High-strength recycled concrete and method for manufacturing the same

Abstract

The application relates to the field of concrete, and specifically discloses a high-strength recycled concrete, which comprises the following raw materials in parts by weight: modified recycled aggregate 100-150 parts, cement 80-95 parts, dihydroxyphenylalanine 4.5-9 parts, composite mineral aggregate 15-38 parts, water reducing agent 1-3 parts, machine-made sand 45-65 parts and water 38-50 parts; a preparation method of the recycled concrete, which comprises the following steps: uniformly mixing the modified recycled aggregate, the cement, the dihydroxyphenylalanine, the composite mineral aggregate, the water reducing agent, the machine-made sand and the water according to the formula amount to obtain the recycled concrete. The obtained recycled concrete has a compact internal structure, good compactness, excellent mechanical properties and high compressive strength, and the quality loss of the concrete is small in a salt-frozen environment, and the service life is long.

Description

Technical Field

[0001] This application relates to the field of concrete, and more specifically, to a high-strength recycled concrete and a method for its preparation. Background Technology

[0002] With the rapid development of urbanization, the application of concrete in engineering has also brought about a large amount of construction waste. Recycled concrete refers to concrete made by crushing, screening, and removing impurities from waste concrete to produce recycled aggregates, which are then used to replace natural aggregates in a certain proportion. The emergence of recycled concrete can effectively alleviate the problems of construction waste accumulation and natural sand and gravel shortage.

[0003] For example, Chinese invention patent CN107010896A discloses a recycled concrete incorporating chopped basalt fiber and recycled coarse aggregate, made from the following raw materials in parts by weight: 100-300 parts water, 300-500 parts ordinary Portland cement, 500-700 parts medium sand, 500-650 parts natural crushed stone, 500-650 parts recycled coarse aggregate, 30-50 parts fly ash, 1-5 parts water-reducing agent, and 1-6 parts chopped basalt fiber. While this recycled concrete can improve its compressive strength to some extent, in northern my country, the soil contains large amounts of chloride and sulfate ions, and the large diurnal temperature range creates a freeze-thaw environment. This causes the concrete to suffer from both salt ion erosion and freeze-thaw damage, resulting in significant quality loss and greatly reducing its service life. Summary of the Invention

[0004] In order to significantly reduce the quality loss of concrete in a salt-freezing environment and extend the service life of concrete, this application provides a high-strength recycled concrete and a method for preparing the same.

[0005] In the first aspect, this application provides a high-strength recycled concrete, employing the following technical solution:

[0006] A high-strength recycled concrete comprises the following raw materials in parts by weight: 100-150 parts modified recycled aggregate, 80-95 parts cement, 4.5-9 parts dihydroxyphenylalanine, 15-38 parts composite mineral aggregate, 1-3 parts water-reducing agent, 40-60 parts manufactured sand, 20-30 parts crushed stone, and 30-40 parts water.

[0007] The modified recycled aggregate includes the following preparation steps: crushing, screening, and removing impurities from waste concrete to obtain aggregate with a gradation range of 5-25mm; adding a calcium ion-containing accelerator to the aggregate; and adding a carbonate solution during stirring to obtain the modified recycled aggregate.

[0008] By adopting the above technical solution, waste concrete is pretreated to obtain aggregates with the corresponding gradation range. The aggregates are modified using a calcium-ion-containing accelerator and carbonates. The calcium ions in the carbonate solution and the calcium-ion-containing accelerator combine to form calcium carbonate, which adheres to the aggregate surface. This stabilizes calcium hydroxide in the concrete, slows down the alkali-skeleton reaction, and prevents calcium hydroxide from dissolving and leaching in humid environments, thus maintaining the mechanical properties of the concrete. Simultaneously, under the action of the accelerator, the modified recycled aggregates effectively bind other raw material components, fill micropores and voids in the concrete, reduce the void ratio, improve the density of the concrete, enhance its mechanical properties, reduce mass loss in salt-freezing environments, and extend the service life of the concrete.

