A controllable expansion filling cementitious material prepared by circulating fluidized bed fly ash and a preparation method thereof

Abstract

This invention relates to the fields of backfilling engineering and solid waste resource utilization technology, specifically to a controllable expansion backfilling cementitious material prepared from circulating fluidized bed fly ash and its preparation method. The controllable expansion backfilling cementitious material uses 20-50 parts of circulating fluidized bed fly ash, 10-40 parts of slag powder, 5-30 parts of steel slag powder, and 8-30 parts of silicate cement clinker powder as the main cementitious components, compounded with 0.1-1 parts of an expansion agent and 0.1-1 parts of an expansion stabilizer. The expansion agent's hydrolysis and gasification reaction is precisely triggered by microwave heating, achieving a controllable expansion process of "filling first, then expanding" for the backfilling material. In engineering scenarios such as goaf backfilling, deep foundation pit backfilling, and self-compacting backfilling of karst caves, this material can effectively avoid the pipe blockage risk during the transportation process of traditional foamed materials, eliminate the shrinkage and cracking problem after the backfill material solidifies, and achieve a tight fit between the backfill material and the surrounding rock.

Description

Technical Field

[0001] This invention relates to the fields of backfilling engineering and solid waste resource utilization technology, specifically to a controllable expansion backfilling cementitious material prepared from circulating fluidized bed fly ash and its preparation method. Background Technology

[0002] Circulating fluidized bed (CFB) combustion technology is a mainstream clean coal-fired power generation technology. It typically uses low-calorific-value fuels such as coal gangue and coal slime to co-fire high-calorific-value coal, and is equipped with in-furnace calcium injection for desulfurization. A large amount of circulating fluidized bed fly ash (CFB fly ash) is produced as a byproduct. CFB fly ash is rich in active aluminosilicate minerals and has potential hydraulic activity. At the same time, due to its high calcium and sulfur content, it contains components such as free calcium oxide and anhydrite, which have significant self-expansion characteristics. It cannot be directly used in conventional concrete preparation, resulting in a resource utilization rate of less than 15%. Large-scale stockpiling occupies land and poses environmental risks. Large-scale disposal and high-value utilization have become industry challenges.

[0003] Filling materials are widely used in engineering fields such as mine goaf filling, underground foundation pit backfilling, and karst cave sealing. Existing filling materials mostly use cement as the main binder, which leads to problems such as high production costs, large carbon emissions, and insufficient environmental friendliness. Furthermore, for irregularly shaped and complex filling spaces such as roadways and karst caves, traditional filling materials have poor fluidity and insufficient density, making it difficult to achieve gapless, seamless filling.

[0004] Patent CN112679168A discloses a high-strength inorganic foamed filling material for mining and its preparation method. It uses cement, fly ash, and silica fume as the matrix, and combines them with an inorganic foaming agent to achieve foaming expansion, which can improve the compactness of the filling to a certain extent. However, the inorganic foaming agent decomposes rapidly upon contact with water, producing gas. This causes premature foaming of the slurry during pipeline transportation, easily leading to pipe blockage and affecting the safety of underground construction. Furthermore, the cement-based system is prone to water loss shrinkage and chemical shrinkage after solidification, causing the filling material to detach and crack from the surrounding rock, reducing the stability and support effect of the filling material. Summary of the Invention

[0005] This invention addresses the challenges of high-value utilization of bulk solid waste from circulating fluidized bed (CFB) fly ash, the high cost and tendency for shrinkage and voiding of traditional cement-based backfill materials, and the uncontrollable foaming and pipe blockage issues of existing foamed backfill materials. It provides a controllable expansion backfill cementitious material prepared from CFB fly ash and its preparation method. This invention fully utilizes the high hydration activity and inherent expansion characteristics of CFB fly ash, in conjunction with industrial solid wastes such as slag powder and steel slag powder, and blends a small amount of silicate cement clinker powder, an expansion agent, and an expansion stabilizer. Combined with a microwave-activated foaming process, it achieves a controllable expansion process of the backfill material, "filling first, then expanding," effectively solving technical problems such as premature foaming and pipe blockage, shrinkage and cracking of the backfill body, and difficulties in achieving dense filling. This results in a low-cost, low-carbon-emission backfill cementitious material with controllable expansion, enabling the large-scale resource utilization of CFB fly ash. It has significant application value in scenarios such as mine backfilling and underground engineering backfilling. At the same time, by utilizing the hydration and expansion characteristics brought about by the high sulfur and calcium content of CFB fly ash, the risk of cracking caused by the later drying and shrinkage of the expansion filler is avoided, thereby obtaining a filler that is tightly bonded to the surrounding rock, has no shrinkage, and has high strength.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a controllable expansion filling cementitious material prepared by circulating fluidized bed fly ash, which is composed of the following raw materials in the following mass ratio: 20-50 parts of circulating fluidized bed fly ash, 10-40 parts of slag powder, 5-30 parts of steel slag powder, 8-30 parts of silicate cement clinker powder, 0.1-1 parts of expansion agent, 0.1-1 parts of expansion stabilizer, and 30-55 parts of cold water, wherein the temperature of the cold water is 0-20℃.

