A design method of a goaf grouting material, a grouting material and a grouting method

Abstract

The application discloses a kind of goaf grouting material design method, grouting material and grouting method, can realize following goal: establish and goaf grouting performance, the strong connection of economy of fly ash grading system, break the limitation of traditional concrete industry grading standard;Provide the fly ash grade discrimination method that engineering site can be quickly operated, realize the continuous control of incoming material quality;Formulate directional improvement and application scheme for different grades of fly ash, solve the adaptability problem of various fly ash in grouting engineering;Finally realize the cost reduction and efficiency increase of goaf grouting engineering, promote the efficient utilization of resource of bulk solid waste.

Description

Technical Field

[0001] This invention belongs to the field of goaf grouting engineering technology, specifically relating to a design method for goaf grouting materials, grouting materials and grouting methods, and is particularly suitable for large-scale goaf remediation projects with dual requirements for the performance and economy of grouting materials. Background Technology

[0002] Fly ash, a major solid waste generated from coal combustion, is produced in huge quantities in my country every year. Its efficient and comprehensive utilization is a key measure to implement the sustainable development strategy. In grouting projects for goaf remediation, cement-fly ash slurry has become the mainstream filling material due to its cost advantages and filling effect. The fly ash content in this slurry is usually as high as 70% or more, and its quality directly determines the safety, effectiveness, and economy of the grouting project.

[0003] Currently, the selection of fly ash in goaf grouting projects mainly follows GB / T 51180-2016 "Technical Specification for Foundation Treatment of Buildings (Structures) in Coal Mine Goaf Areas," which requires fly ash to meet the Class III or higher standard in GB / T 1596-2017 "Fly Ash Used in Cement and Concrete." However, the aforementioned standard is essentially formulated for the cement concrete industry, with its core objective being to improve the fluidity, durability, and long-term high-strength performance of concrete. The fineness, water demand ratio, and loss on ignition indicators set therein are fundamentally different from the needs of goaf grouting projects.

[0004] 1. Differences in performance requirements: The core focus of grouting projects in goaf areas is on the stone-setting rate of the grout (which directly affects the filling efficiency of the goaf area), pumpability (the fluidity needs to be controlled within a reasonable range; too high a fluidity can easily cause grout loss, while too low a fluidity can cause pipe blockage accidents), and the early and long-term strength of the stone body under low cement content (meeting the specification of 90d strength ≥2MPa is sufficient), rather than the high strength and high durability required for concrete.

[0005] 2. Differences in economic orientation: Grouting projects in goaf areas usually involve huge volumes and have a very high proportion of material costs. Under the premise of meeting the specifications (such as 90d strength ≥ 2MPa), low-cost fly ash should be given priority to control the total cost of the project.

[0006] Practice has shown that directly applying current concrete industry grading standards to the design of grouting materials leads to a prominent problem in goaf grouting projects: a lack of strong correlation between grading level, performance, and economic cost. For example, pulverized coal boiler fly ash (PC fine ash), classified as "Grade 1 ash" according to current standards, has a much lower cost-effectiveness in grouting projects due to its rapid slurry water separation and low stone-forming rate compared to circulating fluidized bed boiler fly ash (CFB ash), which is deemed "inferior" under current standards. Furthermore, existing technologies lack systematic solutions for coarser fly ash particles such as PC ash and CFB ash, and for improving the grouting compatibility of different fly ash qualities through technical means. In addition, some evaluation indicators in current related technologies rely on professional laboratory testing, which is difficult to obtain quickly on-site, resulting in inconsistent and inefficient control of the quality of incoming fly ash, seriously affecting the quality and progress of grouting construction.

[0007] Therefore, a design method for grouting materials in goaf areas, as well as grouting materials and grouting methods, are of great significance for reducing engineering costs, improving construction quality, and promoting the resource utilization of solid waste. Summary of the Invention

[0008] The purpose of this invention is to provide a design method, grouting material and grouting method for goaf grouting, which can achieve precise screening, targeted improvement and efficient utilization of fly ash, and is of great significance for reducing engineering costs, improving construction quality and promoting the resource utilization of solid waste.

[0009] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0010] A design method for grouting materials in goaf areas includes:

[0011] S1. The fly ash grade is determined based on grading indicators, including the bulk density, calcium oxide content, and single-slurry stone formation rate of the fly ash. The fly ash grades include superior grade, good grade, medium grade, and poor grade, wherein the bulk density of superior grade fly ash is not greater than 0.55 g / cm³. 3 The calcium oxide content is not less than 10%, the stone-setting rate of the single slurry is in the range of 92%~98%, and the bulk density of the good grade lime is not greater than 0.55g / cm³. 3 The calcium oxide content is less than 10%, the stone-setting rate of the single slurry is in the range of 92%~98%, and the bulk density of the medium-grade ash is not less than 0.65g / cm³. 3 The calcium oxide content is less than 10%, the stone-forming rate of the single slurry is in the range of 75%~85%, and the bulk density of the inferior grade ash is not less than 0.65g / cm³. 3 The calcium oxide content is less than 10%, and the stone formation rate of the slurry is less than 80%.

[0012] S2, different proportioning strategies are selected for different grades of fly ash to improve the grouting material. Among them, high-grade or good-grade fly ash is improved with calcium oxide-based or calcium hydroxide-based activators, medium-grade fly ash is improved with cement and calcium sulfate synergistic activation, and poor-grade fly ash is improved with suspending agents, including hydroxypropyl methylcellulose.

[0013] In one or more embodiments of the present invention, the bulk density of the superior grade ash is 0.45 g / cm³. 3 ~0.55g / cm 3 The bulk density of the good grade ash is between 0.45 g / cm³. 3 ~0.55g / cm 3 between.

[0014] In one or more embodiments of the present invention, the grading indicators further include the single-slurry flowability, fineness, and moisture content of fly ash; wherein, the single-slurry flowability of superior grade fly ash is in the range of 100mm~180mm, the fineness is less than 45%, and the moisture content is less than 1%; the single-slurry flowability of good grade fly ash is in the range of 100mm~180mm, the fineness is less than 45%, and the moisture content is less than 1%; the single-slurry flowability of medium grade fly ash is not less than 250mm, the fineness is not less than 80%, and the moisture content is less than 3%; the single-slurry flowability of poor grade fly ash is not less than 250mm, the fineness is not less than 80%, and the moisture content is less than 3%; the single slurry refers to a slurry prepared solely from fly ash and water at a water-to-solid ratio of 1:1, and the fineness is the residue on a 45φm square-hole sieve.

[0015] In one or more embodiments of the present invention, determining the fly ash grade based on a grading index includes:

[0016] Take 100g of fly ash sample and slowly pour it into a 250mL graduated cylinder. Under natural conditions, read the bulk volume V and calculate the bulk density ρ = 100 / V. If the bulk density is not greater than 0.55g / cm³... 3 It is classified as superior grade or good grade ash, if the bulk density is greater than 0.65 g / cm³. 3 It is then classified as medium-grade or poor-grade gray; and / or,

[0017] Prepare fly ash slurry with a water-to-solid ratio of 1:1. Test the flow diameter using the cement paste fluidity test method in GB / T 8077-2012. If the slurry fluidity is within the range of 100mm~180mm, it is classified as superior or good grade fly ash; if the fluidity is greater than or equal to 250mm, it is classified as medium or poor grade fly ash; and / or,

[0018] Observe the appearance characteristics of fly ash and the self-coagulation property of the slurry after 24 hours. If the color is light yellow or yellowish-brown and the slurry self-coagulates after 24 hours, it is a superior grade of fly ash. If the color is dark gray or blackish-gray and the slurry self-coagulates after 24 hours, it is a good grade of fly ash. If the color is grayish-white to light gray and the slurry does not self-coagulate after 24 hours, it is a medium grade of fly ash. If the particles are coarse and the slurry does not self-coagulate after 24 hours, it is a poor grade of fly ash.