[0009] Dihydroxyphenylalanine not only acts as a modifier to adjust the setting time of concrete, but also effectively improves the salt resistance of concrete, reduces the mass loss of concrete in salt-freezing environments, and extends the service life of concrete. Simultaneously, both carbonate solutions and organic calcium solutions are weakly alkaline, which can make the modified recycled aggregate weakly alkaline, further reducing the erosion of concrete by sulfates and chloride ions, improving the stability of concrete, and minimizing the mass loss of concrete in salt-freezing environments.

[0010] The modified recycled aggregates described above can be used immediately after mixing. The modified recycled aggregates have a certain moisture content, which can further reduce the amount of water used when preparing concrete according to actual needs. They can also work synergistically with dihydroxyphenylalanine to significantly reduce the quality loss of concrete in salt-freeze environments and extend the service life of concrete.

[0011] Preferably, the calcium-containing promoting liquid comprises dopamine powder and organic calcium solution in a weight ratio of 1:(8-17).

[0012] Dihydroxyphenylalanine can further combine with dopamine in the accelerator to form a substance with excellent adhesion, which facilitates a tight bond between the modified recycled aggregate and the various raw material components. Both carbonate and organic calcium solutions are weakly alkaline, which can further promote the self-polymerization of some dopamine powder to form polydopamine with excellent adhesive properties, thereby improving the internal density of concrete and enhancing its mechanical properties.

[0013] Further experimental research revealed that excessive dopamine powder or organic calcium solution is detrimental to optimizing the internal structure of the concrete system. When the weight ratio of dopamine powder to organic calcium solution is 1:(8-17), the concrete exhibits better compressive strength and superior salt-freezing resistance.

[0014] Preferably, the organic calcium solution is a calcium acetate solution and / or a calcium lactate solution.

[0015] Furthermore, the organic calcium solution is preferably a mixture of calcium acetate and calcium lactate solutions, with the calcium acetate solution having a mass fraction of 18-30% and the calcium lactate solution having a mass fraction of 15-22%.

[0016] Both calcium acetate and calcium lactate solutions can provide a weakly alkaline environment for the system, creating favorable conditions for subsequent reactions. Using calcium acetate and calcium lactate solutions with higher mass fractions can not only effectively promote the reaction and provide favorable conditions, but also save costs to some extent.

[0017] Preferably, the carbonate solution is a sodium carbonate solution or a potassium carbonate solution.

[0018] The sodium carbonate solution is further preferred, with a mass fraction of 13-21%.

[0019] Using sodium carbonate or potassium carbonate solution can help obtain higher quality modified recycled aggregates, thereby helping to improve the overall performance of concrete.

[0020] Preferably, the components used in the modified recycled aggregate are as follows: by weight, 90-110 parts waste concrete, 20-32 parts calcium ion-containing accelerator, and 16-25 parts carbonate solution.

[0021] By adopting the above technical solution, the amount of components used in the modified recycled aggregate is optimized, and the quality of the modified recycled aggregate is further improved. At the same time, the carbonate solution is appropriately excessive compared with the organic calcium solution. The excessive carbonate solution can also regulate the cement hydration rate, reduce the heat of cement hydration reaction, enhance the bonding strength of each component of concrete, thereby further improving the mechanical properties of concrete and reducing the quality loss of concrete in the salt-freeze environment.

[0022] Preferably, the composite mineral material includes at least two of fly ash, silica fume, and slag powder.

[0023] Further preferred, the composite mineral material is a mixture of fly ash, silica fume and slag powder, with a weight ratio of fly ash, silica fume and slag powder of 1:(0.8-1.7):(0.5-1).

[0024] Furthermore, the fly ash is grade 1, the silica fume grade is SF88, and the loss on ignition is 2.5-2.8%; the slag powder is grade S95, and the moisture content is ≤0.3%.

