Multi-source solid waste grouting material and preparation method thereof

Abstract

The invention discloses a multi-source solid waste grouting material and a preparation method thereof in the field of civil engineering grouting materials and solid waste resource utilization, the multi-source solid waste grouting material comprises 2%-10% of coffee ground fine powder, 10%-20% of calcium carbide dust and the balance of fly ash, Na2O contribution in NaOH and Na2SiO3 is added to obtain the equivalent amount of Na2O, and the alkali dosage is obtained by comparing the equivalent amount of Na2O with the mass of a dry material; the total water consumption is calculated according to the water-solid ratio of 0.75, NaOH solid, a Na2SiO3 solution and water are mixed in batches and stirred to obtain an alkali activator, coffee ground fine powder, calcium carbide dust and fly ash are mixed and subjected to dry stirring, then the alkali activator is added at a constant speed for wet stirring, and preparation of the grouting material is completed; the characteristics of low density, porosity and light weight of the coffee ground fine powder are utilized to realize light weight and microstructure regulation of the material, calcium carbide dust provides Ca < 2 + > to promote activation of Si and Al in the fly ash and generate a compact gel network, active components in the fly ash are synergistically excited, a compact gel network structure mainly comprising hydrated calcium aluminosilicate is formed, and the micro-structure of the material is improved. And the slurry has excellent fluidity, forming stability and early strength.

Description

Technical Field

[0001] This invention belongs to the technical field of grouting materials and solid waste resource utilization in civil engineering, specifically relating to a multi-source solid waste alkaline-activated grouting slurry, its preparation method, and its application. Background Technology

[0002] In grouting reinforcement projects, grouting materials need to achieve long-distance pumping, effective diffusion, and stable hardening within fracture networks and large-volume voids, while simultaneously meeting multiple objectives related to density, fluidity, volume stability, mechanical properties, durability, cost, and carbon emissions. Excessive density significantly increases the additional load on the surrounding rock and induces secondary settlement; insufficient fluidity and filtration effects lead to small penetration radius and incomplete filling; bleeding and segregation weaken early formation and create durability risks; and if the system is highly dependent on cement clinker, carbon emissions and material costs are difficult to control. Therefore, novel grouting materials that combine high injectability, suitable strength, and low carbon footprint have become an urgent need in this field.

[0003] Mineral admixtures (such as fly ash and slag), as fine inorganic mineral powders, can improve the performance of freshly mixed grout and grout aggregates when added to grouting slurries. This not only reduces the amount of cement used in the grouting slurry, thus reducing carbon emissions, but also lowers production costs and improves environmental friendliness by hardening the slurry in cracks. Carbide lime, an industrial byproduct of acetylene gas production, is mainly composed of calcium oxide (CaO). As a cementing material, carbide lime can undergo a pozzolanic reaction with the active silica and alumina in fly ash under appropriate hydration conditions, generating CSH and CAH gels, thereby improving the structural density and compressive strength of the mixed material. However, there are significant interactions between different solid waste admixture amounts and alkali dosages, necessitating the establishment of standardized preparation pathways and statistical optimization frameworks to achieve a balance and replicability of strength, fluidity, and construction adaptability.

[0004] Global coffee consumption is on a continuous upward trend. Based on the calculation that each ton of coffee beans generates 650 kg of coffee grounds, the current global annual production exceeds 10 million tons. Coffee grounds are generally disposed of using traditional methods such as incineration and landfill, which not only waste organic resources but also exacerbate the environmental burden due to CH4 release and leachate pollution. Therefore, exploring the efficient utilization of SCG resources has become an urgent need to achieve the goals of a circular economy and carbon neutrality.

[0005] In the field of grouting materials, there are already cases of using coffee-related waste as raw materials. For example, Chinese patent application No. 201910367148.1 discloses a slurry for molding ceramic sanitary ware. It uses coffee mud as one of the raw materials, combined with traditional ceramic raw materials such as feldspar, white mud, and black mud. It is prepared through processes such as ball milling and iron removal. By adjusting the thixotropic index and temperature of the slurry, it can be adapted to micro-pressure or high-pressure grouting processes. Although this technology has achieved compatibility of a single slurry formula with multiple processes to a certain extent and reduced equipment costs, its core purpose is limited to the molding of ceramic products. The material system relies on mineral resources such as kaolin and porcelain clay. Coffee mud is only used as a small amount of additive to improve the slurry's absorbency and plasticity. It does not involve the high-proportion resource utilization of industrial solid waste. Furthermore, the performance indicators of this slurry (such as slurry absorption rate and green body cracking time) are designed for ceramic molding and do not match the key parameters required for grouting in civil engineering, such as fluidity, compressive strength, bulk density and durability. Its preparation method also does not introduce an alkali activation mechanism, which cannot activate the active components in solid waste to form a dense gel network. Therefore, it does not have the comprehensive advantages of being lightweight, low-carbon and cost-effective. Summary of the Invention