[0019] In one or more embodiments of the present invention, the proportioning strategy for superior or good grade fly ash is as follows: fly ash accounts for more than 90% of the total solid mass, calcium oxide-based or calcium hydroxide-based activator accounts for less than 10% of the total solid mass, the water-to-solid ratio ranges from (1:0.9) to (1:1.2), and the cement content is zero; and / or,

[0020] The proportioning strategy for intermediate-grade fly ash is as follows: fly ash accounts for 70%~80% of the total solid mass, cement accounts for 10%~20% of the total solid mass, calcium sulfate accounts for 3%~6% of the total solid mass, and the water-to-solid ratio ranges from (1:1.2) to (1:1.5); and / or,

[0021] The proportioning strategy for fly ash is as follows: fly ash accounts for more than 85% of the total solid mass, cement accounts for 10% to 20% of the total solid mass, and the amount of suspending agent added is 0.1% to 0.3% of the mixing water mass.

[0022] A grouting material suitable for grouting projects in goaf areas includes superior or good grade lime as determined by the above design method, calcium oxide-based or calcium hydroxide-based activator, wherein superior or good grade lime accounts for more than 90% of the total solid mass, calcium oxide-based or calcium hydroxide-based activator accounts for less than 10% of the total solid mass, the water-to-solid ratio ranges from (1:0.9) to (1:1.2), and the cement content is zero.

[0023] A grouting material suitable for grouting engineering in goaf areas includes medium-grade lime, cement and calcium sulfate as determined in the above design method, wherein the medium-grade lime accounts for 70% to 80% of the total solid mass, the cement accounts for 10% to 20% of the total solid mass, the calcium sulfate accounts for 3% to 6% of the total solid mass, and the water-to-solid ratio ranges from (1:1.2) to (1:1.5).

[0024] A grouting material for goaf grouting projects includes graded lime, cement, and a suspending agent as determined in the above design method. The suspending agent includes hydroxypropyl methylcellulose. The graded lime accounts for more than 85% of the total solid mass, the cement accounts for 10% to 20% of the total solid mass, and the amount of suspending agent added is 0.1% to 0.3% of the mass of the mixing water.

[0025] A grouting method for goaf grouting using fly ash as the grouting material includes:

[0026] For each batch of incoming fly ash, the fly ash grade is determined according to grading indicators, including the bulk density, calcium oxide content, and single slurry stone formation rate. The fly ash grades include superior grade, good grade, medium grade, and poor grade, wherein the bulk density of superior grade fly ash is not greater than 0.55 g / cm³. 3 The calcium oxide content is not less than 10%, the stone-setting rate of the single slurry is in the range of 92%~98%, and the bulk density of the good grade lime is not greater than 0.55g / cm³. 3 The calcium oxide content is less than 10%, the stone-setting rate of the single slurry is in the range of 92%~98%, and the bulk density of the medium-grade ash is not less than 0.65g / cm³. 3 The calcium oxide content is less than 10%, the stone-forming rate of the single slurry is in the range of 75%~85%, and the bulk density of the inferior grade ash is not less than 0.65g / cm³. 3 The calcium oxide content is less than 10%, and the stone formation rate of the slurry is less than 80%.

[0027] For superior or good grade ash, calcium oxide-based or calcium hydroxide-based activators are used to improve it and form a grouting material. The superior or good grade ash accounts for more than 90% of the total solid mass, and the calcium oxide-based or calcium hydroxide-based activator accounts for less than 10% of the total solid mass. The water-to-solid ratio ranges from (1:0.9) to (1:1.2).

[0028] For medium-grade lime, cement and calcium sulfate are used in a synergistic activation and modification process to form a grouting material. The medium-grade lime accounts for 70% to 80% of the total solid mass, cement accounts for 10% to 20% of the total solid mass, and calcium sulfate accounts for 3% to 6% of the total solid mass. The water-to-solid ratio ranges from (1:1.2) to (1:1.5).

[0029] For the use of substandard cement ash, a suspending agent is used to improve it and form a grouting material. The suspending agent includes hydroxypropyl methylcellulose. The substandard cement ash accounts for more than 85% of the total solid mass, and the cement accounts for 10% to 20% of the total solid mass. The amount of suspending agent added is 0.1% to 0.3% of the mass of the mixing water.

[0030] Improved fly ash was used as grouting material to grout the goaf.

[0031] In one or more embodiments of the present invention, the grading indicators further include the single-slurry flowability, fineness, and moisture content of fly ash; wherein, the single-slurry flowability of superior grade fly ash is in the range of 100mm~180mm, the fineness is less than 45%, and the moisture content is less than 1%; the single-slurry flowability of good grade fly ash is in the range of 100mm~180mm, the fineness is less than 45%, and the moisture content is less than 1%; the single-slurry flowability of medium grade fly ash is not less than 250mm, the fineness is not less than 80%, and the moisture content is less than 3%; the single-slurry flowability of poor grade fly ash is not less than 250mm, the fineness is not less than 80%, and the moisture content is less than 3%; the single slurry refers to a slurry prepared solely from fly ash and water at a water-to-solid ratio of 1:1, and the fineness is the residue on a 45φm square-hole sieve.

[0032] Compared with existing technologies, the design method, grouting material and grouting method of the present invention establishes for the first time a fly ash grading system specifically for goaf grouting projects. The grading index is directly related to the core performance of grouting (stone rate, pumpability, strength), which solves the pain point that the traditional concrete industry grading standards are "unsuitable" for goaf areas.

[0033] The design method, grouting material, and grouting method of the present invention for goaf grouting are based on the intrinsic relationship between the microstructure (spherical / irregular particles), chemical composition (CaO content), and grouting performance of fly ash. The classification logic is clear, and the results can accurately predict the grouting performance of fly ash.

[0034] The present invention provides a design method for grouting materials in goaf areas, as well as grouting materials and grouting methods. It formulates targeted improvement and application schemes for different grades of fly ash, solves the compatibility problem of various types of fly ash in grouting projects, and reduces the cost of superior fly ash by 40% to 80% and medium-grade fly ash by 10% to 20% through graded screening and targeted improvement. It also turns inferior fly ash into a valuable resource, significantly reducing the total cost of the project.

[0035] The design method, grouting material, and grouting method of this invention for goaf grouting materials provide a rapid on-site identification method that requires no complex equipment, is easy to operate, and enables continuous quality control of incoming materials. The integrated "grading-improvement-application" solution can directly guide engineering practice and solve practical construction pain points. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1This is a comparison diagram of the differences in microstructure of fly ash of different grades in one embodiment of the present invention.

[0038] Figure 2 This is a bar chart showing the bulk density of fly ash of different grades in one embodiment of the present invention;

[0039] Figure 3 This is a bar chart showing the flowability of single slurry of different grades of fly ash under a water-to-solid ratio of 1:1 in one embodiment of the present invention.

