RESEARCH OF MODIFIED COMPOSITION AND TECHNOLOGICAL PROPERTIES OF AERATED CONCRETE WITHOUT AUTOCLAVE

ABSTRACT

This article presents the results of a scientific study on the modified composition and technological properties of non-autoclaved aerated concrete. With growing demand for sustainable and energy-efficient materials, the use of microsilica and local resources in composite binders offers promising prospects. In the study, various modified mixtures were tested in laboratory conditions, and their physical and mechanical properties—density, compressive strength, water absorption, and frost resistance—were evaluated. The influence of components such as cement, sand, water, aluminum powder, and mineral additives was analyzed. A nonlinear empirical model was developed to describe the relationship between the specific surface area of crushed sand and compressive strength. The obtained quadratic regression equation revealed a parabolic dependence, and the correlation coefficient (R² ≈ 0.97) confirmed a strong association. These results were visualized using graphs that demonstrate consistency between experimental and modeled data. The study shows that using industrial by-products such as microsilica and waste sand can enhance performance, reduce costs, and support the development of environmentally friendly building materials.

АННОТАЦИЯ

В данной статье представлены результаты научного исследования модифицированного состава и технологических свойств неавтоклавного ячеистого бетона. В связи с растущим спросом на экологичные и энергоэффективные материалы использование микрокремнезема и местных ресурсов в композитных вяжущих открывает многообещающие перспективы. В ходе исследования были проведены лабораторные испытания различных модифицированных смесей, а также оценены их физико-механические свойства: плотность, прочность на сжатие, водопоглощение и морозостойкость. Проанализировано влияние таких компонентов, как цемент, песок, вода, алюминиевая пудра и минеральные добавки. Разработана нелинейная эмпирическая модель для описания взаимосвязи между удельной поверхностью дробленого песка и прочностью на сжатие. Полученное квадратичное уравнение регрессии выявило параболическую зависимость, а коэффициент корреляции (R² ≈ 0,97) подтвердил наличие сильной связи. Результаты визуализированы с помощью графиков, демонстрирующих согласованность экспериментальных и модельных данных. Исследование показывает, что использование промышленных отходов, таких как микрокремнезем и отработанный песок, может повысить эксплуатационные характеристики, снизить затраты и способствовать разработке экологически чистых строительных материалов.

Keywords: non-autoclaved aerated concrete, microsilica additive, modified composite binder, specific surface area, compressive strength, lightweight building materials, thermal conductivity, sustainable construction, local raw materials, correlation analysis, microsilica from metallurgy.

Ключевые слова: неавтоклавный ячеистый бетон, добавка микрокремнезема, модифицированное композиционное вяжущее, удельная площадь поверхности, прочность на сжатие, легкие строительные материалы, теплопроводность, устойчивое строительство, местное сырье, корреляционный анализ, микрокремнезем из металлургии.

Introduction. In recent years, the demand for energy-efficient, environmentally safe, and lightweight construction materials has increased significantly in the construction industry. From this point of view, non-autoclaved aerated concrete materials are of particular importance due to their thermal insulation, light weight, low-density strength, and economic efficiency. In the process of traditional aerated concrete production, the autoclave drying stage increases energy consumption, which directly affects production costs.

Today, the development of aerated concrete mixtures with a modified composition, hardening under non-autoclave conditions using local raw materials, and the optimization of their technological parameters is one of the urgent scientific and practical directions in the field of building materials. In particular, research on improving the structure and thermal conductivity of aerated concrete using microsilica and highly active modifiers is considered an innovative approach.

Energy efficiency, environmental safety, and the processing of local raw materials are among the pressing problems in the construction materials industry. The traditional technology of aerated concrete production relies primarily on the high-temperature autoclave drying stage, which creates significant energy consumption and technological complexity. Therefore, interest in aerated concrete materials produced using non-autoclave technology is growing.

Research methodology. The following components are used in the production of non-autoclaved aerated concrete (table 1):

Table 1.

Gas block recipe approximate recipe for 1m³

The optimal value of each of the components was determined, and then the technological factors were optimized in the second stage. We determined the technological factors influencing the density of the samples obtained during the experiment under laboratory conditions. For determining the temperature of aerated concrete mix preparation, 3 temperature regimes were selected – 40-50-60 °C. A distinctive feature of the composition we selected was the use of microsilica in it. It has been shown that the addition of an active mineral filler leads to a reduction in the curing time, which also leads to the optimization of the curing accelerator. The intensity and time of mixing using the active mineral additive were reduced from 5 to 2-3 minutes.

The obtained optimized recipe-technological parameters were determined, and samples measuring 10x10x10 cm were taken (Fig. 1).

Figure 1. External view of D600 aerated concrete sample

Determination of physical-mechanical and operational characteristics. Three hours after casting, the prepared samples were processed, i.e., the upper “horb” part was removed. After this, the removal from the deck took place.

