METHOD FOR ECOLOGICAL FILLING WITH MIXED COAL GANGUE AND FLY ASH

Abstract

A method for ecological filling with mixed coal gangue and fly ash includes the following steps: S1: construction of a double-impermeable base layer: leveling a pit or gully, laying a fly ash-based cementitious material, compacting and curing; spraying a layer of polymer waterproof coating on a surface of the fly ash-based cementitious material, and fully curing to obtain a double-impermeable protective structure; S2: three-dimensional layered filling: dumping coal gangue and fly ash in sequence on the double-impermeable protective structure formed in S1, where the coal gangue and the fly ash are three-dimensionally layered and well graded; the coal gangue is coal gangue after coal washing, which is used as an aggregate; the fly ash is used as a filler and cementitious material to achieve a compact filling structure; and S3: rolling: rolling by a roller after the three-dimensional layered filling.

Claims

1. A method for an ecological filling with mixed coal gangue and fly ash, comprising the following steps: S1: a construction of a double-impermeable base layer: leveling a pit or a gully, laying a fly ash-based cementitious material on the pit or the gully, compacting and curing; then spraying a layer of a polymer waterproof coating on a surface of the fly ash-based cementitious material, and fully curing to obtain a double-impermeable protective structure; wherein the fly ash-based cementitious material is prepared by mixing the fly ash, an ultra-fine ash, a cement and water in proportions; a mass ratio of the fly ash, the ultra-fine ash and the cement is (6-8): (1-2):1, and a water-ash ratio is (2-3):10; wherein the polymer waterproof coating is an organic-inorganic composite coating prepared by mixing the fly ash, the cement and an emulsion; the fly ash accounts for 60-90% of a powder filler, and a ratio of the emulsion to the powder filler is 0.1-0.3; S2: a three-dimensional layered filling: dumping coal gangue and a fly ash in sequence on the double-impermeable protective structure formed in S1, wherein the coal gangue and the fly ash are three-dimensionally layered and well graded; the coal gangue is the coal gangue after a coal washing, and the coal gangue is used as an aggregate; the fly ash is used as a filler and a cementitious material to achieve a compact filling structure; the fly ash is fluidized bed fly ash, and the fly ash is sprayed with water to a humidity of 15-30% before use; and S3: a rolling: rolling by a roller after the three-dimensional layered filling.

2. The method for the ecological filling with the mixed coal gangue and fly ash according to claim 1, wherein the fly ash-based cementitious material in step S1 has a thickness of 5-10 cm; the coal gangue dumped on the double-impermeable protective structure in step S2 has a thickness of 0.4-0.6 m, and the fly ash dumped on the double-impermeable protective structure has a thickness of 0.2-0.3 m.

3. (canceled)

4. The method for the ecological filling with the mixed coal gangue and fly ash according to claim 1, wherein the fly ash is pulverized coal furnace fly ash or circulating fluidized bed (CFB) boiler fly ash; the ultra-fine ash is ultra-finely pulverized fly ash with a particle size of 510 μm; the cement is ordinary Portland cement or Portland slag cement.

5. The method for the ecological filling with the mixed coal gangue and fly ash according to claim 1, wherein the polymer waterproof coating has a thickness of 2-3 mm.

6. (canceled)

7. The method for the ecological filling with the mixed coal gangue and fly ash according to claim 1, wherein the emulsion is a styrene-acrylic emulsion and/or an acrylic emulsion.

8. The method for the ecological filling with the mixed coal gangue and fly ash according to claim 1, wherein the polymer waterproof coating is specifically prepared as follows: mixing the fly ash and the cement to obtain the powder filler; adding water to the emulsion and stirring at a low speed; adding the powder filler and stirring at a constant speed for 15 min to obtain the polymer waterproof coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a schematic diagram of a method for ecological filling with mixed coal gangue and fly ash that are double-impermeable, oxygen-insulating and flame-retardant according to the present disclosure.

[0025] FIG. 2 shows a double-impermeable structure.

[0026] FIG. 3 shows an oxygen-insulating and flame-retardant structure in which a fly ash hydrated product coats coal gangue.

[0027] FIG. 4 shows a scanning electron microscope (SEM) image of an internal structure of a coating prepared in Example 5.

[0028] FIG. 5 shows a surface image of a sample prepared in Example 5 after testing by a water impermeability tester for 30 min.

[0029] FIG. 6 shows a SEM image of an internal structure of a coating prepared in Example 6.

