Novel high-solid-waste-based paste filling material and preparation method thereof

Abstract

The invention discloses a novel high-solid-waste-based paste filling material which takes coal gangue as aggregate and coal ash, slag powder, desulfurized gypsum and cement as cementing materials, so that resource utilization of industrial solid wastes can be realized, land occupation is avoided, and environmental pollution is reduced; the fly ash, the slag powder and the desulfurized gypsum can be subjected to a hydration reaction in an alkaline environment provided by cement hydration, the uniaxial compressive strength of the material in 28 days can reach 4-6 MPa due to generated hydration products such as hydrated calcium silicate and ettringite, meanwhile, the micro slump and the micro expansion degree of freshly mixed slurry can reach 135-140 mm and 290-315 mm, the bleeding rate is lower than 3%, the cement accounts for 2% of the total mass, and the water retention rate is lower than 3%. Due to the addition of the desulfurized gypsum, the filling material cannot be quickly condensed within 4 hours after preparation, and has certain fluidity, so that normal pumping can be realized after emergency repair when pressure pumping equipment breaks down. And the requirements of pressure pumping are met, and good economic and social benefits are created for mine enterprises.

Description

Technical Field

[0001] This invention relates to the field of filling material preparation technology, and in particular to a novel high-solids waste-based paste filling material and its preparation method. Background Technology

[0002] Paste backfilling technology is a green mining technology based on the resource utilization of solid waste. Its core principle is to mix solid waste such as tailings and waste rock with a binder and an appropriate amount of water to create a paste material with high concentration, certain fluidity, and suitable strength, which is then backfilled into the underground goaf. This technology can not only effectively solve the problem of solid waste accumulation during mining, but also provide reliable support for the goaf, avoid geological disasters such as surface subsidence and mine tremors, and improve the safety of mining operations.

[0003] The high cost of paste backfilling mining currently hinders the widespread application of conventional backfilling mining techniques. Furthermore, cement, the primary cementing material, accounts for over 75% of the backfilling cost. Therefore, reducing cement usage to lower backfilling costs is crucial for improving the economic efficiency of mining areas. Simultaneously, paste backfilling materials must possess good fluidity and not rapidly solidify within 4 hours of preparation, maintaining a certain level of fluidity to ensure normal pumping after emergency repairs in case of pressurized pumping equipment failure. To achieve this, admixtures are typically used to adjust fluidity and setting time; however, these admixtures are expensive, further increasing the cost of paste backfilling mining. Summary of the Invention

[0004] The purpose of this invention is to provide a novel high-solids waste-based paste filling material and its preparation method in order to solve the above-mentioned problems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A novel high-solids waste-based paste filling material comprises solids and water, wherein the mass concentration of the solids in the filling material is 74%; the solids include aggregates and cementing materials, wherein the aggregates are coal gangue, accounting for 60% of the solids, and the cementing materials are composed of fly ash, slag powder, desulfurized gypsum, and cement, accounting for 40% of the solids; the cementing materials are composed of the following components by mass percentage: 58%~73% fly ash, 15% slag powder, 5%~20% desulfurized gypsum, and 7% cement.

[0007] Preferably, the particle size composition and proportion of the coal gangue aggregate are as follows: 25% for particles of 1.25mm to 2.5mm, 50% for particles of 0.16mm to 1.25mm, and 25% for particles <0.16mm.

[0008] Preferably, the fly ash has a particle size of D50 = 50.325 μm and D90 = 186.699 μm; the slag powder has a particle size of D50 = 13.112 μm and D90 = 28.618 μm; the desulfurized gypsum has a particle size of D50 = 28.387 μm and D90 = 64.087 μm; and the cement has a particle size of D50 = 20.577 μm and D90 = 51.813 μm.

[0009] Preferably, the fly ash is Class III fly ash collected by the dust collector of a coal-fired power plant, the slag powder is S95 grade ground slag, and the cement is P.S32.5 slag silicate cement.

[0010] Preferably, the coal gangue is composed of the following chemical components by weight percentage: CaO 2.62%, Fe2O3 6.97%, SiO2 55.19%, Al2O3 23.94%, MgO 0.45%, SO3 0.38%, and K2O 6.31%.

[0011] Preferably, the fly ash is composed of the following chemical components by weight percentage: CaO 3.84%, Fe2O3 8.96%, SiO2 48.01%, Al2O3 29.37%, MgO 0.49%, SO3 0.54%, and K2O 3.17%.