[0040] Figure 4 This is a comparison of the 90-day strength of fly ash slurry aggregates with different calcium oxide content in one embodiment of the present invention;

[0041] Figure 5 Strength diagrams of grout stones with different calcium oxide content in superior grade lime or good grade lime (CFB lime);

[0042] Figure 6 SEM images of 3% calcium oxide as a single additive in superior or good grade ash (CFB ash);

[0043] Figure 7 Figures showing the strength of grout stones with different calcium sulfate content in medium-grade lime (PC lime);

[0044] Figure 8 SEM image of 9% calcium sulfate-doped medium-grade ash (PC ash);

[0045] Figure 9 Line graphs showing the segregation rate of slurry under different suspending agent dosages of 0.3% for different grades of ash (ash slag);

[0046] Figure 10 This is a flowchart of a method for grouting goaf using fly ash as a grouting material in one embodiment of the present invention. Detailed Implementation

[0047] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0048] As mentioned in the background section, existing grading systems for fly ash (such as GB / T 1596-2017 and ASTM C618) are designed for the cement concrete industry, with the core objective of improving the workability, durability, and long-term strength of concrete. Table 1 shows the grading standards for fly ash in the existing GB / T 1596-2017 standard, "Fly Ash for Cement and Concrete".

[0049] Table 1 Fly ash in cement concrete and mortar

[0050]

[0051] This classification standard focuses on concrete-oriented indicators such as "water requirement ratio" and "loss on ignition ratio," which are not applicable to grouting projects. Furthermore, there is currently no fly ash classification method specifically designed for the characteristics of grouting projects in goaf areas (high fly ash content, low strength requirements, and high economic sensitivity).

[0052] In summary, existing related technologies have the following shortcomings:

[0053] The grading system lacks specificity: Existing grading standards such as GB / T 1596-2017 and ASTM C618 are all geared towards the cement concrete industry and do not take into account the core characteristics of grouting projects in goaf areas, which are characterized by "high dosage, low strength requirements, and high economic sensitivity". The correlation between grading indicators and grouting performance is weak.

[0054] Narrow technical coverage: Existing patents (such as CN114634332A) only target the preparation of grouting materials for a single type of fly ash (such as CFB ash), and have not constructed a complete classification system and supporting application schemes covering various types of fly ash such as PC ash, CFB ash, and ash slag, resulting in poor technical universality.

[0055] Low technology integration: Although individual technologies such as chemical activation and suspension modification have been applied in the building materials field, they have not been accurately matched with the fly ash classification system in the goaf grouting scenario, making it impossible to achieve an integrated solution of "classification-improvement-application" and difficult to solve the actual pain points of the project.

[0056] Based on this, the present invention provides a design method for grouting materials in goaf areas, grouting materials, and grouting methods, which can achieve the following objectives: establishing a fly ash grading system that is strongly correlated with the performance and economy of goaf grouting, breaking the limitations of traditional concrete industry grading standards; providing a fly ash grade identification method that can be quickly operated on-site, realizing continuous control of the quality of incoming materials; developing targeted improvement and application schemes for different grades of fly ash, solving the compatibility problem of various types of fly ash in grouting projects; and ultimately achieving cost reduction and efficiency improvement in goaf grouting projects, promoting the resource-efficient utilization of bulk solid waste.

[0057] The design method for grouting materials in goaf areas according to one embodiment of the present invention first determines the fly ash grade based on grading indicators. Grading indicators include the bulk density of fly ash, the fluidity of a single slurry, the stone-forming rate of a single slurry, the calcium oxide content, as well as fineness and moisture content; fly ash grades include four levels: superior grade, good grade, medium grade, and poor grade. Specific grading standards are shown in the table below:

[0058] Table 2. Fly ash classification method for grouting projects in goaf areas

[0059]

[0060] Note: Single slurry refers to a slurry prepared solely from fly ash and water at a water-to-solid ratio of 1:1, without the addition of any admixtures, cement, or other additives. Fineness is measured as residue on a 45µm square-hole sieve.

[0061] In Table 2, the bulk density of premium grade lime is no greater than 0.55 g / cm³. 3 The single-slurry fluidity is within the range of 100mm to 180mm, the single-slurry stone rate is within the range of 92% to 98%, the calcium oxide content is not less than 10%, the fineness is less than 45%, and the water content is less than 1%. The bulk density of good-grade lime is not greater than 0.55g / cm³. 3 The slurry fluidity is within the range of 100mm to 180mm, the slurry stone rate is within the range of 92% to 98%, the calcium oxide content is less than 10%, the fineness is less than 45%, and the water content is less than 1%. The bulk density of the medium-grade lime is not less than 0.65g / cm³. 3 The single-layer slurry fluidity should be no less than 250 mm, the single-layer slurry stone rate should be within the range of 75%~85%, the calcium oxide content should be less than 10%, the fineness should be no less than 80%, and the water content should be less than 3%. The bulk density of the inferior grade ash should be no less than 0.65 g / cm³. 3 The fluidity of the slurry is not less than 250 mm, the stone rate of the slurry is less than 80%, the calcium oxide content is less than 10%, the fineness is not less than 80%, and the water content is less than 3%.

[0062] Preferably, the bulk density of the superior grade ash is 0.45 g / cm³. 3 ~0.55g / cm 3 Between; the bulk density of good grade ash is 0.45 g / cm³. 3 ~0.55g / cm 3 between.

[0063] The technical solution of the present invention will be explained in detail below through specific experiments and related drawings.

[0064] refer to Figure 1 As shown, Figure 1 A comparison of the microstructures of PC gray and CFB gray. Figure 1In the diagram, a and c represent PC gray (spherical glass microspheres with a smooth surface), while b and d represent CFB gray (irregular particles with a loose and porous surface).

[0065] PC ash is mainly composed of spherical glass microspheres with smooth surfaces. Smaller, irregularly shaped particles, primarily glass slag, can also be observed. The formation of these glass microspheres is as follows: the inorganic components in fly ash burn at high temperatures of 1400℃ to 1700℃ in a pulverized coal furnace. The resulting fly ash cools rapidly in the flue, reducing surface tension and forming glass microspheres.

[0066] CFB ash is mainly composed of irregularly shaped particles, with almost no spherical particles. The surface structure of the particles is also relatively loose, with numerous pores interconnected to the outside environment. This is primarily because the combustion temperature of CFB boilers is between 850℃ and 900℃, at which point most minerals only soften and do not melt to undergo further chemical reactions, making it difficult to form spherical microspheres. The irregularly shaped particles are mainly unburned carbon particles, anhydrite, and calcite.

[0067] Microstructural analysis of fly ash reveals that:

[0068] PC ash is mainly composed of spherical glass microspheres. The surface of the spherical microspheres is smooth, so their bulk density is relatively high and their ability to adsorb water is relatively weak. The slurry prepared has high fluidity, fast water separation speed, and low stone formation rate.

[0069] CFB ash is mainly composed of irregularly shaped particles with a relatively loose surface structure and a large number of pores that are interconnected with the outside world. Therefore, it has a low bulk density, a strong ability to absorb water, poor fluidity of the prepared slurry, slow water separation rate, and high stone formation rate.

[0070] Therefore, the grading indicators characterized by differences in the microstructure of fly ash are mainly bulk density, single slurry fluidity, single slurry stone formation rate, and water separation rate.