[0007] As a further limitation of the technical solution of the present invention, the specific surface area of ​​the circulating fluidized bed fly ash is 500~1000 m². 2 / kg, 45μm sieve residue <5%, loss on ignition <8%, 28d activity index >85%, chemical composition of CaO ≥10% and SO3 ≥8%.

[0008] As a further limitation of the technical solution of the present invention, the expanding agent is aluminum powder or powdered industrial solid waste containing metallic aluminum, and the total gas production after complete hydrolysis is ≥300L / kg.

[0009] As a further limitation of the technical solution of the present invention, the expansion stabilizer is at least one of polyoxyethylene polyoxypropylene ether block copolymer and N-isopropylacrylamide copolymer.

[0010] As a further limitation of the technical solution of the present invention, the specific surface area of ​​the slag powder is 400~500m² / kg, the residue on the 45μm sieve is <5%, and the 28d activity index is >95%.

[0011] As a further limitation of the technical solution of the present invention, the cold water is tap water or surface water.

[0012] In addition, the present invention also provides a method for preparing a controllable expansion filling cementitious material prepared from circulating fluidized bed fly ash, comprising the following steps: S1. Weigh out the swelling stabilizer according to the ratio, add an equal amount of cold water to pre-dissolve it, then add the swelling agent according to the ratio and stir evenly to form a paste. S2. Weigh out the circulating fluidized bed fly ash, slag powder, steel slag powder, and silicate cement clinker powder according to the proportions, and pre-mix them using a powder mixer to obtain a uniform powder mixture; S3. Add the powder mixture obtained in step S2 and the paste obtained in step S1 into a paddle mixer, add the remaining cold water in proportion, stir, and then pour it into the foundation pit or laboratory plastic mold that needs to be filled. S4. Within 15 minutes after pouring, use a microwave generator to heat the filling grout until the grout begins to expand. S5. After standing for 1-3 hours until the expansion is basically completed, cover with film and let stand for curing until the filling material is completely hardened.

[0013] As a further limitation of the technical solution of the present invention, the pre-mixing time of the powder mixer in step S2 is 3~10min; the stirring time in step S3 is 3~5min.

[0014] As a further limitation of the technical solution of the present invention, the heating time of the microwave generator in step S4 is 1~5 min; the curing time of the film covering in step S5 is 24~48 h.

[0015] As a further limitation of the technical solution of the present invention, the heating frequency of the microwave generator in step S4 is 2.45 GHz.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention makes full use of the spontaneous hydration expansion characteristics brought about by the high sulfur and calcium content of circulating fluidized bed fly ash, transforming it from a harmful component in ordinary concrete into a beneficial expansion source in filling materials. By using an expansion agent in conjunction, the invention achieves full-cycle expansion control of filling materials in the flowable and plastic stages and the hardening stages, while realizing the large-scale resource utilization of CFB fly ash.

[0017] (2) This invention constructs a multi-component solid waste-based cementitious system by synergistically using slag powder, steel slag powder, and a small amount of silicate cement clinker powder. Under the alkaline activation environment provided by silicate cement clinker powder, the sulfate in CFB fly ash can effectively activate slag powder and steel slag powder. Therefore, CFB fly ash can act as a highly active admixture and also as an activator for slag powder and steel slag powder, achieving low-cost and high-strength filling materials.

[0018] (3) This invention innovatively introduces an expanding agent with aluminum as the core component and coordinates it with a microwave-activated foaming process. After the filling slurry is poured but before it solidifies, a short-time microwave heating precisely triggers the hydrolysis and gasification reaction of the expanding agent (aluminum), so that the foaming process occurs after filling, completely avoiding the risk of pipe blockage caused by premature foaming of traditional foaming materials in the conveying pipeline.