[0012] Preferably, the slag powder is composed of the following chemical components by weight percentage: CaO 57.86%, Fe2O3 0.78%, SiO2 19.41%, Al2O3 10.04%, MgO 6.88%, SO3 1.18%, and K2O 0.37%.

[0013] Preferably, the desulfurized gypsum is composed of the following chemical components by weight percentage: 62.7% CaO, 0.45% Fe2O3, 0.87% SiO2, 0.45% Al2O3, 1.04% MgO, 33.66% SO3, and 0.06% K2O.

[0014] Preferably, the cement is composed of the following chemical components by weight percentage: 56.34% CaO, 4.39% Fe2O3, 19.19% SiO2, 10.35% Al2O3, 3.95% MgO, 2.29% SO3, and 0.55% K2O.

[0015] The method for preparing the filling material includes the following steps:

[0016] S1: First, screen the crushed coal gangue into a particle size composition of 25% for 1.25mm~2.5mm, 50% for 0.16mm~1.25mm, and 25% for <0.16mm. Then, place the coal gangue, fly ash, slag powder, desulfurized gypsum, and cement in a drying oven and dry for 24 hours at a temperature of 105±5℃.

[0017] S2: Weigh the raw materials. The mass concentration of the solids is 74%, and the mass concentration of tap water is 26%. The solids include aggregates and cementitious materials. The aggregates are coal gangue, accounting for 60% of the solids. The cementitious materials are composed of fly ash, slag powder, desulfurized gypsum, and cement, accounting for 40% of the solids. The cementitious materials are composed of the following components by mass percentage: 58%~73% fly ash, 15% slag powder, 5%~20% desulfurized gypsum, and 7% cement. S3: Pour the weighed fly ash, slag powder, desulfurized gypsum, and cement into a cement mortar mixer and mix at low speed for about 60 seconds to ensure that the raw materials are evenly mixed.

[0018] S4: After the raw materials are mixed evenly, slowly add the weighed 50% tap water and continue to stir at low speed for about 120 seconds. Then add the coal gangue aggregate and the remaining 50% tap water, continue to stir at low speed for about 120 seconds, and then stir at high speed for about 120 seconds to ensure that the slurry is fully mixed evenly and does not separate into layers.

[0019] S5: Immediately after the slurry is fully mixed, test the micro slump, micro spread and bleeding rate of the fresh slurry. After the test, let it stand for 4 hours, and then test the micro slump and micro spread again after 4 hours.

[0020] S6: After the test is completed, the paste filling material is put into a 40×40×40mm triple square detachable steel mold. After the mold is filled, it is placed on the mortar vibration table and vibrated for about 120 seconds to ensure that all air bubbles in the material are expelled. After the vibration is completed, the surface is smoothed and covered with plastic wrap. After 3 days, the mold is removed and the compressive strength test is carried out.

[0021] S7: Place the demolded test blocks in a standard curing room for curing. The temperature is set to 20℃±2℃ and the humidity is set to 95%±1%. Compressive strength tests are conducted after curing for 7 days, 14 days and 28 days.

[0022] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0023] Using coal gangue as aggregate and fly ash, slag powder, desulfurized gypsum, and cement as cementing materials not only achieves the resource utilization of industrial solid waste, avoiding land occupation and reducing environmental pollution, but also allows fly ash, slag powder, and desulfurized gypsum to undergo hydration reactions in the alkaline environment provided by cement hydration. The resulting hydration products, such as hydrated calcium silicate and ettringite, enable the material to achieve a uniaxial compressive strength of 4-6 MPa at 28 days. Simultaneously, the freshly mixed slump and micro-expansion of the grout reach 135-140 mm and 290-315 mm, respectively, with a bleeding rate of less than 3%. Cement accounts for only 2% of the total mass. The addition of desulfurized gypsum prevents the filling material from rapidly setting within 4 hours of preparation and maintains a certain degree of fluidity, allowing for normal pumping after emergency repairs in case of pressurized pumping equipment failure. This meets the requirements of pressurized pumping and creates significant economic and social benefits for mining enterprises. Attached Figure Description

[0024] Figure 1 This is a particle size distribution diagram of fly ash, slag powder, desulfurized gypsum and cement in a novel high-solids waste-based paste filling material of the present invention.

