RU2528718C1 - Method of tempering moulding mixtures - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of tempering moulding mixtures includes mixing dry components and preparing tempering water by passing said water between electrodes while applying an alternating or constant potential difference with rate or strength of current which provides charge saturation density of water that has passed between the electrodes of not less than 825 kC/m³, saturating the tempering water during electrolysis with Fe³⁺ ions of the electrode until saturation of the water with iron ions reaches 30-35%. Ascorbic solution is first added to said water in amount of 0.1 g/l.

EFFECT: increasing mobility of moulding mixtures without increasing the total amount of tempering water, thereby considerably improving operational characteristics of the finished articles and saving binding materials.

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Description

The invention relates to non-reagent methods for increasing the workability of molding sand by treating water and can be used in the production of silicate, ceramic, concrete, reinforced concrete and other products, as well as in technologies based on the use of various mineral binders, for which the problem of workability and increasing positive dynamics is relevant increasing the strength of finished products.

A known method of mixing molding sand (see Batrakov V.G., Modified Concretes. - M., Stroyizdat, 1990, p.142-145), in which special chemical plasticizers - thinners based on sulfonated naphthalene formaldehyde compounds are added to the mixing water, representing an oligomer-polymer mixture, which contains an unreacted salt - naphthalene sulfonic acid and sodium sulfate. The most widely used in the production of concrete and reinforced concrete products was superplasticizer, known as C-3. Its use allows you to reduce the required amount of water used, which, of course, reduces porosity, increases strength and frost resistance, improves other service characteristics of the finished product.

However, due to the fact that this additive was obtained on the basis of sodium salts of the condensation products of naphthalenesulfonic acid and formaldehyde, it belongs to toxic substances. Vapors and airborne particles of dried substance (dust). Those. even finished products, in the production of which this thinner was used, adversely affect the mucous membrane of the nasopharynx and eyes and unprotected skin. Workers involved in the technological process using C-3 must use personal protective equipment (rubber gloves, respirators, etc.) (See ″ Manual on the use of chemical additives in the manufacture of precast concrete structures of products ″, SNiP 3.09.01-85 , NII KB - M., Stroyizdat, 1989, 39 pp.). In addition, C-3 is a rather expensive drug.

The closest in technical essence is the method of preparation of mixing water (USSR AS No. 1122617, bull. No. 41 of 11/07/84), according to which the source water is supplied to the diaphragm electrolyzer, where it is treated with a constant electric current to values of 200-700 kC / m ³ . From the zone of the main negative electrode of the electrolyzer, water flows into the clarifier for 2 hours, and then through a filter filled with anthracite into the mixer for acidification with sulfuric acid. After acidification, water passes through a cationic buffer filter, enters the decanter, and then into the cathode chamber of the second cell and then into the deaerator.

Water is treated in the cathode chamber of the second cell until the redox potential of 100-150 mV and pH values of 8-8.6 are reached.

The disadvantage of this method is the low workability and rather high energy costs, since, due to the fundamental features of the device of diaphragm electrolyzers, less than 40 of the treated water (catholyte) goes into the process, and the rest of the treated water (atulite) is not used and must be disposed of. According to the technological cycle, chemical reagents must be added to the water of the cathode chamber. The use of two electrolysis cells in the technological cycle doubles the energy costs and the consumption of chemicals. To bubble water in the clarifier, compressors or compressed gas cylinders are needed. To supply water to the filter, to the mixer, and then to the decarbonizer and cathode chamber of the second electrolyzer, it is necessary to use additional pumps. The method requires more than double the flow of water.

This method is the closest in technical essence and the achieved result.

The technical result is an increase in the mobility of the molding sand without an increase in the total amount of mixing water, and as a result of this, a significant improvement in the service characteristics of the finished products and saving binders.

The problem is solved in that in the method of mixing molding sand, including mixing dry components and preparing mixing water, i.e. the treated water is passed between the electrodes when a variable or constant potential difference is applied to them with a speed or electric current providing a saturation density of the charge passed between the electrodes of water of at least 825 kC / m ³ , mixing water during electrolysis is saturated with metal ions of a Fe ³⁺ electrode until water with iron ions of 30-35%, previously a solution of ascorbic acid in an amount of 0.1 g / l is introduced into said water.

The method is based on the well-known fact that the process of maturation of cement stone is significantly intensified by the concentration of solid phase nuclei in the hardening mixture, which act as microcrystallization centers acting as process catalysts. The role of such crystallization centers can be played by metal ions released from electrodes during electrolysis. In order to saturate the mixing water with microcrystallization centers, it was treated according to RU patent No. 2096336 (″ Method for preparing water for a power system ″, Pomazkin V.A., Bull. No. 32, 11/20/97). From general physical considerations it follows that the saturation of water with metal ions of the electrodes will be proportional to the transferred charge.

The concentration of ions can be determined by the formula:

n ₀ = It / e,

where n ₀ is the number of ions per unit volume, I is the current flowing between the electrodes, t is the current passage time, e is the electron charge.

According to patent RU No. 2096336 it was found that the ion concentration depends not only on the density of saturation of water with a charge, but also on the polarity of the electrodes, and on the material from which the electrodes are made. For electroactivation, water was passed between electrodes made of metals, whose ions take an active part in the structure and phase formation of molding sand. The authors found that for molding mixtures, the most effective pair of electrodes are the iron cathode and anode. During the electrolysis of untreated, including tap water, with a dissolved anode, the latter exhibits a high content of chlorine and its anionic forms. To prevent the possible oxidation of metal ions in lower or intermediate oxidation states, it is necessary to introduce substances that impede this process into the electrolyte. Therefore, when electroactivating water with an iron anode, to prevent oxidation, we introduced a solution of ascorbic acid in an amount of 0.1 g / l, which almost completely inhibits the oxidation of iron Fe ²⁺ -E → Fe ³⁺ . Such a concentration of ascorbic acid is minimal, which does not affect the curing process of the system and its further use.