[0071] refer to Figure 2 As shown, Figure 2 This is a bar chart showing the bulk density of different grades of fly ash. The horizontal axis represents the fly ash samples (HR1~HR3 are PC ash, JSQ1~JSQ2, HM1~HM3 are CFB ash / ash residue); the vertical axis represents the bulk density (g / cm³). 3 ).

[0072] Based on the bulk density test results of HR1 (currently classified as Grade I), HR2 (currently classified as Grade III), and HR3 (fineness not meeting the current Grade III classification), it can be seen that the bulk density of PC ash gradually increases with the increase of particle size, and the minimum bulk density of PC ash is approximately 0.7 g / cm³. 3HM3, a type of CFB ash (whose fineness does not meet the current Class III classification), had the largest particle size and the highest bulk density among the sampled fly ash types, reaching 0.962 g / cm³. 3 The bulk density of both PC ash and ash residue is ≥0.7 g / cm³. 3 .

[0073] The bulk density of CFB ash is significantly lower than that of PC ash, with both bulk densities concentrated around 0.5 g / cm³. 3 ~0.535g / cm 3 The difference is mainly caused by the loose and porous microstructure of CFB ash.

[0074] Therefore, the bulk density test method can effectively distinguish between PC ash and CFB ash.

[0075] refer to Figure 3 As shown, Figure 3 The bar chart shows the flowability of single slurry of fly ash of different grades under a water-to-solid ratio of 1:1. The horizontal axis represents the fly ash sample, and the vertical axis represents the flowability (mm).

[0076] The fluidity of each fly ash slurry was tested using the cement paste fluidity test method in GB / T 8077-2012 "Test Method for Homogeneity of Concrete Admixtures". The test results are as follows: Figure 3 As shown.

[0077] Under a water-to-solid ratio of 1:1, the single slurry fluidity of PC ash (HR1 (currently classified as Grade I), HR2 (currently classified as Grade III), and HR3 (fineness not meeting current grade III standards)) is all above 300 mm (greater than or equal to 250 mm), which is much greater than that of CFB ash (JSQ1 (water demand ratio not meeting current grade III standards), JSQ2 (water demand ratio not meeting current grade III standards), and HM1 (currently classified as Grade III)) which ranges from 115 mm to 154 mm (between 100 mm and 180 mm). HM3 (fineness not meeting current grade III standards), as CFB ash slag, has the largest particle size and the highest slurry fluidity among the sampled fly ash types, reaching 355 mm.

[0078] The flowability of the single slurry is HR1 > HR2 > HR3, indicating that the flowability of the single slurry decreases with increasing fly ash fineness for different grades of PC ash, but the difference is small. The flowability of the single slurry of HM1 is better than that of JSQ1 and JSQ2. The particle size of HM1 is smaller than that of JSQ1 and larger than that of JSQ2, but the carbon content (loss on ignition) of HM1 is much smaller than that of JSQ1 and JSQ2. Therefore, the higher the carbon content of the fly ash slurry, the worse its flowability.

[0079] In summary, the main factors affecting the fluidity of fly ash slurry include: fly ash type (microstructural characteristics of fly ash), fineness, and loss on ignition. Among these, fly ash type (microstructural characteristics of fly ash) has the greatest impact; the finer the fineness, the better the slurry fluidity, and the higher the carbon content, the worse the slurry fluidity.

[0080] refer to Figure 4 As shown, Figure 4 A comparison chart of the 90-day strength of fly ash slurry aggregates with different CaO contents is shown. The horizontal axis represents the CaO content (%), and the vertical axis represents the 90-day unconfined compressive strength (MPa).

[0081] When the CaO content is ≥10%, the strength of the stone is significantly improved. Figure 4 This study demonstrated the superior strength of high-grade lime (CFB high-calcium lime), verified the scientific validity of CaO content as an indicator for determining high-grade lime, and confirmed the effectiveness of CaO activation.

[0082] For grouting projects in goaf areas, superior grade lime should be given priority; good grade lime should be the second choice; medium grade lime should be used with caution due to economic deviations; poor grade lime is not recommended for direct use under current technical conditions, and can only be used in limited ways under special circumstances after special improvements.

[0083] To enable rapid quality screening of incoming fly ash at engineering sites, this invention also provides a specific method for determining the grade of fly ash based on grading indicators. This method quickly identifies which grade of fly ash it belongs to, and preliminary grading can be completed without complex equipment. The specific method is as follows:

[0084] 1. Rapid method for determining bulk density.

[0085] Take 100g of fly ash and slowly pour it into a 250mL graduated cylinder with a spoon. Gently shake until the surface is smooth (without applying external vibration force). Record the bulk volume V (mL). Calculate the bulk density (g / cm³) using the formula ρ=100 / V. 3 If the bulk density is 0.45 g / cm³ 3 ~0.55g / cm 3 Within the specified range, it is preliminarily classified as excellent / good grade ash (CFB ash); if the bulk density is 0.65 g / cm³ 3 ~0.75g / cm 3 The above grades are preliminarily classified as medium / poor grade ash (PC ash or ash residue).

[0086] 2. Rapid method for determining the fluidity of a single slurry.

[0087] Prepare a pure fly ash slurry with a water-to-solid ratio of 1:1. Use the cement paste fluidity test method (using fly ash instead of cement) from GB / T 8077-2012 "Test Method for Homogeneity of Concrete Admixtures" to test the free-flow diameter of the slurry on a horizontal glass plate. If the fluidity is within the range of 100mm to 180mm, it is further confirmed as a superior / good grade fly ash; if the fluidity is greater than or equal to 250mm, it is further confirmed as a medium / poor grade fly ash (PC fly ash or ash residue).

[0088] 3. Appearance and self-coagulation auxiliary judgment method.

[0089] The color of fly ash varies depending on the combustion conditions of the pulverized coal and the properties of the raw coal. PC ash, with a lower carbon content, is generally silver-gray or gray, while ash with a higher carbon content tends to be darker or black. CFB ash exhibits significant color variations depending on the power plant and the type of coal. The presence of hematite in the raw coal imparts a reddish-brown hue to CFB ash after combustion; the higher the hematite content, the darker the CFB ash. Carbon content also affects the color of high-calcium ash; higher carbon content results in a dark purple or black color. Higher calcium oxide content leads to a lighter, more yellowish color in high-calcium ash.

[0090] In this embodiment, HX1 (medium-grade ash) is PC ash produced by a pulverized coal boiler, with low carbon content and a light gray color. HR1 (medium-grade ash) is PC ash produced by a pulverized coal boiler, and its color indicates a higher carbon content. JSQ1 (superior-grade ash) is CFB high-calcium ash produced by a circulating fluidized bed boiler, with a higher carbon content, hence its darker color. HM1 (superior-grade ash) is CFB high-calcium ash produced by a circulating fluidized bed boiler, with a lower carbon content and a higher calcium oxide content, resulting in a yellowish color.

[0091] Therefore, the grade of fly ash can be determined by its appearance.

[0092] Superior grade ash - CFB high-calcium ash is mostly light yellow or yellowish-brown in color; good grade ash - CFB low-calcium ash is dark gray or blackish-gray in color; medium grade ash - PC ash is mostly grayish-white to light gray; poor grade ash - slag particles are coarse, and obvious solid particles are visible to the naked eye.

[0093] Furthermore, the self-coagulation property of fly ash can be observed and judged.