[0025] Figure 2 This is a curve showing the change in the water bleeding rate of the paste filling material under different desulfurization gypsum parameters in an embodiment of the present invention;

[0026] Figure 3 This is a graph showing the microslump of freshly mixed slurry and the change in microslump after 4 hours under different desulfurization gypsum parameters in this embodiment of the invention.

[0027] Figure 4 This is a graph showing the micro-expansion of freshly mixed slurry and the change in expansion after 4 hours under different desulfurization gypsum parameters in this embodiment of the invention.

[0028] Figure 5 This is a graph showing the variation of uniaxial compressive strength at different curing ages under different desulfurization gypsum parameters in the embodiments of the present invention; Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see Figure 1-5 The present invention provides a technical solution:

[0031] A novel high-solids-based paste filling material comprises solids and water, wherein the mass concentration of the solids in the filling material is 74%; the solids include aggregates and cementitious materials, wherein the aggregates are coal gangue, accounting for 60% of the solids, and the cementitious materials are composed of fly ash, slag powder, desulfurized gypsum and cement, accounting for 40% of the solids; the cementitious materials are composed of the following components by mass percentage: 58%~73% fly ash, 15% slag powder, 5%~20% desulfurized gypsum, and 7% cement;

[0032] The particle size composition and proportion of coal gangue aggregate are as follows: 1.25mm~2.5mm accounts for 25%, 0.16mm~1.25mm accounts for 50%, and <0.16mm accounts for 25%; the particle size of fly ash is: D50=50.325μm, D90=186.699μm; the particle size of slag powder is: D50=13.112μm, D90=28.618μm; the particle size of desulfurized gypsum is: D50=28.387μm, D90=64.087μm; the particle size of cement is: D50=20.577μm, D90=51.813μm; the fly ash is Class III fly ash collected by the dust collector of the coal-fired power plant, the slag powder is S95 grade ground slag, and the cement is P.S32.5 slag silicate cement;

[0033] Coal gangue is composed of the following chemical components by weight percentage: CaO 2.62%, Fe2O3 6.97%, SiO2 55.19%, Al2O3 23.94%, MgO 0.45%, SO3 0.38%, and K2O 6.31%; fly ash is composed of the following chemical components by weight percentage: CaO 3.84%, Fe2O3 8.96%, SiO2 48.01%, Al2O3 29.37%, MgO 0.49%, SO3 0.54%, and K2O 3.17%; slag powder is composed of the following chemical components by weight percentage: CaO 57.86%, Fe2O3 0.78%, and SiO2 1%. The desulfurized gypsum is composed of the following chemical components by weight percentage: CaO 62.7%, Fe2O3 0.45%, SiO2 0.87%, Al2O3 0.45%, MgO 1.04%, SO3 33.66%, and K2O 0.06%. The cement is composed of the following chemical components by weight percentage: CaO 56.34%, Fe2O3 4.39%, SiO2 19.19%, Al2O3 10.35%, MgO 3.95%, SO3 2.29%, and K2O 0.55%.

[0034] The filling material is pumped and pressurized to transport the filling slurry to the underground goaf area, and after solidification, it forms a load-bearing structure with a certain supporting function.

[0035] After the paste filling material is prepared, slump, spread, and bleeding rate tests are required. Given the limited raw materials in the laboratory, a micro-slump cone was selected for this work. A truncated cone with a top diameter of 50 mm, a bottom diameter of 100 mm, and a cone height of 150 mm was used. Micro-slump tests were conducted according to the method specified in ASTM C1437-20 to measure the micro-slump and spread of the slurry. Before testing, the slump cone and base plate were cleaned to ensure there were no impurities or standing water. The inner wall of the slump cone and the surface of the base plate were moistened with a damp cloth. The slump cone was placed in the center of the base plate, ensuring it remained fixed and vertical during the test. The sample was loaded into the cone in three layers using a small shovel. After each layer was loaded, a tamping rod was used to tamp the sample evenly 25 times in a spiral motion along the cone wall from the outside to the center. The tamping depth should penetrate the layer, with even force applied, avoiding impact. After loading the top layer, excess sample was removed from the top of the cone, and the surface was smoothed so that the sample was flush with the top of the cone. The sample on the base plate around the cone was cleaned. Within 5-10 seconds after filling, lift the slump cone smoothly, vertically, and without impact. The lifting process should be completed within 3-7 seconds, and the slump cone should not be rotated or struck during the process. After the sample has fallen steadily, immediately measure the height difference between the cone height and the center point of the filled material; this is the micro-slump. Measure the diameter of the sample from top to bottom and left to right and calculate the average value; this is the micro-spread. The bleeding rate of the sample is tested according to the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T5008-2016). The compressive strength of paste filling materials at different ages is tested according to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T50081-2002).