[0030] FIG. 7 shows a surface image of a sample prepared in Example 6 after testing by a water impermeability tester for 30 min.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following clearly and completely describes the technical solutions in the examples of the present disclosure. Apparently, the described examples are merely a part rather than all of the examples of the present disclosure. All other examples obtained by a person of ordinary skill in the art based on the examples of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

[0032] As shown in FIG. 1, a method for ecological filling with mixed coal gangue and fly ash includes the following steps:

[0033] S1: Construction of a double-impermeable base layer: level a pit or gully, lay a fly ash-based cementitious material, compact and cure; then spray a layer of polymer waterproof coating on a surface of the fly ash-based cementitious material, and fully cure to obtain a double-impermeable protective structure, as shown in FIG. 2.

[0034] S2: Three-dimensional layered filling: dump coal gangue and fly ash in sequence on the double-impermeable protective structure formed in S1, where the coal gangue and the fly ash are three-dimensionally layered and well graded. The coal gangue is coal gangue after coal washing, which is used as an aggregate; the fly ash is used as a filler and cementitious material to achieve a compact filling structure. The fly ash is fluidized bed fly ash, which is sprayed with water to a humidity of 15-30% before use. The fly ash humidified in advance by spraying water and the coal gangue after coal washing both have a certain humidity and a low fluidity during dumping, facilitating the dumping and layering during the implementation process.

[0035] S3: Rolling: roll by a roller after the three-dimensional layered filling.

[0036] In this example, the fly ash-based cementitious material in step S1 has a thickness of 5-10 cm. The dumped coal gangue on the double-impermeable protective structure in step S2 has a thickness of 0.4-0.6 m, and the dumped fly ash has a thickness of 0.2-0.3 m. The fly ash-based cementitious material is prepared by mixing fly ash, ultra-fine ash, cement and water in proportions; a mass ratio of the fly ash, the ultra-fine ash and the cement is (6-8): (1-2):1, and a water-ash ratio is (2-3):10. The fly ash is pulverized coal furnace fly ash or circulating fluidized bed (CFB) boiler fly ash. The ultra-fine ash is ultra-finely pulverized fly ash with a particle size of 5-10 μm. The cement is ordinary Portland slag cement.

[0037] In this example, the polymer waterproof coating has a thickness of 2-3 mm. The polymer waterproof coating is an organic-inorganic composite coating prepared by mixing fly ash, cement and an emulsion. The fly ash accounts for 60-90% of a powder filler, and a ratio of the emulsion to the powder filler is 0.1-0.3. The emulsion is a styrene-acrylic emulsion and/or an acrylic emulsion. The polymer waterproof coating is specifically prepared as follows: mix the fly ash and the cement to obtain the powder filler; add the water to the emulsion and stir at a low speed; add the powder filler and stir at a constant speed for 15 min to obtain the polymer waterproof coating.

EXAMPLE 1

[0038] 70 kg of CFB boiler fly ash, 20 kg of CFB boiler fly ash with a particle size of 5-10 μm and 10 kg of Grade 32.5 Portland slag cement were mixed uniformly. 22 kg of water was added, and the materials were stirred evenly to obtain a fly ash-based cementitious material. 60 kg of ultra-fine CFB boiler fly ash with a particle size of 5-10 μm and 40 kg of Grade 32.5 Portland slag cement were mixed uniformly to obtain a powder. 30 kg of S400F styrene-acrylic emulsion and 40 kg of water were stirred at a low speed for 2 min. Then the pre-mixed powder was added, and the stirring was continued at a constant speed of 600 r/min for 15 min to obtain a polymer waterproof coating. A 6 cm thick fly ash-based cementitious material was laid on a soil layer at the bottom of a pit, compacted and cured. Then, a layer of about 2.5 mm polymer waterproof coating was sprayed on a surface of the fly ash-based cementitious material to form a double-impermeable structure of cementitious solidification with coating film blocking to effectively prevent the infiltration of leachate.

[0039] 0.4 m of coal gangue and 0.2 m of CFB boiler fly ash were sequentially dumped into the pit from one side to the other to form different layers. The layers had a height of about 10 m in a horizontal direction. They were sprinkled with water to maintain a humidity of 18%, and were compacted by a roller. After 3 days of natural curing, a compressive strength reached 6.4 MPa, and after 7 days of curing, the compressive strength increased to 7.6 MPa. The fly ash formed a hydrated cementitious product to coat the surface of the coal gangue, such that the filled coal gangue and the fly ash formed a tightly integrated whole, which effectively blocked a large amount of air from entering the accumulated body to cause spontaneous combustion or re-ignition. As shown in FIG. 3, during humidification and rolling, free Ca.sup.2+ in the fly ash promotes the formation of the hydrated cementitious product to coat the surface of the coal gangue, which has an oxygen-insulating and flame-retardant effect on the coal gangue. In addition, the hydration expansibility of the fly ash also promotes a more compact structure of the fly ash and the coal gangue.

