Natural hydraulic lime based on construction waste and preparation method thereof

Abstract

The invention belongs to the technical field of resource utilization of inorganic non-metallic materials and solid wastes, and discloses natural hydraulic lime based on construction wastes and a preparation method of the natural hydraulic lime. The natural hydraulic lime comprises the following raw materials in percentage by mass: 5-35% of waste concrete powder, 60-90% of carbide slag powder and 1-5% of red mud powder. According to the present invention, three bulk solid wastes are adopted as main raw materials, such that the effects of waste treatment with waste and synergistic utilization are achieved, the prepared product is the high value-added natural hydraulic lime, and can replace the traditional NHL, and the ratio of the three waste residues is accurately adjusted so as to stably produce the series products with different strength grades of NHL2, NHL3.5 and NHL5 so as to meet different market requirements.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials and solid waste resource utilization technology, and in particular to a natural hydraulic lime based on construction waste and its preparation method. Background Technology

[0002] Natural hydraulic lime (NHL) is a high-performance cementitious material that combines the good workability and permeability of lime with the underwater hardening ability similar to cement. It is widely used in the restoration of ancient buildings, the preservation of historical buildings, and modern green building applications. Traditional NHL is obtained by calcining siliceous limestone (CaCO3·SiO2·Al2O3, etc.) containing clay impurities. Its hydraulic properties primarily originate from the large amount of dicalcium silicate (C2S), and small amounts of tricalcium silicate (C3S) and calcium aluminate (C3A, C2S) generated during the calcination process. 12 A7) and other hydraulic minerals.

[0003] Currently, NHL production heavily relies on specific natural raw materials, which are limited and costly. On the other hand, my country faces severe pressure in solid waste management. Construction waste (mainly waste concrete) is generated in enormous quantities annually, and its disposal primarily relies on landfill and stockpiling, occupying land and polluting the environment. Calcium carbide slag, an industrial waste produced during acetylene production, is mainly composed of Ca(OH)2; large-scale accumulation easily causes dust and alkaline pollution. Red mud, a byproduct of alumina smelting, is rich in SiO2, Al2O3, Fe3O4, etc., is highly alkaline, has high treatment costs, and poses significant environmental risks.

[0004] While there are reports of using single or two types of industrial waste to prepare cementitious materials in existing technologies, most of these processes are complex or the products have limited performance and are difficult to directly replace standard NHL products. In particular, how to stably prepare different grades (NHL2, NHL3.5, NHL5) of natural hydraulic lime that meet international standards (such as EN 459-1) through precise batching design using solid waste with complex compositions remains a technical challenge.

[0005] Therefore, developing a technology that can synergistically process multiple bulk solid wastes and produce high-value-added NHL products has significant environmental and economic benefits. Summary of the Invention

[0006] The purpose of this invention is to provide a natural hydraulic lime based on construction waste and its preparation method, thereby solving the above-mentioned problems existing in the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a natural hydraulic lime based on construction waste, comprising the following raw materials by mass fraction: 5-35% waste concrete powder, 60-90% carbide slag powder, and 1-5% red mud powder.

[0008] Preferably, the specific surface area of ​​the waste concrete powder, carbide slag powder, and red mud powder is independently 400~550m². 2 / kg.

[0009] This invention also provides a method for preparing natural hydraulic lime based on construction waste, comprising the following steps: (1) The waste concrete is crushed, cleaned and ground to obtain waste concrete powder; the carbide slag is dried and ground to obtain carbide slag powder; the red mud is dried and ground to obtain red mud powder. (2) Mix waste concrete powder, carbide slag powder and red mud powder to obtain mixed raw meal; add water to the mixed raw meal and form it to obtain raw meal blank; calcine the raw meal blank to obtain calcined product; (3) Add water to the calcined product for digestion to obtain clinker; grind the clinker to obtain the natural hydraulic lime based on construction waste.

[0010] Preferably, the water in step (2) is 5-10% of the mass of the mixed raw material.

