Modified recycled coarse aggregate and preparation method thereof

Abstract

The invention discloses a modified recycled coarse aggregate and a preparation method thereof, and belongs to the field of recycled coarse aggregate concrete. The modified recycled coarse aggregate is prepared from the following raw materials: recycled coarse aggregate, water, a biomass ash composite modifier, sodium hydroxide, polyethyleneimine and cyclodextrin, wherein the biomass ash composite modifier comprises biomass ash, lime, gypsum, methyl cellulose, polyethylene glycol and a composite suspension stabilizer. The preparation method comprises the following steps: preparing a biomass ash composite modifier; mixing the raw materials: uniformly mixing the water, the biomass ash composite modifier and cyclodextrin, and adding the cleaned recycled coarse aggregate; performing electrochemical modification treatment on the mixed slurry; and carrying out post-treatment on the electrochemical modified slurry. The modified recycled coarse aggregate provided by the invention can achieve the effects of high strength, strong durability and low water absorption. The preparation method of the modified recycled coarse aggregate provided by the invention can achieve the effects of saving cost and protecting environment.

Description

Technical Field

[0001] The present invention relates to recycled coarse aggregate concrete, and particularly to a modified recycled coarse aggregate and a preparation method thereof. Background Art

[0002] With the acceleration of the urbanization process and the continuous advancement of infrastructure construction, the generation amount of construction waste increases year by year, and concrete construction waste occupies a quite large proportion. As the main component of concrete construction waste, the reuse of recycled coarse aggregate is of great significance for reducing resource waste and environmental pollution. However, the old mortar layer attached to the surface of recycled coarse aggregate results in high water absorption rate, low apparent density and large crushing value, seriously affecting its application performance in concrete.

[0003] At present, domestic and foreign scholars have carried out modification treatments on recycled coarse aggregate by physical, chemical and biological methods to improve its performance.

[0004] Physical methods such as mechanical grinding and heat treatment can remove part of the old mortar, but fine cracks are easily generated in the recycled coarse aggregate during the mechanical grinding process, resulting in secondary damage to the recycled coarse aggregate; the heat grinding method not only has high requirements for processing equipment, but also has deficiencies such as high energy consumption.

[0005] Chemical methods such as acid pickling use acid solution to dissolve the mineral components in the old mortar on the surface of recycled coarse aggregate, so that the old mortar is peeled off from the surface of the original aggregate. Although it can improve the activity of recycled coarse aggregate, there are problems of environmental pollution and high treatment cost.

[0006] Biological methods such as microbial mineralization deposition method selectively fill the fine cracks of recycled coarse aggregate by inducing the calcium carbonate deposition function of microorganisms. The biological method can effectively reduce the water absorption rate of recycled coarse aggregate, but the survival ability of microorganisms in cement concrete is weak, and pores will remain in the matrix after they lose their activity, thus having an adverse effect on the performance of recycled coarse aggregate concrete. Summary of the Invention

[0007] Object of the Invention: The object of the present invention is to provide a modified recycled coarse aggregate with high strength, strong durability and low water absorption rate.

[0008] Another object of the present invention is to provide a preparation method of modified recycled coarse aggregate that saves cost and protects the environment.

[0009] Technical solution: The modified recycled coarse aggregate of the present invention, by weight, comprises the following raw materials: 800 - 1100 parts of recycled coarse aggregate, 280 - 430 parts of water, 185 - 270 parts of biomass ash composite modifier, 14 - 22 parts of sodium hydroxide, 5 - 8 parts of polyethyleneimine, and 3 - 7 parts of cyclodextrin; wherein, the biomass ash composite modifier, by weight, comprises the following raw materials: 85 - 125 parts of biomass ash, 45 - 70 parts of lime, 30 - 50 parts of gypsum, 8 - 13 parts of methyl cellulose, 7 - 10 parts of polyethylene glycol, and 2 - 5 parts of composite suspension stabilizer; the composite suspension stabilizer is xanthan gum / Na2SiO3 with a mass ratio of 1:25.

[0010] Preferably, the modified recycled coarse aggregate is prepared by an electrochemical modification technique.