[0006] The purpose of this invention is to address the specific needs of grouting reinforcement in civil engineering by proposing a grouting material for multi-source solid waste and its preparation method, which achieves a grouting material with comprehensive properties of high strength and pumpability and diffusion, possessing fluidity, compressive strength, density, and durability, and is also lightweight, low-carbon, and cost-effective.

[0007] The technical solution proposed in this invention for grouting materials used in multi-source solid waste is as follows: it consists of a solid phase and a liquid phase, with a water-to-solid ratio of 0.75; the solid phase is composed of fine coffee grounds powder, carboxylic acid, and fly ash, with the fine coffee grounds powder accounting for 2%–10% of the solid phase by weight of dry solids, carboxylic acid accounting for 10%–20%, and the remainder being fly ash; the liquid phase is an alkali activator composed of solid NaOH, Na2SiO3 solution, and water, with Na2O accounting for 12% of the alkali content by weight of dry solids, and the molar ratio of SiO2 to Na2O being 1.2.

[0008] The technical solution of the preparation method for grouting materials for multi-source solid waste proposed in this invention includes the following steps:

[0009] Step 1): Dry and sieve the coffee grounds to obtain fine coffee ground powder, and sieve the electric lime; based on 100 parts of dry material, the fine coffee ground powder accounts for 2%-10%, the electric lime accounts for 10%-20%, and the fly ash is used to make up the remainder;

[0010] Step 2): The equivalent amount of Na2O is obtained by summing the contributions of Na2O in NaOH and Na2SiO3, and the amount of alkali is obtained by comparing it with the mass of dry material;

[0011] Step 3): Calculate the total water consumption based on the water-to-solid ratio of 0.75. Mix NaOH solid, Na2SiO3 solution and water in batches and stir. After stirring evenly, seal and let stand to obtain the alkali activator.

[0012] Step 4): Mix coffee grounds powder, carboxylic acid and fly ash, and dry mix until the dry material is uniform in color. Then, add the prepared alkali activator at a uniform speed and wet mix. After mixing evenly, switch to a higher speed for secondary mixing to complete the preparation of the grouting material.

[0013] Further, in step 2), the equivalent amount of Na2O is calculated based on the Na2O mass fraction in the labels of NaOH and Na2SiO3 solutions, and the effective content is calculated based on the purity of NaOH solid to obtain the provided Na2O mass; the Na2O mass provided by the solution is calculated based on the Na2O mass fraction in the label of Na2SiO3 solution, and the two parts of Na2O are added together to obtain the equivalent amount of Na2O.

[0014] Furthermore, in step 3), after deducting the water contained in the Na2SiO3 solution and the water required to dissolve NaOH, the remainder is made up with water, and the alkali dosage is 12%.

[0015] The advantages of this invention using the above technical solution are:

[0016] 1. This invention innovatively uses coffee grounds powder, carboxylic acid, and fly ash as a composite solid phase, and introduces an alkali activator composed of NaOH and Na2SiO3. Through standardized preparation and stirring processes, a gel structure mainly composed of hydrated calcium aluminosilicate is formed. This material system can absorb a high proportion of various industrial and biomass solid wastes, significantly reducing the dependence on cement clinker. Thus, while ensuring the injectability and early strength of the slurry, it achieves a high proportion of absorption of multi-source solid wastes (industrial by-products and biomass wastes). This not only significantly reduces the dependence on cement clinker and expands the application of solid waste resource utilization in engineering fields such as goaf filling and tunnel surrounding rock reinforcement, but also has outstanding advantages in terms of material lightweighting, low carbonization, and cost control.

[0017] 2. This invention utilizes the low-density, porous, and lightweight properties of fine coffee grounds to achieve material lightweighting and microstructure control. Combined with the calcium source and alkaline environment provided by quicklime, the quicklime provides Ca... 2+ This method promotes the activation of Si and Al in fly ash and the formation of a dense gel network, synergistically stimulating the active components in fly ash to form a dense gel network structure mainly composed of hydrated calcium aluminosilicate. This approach addresses the issues of injectability, molding stability, and strength compatibility from the source, thereby enabling the slurry to possess excellent fluidity, molding stability, and early strength.