[0036] Specifically, the preparation and testing process for the filling material is as follows:

[0037] S1: First, screen the crushed coal gangue into a particle size composition of 25% for 1.25mm~2.5mm, 50% for 0.16mm~1.25mm, and 25% for <0.16mm. Then, place the coal gangue, fly ash, slag powder, desulfurized gypsum, and cement in a drying oven and dry for 24 hours at a temperature of 105±5℃.

[0038] S2: Weigh the raw materials. The mass concentration of the solids is 74%, and the mass concentration of tap water is 26%. The solids include aggregates and cementitious materials. The aggregates are coal gangue, accounting for 60% of the solids. The cementitious materials are composed of fly ash, slag powder, desulfurized gypsum, and cement, accounting for 40% of the solids. The cementitious materials are composed of the following components by mass percentage: 58%~73% fly ash, 15% slag powder, 5%~20% desulfurized gypsum, and 7% cement.

[0039] S3: Pour the weighed fly ash, slag powder, desulfurized gypsum and cement into the cement mortar mixer and mix at low speed for about 60 seconds to ensure that the raw materials are evenly mixed.

[0040] S4: After the raw materials are mixed evenly, slowly add the weighed 50% tap water and continue to stir at low speed for about 120 seconds. Then add the coal gangue aggregate and the remaining 50% tap water, continue to stir at low speed for about 120 seconds, and then stir at high speed for about 120 seconds to ensure that the slurry is fully mixed evenly and does not separate into layers.

[0041] S5: Immediately after the slurry is fully mixed, test the micro slump, micro spread and bleeding rate of the fresh slurry. After the test, let it stand for 4 hours, and then test the micro slump and micro spread again after 4 hours.

[0042] S6: After the test is completed, the paste filling material is put into a 40×40×40mm triple square detachable steel mold. After the mold is filled, it is placed on the mortar vibration table and vibrated for about 120 seconds to ensure that all air bubbles in the material are expelled. After the vibration is completed, the surface is smoothed and covered with plastic wrap. After 3 days, the mold is removed and the compressive strength test is carried out.

[0043] S7: Place the demolded test blocks in a standard curing room for curing. The temperature is set to 20℃±2℃ and the humidity is set to 95%±1%. Compressive strength tests are conducted after curing for 7 days, 14 days and 28 days.

[0044] The following steps will be used to prepare test blocks for performance testing. Specific embodiments will be used to provide a more systematic, clear, and complete description of the purpose and advantages of this invention:

[0045] Example 1:

[0046] With all other steps remaining unchanged,

[0047] S2: Weigh the raw materials. The mass concentration of the solids is 74%, and the mass concentration of tap water is 26%. The solids include aggregates and cementitious materials. Coal gangue aggregates account for 60% of the solids, and cementitious materials composed of fly ash, slag powder, desulfurized gypsum, and cement account for 40% of the solids. The components of the cementitious materials are expressed as follows by mass percentage: 73% fly ash, 15% slag powder, 5% desulfurized gypsum, and 7% cement.

[0048] Example 2:

[0049] With all other steps remaining unchanged,

[0050] S2: Weigh the raw materials. The mass concentration of the solids is 74%, and the mass concentration of tap water is 26%. The solids include aggregates and cementitious materials. The aggregates are coal gangue, accounting for 60% of the solids. The cementitious materials are composed of fly ash, slag powder, desulfurized gypsum, and cement, accounting for 40% of the solids. The cementitious materials are composed of the following components by mass percentage: 68% fly ash, 15% slag powder, 10% desulfurized gypsum, and 7% cement.

[0051] Example 3:

[0052] With all other steps remaining unchanged,

[0053] S2: Weigh the raw materials. The mass concentration of the solids is 74%, and the mass concentration of tap water is 26%. The solids include aggregates and cementitious materials. The aggregates are coal gangue, accounting for 60% of the solids. The cementitious materials are composed of fly ash, slag powder, desulfurized gypsum, and cement, accounting for 40% of the solids. The cementitious materials are composed of the following components by mass percentage: 63% fly ash, 15% slag powder, 15% desulfurized gypsum, and 7% cement.