[0025] Selecting appropriate composite aggregates can not only adjust the fluidity of concrete to improve its workability, but also improve the internal structure and density of concrete by effectively participating in the hydration of cement, thus reducing the quality loss of concrete in salt-freezing environments.

[0026] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent with a solid content of 30-45% and a water reduction rate of 20%-40%.

[0027] By adopting the above technical solutions and optimizing the selection of water-reducing agents, it is beneficial to achieve better dispersion of cement particles, effectively reduce the sliding resistance between cement particles, improve the workability and fluidity of concrete, and help improve the overall performance of concrete.

[0028] Secondly, this application provides a method for preparing high-strength recycled concrete, employing the following technical solution:

[0029] A method for preparing high-strength recycled concrete includes the following steps: mixing modified recycled aggregate, cement, dihydroxyphenylalanine, composite mineral aggregate, water-reducing agent, manufactured sand and water evenly according to the formula to obtain recycled concrete.

[0030] The recycled concrete obtained above has a dense internal structure, good compactness, excellent mechanical properties, high compressive strength, and minimal mass loss and long service life under salt-freezing conditions.

[0031] In summary, this application has the following beneficial effects:

[0032] 1. Waste concrete is pretreated to obtain aggregates with the corresponding gradation range. The aggregates are modified using a calcium-ion-containing accelerator and carbonates. The calcium ions in the carbonate solution and the calcium-ion-containing accelerator combine to form calcium carbonate, which adheres to the aggregate surface. This stabilizes the calcium hydroxide in the concrete, slows down the alkali-skeleton reaction, and prevents calcium hydroxide from dissolving and leaching in humid environments, thus maintaining the mechanical properties of the concrete. Simultaneously, under the action of the accelerator, the modified recycled aggregates effectively bind other raw material components, fill micropores and voids in the concrete, reduce the void ratio, improve the density of the concrete, enhance its mechanical properties, reduce mass loss in salt-freezing environments, and extend the service life of the concrete.

[0033] 2. Dihydroxyphenylalanine not only acts as a modifier to adjust the setting time of concrete, but also effectively improves the salt resistance of concrete, reduces the mass loss of concrete in salt-freezing environments, and extends the service life of concrete. Simultaneously, both carbonate solutions and organic calcium solutions are weakly alkaline, which can make the modified recycled aggregate weakly alkaline, further reducing the erosion of concrete by sulfates and chloride ions, improving the stability of concrete, and minimizing the mass loss of concrete in salt-freezing environments.

[0034] 3. Dihydroxyphenylalanine can further combine with dopamine in the accelerator to form a substance with excellent adhesion, which facilitates a tight bond between the modified recycled aggregate and the various raw material components. Both carbonate and organic calcium solutions are weakly alkaline, which can further promote the self-polymerization of some dopamine powder to form polydopamine with excellent adhesion, thereby improving the internal density of concrete and enhancing its mechanical properties. Detailed Implementation

[0035] The present application will be further described in detail below with reference to the embodiments.

[0036] Example of modified recycled aggregate preparation

[0037] Preparation Example 1

[0038] Modified recycled aggregate includes the following preparation steps: 9 kg of waste concrete is crushed, screened, and impurities are removed to obtain aggregate with a gradation range of 5-25 mm. 2 kg of calcium ion-containing accelerator liquid is added to the aggregate, and 1.6 kg of sodium carbonate solution is added during the stirring process to obtain modified recycled aggregate.

[0039] The calcium ion-containing promoting solution is composed of dopamine powder and calcium acetate solution in a weight ratio of 1:8, with the calcium acetate solution having a mass fraction of 30%.