EXAMPLE 2

[0040] 80 kg of CFB boiler fly ash, 10 kg of CFB boiler fly ash with a particle size of 5-10 μm and 10 kg of Grade 32.5 ordinary Portland cement were mixed uniformly. 25 kg of water was added, ordinary mixed materials were stirred evenly to obtain a fly ash-based cementitious material. 80 kg of CFB boiler fly ash with a particle size of 5-10 μm and 20 kg of Grade 32.5 Portland slag cement were mixed uniformly to obtain a powder. 20 kg of acrylic emulsion and 50 kg of water were stirred at a low speed for 2 min. Then, the pre-mixed powder was added, and the stirring was continued at a constant speed of 600 r/min for 15 min to obtain a polymer waterproof coating. A 6 cm thick fly ash-based cementitious material was injected onto a soil layer at the bottom of a pit, and was cured. Then, a layer of about 2.5 mm of polymer waterproof coating was sprayed on a surface of the fly ash-based cementitious material to form a double-impermeable structure of cementitious solidification with coating film blocking to effectively prevent the infiltration of leachate.

[0041] 0.5 m of coal gangue and 0.25 m of CFB boiler fly ash were sequentially dumped into the pit from one side to the other to form different layers. The layers had a height of about 10 m in a horizontal direction. They were sprinkled with water to maintain a humidity of 22%, and were compacted by a roller. After 3 days of natural curing, a compressive strength reached 6.4 MPa, and after 7 days of curing, the compressive strength increased to 7.6 MPa. The fly ash formed a hydrated cementitious product to coat the surface of the coal gangue, such that the filled coal gangue and the fly ash formed a tightly integrated whole. After the ecological filling was completed, the process of filling, reclamation, greening and ecological reconstruction could be continued.

EXAMPLE 3

[0042] Fly Ash-Based Cementitious Material

[0043] 70 kg of CFB boiler fly ash, 20 kg of CFB boiler fly ash with a particle size of 5-10 μm and 10 kg of Grade 32.5 Portland slag cement were mixed uniformly. 22 kg of water was added, and the materials were stirred evenly to obtain a fly ash-based cementitious material. After curing, a compressive strength was tested by a mechanical strength tester. It was 3.8 MPa after 1 d, 8.5 MPa after 3 d, and 21.6 MPa after 7 d.

EXAMPLE 4

[0044] Fly Ash-Based Cementitious Material

[0045] 80 kg of CFB boiler fly ash, 10 kg of CFB boiler fly ash with a particle size of 5-10 μm and 10 kg of Grade 32.5 ordinary Portland cement were mixed uniformly. 25 kg of water was added, ordinary mixed materials were stirred evenly to obtain a fly ash-based cementitious material. After curing, a compressive strength was tested by a mechanical strength tester. It was 3.4 MPa after 1 day, 8.3 MPa after 3 days, and 20.3 MPa after 7 days.

EXAMPLE 5

[0046] Polymer Waterproof Coating

[0047] 60 kg of CFB boiler fly ash with a particle size of 5-10 μm and 40 kg of Grade 32.5 Portland slag cement were mixed uniformly to obtain a powder. 30 kg of S400F styrene-acrylic emulsion and 40 kg of water were stirred at a low speed for 2 min. Then the pre-mixed powder was added, and the stirring was continued at a constant speed of 600 r/min for 15 min to obtain a polymer waterproof coating. The polymer waterproof coating was poured into a φ200 circular mold frame, and was naturally cured for 7 d to obtain a sample with a thickness of 2.8 mm. FIG. 4 shows a cross section of the coating. There were no voids in the coating and the structure of the coating was dense and firm. The impermeability of the coating was tested by a water impermeability tester, and the coating was impermeable after 30 min. As shown in FIG. 5, the surface of the coating after the test was still dense without obvious voids.

EXAMPLE 6

[0048] Polymer Waterproof Coating

[0049] 80 kg of CFB boiler fly ash with a particle size of 5-10 μm and 20 kg of Grade 32.5 Portland slag cement were mixed uniformly to obtain a powder. 20 kg of acrylic emulsion and 50 kg of water were stirred at a low speed for 2 min. Then the pre-mixed powder was added, and the stirring was continued at a constant speed of 600 r/min for 15 min to obtain a polymer waterproof coating. The polymer waterproof coating was poured into a φ200 circular mold frame, and was naturally cured for 7 days to obtain a sample with a thickness of 2.6 mm. FIG. 6 shows a cross section of the coating. The internal structure of the coating was compact without obvious voids. The impermeability of the coating was tested by a water impermeability tester, and the coating was impermeable after 30 min. As shown in FIG. 7, the surface of the coating after the test had fine pores, but they were very shallow and impermeable.