[0019] (4) This invention uses polyoxyethylene polyoxypropylene ether block copolymer or N-isopropylacrylamide copolymer as an expansion stabilizer and pre-coats the expansion agent particles. Since this type of expansion stabilizer is a thermoplastic polymer, it can encapsulate the bubbles generated by the decomposition of the expansion agent during microwave heating, and regulate the surface tension and viscoelasticity of the liquid film, inhibiting bubble coalescence and rupture, thereby obtaining a uniform and fine closed-cell structure, thus ensuring the volume stability and mechanical properties of the filling material after expansion.

[0020] (5) The controllable expansion filling cementitious material prepared by this invention has comprehensive performance advantages such as good fluidity, adjustable expansion ratio (volume expansion rate of 10%~100%), tight bonding with the surrounding rock interface, and a 28-day compressive strength of 2~10 MPa. This material is particularly suitable for engineering scenarios requiring non-shrink compaction filling, such as goaf filling, deep foundation pit backfilling, and karst cave self-compacting filling, and has broad engineering application prospects and significant environmental and economic benefits. Attached Figure Description

[0021] Figure 1 The image shows the microstructure of the expanded filling gel material sample prepared in Example 1. Detailed Implementation

[0022] The embodiments given below are intended to further illustrate the present invention, but should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made to the present invention by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0023] This invention discloses a controllable expansion filling cementitious material prepared from circulating fluidized bed fly ash, which is composed of the following raw materials in the indicated mass ratios: 20-50 parts circulating fluidized bed fly ash, 10-40 parts slag powder, 5-30 parts steel slag powder, 8-30 parts silicate cement clinker powder, 0.1-1 part expansion agent, 0.1-1 part expansion stabilizer, and 30-55 parts cold water at a temperature of 0-20℃.

[0024] This invention provides a method for preparing a controllable expansion filling cementitious material made from circulating fluidized bed fly ash, comprising the following steps: S1. Weigh out the swelling stabilizer according to the ratio, add an equal amount of cold water to pre-dissolve it, then add the swelling agent according to the ratio and stir evenly to form a paste. S2. Weigh out the circulating fluidized bed fly ash, slag powder, steel slag powder, and silicate cement clinker powder according to the proportions, and pre-mix them using a powder mixer to obtain a uniform powder mixture; S3. Add the powder mixture obtained in step S2 and the paste obtained in step S1 into a paddle mixer, add the remaining cold water in proportion, stir, and then pour it into the foundation pit or laboratory plastic mold that needs to be filled. S4. Within 15 minutes after pouring, use a microwave generator to heat the filling grout until the grout begins to expand. S5. After standing for 1-3 hours until the expansion is basically completed, cover with film and let stand for curing until the filling material is completely hardened.

[0025] In the following examples and comparative examples, the circulating fluidized bed fly ash (CFB fly ash) used has a specific surface area of ​​650 m². 2 / kg, 45μm sieve residue 2.5%, loss on ignition 6.8%, 28-day activity index 88%, CaO content 12.5%, SO3 content 9.2%; slag powder specific surface area 450m² 2 / kg, 45μm sieve residue 2.1%, 28-day activity index 97%; steel slag powder specific surface area 400m² 2 / kg, 45μm sieve residue 7.5%, 28-day activity index 78%; silicate cement clinker powder specific surface area 350m² 2 / kg; the expanding agent is metallic aluminum powder, and the total gas production is 950L / kg; the expanding stabilizer is polyoxyethylene polyoxypropylene ether block copolymer (Planic); the cold water temperature is 10℃.

[0026] Example 1 In this embodiment, the raw material composition of the controllable expansion filling cementitious material is as follows (parts by mass): 35 parts CFB fly ash, 20 parts slag powder, 15 parts steel slag powder, 18 parts silicate cement clinker powder, 0.1 parts expansion agent, 0.3 parts expansion stabilizer, and 35.3 parts cold water (added in two batches during the process).

[0027] The preparation steps are as follows: S1. Weigh 0.3 parts of swelling stabilizer according to the ratio, add it to an equal amount of cold water (0.3 parts) to pre-dissolve, then add 0.1 parts of swelling agent and stir evenly to form a paste; S2. Weigh out 35 parts of CFB fly ash, 20 parts of slag powder, 15 parts of steel slag powder, and 18 parts of silicate cement clinker powder according to the proportion, and mix them in a powder mixer for 5 minutes to obtain a uniform powder mixture. S3. Add the powder mixture obtained in step S2 and the paste obtained in step S1 to a paddle mixer, add the remaining 35 parts of cold water, stir for 4 minutes, and then pour into a 40mm×40mm×160mm triple mold. S4. Ten minutes after pouring, use a microwave generator to heat the filling grout for 3 minutes, and stop when the grout begins to expand. S5. After standing for 2 hours until the expansion is basically completed, cover with film and let stand for 48 hours until the filling material is completely hardened.

