A method for alkali fusion activation and activity improvement of recycled concrete micro powder based on industrial salt mud

Abstract

The application discloses a method for alkali fusion activation and activity improvement of recycled concrete micro powder based on industrial salt mud. The method is to take recycled concrete micro powder and industrial salt mud as base materials, and to realize calcination in a muffle furnace after adding a fluxing agent. The method for alkali fusion activation and activity improvement of recycled concrete micro powder based on industrial salt mud provided by the application can significantly improve the soluble Si and Al content and the activity index of the recycled concrete micro powder, and determines the relationship among the content of industrial salt mud, the content of the fluxing agent, the calcination temperature and the calcination time, so that the activity of the recycled concrete micro powder is designable and predictable. The method is convenient to operate, saves energy consumption and has excellent activity improvement effect. The method can realize full utilization of resources and meets the demand for sustainable development.

Description

Technical Field

[0001] The present invention belongs to the field of resource utilization of construction solid waste, and relates to a method for enhancing the activity of recycled concrete micropowder, and specifically to a method for alkali fusion activation and activity enhancement of recycled concrete micropowder based on industrial salt mud. Background Art

[0002] Currently, the primary method for disposing of waste concrete is open-air storage and landfill, which causes serious environmental problems and wastes resources. Waste concrete can be crushed and recycled to produce recycled aggregate for resource utilization. Current research shows that recycled aggregate, after various strengthening methods, can meet the requirements of a variety of engineering environments. The production of recycled aggregate produces a large amount of concrete fines, accounting for approximately 20-30% of the total mass. Concrete fines have a complex composition and low activity. Directly incorporating them into concrete can lead to adverse effects such as a significant decrease in mechanical properties, reduced fluidity, and increased shrinkage.

[0003] Since concrete micropowder contains some unhydrated cement particles, it has potential volcanic ash activity. In order to improve the activity of recycled micropowder, commonly used methods include mechanical ball milling, carbonization modification, high temperature treatment, nano-modification and microwave treatment. The invention patent with application number 202210331372.7 discloses a method for preparing a curing agent for the activation and utilization of recycled concrete micropowder. The method uses composite microorganisms to degrade and transform organic matter in silt / sludge into acidic substances, and further activates effective components such as calcium hydroxide in the recycled concrete powder, thereby improving the activity of the concrete powder; the invention patent with application number 202310373276.3 discloses a method for preparing carbon mineralized recycled micropowder, a carbon mineralized enhanced solid waste-based low-carbon concrete and a preparation method based on the same, which strengthens the recycled concrete micropowder by carbon dioxide, and composites the strengthened recycled concrete micropowder with calcined clay, cement clinker and gypsum to prepare a low-carbon cementitious material; the invention patent with application number 202410029203.7 discloses a method for preparing a concrete active regeneration solid waste-based low-carbon concrete. Raw micropowder and its preparation method, which activates recycled concrete micropowder through microwave excitation, thereby increasing the activity index of recycled concrete micropowder by about 10%; the invention patent with application number 202010820065.6 discloses a method for wet carbonization activation of waste concrete recycled micropowder and the application of recycled micropowder. The invention disperses the recycled concrete powder in water and introduces carbon dioxide to cause the recycled powder to undergo carbonization reaction to generate calcium carbonate and silicon dioxide, thereby increasing the volcanic ash activity of the recycled concrete micropowder; the invention patent with application number 202110353420.8 discloses a method for modifying concrete recycled micropowder and its application. The invention immerses the recycled concrete powder in tannic acid solutions of different concentrations to promote further hydration of active substances in the recycled concrete, thereby increasing the activity of the recycled concrete powder.

[0004] The above methods primarily target the incompletely hydrated active substances in recycled micropowder, promoting further hydration of these incompletely hydrated substances to enhance the pozzolanic activity of the recycled micropowder. In reality, the unhydrated particles contained in recycled micropowder are very limited, primarily consisting of mica, feldspar, and quartz. Furthermore, the potential active substance content in concrete micropowder after long-term service is even lower. Therefore, traditional modification methods have limited effectiveness in enhancing the activity of recycled micropowder.

[0005] Therefore, it is urgent to develop a method that can break through the limitation of low active substance content to further enhance the activity of recycled concrete powder to meet actual engineering needs. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for alkali melting activation and activity enhancement of recycled concrete based on industrial salt mud, which has the characteristics of simple operation, good activity enhancement effect and wide applicability. - , and invade the crystalline aluminosilicate structure in the recycled concrete powder, causing the breaking of chemical bonds such as Al-O and Si-O, increasing the number of non-bridging oxygen, and increasing the soluble silicon and aluminum content, thereby improving the activity of the recycled concrete powder.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for alkali fusion activation and activity enhancement of recycled concrete fine powder based on industrial salt mud. The method comprises: uniformly mixing the following raw materials in parts by weight: 65-100 parts of recycled concrete fine powder, 0-30 parts of industrial salt mud, and 0-5 parts of flux, and calcining the mixture in a muffle furnace, wherein the mixture has a total of 100 parts and the industrial salt mud and the flux are not taken as 0.

