Alkali fusion activation and activity improvement method for recycled concrete micropowder based on industrial salty mud

Abstract

The invention discloses a recycled concrete micro-powder alkali fusion activation and activity improvement method based on industrial salty mud. Recycled concrete micro powder and industrial salty mud are used as base materials, and after a fluxing agent is doped, calcination is carried out in a muffle furnace. According to the industrial salty mud-based regenerated concrete micro-powder active alkali fusion activation and activity improvement method provided by the invention, the content of soluble Si and Al and the activity index of the regenerated concrete micro-powder can be remarkably improved; the relationship among the industrial salty mud content, the fluxing agent content, the calcining temperature and the calcining time is determined, and the activity of the recycled concrete micro powder can be designed and predictable; the method is convenient to operate, energy consumption is reduced, and the activity improving effect is excellent. Resources can be fully utilized, and the sustainable development requirement is met.

Description

Technical Field

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

[0002] The main treatment method for waste concrete is open-air placement and landfill, which has caused serious environmental problems and waste of resources. Waste concrete can be crushed to prepare recycled aggregate for resource utilization. Current research shows that recycled aggregate can meet the requirements of various engineering environments after various strengthening methods. In the process of preparing recycled aggregate, a large amount of concrete powder will be produced, accounting for about 20-30% of the total mass. Concrete powder has complex composition and low activity. Directly adding it to concrete will cause adverse effects such as a significant decrease in mechanical properties, reduced fluidity and large shrinkage.

[0003] Since concrete powder contains some unhydrated cement particles, it has potential volcanic ash activity. In order to improve the activity of recycled powder, 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 powder. The method uses composite microorganisms to degrade and transform organic matter in sludge / 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 powder, a carbon mineralized enhanced solid waste-based low-carbon concrete and a preparation method based thereon. The method strengthens the recycled concrete powder by carbon dioxide, and composites the strengthened recycled concrete powder 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, so that the activity index of recycled concrete micropowder is increased 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 carbonize the recycled powder to generate calcium carbonate and silicon dioxide, thereby improving 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 improving the activity of the recycled concrete powder.

[0004] The above methods mainly target the active substances in the recycled micropowder that are not fully hydrated, and promote the further hydration of these incompletely hydrated substances to enhance the volcanic ash activity of the recycled micropowder. In fact, the unhydrated particles contained in the recycled micropowder are very limited, and the main mineral components are mica, feldspar and quartz, etc., and the potential content of active substances in concrete micropowder after long-term service is even lower. Therefore, traditional modification methods have limited effect on improving 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 prior art, the present invention aims to provide a method for alkali melting activation and activity enhancement of recycled concrete micropowder based on industrial salt mud, which has the characteristics of simple operation, good activity enhancement effect and wide applicability. In the present invention, industrial salt mud and flux are ionized to produce OH under high temperature. - , and invade the crystalline aluminosilicate structure in the recycled concrete powder, causing the breakage 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 enhancing 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 invention provides a method for alkali fusion activation and activity improvement of recycled concrete fine powder based on industrial salt mud. The method comprises: 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 then calcining them in a muffle furnace, wherein the mixture has a total of 100 parts and the industrial salt mud and the flux are not taken to be 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 can be further controlled to be 50° C. / min.

[0013] On the other hand, the present invention also provides a design method for alkali fusion activation of recycled concrete micropowder derived from the above-mentioned activity enhancement method, which designs the alkali fusion activation scheme of recycled concrete micropowder according to 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 regenerated 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, with the addition of alkali flux and flux, the decomposition temperature of recycled concrete powder is reduced, and the aluminosilicate network structure in the recycled concrete powder is depolymerized, and the depolymerized Si and Al form a disordered structure in the ionic environment. This process promotes the soluble silicon and aluminum content, thereby improving the activity index of recycled concrete powder.

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

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

[0026] 2) The method of the present invention breaks through the limitation of low content of active substances in recycled concrete micropowder by combining alkali melting activation with industrial salt mud, significantly improves the activity of recycled concrete micropowder, and is particularly suitable for abandoned concrete structures with a long service life, meeting the needs of actual engineering;

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

[0028] 4) Through a large number of 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, 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 improvement effect. DETAILED DESCRIPTION

[0030] The technical scheme 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 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 all be obtained through commercial channels. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the technical field without making creative work belong to the scope of protection of the present invention.

[0031] In the embodiment, the industrial salt mud is crushed, ground and sieved, and the average particle size is 200 mesh, the flux is industrial caustic soda, and the main component NaOH has a purity of more than 96%, and the recycled concrete powder is a building concrete structure with a service life of more than 20 years, which is crushed, ground and sieved, and the average particle size is 200 mesh; first, the industrial salt mud, the flux and the recycled concrete powder are mixed in a certain proportion, placed in a mixer and stirred at a speed of 150rpm for 5 minutes, and then about 1000 grams of the mixed material is weighed and placed in a muffle furnace for calcination. After the calcined material is cooled to room temperature, it is crushed and ground to prepare a powder of about 200 mesh. The proportions and treatment methods in the embodiments are shown in Table 1.

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

[0033]

[0034]

[0035] The recycled concrete powder after alkali fusion activation obtained in each embodiment was ground and sieved to make the particles about 200 meshes, and its soluble Si and Al content was tested. The specific steps are 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, stir at a rate of 200 rpm, and place 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-melting activated regenerated micropowder obtained in each embodiment is tested according to GB / T1596-2017 for the activity index R of the regenerated concrete micropowder after alkali-melting 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 above-obtained soluble Si and Al content activity indexes 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] The embodiments 3-5 change the dosage of industrial salt mud so that the soluble Si, Al content and activity index are significantly improved compared with embodiments 1 and 2, indicating that increasing the content of industrial salt mud can significantly improve the activity of recycled concrete powder; the embodiments 5-7 change the calcination temperature so that the soluble Si, Al content and activity index first increase and then decrease with increasing 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 alkali-melting activated recycled powder; the embodiments 5, 9 and 10 change the dosage of flux so that the soluble Si, Al content and activity index are improved, indicating that adding flux is beneficial to improving the activity of alkali-melting activated recycled concrete powder; the embodiments 5, 11 and 12 change the calcination time so that the soluble Si, Al content and activity index first increase and then decrease with 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 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] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the embodiments listed. Without departing from the scope and spirit of the embodiments described, it is possible for a person of ordinary skill in the art to make some modifications and improvements, so the scope of protection of the present invention shall be based on the definition of the claims.

Claims

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

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

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

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

7. The method for alkali fusion activation and activity enhancement of recycled concrete micropowder 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: According to the relationship between the activity index and the industrial salt mud content, flux content, calcination temperature and calcination time, the alkali melting activation scheme of recycled concrete powder is designed as follows: R=0.18(C+1.5Z)+0.07e -4(s-1)2 +0.1e -0.001(T-300)2 +0.633 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 ℃.

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