EXAMPLE 7

[0050] A 6 cm thick fly ash-based cementitious material prepared in Example 3 was laid on a simulated soil layer, and was compacted and cured. Then, a layer of about 2.5 mm polymer waterproof coating prepared in Example 5 was sprayed on a surface of the fly ash-based cementitious material to form a double-impermeable structure of cementitious solidification with coating film blocking. This structure was tested to have a permeability coefficient of 1.7×10.sup.−10 m/s, and was able to effectively prevent the infiltration of leachate.

[0051] The cost accounting is shown in Table 1. The fly ash-based cementitious material cost 2.59 yuan/m.sup.2, and the polymer waterproof coating material cost 6.42 yuan/m.sup.2. In the early stage, the construction cost and labor cost for simple leveling, laying, compacting, spraying, etc. of the pit bottom were about 16 yuan/m.sup.2. In total, the implementation cost of the double-impermeable method of the present disclosure was about 25.0 yuan/m.sup.2.

[0052] A conventional impermeable film was made of a 0.5-0.75 mm thick high-density polyethylene impermeable film, which cost 10-15 yuan/m.sup.3. Before the film was laid, the bottom of the pit was finely leveled and covered with a thick layer of loess, which cost 40 yuan/m.sup.3. Plus the construction cost and labor cost, etc., the comprehensive cost of the film-based impermeable method was about 30 yuan/m.sup.3.

[0053] Compared with the film laying method, the cost of the method of the present disclosure was reduced by more than 16.7%.

TABLE-US-00001 TABLE 1 Cost accounting of Example 7 Materials Fly ash-based cementitious material Polymer waterproof coating Grade Grade Ultra-fine 32.5 Ultra-fine 32.5 Composition Fly ash ash cement Water ash cement Emulsion Water Amount (%) 70 20 10 22 60 40 30 40 Amount (t) 0.7 0.2 0.1 0.22 0.6 0.4 0.3 0.4 Unit price 25% of 80 300 3 80 300 8000 3 (yuan/t) environmental protection tax, 20 of freight Subtotal −3.5 16 30 0.66 48 120 2400 1.2 (yuan/t) Total (2 t/m.sup.3) 43.16 yuan/m.sup.3 2569.2 yuan/1.7 t (about 1 m.sup.3) Costs (Cementitious material, 6 cm thick) 2.59 yuan/m.sup.2 (Coating, 2.5 mm thick) 6.42 yuan/m.sup.3

EXAMPLE 8

[0054] A 6 cm thick fly ash-based cementitious material prepared in Example 4 was laid on a simulated soil layer, and was compacted and cured. Then, a layer of about 2.5 mm polymer waterproof coating prepared in Example 6 was sprayed on a surface of the fly ash-based cementitious material to form a double-impermeable structure of cementitious solidification with coating film blocking. This structure was tested to have a permeability coefficient of 6.3×10.sup.−10 m/s, and was able to effectively prevent the infiltration of leachate.

[0055] The cost accounting is shown in Table 2. The fly ash-based cementitious material cost 2.09 yuan/m.sup.2, and the polymer waterproof coating material cost 4.31 yuan/m.sup.2. In the early stage, the construction cost and labor cost for simple leveling, laying, compacting, spraying, etc. of the pit bottom were about 16 yuan/m.sup.2. In total, the implementation cost of the double-impermeable method of the present disclosure was about 22.40 yuan/m.sup.2. The comprehensive cost of a film-based impermeable method was about 30 yuan/m.sup.3, and compared with the film laying method, the cost of the method of the present disclosure was reduced by 25.3%.

TABLE-US-00002 TABLE 2 Cost accounting of Example 8 Materials Fly ash-based cementitious material Polymer waterproof coating Grade Grade Ultra-fine 32.5 Ultra-fine 32.5 Composition Fly ash ash cement Water ash cement Emulsion Water Amount (%) 80 10 10 25 80 20 20 50 Amount (t) 0.8 0.1 0.1 0.25 0.8 0.2 0.2 0.5 Unit price 25% of 80 300 3 80 300 8000 3 (yuan/t) environmental protection tax, 20 of freight Subtotal −4 8 30 0.75 64 60 1600 1.5 (yuan/t) Total (2 t/m.sup.3) 34.75 yuan/m.sup.3 1725.5 yuan/1.7 t (about 1 m.sup.3) Costs (Cementitious material, 6 cm thick) 2.09 yuan/m.sup.2 (Coating, about 2.5 mm thick) 4.31 yuan/m.sup.2

[0056] Only preferred examples of the present disclosure are described in detail above, but the present disclosure is not limited to the above examples. Within the knowledge of a person of ordinary skill in the art, various variations can also be made without departing from the spirit of the present disclosure and all should be included in a protection scope of the present disclosure.