A low-shrinkage recycled concrete and its preparation method

Abstract

This application belongs to the technical field of concrete, and specifically discloses a low-shrinkage recycled concrete and its preparation method. The low-shrinkage recycled concrete, by weight, comprises the following raw materials: 120-180 parts of cement, 60-120 parts of construction waste materials, 20-35 parts of composite fiber pulp, 30-50 parts of fly ash, 30-80 parts of fine aggregate, 10-15 parts of sepiolite fiber, 1-3 parts of polycarboxylate water reducer, and 150-200 parts of water; the construction waste materials comprise the following raw materials by weight: 40-80 parts of waste building bricks, 15-45 parts of gypsum, 10-20 parts of water-based epoxy resin, 6-25 parts of carbon fiber, 15-30 parts of chitosan microcapsules, 20-40 parts of silica sol, and 100-200 parts of water. The low-shrinkage recycled concrete prepared in this application has good strength, compactness and low shrinkage rate.

Description

Technical Field

[0001] The present application relates to the technical field of concrete, and in particular to a low-shrinkage recycled concrete and a preparation method thereof. Background Art

[0002] Recycled concrete is a new type of recyclable building material. It is obtained by crushing, cleaning and grading the waste concrete blocks generated by building demolition. It is used to partially or completely replace natural aggregates and then added with cement, water, etc. to be used in fresh concrete. This method of making construction waste into recycled concrete recycles resources and reduces the consumption of natural sand and stone resources, which is in line with the national development policy of sustainability and green environmental protection.

[0003] However, waste concrete is subjected to large external forces during the crushing process, and a large number of fine cracks will appear inside the concrete blocks, resulting in low strength and high water absorption of the concrete blocks. The prepared recycled concrete has low density, fast slump loss, and large shrinkage, which further greatly limits the application of recycled concrete. Summary of the invention

[0004] In order to improve the problem that waste concrete is prone to cracks during the crushing process, thereby affecting the strength of recycled concrete, the present application provides a low-shrinkage recycled concrete and a preparation method thereof.

[0005] The present application provides a low shrinkage recycled concrete, which adopts the following technical solution:

[0006] A low shrinkage recycled concrete comprises the following raw materials, measured by weight: 120-180 parts of cement, 60-120 parts of construction waste materials, 20-35 parts of composite fiber slurry, 30-50 parts of fly ash, 30-80 parts of fine aggregate, 10-15 parts of sepiolite fiber, 1-3 parts of polycarboxylate water reducer and 150-200 parts of water;

[0007] The construction waste materials include the following raw materials in parts by weight: 40-80 parts of waste building bricks, 15-45 parts of gypsum, 10-20 parts of water-based epoxy resin, 6-25 parts of carbon fiber, 15-30 parts of chitosan microcapsules, 20-40 parts of silica sol and 100-200 parts of water.

[0008] By adopting the above technical solutions, the construction waste materials are recycled, reducing the production cost, saving resources and protecting the environment. However, a large number of fine cracks will appear during the crushing process of the construction waste materials, resulting in low strength, low compactness and large shrinkage of the concrete. The cement paste formed by dissolving cement wraps around the surface of the construction waste materials and fine aggregates and fills part of the voids in the construction waste materials. Fly ash can further fill the gaps between the construction waste materials and fine aggregates and the voids in the construction waste materials, improving the structural strength of the construction waste materials, increasing the slump of the concrete, enhancing the strength. The mixture of fly ash and cement can play a lubricating role, helping the components of the concrete to be evenly mixed, having good workability, and reducing the shrinkage during the hardening process of the concrete.