[0018] 3. In engineering applications, it can achieve high strength and pumpable diffusion properties without the need for foaming or high-cost chemical monomers. It is also highly compatible with existing grouting processes and equipment, and can be widely used in various scenarios such as goaf filling, tunnel surrounding rock fissure repair, and roadbed / bridge foundation reinforcement. At the same time, it significantly reduces clinker dependence through the high proportion of multi-source solid waste utilization, combining green and low-carbon features with cost-effectiveness. Attached Figure Description

[0019] Figure 1 These are the results of the compressive strength test in the embodiments of the present invention;

[0020] Figure 2 These are the flexural strength test results from the embodiments of the present invention;

[0021] Figure 3 The results are from the fluidity test in the examples. Detailed Implementation

[0022] This invention discloses a grouting material for multi-source solid waste, comprising a solid phase and a liquid phase, with a water-to-solid ratio of 0.75. The solid phase consists of fine coffee grounds powder, carboxylic acid, and fly ash. Based on the dry weight of the solid material, the fine coffee grounds powder accounts for 2%–10% of the solid phase, carboxylic acid accounts for 10%–20%, and the remainder is made up with fly ash. The optimal proportion of fine coffee grounds powder is 2%–4%. The liquid phase is an alkali activator composed of solid NaOH, Na₂SiO₃ solution, and water. The alkali content, based on the dry weight of Na₂O, is 12%, and the activator modulus is 1.2, i.e., modulus M = SiO₂ / Na₂O, where M is the molar ratio of SiO₂ to Na₂O.

[0023] Using fine coffee grounds, carboxylic acid, and fly ash as solid phases, and introducing an alkali activator composed of solid NaOH, Na2SiO3 solution, and water, the grout achieves good injectability and meets the 28-day strength requirement within the feasible engineering range of a water-to-solid ratio of 0.75 and an alkali dosage of 12%.

[0024] The preparation method of the multi-source solid waste grouting material includes the following steps:

[0025] Step 1: Raw material pretreatment and solid phase proportioning

[0026] Based on 100 parts of dry materials, coffee grounds fine powder accounts for 2%-10%, carboxylic acid accounts for 10%-30%, and fly ash makes up the remainder.

[0027] Coffee grounds are dried at 60℃ for 24 hours and then passed through a 20-mesh sieve to obtain fine coffee grounds powder. This stabilizes the moisture content and reduces the impact of particle size unevenness on flowability and strength. Carbohydrate lime must be passed through a 20-mesh sieve and sealed to prevent moisture. Fly ash must meet the Class III technical requirements specified in "Fly Ash for Cement and Concrete" (GB1596-2017).

[0028] Step 2: Preparation of Alkali Activator

[0029] Activator Quantification: The equivalent amount of Na2O is calculated based on the Na2O mass fraction stated on the labels of the NaOH and Na2SiO3 solutions. The equivalent amount of Na2O in the alkali activator is obtained by summing the Na2O contributions from NaOH and Na2SiO3. This is used to verify the alkali dosage: The effective content is converted based on the purity of the NaOH solid to obtain the mass of Na2O it can provide. The mass of Na2O provided by the Na2SiO3 solution is calculated based on the Na2O mass fraction stated on the label. The alkali dosage is obtained by adding the two Na2O portions together and comparing them with the dry material mass.

[0030] Water balance: Calculate the total water consumption based on the target water-to-solid ratio; deduct the water contained in the Na2SiO3 solution and the water required to dissolve NaOH, and make up the rest with water, with an alkali dosage of 12% (based on Na2O as a percentage of dry material mass).

[0031] Preparation of alkali activator: In an alkali-resistant container, NaOH solid, Na2SiO3 solution and water are mixed in batches and stirred while adding water and stirring, and the temperature is controlled to avoid overheating. The stirring speed is 150 r / min and the stirring time is 30 minutes. After stirring evenly, the container is sealed with plastic wrap and left to stand for 24 hours to obtain the alkali activator for later use.

[0032] Step 3: Preparation of slurry materials

[0033] Mixing into slurry: Mix fine coffee grounds, carboxylic acid and fly ash, and dry mix at low speed for 60-90 seconds until the dry material is uniform in color. Then, add the prepared alkali activator liquid at a uniform speed and wet mix for 90 seconds until the mixture is uniform. Then, switch to a higher speed for strong secondary mixing for 60 seconds to complete the preparation of the grouting material.

