A waste fly ash block and its preparation method

Abstract

This application relates to the field of concrete block technology, specifically to a waste fly ash block and its preparation method. In this application, by treating waste fly ash raw materials and then agglomerating them with an acrylamide system, and adding asphalt as a binder, the processing performance and mechanical strength of the prepared blocks are improved.

Description

Technical Field

[0001] This application relates to the field of concrete block technology, specifically to a waste fly ash block and its preparation method. Background Technology

[0002] The treatment of fly ash from municipal solid waste has always been a challenge in urban waste management. Fly ash primarily consists of metal oxides, such as a silica-alumina composite system, and also contains components like calcium oxide, magnesium oxide, and iron oxide. Currently, using fly ash as a concrete raw material is an important approach. By replacing part of the cement with fly ash as a gelling material, it can participate in the hydration reaction, and the fly ash itself can also act as a gas-generating agent, thus enabling the production of concrete blocks with lower density.

[0003] While fly ash contains elements like calcium oxide and silica, which can participate in hydration reactions, in practice, it can impair the cohesion and workability of concrete to some extent. Measurements show that when the fly ash to cement ratio is close to 1:1, a higher water-cement ratio is required to achieve good workability in high-pressure block production, but this higher ratio negatively impacts the system's strength. Summary of the Invention

[0004] This application provides a waste fly ash block and its preparation method, which can be configured with a low water-cement ratio, and the prepared block has good workability and can ensure that its strength and density are at a high level.

[0005] First, this application provides a waste fly ash block, the material of which comprises the following components by weight:

[0006] 40 parts cement

[0007] 58-66 parts coarse aggregate

[0008] 24-30 portions of sand

[0009] 55-60 parts of fly ash granules from waste

[0010] 1.5 to 3 parts asphalt

[0011] Activator 0.1 to 1 part

[0012] 2-3 parts water-reducing agent

[0013] 10-15 parts water

[0014] The waste fly ash granules are obtained through the following steps:

[0015] S1. Thoroughly soak the waste fly ash raw material in ammonium chloride;

[0016] S2. Add polyacrylamide to the system to induce coagulation, obtain the precipitate, and dry it.

[0017] S3. Crush the dried system to a size not exceeding 325 mesh;

[0018] In addition, in step S3, a silicon-calcium-aluminum regulator may be optionally added. The silicon-calcium-aluminum regulator is any number of calcium sulfate, aluminum powder or silicon dioxide. After the waste fly ash granules and the silicon-calcium-aluminum regulator are mixed, the mass ratio of silicon (calculated as silicon dioxide), calcium (calculated as calcium oxide) and aluminum (calculated as aluminum oxide) is 10:(7.5-8):(0.3-0.4).

[0019] In the above scheme, asphalt is first added to the system. Although asphalt has a high density, which is contrary to the purpose of reducing the overall weight, it can adjust the cohesion in the system and form a better flow system, so that the prepared waste fly ash block mortar has good fluidity and good curability.

[0020] Based on the above, this application further processes the waste fly ash raw material. First, after soaking in ammonium chloride, the waste fly ash raw material can effectively remove harmful components and reduce environmental pollution. Whether used for concrete pouring or for precast components or blocks, it can reduce its damage to the environment. Based on the above, the waste fly ash is settled by polyacrylamide, dried and crushed to form a composite structure of waste fly ash and polyacrylamide. This structure has good dispersibility and flowability in the system and slightly slows down the hydration reaction. Therefore, in the system, the cement system will hydrate first, while the waste fly ash particles will be supplemented later, achieving a good hydration reaction process. The surface is stable and the cohesion is good, resulting in high strength blocks.

[0021] Preferably, in the waste ash pellet treatment step S1, the ammonium chloride solution is 10-20 g / L; the treatment time is 30-50 min.

[0022] The above treatment steps can effectively remove impurities from waste fly ash and have little impact on the silicon, calcium, and aluminum systems in the waste fly ash, thereby improving the application effect of waste fly ash when used in building blocks.

[0023] Preferably, in step S2, the mass ratio of polyacrylamide to fly ash raw material is 1:20 to 50.

[0024] Within this range, it can not only better settle the solid components of waste ash in the system, but also improve the ability of waste ash to participate in the reaction within the system and improve its workability, resulting in blocks with better strength.

[0025] Preferably, it also includes 1 to 1.5 parts by weight of borate.

