Coal-based solid waste recycled aggregate shotcrete and preparation method thereof

Abstract

A coal-based solid waste regenerated aggregate shotcrete and a preparation method thereof, comprising cementitious material 100 parts, coarse aggregate 150-200 parts, fine aggregate 150-200 parts, polycarboxylate superplasticizer 2-4 parts, anti-adsorption agent 0.5-1.5 parts, water 35-60 parts, and defoaming agent 0.1-0.3 parts. The cementitious material is composed of cement and waste desulfurization gypsum; the coarse and fine aggregates are all coal gangue or gasification slag; the polycarboxylate superplasticizer is a slow-release polycarboxylate superplasticizer containing phosphate ester groups in the side chain; and the anti-adsorption agent is bentonite modified by a silane coupling agent. The modified bentonite anti-adsorption agent preferentially blocks the porous surface adsorption sites of the coal-based solid waste aggregate, and the slow-release polycarboxylate superplasticizer continuously provides dispersion force, effectively reduces the invalid consumption of the superplasticizer, significantly reduces the 1h slump loss rate of the concrete, reduces the rebound rate of the shotcrete construction to below 15%, and the total solid waste content is above 70%, realizing large-scale collaborative utilization of coal-based solid waste and waste desulfurization gypsum.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a recycled aggregate shotcrete with coal-based solid waste as the core raw material, which is suitable for engineering scenarios such as mine shaft support, tunnel lining, and slope reinforcement, and realizes the high-value utilization of industrial solid waste such as coal gangue, gasification slag, and waste desulfurization gypsum. Background Technology

[0002] Shotcrete, as a key material for rapid support and structural repair, relies on natural sand and gravel aggregates and a pure cementitious system in its traditional formulation, resulting in high resource consumption and carbon emissions. Meanwhile, my country's coal industry generates hundreds of millions of tons of coal gangue, gasification slag, and other coal-based solid waste annually, which occupy land and pollute the environment when stockpiled; waste desulfurization gypsum generated during the desulfurization process of thermal power plants also faces disposal challenges. While there have been attempts to replace some aggregates with single coal-based solid waste (such as coal gangue) in existing technologies, the following drawbacks exist: 1. Insufficient aggregate performance: Coal gangue and gasification slag have porous surfaces and high water absorption rates. Directly replacing natural aggregates can easily lead to poor concrete workability, especially in shotcrete construction, where pipe blockage and high rebound rates are common problems. 2. Poor compatibility of cementitious system: As an industrial by-product, waste desulfurization gypsum has insufficient compatibility with cement due to its retarding properties. Adding it alone can easily lead to low early strength of concrete and loss of control over setting time. 3. Severe slump loss: The high adsorption of coal-based solid waste aggregate will exacerbate the consumption of water-reducing agents, resulting in rapid slump loss of concrete from mixing to spraying, which cannot meet the timeliness requirements of construction. 4. Lack of functional admixtures: There is a lack of specialized admixtures for the high adsorption characteristics of coal-based solid waste, making it difficult to balance the contradiction between workability, strength and durability. Therefore, developing a shotcrete that uses coal-based solid waste as the sole aggregate, is compatible with waste desulfurization gypsum cementitious systems, and can effectively control slump loss has become the key to solving the problems of solid waste disposal and green building materials. Summary of the Invention

[0003] The purpose of this invention is to provide a coal-based solid waste recycled aggregate shotcrete and its preparation method, in order to solve the technical problems of traditional shotcrete which relies on natural aggregates, consumes a lot of resources, and has high carbon emissions, as well as the existing coal-based solid waste utilization technologies that suffer from poor concrete workability, low early strength, serious slump loss, and lack of special admixtures.

[0004] To achieve the above objectives, the present invention adopts the following technical solution.

[0005] A coal-based solid waste recycled aggregate shotcrete comprises the following components in parts by weight: 100 parts cementitious material, 150-200 parts coarse aggregate, 150-200 parts fine aggregate, 2-4 parts polycarboxylate superplasticizer, 0.5-1.5 parts anti-adsorption agent, 35-60 parts water, and 0.1-0.3 parts defoamer; The cementitious material includes cement and waste desulfurization gypsum; 60-100 parts cement and 0-40 parts waste desulfurization gypsum; The coarse aggregate is coal gangue or gasification slag with a particle size of 5-10 mm. The fine aggregate is one or a mixture of both of coal gangue or gasification slag with a particle size of 0-5 mm. The polycarboxylate superplasticizer is a slow-release polycarboxylate superplasticizer with phosphate ester groups in its side chain.