[0094] Pour a slurry with a water-to-solid ratio of 1:1 into a beaker and let it stand for 24 hours. If self-coagulation occurs (the slurry solidifies and forms a solid shape with no obvious water separation), it is CFB ash (excellent / good grade); if self-coagulation does not occur, it is PC ash or ash residue (medium / poor grade).

[0095] The above simple method can be used to quickly determine the grade of incoming fly ash, guiding subsequent applications.

[0096] Secondly, different proportioning strategies are selected for different grades of fly ash to improve the grouting material.

[0097] This invention further develops specific improvement technologies and proportioning schemes for different grades of fly ash, based on their performance characteristics, to achieve precise adaptation.

[0098] First, the strength improvement application for superior grade gray and good grade gray (CFB gray).

[0099] This type of fly ash is CFB ash produced by circulating fluidized bed boilers. Circulating fluidized bed boilers burn low-calorific-value coal at low temperatures (850℃~950℃). Due to the low furnace temperature, impurities can only soften, not melt. The ash particles are coarse, with few spherical particles, high carbon content, low bulk density, and strong water adsorption capacity. It has a high stone formation rate in single slurry but relatively low fluidity.

[0100] refer to Figure 5 , Figure 6 As shown, Figure 5 The strength diagram of grout aggregate with different calcium oxide content in CFB ash for water-to-solid ratio of 1:1 and solid ratio of (cement:fly ash = 2:8). Figure 6 SEM image of 3% CFB-doped calcium oxide. Figure 5 and Figure 6 It is known that a large amount of ettringite is generated in the slurry aggregate after CFB ash is incorporated with calcium oxide. The amount of ettringite increases with increasing calcium oxide content, while the black pores decrease and the aggregate density increases. The main reason is that CFB ash is formed from low-calorific-value coal at relatively low combustion temperatures. To prevent sulfur dioxide emissions from coal combustion into the air, calcium oxide is usually added during combustion to adsorb sulfur dioxide. Therefore, CFB ash contains a high amount of calcium oxide and calcium sulfate. Thus, even with only 20% cement content, the addition of calcium oxide alone in CFB ash still generates a large amount of ettringite, increasing the aggregate strength. Furthermore, with increasing calcium oxide content, active aluminum and silicon dissolve more easily during hydration in the resulting alkaline system. The calcium-containing components in CFB ash can generate hydrated calcium aluminate and hydrated calcium silicate gels during alkali activation, which is beneficial for improving the compressive strength of the material.

[0101] Therefore, for high-grade fly ash, the high CaO content (≥10%) of the fly ash itself, combined with the synergistic effect of added calcium oxide-based (CaO)-based and calcium hydroxide (Ca(OH)2)-based activators, creates a strongly alkaline environment, fully activating the pozzolanic activity of fly ash and generating strength supports such as hydrated calcium silicate (CSH) gel and ettringite (AFt), thus achieving partial or complete replacement of cement and significantly reducing material costs.

[0102] For high-quality fly ash, calcium oxide (CaO)-based and calcium hydroxide (Ca(OH)2)-based activators can be used in synergy to create a strongly alkaline environment, fully activating the pozzolanic activity of fly ash and generating strength supports such as hydrated calcium silicate (CSH) gel and ettringite (AFt), achieving partial or complete replacement of cement and significantly reducing material costs.

[0103] The slurry prepared from this type of fly ash has a high solidification rate and generally low fluidity. The proportioning strategy for superior or good grade fly ash is as follows: fly ash accounts for 90%~100%, calcium oxide-based activator (industrial grade quicklime powder can be used) or calcium hydroxide-based activator (large industrial solid waste carbide slag can be used, the main component of which is Ca(OH)2) accounts for 0%~10%, and the water-to-solid ratio is recommended to be (1:0.9)~(1:1.2).

[0104] With this mix proportion, the 90-day grout strength can exceed 2.0 MPa, meeting the specifications. Compared to traditional mix proportions of 20% or more cement, material costs can be reduced by approximately 40% to 80%, achieving "superior ash quality" and all-solid-waste grouting.

[0105] Secondly, applications for strength improvement of medium-grade gray (PC gray).

[0106] This type of fly ash is PC ash produced by pulverized coal furnace combustion. Pulverized coal furnaces burn high-calorific-value coal at high temperatures (above 1400℃), and the resulting fly ash is a product of high-temperature melting and quenching. The ash is mainly composed of spherical glassy particles, generally with low carbon content, high bulk density, weak water adsorption capacity, high single-slurry fluidity, but low stone formation rate.

[0107] refer to Figure 7 and Figure 8 As shown, Figure 7 The strength diagram of the slurry aggregate with different calcium sulfate content in PC ash is shown. Figure 8 SEM image of PC ash with 9% calcium sulfate doping. (via...) Figure 7 and Figure 8 It can be seen that after adding calcium sulfate, the grout stone body prepared with PC ash generates both a large amount of hydrated calcium silicate gel and a large amount of ettringite, thus resulting in higher strength of the grout stone body. The active SiO2 and Al2O3 content in PC ash is higher than that in CFB ash. Under the action of cement, the grout stone body prepared with PC ash generates a certain amount of hydrated calcium silicate gel. The addition of calcium sulfate further improves the strength of the grout stone body. The content of Ca increased. 2+ The increased content of precipitate promotes the formation of more ettringite. Etringite has a certain expanding effect, which can fill the gaps in the hydration space, increase the density of the stone, compensate for shrinkage, and thus improve the strength of the stone.

[0108] Therefore, for medium-grade ash, SO4 in the system can be replenished by adding calcium sulfate-based additives (preferably desulfurization gypsum from coal-fired power plant solid waste). 2- and Ca 2+ It promotes the formation of ettringite, and works synergistically with cement hydration products to compensate for its own insufficient calcium content, thereby improving the strength and density of the stone body.

[0109] The slurry prepared with this type of fly ash has a low solidification rate and high fluidity. The proportioning strategy for medium-grade fly ash is as follows: fly ash accounts for 70%~80%, desulfurized gypsum accounts for 0%~10%, cement accounts for 10%~20%, and the water-to-solid ratio is recommended to be (1:1.2)~(1:1.5).

[0110] Under this mix ratio, the 90-day aggregate strength increases by 20% to 40% compared to the mix without desulfurized gypsum, all exceeding 2.0 MPa, meeting the specifications. Compared to the traditional cement-fly ash mix ratio, material costs can be reduced by approximately 10% to 20%, while simultaneously utilizing large quantities of industrial solid waste desulfurized gypsum.

[0111] Finally, an application was made to improve the pumping stability of differential grade ash (ash residue).

[0112] Different-grade fly ash is fly ash produced by a different combustion method than the two types mentioned above (CFB ash and PC ash), resulting in larger particle sizes after screening. Typically, the residue on a 45φm sieve is greater than or equal to 80%. This type of fly ash has coarse particles, is prone to segregation and sedimentation, and is likely to cause pipe and pump blockages during pumping. It also has low strength in the aggregate form.

[0113] refer to Figure 9 As shown, Figure 9 The graph shows the segregation rate of the slurry at different 0.3% suspending agent dosages when the water-to-solid ratio is 1:1.2 and the solid ratio is (cement:fly ash 2:8). Figure 9 The changes in the segregation rate of the grout before and after the addition of hydroxypropyl methylcellulose (HPMC) suspending agent demonstrate the crucial role of the suspending agent in ensuring pumping stability. Specifically, when the dosage is 0.1%~0.3% of the water mass, the segregation stabilization time of the grout can be extended from 20-40 minutes to over 60 minutes, and the solidification rate can be increased by 10%~33%, perfectly covering the pumping and pause times required for grouting construction.

