Carbon-negative low-strength backfill material, preparation method and application

Abstract

The application provides a negative carbon type low-strength backfill material, a preparation method and application, and belongs to the technical field of building materials. The preparation raw materials of the backfill material include steel slag powder, desulfurization gypsum, slag powder, carbide slag, sodium sulfate, a water reducing agent, construction waste, water and CO2 gas. The backfill material can realize an expansion degree of greater than or equal to 320 mm, a 28d compressive strength of greater than or equal to 4.0 MPa, a 3d shrinkage rate of less than or equal to 0.12% and negative carbon emission under a low water reducing agent dosage, and can be used for complex working conditions such as tunnels, foundation pits, contaminated site remediation backfill and the like, so that the negative carbon emission of the material is realized.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and relates to a negative carbon type low strength backfill material, its preparation method and application. Background Technology

[0002] Controlled low-strength backfill materials not only possess advantages similar to concrete, such as rapid construction, good impermeability, and high durability, but also retain characteristics similar to compacted soil backfill and gravel backfill, such as low cost and ease of subsequent pipeline excavation. This can significantly reduce the amount of solid waste such as construction debris in urban areas. Therefore, using controlled low-strength backfill materials for foundation trench backfilling, mine filling, underwater filling, and pipeline laying offers excellent environmental and economic benefits.

[0003] However, existing controllable low-strength backfill materials have several technical drawbacks: First, most use cement as a single binder, and the cement particle size is generally larger than that of the slag particles, which cannot effectively bond the slag particles, resulting in insufficient backfill density and easy occurrence of voids and settlement problems in the later stages; Second, the soil particles in the slag are mainly layered, which easily intercalates with the water-reducing agent, reducing the effect of the water-reducing agent and resulting in poor fluidity of the backfill material, requiring an increase in the amount of water-reducing agent, which increases costs; Third, the binder components are mainly composed of hydrated calcium silicate, which cannot be controlled, resulting in large volume shrinkage after the backfill material hardens, which easily leads to poor long-term stability during service; Fourth, the binder materials have high carbon emissions, making it difficult to meet the low-carbon development requirements of modern building materials.

[0004] Therefore, developing a controllable low-strength backfill material that combines high performance, excellent mechanical properties, low shrinkage, and negative carbon emissions has become the key to solving the current technical bottleneck. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon-negative low-strength backfill material, its preparation method, and its application, in order to solve the problems of high carbon emissions and large amounts of additives in existing controllable low-strength backfill materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This application provides a negative carbon type low strength backfill material, the raw materials for which the backfill material is prepared include steel slag powder, desulfurized gypsum, slag powder, carbide slag, sodium sulfate, water-reducing agent, construction waste, water and CO2 gas.

[0007] This application provides a method for preparing a negative carbon type low-strength backfill material, the method comprising: After mixing a portion of steel slag powder, calcium carbide slag, construction waste, a portion of water-reducing agent and water, CO2 gas is injected under stirring conditions to form a slurry. The remaining steel slag powder, desulfurized gypsum, slag powder, sodium sulfate, and remaining water-reducing agent are added to the slurry and stirred evenly to form a negative carbon type low-strength backfill material.

[0008] In addition, this application also provides an application of a negative carbon type low strength backfill material, namely its application in the remediation and backfilling of tunnels, foundation pits, and contaminated sites.

[0009] The present invention has the following beneficial effects: (1) Steel slag powder and slag powder are the core materials for hydration reaction. Their particle size is smaller than that of soil particles, which can efficiently fill the gaps between soil particles, increase the bonding efficiency between hydration products and soil particles, and thus effectively reduce the amount of water-reducing agent used.

[0010] (2) Both steel slag powder and blast furnace slag powder contain a large amount of alkali metal ions, and carbide slag contains a large amount of calcium hydroxide. After reacting with carbon dioxide, the resulting carbonates seal the layered structure of soil particles, reducing the amount of subsequent water-reducing agents used and lowering costs. At the same time, it can also achieve the purpose of carbon sequestration. In addition, the free calcium oxide in steel slag powder can reduce the shrinkage of backfill materials after absorbing water and expanding.