[0006] Preferably, the cement in the cementitious material is P·O 42.5 or P·O 52.5 ordinary Portland cement.

[0007] Preferably, the waste desulfurization gypsum is a byproduct of wet desulfurization in thermal power plants.

[0008] Preferably, the crushing index of the coarse aggregate and fine aggregate, which are coal gangue or gasification slag, is ≤20%, and the water absorption rate is ≤15%.

[0009] Preferably, the anti-adsorption agent is bentonite modified with a silane coupling agent. Preferably, the mass ratio of the polycarboxylate superplasticizer to the anti-adsorption agent is 8:1-4:3. A method for preparing coal-based solid waste recycled aggregate shotcrete includes the following steps: Step 1: Put the cement and waste desulfurization gypsum into the mixer and dry mix them evenly; Step 2: Add coarse aggregate, fine aggregate, anti-adsorption agent and defoamer, and continue dry mixing; Step 3: Dissolve the polycarboxylate superplasticizer in water, add it to a mixer, and wet mix to obtain a uniform concrete mixture.

[0010] Preferably, the dry mixing time in step one is 30-60 seconds; the dry mixing time in step two is 1-2 minutes; and the wet mixing time in step three is 2-4 minutes.

[0011] Preferably, the method further includes step four, which involves spraying the concrete mixture using a wet spraying machine with a working air pressure of 0.4-0.6 MPa and a spraying distance of 1.0-2.0 m.

[0012] Compared with the prior art, the present invention has the following features and beneficial effects.

[0013] 1. This invention abandons the traditional system of natural sand and gravel aggregates and pure cement. All coarse and fine aggregates are made from pre-treated coal gangue or gasification slag, while 0-40 parts of waste desulfurization gypsum are added to the cementitious material to replace part of the cement. This results in the total amount of solid waste accounting for more than 70% of the total concrete mass, enabling the large-scale disposal of various coal-based solid wastes and desulfurization byproducts in a single process. This solution significantly reduces the land occupation and environmental pollution caused by natural mineral resource mining and solid waste storage, while simultaneously reducing cement usage and the high carbon emissions during cement production, achieving a fundamental transformation from "solid waste" to "green building materials."

[0014] 2. This invention addresses industry challenges such as water-reducing agent failure, rapid slump loss, and easy pipe blockage and rebound caused by the porous and highly adsorbent surface of coal-based solid waste aggregates. It innovatively adopts a synergistic compounding technology of a special slow-release polycarboxylate water-reducing agent and a modified bentonite anti-adsorption agent, resulting in excellent and stable concrete workability and completely overcoming the key obstacles in shotcrete construction.

[0015] 3. The bentonite modified with a silane coupling agent in this invention can preferentially adsorb onto the porous surface of coal gangue and gasification slag, forming a hydrophobic "protective film" that effectively blocks adsorption sites, thereby significantly reducing the ineffective adsorption and consumption of subsequently added water-reducing agents and water by the aggregate. The mass ratio of polycarboxylate water-reducing agent to anti-adsorption agent is shown. Furthermore, the slow-release polycarboxylate water-reducing agent with phosphate ester groups in its side chain in this invention not only has a high water reduction rate, but its unique slow-release properties also allow it to continue to function during stirring and settling. Furthermore, the polycarboxylate superplasticizer and anti-adsorption agent are compounded in a mass ratio of 8:1 to 4:3. The anti-adsorption agent preferentially occupies or shields the adsorption sites of highly adsorbent substances, reducing the ineffective consumption of the polycarboxylate superplasticizer and ensuring its more effective adsorption on the surface of cement particles. It exerts the dispersing effect of steric hindrance and electrostatic repulsion, thereby significantly improving the workability and stability of concrete, increasing the initial slump of concrete, and reducing the slump loss rate within 1 hour, meeting the timeliness requirements of shotcrete construction. The anti-adsorption agent provides "early protection," creating conditions for the superplasticizer to act efficiently on cement particles; the superplasticizer provides lasting dispersing force; at the same time, the excellent fluidity retention ability ensures that the concrete maintains good pumpability and sprayability during transportation from the mixing plant to the shotcrete working surface, effectively avoiding pipe blockage during on-site construction and controlling the shotcrete rebound rate to an extremely low level, significantly improving construction efficiency, material utilization, and operational safety.