[0011] Preferably, the recycled coarse aggregate further comprises 2 - 5 parts by weight of anhydrous calcium chloride.

[0012] A preparation method of the modified recycled coarse aggregate according to claim 1, comprising the following steps:

[0013] (1) Prepare the biomass ash composite modifier: Calcinate and grind the biomass ash, and then fully mix it with lime, gypsum, dispersant, and suspension stabilizer;

[0014] (2) Mix the raw materials: Mix water, biomass ash composite modifier, and cyclodextrin evenly, add the washed recycled coarse aggregate, and then mix and let stand to obtain a recycled coarse aggregate mixed slurry;

[0015] (3) Electrochemical modification: Add sodium hydroxide electrolyte to the mixed slurry obtained in step (2), and perform electrochemical modification treatment on it using a DC power supply;

[0016] (4) Post-treatment: Cure, wash, and dry the electrochemically modified slurry to obtain the modified recycled coarse aggregate.

[0017] Preferably, the biomass ash in step (1) is one or more of rice husk ash, bark ash, wheat straw ash, corn stalk ash, and cotton stalk ash; its preparation method is to calcine commercially available biomass into ash.

[0018] The dispersant is one or more of methyl cellulose and polyethylene glycol; the suspension stabilizer is a xanthan gum / Na2SiO3 composite suspension stabilizer with a mass ratio of 1:25.

[0019] Preferably, the average particle size of the recycled coarse aggregate in step (1) is 9.5 - 26.5 mm; the equipment used for grinding is a ball mill, and the grinding duration is 60 - 90 min.

[0020] Preferably, the calcination temperature in step (1) is 600 - 900 °C, and the calcination time is 3 - 6 h.

[0021] Preferably, the static temperature in step (2) is 20 - 30 °C, and the static time is 1 - 3 h.

[0022] Preferably, the addition amount of the biomass ash composite modifier in step (2) is 185 - 270 parts by weight.

[0023] Preferably, the current used in the electrochemical modification treatment in step (3) is 3 - 7 A, and the treatment duration is 45 - 110 min.

[0024] Preferably, the equipment used for curing in step (4) is a standard constant temperature and humidity curing box, the curing temperature is 25 ± 2 °C, the curing humidity is 95 ± 3%, and the curing duration is 48 - 72 h; the drying temperature in step (4) is 40 - 70 °C, and the duration is 36 - 60 h.

[0025] Principle of the invention: Biomass ash is the particulate powder formed by the combustion and grinding of agricultural and forestry waste. Its chemical composition is similar to that of traditional mineral admixtures, containing abundant active components such as SiO2 and Al2O3, and having high pozzolanic activity. It reacts with the hydration product Ca(OH)2 in the old mortar on the surface of recycled coarse aggregate to generate gels such as C - S - H and C - A - H, or convert C - S - H with a high calcium - silicon ratio into C - S - H with a low calcium - silicon ratio. These gels will fill part of the pores in the old mortar layer, improve the mortar density, enhance the bonding degree of each component, thereby improving the new - old mortar interface performance and enhancing the strength and durability of recycled coarse aggregate.

[0026] Due to the high - temperature combustion during the formation process of biomass ash, the active particles such as SiO2 and Al2O3 in its microstructure are sintered into glass - like particles, and the silicon - aluminum bonds are combined and difficult to break in the water environment, resulting in the difficulty of fully exerting the pozzolanic activity of biomass ash at normal temperature and the need for certain activation means to improve its reaction efficiency.

[0027] Electrochemical surface modification occurs by changing the oxidation state through electron transfer. Electrochemical oxidation is usually used for the functionalization of solid material surfaces to increase the surface energy and roughness of the mortar layer on the surface of recycled coarse aggregates, provide the activation energy required for the reaction, and significantly improve its adhesion to the matrix polymer, enabling the effective components in the paste to form an adsorption layer with a larger coverage on the mortar surface, increasing the total amount of effective components adsorbed per unit area of the mortar, and accelerating the hydration reaction rate of the cementitious material. Electrochemical modification is usually used for the grafting of surface coatings or functional groups on solid materials, and electrochemical oxidation is selective and will preferentially occur at cracks or depressions in the material. In the application of recycled coarse aggregate modification, it can repair the surface defects of the mortar layer and improve the strength of recycled coarse aggregates.