[0009] Preferably, the recycled concrete powder comes from waste concrete, such as building concrete structures with a service life of more than 20 years, and is obtained after crushing, grinding and screening, with an average particle size of 200 mesh, wherein the SiO2 component content is usually about 55%, the Al2O3 content is about 30%, and the CaO content is about 15%.

[0010] Preferably, the industrial salt mud is derived from waste mud generated in the industrial alkali production process, which is obtained after crushing, grinding and screening, with an average particle size of 200 mesh, and its main components are Mg(OH)2, CaCO3, BaSO4, etc.

[0011] Preferably, the flux is industrial caustic soda, the main component of which is NaOH, and the purity is above 96%.

[0012] Preferably, the material is placed in a muffle furnace for calcination, the calcination temperature is controlled to be 200-500°C, the calcination time is 0.5-2 hours, and the muffle furnace heating rate can be further controlled to be 20°C / min and the cooling rate to be 50°C / min.

[0013] In another aspect, the present invention also provides a design method for alkali fusion activation of recycled concrete fine powder derived from the above-mentioned activity enhancement method. The design method for alkali fusion activation of recycled concrete fine powder is based on the functional relationship between the activity index and the industrial salt mud content, flux content, calcination temperature, and calcination time. The details are as follows:

[0014]

[0015] in:

[0016] R——activity index;

[0017] C——mass percentage of industrial salt mud in the mixture of recycled concrete powder, industrial salt mud and flux;

[0018] Z——mass percentage of flux in the mixture of recycled concrete powder, industrial salt mud and flux;

[0019] S——calcination time, unit: h;

[0020] T——calcination temperature, unit ℃;

[0021] The industrial salt mud alkali fusion activated recycled concrete powder prepared by the above-mentioned activity enhancement method of the present invention meets the following requirements: the soluble silicon content is increased by 2-8 times, the soluble aluminum content is increased by 1-2.5 times, and the activity index is increased by 1-1.5 times within 24 hours.

[0022] The principle of the present invention is:

[0023] Under high temperature conditions, the addition of alkali solvents and fluxes reduces the decomposition temperature of recycled concrete powder. Simultaneously, the aluminosilicate network in the recycled concrete powder depolymerizes, and the depolymerized Si and Al form a disordered structure in an ionic environment. This process increases the soluble silicon and aluminum content, thereby improving the activity index of the recycled concrete powder.

[0024] Compared with traditional activation methods, the present invention has at least the following advantages:

[0025] 1) The alkali fusion activation and activity enhancement method of the present invention uses industrial salt mud and recycled concrete powder as the main raw materials, and realizes resource recycling through the coordinated disposal of multi-source solid waste, which meets the needs of sustainable development;

[0026] 2) The method of the present invention overcomes the limitation of low active substance content in recycled concrete powder by combining alkali fusion activation with industrial salt mud, significantly improving the activity of recycled concrete powder. It is particularly suitable for abandoned concrete structures with long service life and meets the needs of practical engineering.

[0027] 3) The method of the present invention effectively reduces the alkali melting activation temperature by introducing a flux, thereby effectively reducing production energy consumption.

[0028] 4) Through extensive research and analysis, the present invention has determined the strong correlation between the activity index and the industrial salt mud content, flux content, calcination temperature and calcination time, and has given a corresponding relationship formula, which has accurate and reliable predictability of the activity index and can provide powerful guidance for the alkali fusion activation design of recycled concrete micropowder.

[0029] 5) The method of the present invention has simple steps, convenient operation and good activity-enhancing effect. DETAILED DESCRIPTION

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The embodiments described are only a part of the embodiments of the present invention, rather than all of the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art, and the test methods in the following embodiments are conventional methods unless otherwise specified. Unless otherwise specified, the reagents and materials used can be obtained through commercial channels. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0031] In the examples, industrial salt mud was crushed, ground, and sieved to an average particle size of 200 mesh. The flux was industrial caustic soda, with the main component, NaOH, having a purity of 96% or higher. Recycled concrete powder was obtained by crushing, grinding, and sieving building concrete structures with a service life of more than 20 years, with an average particle size of 200 mesh. The industrial salt mud, flux, and recycled concrete powder were first mixed in a specific proportion and stirred in a blender at 150 rpm for 5 minutes. Approximately 1000 grams of the mixed material was then weighed and calcined in a muffle furnace. The calcined material was cooled to room temperature and then crushed and ground to produce a fine powder of approximately 200 mesh. The proportions and processing methods for each example are shown in Table 1.

[0032] Table 1: Example of alkali fusion activation process of recycled concrete micropowder based on industrial salt mud

[0033]

[0034]

[0035] The alkali-activated recycled concrete powder obtained in each example was ground and sieved to a particle size of about 200 mesh, and its soluble Si and Al contents were tested. The specific steps were as follows:

[0036] (1) Prepare a 1 mol / L sodium hydroxide solution using deionized water and chemically pure sodium hydroxide and place it at room temperature for more than 8 hours;

[0037] (2) Weigh 1.000 g of the recycled concrete powder to be tested and 100 mL of sodium hydroxide solution;

[0038] (3) Pour the recycled concrete powder and sodium hydroxide solution into a 200 mL plastic beaker, add a magnetic stirrer to the container at a stirring rate of 200 rpm, and place it in a 20 °C water bath to dissolve for 24 h;

[0039] (4) Take an appropriate amount of solution, filter it through 0.22 μm filter paper, and acidify the clear solution with 2% dilute nitric acid solution;

[0040] (5) The Al and Si contents in the solution were tested using an inductively coupled plasma mass spectrometer.