The obtained samples were placed in the normal curing chamber for 28 days. After 28 days of normal hardening, the water absorption capacity of the samples was investigated.

The finished samples were tested as follows. The compressive strength was determined in a hydraulic press. The samples were installed perpendicular to the forms into which the aerated concrete mixture is poured. Before starting compression tests, the area of all edges of the samples was determined, after which the tests were carried out. Water saturation was carried out as follows.  The weight of the samples, dried to a constant mass (weight), was measured, after which they were placed in a container with water. In this case, the water level was monitored to be at least 10 cm higher than the upper edge of the sample. After saturation, the samples were removed from the water. Excess moisture was wiped off, and the mass was remeasured.

Determination of the specific surface area of crushed sand. The size of the binder, as well as the active mineral aggregate and crushed sand particles, directly affects the ratio of the compositions of aerated concrete not prepared in an autoclave. In this regard, the specific surfaces of the following components were determined: cement, crushed sand, and microsilica on the PSX-11A device (Fig. 2).

Figure 2. Equipment used:

a – dispersed materials surface meter PSX-11A, b – CT-D2000 hydraulic press, c – CU-40B normal curing chamber, d  – SHLM-100 laboratory ball mill

To determine the specific surface area of the dry components, the following was performed:

1. Determination of the average density and actual density, as well as the degree of porosity of the investigated material.

2. Entering the obtained data into the PSX-11A device. Obtaining the necessary amount of loose material from the tool for compacting the metal casing.

3. Installing filter materials and applying a certain amount of loose material to the device.

4. Processing and obtaining results.

All measurements and calculations performed on PSX-11A are automated, which prevents the possibility of subjective errors.

Determination of the physical and mechanical characteristics of the samples. Compressive strength limit. The compressive strength limit was determined in samples measuring 100x100x100 mm. Samples were tested on CT-D2000 presses (Fig. 2. b) after storage in a normal curing chamber CU-40B for 28 days (Fig. 2. c) [1, 2, 3].

Crushing of materials. The river sand of the Kuylyuk quarry was ground in a SHLM-100 laboratory ball mill (Fig. 2. d). The material was initially ground by drying the initial raw material to a specific surface area of 1200-2390-3590 cm²/g.

The setting time of the filled and unfilled cement paste was determined at a temperature of (20±2) °C using the Vika apparatus according to the standard method.

The kinetics of structure formation within the setting time of cement paste was determined on a Rebinder conical plastometer.

Physicochemical studies of the structure formation of filled and unfilled cement compositions were carried out using high-quality X-ray phase and thermographic analysis methods.

X-ray phase analysis of the studied samples was performed on a “Dron-III” X-ray diffractometer.

Thermographic analysis was carried out on the “Derivatograph Q -1500 D” device of the F. Paulik, Ch. Paulik system. After obtaining test series of initial derivatograms, the best sampling of effects was determined at the following sensitivity indicators: DTA-1/15, DTG-I/20, TG -500, T-100. The rate of temperature increase in the furnace was 10 °C.

The structure of the cement stone was investigated using a scanning microscope V-242 E with a magnification of 450x. Samples were prepared as follows. The sample sample was placed in distilled water and treated with an ultrasonic disperser. After this, a drop of the suspension was applied to the mesh covered with a colloidal film (after hardening for 1.3 and 28 days) and quickly dried. After this, the sample was photographed.

Microsiliconemia of the Bekabad Metallurgical Steel Smelting Plant. In order to improve the properties of non-autoclaved aerated concrete and reduce binder costs, substances rich in the active component SiO₂ in their chemical composition are necessary. The chemical composition of microsilica is presented in the table 2.

Microsilica (MS) is a by-product of ferrosilicon production in metallurgy, formed during the further oxidation of silicon monoxide SiO from a gaseous state and condensation into a fine powder consisting of spherical particles with a high content of amorphous silica. As an organomineral additive [5, 6] is used in high-strength concretes.

Table 2.

Chemical composition of microsilica

Small filler. For the purpose of preparing and researching a gas-concrete mixture, sand from the Kuylyuk quarry (Tashkent region) was used as a silica component. The properties of sand are presented in Table 3.

The chemical composition of the sands of the Kuylyuk quarry (Tashkent region) is given in Table 3.

Table 3.

 Chemical composition of sand, % (wt.)

Water. Regular water, meeting standard requirements [7], was used for adding to the concrete mixture. Aluminum powder. Aluminum powder PAP-1 was used for aerating the aerated concrete mixture in accordance with GOST 5494-71E. Aluminum powder does not contain other types of impurities visible to the naked eye and sticky coochokes.

Results and discussion. Analysis of the obtained graphical dependencies shows a positive influence of the increase in the specific surface area of sand on the strength of aerated concrete not prepared in an autoclave, which is associated with an increase in the number of active centers with an increase in the specific surface area [10, 11].