[0114] Therefore, for ash of poor grade, the viscosity and stability of the slurry can be improved by adding a suspending agent, which can slow down the particle settling rate and ensure smooth pumping. The recommended suspending agent is hydroxypropyl methylcellulose (HPMC), and its addition amount is 1‰ to 3‰ of the mass of the mixing water. The application method is to first dissolve the suspending agent in part of the mixing water, stir thoroughly until it is completely dissolved and releases its viscosity, and then mix it with ash, cement and other materials to make slurry.

[0115] After adding a suspending agent, the segregation and sedimentation time of the differential grade grout can be extended to more than 60 minutes, ensuring the smoothness of the grouting pumping process, meeting the pumping and pausing requirements of grouting construction, increasing the stone-setting rate by 10%~33%, and realizing the resource utilization of differential grade grout.

[0116] Table 3. Analysis of fly ash mix proportions and costs for grout-bonded masses meeting a 90-day unconfined compressive strength of 2 MPa.

[0117]

[0118] Note: All data are from actual grouting projects in mined-out areas in 2025.

[0119] As shown in Table 3, the conventional mix proportions are as follows, provided that the grout achieves good injectability and the 90-day unconfined compressive strength of the grout aggregate meets 2 MPa. Specifically, when using the current fly ash grading method without any specific mix proportion modifications, the per cubic meter... 3 The cost of the grouting material for the filling body is approximately 108.7 yuan. After adopting the novel fly ash grading method proposed in this invention, for superior / good grade fly ash, after targeted improvements, the cost per cubic meter... 3 The cost of grouting materials for filling bodies has been reduced by approximately 67%. For medium-grade fly ash, after targeted improvements, the cost per cubic meter has been reduced. 3 The cost of grouting materials for filling bodies is reduced by approximately 10%.

[0120] refer to Figure 10 As shown, the present invention also provides a grouting method for grouting goaf areas using fly ash as a grouting material, comprising:

[0121] For each batch of incoming fly ash, the fly ash grade is determined according to the grading indicators in the above design method;

[0122] For superior or good grade ash, calcium oxide-based or calcium hydroxide-based activators are used to improve it and form a grouting material. The superior or good grade ash accounts for more than 90% of the total solid mass, and the calcium oxide-based or calcium hydroxide-based activator accounts for less than 10% of the total solid mass. The water-to-solid ratio ranges from (1:0.9) to (1:1.2).

[0123] For medium-grade lime, cement and calcium sulfate are used in a synergistic activation and modification process to form a grouting material. The medium-grade lime accounts for 70% to 80% of the total solid mass, cement accounts for 10% to 20% of the total solid mass, and calcium sulfate accounts for 3% to 6% of the total solid mass. The water-to-solid ratio ranges from (1:1.2) to (1:1.5).

[0124] For the use of substandard cement ash, a suspending agent is used to improve it and form a grouting material. The suspending agent includes hydroxypropyl methylcellulose. The substandard cement ash accounts for more than 85% of the total solid mass, and the cement accounts for 10% to 20% of the total solid mass. The amount of suspending agent added is 0.1% to 0.3% of the mass of the mixing water.

[0125] Improved fly ash was used as grouting material to grout the goaf.

[0126] Compared with existing technologies, the design method, grouting material and grouting method of the present invention establishes for the first time a fly ash grading system specifically for goaf grouting projects. The grading index is directly related to the core performance of grouting (stone rate, pumpability, strength), which solves the pain point that the traditional concrete industry grading standards are "unsuitable" for goaf areas.

[0127] The design method, grouting material, and grouting method of the present invention for goaf grouting are based on the intrinsic relationship between the microstructure (spherical / irregular particles), chemical composition (CaO content), and grouting performance of fly ash. The classification logic is clear, and the results can accurately predict the grouting performance of fly ash.

[0128] The present invention provides a design method for grouting materials in goaf areas, as well as grouting materials and grouting methods. It formulates targeted improvement and application schemes for different grades of fly ash, solves the compatibility problem of various types of fly ash in grouting projects, and reduces the cost of superior fly ash by 40% to 80% and medium-grade fly ash by 10% to 20% through graded screening and targeted improvement. It also turns inferior fly ash into a valuable resource, significantly reducing the total cost of the project.

[0129] The design method, grouting material, and grouting method of this invention for goaf grouting materials provide a rapid on-site identification method that requires no complex equipment, is easy to operate, and enables continuous quality control of incoming materials. The integrated "grading-improvement-application" solution can directly guide engineering practice and solve practical construction pain points.

[0130] The technical solution of the present invention will be described in detail below through a specific embodiment.

[0131] First, an on-site investigation was conducted on the sources of fly ash within the grouting area of ​​the goaf.

[0132] Project Overview: A subsidence area remediation project in Jiawang District, Xuzhou City, with a designed grouting volume of approximately 500,000 m³. 3 Within a 50-kilometer economic transportation radius of the project, there are four major coal-fired power plants: Power Plant A (China Resources), Power Plant B (Huamei), Power Plant C (Jinshanqiao), and Power Plant D (Huaxin).

[0133] Survey content: A survey was conducted at four power plants, recording the type of fly ash (PC ash / CFB ash), approximate price, production capacity stability, and transportation distance for each plant. Representative fly ash samples (50 kg each) were collected from the ash storage facilities of each power plant, sealed, labeled, and sent back to the laboratory.

[0134] Secondly, precise laboratory testing and grading.

[0135] The four fly ash samples (numbered A, B, C, and D) were tested for the key indicators specified in this invention.

[0136] Test items and methods:

[0137] Bulk density: Determined using the graduated cylinder vibration method according to specifications. Result: Sample A: 0.71 g / cm³ 3 Sample B: 0.52 g / cm³ 3 Sample C: 0.50 g / cm³ 3 Sample D: 0.69 g / cm³ 3 .

[0138] Single slurry performance: Pure fly ash slurry is prepared at a water-to-solid ratio of 1:1.

[0139] Single slurry flowability: determined according to GB / T8077-2012 "Test Method for Homogeneity of Concrete Admixtures". Results: Sample A 155mm; Sample B 150mm; Sample C 125mm; Sample D 295mm.

[0140] Stone formation rate of single slurry: The slurry was poured into a 1L graduated cylinder and allowed to stand until the volume stabilized. The volume percentage of stones was then calculated. Results: Sample A 75%; Sample B 96%; Sample C 98%; Sample D 72%.

[0141] Chemical composition (CaO): Analyzed using X-ray fluorescence spectrometry (XRF). Results: Sample A CaO = 4.5%; Sample B CaO = 11.5%; Sample C CaO = 9.5%; Sample D CaO = 3.8%.

[0142] Boiler type: After consulting with the power plant, it was confirmed that A and D are pulverized coal boilers (PC boilers), and B and C are circulating fluidized bed boilers (CFB boilers).

[0143] According to the fly ash grading method for goaf grouting projects in Table 2, samples A, B, C, and D were judged. The judgment results are as follows: sample B is superior grade fly ash; sample C is good grade fly ash; sample A is medium grade fly ash; and sample D is poor grade fly ash.