[0011] Preferably, the calcination temperature in step (2) is 950~1150℃; and the calcination time is 2~4h.

[0012] Preferably, the molding method in step (2) is pressing or granulation.

[0013] Preferably, the mass ratio of calcium oxide to water in the calcined product in step (3) is 1:1.1.

[0014] Preferably, the digestion time in step (3) is 3 to 5 days; the digestion temperature is 20 to 25°C.

[0015] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses three major solid wastes—waste concrete, carbide slag, and red mud—as the main raw materials, realizing “using waste to treat waste and synergistic utilization”, solving their environmental pollution problems, and conforming to the concept of circular economy.

[0016] (2) The product prepared is a high-value-added natural hydraulic lime, which can replace traditional NHL and is widely used in building repair and green building materials.

[0017] (3) High controllability: By precisely adjusting the proportion of the three types of waste residue, it is possible to stably produce a series of products with different strength grades (NHL2, NHL3.5, NHL5) just like "mixing a formula" to meet different market demands.

[0018] (4) Na2O and K2O in red mud act as natural mineralizers, effectively reducing the calcination temperature and saving energy.

[0019] (5) Simple process and easy to industrialize: The entire process is highly compatible with traditional cement and lime production processes, requires no complex equipment modification, and is easy to achieve large-scale industrial production. Detailed Implementation

[0020] This invention provides a natural hydraulic lime based on construction waste, comprising the following raw materials by mass fraction: 5-35% waste concrete powder, 60-90% carbide slag powder, and 1-5% red mud powder.

[0021] In this invention, the specific surface area of ​​the waste concrete powder, carbide slag powder, and red mud powder is preferably 400-550 m². 2 / kg.

[0022] In this invention, when the mass fraction of the raw materials is 8-18% waste concrete powder, 80-90% carbide slag powder, and 1-2% red mud powder, the content of hydraulic minerals (mainly C2S) in the natural hydraulic lime is relatively low, which meets the NHL2 standard. Its characteristics are slow strength development and good flexibility.

[0023] In this invention, when the mass fraction of the raw materials is 18-25% waste concrete powder, 70-80% carbide slag powder, and 1-5% red mud powder, the content of hydraulic minerals in the natural hydraulic lime is moderate and meets the NHL3.5 standard. Its characteristics are that the strength and flexibility are relatively balanced.

[0024] In this invention, when the mass fraction of the raw materials is 27-35% waste concrete powder, 60-70% carbide slag powder, and 1-5% red mud powder, the natural hydraulic lime has a high content of hydraulic minerals, which meets the NHL5 standard. Its characteristics are high strength and outstanding hydraulic properties.

[0025] This invention also provides a method for preparing natural hydraulic lime based on construction waste, comprising the following steps: (1) The waste concrete is crushed, cleaned and ground to obtain waste concrete powder; the carbide slag is dried and ground to obtain carbide slag powder; the red mud is dried and ground to obtain red mud powder. (2) Mix waste concrete powder, carbide slag powder and red mud powder to obtain mixed raw meal; add water to the mixed raw meal and form it to obtain raw meal blank; calcine the raw meal blank to obtain calcined product; (3) Add water to the calcined product for digestion to obtain clinker; grind the clinker to obtain the natural hydraulic lime based on construction waste.

[0026] In this invention, the mass of water in step (2) is preferably 5 to 10% of the mass of the mixed raw material, more preferably 5 to 8%, and even more preferably 5%.

[0027] In this invention, the calcination temperature in step (2) is preferably 950~1150℃, more preferably 980~1100℃, and even more preferably 1000℃; the calcination time is preferably 2~4h, more preferably 2.5~3.5h, and even more preferably 3h. During the calcination process of this invention, the following main reactions occur: Ca(OH)2 in carbide slag powder and waste concrete powder decomposes into CaO; CaCO3 in carbide slag powder and waste concrete powder decomposes into CaO; The clay components (SiO2 and Al2O3) in waste concrete powder, carbide slag powder, and red mud powder react with newly formed CaO to produce dicalcium silicate (C2S) and calcium aluminate (C3A, C2S). 12 A7) and other hydraulic minerals; The abundant Na2O and K2O in red mud powder act as mineralizers, lowering the calcination temperature and promoting mineral formation.

