RU2479525C2 - Method of preparing concrete mixture - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the industry of construction materials and specifically to methods of preparing a concrete mixture. The method of preparing a concrete mixture involves measured feeding into a concrete mixture of cement, aggregate and hardening liquid, followed by agitation of said mixture. The disclosed method is characterised by that before feeding cement into the concrete mixture, the cement particles are charged with a positive or negative electrostatic charge by passing them through a mesh electrode across which a high negative or positive potential is applied, the magnitude of which lies in the (8-10) kV range. The hardening liquid used is activated water, wherein if the cement particles are charged with a negative electrostatic charge, the activated hardening liquid is an anolyte having redox potential (Eh)_an in the range of [250≤(Eh)_an≤1200] mV, and if the cement particles are charged with a positive electrostatic charge, the activated hardening liquid used is a catholyte having redox potential (Eh)_cat in the range of [-820≤(Eh)_cat≤300] mV.

EFFECT: more efficient use of cement and high strength of the hardened cement, as well as faster setting of the cement.

2 tbl, 1 dwg

Description

The invention relates to the building materials industry, and in particular to methods for preparing a concrete mixture, and is aimed at a more efficient use of cement and increase the strength of cement stone.

There is a method of separate preparation of concrete mix by preliminary preparation of cement dough in a high-speed mixer-activator, followed by mixing it with aggregate in a concrete mixer to obtain a finished concrete mixture [1].

The disadvantage of this method is the high complexity of the process, the low degree of hydration and activation of cement paste and the slow rate of hardening of concrete.

Closest to the claimed method is a method of preparing a concrete mixture, which consists in a metered supply of cement, aggregate and tap water to a concrete mixer and subsequent mixing of the resulting mixture in a concrete mixer [2].

The specified method is not economical, does not effectively use cement and water. The prototype method does not allow sufficient use of the potential activity of cement, since 30-40% of the clinker component does not participate in hydration processes and acts as an inert aggregate. In addition, the strength of the concrete stone obtained by the prototype method is low.

The technical problem to which this invention is directed is to increase the efficiency of use of cement and increase the strength of concrete stone.

The solution of this problem is achieved by the fact that in the method of preparing the concrete mixture, which consists in the dosed supply of cement, aggregate and mixing fluid into the concrete mixer, followed by mixing of the mixture, cement particles are charged with positive or negative electrostatic charge immediately before cement is supplied to the concrete mixer. For electrostatic charging of cement particles, they are passed through a mesh electrode, to which a high-voltage negative or positive potential is applied, the absolute value of which lies in the range of (8 ÷ 10) kV. When mixing the mixture, activated water is used as the mixing liquid.

In this case, when charging cement particles with a negative electrostatic charge, anolyte with a redox potential value (Eh) _en lying in the range [250≤ (Eh) _en ≤1200] mV is used as an activated mixing liquid.

When cement particles are charged with a positive electrostatic charge, catholyte with a redox potential value (Eh) _cat lying in the range [-820≤ (Eh) _cat ≤300] mV is used as an activated mixing liquid.

Figure 1 shows a diagram of a device for preparing a concrete mixture, which serves to explain the essence of the invention.

A device for preparing a concrete mixture contains a cement accumulator 1, aggregate accumulator 2, cement dispenser 3, aggregate dispenser 4, water treatment plant 5, pump 6, prefabricated funnel 7, concrete mixer 8, hopper 9. A cement activator 10 is additionally introduced into the device, a control unit 11 and a pH meter 12 with activated water parameters sensors 13 and 14. In this case, the cement activator includes a high-voltage source of adjustable constant bipolar voltage 15, a bushing 16, a dielectric funnel 17 mesh electrode 18. The water treatment plant 5 includes an adjustable power source 19 and is made in the form of an electrolyzer divided by a membrane 20 into the cathode and anode chambers into which the anode 21 and cathode 22, anolyte level sensor 23 and catholyte level sensor 24 are inserted. The cell is equipped with a dielectric cover 25, through which water pipes 26 and 27 are respectively introduced into the anode and cathode chambers. Water pipes 26 and 27 are connected through a solenoid valve 28 and 29 to pump 6. Water pipes 30 and 31 are removed from the cathode and anode chambers of the electrolyzer to drain the anolyte and catholyte into a collection funnel 7. Water pipes 30 and 31 are equipped with electromagnetic shutters 32 and 33. High-voltage output of the high-voltage adjustable constant bipolar voltage source 15 is connected to the input of the bushing 16, and the low-voltage output of the said source is connected to the housing of the concrete mixer 8 and is grounded. The output of the bushing 16 is connected to the mesh electrode 18. The mesh electrode 18 is located inside the dielectric funnel 17 and is fixed to the inner generatrix of the said funnel. The plane of the mesh electrode 18 is perpendicular to the inner generatrix of the dielectric funnel 17. The dielectric funnel 17 is located between the cement dispenser 3 and the collection funnel 7. The collection funnel 7 is installed between the dielectric funnel 17 and concrete mixer 8. The activated water parameters sensors 13 and 14 are connected to the input of the pH meter 12 The output of the pH meter 12 is connected to the input of the control unit 11. The positive pole of the regulated power source 19 is connected to the anode 21, and the negative pole of the adjustable power source 19 is connected to the cathode 22. The input of the regulated power source 19 is connected to the input of the control unit 11. The level sensors of anolyte 23 and catholyte 24 are connected to the input of the control unit 11.