[0144] Next, based on the grading results, targeted improvements were made to fly ash of each grade.

[0145] Based on the grading results, sample B (superior grade ash) was determined to be the optimal choice, and sample C (good grade ash) was the second-best choice.

[0146] For the improvement of high / good grade lime (samples B and C): the "calcium oxide activation" route is adopted. The technical principle is to utilize its own high CaO characteristics, and add calcium oxide (quicklime) to further enhance the alkaline environment, fully activate its pozzolanic activity, and generate a large amount of hydrated calcium silicate (CSH) gel and ettringite (AFt), thereby significantly improving the strength and achieving the goal of significantly reducing or completely replacing cement.

[0147] The improvement route for medium-grade ash (sample A) adopts the "co-activation of cement and calcium sulfate" route. SO4 is supplemented by external addition of calcium sulfate (gypsum). 2- and Ca 2+ It promotes the formation of more ettringite, which works synergistically with cement hydration products to make up for its own insufficient calcium content.

[0148] The improvement approach for substandard grout (sample D) involves incorporating a suspending agent to ensure stable operation during mixing, pumping, and grouting, thus avoiding practical engineering problems such as pump blockage, pipe blockage, and borehole blockage. It should be noted that substandard grout should generally not be used in grouting projects, as its particle size is too large, its activity is low, and its water separation rate is too fast, resulting in poor performance in terms of grout stability and strength activation.

[0149] Then, indoor proportioning tests were conducted to verify and fine-tune the optimization.

[0150] Detailed mix design tests were conducted on the selected sample B to determine the most economical mix design that meets the engineering requirements (90d strength ≥ 2MPa).

[0151] Experimental scheme: The water-to-solid ratio was fixed at 1:1, and multiple mix proportions were designed. The core was to change the amount of carbide slag added.

[0152] Key proportions and results: The proportion (carbide slag: fly ash = 10:90) achieved a 90-day strength of 2.4 MPa without the use of cement, and the cost of grouting materials was reduced by approximately 67%.

[0153] Finally, rapid testing of incoming samples and their application in engineering fields.

[0154] Rapid on-site testing method: To ensure that the quality of each truckload of fly ash delivered to the site is consistent with the laboratory samples, a rapid on-site testing procedure—rapid determination of bulk density—was established. Take 100g of fly ash, gently pour it into a 250mL graduated cylinder, and gently shake until the volume remains constant. Calculate the reading. If the result is within 0.50g / cm³... 3 ~0.55g / cm 3Within this range, it is preliminarily identified as CFB ash. Simultaneously, visual inspection is conducted: superior grade ash (high-calcium CFB ash) is often light yellow or yellowish-brown; low-calcium CFB ash is dark gray or blackish-gray; medium grade ash (PC ash) is mostly grayish-white to light gray; inferior grade ash has coarse particles, with clearly visible particles.

[0155] Grouting was used to improve and apply different grades of fly ash entering the site.

[0156] 1. Application of grouting improvement for superior grade lime.

[0157] Materials: Fly ash sample B, which was judged to be of "superior" grade, calcium carbide slag powder (Ca(OH)2 content approximately 85%), and water.

[0158] Mixing ratio: fly ash: calcium carbide slag powder = 90:10, water-solid ratio is 1:1.0.

[0159] Results: When prepared according to this ratio, the slurry has good fluidity and a stone formation rate of 95%. After 90 days of standard curing, the unconfined compressive strength of the stone was measured to be 2.4 MPa, which is much higher than the standard requirement of 2.0 MPa. Compared with the traditional ratio of 20% cement, the material cost is reduced by about 67%.

[0160] In the treatment of goaf in a coal mine, a high-grade fly ash ratio (fly ash: carbide slag = 90:10) was used for grouting. Field tests showed that the grout stone formation rate exceeded 95%, the water separation rate was controllable, and the strength of post-work core samples remained stable at 2.0~2.5MPa.

[0161] 2. Application of grouting improvement for medium-grade lime.

[0162] Intermediate fly ash refers to fly ash (PC ash) produced by pulverized coal boilers. It has weak cementitious properties and relies on cement to provide basic strength. However, when cement is added alone (such as 20% cement + 80% fly ash), the 90-day strength is about 1.5 MPa, which is difficult to meet the specifications.

[0163] Materials: Fly ash sample A, which was judged to be "medium" grade, desulfurized gypsum (2H2O·CaSO4 content approximately 80%), PO42.5 cement, and water.

[0164] Mixing ratio: fly ash: cement: desulfurized gypsum powder = 75:20:5, water-to-solid ratio is 1:1.2.

[0165] Implementation Results: When prepared according to this ratio, the grout has good fluidity and a stone-forming rate of approximately 80%. After 90 days of standard curing, the unconfined compressive strength of the stone-forming material was measured to be 2.1 MPa, meeting the pre-specified strength requirements. Compared to a solid-liquid ratio of cement:fly ash (25:75) that meets the specified strength requirements, the cost of the grouting material is reduced by approximately 10%.

[0166] 3. Application of grouting improvement for differential grade ash.

[0167] Materials: Ash slag from a power plant (classified as "poor" grade), PO42.5 cement, hydroxypropyl methylcellulose (HPMC), and water.

[0168] Mixing ratio: cement: ash = 2:8, HPMC addition is 0.2% of water mass, water-solid ratio is 1:1.4.

[0169] Implementation Results: HPMC was first dissolved in water and stirred for 10 minutes until completely dissolved. Then, it was mixed with cement and ash to form a slurry. After adding HPMC, the slurry showed no significant segregation or sedimentation within 60 minutes of standing. It successfully passed through a 300m pipeline circulation pumping test using a BW250 mud pump without any pipe blockage.

[0170] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0171] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A design method for grouting materials in goaf areas, characterized in that, include: S1. The fly ash grade is determined based on grading indicators, including the bulk density, calcium oxide content, and single-slurry stone formation rate of the fly ash. The fly ash grades include superior grade, good grade, medium grade, and poor grade, wherein the bulk density of superior grade fly ash is not greater than 0.55 g / cm³. 3 The calcium oxide content is not less than 10%, the stone-forming rate of the single slurry is in the range of 92%~98%, and the bulk density of good-grade lime is not greater than 0.55g / cm³. 3 The calcium oxide content is less than 10%, the stone-forming rate of the single slurry is in the range of 92%~98%, and the bulk density of the medium-grade ash is not less than 0.65g / cm³. 3 The calcium oxide content is less than 10%, the stone-forming rate of the single slurry is in the range of 75%~85%, and the bulk density of the inferior grade ash is not less than 0.65g / cm³. 3 The calcium oxide content is less than 10%, and the stone formation rate of the slurry is less than 80%. S2, different proportioning strategies are selected for different grades of fly ash to improve the grouting material, wherein: Superior or good grade ash is modified with calcium oxide-based or calcium hydroxide-based activators: The proportioning strategy for superior or good grade fly ash is as follows: fly ash accounts for more than 90% of the total solid mass, calcium oxide-based or calcium hydroxide-based activator accounts for less than 10% of the total solid mass, the water-to-solid ratio ranges from (1:0.9) to (1:1.2), and the cement content is zero. Medium-grade lime is improved by synergistic activation of cement and calcium sulfate: The proportioning strategy for intermediate-grade fly ash is as follows: fly ash accounts for 70% to 80% of the total solid mass, cement accounts for 10% to 20% of the total solid mass, calcium sulfate accounts for 3% to 6% of the total solid mass, and the water-to-solid ratio ranges from (1:1.2) to (1:1.5). Different grade ash is improved using a suspending agent: The proportioning strategy for the fly ash is as follows: fly ash accounts for more than 85% of the total solid mass, cement accounts for 10% to 20% of the total solid mass, and the amount of suspending agent added is 0.1% to 0.3% of the mass of mixing water. The suspending agent includes hydroxypropyl methylcellulose.