[0028] The microstructure of the expanded filling gel material sample prepared in this embodiment is shown in the image below. Figure 1 As shown, the expandable filling material prepared according to the method proposed in this invention has a high porosity, uniform pore size, and all pores are closed pores. A large number of needle-like hydration products are formed on the pore walls, indicating that the circulating fluidized bed fly ash reacts synergistically with slag, steel slag, etc., providing good strength assurance for the lightweight filler.

[0029] Example 2 In this embodiment, the raw material composition of the controllable expansion filling cementitious material is as follows (parts by mass): 25 parts CFB fly ash, 30 parts slag powder, 20 parts steel slag powder, 12 parts silicate cement clinker powder, 0.15 parts expansion agent, 0.4 parts expansion stabilizer, and 35.4 parts cold water (added in two batches during the process).

[0030] The preparation steps are the same as in Example 1, except that the microwave heating time in step S4 is 4 minutes.

[0031] Example 3 In this embodiment, the raw material composition of the controllable expansion filling cementitious material is as follows (parts by mass): 45 parts CFB fly ash, 15 parts slag powder, 10 parts steel slag powder, 20 parts silicate cement clinker powder, 0.1 parts expansion agent, 0.5 parts expansion stabilizer, and 45.5 parts cold water (added in two batches during the process).

[0032] The preparation steps are the same as in Example 1, except that the microwave heating time in step S4 is 2 minutes.

[0033] Example 4 In this embodiment, the raw material composition of the controllable expansion filling cementitious material is as follows (parts by mass): 30 parts CFB fly ash, 25 parts slag powder, 25 parts steel slag powder, 10 parts silicate cement clinker powder, 0.2 parts expansion agent, 0.2 parts expansion stabilizer, and 40.2 parts cold water (added in two batches during the process).

[0034] The preparation steps are the same as in Example 1, except that the microwave heating time in step S4 is 5 minutes.

[0035] Example 5: The raw material composition of the controllable expansion filling cementitious material in this example is as follows (parts by mass): 40 parts CFB fly ash, 10 parts slag powder, 8 parts steel slag powder, 28 parts silicate cement clinker powder, 0.8 parts expansion agent, 0.6 parts expansion stabilizer, and 42.6 parts cold water (added in two batches during the process).

[0036] The preparation steps are the same as in Example 1, except that the microwave heating time in step S4 is 1.5 min.

[0037] Comparative Example 1 The raw material composition in this comparative example is exactly the same as that in Example 1.

[0038] The preparation steps are as follows: S1~S3 are the same as in Example 1; S4. Eliminate the microwave heating step and let it stand for 2 hours directly after pouring; S5 is the same as in Example 1.

[0039] Comparative Example 2 The raw material composition in this comparative example is as follows (mass percentage): 35 parts CFB fly ash, 20 parts slag powder, 15 parts steel slag powder, 18 parts silicate cement clinker powder, 0.1 parts expansion agent, and 35 parts cold water (without expansion stabilizer).

[0040] The preparation steps are the same as in Example 1, except that in step S1, the swelling agent is added to cold water and stirred into a paste (without adding a swelling stabilizer).

[0041] Comparative Example 3 In this comparative example, ordinary Class I fly ash is used to replace CFB fly ash. The raw material composition is as follows (mass percentage): 35 parts ordinary fly ash, 20 parts slag powder, 15 parts steel slag powder, 18 parts silicate cement clinker powder, 0.3 parts expansion agent, 0.3 parts expansion stabilizer, and 35.3 parts cold water.

[0042] The preparation steps are the same as in Example 1.

[0043] Table 1. Properties of the controllable expansion filling cementitious materials prepared in each example and comparative example.

[0044] As shown in Table 1: (1) Examples 1 to 5 all achieved high foaming ratios (68% to 105%) and moderate setting times (30 to 60 min for initial setting and 90 to 150 min for final setting). The 28-day compressive strength reached 5.9 to 10.2 MPa, and the 28-day expansion rate was 0.22% to 0.55%, demonstrating good expansion controllability and mechanical properties, and are suitable for filling engineering scenarios with different strength requirements.

