CC BY
2
ХИМИЧЕСКИЕ НАУКИ
PROPERTIES OF GYPSUM WITH THE ADDITION OF
MICROSILICA Jabbarova N.E.1, Mirzayeva Ch.G.2
1Jabbarova Natella - candidate of chemistry, associate Professor; 2Mirzayeva Chichak Garib - Master student, DEPARTMENT OF CHEMISTRY AND TECHNOLOGY OFNON-ORGANIC SUBSTANCES, CHEMICALAND TECHNOLOGICAL FACULTY. AZERBAIJAN STATE OIL AND INDUSTRY UNIVERSITY, BAKU, REPUBLIC OF AZERBAIJAN
Abstract: the work presents the results of a study of the possibility of using industrial solid waste in construction materials. The compositions of the initial raw materials - gypsum and microsilica - a waste product from the production of ferroalloys at the Sumgait plant (Azerbaijan) have been determined. The influence of microsilica on the compressive and bending strength of gypsum binder was studied. It has been established that with the introduction of microsilica additive in an amount of 15-17%, the compressive and bending strength reaches a maximum value of 15.1 and 5.3 MPa, respectively. A further increase in the amount of microsilica by more than 20% leads to a decrease in the strength of the gypsum binder.
Keywords: composition ofraw materials,production 'waste, microsilica, gypsum, strength.
СВОЙСТВА ГИПСА С ДОБАВЛЕНИЕМ МИКРЕМНЕЗЕМЛЯ Джаббарова Н.Э.1, Мирзаева Ч.Г.2
1Джаббарова Нателла - кандидат химических наук, доцент; 2Мирзаева Чичак Гариб - магистрант, кафедра химии и технологии неорганических веществ, химико-технологический факультет, Азербайджанский государственныйуниверситет нефти и промышленности, г. Баку, Азербайджанская Республика
Аннотация: в работе представлены результаты исследования возможности использования твердых промышленных отходов в строительных материалах. Определены составы исходного сырья - гипса и микрокремнезема - отходов производства ферросплавов на Сумгаитском заводе (Азербайджан). Изучено влияние микрокремнезема на прочность гипсового вяжущего на сжатие и изгиб. Установлено, что при введении добавки микрокремнезема в количестве 15-17 % прочность на сжатие и изгиб достигает максимального значения 15,1 и 5,3 МПа соответственно. Дальнейшее увеличение количества микрокремнезема более чем на 20 % приводит к снижению прочности гипсового вяжущего.
Ключевые слова: состав сырья, отходы производства, микрокремнезем, гипс, прочность.
UDC 691.32
1. Introduction
Due to the ever-increasing requirements for the environmental safety of building materials and their production, and the need to save energy resources, it is urgent to reorient the construction industry towards more efficient composites, one of which is composite gypsum binders. This is justified by the environmental advantage of the existing technology
for producing gypsum binders, which does not involve high-temperature synthesis, which is the basis for the vast majority of technologies for producing mineral binders.
In addition, there are no emissions of C02, dust and other harmful components, and the production of binders themselves and materials based on them is less energy-intensive compared to the production of clinker and lime [1].
Most of the existing composite gypsum binders (gypsum-cement-pozzolanic binders, gypsum-lime-slag binders, etc.) are moisture resistant, which, in turn, when used as a material for internal wall structures, can serve as a negative factor, since when obtaining water-resistant binders eliminate the hygroscopic effect, which ensures optimal temperature and humidity conditions in any room and in any climatic conditions.
In this regard, it is necessary to use modern technological approaches that make it possible to control structure formation at the micro- and nanolevel to create effective cementless composite gypsum binders and materials based on them [2-7].
The goal of the work is to develop a cementless composite gypsum binder using a nanostructured silica component - microsilica - a waste product from the production of ferroalloys.
Currently, there is a fairly wide selection of composite gypsum binders, and in most cases one of the components is silica [8-11].
A number of studies [12-15] aimed at studying gypsum-cement-pozzolanic binder suggest its preparation by mixing semi-aqueous gypsum (building or high-strength), Portland cement and an acidic active mineral (pozzolanic) additive.