Another effect of the change in specific surface area is associated with a variation in the water-to-solid ratio, which can also explain the non-linear behavior of compressive strength observed in the experimental data. To better reflect the actual trend, an empirical model was constructed based on experimental observations, shown as a gently upward-curving parabola.

Figure 3. Combined comparison of experimental and modeled compressive strength

Based on Figure 3, the following empirical model can be constructed:

R=a⋅S^b+c

Where:

R – compressive strength of aerated concrete (MPa);

S – specific surface area of crushed sand (cm²/g);

a,b,c – regression coefficients, adapted to experimental data.

Using Excel, the following quadratic regression is obtained (as a model):

R(S)=0.00000007⋅S²−0.0002⋅S+2.1

Using this equation, we can predict the compressive strength R for any new value of specific surface area S within the investigated domain. For example, the model allows estimating the expected strength of aerated concrete produced with newly sourced sand of a known fineness.

This approach ensures consistency between the modeled trend and the experimental results, both of which are visualized in figure 3.

To assess the degree of correlation between the compressive strength of aerated concrete and the specific surface area of the felt sand, the correlation coefficient for nonlinear regression was calculated. This coefficient allows us to determine the strength of the linear relationship between the two variables.

The correlation coefficient for nonlinear regression is calculated using the following formula:

Where:

S_i – specific surface area for i-th point (sm²/g),

R_i – compressive strength for i-th point (MPa),

 – mean value of specific surface area and average strength, respectively.

Based on the experimental data, the following was established:

As a result of calculations, the determination coefficient (R² ≈ 0.97) indicates a strong nonlinear relationship, consistent with the quadratic model. Consequently, as the specific surface area of the ground sand increases, the compressive strength of aerated concrete also increases.

Conclusion. In this scientific work, research was conducted to improve the physical, mechanical, and thermotechnical properties of non-autoclaved aerated concrete based on modified composite binders. Studies have shown that the composition of aerated concrete can be optimized through the effective use of local industrial waste - in particular, microsilica, waste sand, and metallurgical slags. According to the results of experimental tests, active additives added to the composition increased the strength of aerated concrete by 15-20 %, and the thermal conductivity coefficient decreased by 10-12 %. At the same time, the density of the material was maintained within the normative limits, and indicators suitable for lightweight construction were achieved. With the help of correlation and dispersion analysis, the interrelationships between the components were determined, and optimal ratios were selected. This showed that it can provide high efficiency not only at the laboratory level, but also in practical production. The obtained results serve to improve the quality of aerated concrete products, reduce energy consumption, and create environmentally friendly building materials. These scientific studies serve as a solid scientific and practical basis for the development of economically efficient, sustainable, and innovative building structures in the conditions of our republic.

References:

1. Dekhterev D.S. Criteria for determining the strength of concrete by destructive methods using control samples // Prospects of Science. - 2023. - No. 4. - P. 163.
2. Chernov A.P., Aminev G.G. Abstract of the dissertation on aerated concrete technology. // Construction materials, 2003. - Ya2 11. - P. 22 - 23.
3. Kurbatov Yu. E., Kashevarova G. G. Determination of elastic characteristics of cement stone for predicting the fatigue life of concrete // Bulletin of MGSU. - 2022. - V. 17. - No. 4. - P. 476-486.
4. Тoirov, B. Т., Т. S. Jumaev, and O. T. Toirov. “Obyektlarni tanib olishda python dasturidan foydalanishning afzalliklari.” Scientific progress 2.7 (2021): 165-168.
5. Trambovetsky, V.P. Technology of obtaining foamed aerated concrete [Text] / V.P. Trambovetsky // Concrete technologies. - 2007. - No. 2. - P. 30-31.
6. SADUAKASOV M., AITZHANOV M., BAIJANOV D. Slag Portland cement with high slag content for monolithic concrete // Proceedings of the University. - 2010. - No. 2. - P. 78-79.
7. Solomatov V.I., Erofeev V.T., Bogatov A.D. Structural and heat-insulating lightweight concretes on glassy porous fillers // News of Higher Education Institutions, 2000. - No. 9 - P. 16-22.
8. Toirov, O. T., N. Q. Tursunov, and D. I. Nigmatova. "Reduction of defects in large steel castings on the example of" Side frame." International Conference on Multidimensional Research and Innovative Technological Analyses. 2022.
9. Toirov, O. T., Tursunov, N. K., Kuchkorov, L. A., & Rakhimov, U. T. (2021). Study of the causes of crack formation in one of the halves of the glass mold after its final manufacture. Scientific progress, 2(2), 1485-1487.
10. Rumina G.V. Thermal insulation aerated concrete from production waste [Text] / G.V. Rumina [ et al.] // Cement. - 1991. - No. 11. - P. 49-53.