[0040] Preparation Example 2

[0041] Modified recycled aggregate includes the following preparation steps: 11 kg of waste concrete is crushed, screened, and impurities are removed to obtain aggregate with a gradation range of 5-25 mm. 3.2 kg of calcium ion-containing accelerator is added to the aggregate, and 2.5 kg of potassium carbonate solution is added during the stirring process to obtain modified recycled aggregate.

[0042] The calcium ion-containing promoting solution is composed of dopamine powder and calcium lactate solution in a weight ratio of 1:8, with the calcium lactate solution having a mass fraction of 22%.

[0043] Preparation Example 3

[0044] Modified recycled aggregate includes the following preparation steps: 10 kg of waste concrete is crushed, screened, and impurities are removed to obtain aggregate with a gradation range of 5-25 mm. 3 kg of calcium ion-containing accelerator liquid is added to the aggregate, and 2.2 kg of sodium carbonate solution is added during the stirring process to obtain modified recycled aggregate.

[0045] The calcium ion-containing promoting solution is composed of dopamine powder and organic calcium solution in a weight ratio of 1:17. The organic calcium solution is composed of 15% calcium lactate solution and 18% calcium acetate solution, with a weight ratio of 1:1 between the calcium lactate solution and the calcium acetate solution.

[0046] Preparation Example 4

[0047] The difference from Preparation Example 3 is that the calcium ion-containing promoting solution is a dopamine powder and an organic calcium solution in a weight ratio of 1:15. The organic calcium solution is a calcium lactate solution with a mass fraction of 25% and a calcium acetate solution with a mass fraction of 20%. The rest is the same as Preparation Example 3.

[0048] Preparation Example 5

[0049] The difference from Preparation Example 4 is that the modified recycled aggregate includes the following preparation steps: 12 kg of waste concrete is crushed, screened and impurities are removed to obtain aggregate with a gradation range of 5-25 mm, 1 kg of calcium ion-containing accelerator is added to the aggregate, and 1.2 kg of sodium carbonate solution is added during the stirring process to obtain the modified recycled aggregate; the rest is the same as Preparation Example 4.

[0050] Comparative Preparation Example 1

[0051] Modified recycled aggregate includes the following steps: 10 kg of waste concrete is crushed, screened, and impurities are removed to obtain aggregate with a gradation range of 5-25 mm. 4 kg of water glass solution is added to the aggregate and soaked for 2 hours. The mass fraction of the water glass solution is 5%.

[0052] Comparative Preparation Example 2

[0053] The difference from Preparation Example 4 is that the sodium carbonate solution is replaced with an equal amount of sodium nitrate solution, while the rest is the same as Preparation Example 4.

[0054] Comparative preparation example 3

[0055] The difference from Preparation Example 4 is that dopamine powder was not added; otherwise, they are the same as Preparation Example 4.

[0056] Example

[0057] Example 1

[0058] A high-strength recycled concrete comprises the following raw materials: 10 kg of modified recycled aggregate prepared in Preparation Example 1, 8 kg of cement, 0.45 kg of dihydroxyphenylalanine, 1.5 kg of composite mineral aggregate, 0.1 kg of polycarboxylate superplasticizer, 4 kg of manufactured sand, 2 kg of crushed stone, and 3 kg of water.

[0059] The composite mineral material is fly ash and slag powder in a weight ratio of 1:0.8;

[0060] A method for preparing high-strength recycled concrete includes the following steps: mixing the above-mentioned modified recycled aggregate, cement, dihydroxyphenylalanine, composite mineral aggregate, water-reducing agent, manufactured sand and water evenly according to the formula to obtain recycled concrete.

[0061] Example 2

[0062] A high-strength recycled concrete comprises the following raw materials: 15 kg of modified recycled aggregate prepared in Preparation Example 1, 9.5 kg of cement, 0.9 kg of dihydroxyphenylalanine, 3.8 kg of composite mineral aggregate, 0.3 kg of polycarboxylate superplasticizer, 6 kg of manufactured sand, 3 kg of crushed stone, and 4 kg of water.