[0026] Borate further improves the fluidity and leveling properties of the slurry in the system, while also significantly enhancing its crack resistance.

[0027] Preferably, the asphalt is SBS modified asphalt.

[0028] In the above scheme, SBS modified asphalt was used. Compared with unmodified asphalt, SBS modified asphalt can improve the overall dispersibility and flowability while maintaining good viscosity. Under this system, the flowability and leveling properties of the slurry can be improved while maintaining similar strength. In addition, SBS modified asphalt can also improve visual dispersibility, further reducing the effect of asphalt on increasing density, so that the prepared blocks have a density system that is basically the same as that of blocks without added asphalt.

[0029] Further preferably, SBS modified asphalt can be obtained by stirring and heating asphalt raw materials, SBS, crosslinking agents, and other additives in a high-speed mixer at a certain temperature, typically 120–170°C, to achieve the reaction. In some preferred embodiments, the SBS in the SBS modified asphalt accounts for 4.0–4.2% of the initial asphalt mass. In other preferred embodiments, the SBS modified asphalt is obtained by co-modifying the initial asphalt and SBS with a vulcanizing crosslinking agent accounting for 1–1.5% of the pure asphalt mass and a polyethylene wax accounting for 2–2.5% of the asphalt mass.

[0030] The SBS modified asphalt obtained through the above modifications exhibits better overall performance in the system and shows a significant improvement in the mechanical properties of the prepared blocks.

[0031] Preferably, the activator is a sodium silicate activator, and the water-reducing agent is a compound system formed by polycarboxylate water-reducing agent and calcium lignosulfonate water-reducing agent in a mass ratio of 1:4 to 8.

[0032] Experiments have shown that the above-mentioned activator and water-reducing agent can achieve a more balanced reaction rate, mechanical strength and workability in the system.

[0033] In addition, this application also relates to a method for preparing the above-mentioned waste fly ash blocks, including the following steps:

[0034] A. Mix cement, fly ash granules, and water to initially form a slurry;

[0035] B. Mix the remaining materials with the above slurry and stir until homogeneous;

[0036] C. After the above materials are mixed evenly, they are injected into the mold to form the product;

[0037] D. Initial setting at 40-50℃ for 200-270 minutes;

[0038] E. Curing with pressurized steam until it is formed.

[0039] The blocks prepared by the above method have high overall strength, strong mortar fluidity, and are relatively easy to construct. The strength of the blocks is comparable to that of precast concrete components, showing broad application prospects. Based on the above, the parameters in step E are preferably within the following ranges: pressure 0.8–1.0 MPa, temperature 180–185℃. Blocks cured within the above parameter range have better mechanical properties, a smooth and crack-free surface, and good strength.

[0040] It should be noted that during the above process, the concrete can be cut after initial setting to prepare a block system with the target size. Alternatively, it can be directly added to a mold of the corresponding shape for testing.

[0041] In summary, this application provides a waste fly ash block and its preparation method. By adding asphalt components and pretreating the waste fly ash, the fly ash and polyacrylamide form granules that participate in the hydration reaction, improving the system's strength and flowability. Even with a low water-cement ratio, good processing performance is maintained. Furthermore, by using SBS-modified asphalt, better flow and leveling properties can be achieved compared to ordinary asphalt. Detailed Implementation

[0042] In the description of this specification, the references to "certain embodiments," "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples" refer to specific features, structures, materials, or characteristics described in connection with the described embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0043] The technical solution of this application is verified through the following embodiments.

[0044] In this application, the quality of the product is determined by measuring the mechanical properties of the final product and the slump of the concrete during processing. Specifically, a higher slump indicates stronger fluidity. Therefore, under the same water-cement ratio, concrete with a better slump has stronger processing performance when the density and compressive strength are similar. Correspondingly stronger processing performance also means that the concrete blocks themselves have good uniformity and are less prone to internal or surface cracks.

[0045] In Example 1, the main focus was on the waste fly ash aggregate used in the concrete, and it was compared with a comparative example, as follows.

[0046] Example 1 relates to a waste fly ash block and its preparation method, with the following specific components:

[0047] 40 parts of cement: 42.5 silicate cement should be used;

[0048] 60 parts coarse aggregate: Perlite is selected. Perlite itself has a low density, which can further reduce the density of the blocks.