The invention consists in the following.

When the “anolyte” button located on the control unit is pressed, the pump 6 starts and at the same time the electromagnetic valves 28 and 29 open. The tap water begins to flow into the electrolyzer 5. Anolyte level sensor 23 and catholyte level sensor 24 are set to two values: h _max and h _min . The values of h _max and h _min selected from the following considerations. The volume of the cell is directly dependent on the volume of the concrete mixer and the formulation of the concrete mixture being prepared, but in each case it has its own specific value V. The volume of the cell V is equal to the product V = Sh of the cross-section S of the cell and its height h. Since the S value of the electrolyzer is constant and is determined only by the geometrical dimensions of the electrolyzer, the volume of water V _el that can be poured into this particular electrolyzer can be determined from the expression V _el = Sh _max , where h _{max is} the limiting water level above which it should be poured into the electrolyzer water is not recommended in order to avoid its outflow through the edges of the cell. Depending on the brand of cement, the characteristics of the aggregate, the purpose of the concrete mix, and other factors, the ratio of the volume of cement, aggregates and barrier fluid can be very diverse. Suppose, for some selected recipe of a mixture and a specific volume of a concrete mixer, concrete needs some specific volume of a _barrier fluid V _shutter . Since the diaphragm 20 divides the volume of the electrolyzer 5 into the cathode and anode chambers, the volumes of which are equal to each other, the value of h _min is determined by the volume of the gate fluid V _gate in accordance with the expression

.

.

The process of filling the cathode and anode chambers with water is controlled by catholyte 24 and anolyte 25 level sensors. As soon as the water level in the cathode and anode chambers of the cell reaches h _max , a command is _sent from the control unit, by which pump 6 is turned off, solenoid valves 28 and 29, and the regulated power supply 19 is turned on. From the regulated power supply, the positive potential is supplied to the anode 21, and the negative potential is supplied to the cathode 22 of the electrolyzer. In the electrolyzer, the electrolysis process begins, in which the values of the hydrogen indicators (pH) _cat and (pH) _en and the redox potentials (Eh) _cat and (Eh) _en in the cathode and anode chambers, respectively, change. Hydrogen indicators and redox potentials are measured with a pH meter 12 using sensors 13 and 14. When the anolyte in the anode chamber reaches the specified value of the redox potential (Eh) _en , lying in the range [250≤ (Eh) _en ≤1200] mV, in the block a command is generated that turns on the high-voltage source of regulated constant bipolar voltage 15, and a high-voltage negative potential appears on its high-voltage output, the value of which lies in the range (-8 ÷ -10) kV, which through the bushing 16 passes to the grid ele ktrod 18. The low-voltage output of a high-voltage source of adjustable constant bipolar voltage 15 is connected to the housing of the concrete mixer 8 and is grounded. The choice of the range of voltages supplied to the mesh electrode is due to the following considerations. The effect of electrostatic charging of cement particles depends on the magnitude of the high voltage potential supplied to the mesh electrode. However, it is impossible to increase this potential without limit. The upper voltage limit chosen by us minus 10 kV allows, on the one hand, to achieve a sufficiently effective electrostatic charging of cement particles, and on the other hand, to avoid undesirable breakdowns and discharges on the surface of the funnel, allows you to use a relatively simple small-sized bushing and a fairly simple and relatively cheap design high-voltage source of regulated constant bipolar voltage. The lower voltage limit chosen by us minus 8 kV allows us to maintain a sufficiently high efficiency of electrostatic charging of cement particles. A decrease in the absolute value of the high voltage potential at the mesh electrode leads to a decrease in the efficiency of electrostatic charging of cement particles. Simultaneously with the supply of high potential to the mesh electrode 18 from the control unit 11, a command is sent to the gate of the cement dispenser 1, by which the gate is opened, and the cement is poured from the dispenser into the cement activator 10. Passing through the mesh electrode 18, the cement particles acquire a negative electrostatic charge. After this, negatively charged particles of cement enter the prefabricated funnel 7 and from it to the concrete mixer 8. Simultaneously with the command from the control unit 11 to the gate of the cement batcher 10 and to the high-voltage source of regulated constant bipolar voltage 15, a command to start the concrete mixer is sent from control unit 11 8. Cement particles from cement dispenser 1 enter the cement activator 10 and, passing through the mesh electrode 18, acquire a negative electrostatic charge. After the rash of a given dose of cement, the gate of the cement dispenser 10 closes. After closing the gate, the control unit 11 generates a command by which the high-voltage source of adjustable bipolar voltage 15 is turned off and the electromagnetic valve 32 is activated. The electromagnetic valve 32 opens and the anolyte starts to flow out of the electrolyzer. Anolyte through the pipe 30 is poured into a collection funnel 7, and from it into a rotating concrete mixer 8. The process of draining the anolyte into the concrete mixer is controlled by the anolyte level sensor 23. As soon as the anolyte level in the anode chamber of the electrolyzer is reduced to h _min , a command is generated in the control unit, by which closes the solenoid valve 32, preventing the further flow of anolyte into the concrete mixer 8. At the same time, a command is sent to the gate of the filler dispenser 4, the gate opens, and the filler, through the accumulator the funnel 7, enters the concrete mixer 8. The mixture in the concrete mixer is mixed for a predetermined time, after which a command is generated in the control unit, by which the gate in the aggregate dispenser 4 is closed and the concrete mixer 8 is turned off. The resulting mixture enters and from the hopper 9 to the consumer.