[0011] (3) After steel slag powder, slag powder, desulfurized gypsum and sodium sulfate are combined, the sodium sulfate combines with the calcium ions released by the initial self-hydration of steel slag powder, and slowly increases the alkalinity of the whole system after 30 minutes, which effectively promotes the dissolution of slag and accelerates the hydration reaction. At the same time, it ensures that its fluidity does not change significantly within 30 minutes, so as to facilitate construction preparation.

[0012] (4) The reaction products of steel slag powder, slag powder and desulfurized gypsum are mainly calcium vanadium expansive products, which can reduce the early shrinkage of backfill materials. In addition, the free calcium oxide in steel slag powder participates in the reaction in the later stage, producing micro-expansion, which reduces the later shrinkage of backfill materials, so that shrinkage cracking will not occur in the backfill materials throughout the entire service life.

[0013] (5) The backfill material in this application can achieve an expansion of ≥320mm, a 28d compressive strength of ≥4.0MPa, and a 3d shrinkage rate of ≤0.12% with low water-reducing agent dosage, and achieves negative carbon emissions. It can be used in complex working conditions such as tunnels, foundation pits, and remediation backfilling of contaminated sites, and achieves negative carbon emissions of the material. Attached Figure Description

[0014] Figure 1 Figure showing the effect of sand content on the plastic and liquid limits of construction waste. Figure 2The images shown are SEM (Scanning Electron Microscope) images of the negative carbon type low strength backfill materials prepared in Examples 1-4, where a is the SEM image of Example 1, b is the SEM image of Example 2, c is the SEM image of Example 3, and d is the SEM image of Example 4. Figure 3 The images show the compressive strength test results of the negative carbon type low-strength backfill materials prepared in Examples 1-6. The top row of images shows the negative carbon type low-strength backfill materials prepared in Examples 1-3, and the bottom row of images shows the negative carbon type low-strength backfill materials prepared in Examples 4-6. Figure 4 The flowability test diagram is shown for the negative carbon type low strength backfill material prepared in Example 1. Detailed Implementation

[0015] In one aspect, this application provides a negative carbon type low strength backfill material, the raw materials for which the preparation of the backfill material includes steel slag powder, desulfurized gypsum, slag powder, carbide slag, sodium sulfate, water-reducing agent, construction waste, water and CO2 gas.

[0016] Steel slag powder is a byproduct of steelmaking. Mineral slag powder is a powder formed by grinding granulated blast furnace slag produced during blast furnace ironmaking, which is molten calcium aluminosilicate quenched in water. Calcium carbide slag is a waste residue mainly composed of calcium hydroxide, produced after the hydrolysis of calcium carbide to obtain acetylene gas. In the embodiments of this application, the specific surface area of ​​both steel slag powder and mineral slag powder is ≥470 m². 2 / kg, with particle size less than 12μm.

[0017] Both steel slag powder and blast furnace slag powder contain a large amount of alkali metal ions, while carbide slag contains a large amount of calcium hydroxide. After reacting with carbon dioxide, the resulting carbonates seal the layered structure of soil particles, reducing the amount of subsequent water-reducing agents needed and lowering costs, while also achieving carbon sequestration. In addition, the free calcium oxide in steel slag powder expands after absorbing water, which can reduce the shrinkage of backfill materials.

[0018] Furthermore, since the particle size of both steel slag powder and slag powder is less than 12μm, which is smaller than the size of soil particles, steel slag powder and slag powder can efficiently fill the spaces between soil particles, increase the bonding efficiency between hydration products and soil particles, and thus effectively reduce the amount of water-reducing agent required.

[0019] The desulfurized gypsum is dihydrate desulfurized gypsum, and the sodium sulfate is industrial alum with Na2SO4 as the main component, with an effective content of ≥98%; construction waste includes on-site excavation materials, engineering waste, or recycled construction waste, with a sand content of ≤20%, an organic matter content of ≤5%, and a bentonite content of ≤5%; the water-reducing agent is anionic polycarboxylate water-reducing agent with a water reduction rate of ≥25%, such as APEG (allyl polyoxyethylene ether) type water-reducing agent, HPEG (methyl allyl polyoxyethylene ether) type water-reducing agent, TPEG (isoprene alcohol polyoxyethylene ether) type water-reducing agent, etc.