[0063] The composite mineral material is silica fume and slag powder in a weight ratio of 1.7:0.5;

[0064] The preparation method of recycled concrete is the same as in Example 1.

[0065] Example 3

[0066] A high-strength recycled concrete comprises the following raw materials: 13.5 kg of modified recycled aggregate prepared in Preparation Example 1, 8.9 kg of cement, 0.78 kg of dihydroxyphenylalanine, 3 kg of composite mineral aggregate, 0.2 kg of polycarboxylate superplasticizer, 5 kg of manufactured sand, 2.7 kg of crushed stone, and 3.4 kg of water.

[0067] The composite mineral material consists of fly ash, silica fume, and slag powder in a weight ratio of 1:1.3:1.

[0068] The preparation method of recycled concrete is the same as in Example 1.

[0069] Example 4

[0070] The difference from Example 3 is that the composite mineral material is fly ash, silica fume and slag powder in a weight ratio of 1:1.5:0.7; the rest are the same as in Example 3.

[0071] Example 5

[0072] The difference from Example 4 is that the modified recycled aggregate prepared in Preparation Example 2 was used, while the rest were the same as in Example 4.

[0073] Example 6

[0074] The difference from Example 4 is that the modified recycled aggregate prepared in Preparation Example 3 was used, while the rest were the same as in Example 4.

[0075] Example 7

[0076] The difference from Example 4 is that the modified recycled aggregate prepared in Example 4 was used, while the rest are the same as in Example 4.

[0077] Example 8

[0078] The difference from Example 4 is that the modified recycled aggregate prepared in Preparation Example 5 was used, while the rest are the same as in Example 4.

[0079] Comparative Example

[0080] Comparative Example 1

[0081] The difference from Example 7 is that glycine is used in place of dihydroxyphenylalanine in equal amounts, while the rest are the same as in Example 7.

[0082] Comparative Example 2

[0083] The difference from Example 7 is that the modified recycled aggregate prepared in Comparative Preparation Example 1 was used, while all other aspects were the same as in Example 7.

[0084] Comparative Example 3

[0085] The difference from Example 7 is that the modified recycled aggregate prepared in Comparative Preparation Example 2 was used, while the rest were the same as in Example 7.

[0086] Comparative Example 4

[0087] The difference from Example 7 is that the modified recycled aggregate prepared in Comparative Preparation Example 3 was used, while all other aspects were the same as in Example 7.

[0088] Performance testing

[0089] The specimens obtained from Examples 1-8 and Comparative Examples 1-4 were subjected to compressive strength tests according to GB / T 50081-2019 "Test Methods for Physical and Mechanical Properties of Concrete", and the results are recorded in Table 1.

[0090] Freeze-thaw cycle tests were conducted in accordance with GB / T 50082-2009 "Test Methods for Long-Term Performance and Durability of Ordinary Concrete". The freeze-thaw media were 3.5% sodium chloride solution and 5% sodium sulfate solution, respectively. After 300 freeze-thaw cycles, the mass loss of the test specimens was measured and the results were recorded in Table 1.

[0091] Table 1

[0092]

[0093] As can be seen from Examples 1-8 and Table 1, the recycled concrete prepared using the specific raw materials of this application meets the C60 standard, has a dense internal structure, and has excellent compressive strength. At the same time, when sodium chloride solution and sodium sulfate solution are used as freeze-thaw media, the concrete undergoes up to 300 freeze-thaw cycles in a salt-freeze environment with little mass loss and a long service life.

[0094] As can be seen from Example 7 and Comparative Example 1, and Table 1, replacing the dihydroxyphenylalanine in this application with other amino acids, such as glycine, cannot effectively improve the overall performance of concrete. This is because dihydroxyphenylalanine can not only act as a regulator to adjust the setting time of concrete, but also effectively improve the salt resistance of concrete and reduce the erosion of concrete by sulfates, chloride ions, etc. At the same time, dihydroxyphenylalanine can further combine with dopamine in the accelerator to form a substance with excellent adhesion, which is conducive to the formation of a tight bond between the modified recycled aggregate and each raw material component, thereby effectively improving the compressive strength of concrete, significantly reducing the mass loss of concrete in the salt-freeze environment, and extending the service life of concrete.