[0049] Sand 27 parts: uniformly graded manufactured sand was selected;

[0050] 58 portions of waste fly ash granules;

[0051] Two parts of SBS modified bitumen;

[0052] Sodium silicate activator 0.5 parts;

[0053] Two parts of water-reducing agent, specifically BASF polycarboxylate superplasticizer RHEOPLUS 420 and calcium lignosulfonate, wherein the mass of polycarboxylate superplasticizer is 0.4 parts and the mass of calcium lignosulfonate is 1.6 parts.

[0054] 12 parts water;

[0055] 1.5 parts of borate.

[0056] Specifically, the preparation method of waste fly ash granules is as follows:

[0057] S1. Treat the fly ash from the waste in a 10 g / L ammonium chloride solution for 50 min;

[0058] S2. Add polyacrylamide to the system to cause it to precipitate, then separate it by spun filtration and dry it.

[0059] S3. After drying, the system is crushed to 325 mesh.

[0060] It should be noted that in the above steps, the concentration of ammonium chloride can be 10-20 g / L, and the corresponding treatment time can be 30-50 min. Generally, the higher the concentration of ammonium chloride, the shorter the treatment time. Step S3 can be carried out by grinding, air drying, and crushing. This system is relatively easy to crush after air drying. Specifically, in this embodiment, different amounts of polyacrylamide were selected to obtain different experimental groups. The mass fractions of polyacrylamide used for each mass fraction of waste fly ash raw material in different experimental groups are as follows:

[0061] Example 1-1: 0.01 parts

[0062] Example 1-2: 0.02 parts

[0063] Examples 1-3: 0.025 parts

[0064] Examples 1-4: 0.03 parts

[0065] Examples 1-5: 0.04 parts

[0066] Examples 1-6: 0.05 parts

[0067] Examples 1-7: 0.06 parts

[0068] Examples 1-8: 0.08 copies.

[0069] Furthermore, in this embodiment, the mass of the materials in the waste fly ash raw material is determined by elemental analysis, and a calcium-silicon-aluminum regulator is added in step S3 to adjust the proportions. The mass ratio of silicon (calculated as silicon dioxide), calcium (calculated as calcium oxide), and aluminum (calculated as aluminum oxide) in the waste fly ash raw material is 10:5.549:2.107. Therefore, aluminum powder and silicon dioxide need to be added to make the mass ratio of silicon (calculated as silicon dioxide), calcium (calculated as calcium oxide), and aluminum (calculated as aluminum oxide) in the final waste fly ash granules 10:7.5:0.36. In other embodiments, if the source of the waste fly ash raw material is different, the mass of calcium, silicon, and aluminum it contains will also be different. Calcium sulfate, aluminum powder, or silicon dioxide can be optionally added to adjust the composition.

[0070] The preparation method of SBS modified bitumen is as follows:

[0071] After mixing pure asphalt with SBS, vulcanizing crosslinking agent and polyethylene wax, the mixture is stirred at high speed at 180°C for 120 minutes. Specifically, SBS accounts for 4% of the mass of pure asphalt, polyethylene wax accounts for 2.5% of the mass of pure asphalt, and dithiodimorpholine is selected as the vulcanizing crosslinking agent.

[0072] Accordingly, in Comparative Example 1, the same silicon-calcium-aluminum ratio as in the Example was adjusted to the same mass of untreated waste ash and silicon-calcium-aluminum modifier, and the same blocks were prepared.

[0073] The preparation methods of the waste fly ash blocks in Example 1 and Comparative Example 1 include the following steps:

[0074] A. Mix cement, fly ash granules, and water to initially form a slurry;

[0075] B. Mix the remaining materials with the above slurry and stir until homogeneous;

[0076] C. After the above materials are mixed evenly, they are injected into the mold to form the product;

[0077] D. Initial setting for 250 minutes within a controlled temperature range of 40–50℃. It should be noted that a good initial setting effect can be achieved within this temperature range. The surface condition can be observed during initial setting to determine the desired result; once initial setting is achieved, it is sufficient. Due to the addition of sodium borate, the setting time of the above system is relatively long, making it more suitable for actual processing. The setting time will vary slightly depending on the temperature and can be adjusted according to the actual process. However, it is important to note that excessively high temperatures can cause instability in the gas within the system, leading to bubble collapse and defects or cracks on the surface of the blocks.