[0045] (2) Comparative Example 1 did not use microwave heating, and the expanding agent was not effectively activated, with a foaming ratio of only 12%, indicating that microwave heating is the key process for triggering controllable expansion. Moreover, due to the low porosity, the mechanical properties of the material were improved, and its compressive strength reached 28.9 MPa.

[0046] (3) Comparative Example 2 did not add expansion stabilizer. Although the amount of expansion agent added was the same, the foaming ratio was only 72%, and the bubbles were easy to merge and break, resulting in uneven pore structure, significantly reduced compressive strength (4.2 MPa), and poor bubble stability, which easily caused the filling body to collapse and crack.

[0047] (4) In Comparative Example 3, ordinary fly ash was used instead of CFB fly ash. Due to the lack of spontaneous expansion and sulfate activation effect brought about by high sulfur and calcium components, the paste specimens showed shrinkage (-0.18%), and the compressive strength of the filled foam was only 6.8 MPa, indicating that the inherent characteristics of CFB fly ash have an irreplaceable role in this invention.

[0048] In summary, this invention, through the synergistic effect of CFB fly ash, slag powder, steel slag powder, silicate cement clinker powder, expansion agent, and expansion stabilizer, combined with microwave activation technology, successfully achieves controllable expansion of the filling material by "filling first and then expanding," solving the technical problems of pipe blockage and shrinkage cracking of traditional foaming materials, and has good prospects for engineering applications.

Claims

1. A controllable expansion filling cementitious material prepared from circulating fluidized bed fly ash, characterized in that, It is composed of the following raw materials in the indicated mass ratios: 20-50 parts circulating fluidized bed fly ash, 10-40 parts slag powder, 5-30 parts steel slag powder, 8-30 parts silicate cement clinker powder, 0.1-1 part expansion agent, 0.1-1 part expansion stabilizer, and 30-55 parts cold water at a temperature of 0-20℃.

2. The controllable expansion filling cementitious material prepared from circulating fluidized bed fly ash according to claim 1, characterized in that, The specific surface area of ​​the circulating fluidized bed fly ash is 500~1000 m². 2 / kg, 45μm sieve residue <5%, loss on ignition <8%, 28d activity index >85%, chemical composition of CaO ≥10% and SO3 ≥8%.

3. The controllable expansion filling cementitious material prepared from circulating fluidized bed fly ash according to claim 1, characterized in that, The expanding agent is aluminum powder or powdered industrial solid waste containing metallic aluminum, with a total gas production of ≥300L / kg after complete hydrolysis.

4. The controllable expansion filling cementitious material prepared from circulating fluidized bed fly ash according to claim 1, characterized in that, The swelling stabilizer is at least one of polyoxyethylene polyoxypropylene ether block copolymer and N-isopropylacrylamide copolymer.

5. The controllable expansion filling cementitious material prepared from circulating fluidized bed fly ash according to claim 1, characterized in that, The specific surface area of ​​the slag powder is 400~500 m². 2 / kg, 45μm sieve residue <5%, 28d activity index >95%.

6. A method for preparing a controllable expansion filling cementitious material from circulating fluidized bed fly ash according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Weigh out the swelling stabilizer according to the ratio, add an equal amount of cold water to pre-dissolve it, then add the swelling agent according to the ratio and stir evenly to form a paste. S2. Weigh out the circulating fluidized bed fly ash, slag powder, steel slag powder, and silicate cement clinker powder according to the proportions, and pre-mix them using a powder mixer to obtain a uniform powder mixture; S3. Add the powder mixture obtained in step S2 and the paste obtained in step S1 into a paddle mixer, add the remaining cold water in proportion, stir, and then pour it into the foundation pit or laboratory plastic mold that needs to be filled. S4. Within 15 minutes after pouring, use a microwave generator to heat the filling grout until the grout begins to expand. S5. After standing for 1-3 hours until the expansion is basically completed, cover with film and let stand for curing until the filling material is completely hardened.

7. The method for preparing a controllable expansion filling cementitious material from circulating fluidized bed fly ash according to claim 6, characterized in that, In step S2, the pre-mixing time of the powder mixer is 3~10 min; in step S3, the stirring time is 3~5 min.

8. The method for preparing a controllable expansion filling cementitious material from circulating fluidized bed fly ash according to claim 6, characterized in that, In step S4, the microwave generator heating time is 1~5 min; in step S5, the film covering and static curing time is 24~48 h.

9. The method for preparing a controllable expansion filling cementitious material from circulating fluidized bed fly ash according to claim 6, characterized in that, In step S4, the microwave generator heats at a frequency of 2.45 GHz.

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