[0054] Example 4:

[0055] With all other steps remaining unchanged,

[0056] S2: Weigh the raw materials. The mass concentration of the solid material is 74%, and the mass concentration of tap water is 26%. The solid material includes aggregate and cementitious material. The aggregate is coal gangue, accounting for 60% of the solid material. The cementitious material is composed of fly ash, slag powder, desulfurized gypsum and cement, accounting for 40% of the solid material. The cementitious material is composed of the following components by mass percentage: 58% fly ash, 15% slag powder, 20% desulfurized gypsum and 7% cement.

[0057] The transport performance and mechanical properties of the paste filling materials in Examples 1-4 are shown in the table below:

[0058]

[0059] A comparison of the four embodiments above shows that when the total amount of fly ash and desulfurized gypsum in the cementitious material remains constant, the bleeding rate, micro-slump, and micro-expansion of the paste filling material all increase and then decrease with the increase of desulfurized gypsum content. Since the particle size of desulfurized gypsum is much smaller than that of coal gangue, a small amount of desulfurized gypsum can fill the voids, reducing the porosity of the material and increasing excess water, thus providing better fluidity. However, as the desulfurized gypsum content continues to increase, the specific surface area of ​​the solid material continues to increase, leading to more excess water adsorbed on the particle surface to form a water film. The reduction in excess water leads to thickening of the slurry and a decrease in the thickness of the particle water film, resulting in a decrease in micro-slump and micro-expansion. When there is an excess of desulfurized gypsum, a large amount of SO3 in the gypsum will continue to react with C3A in the cement to generate AFt, which covers the surface of cement particles to form a dense layer, hindering the contact of water molecules, significantly delaying cement hydration, and slowing down the setting rate of the new slurry within 4 hours, so as to ensure normal pumping after emergency repairs in case of pressurized pumping equipment failure.

[0060] The strength of the paste-like filling material gradually increases with the curing age, initially increasing and then decreasing with increasing desulfurized gypsum content, reaching its highest strength at a desulfurized gypsum content of 10%. This is because the addition of desulfurized gypsum provides the material with abundant Ca... 2+ The presence of ions + and SO4²⁻ provides more ion sources for the formation of hydration products such as CS(A)-H and AFt, promoting the formation of these products and providing a strong driving force for rapid strength improvement. Excess sulfate ions in the cement system cannot promote the consolidation of AFt into an ultra-dense phase, which inhibits strength development. The 28-day strength meets the requirements for mine filling.

[0061] It can be observed that when the mass concentration of solids is 74%, tap water is 26%, aggregate is 60%, and cementitious material is 40%, and the cementitious material is composed of the following components by mass percentage: 63% fly ash, 15% slag powder, 15% desulfurized gypsum, and 7% cement, the uniaxial compressive strength of the paste filling material can reach 5.49 MPa at 28 days. At the same time, the micro-slump and micro-expansion of the freshly mixed slurry can reach 138 mm and 300 mm, respectively, and the micro-slump and micro-expansion after 4 hours can reach 131 mm and 245 mm, respectively. The bleeding rate is 2.4%, which meets the basic requirements of pressurized pumping.

[0062] The above description of the embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A novel high-solids-waste-based paste filling material, characterized in that, The filling material comprises solids and water, wherein the mass concentration of the solids is 74%. The solid material includes aggregate and cementitious material. The aggregate is coal gangue, accounting for 60% of the solid material, and the cementitious material is composed of fly ash, slag powder, desulfurized gypsum and cement, accounting for 40% of the solid material. The cementitious material is composed of the following components by mass percentage: 58%~73% fly ash, 15% slag powder, 5%~20% desulfurized gypsum, and 7% cement.

2. The novel high-solids-waste-based paste filling material according to claim 1, characterized in that, The particle size composition and proportion of the coal gangue aggregate are as follows: 1.25mm~2.5mm accounts for 25%, 0.16mm~1.25mm accounts for 50%, and <0.16mm accounts for 25%.

3. The novel high-solids-waste-based paste filling material according to claim 1, characterized in that, The particle size of the fly ash is: D50=50.325μm, D90=186.699μm; The particle size of the slag powder is: D50=13.112μm, D90=28.618μm; The particle size of the desulfurized gypsum is: D50=28.387μm, D90=64.087μm; The cement has the following particle sizes: D50 = 20.577 μm, D90 = 51.813 μm.