[0020] When steel slag powder, blast furnace slag powder, desulfurized gypsum, and sodium sulfate are combined, the sodium sulfate binds with the calcium ions initially released during the autohydration of the steel slag powder. This slowly increases the alkalinity of the entire system after 30 minutes, effectively promoting slag dissolution and accelerating the hydration reaction. Simultaneously, the fluidity remains relatively stable within 30 minutes, facilitating construction preparation. Furthermore, the reaction products of steel slag powder, blast furnace slag powder, and desulfurized gypsum are primarily expansive products of calcium vanadate, which reduce the early shrinkage of the backfill material. In addition, the free calcium oxide in the steel slag powder participates in the later stages of the reaction, generating micro-expansion and reducing the later shrinkage of the backfill material, thus preventing shrinkage cracking throughout the entire service life of the backfill material.

[0021] This application investigated the effect of sand content in construction waste on the plastic and liquid limits of construction waste, and obtained the following results. Figure 1 From the appendix Figure 1 It is evident that as the sand content increases, the plastic limit and liquid limit of construction waste gradually decrease. Therefore, the preferred sand content in the construction waste in this application is 20%.

[0022] In this application, the raw materials for preparing the negative carbon type low strength backfill material include, by weight, 70-80 parts of steel slag powder, 10-18 parts of desulfurized gypsum, 30-40 parts of slag powder, 10-20 parts of calcium carbide slag, 3-5 parts of sodium sulfate, 6-15 parts of water-reducing agent, 1300-1400 parts of construction waste, 800-900 parts of water, and 100L of CO2 gas.

[0023] Secondly, this application provides a method for preparing a negative carbon type low-strength backfill material, the method comprising: S01: Add a portion of steel slag powder, carbide slag, construction waste, a portion of water-reducing agent, and water to a twin-shaft mixer and mix at 200 r / min until the materials are uniformly mixed to form a mixture. During continuous mixing, inject 20% CO2 gas into the mixture at a flow rate of 5 L / min for 20 min to form a slurry.

[0024] During the CO2 gas injection process, alkali metal ions in steel slag powder and slag powder, and calcium hydroxide in carbide slag, react with carbon dioxide in water. The resulting carbonates seal the layered structure of soil particles, reducing the amount of subsequent water-reducing agents used and lowering costs. At the same time, it can also achieve carbon sequestration and realize negative carbon emissions from backfill materials.

[0025] S02: Add the remaining steel slag powder, desulfurized gypsum, slag powder, sodium sulfate, and remaining water-reducing agent to the slurry and stir evenly to form a negative carbon type low-strength backfill material.

[0026] The remaining steel slag powder, desulfurized gypsum, slag powder, sodium sulfate, and remaining water-reducing agent are added to the slurry and stirred at 200 rpm until the materials are uniformly mixed, forming a negative carbon type low-strength backfill material. During this process, the free calcium oxide in the steel slag powder absorbs water and expands, reducing the shrinkage of the backfill material. Simultaneously, the reaction of steel slag powder, slag powder, and desulfurized gypsum to generate calcium vanadium stone expansion products further compensates for the shrinkage of the backfill material, ultimately achieving large-scale utilization of the steel slag powder.

[0027] Thirdly, this application also provides an application of a negative carbon type low-strength backfill material, namely, its application in the remediation and backfilling of tunnels, foundation pits, and contaminated sites.

[0028] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0029] Example 1 This application provides a negative carbon type low strength backfill material. The raw materials for preparing the backfill material include, by weight, 700 parts steel slag powder, 10 parts desulfurized gypsum, 30 parts slag powder, 10 parts carbide slag, 3 parts sodium sulfate, 6 parts APEG type water-reducing agent, 1300 parts construction waste soil, 800 parts water, and 100L CO2 gas. The particle size of both steel slag powder and slag powder is 5μm, and the sand content of construction waste soil is 20%.

[0030] This application also provides a method for preparing a negative carbon type low-strength backfill material, the method comprising: S101: Add half of the steel slag powder, carbide slag, construction waste, a portion of the water-reducing agent, and water to a twin-shaft mixer and mix at 200 r / min until the materials are uniformly mixed to form a mixture. During continuous mixing, inject 20% CO2 gas into the mixture at a flow rate of 5 L / min for 20 min to form a slurry.