[0078] E. Curing under pressure at 1.0 MPa and 180°C until molded.

[0079] It should be noted that in this application, the amount of coarse aggregate can be arbitrarily adjusted from 58 to 66 parts, while the amount of sand can be adjusted from 24 to 30 parts. The amounts of both are related to gradation and materials, and overall, the above ranges are acceptable. The amount of activator can be adjusted according to actual needs. It can promote concrete reaction and crystallization, and correspondingly accelerate concrete setting. If a certain degree of retarding is required, the amount of activator can be reduced, which will correspondingly extend the autoclaving time. Overall, adjustments within the range of 0.1 to 1 part are feasible.

[0080] The overall results for the waste fly ash blocks in Example 1 and Comparative Example 1 are shown in Table 1.

[0081] Table 1. Experimental results of Example 1 and Comparative Example 1

[0082]

[0083]

[0084] It is easy to see from the above data that, compared with Example 1 and Comparative Example 1, the addition of polyacrylamide to treat waste fly ash can effectively improve the workability and strength of the system. Overall, the relationship between the amount of polyacrylamide added to the system and the strength is that it first increases and then decreases. Although the increase in the amount of polyacrylamide will improve the fluidity, it will also have a certain impact on the participation of the waste fly ash system in the hydration reaction, which will lead to a decrease in the strength of the prepared blocks.

[0085] Example 2, based on Examples 1-4, evaluates the impact of different silicon-calcium-aluminum modifiers on the composition of waste fly ash on the block structure by adding different modifiers. The proportions of silicon-calcium-aluminum components in each experimental group are shown in Table 2.

[0086] Table 2. Composition ratio of fly ash particles in Example 2

[0087]

[0088] Experiments were conducted on Example 2 and the corresponding comparative examples, and the results are shown in Table 3.

[0089] Table 3 shows the experimental results of Example 2 and Comparative Examples 2-5.

[0090]

[0091]

[0092] The experimental results above show that the mass ratio of silicon, calcium, and aluminum in the waste ash should be strictly controlled within a certain range. Excessive aluminum content will severely affect the strength of the system, while insufficient aluminum content will lead to poor gas production, resulting in a significant increase in the dry density of the blocks. Calcium, on the other hand, has a significant regulatory effect on hydration; too much or too little calcium will significantly affect compressive strength.

[0093] Example 3: In this example, based on Examples 1-4, the overall dosage of waste ash fly granules and the overall water-cement ratio were further adjusted, as shown in Table 4.

[0094] Table 4

[0095]

[0096] The results of the test on Example 3 are shown in Table 5.

[0097] Table 5. Experimental results of Example 3

[0098]

[0099]

[0100] The experimental data above shows that when the selection and dosage of water-reducing agent are the same, and the amount of fly ash granules is 55-60 parts, a relatively good balance between compressive strength and workability can be achieved within a wide water-cement ratio range. Within the block system, workability is directly related to strength; poor flowability of the mortar usually leads to a decrease in overall strength. This is because internal cracks and large voids are prone to occur, especially in the aerated system of this application. If the flowability is poor, the internal air is easily agglomerated into large air bubbles, which significantly impairs strength. In this application, whether the amount of fly ash granules is too much or too little, it will adversely affect the strength of the system, resulting in a smaller usable water-cement ratio range. Adding less water to improve overall strength leads to a lower yield and less effective strength improvement. Furthermore, insufficient addition of fly ash granules can also result in poorer gas generation and increased dry density.

[0101] Example 4: This example further studies the effect of asphalt modification on the system based on Examples 1-4. It should be noted that in the specific process of asphalt modification, the amount of vulcanizing crosslinking agent and the processing time can be selected according to existing technical literature. Different vulcanizing crosslinking agents have different applicable temperatures and different processing times, and all have a modification effect on the system. In this example, only the effects of SBS addition and polyethylene wax addition on the performance of asphalt in blocks are discussed. The specific experimental groups are shown in Table 6.

[0102] Table 6

[0103]

[0104]

[0105] Another comparative example, Example 6, was provided, in which only unmodified asphalt was used. The experimental results of Example 4 and Comparative Example 6 are shown in Table 7.