[0028] The present invention applies the electrochemical modification technology to the strengthening treatment of recycled coarse aggregates, fully activates the activity of biomass ash through the method of electrochemical modification, enables the biomass ash to react with the old mortar on the surface layer of recycled coarse aggregates, generates gels to fill part of the pores of the old mortar layer, improves the mortar density, and further improves the strength and durability of recycled coarse aggregates. This method can not only improve the modification efficiency, but also save the treatment time and raw material consumption.

[0029] This method uses xanthan gum (HJ) / Na2SiO3 as a composite suspension stabilizer. The suspension stabilizer is composed of an insoluble or slightly soluble solid active ingredient with the help of certain auxiliaries, and is uniformly dispersed in water through ultrafine grinding to form a stable liquid-solid system with fine particles, high suspension, and fluidity. The addition of the suspension stabilizer can increase the suspension stability of the modified recycled coarse aggregate paste system, reduce the sedimentation rate of the particles therein, and make the reaction between the effective components in the paste and the old mortar on the surface layer of recycled coarse aggregates more sufficient.

[0030] Lime and gypsum participate in the hydration reaction to generate ettringite and calcium silicate hydrate gels, forming a stable crystal structure while providing a certain strength, playing a skeletal role.

[0031] Polyethylene glycol and methyl cellulose are used as dispersants. The lipophilic groups therein adsorb on the surfaces of biomass ash, lime, and gypsum particles, and the hydrophilic groups combine with water, reducing the interfacial free energy, increasing the degree of wetting of solid particles by water, and at the same time forming a double electric layer, making the solid particles move away from each other due to electrostatic repulsion. These two aspects make these effective components more easily and evenly distributed in water, making it easier to react with Ca(OH)2, C-S-H gels, etc. in the old mortar. After the dispersant adsorbs on the particle surface, the steric hindrance effect between the dispersant molecules can be used to prevent the agglomeration of particles, thereby reducing the viscosity of the paste and forming a steric hindrance effect.

[0032] Cyclodextrin, as a commonly used retarder, adsorbs on the surfaces of solid particles in the paste, playing a role in prolonging the setting time of the paste.

[0033] Polyethyleneimine plays the role of a catalyst and a supporting framework during the reaction process.

[0034] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) This method applies the electrochemical modification technology to the strengthening treatment of recycled coarse aggregates, stimulates the activity of biomass ash through the method of electrochemical modification, and improves the strength and durability of recycled coarse aggregates; (2) This method uses a composite modifier mainly composed of biomass ash to strengthen recycled coarse aggregates, effectively realizing the comprehensive utilization of biomass ash, a kind of agricultural and forestry waste, which helps to solve the problem of surplus agricultural and forestry waste and insufficient mineral raw materials in some areas, and provides a solution idea for replacing industrial waste with agricultural and forestry waste; (3) This method applies the electrochemical modification technology to the field of strengthening recycled coarse aggregates, treats the surface mortar layer of recycled coarse aggregates, further improves the strengthening efficiency and effect of recycled coarse aggregates, can save the treatment time and raw material consumption of recycled coarse aggregates, and helps to promote the practical application; (4) Through the reasonable blending of various auxiliary materials such as dispersants, suspension stabilizers, retarders, catalysts, etc., the modification effect, rate and reaction stability are further improved, which helps to be practically applied in industrial production; (5) This method can effectively improve the performance of recycled coarse aggregates, broaden their application channels, and also realize the comprehensive utilization of agricultural and forestry waste, having important environmental and economic benefits. Specific embodiments

[0035] The technical solution of the present invention will be further described below in conjunction with the embodiments.