[0009] The sepiolite fibers are distributed in a three-dimensional manner in the concrete, playing a role of skeleton support, increasing the compressive and flexural strength and bonding strength of the concrete, and being evenly mixed with the construction waste materials, fine aggregates and fly ash. The sepiolite fibers can not only fill the microcracks in the construction waste materials, but also reduce the stress that generates microcracks, enabling the tensile stress caused by dry shrinkage of the concrete to be weakened or eliminated, thereby reducing the probability of the occurrence of microcracks; the composite fiber slurry plays the effect of secondary reinforcement in the concrete, improving the compactness of the concrete, having good crack resistance, cooperating with the sepiolite fibers to further reduce the probability of crack generation, cooperating with other components of the concrete, and thus improving the compactness and strength of the recycled concrete and reducing the shrinkage of the recycled concrete.

[0010] In addition, in the construction waste materials, waste building bricks and gypsum are mixed. The gypsum can fill the gaps in the waste building bricks, improving the strength of the waste building bricks and the bonding property between the waste building bricks. The waterborne epoxy resin cooperates with the gypsum to further improve the bonding performance between the waste building bricks, playing a role in anti-seepage and leak stoppage. The carbon fiber has high strength and has the effect of enhancing crack resistance. Cooperating with the gypsum and waterborne epoxy resin can reduce the spread of cracks during the crushing process of the waste building bricks. The chitosan microcapsules have certain viscoelasticity, are evenly mixed with the waste building bricks and gypsum, increasing the compactness, water retention and cohesion of the subsequent recycled concrete, thereby reducing the shrinkage of the recycled concrete; the silica sol has good penetration. The colloidal particles in the silica sol expand to reduce the gaps in the waste building bricks, cooperating with the chitosan microcapsules, carbon fiber and gypsum to jointly improve the structural strength and compactness of the recycled concrete and reduce the shrinkage of the recycled concrete.

[0011] Preferably, the preparation method of the construction waste materials includes the following steps:

[0012] (1) Crush the waste building bricks into fragments with a particle size not greater than 20 mm, then soak them in hydrochloric acid for 3 - 5 h, wash them with water, dry them, add gypsum, stir evenly, and crush them again to obtain fragments not greater than 10 mm.

[0013] (2) Mix waterborne epoxy resin, carbon fiber, chitosan microcapsules, silica sol and water, stir for 1 - 3 h, then add the fragments obtained in step (1), and continue to stir for 3 - 5 h to obtain waste building materials.

[0014] By adopting the above technical solution, the waste building bricks are first crushed into fragments with a particle size not greater than 20 mm. Adding hydrochloric acid not only removes the organic impurities in the fragments, but also reacts with the carbonate radicals in the crushed stones, and has a certain corrosive effect on the crushed stones, making the surface of the fragments become a microporous structure. Then add gypsum, which fills the pores of the fragments and bonds the gaps between the fragments, increasing the bondability between the fragments. Then perform secondary crushing to obtain fragments not greater than 10 mm. Secondary crushing helps to obtain smaller and finer particles.

[0015] Then mix the fragments with waterborne epoxy resin, carbon fiber, chitosan microcapsules, and silica sol. The waterborne epoxy resin cooperates with gypsum to further improve the bonding performance between the waste building bricks. Carbon fiber has high strength and fills the gaps in the crushed stones. Chitosan microcapsules have certain viscoelasticity, increasing the compactness, water retention and cohesion of the subsequent recycled concrete. The colloidal particles in the silica sol expand to reduce the gaps in the waste building bricks, and cooperate with chitosan microcapsules, carbon fiber and gypsum to jointly improve the structural strength and compactness of the recycled concrete, and reduce the shrinkage of the recycled concrete.

[0016] Preferably, the preparation method of the chitosan microcapsules includes the following steps:

[0017] (1) Dissolve chitosan in 0.05 - 1 mol / L citric acid, then add sodium dodecyl sulfate and glutaraldehyde, stir for 1 - 2 h, and then add graphene, and ultrasonicate for 3 - 5 h at a temperature of 50 - 60 °C to obtain a wall material mixture.

[0018] (2) Disperse soy protein isolate in water, add galangal essential oil, polyacrylamide and emulsifier, and homogenize and emulsify to form an emulsion.