[0034] Molding and Curing: The prepared grouting material was poured into a 40*40*160mm triple cuboid mold and compacted on a vibrating table for 60-90 seconds to remove air bubbles. After pouring, the molded specimens were covered with plastic wrap and left to stand for 24 hours before demolding. After demolding, the specimens were covered with plastic wrap and placed in a shaded area for natural curing until the designated curing age of 28 days. After curing, fluidity, bulk density, and compressive strength tests were then conducted.

[0035] To verify the material properties, performance tests are conducted: the fluidity, density, flexural / compressive strength, and other properties of the slurry are tested according to standard methods and in accordance with relevant national or industry standards; the specimens should preferably be made using a 40*40*160mm triple mold.

[0036] The following are four embodiments of the preparation method of the multi-source solid waste grouting material of the present invention:

[0037] Example 1

[0038] The preparation method of the multi-source solid waste grouting material of the present invention is as follows:

[0039] Step 1: Weigh out 2% fine coffee grounds, 10% carboxylic acid, and 88% fly ash by total dry weight, mix them evenly and set aside.

[0040] Step 2: Using Na₂O as the alkali dosage at 12% of the total dry mass and a SiO₂ / Na₂O molar ratio of 1.2 as the modulus, calculate the required amounts of sodium hydroxide solid and sodium silicate solution. Based on a water-to-solid ratio of 0.75, calculate the total water consumption. After deducting the water contained in the sodium silicate solution and the water needed to dissolve the sodium hydroxide, replenish the remaining mixing water. Mix the water, sodium hydroxide solid, and sodium silicate solution in an alkali-resistant container, stir at 150 rpm for 30 minutes, controlling the temperature to prevent overheating, then seal and let stand for 24 hours to obtain the alkali activator.

[0041] Step 3: Dry-mix the dry materials from Step 1 at a low speed for 60-90 seconds until the color is uniform. Add the alkali activator prepared in Step 2 at a uniform speed and wet-mix for 90 seconds. Then switch to a higher speed and mix again for 60 seconds to obtain a uniform slurry.

[0042] Pour the slurry into a 40*40*160mm triple cuboid mold and vibrate it on a vibrating table for 60-90 seconds to remove air bubbles. After molding, cover the surface of the sample with plastic wrap and let it stand for 24 hours before demolding. After demolding, continue to cover the sample with plastic wrap and place it in a shady place for natural curing until the specified age.

[0043] Example 2

[0044] Step 1: Weigh out 2% fine coffee grounds, 20% carbide lime, and 78% fly ash by total dry weight, mix them evenly and set aside.

[0045] Step 2: Same as step 2 in Example 1.

[0046] Step 3: Same as step 3 in Example 1.

[0047] Example 3

[0048] Step 1: Weigh out 4% fine coffee grounds, 15% carbide lime, and 81% fly ash by total dry weight, mix them evenly and set aside.

[0049] Step 2: Same as step 2 in Example 1.

[0050] Step 3: Same as step 3 in Example 1.

[0051] Example 4

[0052] Step 1: Weigh out 10% fine coffee grounds, 10% carbide lime, and 80% fly ash by total dry weight, mix them evenly and set aside.

[0053] Step 2: Same as step 2 in Example 1.

[0054] Step 3: Same as step 3 in Example 1.

[0055] The compressive strength tested for Examples 1-4 is as follows: Figure 1 As shown, the flexural strength is as follows Figure 2 As shown, the flow diameter is as follows Figure 3 As shown in Table 1, the test results of various technical performance aspects of Examples 1-4 are as follows:

[0056] Table 1

[0057]

[0058] Under the conditions of a fixed water-to-solid ratio of 0.75, an activator modulus of 1.2, and an alkali dosage (calculated as Na2O) of 12%, the results are shown in the table above. Figure 1 (compressive strength) Figure 2 (flexural strength) Figure 3 (Flowability) indicates that: ① When using coffee grounds powder as a lightweight skeleton, there is a certain correlation between lightweighting and mechanical properties: as SCG increases from 2% to 6%, the bulk density gradually decreases, but the compressive and flexural strengths decrease simultaneously. Moreover, when the coffee grounds powder content is ≥6%, the strength decreases more significantly, indicating the adverse effect of coffee grounds powder on the early structural density; ② When the coffee grounds powder content is constant (2%), increasing the carboxylic acid to 20% can significantly reduce the bulk density and maintain a high flowability. However, due to the corresponding reduction in the fly ash content, the strength decreases slightly in the later stages, indicating that there is an optimal balance between fly ash and carboxylic acid; ③ Flowability is more sensitive to the amount of coffee grounds powder: when the coffee grounds powder content is ≤4%, the flowability remains at a high level. Further increases in coffee grounds powder content result in a significant decrease; ④ Considering the three indicators of bulk density, flowability, and compressive strength, the combination of approximately 2%–4% coffee grounds powder and approximately 10%–20% carboxylic acid is more conducive to obtaining a lower bulk density and acceptable mechanical properties while maintaining good injectability, reflecting a parameter window that coordinates lightweighting and load-bearing capacity.