[0036] Example 1

[0037] The modified recycled coarse aggregates of the present invention, by weight, include the following raw materials: 950 parts of recycled coarse aggregates with an average particle size of 16 mm, 350 parts of water, 185 parts of biomass ash composite modifier, 18 parts of sodium hydroxide, 3 parts of anhydrous calcium chloride, 7 parts of polyethyleneimine, and 5 parts of cyclodextrin; the biomass ash composite modifier, by weight, includes the following raw materials: 85 parts of biomass ash, 45 parts of lime, 30 parts of gypsum, 11 parts of methyl cellulose, 9 parts of polyethylene glycol, and 5 parts of xanthan gum / Na2SiO3 composite suspension stabilizer with a mass ratio of 1:25.

[0038] The biomass ash is corn stalk ash, and its preparation method is to calcine commercially available corn stalks into ash.

[0039] The preparation method of the modified recycled coarse aggregates of the present invention includes the following steps: (the addition amount of each substance is by weight)

[0040] (1) Calcinate 85 parts of biomass ash in a muffle furnace at 700 °C for 4 h. Place the obtained biomass ash clinker in a ball mill and grind it for 75 min. Thoroughly mix the obtained finely ground biomass ash with 45 parts of lime, 30 parts of gypsum, 11 parts of methyl cellulose, 9 parts of polyethylene glycol, and 5 parts of xanthan gum / Na2SiO3 composite suspension stabilizer with a mass ratio of 1:25 by mechanical stirring to obtain a biomass ash composite modifier.

[0041] (2) Mix 1 / 2 (i.e., 175 parts) of the total amount of water, 2 / 3 (i.e., 123 parts) of the biomass ash composite modifier, and 5 parts of cyclodextrin into a uniform slurry by mechanical stirring. Wash the sediment on the surface of the recycled coarse aggregate by soaking and rinsing, then add it to the slurry and mix evenly by mechanical stirring. Let it stand at 25 °C for 2 h to obtain a recycled coarse aggregate mixed slurry.

[0042] (3) Add the remaining 1 / 2 (i.e., 175 parts) of water, 18 parts of sodium hydroxide, and 3 parts of anhydrous calcium chloride to the mixed slurry obtained in step (2) and mix evenly by mechanical stirring. Use an adjustable regulated DC power supply with an output current of 4 A to perform electrochemical modification treatment on the slurry impregnated with recycled coarse aggregate for 70 min. During this period, pay attention to ensuring full contact between the electrode plate and the slurry, and ensure that the gas generated during the electrochemical modification treatment can be fully released.

[0043] (4) Add the remaining 1 / 3 (i.e., 62 parts) of the biomass ash composite modifier and 9 parts of polyethyleneimine to the slurry obtained in step (3) and mix evenly by mechanical stirring. Place it in a standard constant temperature and humidity curing box (curing temperature 25 °C, curing humidity 95%) for 60 h. Wash off the excess slurry on the surface of the recycled coarse aggregate after curing, and place it in a drying oven to dry at 55 °C for 48 h to obtain modified recycled coarse aggregate.

[0044] Example 2

[0045] In this example, the same parts as in Example 1 will not be elaborated. The difference lies in: the addition amount of the biomass ash composite modifier is 235 parts; the biomass ash composite modifier in parts by weight includes the following raw materials: 110 parts of biomass ash, 60 parts of lime, 40 parts of gypsum, 11 parts of methyl cellulose, 9 parts of polyethylene glycol, and 5 parts of xanthan gum / Na2SiO3 composite suspension stabilizer.

[0046] Example 3

[0047] In this comparative example, the same parts as in Example 1 will not be elaborated again. The differences are as follows: the addition amount of the biomass ash composite modifier is 270 parts; the biomass ash composite modifier comprises the following raw materials in parts by weight: 125 parts of biomass ash, 70 parts of lime, 50 parts of gypsum, 11 parts of methylcellulose, 9 parts of polyethylene glycol, and 5 parts of xanthan gum / Na2SiO3 composite suspension stabilizer.

[0048] Example 4

[0049] In this example, the same parts as in Example 1 will not be elaborated again. The differences are as follows:

[0050] In step (1), the calcination temperature is 900 °C and the calcination time is 6 h.

[0051] Example 5

[0052] In this example, the same parts as in Example 1 will not be elaborated again. The differences are as follows:

[0053] In step (1), the calcination temperature is 800 °C and the calcination time is 5 h.