Negatively charged cement particles have an excess of electrons and are electron donors, a reducing agent. Anolyte having a positive redox potential (Eh) _en lying in the range [250≤ (Eh) _en ≤1200] mV, on the contrary, is an electron acceptor, an oxidizing agent. Therefore, the interaction of negatively charged cement particles with positively charged anolyte ions leads to the activation of redox processes occurring between cement and anolyte that underlie cement hydration and the setting and hardening of concrete mixes. A more effective interaction between electrostatically negatively charged cement particles and positively charged water ions is accompanied by the fact that, under the influence of the Coulomb forces of mutual repulsion of similarly charged cement particles, additional air gaps arise between individual cement layers, which contributes to a more effective washing of each cement particle with anolyte. After anolyte penetrates into the cement, the particles of which are charged with a negative electrostatic charge, the particles of which bear a positive electrostatic charge, an opposite attraction of particles with opposite charges occurs, due to which the resulting mixture is compressed internally. These physical and chemical processes significantly increase the hydration of cement, increase the strength of concrete stone, reduce the amount of water going to mix the mixture, and improve other important characteristics of the concrete mixture. Moreover, the higher the redox potential of the anolyte (Eh) _an , the more intense the redox processes between the cement and anolyte particles will occur. The choice of the range of values (Eh) _en is determined by the following factors. The higher the value of the redox potential of anolyte (Eh) _an , the more intensively it will interact with negatively charged particles of cement. At the same time, it is unrealistic to obtain the redox potential of the anolyte (Eh) _an above +1200 mV. Therefore, the aforementioned value of the redox potential of the anolyte (Eh) _an , equal to 1200 mV, was chosen as the upper limit. When the redox potential of the anolyte (Eh) _{an is} less than +250 mV, the oxidative properties of the anolyte are largely lost. Therefore, the value of +250 mV was taken as the lower value of the redox potential of the anolyte (Eh) _en . The actual values of redox potential (Eh) _an anolyte without any complications that may be prepared in a conventional electrolytic cell is also dependent on cell design, composition of treated water, a water treatment regimes and other factors and generally lie in the range [250≤ (Eh) _en ≤1200] mV. When the catholyte button located on the control unit is pressed, the pump 6 starts and at the same time the electromagnetic valves 28 and 29 open. The tap water begins to flow into the electrolysis cell 5. The process of filling the cathode and anode chambers with water is monitored by catholyte 24 and anolyte 25 level sensors. As soon as the water level in the cathode and anode chambers of the electrolyzer reaches a value h _max, a command is _sent from the control unit to shut down pump 6, solenoid valves 28 and 29 are closed the regulated power source 19 is turned on. From the regulated power source, the positive potential is supplied to the anode 21, and the negative potential is supplied to the cathode 22 of the electrolyzer. In the electrolyzer, the electrolysis process begins, in which the values of the hydrogen indicators (pH) _cat and (pH) _en and the redox potentials (Eh) _cat and (Eh) _en in the cathode and anode chambers, respectively, change. The redox potentials are measured with a pH meter 12 using sensors 13 and 14. When the catholyte reaches the redox potential (Eh) _cat in the cathode chamber, which lies in the range [-820≤ (Еh) _cat ≤-300] mV, in the control unit 11, a command is generated that turns on a high-voltage source of regulated constant bipolar voltage 15, and a high-voltage positive potential appears on its high-voltage output, the value of which lies in the range + (8 ÷ 10) kV, which, through a bushing 16, enters the grid electrode 18. A low-voltage output high-voltage source of regulated constant bipolar voltage 15 is connected to the housing of the concrete mixer 8 and is grounded. At the same time, a command is sent from the control unit 11 to the gate of the cement dispenser 1, by which the gate is opened, and the cement is poured from the dispenser into the cement activator 10. Cement particles passing through the mesh electrode 18 acquire a positive electrostatic charge. After this, positively charged particles of cement enter the prefabricated funnel 7 and from it into the concrete mixer 8. Simultaneously with the command from the control unit 11 to the gate of the cement dispenser 10 and to the high-voltage source of adjustable constant bipolar voltage 15, a command to start the concrete mixer is sent from the control unit 11 8. After filling the concrete dose required in accordance with the selected recipe for cement, the gate of the cement dispenser closes and, at the same time, it closes the input of a high-voltage regulated source DC bipolar voltage 15 receives a command by which it is turned off. After turning off the high-voltage source of regulated constant bipolar voltage 15 to the solenoid valve 33 receives a command. The solenoid valve 33 opens and catholyte begins to flow out of the cell. The catholyte through the pipe 31 is poured into a collection funnel 7, and from it into a rotating concrete mixer 8. The process of discharging the catholyte into the concrete mixer is controlled by a catholyte level sensor 24. As soon as the catholyte level in the cathode chamber of the electrolyzer is reduced to h _min , a command is generated in the control unit 11, by which the electromagnetic valve 33 is closed, preventing further catholyte from entering the concrete mixer 8. At the same time, a command is sent to the gate of the filler dispenser 4, the gate opens, and the filler, black C accumulating funnel 7, enters the concrete mixer 8. The mixture in the concrete mixer is mixed for a predetermined time, after which a command is generated in the control unit, by which the gate in the aggregate dispenser 4 is closed and the concrete mixer 8 is turned off. The resulting mixture enters the transfer hopper 9 and from him to the consumer.