[0106] Table 7, Experimental Results of Example 4 and Comparative Example 6

[0107]

[0108] The above experiments clearly show that unmodified asphalt in this system is prone to reduced fluidity, which in turn leads to a decrease in compressive strength. Overall, the compressive strength of the blocks is correlated with the amount of SBS added, which first increases and then decreases. Excessive SBS addition will cause the asphalt to lose its bonding properties in the system, thus affecting the overall strength.

[0109] The addition of polyethylene wax has a certain impact on the strength and properties of asphalt itself. Examples 4-9, without the addition of polyethylene wax, show a significant decrease in fluidity. Excessive addition of polyethylene wax also affects gas production performance to some extent. For example, although the fluidity of Examples 4-10 is still acceptable, the dry density increases significantly with a small change in compressive strength. This may be because polyethylene wax itself has the effect of inhibiting gas production within concrete.

[0110] Example 5: Based on Examples 1-4, the amount of asphalt was further adjusted, and the experimental results are shown in Table 8.

[0111] Table 8. Experimental results of Example 5 and Comparative Examples 7-9

[0112]

[0113]

[0114] The above experiments show that the amount of asphalt added is generally positively correlated with dry density, but the effect is relatively small. However, when the amount of asphalt added exceeds 4 parts, there is an inflection point where the density of the blocks increases significantly. This may be because after the asphalt exceeds the critical point, it can form a continuous structure within the system, affecting the formation of cavities. Without asphalt, a significant decrease in strength will occur.

[0115] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A type of waste fly ash block, characterized in that, Its materials, by mass, include the following components: 40 parts cement 58-66 parts coarse aggregate 24-30 portions of sand 55-60 parts of fly ash granules from waste 1.5 to 3 parts asphalt Activator 0.1 to 1 part 2-3 parts water-reducing agent 10-15 parts water The waste fly ash granules are obtained through the following steps: S1. Thoroughly soak the waste fly ash raw material in ammonium chloride; S2. Polyacrylamide is added to the system to induce coagulation, and the precipitate is obtained after separation and dried. S3. Crush the dried system to a size not exceeding 325 mesh; In addition, in step S3, a silicon-calcium-aluminum regulator is added. The silicon-calcium-aluminum regulator is any number of calcium sulfate, aluminum powder, or silicon dioxide. After the waste fly ash granules and the silicon-calcium-aluminum regulator are mixed, the mass ratio of silicon, calcium, and aluminum is 10:(7.5-8):(0.3-0.4), wherein the mass of silicon is calculated as silicon dioxide, the mass of calcium is calculated as calcium oxide, and the mass of aluminum is calculated as aluminum oxide.

2. The waste fly ash block according to claim 1, characterized in that, In step S1 of the waste ash and fly ash treatment, the ammonium chloride solution is 10-20 g / L; the treatment time is 30-50 min.

3. The waste fly ash block according to claim 1, characterized in that, In step S2, the mass ratio of polyacrylamide to waste fly ash raw material is 1:20-50.

4. A waste fly ash block according to claim 1, characterized in that, It also includes 1 to 1.5 parts by weight of borate.

5. A waste fly ash block according to claim 1, characterized in that, The asphalt is SBS modified asphalt.

6. A waste fly ash block according to claim 5, characterized in that, In the SBS modified asphalt, the mass of SBS accounts for 4.0 to 4.2% of the initial asphalt mass.

7. A waste fly ash block according to claim 6, characterized in that, The SBS modified asphalt is obtained by co-modifying the initial asphalt and SBS with a vulcanizing crosslinking agent accounting for 1-1.5% of the mass of pure asphalt and a polyethylene wax accounting for 2-2.5% of the mass of asphalt.

8. A waste fly ash block according to claim 1, characterized in that, The activator is a sodium silicate activator, and the water-reducing agent is a compound system formed by polycarboxylate water-reducing agent and calcium lignosulfonate water-reducing agent in a mass ratio of 1:4 to 8.

9. The method for preparing waste fly ash blocks according to any one of claims 1 to 8, characterized in that, Includes the following steps: A. Mix cement, fly ash granules, and water to initially form a slurry; B. Mix the remaining materials with the above slurry and stir until homogeneous; C. After the above materials are mixed evenly, they are injected into the mold to form the product; D. Initial setting at 40-50℃ for 200-270 minutes; E. Curing with pressurized steam until it is formed.

10. The method for preparing a waste fly ash block according to claim 9, characterized in that, In step E, the pressure is 0.8–1.0 MPa and the temperature is 180–185 °C.

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