Karst cave filling material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of karst cave filling materials, in particular to a karst cave filling material and a preparation method and application thereof. The karst cave filling material provided by the invention is prepared from the following components in parts by weight: 183.5 parts of ordinary Portland cement, 17 to 20 parts of sulphoaluminate cement, 13 to 17 parts of calcium-based montmorillonite, 7 to 8 parts of gypsum, 20 to 30 parts of fly ash and water, wherein the dosage of the water is based on a water-cement ratio of 0.45 to 0.60. The karst cave filling material provided by the invention has the advantages of rapid coagulation, low shrinkage rate and high strength, and can meet the filling of different types of karst caves.

Description

Technical Field

[0001] This invention relates to the field of cave filling materials, and in particular to a cave filling material, its preparation method, and its application. Background Technology

[0002] Karst caves are underground cavities formed by the long-term erosion of soluble rocks by groundwater. Highway, railway, and urban rail transit projects often involve tunnel construction, which inevitably traverses high-risk karst areas. Karst caves in these areas pose significant safety hazards to tunnel construction and require pre-construction filling and reinforcement. Failure to effectively fill and reinforce karst caves can easily lead to the collapse of the surrounding rock or the underlying bearing layer during tunnel construction, potentially endangering the safety of the construction workers.

[0003] Traditional karst cave filling materials are mainly ordinary silicate cement-based grouting materials, typically prepared by mixing ordinary silicate cement and water at a water-cement ratio of 0.5-0.6, with some adding 5-10 wt% quartz sand to improve strength. These materials suffer from long initial setting times, failing to meet the requirements of "immediate support" in engineering projects, and poor volume stability, with a 28-day shrinkage rate usually exceeding 0.1%, leading to voids between the karst cave filling material and the surrounding soil, reducing bearing capacity. Further development is needed to create a karst cave filling material that can set rapidly, has low shrinkage, and high strength to meet engineering requirements. Summary of the Invention

[0004] This invention provides a cave filling material, its preparation method, and its application. The cave filling material provided by this invention has the advantages of rapid solidification, low shrinkage, and high strength, and can meet the filling needs of different types of caves.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a cave filling material, comprising the following components in parts by weight: 183.5 parts ordinary Portland cement, 17-20 parts sulfoaluminate cement, 13-17 parts calcium-based montmorillonite, 7-8 parts gypsum, 20-30 parts fly ash, and water, wherein the amount of water is based on a water-cement ratio of 0.45-0.60.

[0006] In some specific embodiments, the cave filling material comprises the following components in parts by weight: The ingredients are: 183.5 parts ordinary silicate cement, 18.75 parts sulfoaluminate cement, 15 parts calcium-based montmorillonite, 7.5 parts gypsum, 25 parts fly ash, and water, with the water content determined by a water-cement ratio of 0.48-0.52.

[0007] In some specific embodiments, the strength grade of the ordinary silicate cement is ≥42.5 MPa.

[0008] In some specific embodiments, the aluminum oxide content of the sulfoaluminate cement is 17-20 wt%.

[0009] In some specific embodiments, the calcium-based montmorillonite has a particle size of 200-400 mesh and a montmorillonite content of ≥96.2 wt%.

[0010] In some specific embodiments, the calcium sulfate dihydrate content in the gypsum is ≥95 wt%.

[0011] In some specific embodiments, the loss on ignition of the fly ash is ≤5 wt%.

[0012] In some specific implementations, the amount of water used is based on a water-cement ratio of 0.50.

[0013] In some specific embodiments, 0.1-0.3 parts of water-reducing agent are also included.

[0014] In some specific embodiments, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent or a calcium lignosulfonate water-reducing agent, and the solid content of the polycarboxylate-based high-efficiency water-reducing agent is 18-22 wt%.

[0015] A second aspect of the present invention also provides a method for preparing the above-mentioned cave filling material, comprising the following steps: (1) Mix ordinary silicate cement, fly ash, and calcium-based montmorillonite, and perform the first stirring to obtain the first mixture. (2) The first mixture is mixed with sulfoaluminate cement, gypsum and water, and then stirred for the second time to obtain the cave filling material; When the raw materials contain a water-reducing agent, the water-reducing agent is added in step (2).

[0016] In some specific embodiments, the second stirring speed is higher than the first stirring speed.

[0017] In some specific embodiments, the temperature of the second stirring is higher than 10°C.