[0054] Example 6

[0055] In this example, the same parts as in Example 1 will not be elaborated again. The differences are as follows:

[0056] In step (1), the calcination temperature is 600 °C and the calcination time is 3 h.

[0057] Example 7

[0058] In this example, the same parts as in Example 1 will not be elaborated again. The differences are as follows:

[0059] In step (3), the current used for the electrochemical modification treatment is 7 A and the treatment duration is 110 min.

[0060] Example 8

[0061] In this example, the same parts as in Example 1 will not be elaborated again. The differences are as follows:

[0062] In step (3), the current used for the electrochemical modification treatment is 6 A and the treatment duration is 90 min.

[0063] Example 9

[0064] In this example, the same parts as in Example 1 will not be elaborated again. The differences are as follows:

[0065] In step (3), the current used for the electrochemical modification treatment is 3 A and the treatment duration is 45 min.

[0066] Comparative Example 1

[0067] Only simple surface treatment is carried out on the recycled coarse aggregate without any modification treatment. The surface treatment method is as follows: Wash the sediment on the surface of the recycled coarse aggregate by soaking and rinsing, and then put it into a drying oven and dry it at 55 °C for 48 h.

[0068] Comparative Example 2

[0069] The same parts as in Example 1 in this comparative example will not be repeated. The differences are as follows:

[0070] No electrochemical modification treatment is carried out on the recycled coarse aggregate.

[0071] Comparative Example 3

[0072] The same parts as in Example 1 in this comparative example will not be repeated. The differences are as follows: The addition amount of the biomass ash composite modifier is 290 parts; The biomass ash composite modifier includes the following raw materials by weight: 135 parts of biomass ash, 75 parts of lime, 55 parts of gypsum, 11 parts of methyl cellulose, 9 parts of polyethylene glycol, and 5 parts of xanthan gum / Na2SiO3 composite suspension stabilizer.

[0073] Comparative Example 4

[0074] The same parts as in Example 1 in this example will not be repeated. The differences are as follows: The addition amount of the biomass ash composite modifier is 140 parts; The biomass ash composite modifier includes the following raw materials by weight: 60 parts of biomass ash, 35 parts of lime, 20 parts of gypsum, 11 parts of methyl cellulose, 9 parts of polyethylene glycol, and 5 parts of xanthan gum / Na2SiO3 composite suspension stabilizer.

[0075] Comparative Example 5

[0076] The same parts as in Example 1 in this comparative example will not be repeated. The differences are as follows: The addition amount of the biomass ash composite modifier is 100 parts; The biomass ash composite modifier includes the following raw materials by weight: 45 parts of biomass ash, 20 parts of lime, 10 parts of gypsum, 11 parts of methyl cellulose, 9 parts of polyethylene glycol, and 5 parts of xanthan gum / Na2SiO3 composite suspension stabilizer.

[0077] Comparative Example 6

[0078] The same parts as in Example 1 in this comparison will not be repeated. The differences are as follows:

[0079] In step (1), the calcination temperature is 1000 °C and the calcination time is 7 h.

[0080] Comparative Example 7

[0081] The same parts as in Example 1 in this comparative example will not be repeated. The differences are as follows:

[0082] In step (1), the calcination temperature is 500 °C and the calcination time is 2 h.

[0083] Comparative Example 8

[0084] The same parts as in Example 1 in this comparative example will not be elaborated, and the differences are as follows:

[0085] In step (3), the current used in the electrochemical modification treatment is 8 A, and the treatment duration is 130 min.

[0086] Comparative Example 9

[0087] The same parts as in Example 1 in this comparative example will not be elaborated, and the differences are as follows:

[0088] In step (3), the current used in the electrochemical modification treatment is 2 A, and the treatment duration is 20 min.

[0089] Referring to the "Test Regulations for Aggregates in Highway Engineering" (JTG E42-2005), the modified recycled coarse aggregates obtained in each example and comparative example were tested, and the test items included apparent density, water absorption rate, and crushing value.

[0090] In order to intuitively show the differences in test conditions and performance characterization results among the examples and comparative examples, the experimental data of each experiment are listed in Table 1.