[0028] In this invention, the molding method in step (2) is preferably pressing or granulation; the particle size of the raw material blank is preferably 5~20mm, more preferably 9~15mm, and even more preferably 10mm.

[0029] In this invention, the mass ratio of calcium oxide to water in the calcined product of step (3) is preferably 1:1.1.

[0030] In this invention, the digestion time in step (3) is preferably 3 to 5 days, more preferably 3 days, 4 days or 5 days, and more preferably 5 days; the digestion temperature is preferably 20 to 25°C, and more preferably 25°C.

[0031] In this invention, step (3) involves grinding the powder to a specific surface area of ​​400-550 m². 2 / kg, further preferably 450~530m 2 / kg, more preferably 500m 2 / kg.

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] This embodiment provides a natural hydraulic lime based on construction waste, comprising the following raw materials by mass fraction: 12% waste concrete powder, 86% carbide slag powder, and 2% red mud powder.

[0035] A method for preparing natural hydraulic lime based on construction waste includes the following steps: (1) The waste concrete was crushed, impurities removed, and ground to obtain a specific surface area of ​​480 m². 2 / kg of waste concrete powder; the carbide slag is dried and ground to obtain a specific surface area of ​​460m². 2 / kg of calcium carbide slag powder; red mud is dried and ground to obtain a specific surface area of ​​450m². 2 / kg of red mud powder; (2) Mix waste concrete powder, carbide slag powder and red mud powder evenly to obtain mixed raw meal; add water (the mass of water is 5% of the mass of mixed raw meal) to the mixed raw meal and press it into shape to obtain raw meal blocks with a diameter of 10 mm; place the raw meal blocks in a 100°C forced-air drying oven for 6 hours to dry them thoroughly; calcine the raw meal blocks at 1000°C for 3 hours, and after calcination, quickly take them out and air cool them to room temperature to obtain calcined products; (3) Calculate the theoretical water consumption required for digestion based on the amount of calcium oxide (CaO) in the calcined product. Multiply by the correction factor 1.1 to get the water consumption required for digestion, i.e., the mass ratio of CaO to H2O = 1:1.1. During digestion, the calcined product to be digested is piled up layer by layer, with each layer being 1 cm thick. Water is sprinkled evenly on each layer until the pile is completed. Stir once every 12 hours during the digestion process to ensure thorough digestion. Take it out after 3 days of digestion. After digestion, measure the free calcium oxide content. When the free calcium oxide content is <2%, it indicates that the digestion process is over. Grind the digested clinker to control the specific surface area of ​​the finished product to be 480 m². 2 / kg, to obtain the natural hydraulic lime based on construction waste.

[0036] Example 2

[0037] This embodiment provides a natural hydraulic lime based on construction waste, comprising the following raw materials by mass fraction: 17% waste concrete powder, 82% carbide slag powder, and 1% red mud powder.

[0038] For a specific method for preparing natural hydraulic lime based on construction waste, please refer to Example 1.

[0039] Example 3

[0040] This embodiment provides a natural hydraulic lime based on construction waste, comprising the following raw materials by mass fraction: 20% waste concrete powder, 78% carbide slag powder, and 2% red mud powder.

[0041] For a specific method for preparing natural hydraulic lime based on construction waste, please refer to Example 1.

[0042] Example 4

[0043] This embodiment provides a natural hydraulic lime based on construction waste, comprising the following raw materials by mass fraction: 24% waste concrete powder, 75% carbide slag powder, and 1% red mud powder.

[0044] For a specific method for preparing natural hydraulic lime based on construction waste, please refer to Example 1.

