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