[0031] S102: Add the other half of the steel slag powder, desulfurized gypsum, slag powder, sodium sulfate, and the remaining water-reducing agent to the slurry, and stir at a speed of 200 r / min until the materials are evenly mixed to form a negative carbon type low-strength backfill material.

[0032] Example 2 This application provides a negative carbon type low strength backfill material. The raw materials for preparing the backfill material include, by weight, 70 parts steel slag powder, 10 parts desulfurized gypsum, 30 parts slag powder, 10 parts carbide slag, 5 parts sodium sulfate, 15 parts APEG type water-reducing agent, 1400 parts construction waste, 900 parts water, and 100L CO2 gas. The particle size of both steel slag powder and slag powder is 7μm, and the sand content of construction waste is 10%.

[0033] This application also provides a method for preparing a negative carbon type low-strength backfill material, which is the same as in Example 1.

[0034] Example 3 This application provides a negative carbon type low strength backfill material. The raw materials for preparing the backfill material include, by weight, 80 parts steel slag powder, 18 parts desulfurized gypsum, 40 parts slag powder, 10 parts carbide slag, 3 parts sodium sulfate, 6 parts HPEG type water reducing agent, 1300 parts construction waste soil, 800 parts water, and 100L CO2 gas. The particle size of the steel slag powder and slag powder is 3μm, and the sand content of the construction waste soil is 0%.

[0035] This application also provides a method for preparing a negative carbon type low-strength backfill material, which is the same as in Example 1.

[0036] Example 4 This application provides a negative carbon type low strength backfill material. The raw materials for preparing the backfill material include, by weight, 70 parts steel slag powder, 10 parts desulfurized gypsum, 40 parts slag powder, 20 parts carbide slag, 3 parts sodium sulfate, 15 parts HPEG type water reducing agent, 1300 parts construction waste soil, 900 parts water, and 100L CO2 gas. The particle size of both steel slag powder and slag powder is 4μm, and the sand content of construction waste soil is 15%.

[0037] This application also provides a method for preparing a negative carbon type low-strength backfill material, which is the same as in Example 1.

[0038] Example 5 This application provides a negative carbon type low strength backfill material. The raw materials for preparing the backfill material include, by weight, 75 parts steel slag powder, 16 parts desulfurized gypsum, 35 parts slag powder, 15 parts carbide slag, 4 parts sodium sulfate, 10 parts TPEG type water reducing agent, 1350 parts construction waste soil, 850 parts water, and 100L CO2 gas. The particle size of both steel slag powder and slag powder is 10μm, and the sand content of construction waste soil is 18%.

[0039] This application also provides a method for preparing a negative carbon type low-strength backfill material, which is the same as in Example 1.

[0040] Example 6 This application provides a negative carbon type low strength backfill material. The raw materials for preparing the backfill material include, by weight, 80 parts steel slag powder, 18 parts desulfurized gypsum, 40 parts slag powder, 20 parts carbide slag, 5 parts sodium sulfate, 15 parts TPEG type water reducing agent, 1400 parts construction waste soil, 900 parts water, and 100L CO2 gas. The particle size of both steel slag powder and slag powder is 10μm, and the sand content of construction waste soil is 10%.

[0041] This application also provides a method for preparing a negative carbon type low-strength backfill material, which is the same as in Example 1.

[0042] Comparative Example 1 This application provides a negative carbon type low strength backfill material. The raw materials for preparing the backfill material include, by weight, 95 parts steel slag powder, 18 parts desulfurized gypsum, 40 parts slag powder, 20 parts carbide slag, 5 parts sodium sulfate, 15 parts APEG type water reducing agent, 1400 parts construction waste, 900 parts water, and 100L CO2 gas. The particle size of both steel slag powder and slag powder is 5μm.

[0043] Comparative Example 2 This application provides a negative carbon type low strength backfill material. The raw materials for preparing the backfill material include, by weight, 80 parts of steel slag powder, 18 parts of desulfurized gypsum, 40 parts of blast furnace slag powder, 20 parts of carbide slag, 5 parts of sodium sulfate, 15 parts of APEG type water-reducing agent, 1400 parts of construction waste, and 900 parts of water. The particle size of both steel slag powder and blast furnace slag powder is 24 μm.