[0018] A third aspect of the present invention also provides the application of a karst cave filling material or a karst cave filling material prepared by the above-described method in karst cave filling projects, foundation reinforcement, and pile foundation projects.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The karst cave filling material provided by this invention combines ordinary silicate cement and sulfoaluminate in a specific ratio. The sulfoaluminate cement preferentially hydrates to form ettringite, providing early strength to the system, while the ordinary silicate cement hydrates later to fill pores, ensuring a 28-day strength ≥32 MPa. Calcium-based montmorillonite inhibits the shrinkage of the karst cave filling material slurry. The addition of gypsum can regulate the hydration rate of sulfoaluminate cement, avoiding excessively rapid early hydration. Fly ash can undergo secondary hydration to fill capillary pores and reduce porosity. The combination of these components achieves a synergistic effect of "rapid setting, low shrinkage, and high strength," breaking through the performance bottleneck of traditional filling materials. Detailed Implementation

[0020] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments described below are for illustrative purposes only and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the following embodiments, conditions and methods known in the art can be used for processing.

[0021] This invention provides a cave filling material, comprising the following components in parts by weight: 183.5 parts ordinary Portland cement, 17-20 parts sulfoaluminate cement, 13-17 parts calcium-based montmorillonite, 7-8 parts gypsum, 20-30 parts fly ash, and water, wherein the amount of water is based on a water-cement ratio of 0.45-0.60.

[0022] This invention combines ordinary silicate cement and sulfoaluminate cement with calcium-based montmorillonite, gypsum, and fly ash. The components work synergistically to obtain a cavern filling material with the advantages of rapid setting, low shrinkage, and high strength.

[0023] In this invention, based on 183.5 parts of ordinary silicate cement, the cavity-filling material includes 17-20 parts of sulfoaluminate cement, specifically 17, 18, 18.75, 19, 19.5, or 20 parts. In this invention, the sulfoaluminate cement preferentially hydrates to form ettringite, providing early strength for the system; while the ordinary cement (ordinary silicate cement) hydrates later to fill pores. The combination of these two ensures a 28-day strength ≥32 MPa.

[0024] In some embodiments of the present invention, the strength grade of the ordinary silicate cement is ≥42.5 MPa, specifically it can be 42.5 grade ordinary silicate cement, 42.5R grade ordinary silicate cement, etc.

[0025] In this invention, the strength grade of ordinary silicate cement is above 42.5 MPa, which can enhance the support and stability of the filling material.

[0026] In some embodiments of the present invention, the alumina content of the sulfoaluminate cement is 17-20 wt%, specifically 17 wt%, 17.5 wt%, 18 wt%, 18.6 wt%, 19 wt%, 20 wt%, etc. In the present invention, the above-mentioned alumina content is moderate, which can keep the formation rate of ettringite within a suitable range and avoid the "mountain-like" phenomenon.

[0027] In this invention, based on 183.5 parts of ordinary silicate cement, the cavern filling material includes 13-17 parts of calcium-based montmorillonite, specifically 13, 14, 15, 16, or 17 parts. In this invention, the interlayer cations (Ca) in the calcium-based montmorillonite... 2+ It can undergo ion exchange with the cement hydration product Ca(OH)2 to generate a stable montmorillonite-calcium hydroxide complex, thereby inhibiting shrinkage.

[0028] In some embodiments of the present invention, the calcium-based montmorillonite has a particle size of 200-400 mesh and a montmorillonite content ≥96.2 wt%. The calcium-based montmorillonite with a particle size within the above range exhibits excellent adsorption performance and can be uniformly dispersed in the medium, filling the micropores of cement stone.

[0029] In this invention, based on 183.5 parts of ordinary silicate cement, the cavity filling material includes 7-8 parts of gypsum, specifically 7 parts, 7.3 parts, 7.5 parts, 7.8 parts, 8 parts, etc. In this invention, the gypsum can regulate the hydration rate of sulfoaluminate cement, preventing excessively rapid early hydration.

[0030] In some embodiments of the present invention, the calcium sulfate dihydrate content in the gypsum is ≥95 wt%.

[0031] In this invention, based on 183.5 parts of ordinary silicate cement, the cavity-filling material includes 20-30 parts of fly ash, specifically 20, 23, 25, 28, or 30 parts. In this invention, the fly ash can undergo secondary hydration after the primary hydration of the cement. The SiO2 and Al2O3 in the fly ash react with the Ca(OH)2 released during the primary hydration of the cement, thereby filling the capillary pores and reducing the porosity to <15%.