[0016] 4. This invention, through optimized mix proportions, ensures that the mechanical properties of the concrete fully meet the standards and that early strength development is rapid, satisfying the engineering requirements for rapid support. While achieving ultra-high solid waste content, it also guarantees the mechanical properties of the concrete. Specifically, the introduction of waste desulfurized gypsum (mainly composed of calcium sulfate dihydrate) forms a composite cementitious system with cement. At an optimal dosage of 20-35%, it not only acts as an active filler and micro-aggregate filler but also participates in the hydration reaction, optimizing the microstructure of the paste. Combined with 0.1-0.3 parts of defoamer to reduce harmful air bubble content, this further enhances the density and later-stage strength of the concrete. Although waste desulfurized gypsum has retarding properties when used alone, its hydration process is optimized under the specific composite cementitious system and admixture control of this invention. Combined with the efficient hydration environment brought about by the low water-cement ratio and high water-reducing agent, the 1-day compressive strength of the concrete can reach the design requirements. This excellent early strength development characteristic fully meets the stringent requirements for rapid support strength formation in engineering projects such as mine roadways and tunnel initial linings.

[0017] 5. The coal gangue, gasification slag, and waste desulfurization gypsum used in this invention are all bulk industrial solid wastes, with wide-ranging sources and low costs. Using them on a large scale to replace the increasingly expensive natural sand and cement can, according to calculations, reduce the overall raw material cost by more than 20% compared to traditional shotcrete. Simultaneously, the extremely low rebound rate further reduces material waste and lowers overall construction costs. This invention transforms environmental burden into economic advantage, solving the serious problem of solid waste disposal while providing engineering construction parties with a high-performance and low-cost material option, achieving an organic unity of environmental and economic benefits, and possessing extremely high market competitiveness and promising application prospects.

[0018] 6. This invention, through the deep integration of raw material innovation, component design and admixture compounding technology, has successfully developed a coal-based solid waste recycled aggregate shotcrete with stable workability, reliable mechanical properties, low cost and significant environmental benefits, providing an efficient and feasible technical solution for the resource utilization of industrial solid waste and the green and low-carbon transformation of the building materials industry. Detailed Implementation Example

[0019] Raw material ratio (parts by weight): Cementing materials: 70 parts of P·O 42.5 cement and 30 parts of waste desulfurized gypsum.

[0020] Coarse aggregate: 180 parts of coal gangue with a particle size of 5-10mm and a water absorption rate of 10%.

[0021] Fine aggregate: 170 parts of coal gangue with a particle size of 0-5mm.

[0022] Polycarboxylate superplasticizer: 3 parts of slow-release polycarboxylate superplasticizer with phosphate ester groups in the side chain have a water reduction rate of 32% and can resist aggregate adsorption.

[0023] Anti-adsorption agent: 0.8 parts of bentonite modified with silane coupling agent can form a protective film on the aggregate surface, reducing the adsorption of water-reducing agent.

[0024] Water: 42 portions.

[0025] Defoamer: 0.2 parts of silicone defoamer.

[0026] Preparation method: Dry mix cement with waste desulfurized gypsum for 40 seconds; Add coarse and fine aggregates, anti-adsorption agent and defoamer, and dry mix for 1.5 minutes; Add the water-reducing agent after dissolving it in water, and mix wet for 3 minutes; Wet spraying is used, with an air pressure of 0.5MPa and a spraying distance of 1.5m.

[0027] Performance tests: initial slump 215mm, 1h slump 205mm; 1d compressive strength 10.5MPa, 28d compressive strength 32MPa, flexural strength 4.8MPa; spray rebound rate ≤8%. Example

[0028] Raw material ratio (parts by weight): Cementitious materials: 65 parts of P·O 52.5 cement, 35 parts of waste desulfurized gypsum, with a specific surface area of ​​440 m² / kg; Coarse aggregate: 190 parts of gasification slag with a particle size of 5-10mm and a water absorption rate of 12%; Fine aggregate: 140 parts of gasification slag with a particle size of 0-5mm; Polycarboxylate superplasticizer: 3.5 parts of slow-release polycarboxylate superplasticizer with phosphate ester groups in the side chain have a water reduction rate of 33% and can resist aggregate adsorption.