[0095] Based on Examples 7 and Comparative Examples 2-4, and referring to Table 1, it can be seen that in Comparative Example 2, only water glass was used for modification treatment in the preparation of modified recycled aggregate; in Comparative Examples 3 and 4, regardless of whether the components were replaced or the corresponding components were missing in the preparation of modified recycled aggregate, the concrete prepared not only showed a significant decrease in compressive strength, but also experienced a multiplied increase in mass loss after 300 freeze-thaw cycles in a salt-freezing environment. This is because the calcium-ion-containing accelerator used in this application can modify the aggregate in conjunction with the carbonate solution. The calcium ions in the carbonate solution and the calcium-ion-containing accelerator combine to form calcium carbonate that adheres to the surface of the aggregate, which can stabilize the calcium hydroxide in the concrete, slow down the alkali skeleton reaction of the concrete, and prevent the calcium hydroxide from dissolving and leaching in a humid environment, thereby maintaining the mechanical properties of the concrete; at the same time, both the carbonate solution and the organic calcium solution are weakly alkaline, which can make the modified recycled aggregate weakly alkaline, further reducing the erosion of concrete by sulfates, chloride ions, etc., improving the stability of the concrete, and significantly reducing the mass loss of concrete in a salt-freezing environment. Furthermore, modified recycled aggregates can effectively bind other raw material components, fill micropores and voids in concrete, reduce the porosity of concrete, improve the density of concrete, significantly enhance the mechanical properties of concrete, and extend the service life of concrete.

[0096] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-strength recycled concrete, characterized in that, The raw materials include the following parts by weight: 100-150 parts modified recycled aggregate, 80-95 parts cement, 4.5-9 parts dihydroxyphenylalanine, 15-38 parts composite minerals, 1-3 parts water-reducing agent, 40-60 parts manufactured sand, 20-30 parts crushed stone, and 30-40 parts water. The modified recycled aggregate includes the following preparation steps: crushing, screening, and removing impurities from waste concrete to obtain aggregate with a gradation range of 5-25mm; adding a calcium ion-containing accelerator to the aggregate; and adding a carbonate solution during stirring to obtain the modified recycled aggregate.

2. The high-strength recycled concrete according to claim 1, characterized in that: The calcium-containing promoting solution comprises dopamine powder and organic calcium solution in a weight ratio of 1:(8-17).

3. The high-strength recycled concrete according to claim 2, characterized in that: The organic calcium solution is a calcium acetate solution and / or a calcium lactate solution.

4. The high-strength recycled concrete according to claim 1, characterized in that: The carbonate solution is a sodium carbonate solution or a potassium carbonate solution.

5. The high-strength recycled concrete according to any one of claims 1-4, characterized in that: The components used in the modified recycled aggregate are as follows: by weight, 90-110 parts waste concrete, 20-32 parts calcium ion-containing accelerator, and 16-25 parts carbonate solution.

6. The high-strength recycled concrete according to claim 1, characterized in that: The composite mineral material includes at least two of fly ash, silica fume, and slag powder.

7. The high-strength recycled concrete according to claim 1, characterized in that: The water-reducing agent is a polycarboxylate water-reducing agent with a solid content of 30-45% and a water reduction rate of 20%-40%.

8. The method for preparing high-strength recycled concrete according to any one of claims 1-7, characterized in that: Includes the following steps: Modified recycled aggregate, cement, dihydroxyphenylalanine, composite mineral aggregate, water-reducing agent, manufactured sand and water are mixed evenly according to the formula to obtain recycled concrete.

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