[0032] In some embodiments of the present invention, the loss on ignition of the fly ash is ≤5 wt%, specifically 5 wt%, 4.2 wt%, 4.0 wt%, 3.5 wt%, etc.; the water requirement ratio of the fly ash is ≤95%. In the present invention, the above-mentioned loss on ignition and water requirement ratio are beneficial to maintaining a balance between fluidity and strength; if the loss on ignition is too high, it will directly affect the strength and durability. In the embodiments of the present invention, the fly ash is Grade I fly ash (according to the national standard GB / T 1596-2017 "Fly Ash for Cement and Concrete").

[0033] In this invention, using 183.5 parts of ordinary silicate cement as a base, the cavern filling material includes water, with the amount of water determined by a water-cement ratio of 0.45-0.60, specifically 0.45, 0.48, 0.50, 0.52, 0.55, 0.60, etc. This water-cement ratio ensures that the resulting cavern filling material has suitable fluidity; specifically, the standard fluidity can be flexibly adjusted within the range of 180-220 mm. Those skilled in the art can adjust the water-cement ratio as needed.

[0034] In some embodiments of the present invention, the cave filling material comprises the following components in parts by weight: The ingredients are: 183.5 parts ordinary silicate cement, 18.75 parts sulfoaluminate cement, 15 parts calcium-based montmorillonite, 7.5 parts gypsum, 25 parts fly ash, and water, with the water content determined by a water-cement ratio of 0.48-0.52.

[0035] In some embodiments of the present invention, the amount of water used is based on a water-cement ratio of 0.50.

[0036] In some embodiments of the present invention, the karst cave filling material further includes 0.1-0.3 parts of a water-reducing agent, specifically 0.1 parts, 0.2 parts, 0.25 parts, 0.3 parts, etc. The water-reducing agent forms an adsorption layer with the surface of cement particles, preventing particle aggregation and agglomeration, reducing the cohesiveness and internal friction of the concrete, and increasing the fluidity of the slurry. Those skilled in the art can choose whether to add a water-reducing agent as needed to meet the requirements of different working conditions; when a karst cave filling material with higher fluidity is required, a water-reducing agent can be added or its dosage increased; when fluidity requirements are not high, a small amount of water-reducing agent can be added or not added at all.

[0037] In some embodiments of the present invention, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent or a calcium lignosulfonate water-reducing agent, wherein the solid content of the polycarboxylate-based high-efficiency water-reducing agent is 18-22 wt%.

[0038] The present invention also provides a method for preparing the cave filling material described in any one of the above technical solutions, comprising the following steps: (1) Mix ordinary silicate cement, fly ash, and calcium-based montmorillonite, and perform the first stirring to obtain the first mixture. (2) The first mixture is mixed with sulfoaluminate cement, gypsum and water, and then stirred for the second time to obtain the cave filling material; When the raw materials contain a water-reducing agent, the water-reducing agent is added in step (2).

[0039] In this invention, by first stirring ordinary silicate cement, fly ash, and calcium-based montmorillonite, the ordinary silicate cement and calcium-based montmorillonite with large density differences can be evenly dispersed, avoiding the "clumping" phenomenon; then, sulfoaluminate cement, gypsum, and water are added, and a second stirring is carried out to start the hydration reaction, so that the fluidity of the slurry of the cave filling material is stabilized at 180-220 mm; the second stirring can promote the rapid reaction of sulfoaluminate cement and gypsum to form the initial skeleton structure.

[0040] In some embodiments of the present invention, the speed of the second stirring is higher than that of the first stirring. In the present invention, the first and second stirring are sufficient to mix the raw materials evenly, and the conditions for the first and second stirring are not particularly limited.

[0041] In this invention, there is no special limitation on the method of adding water in step (2). All water can be added at once, or water can be added in batches. In some embodiments of this invention, the process of mixing the first mixture with sulfoaluminate cement, gypsum, and water in step (2) involves first mixing a portion of the water with the first mixture, sulfoaluminate cement, and gypsum, and then adding the remaining water according to the required standard flowability value. In an embodiment of this invention, specifically, water is first measured at a water-cement ratio of 0.5, then 80% of the water is mixed with sulfoaluminate cement and gypsum, the consistency of the resulting mixture is tested, and water is added to adjust the consistency according to the required consistency, thereby achieving precise control of the flowability of the resulting karst filling material.