[0029] Anti-adsorption agent: 1.0 part of bentonite modified with silane coupling agent can form a protective film on the aggregate surface, reducing the adsorption of water-reducing agent.

[0030] Water: 45 parts; Defoamer: 0.25 parts of silicone defoamer.

[0031] The preparation method is the same as in Example 1.

[0032] Performance tests: initial slump 220mm, 1h slump 210mm; 1d compressive strength 11MPa, 28d compressive strength 35MPa, flexural strength 5.1MPa; spray rebound rate ≤7%. Example

[0033] Raw material ratio (parts by weight): Cementitious materials: 80 parts of P·O 42.5 cement, 20 parts of waste desulfurization gypsum; Coarse aggregate: 160 parts of coal gangue with a particle size of 5-10mm and a water absorption rate of 8%; Fine aggregate: 180 parts of gasification slag with a particle size of 0-5mm; Polycarboxylate superplasticizer: 2.5 parts of slow-release polycarboxylate superplasticizer with phosphate ester groups in the side chain have a water reduction rate of 30% and can resist aggregate adsorption.

[0034] Anti-adsorption agent: 0.6 parts of bentonite modified with silane coupling agent; Water: 38 parts; Defoamer: 0.15 parts of silicone defoamer.

[0035] The preparation method is the same as in Example 1.

[0036] Performance tests: initial slump 205mm, 1h slump 195mm; 1d compressive strength 12MPa, 28d compressive strength 38MPa, flexural strength 5.3MPa; spray rebound rate ≤6%.

[0037] In Examples 1-3, the waste desulfurization gypsum is a byproduct of wet desulfurization in thermal power plants, and its main chemical components are calcium sulfate dihydrate (CaSO4·2H2O), calcium sulfite (CaSO3·1 / 2H2O), calcium carbonate (CaCO3) / calcium oxide (CaO). The content of calcium sulfate dihydrate (CaSO4·2H2O) is over 90%, and its crystal structure is similar to that of natural gypsum, exhibiting gelling properties.

[0038] Calcium sulfite (CaSO3·1 / 2H2O) is an incompletely oxidized intermediate product with a content of <3%. If the content is too high, it may affect the properties of gypsum.

[0039] Calcium carbonate (CaCO3) / calcium oxide (CaO) originates from incompletely reacted desulfurizing agents (limestone or lime) and affects pH and impurities.

[0040] Impurities include trace amounts of chloride ions (Cl⁻), fluoride ions (F⁻), magnesium oxide (MgO), potassium oxide (K₂O), sodium oxide (Na₂O), silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), iron oxide (Fe₂O₃), etc.

[0041] Comparative Example The process uses ordinary natural aggregates (crushed stone, river sand) and a pure cementitious system, employs ordinary polycarboxylate superplasticizer, does not add anti-adsorption agents, has a water-cement ratio of 0.45, and the rest of the process is the same.

[0042] Test results: initial slump 220mm, 1h slump 180mm; 1d compressive strength 9MPa, 28d compressive strength 35MPa.

[0043] Table 1 Comparison of Concrete Performance Test Results Initial slump (mm) 215 220 205 220 1-hour slump (mm) 205 210 195 180 1d compressive strength 10.5MPa 11MPa 12MPa 9MPa 28-day compressive strength 32MPa 35MPa 38MPa 35MPa Flexural strength 4.8MPa 5.1MPa 5.3MPa Spray rebound rate ≤8% ≤7% ≤6% Approximately 15-25% The test data in the table above shows that: The slump loss in all three embodiments was only 10 mm after one hour, with a loss rate of less than 5%. In contrast, the slump loss in the comparative example reached 40 mm after one hour, with a loss rate exceeding 18%. This demonstrates that the concrete slump of the present invention is excellent, which is due to the "sealing" effect of the anti-adsorbent on the porous surface of coal-based solid waste and the continuous plasticity retention of the slow-release polycarboxylate superplasticizer. This fundamentally solves the problems of pipe blockage and rebound caused by the high adsorption of aggregates, ensuring the smoothness and quality of shotcrete construction.