Positive particles of cement are electron acceptors, an oxidizing agent. A catholyte having a negative redox potential (Eh) _cat lying in the range [-820≤ (Eh) _cat ≤-300] mV, on the contrary, is an electron donor, a reducing agent. Therefore, the interaction of positively charged particles of cement with negatively charged catholyte ions leads to the activation of redox processes occurring between cement and catholyte that underlie the hydration of cement and the basis of the setting and hardening of concrete mixes. These physical and chemical processes should significantly increase the hydration of cement, the strength of concrete stone and other important characteristics of the concrete mixture.

Moreover, the lower the redox potential of the catholyte (Eh) _cat , the more intense the redox processes between positively charged cement particles and negative catholyte particles. The choice of a specific value (Eh) _cat in the above range depends on the parameters of the source water subjected to electrolysis, the design of the electrolyzer, and a number of other factors. Moreover, the lower the redox potential of the catholyte (Eh) _cat , the more intense it will interact with positively charged particles of cement. Obtaining the redox potential of catholyte (Eh) _cat below -820 mV is unrealistic. Therefore, the aforementioned value of the redox potential of catholyte (Eh) _cat , equal to -820 mV, was chosen as the lower limit. When the redox potential of the anolyte (Eh) _cat is greater than minus 300 mV, the oxidative properties of catholyte are largely lost. Therefore, minus 300 mV was taken as the upper value of the redox potential of catholyte (Eh) _cat . The actual values of redox potential (Eh) _Cat catholyte without any complications that may be prepared in a conventional electrolytic cell lie in the range [-850≤ (Eh) ≤-300 _en] mV.