[0042] In some embodiments of the present invention, the temperature of the second stirring is higher than 10°C, preferably 15-25°C, and more preferably 20°C. In the present invention, if the temperature of the second stirring is too low, the normal hydration of sulfoaluminate cement cannot be guaranteed. Therefore, the second stirring is carried out at a temperature higher than 10°C. When the temperature is lower than 10°C, heating is used to increase the stirring temperature.

[0043] The present invention also provides the application of the karst cave filling material or the karst cave filling material prepared by any one of the above technical solutions in karst cave filling projects, foundation reinforcement, and pile foundation projects.

[0044] In some embodiments of the present invention, the application includes the following steps: The karst filling material is injected into the karst cave, foundation, or pile foundation hole.

[0045] In this invention, when the karst cave filling material is used in karst cave filling projects, there are no special limitations on the grouting pressure and grouting speed; conventional techniques in the art can be used to complete the grouting. In some embodiments of this invention, when the karst cave filling material is used in karst cave filling projects, the grouting pressure is 0.3-0.8 MPa, and the grouting speed is 5-15 L / min.

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] The technical specifications of calcium-based montmorillonite in the following examples and comparative examples are shown in Table 1 below.

[0048] Table 1 Technical Specifications of Calcium-based Montmorillonite

[0049] In the following examples and comparative examples, the polycarboxylate superplasticizer is model HPWR-S.

[0050] The technical specifications of Class I fly ash in the following examples and comparative examples are shown in Table 2.

[0051] Table 2 Technical Specifications of Grade I Fly Ash

[0052] The technical specifications of sulfoaluminate cement in the following examples and comparative examples are shown in Table 3.

[0053] Table 3 Technical Specifications of Sulfoaluminate Cement

[0054] Example 1 In this embodiment, a cave filling material was prepared to fill small fissure caves at 18°C. These caves are relatively small in volume and contain many small fissures, requiring rapid filling to prevent the fissures from expanding and causing collapse. Therefore, the material requires high early strength and resistance to leakage.

[0055] 1. According to weight parts, the allocation of each group in this embodiment is as follows: 183.5 parts of 42.5R grade ordinary Portland cement 18.75 parts of sulfoaluminate cement (Al2O3 18.6 wt%) 15 parts of calcium-based montmorillonite (particle size 200-400 mesh), 7.5 parts of gypsum (calcium sulfate dihydrate, 95 wt%) 25 parts of Grade I fly ash (loss on ignition 2.62 wt%) The amount of water used should be measured with a water-cement ratio of 0.5. 0.25 parts of polycarboxylate superplasticizer.

[0056] 2. Preparation of cave filling material: At room temperature (20°C), perform the following operations: 42.5R grade ordinary Portland cement, fly ash, and calcium-based montmorillonite were mixed at a low speed of 140 r / min for 4 minutes to obtain the first mixture. Then, sulfoaluminate cement, gypsum, polycarboxylate superplasticizer and water are added to the first mixture, and stirred at medium speed of 285 r / min for 4 min to obtain the cave filling material.

[0057] Example 2 In this embodiment, a cave filling material was prepared for filling a large waterlogged cave at 18°C. The cave is relatively large in volume and has a small amount of water at the bottom. The material needs to have good fluidity to spread to the waterlogged area while resisting the dilution effect of water.

[0058] 1. The only difference between the components in this embodiment and those in Example 1 is that the amount of polycarboxylate superplasticizer used is 0.3 parts.

[0059] 2. Preparation of cave filling material: 42.5R grade ordinary Portland cement, fly ash, and calcium-based montmorillonite were mixed at a low speed of 140 r / min for 3 minutes to obtain the first mixture. Then, sulfoaluminate cement, gypsum, polycarboxylate superplasticizer and water are added to the first mixture, and stirred at medium speed of 285 r / min for 5 min to obtain the cave filling material.

[0060] Example 3 The cave filling material was prepared according to Example 1, except that polycarboxylate superplasticizer was not added, and the amount of water was determined by a water-cement ratio of 0.5.

[0061] Example 4 The cave filling material was prepared according to Example 1, except that the polycarboxylate superplasticizer was replaced with calcium lignosulfonate superplasticizer (brand: Gongyi Yuyuan, model: ZWM-Ⅰ).

[0062] Example 5 The cave filling material was prepared according to Example 1, except that the amount of sulfoaluminate cement used was 20 parts.

[0063] Example 6 The cave filling material was prepared according to Example 1, except that the amount of sulfoaluminate cement was 17.5 parts.