As a control of the effectiveness of electroactivation, we used the method developed by us, which is protected by patent RU No. 2096759 (″ Express analysis of the physical activation of liquids ″, Pomazkin V.A., Bull. No. 32, 11/20/97).

The method was tested in the laboratory of building materials of the Department of TeSMI OSU together with the staff of the Intersectoral Scientific and Technical Enterprise of physical methods for influencing gaseous, liquid and viscous media (MNTP Gradient), OJSC Maxmir and the Department of Physics of OSU. In total, more than 200 experimental samples were examined (cubes 15 × 15 × 15 CM.). Strength was determined by the destruction method on a P-125 press, density was determined by weighing on an analytical balance, rigidity was determined by the Krasnov method, and mobility was determined using the Abrams cone. Studies were carried out on concrete mixtures of various stiffness.

The method was carried out as follows. The preparation of water was carried out according to patent RU No. 2096336. Prepared a dry mixture, adhering to the following ratio of components (taking into account our needs for the manufacture of experimental cubes):

Cement: Sand: Crushed stone: = 1: 1.8: 4.1

The mixture was shut with non-activated water, its rigidity and mobility were measured. Then the same mixture of dry components was closed with electroactivated water, adding it until the workability of the concrete mixture prepared with activated and plain water became the same. It was found that the mobility of the sealed mixtures increased to 20, sometimes experimental cubes of concrete electro-activated water, and higher. The molds were filled with a mixture and, after processing on a vibrating platform, left to ripen under natural conditions. For each mode, 4-6 experimental cubes were prepared. After 7 days, part of the cubes was freed from the formwork and measurements were made. Significantly established a significant increase in the dynamics of the increase in strength. So, some cubes had the same strength as closed with ordinary water after 28 days of storage. On day 28, the remaining samples were examined. The results of the study are summarized in table 1, from which it is clear that increasing the degree of electroactivation over 35 is impractical, because there is no increase in strength, and a decrease in the degree of electroactivation below 30 leads to a sharp drop in the strength of the system.

Table 1 The degree of saturation of water with metal ions,% w / c Stiffness, s Density, kg / m ³ Strength, MPa Strength gain 0 0.42 7 2400 31.0 - thirty 0.40 7 2420 39.7 28 32 0.39 7 2450 40.3 thirty 35 0.41 7 2420 37.2 twenty 36 0.41 7 2430 37.2 twenty

It can be seen that with the same stiffness of the concrete mixture and the same cement consumption, an increase in the strength of concrete closed with activated water increases by an average of 24.5. This allows you to save up to 8-12% of cement in the production of concrete and reinforced concrete products. We conducted an experiment in which 12% less cement was taken in a product made from a concrete mixture closed with activated water. The results are shown in table 2.

It is seen that a decrease in the amount of cement by 12% does not lead to a decrease in the strength of the product.

Thus, in comparison with the prototype, the claimed method allows to increase the mobility of the molding sand without increasing the total amount of mixing water, which gives a significant improvement in the service characteristics of the finished products and the economy of the binder.

The principal difference of the proposed method lies in the fact that in the prototype method, a positive effect is achieved by changing the redox potential and its pH in the mixing water, while in our method we saturate the water with microcrystallization centers that catalyze the acceleration of hydration processes and concrete hardening processes.

From the above it can be seen that the inventive method for mixing molding sand in comparison with the prototype has the following significant advantages:

- Significantly reduced power consumption. So, if in the prototype to achieve the desired efficiency of electroactivation of mixing water it is necessary to saturate the water with a charge up to the level of 200-700 C / l, then for our method only 15-30 C / l is enough, which is 13-33 times less. For the processing of 2 m ³ per hour according to the prototype method, a power of 35-40 kW is required (see ″ Installation of electro-activation of water UEV-7 ″, NPF ″ Espero ″, Tashkent, 1990). According to our method - 0.8-1 kW, which is 35-40 times less;

- There is no need to use chemicals;

- Only less than half of the water (catholyte) is used in the process, and the rest (anolyte) must be disposed of. According to the claimed method, only water is processed that goes into the production cycle;

- The mass of the installation for the implementation of the prototype method (UEV-7, including equipment) - 700 kg The mass of the installation of the same capacity in our method, including the power supply is 40-50 kg, that is, the metal consumption for devices preparing mixing water according to our method is 12-17 times less;

- To install equipment according to the prototype method (for example, UEB-7), an additional area of at least 20 m ² is required. For the installation of electroactivation of mixing water according to our method, the need for additional areas practically disappears.

Claims (1)

A method for mixing molding sand, comprising mixing dry components and preparing mixing water, i.e. the treated water is passed between the electrodes when a variable or constant potential difference is applied to them with a speed or electric current providing a saturation density of the charge passing between the electrodes of water of at least 825 kC / m ³ , characterized in that the mixing water during electrolysis is saturated with Fe metal ions ³⁺ until water is saturated with iron ions of 30-35%, previously a solution of ascorbic acid in an amount of 0.1 g / l is introduced into the specified water.