As is known, mixtures of gypsum binders with Portland cement are characterized by structural instability during hardening. When mixed with water, they initially harden intensively, but after 1-3 months, and sometimes later, deformations occur, which usually cause not only a decrease in strength, but even the destruction of the system. This behavior of mixtures of gypsum binders with Portland cement during hardening is a consequence of the formation of the trisulfate form of calcium hydrosulfoaluminate from highly basic calcium aluminates contained in Portland cement and calcium sulfate.
2. Materials and methods
In the course of the work, various methods were used to study and analyze the results obtained, both raw materials and materials based on them.
The characteristics of the binder, accordingly, influence the formation of the structure and technical and operational properties of materials. To obtain reliable results, experiments were carried out on modern equipment in accordance with generally accepted methods.
For research and development of gypsum composite materials with expanded clay dust additives, G-5BP building gypsum produced locally by BINA was used. The composition of gypsum is given in table 1.
Table 1. Chemical composition of microsilica, %.
Si02 КгО CaO FeiOa MgO AI2O3 SO3 Na20
95,7 0.74 0.42 0.04 0.41 0.42 0.43 0.21
Liquid glass is used as an activator in the process of obtaining the binder (Table 2).
Table 2. Chemical composition of activator.
Index Standard for dry concentrate
Appearance Dark liquid
SiÛ2, % 16-28
Na20, % 5,8-11,7
K20, % 0
Silicate module, units. 1,7-3,1
Determination of bending and compressive strength.
Table 3. Physico-mechanicalproperties of gypsum binder.
№ Index Unit Gypsum binder
1 Grinding fineness, residue on sieve No. 02 % 2,4
2 Normal thickness % 52
3 Bending strength: - In 2 hours - dried until permanent mass condition MPa 3,2 5,8
4 Compressive strength: - In 2 hours - d ried to constant weight MPa 6,1 16,2
5 Softening coefficient - 0,33
The essence of the method is to determine the minimum loads that destroy the sample.
To carry out the test, we used: a mold measuring 40x40x160 mm for making binder beam samples for testing; press for compression testing according to GOST 310.4-81 [16]; device for tensile testing during bending of beam samples measuring 40x40x160 mm in accordance with GOST 310.4-81 [16]; vibration platform; load transfer plates; drying cabinet providing a heating temperature of 105-110 °C.
After manufacturing, the samples in the molds were kept for 12±2 hours in a drying oven at a temperature of 105-110 °C, or under normal conditions at a temperature of (20±3) °C they were kept for (36±3) hours.
After the specified storage time, the samples were carefully unmolded and left to harden under natural conditions for 28 days, or dried to constant weight in an oven at a temperature of 105-110 °C.
To test samples, it is allowed to use instruments of any design that provide the ability to apply a load according to a given pattern (Fig. 3.3) with an average rate of load increase (10±2) N/s, as well as instruments that allow measuring the breaking load with an error of no more than ±1 %.
Preliminary studies were carried out on the effect of the concentration of microsilica on the physical and mechanical characteristics of the gypsum binder system. Materials research was carried out according to the accepted methods of GOST 23789-79 "Gypsum binders. Test methods" [7], on standard beam samples measuring 16x4x4 cm. Water consumption per 1 m of molding sand was regulated depending on the standard consistency (normal thickness) of the gypsum dough. The non-additive binder composition served as a control.
The amount of microsilica varied from 10 to 30%, with a variation step of 5%.
Statistical methods were used when processing experimental data.
3. Results and discussions
Fig.l. Effect of microsilica concentration on strength properties -when introduced into a gypsum
system.
The diagram shows the test results of gypsum binder samples with the addition of waste from the production of ferroalloys - microsilica.
Analysis of the data obtained on the main operational characteristics of the experimental compositions allowed us to draw the following conclusions: the introduction of microsilica increases the strength properties, has a plasticizing effect, while increasing the hardening time and slightly increasing the density of the composition compared to the control composition.
A further increase in the content of microsilica in the system is impractical, since a decrease in strength properties occurs, which can be explained by the oversaturation of the solid phase system and the lack of a dispersion medium involved in the hydration process.
Based on the data obtained, compositions were developed; when analyzing the main experimental characteristics, it can be argued that the introduction of microsilica increases the strength properties has a plasticizing effect, while the hardening time increases and the density of the composition slightly increases compared to the control composition. It has been established that the optimal content of microsilica in the system is 15-20%. This amount of microsilica provides an increase in strength of up to 40% compared to control samples.
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