4. The novel high-solids-waste-based paste filling material according to claim 1, characterized in that, The fly ash is Class III fly ash collected by the dust collector of a coal-fired power plant, the slag powder is S95 grade ground slag, and the cement is P.S32.5 slag silicate cement.

5. A novel high-solids-waste-based paste filling material according to claim 1, characterized in that, The coal gangue is composed of the following chemical components by weight percentage: CaO 2.62%, Fe2O3 6.97%, SiO2 55.19%, Al2O3 23.94%, MgO 0.45%, SO3 0.38%, and K2O 6.31%.

6. The novel high-solids-waste-based paste filling material according to claim 1, characterized in that, The fly ash is composed of the following chemical components by weight percentage: CaO 3.84%, Fe2O3 8.96%, SiO2 48.01%, Al2O3 29.37%, MgO 0.49%, SO3 0.54%, and K2O 3.17%.

7. The novel high-solids-waste-based paste filling material according to claim 1, characterized in that, The slag powder is composed of the following chemical components by weight percentage: CaO accounts for 57.86%, Fe2O3 accounts for 0.78%, SiO2 accounts for 19.41%, Al2O3 accounts for 10.04%, MgO accounts for 6.88%, SO3 accounts for 1.18%, and K2O accounts for 0.37%.

8. A novel high-solids-waste-based paste filling material according to claim 1, characterized in that, The desulfurized gypsum is composed of the following chemical components by weight percentage: CaO 62.7%, Fe2O3 0.45%, SiO2 0.87%, Al2O3 0.45%, MgO 1.04%, SO3 33.66%, and K2O 0.06%.

9. A novel high-solids-waste-based paste filling material according to claim 1, characterized in that, The cement is composed of the following chemical components by weight percentage: CaO 56.34%, Fe2O3 4.39%, SiO2 19.19%, Al2O3 10.35%, MgO 3.95%, SO3 2.29%, and K2O 0.55%.

10. A method for preparing the filling material according to any one of claims 1-9, characterized in that, Includes the following steps: S1: First, screen the crushed coal gangue into a particle size composition of 25% for 1.25mm~2.5mm, 50% for 0.16mm~1.25mm, and 25% for <0.16mm. Then, place the coal gangue, fly ash, slag powder, desulfurized gypsum, and cement in a drying oven and dry for 24 hours at a temperature of 105±5℃. S2: Weigh the raw materials. The mass concentration of the solids is 74%, and the mass concentration of tap water is 26%. The solids include aggregates and cementitious materials. The aggregates are coal gangue, accounting for 60% of the solids. The cementitious materials are composed of fly ash, slag powder, desulfurized gypsum, and cement, accounting for 40% of the solids. The cementitious materials are composed of the following components by mass percentage: 58%~73% fly ash, 15% slag powder, 5%~20% desulfurized gypsum, and 7% cement. S3: Pour the weighed fly ash, slag powder, desulfurized gypsum and cement into the cement mortar mixer and mix at low speed for about 60 seconds to ensure that the raw materials are evenly mixed. S4: After the raw materials are mixed evenly, slowly add the weighed 50% tap water and continue to stir at low speed for about 120 seconds. Then add the coal gangue aggregate and the remaining 50% tap water, continue to stir at low speed for about 120 seconds, and then stir at high speed for about 120 seconds to ensure that the slurry is fully mixed evenly and does not separate into layers. S5: Immediately after the slurry is fully mixed, test the micro slump, micro spread and bleeding rate of the fresh slurry. After the test, let it stand for 4 hours, and then test the micro slump and micro spread again after 4 hours. S6: After the test is completed, the paste filling material is put into a 40×40×40mm triple square detachable steel mold. After the mold is filled, it is placed on the mortar vibration table and vibrated for about 120 seconds to ensure that all air bubbles in the material are expelled. After the vibration is completed, the surface is smoothed and covered with plastic wrap. After 3 days, the mold is removed and the compressive strength test is carried out. S7: Place the demolded test blocks in a standard curing room for curing. The temperature is set to 20℃±2℃ and the humidity is set to 95%±1%. Compressive strength tests are conducted after curing for 7 days, 14 days and 28 days.

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