[0091] Table 1 Test Conditions and Performance Characterization of Examples 1-9 and Comparative Examples 1-9

[0092]

[0093]

[0094] According to the experimental data in Table 1, it can be seen that the apparent density of the modified recycled coarse aggregates prepared by this method has been improved to varying degrees compared with that before modification (that is, compared with Comparative Example 1 for Examples 1-9), with the highest increase of 10.93%, and the water absorption rate and crushing value have both decreased significantly, with the maximum decreases of 60.42% and 46.20% respectively.

[0095] According to the experimental data of Examples 1-3 and Comparative Examples 3-5 in Table 1, it can be seen that the performance improvement effect of the modified recycled coarse aggregate prepared by this method is affected by the biomass ash composite modifier. The higher its addition amount, the better the performance of the modified recycled coarse aggregate. This is because the active components (such as SiO2 and Al2O3) in the biomass ash composite modifier react with the old mortar on the surface of the recycled coarse aggregate to generate gels such as C-S-H and C-A-H, filling the pores in the old mortar layer, improving the density of the mortar, enhancing the bonding degree of each component, and thus improving the strength and durability of the recycled coarse aggregate. In Examples 1-3, the addition amount of the biomass ash composite modifier is within the preferred range (185-270 parts), which can effectively improve the performance of the recycled coarse aggregate. The apparent density, water absorption rate and crushing value are significantly better than those of Comparative Examples 4-5 with less addition amount of the biomass ash composite modifier. In Comparative Example 3, the addition amount of the biomass ash composite modifier is 290 parts. Although the performance of the prepared modified recycled coarse aggregate is slightly better than that of Example 3, the improvement effect is not obvious. This shows that when the addition amount of the biomass ash composite modifier increases to a certain extent, the performance of the modified recycled coarse aggregate will reach a plateau, and too high an addition amount of the modifier will lead to an increase in cost and a low cost performance. In Comparative Examples 4 and 5, the addition amounts of the biomass ash composite modifier are 140 parts and 100 parts respectively, which are both lower than the preferred range, resulting in poor apparent density, water absorption rate and crushing value, indicating that when the addition amount of the modifier is insufficient, the modification effect is significantly reduced. Therefore, too low an addition amount of the modifier will result in poor performance of the prepared modified recycled coarse aggregate, while too high an addition amount will lead to an increase in cost and a low cost performance.

[0096] It can be seen from Examples 1, 4-6 and Comparative Examples 6-7 in Table 1 that the performance improvement effect of the modified recycled coarse aggregate prepared by this method is affected by the calcination conditions of the biomass ash. In Example 1, the calcination temperature of the biomass ash is 700 °C and the calcination time is 4 h. These parameters are all within the preferred range and can effectively improve the performance of the recycled coarse aggregate. In Example 4, both the calcination temperature and time are the maximum values within this parameter range. Although the higher calcination temperature and time can further promote the reaction of the biomass ash, it may cause slight changes in the internal structure of the material, resulting in a marginal effect on performance improvement, and at the same time increasing energy consumption and cost. In Comparative Example 7, both the calcination temperature and time are relatively low, resulting in poor apparent density, water absorption rate and crushing value, indicating that too low a calcination temperature and treatment time cannot fully play the role of the composite modifier and will significantly reduce the modification effect.

[0097] As can be seen from Examples 1, 7-9 and Comparative Examples 8-9 in Table 1, the improvement effect of the performance of the modified recycled coarse aggregate prepared by this method is affected by the electrochemical modification conditions. According to Examples 1 and 7-9, the longer the electrochemical treatment time and the higher the current, the better the performance of the prepared modified recycled coarse aggregate; if the electrochemical treatment time is too short and the current is too low, the performance of the modified recycled coarse aggregate will be reduced. Electrochemical modification treatment can fully stimulate the activity of biomass ash, cause biomass ash to react with the old mortar on the surface of recycled coarse aggregate, generate gel to fill part of the pores in the old mortar layer, improve the mortar density, and thus improve the strength and durability of recycled coarse aggregate. However, when the electrochemical treatment level exceeds the upper limit of the preferred range, it will exceed the activation energy required for the reaction. Therefore, continuing to increase the current magnitude and treatment duration will not result in a more significant improvement in performance.