[0064] Comparative Example 1 The cave filling material was prepared according to Example 1, except that sulfoaluminate cement was not added, while the amount of 42.5R grade ordinary silicate cement was 202.25 parts, that is, the total amount of cement remained unchanged.

[0065] Comparative Example 2 The cave filling material was prepared according to Example 1, except that 42.5R grade ordinary silicate cement was not added, while the amount of sulfoaluminate cement was 202.25 parts, that is, the total amount of cement remained unchanged.

[0066] Performance characterization: (1) Slurry consistency test The consistency of the slurry filling material obtained from the examples and comparative examples was tested using the standard funnel method. The outflow time of the test results is shown in Table 4.

[0067] (2) Initial setting and final setting time determination: According to the "Standard for Test Method of Performance of Ordinary Concrete Mixture" (GB / T50080-2016), the initial setting and final setting times of the filler materials prepared in the examples and comparative examples were determined, and the results are shown in Table 4.

[0068] (3) Compressive strength test: The compressive strength of the karst filling materials obtained in the examples and comparative examples was tested at curing ages of 3 days, 7 days and 28 days, respectively, using the method in the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019). The results are shown in Table 4.

[0069] (4) 28-day shrinkage rate determination: The 28-day shrinkage rate of the karst filling material was determined according to the contact method test example and comparative example in the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082-2009). The results are shown in Table 4.

[0070] (5) Impermeability test: The 28-day impermeability of the karst filling material obtained by the stepwise pressure test method in the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082-2009) is shown in Table 4.

[0071] Table 4 Performance test results of the cave filling materials obtained in the examples and comparative examples

[0072] As can be seen from the data in Table 1, the karst cave filling material obtained by this invention has excellent performance. This indicates that by using the materials and proportions of this invention, the most suitable filling material can be formulated, with optimal fluidity, initial and final setting times, compressive strength, shrinkage rate, and impermeability.

[0073] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims.

Claims

1. A cave filling material, characterized in that, The components include the following parts by weight: 183.5 parts ordinary Portland cement, 17-20 parts sulfoaluminate cement, 13-17 parts calcium-based montmorillonite, 7-8 parts gypsum, 20-30 parts fly ash, and water, wherein the amount of water is based on a water-cement ratio of 0.45-0.

60.

2. The cave filling material according to claim 1, characterized in that, The components include the following parts by weight: The ingredients are: 183.5 parts ordinary silicate cement, 18.75 parts sulfoaluminate cement, 15 parts calcium-based montmorillonite, 7.5 parts gypsum, 25 parts fly ash, and water, with the water content determined by a water-cement ratio of 0.48-0.

52.

3. The cave filling material according to claim 1 or 2, characterized in that, The strength grade of the ordinary Portland cement is ≥42.5 MPa. The sulfoaluminate cement has an aluminum oxide content of 17-20 wt%. The calcium-based montmorillonite has a particle size of 200-400 mesh and a montmorillonite content ≥96.2 wt%. The gypsum contains ≥95 wt% calcium sulfate dihydrate. The loss on ignition of the fly ash is ≤5 wt%.

4. The cave filling material according to claim 1 or 2, characterized in that, The amount of water used should be based on a water-cement ratio of 0.

50.

5. The cave filling material according to claim 1 or 2, characterized in that, It also includes 0.1-0.3 parts of water-reducing agent.

6. The cave filling material according to claim 5, characterized in that, The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent or a calcium lignosulfonate water-reducing agent, and the solid content of the polycarboxylate-based high-efficiency water-reducing agent is 18-22 wt%.

7. A method for preparing a cave filling material according to any one of claims 1-6, comprising the following steps: (1) Mix ordinary silicate cement, fly ash, and calcium-based montmorillonite, and perform the first stirring to obtain the first mixture. (2) The first mixture is mixed with sulfoaluminate cement, gypsum and water, and then stirred for the second time to obtain the cave filling material; When the raw materials contain a water-reducing agent, the water-reducing agent is added in step (2).

8. The method for preparing the cave filling material according to claim 7, characterized in that, The second stirring speed is higher than the first stirring speed.

9. The preparation method according to claim 7, characterized in that, The temperature of the second stirring is higher than 10°C.

10. The application of the karst cave filling material according to any one of claims 1-6 or the karst cave filling material obtained by the preparation method according to any one of claims 7-9 in karst cave filling projects, foundation reinforcement, and pile foundation projects.

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