[0045] Example 5

[0046] This embodiment provides a natural hydraulic lime based on construction waste, comprising the following raw materials by mass fraction: 30% waste concrete powder, 69% carbide slag powder, and 1% red mud powder.

[0047] For a specific method for preparing natural hydraulic lime based on construction waste, please refer to Example 1.

[0048] Example 6

[0049] This embodiment provides a natural hydraulic lime based on construction waste, comprising the following raw materials by mass fraction: 34% waste concrete powder, 64% carbide slag powder, and 2% red mud powder.

[0050] For a specific method for preparing natural hydraulic lime based on construction waste, please refer to Example 1.

[0051] The chemical composition of the raw materials used in Examples 1-6, namely waste concrete, carbide slag, and red mud, is shown in Table 1.

[0052] Table 1 Chemical composition of raw materials for waste concrete, carbide slag, and red mud

[0053] The chemical composition of the raw materials in Examples 1-6 is shown in Table 2.

[0054] Table 2 Chemical composition after raw material ratio

[0055] Comparative Examples 1-3

[0056] Comparative examples 1-3 used commercially available NHL2, NHL3.5, and NHL5, respectively.

[0057] The compressive strength of the natural hydraulic lime prepared in Examples 1-6 and the NHL2, NHL3.5, and NHL5 of Comparative Examples 1-3 were tested according to the test methods specified in European standards BS-EN-459 and BS-EN-196. Specifically, 450±2g of natural hydraulic lime, 1350g±5g of standard sand, and 225g±1g of water were weighed, with a water-cement ratio of 0.5, and 40mm×40mm×160mm standard specimens were prepared. The prepared specimens were cured in a constant temperature and humidity standard curing chamber for 28 days, and various indicators of the natural hydraulic lime were measured. The results are shown in Table 3.

[0058] Table 3 Test results of the properties of natural hydraulic lime

[0059] The above results demonstrate that by flexibly adjusting the proportions of waste concrete, carbide slag, and red mud, this invention can successfully prepare natural hydraulic lime of different grades. The process route is feasible, and the product performance meets the standards.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A natural hydraulic lime based on construction waste, characterized in that, Raw materials containing the following mass fractions: 5-35% waste concrete powder, 60-90% carbide slag powder, and 1-5% red mud powder.

2. The natural hydraulic lime based on construction waste according to claim 1, characterized in that, The specific surface area of ​​the waste concrete powder, carbide slag powder, and red mud powder is independently 400~550m². 2 / kg.

3. A method for preparing natural hydraulic lime based on construction waste as described in claim 1 or 2, characterized in that, Includes the following steps: (1) The waste concrete is crushed, cleaned and ground to obtain waste concrete powder; the carbide slag is dried and ground to obtain carbide slag powder; the red mud is dried and ground to obtain red mud powder. (2) Mix waste concrete powder, carbide slag powder and red mud powder to obtain mixed raw meal; add water to the mixed raw meal and form it to obtain raw meal blank; calcine the raw meal blank to obtain calcined product; (3) Add water to the calcined product for digestion to obtain clinker; grind the clinker to obtain the natural hydraulic lime based on construction waste.

4. The method for preparing natural hydraulic lime based on construction waste according to claim 3, characterized in that, The mass of water in step (2) is 5-10% of the mass of the mixed raw material.

5. The method for preparing natural hydraulic lime based on construction waste according to claim 4, characterized in that, The calcination temperature in step (2) is 950~1150℃; the calcination time is 2~4h.

6. The method for preparing natural hydraulic lime based on construction waste according to claim 5, characterized in that, The molding method described in step (2) is pressing or granulation.

7. The method for preparing natural hydraulic lime based on construction waste according to claim 5, characterized in that, In step (3), the mass ratio of calcium oxide to water in the calcined product is 1:1.

1.

8. The method for preparing natural hydraulic lime based on construction waste according to claim 7, characterized in that, The digestion time in step (3) is 3 to 5 days; the digestion temperature is 20 to 25°C.

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