[0098] In summary, the addition amount of biomass ash composite modifier, the calcination conditions of biomass ash, and the test conditions of electrochemical modification technology have a significant impact on the performance of recycled coarse aggregate. Appropriate addition amount of modifier, calcination conditions of biomass ash, and moderate electrochemical modification technology can provide the optimal strengthening efficiency and relatively high cost performance while ensuring the material performance. Too low addition amount of modifier and too low treatment level will lead to poor modification effect. Too high addition amount of modifier and too strict test conditions do not necessarily significantly improve the material performance, but may instead increase the cost and treatment difficulty.

Claims

1. A modified recycled coarse aggregate, characterized in that, Comprising the following raw materials by weight parts: 800 - 1100 parts of recycled coarse aggregate, 280 - 430 parts of water, 185 - 270 parts of biomass ash composite modifier, 14 - 22 parts of sodium hydroxide, 5 - 8 parts of polyethyleneimine, 3 - 7 parts of cyclodextrin; wherein, the biomass ash composite modifier comprises the following raw materials by weight parts: 85 - 125 parts of biomass ash, 45 - 70 parts of lime, 30 - 50 parts of gypsum, 8 - 13 parts of methyl cellulose, 7 - 10 parts of polyethylene glycol, 2 - 5 parts of composite suspension stabilizer; the composite suspension stabilizer is xanthan gum / Na2SiO3 with a mass ratio of 1:

25.

2. The modified recycled coarse aggregate according to claim 1, wherein The modified recycled coarse aggregate is prepared by an electrochemical modification technique; the recycled coarse aggregate further comprises 2 - 5 weight parts of anhydrous calcium chloride.

3. The preparation method of the modified recycled coarse aggregate according to claim 1, characterized in that, Including the following steps: (1) Prepare the biomass ash composite modifier: Calcinate and grind the biomass ash, and then fully mix it with lime, gypsum, dispersant, and suspension stabilizer; (2) Mix the raw materials: Mix water, biomass ash composite modifier, and cyclodextrin evenly, add the washed recycled coarse aggregate, and then mix and stand still to obtain a recycled coarse aggregate mixed slurry; (3) Electrochemical modification: Add sodium hydroxide electrolyte to the mixed slurry obtained in step (2), and perform electrochemical modification treatment on it using a DC power supply; (4) Post-treatment: Cure, wash, and dry the electrochemically modified slurry to obtain modified recycled coarse aggregate.

4. The preparation method according to claim 3, wherein, The biomass ash in step (1) is one or more of rice husk ash, bark ash, and straw ash; the dispersant is one or more of methyl cellulose and polyethylene glycol; the suspension stabilizer is a xanthan gum / Na2SiO3 composite suspension stabilizer with a mass ratio of 1:

25.

5. The preparation method according to claim 3, characterized in that, The average particle size of the recycled coarse aggregate in step (1) is 9.5 - 26.5 mm; the equipment used for grinding is a ball mill, and the grinding time is 60 - 90 min.

6. The preparation method according to claim 3, characterized in that, The calcination temperature in step (1) is 600 - 900 °C, and the calcination time is 3 - 6 h.

7. The preparation method according to claim 3, characterized in that, The standing temperature in step (2) is 20 - 30 °C, and the standing time is 1 - 3 h.

8. The preparation method according to claim 3, characterized in that, The addition amount of the biomass ash composite modifier in step (2) is 185 - 270 parts by weight.

9. The preparation method according to claim 3, characterized in that The electrolyte in step (3) includes an anhydrous calcium chloride stabilizer; the current used in the electrochemical modification treatment is 3 - 7 A, and the treatment time is 45 - 110 min.

10. The preparation method according to claim 3, characterized in that, The equipment used for curing in step (4) is a standard constant temperature and humidity curing box, the curing temperature is 25 ± 2 °C, the curing humidity is 95 ± 3%, and the curing time is 48 - 72 h; the drying temperature in step (4) is 40 - 70 °C, and the time is 36 - 60 h.

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