[0041] The alkali fusion activated regenerated fine powder obtained in each embodiment was tested according to GB / T1596-2017 for the activity index R of the regenerated concrete fine powder after alkali fusion activation. a The corresponding activity index R is calculated based on the intrinsic correlation between the activity index and the industrial salt mud content, flux content, calcination temperature and calcination time proposed by the present invention through a large number of experimental studies.

[0042] The soluble Si and Al content activity indices obtained above are shown in Table 2.

[0043] Table 2: Soluble Si and Al content and activity index of alkali-melting activated recycled concrete powder

[0044]

[0045]

[0046] In Examples 3-5, the soluble Si, Al content and activity index are significantly improved relative to Examples 1 and 2 by changing the industrial salt mud dosage, indicating that increasing the industrial salt mud content can significantly improve the activity of the recycled concrete powder; in Examples 5-7, the soluble Si, Al content and activity index first increase and then decrease with increasing temperature by changing the calcination temperature, and the best condition is when the calcination temperature is 300°C, indicating that increasing the calcination temperature first increases and then decreases the activity of the alkali-melting activated recycled powder; in Examples 5, 9 and 10, the soluble Si, Al content and activity index are increased by changing the flux dosage, indicating that adding flux is beneficial to improving the activity of alkali-melting activated recycled concrete powder; in Examples 5, 11 and 12, the soluble Si, Al content and activity index first increase and then decrease with time by changing the calcination time, and the best condition is when the calcination time is 1 hour, indicating that increasing the calcination time first increases and then decreases the activity of the alkali-melting activated recycled concrete powder. The errors between the measured activity index of each example and the calculated value proposed by the present invention are mostly less than 5%, and the individual error value is 10.4%, which are all within the acceptable range.

[0047] While various embodiments of the present invention have been described above, the above descriptions are intended to be illustrative and non-exhaustive, and are not intended to limit the present invention to the embodiments described. Modifications and improvements may be made by those skilled in the art without departing from the scope and spirit of the embodiments described, and the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for alkali fusion activation and activity enhancement of recycled concrete fine powder based on industrial salt mud, characterized in that: The method comprises: mixing 65-100 parts by mass of recycled concrete micropowder, 0-30 parts by mass of industrial salt mud, and 0-5 parts by mass of flux, and then calcining the mixture in a muffle furnace to enhance the activity of the recycled concrete micropowder, wherein the mixture has a total of 100 parts and the industrial salt mud and the flux are not taken to be 0; the flux is industrial caustic soda.

2. The method for alkali fusion activation and activity enhancement of recycled concrete fine powder based on industrial salt mud according to claim 1, characterized in that: The industrial salt mud is obtained by grinding and screening the industrial salt mud, and the average fineness is 200 meshes.

3. The method for alkali fusion activation and activity enhancement of recycled concrete fine powder based on industrial salt mud according to claim 1, characterized in that: The recycled concrete powder is obtained by crushing, sorting, grinding and screening discarded concrete structures, and has an average fineness of 200 meshes.

4. The method for alkali fusion activation and activity enhancement of recycled concrete fine powder based on industrial salt mud according to claim 1, characterized in that: The purity of NaOH in the flux is above 96%.

5. The method for alkali fusion activation and activity enhancement of recycled concrete fine powder based on industrial salt mud according to claim 1, characterized in that: The calcination is carried out in a muffle furnace at a temperature of 200-500° C. and a calcination time of 0.5-2 hours.

6. The method for alkali fusion activation and activity enhancement of recycled concrete fine powder based on industrial salt mud according to claim 1, characterized in that: The activity improvement includes an increase in soluble silicon content, an increase in soluble aluminum content and an increase in activity index.

7. The method for alkali fusion activation and activity enhancement of recycled concrete fine powder based on industrial salt mud according to claim 1, characterized in that: The treated recycled concrete powder: the soluble silicon content increases by 2-8 times in 24 hours, the soluble aluminum content increases by 1-2.5 times, and the activity index increases by 1-1.5 times.

8. A design method for alkali fusion activation of recycled concrete based on industrial salt mud, characterized in that: Based on the relationship between the activity index and the industrial salt mud content, flux content, calcination temperature and calcination time, the alkali fusion activation scheme of recycled concrete powder is designed as follows: ； in: R——activity index; C——mass percentage of industrial salt mud in the mixture of recycled concrete powder, industrial salt mud and flux; Z——mass percentage of flux in the mixture of recycled concrete powder, industrial salt mud and flux; S——calcination time, unit: h; T——calcination temperature, unit ℃; The flux is industrial caustic soda.

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