[0044] Meanwhile, the 1-day compressive strength of the three embodiments (10.5-12 MPa) was significantly higher than that of the comparative example (9 MPa). This indicates that the composite cementitious system of waste desulfurized gypsum and cement, with the addition of special admixtures, not only did not delay strength development due to its retarding properties, but also accelerated early strength growth by optimizing the hydration process. This significant improvement in early strength makes it more suitable for rapid support, which is crucial for tunnel and roadway engineering projects that require rapid support.

[0045] Although the aggregates in Examples 1-3 were 100% made from relatively weak coal-based solid waste and contained a large proportion of 20-35% waste desulfurization gypsum, the 28-day strength of these examples was 32-38 MPa, fully meeting the design requirement of ≥30 MPa. Two of these examples even exceeded the performance of the pure cement system in the comparative example. Despite the extremely high solid waste content, the mechanical properties were fully compliant and even superior. This demonstrates the synergistic strengthening effect of the cementitious system and aggregates, as well as the effect of the defoamer in improving density, achieving a transformation from waste to strength.

[0046] The example demonstrates a rebound rate controlled at ≤8%, significantly lower than the average of 15-25% for conventional wet spraying processes on-site. Low rebound translates to less material waste, higher construction efficiency, and a safer working environment. More importantly, with a solid waste content exceeding 70%, it provides a high-value utilization outlet for large stockpiles of coal gangue, gasification slag, and desulfurization gypsum, resulting in substantial environmental benefits and aligning with the development direction of green building materials.

[0047] The above embodiments are not exhaustive examples of specific implementation methods, and other embodiments are also possible. The purpose of the above embodiments is to illustrate the present invention, rather than to limit the scope of protection of the present invention. All applications derived from simple variations of the present invention fall within the scope of protection of the present invention.

Claims

1. A type of shotcrete made from recycled coal-based solid waste aggregate, characterized in that, The components include the following parts by mass: 100 parts cementitious material, 150-200 parts coarse aggregate, 150-200 parts fine aggregate, 2-4 parts polycarboxylate superplasticizer, 0.5-1.5 parts anti-adsorption agent, 35-60 parts water, and 0.1-0.3 parts defoamer; The cementitious material includes cement and waste desulfurization gypsum; 60-100 parts cement, 0-40 parts waste desulfurization gypsum; The coarse aggregate is coal gangue or gasification slag with a particle size of 5-10 mm. The fine aggregate is one or a mixture of both of coal gangue or gasification slag with a particle size of 0-5 mm. The polycarboxylate superplasticizer is a slow-release polycarboxylate superplasticizer with phosphate ester groups in its side chain.

2. The coal-based solid waste recycled aggregate shotcrete according to claim 1, characterized in that: The cement in the cementitious material is P·O 42.5 or P·O 52.5 ordinary Portland cement.

3. The coal-based solid waste recycled aggregate shotcrete according to claim 1, characterized in that: The waste desulfurization gypsum is a byproduct of wet desulfurization in thermal power plants.

4. The coal-based solid waste recycled aggregate shotcrete according to claim 1, characterized in that: The crushing index of the coarse aggregate and fine aggregate, specifically the coal gangue or gasification slag, is ≤20%, and the water absorption rate is ≤15%.

5. The coal-based solid waste recycled aggregate shotcrete according to claim 1, characterized in that: The anti-adsorption agent is bentonite modified with a silane coupling agent.

6. The coal-based solid waste recycled aggregate shotcrete according to claim 1 or 4, characterized in that: The mass ratio of the polycarboxylate superplasticizer to the anti-adsorption agent is 8:1-4:

3.

7. A method for preparing coal-based solid waste recycled aggregate shotcrete according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Put the cement and waste desulfurization gypsum into the mixer and dry mix them evenly; Step 2: Add coarse aggregate, fine aggregate, anti-adsorption agent and defoamer, and continue dry mixing; Step 3: Dissolve the polycarboxylate superplasticizer in water, add it to a mixer, and wet mix to obtain a homogeneous concrete mixture.

8. The method for preparing coal-based solid waste recycled aggregate shotcrete according to claim 7, characterized in that: The dry mixing time in step one is 30-60 seconds; the dry mixing time in step two is 1-2 minutes; and the wet mixing time in step three is 2-4 minutes.

9. The method for preparing coal-based solid waste recycled aggregate shotcrete according to claim 7, characterized in that: The process also includes step four, in which the concrete mixture is sprayed using a wet spraying machine with a working air pressure of 0.4-0.6 MPa and a spraying distance of 1.0-2.0 m.