An example of a specific reproduction of the method. The inventive method was carried out on the device depicted in figure 1.

The study of the effect of electrostatic charging of cement particles and the use of activated water as a gate fluid was carried out in two stages. At the first stage, the experiments were carried out on cement stone, while such characteristics as the setting time of the cement, the degree of cement hydration, and the increase in the strength of the cement stone were investigated. Portland cement was used in the batches. The water-cement ratio in these experiments was equal to B / C = 0.54, where B is the water consumption per 1 m ^{3 of} concrete, kg; C - cement consumption per 1 m ³ concrete, kg Cement hydration was investigated by the X-ray diffraction method using DRON-4 units. Studies have shown that in the cement test prepared by the prototype method, the hydration of cement was 65%, while according to the claimed method it was equal to 92-95%.

The results of the first stage of research are shown in table 1.

At the second stage of research, the strength of concrete under normal conditions was also evaluated. To assess the strength of concrete under normal conditions, control cubes were made with an edge of 150 × 150 × 150 mm, which were tested at the age of 28 days in a normal hardening chamber.

To compare the proposed method with the prototype method, 5 batches were also prepared. Kneading No. 1 was prepared by the prototype method. As mixing fluid in this batch, ordinary tap water was used. The concrete mixture was prepared in accordance with the real (production) compositions of concrete mixtures [3, p. 49, table 3]. A concrete mix was prepared for concrete of grade 50. In the batch, cement of grade 300 was used. The water-cement ratio was V / C = 0.54, where B is the water consumption per 1 m ^{3 of} concrete, kg; C - cement consumption per 1 m ³ concrete, kg

Kneading No. 2 and mixing No. 3 were prepared similarly to the first batch, only catholyte with a pH of 11.4 and a redox potential of Eh = -520 mV was used in the second batch, and in the third a anolyte with a pH of 2.4 and redox were used -potential Eh = 1000 mV.

In batch No. 4, the concrete mixture was prepared according to the claimed method: the cement was activated with a high voltage potential of + 10 kV, and catholyte with a pH of 11.4 and a redox potential of Eh = -520 mV was used as a mixing liquid.

In experiment No. 5, the concrete mixture was prepared according to the claimed method: the cement was activated with a high voltage potential minus 10 kV, and anolyte with a pH of 2.4 and a redox potential of Eh = 1000 mV was used as a mixing liquid.

Foundation blocks were made from concrete mix with dimensions (2.4 × 0.6 × 0.4) m, which were subsequently tested. To provide an estimate of the concrete strength under normal conditions, control cubes were made with an edge of 150 × 150 × 150 mm, which were tested at the age of 28 days in a normal hardening chamber. This strength value was taken as 100%.

The results of the study of concrete samples prepared by the prototype method and by the present method are shown in table 2.

As follows from table 1 and table 2, the inventive method, compared with the prototype method, allowed: to increase the hydration of cement by 1.4-1.5 times; reduce setting time by 2.4-2.8 times; increase plastic strength by 3.4-3.8 times; increase bending strength by 1.8-1.9 times; increase the compressive strength by 1.4-1.5 times.

Information sources

1. RF patent No. 2093496. The method of preparation of activated concrete mix // Hasanov K.A., class. С04В 40/00, В28С 5/46. Publ. In the BI 10/20/1997.

2. B.C. Batalov. Vibrothermal technology of concrete. Theoretical Foundations: Monograph. - Magnitogorsk: MSTU, 2005.S. 10-11. (Prototype).

3. B.C. Batalov. Theoretical foundations of vibrothermal technology of monolithic concrete: - Magnitogorsk: MGMA, 1998. p. 49.

Claims (1)

A method of preparing a concrete mixture, which consists in the dosed supply of cement, aggregate and mixing fluid into the concrete mixer, followed by mixing of the mixture, characterized in that before the cement is fed into the concrete mixer, the cement particles are charged with a positive or negative electrostatic charge, for which they are passed through a mesh electrode, on which serves a high-voltage negative or positive potential, the absolute value of which lies in the range (8 ÷ 10) kV, while as a liquid atvoreniya use activated water, wherein when charging the cement particles a negative static charge in an activated liquid mixing is used the anolyte, having a value of the redox potential (Eh) _en lying in the range [250≤ (Eh) _en ≤1200] mV and the charging of particles a cement with a positive electrostatic charge, catholyte with a redox potential value (Еh) _cat lying in the range [-820≤ (Еh) _cat ≤ -300] mV is used as an activated mixing liquid.

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