[0044] This application embodiment uses SEM to detect the backfill materials prepared in Examples 1-4, and obtains the attached... Figure 2 From the appendix Figure 2 As can be seen, the backfill material prepared in Example 1 has the most compact structure, with hydration products encapsulating the slag particles; the backfill material prepared in Example 2 has a relatively loose structure, but a large amount of hydration products are still visible; the backfill material prepared in Example 3 has a relatively compact structure, and some unhydrated slag particles can be observed; the backfill material prepared in Example 4 contains a large amount of calcium vanadium and gel products, and has a relatively dense structure.

[0045] In addition, this application embodiment also conducted tests on the spread, compressive strength, and shrinkage rate of the backfill materials prepared in Examples 1-6 and Comparative Examples 1-2 according to the standard DB 13 / T 5821-2023 "Technical Specification for Backfilling of Premixed Flowable Solidified Soil", and obtained Table 1; and took sample images of the backfill materials prepared in Examples 1-6 after the compressive strength test, and obtained... Figure 3 The flowability of the backfill material prepared in Example 1 was tested, and the results were obtained. Figure 4 .

[0046] Table 1: Performance test data of backfill materials prepared in Examples 1-6 and Comparative Example 1 As shown in Table 1, the backfill material prepared in this embodiment exhibits higher expansion and compressive strength than the comparative example, and a lower shrinkage rate, demonstrating better filler performance. Figure 3 As can be seen, the backfill material prepared in Example 1 cracked under a pressure of 4.5 MPa, while the backfill materials prepared in Examples 2-5 did not collapse under a pressure of 4.1-4.4 MPa. This indicates that the backfill materials prepared in the embodiments of this application have good compressive strength under a pressure of 4.1-4.4 MPa, with a maximum compressive strength reaching 4.5 MPa, but they did not collapse, only cracked. Figure 4 It can be seen that the backfill material prepared in Example 1 has good flowability.

[0047] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative carbon type low-strength backfill material, characterized in that, The raw materials for preparation include steel slag powder, desulfurized gypsum, slag powder, carbide slag, sodium sulfate, water-reducing agent, construction waste, water, and CO2 gas.

2. The negative carbon low strength backfill material of claim 1, wherein, The raw materials for preparation include, by weight, 70-80 parts steel slag powder, 10-18 parts desulfurized gypsum, 30-40 parts slag powder, 10-20 parts calcium carbide slag, 3-5 parts sodium sulfate, 6-15 parts water-reducing agent, 1300-1400 parts construction waste, 800-900 parts water, and 100L CO2 gas.

3. The negative carbon type low-strength backfill material according to claim 1, characterized in that, The specific surface area of ​​both the steel slag powder and the slag powder is ≥470m². 2 / kg, with particle size less than 12μm.

4. The negative carbon type low-strength backfill material according to claim 1, characterized in that, The water-reducing agent is an anionic polycarboxylate water-reducing agent with a water reduction rate of ≥25%.

5. The negative carbon type low-strength backfill material according to claim 1, characterized in that, The construction waste includes on-site excavation materials, engineering waste, or recycled construction waste.

6. The negative carbon type low-strength backfill material according to claim 1, characterized in that, The organic matter content, bentonite content, and sand content in the construction waste soil are ≤5%, ≤5%, and ≤20%, respectively.

7. The method for preparing the negative carbon type low-strength backfill material according to any one of claims 1-6, characterized in that, include: After mixing a portion of steel slag powder, calcium carbide slag, construction waste, a portion of water-reducing agent and water, CO2 gas is injected under stirring conditions to form a slurry. The remaining steel slag powder, desulfurized gypsum, slag powder, sodium sulfate, and remaining water-reducing agent are added to the slurry and stirred evenly to form a negative carbon type low-strength backfill material.

8. The method for preparing negative carbon type low-strength backfill material according to claim 7, characterized in that, The stirring speed was 200 r / min, the CO2 gas flow rate was 5 L / min, and the concentration was 20%.

9. The application of the negative carbon type low strength backfill material according to any one of claims 1-6 in the backfilling of tunnels, foundation pits, and contaminated sites.

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