2. The design method for grouting materials in goaf areas according to claim 1, characterized in that, The bulk density of the superior grade ash is 0.45 g / cm³. 3 ~0.55g / cm 3 The bulk density of the good grade ash is between 0.45 g / cm³. 3 ~0.55g / cm 3 between.

3. The design method for grouting materials in goaf areas according to claim 1, characterized in that, The grading indicators also include the fluidity, fineness, and moisture content of fly ash slurry; among which, The fluidity of the single slurry of high-quality lime is in the range of 100mm~180mm, the fineness is less than 45%, and the water content is less than 1%. The single slurry fluidity of good grade lime is in the range of 100mm~180mm, the fineness is less than 45%, and the water content is less than 1%. The fluidity of the medium-grade lime slurry should be no less than 250 mm, the fineness should be no less than 80%, and the moisture content should be less than 3%. The fluidity of the slurry for the lower grade lime should be no less than 250 mm, the fineness no less than 80%, and the moisture content no less than 3%. The single slurry refers to a slurry prepared solely from fly ash and water at a water-to-solid ratio of 1:1, and the fineness is the residue on a 45φm square-hole sieve.

4. The design method for grouting materials in goaf areas according to claim 3, characterized in that, The grade of fly ash is determined based on grading indicators, including: Take 100g of fly ash sample and slowly pour it into a 250mL graduated cylinder. Under natural conditions, read the bulk volume V and calculate the bulk density ρ = 100 / V. If the bulk density is not greater than 0.55g / cm³... 3 It is classified as superior grade or good grade ash, if the bulk density is greater than 0.65 g / cm³. 3 It is then classified as medium-grade or poor-grade gray; and / or, Prepare fly ash slurry with a water-to-solid ratio of 1:

1. Test the flow diameter using the cement paste fluidity test method in GB / T 8077-2012. If the slurry fluidity is within the range of 100mm~180mm, it is classified as superior or good grade fly ash; if the fluidity is greater than or equal to 250mm, it is classified as medium or poor grade fly ash; and / or, Observe the appearance characteristics of fly ash and the self-coagulation property of the slurry after 24 hours. If the color is light yellow or yellowish-brown and the slurry self-coagulates after 24 hours, it is a superior grade of fly ash. If the color is dark gray or blackish-gray and the slurry self-coagulates after 24 hours, it is a good grade of fly ash. If the color is grayish-white to light gray and the slurry does not self-coagulate after 24 hours, it is a medium grade of fly ash. If the particles are coarse and the slurry does not self-coagulate after 24 hours, it is a poor grade of fly ash.

5. A grouting material suitable for grouting projects in goaf areas, characterized in that, It includes the superior or good grade lime, calcium oxide-based or calcium hydroxide-based activator determined in the design method according to any one of claims 1 to 4, wherein the superior or good grade lime accounts for more than 90% of the total solid mass, the calcium oxide-based or calcium hydroxide-based activator accounts for less than 10% of the total solid mass, the water-to-solid ratio is in the range of (1:0.9) to (1:1.2), and the cement content is zero.

6. A grouting material suitable for grouting projects in goaf areas, characterized in that, It includes medium-grade ash, cement and calcium sulfate as determined in the design method according to any one of claims 1 to 4, wherein the medium-grade ash accounts for 70% to 80% of the total solid mass, the cement accounts for 10% to 20% of the total solid mass, the calcium sulfate accounts for 3% to 6% of the total solid mass, and the water-to-solid ratio ranges from (1:1.2) to (1:1.5).

7. A grouting material for grouting projects in goaf areas, characterized in that, It includes the differential ash, cement, and suspending agent determined in the design method according to any one of claims 1 to 4, wherein the suspending agent includes hydroxypropyl methylcellulose, the differential ash accounts for more than 85% of the total solid mass, the cement accounts for 10% to 20% of the total solid mass, and the amount of suspending agent added is 0.1% to 0.3% of the mass of the mixing water.

8. A grouting method for grouting goaf using fly ash as the grouting material, characterized in that, include: For each batch of incoming fly ash, the fly ash grade is determined according to grading indicators, including the bulk density, calcium oxide content, and single slurry stone formation rate. The fly ash grades include superior grade, good grade, medium grade, and poor grade, wherein the bulk density of superior grade fly ash is not greater than 0.55 g / cm³. 3 The calcium oxide content is not less than 10%, the stone-forming rate of the single slurry is in the range of 92%~98%, and the bulk density of good-grade lime is not greater than 0.55g / cm³. 3 The calcium oxide content is less than 10%, the stone-forming rate of the single slurry is in the range of 92%~98%, and the bulk density of the medium-grade ash is not less than 0.65g / cm³. 3 The calcium oxide content is less than 10%, the stone-forming rate of the single slurry is in the range of 75%~85%, and the bulk density of the inferior grade ash is not less than 0.65g / cm³. 3 The calcium oxide content is less than 10%, and the stone formation rate of the slurry is less than 80%. For superior or good grade ash, calcium oxide-based or calcium hydroxide-based activators are used to improve it and form a grouting material. The superior or good grade ash accounts for more than 90% of the total solid mass, and the calcium oxide-based or calcium hydroxide-based activator accounts for less than 10% of the total solid mass. The water-to-solid ratio ranges from (1:0.9) to (1:1.2). For medium-grade lime, cement and calcium sulfate are used in a synergistic activation and modification process to form a grouting material. The medium-grade lime accounts for 70% to 80% of the total solid mass, cement accounts for 10% to 20% of the total solid mass, and calcium sulfate accounts for 3% to 6% of the total solid mass. The water-to-solid ratio ranges from (1:1.2) to (1:1.5). For the use of substandard cement ash, a suspending agent is used to improve it and form a grouting material. The suspending agent includes hydroxypropyl methylcellulose. The substandard cement ash accounts for more than 85% of the total solid mass, and the cement accounts for 10% to 20% of the total solid mass. The amount of suspending agent added is 0.1% to 0.3% of the mass of the mixing water. Improved fly ash was used as grouting material to grout the goaf.

9. The grouting method according to claim 8, characterized in that, The grading indicators also include the fluidity, fineness, and moisture content of fly ash slurry; among which, The fluidity of the single slurry of high-quality lime is in the range of 100mm~180mm, the fineness is less than 45%, and the water content is less than 1%. The single slurry fluidity of good grade lime is in the range of 100mm~180mm, the fineness is less than 45%, and the water content is less than 1%. The fluidity of the medium-grade lime slurry should be no less than 250 mm, the fineness should be no less than 80%, and the moisture content should be less than 3%. The fluidity of the slurry for the lower grade lime should be no less than 250 mm, the fineness no less than 80%, and the moisture content no less than 3%. The single slurry refers to a slurry prepared solely from fly ash and water at a water-to-solid ratio of 1:1, and the fineness is the residue on a 45φm square-hole sieve.

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