Claims

1. A grouting material for multi-source solid waste, characterized in that: It consists of a solid phase and a liquid phase, with a water-to-solid ratio of 0.

75. The solid phase is composed of fine coffee grounds, carboxylic acid, and fly ash. By weight of dry solids, fine coffee grounds account for 2%–10% of the solid phase, carboxylic acid accounts for 10%–20%, and the remainder is fly ash. The liquid phase is an alkali activator composed of solid NaOH, Na2SiO3 solution, and water. Na2O accounts for 12% of the alkali content by weight of dry solids, and the molar ratio of SiO2 to Na2O is 1.

2.

2. The grouting material for multi-source solid waste according to claim 1, characterized in that: The fine coffee grounds account for 2% to 4% of the solid phase.

3. A method for preparing grouting material for multi-source solid waste as described in claim 1, characterized in that... Includes the following steps: Step 1): Dry and sieve the coffee grounds to obtain fine coffee ground powder, and sieve the electric lime; based on 100 parts of dry material, the fine coffee ground powder accounts for 2%-10%, the electric lime accounts for 10%-20%, and the fly ash is used to make up the remainder; Step 2): The equivalent amount of Na2O is obtained by summing the contributions of Na2O in NaOH and Na2SiO3, and the amount of alkali is obtained by comparing it with the mass of dry material; Step 3): Calculate the total water consumption based on the water-to-solid ratio of 0.

75. Mix NaOH solid, Na2SiO3 solution and water in batches and stir. After stirring evenly, seal and let stand to obtain the alkali activator. Step 4): Mix coffee grounds powder, carboxylic acid and fly ash, and dry mix until the dry material is uniform in color. Then, add the prepared alkali activator at a uniform speed and wet mix. After mixing evenly, switch to a higher speed for secondary mixing to complete the preparation of the grouting material.

4. The preparation method according to claim 3, characterized in that: In step 1), the coffee grounds are dried at 60°C for 24 hours and passed through a 20-mesh sieve. The calcium lime also needs to be passed through a 20-mesh sieve and sealed to prevent moisture.

5. The preparation method according to claim 3, characterized in that: In step 2), the equivalent amount of Na2O is calculated based on the Na2O mass fraction in the labels of NaOH and Na2SiO3 solutions, and the effective content is calculated based on the purity of NaOH solid to obtain the provided Na2O mass; the Na2O mass provided by the solution is calculated based on the Na2O mass fraction in the label of Na2SiO3 solution, and the two parts of Na2O are added together to obtain the equivalent amount of Na2O.

6. The preparation method according to claim 3, characterized in that: In step 3), after deducting the water contained in the Na2SiO3 solution and the water required to dissolve NaOH, the remainder is made up with water, and the alkali dosage is 12%.

7. The preparation method according to claim 3, characterized in that: In step 3), NaOH solid, Na2SiO3 solution and water are added in batches while stirring at a speed of 150 r / min for 30 minutes.

8. The preparation method according to claim 3, characterized in that: In step 4), the coffee grounds powder, carboxylic acid and fly ash are mixed and stirred for 60-90 seconds, then the prepared alkali activator liquid is added at a uniform speed and wet-mixed for 90 seconds, followed by a second stirring for 60 seconds.

9. The preparation method according to claim 3, characterized in that: The prepared grouting material was poured into test blocks, and after pouring, the blocks were covered and left to stand for 24 hours before being demolded. After demolding, the blocks were placed in a shady place for natural curing until the desired age was reached. After curing, the flowability, density and compressive strength properties were tested.

10. The preparation method according to claim 9, characterized in that: The prepared grouting material is poured into a 40*40*160mm triple rectangular mold and placed on a vibrating table for 60s-90s to remove air bubbles; the curing time is 28 days.

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