[0019] (3) Add the wall material mixture obtained in step (1) to the emulsion obtained in step (2), carry out a complex coacervation reaction by stirring in a constant temperature water bath at 60 - 70 °C for 1 - 2 h, then add a curing agent (tannic acid), continue to stir and react for 2 - 3 h, and spray dry to obtain chitosan microcapsules.

[0020] By adopting the above technical solutions, chitosan has good film-forming property and heat preservation property. It can not only improve the structural strength of concrete, but also prevent plastic cracking and drying shrinkage of concrete. Sodium dodecyl sulfonate has excellent temperature and humidity control property, foaming power and stability. After being mixed with chitosan, there is a strong intermolecular secondary valence force between chitosan molecules and sodium dodecyl sulfonate, further improving the film-forming performance of chitosan. The aldehyde group of glutaraldehyde reacts with the amino group of chitosan to form a cross-linked structure, enhancing the molecular stability and mechanical properties of chitosan, and further improving the mechanical strength of the chitosan film after film formation; Graphene has good mechanical properties, antibacterial property and lubricity. Cross-linking graphene and chitosan improves the flexibility, mechanical strength and thermal stability of chitosan, contributing to the structural stability of the chitosan film.

[0021] Soybean protein isolate has good water retention property, viscosity and lubricity. Polyacrylamide has good water retention property, adhesiveness and impermeability. The mixture of soybean protein isolate and polyacrylamide has good water retention property and adhesiveness. After long-term use of recycled concrete, when the chitosan wall material breaks later, soybean protein isolate and polyacrylamide enter the structure of the concrete to fill the cracks that appear in the concrete, thereby enhancing the flexural strength, interlayer bonding strength, durability and flexural toughness of the recycled concrete, and enhancing the long-term service performance of the concrete.

[0022] Galangal essential oil not only has good dual properties of sterilization and antifungal resistance, enhancing the antibacterial property of recycled concrete, but also has good antioxidant property, improving the stability of soybean protein isolate and polyacrylamide, contributing to improving the stability of the emulsion. The prepared chitosan microcapsules have good structural strength later. Even if the microcapsule wall material breaks later, it helps to fill the gaps in the recycled concrete, thereby improving the service life of the concrete.

[0023] Preferably, the spray drying adopts the pneumatic spray drying method, the inlet air temperature is 110 - 120 °C, the outlet air temperature is 80 - 90 °C, and the atomization pressure is 0.6 - 0.8 MPa.

[0024] By adopting the above technical solutions, using the pneumatic spray drying method, the operation is continuous, the system can be fully automated for control operation, the drying speed is fast, the drying time is short, the operation is simple, the wear on the equipment is small, and the obtained chitosan microcapsule particles are fine and have a large surface area, which helps for subsequent application in concrete.

[0025] Preferably, the curing agent is genipin and / or tannic acid.

[0026] By adopting the above technical solutions, the curing agent can promote or control the curing reaction, accelerate the drying speed, and thereby shorten the process flow time.

[0027] Preferably, the preparation method of the composite fiber pulp comprises the following steps:

[0028] (1) Stir and mix pulp, cotton linter, and straw debris, then add sodium hydroxide solution, soak at 75 - 85°C for 30 - 60 min, wash with water, filter, dry, and then pulverize to obtain mixed fragments;

[0029] (2) Mix the mixed fragments obtained in step (1) with shell powder and sugarcane pulp fibers, stir for 1 - 2 h, freeze-dry, grind, and pass through a 50-mesh sieve to obtain a mixture for standby;

[0030] (3) Dissolve peach gum in water, stir at 90 - 95°C, then add the mixture obtained in step (2), and continue to stir for 3 - 5 h to obtain composite fiber pulp.

[0031] By adopting the above technical solution, using sodium hydroxide to clean pulp, cotton linter, and straw debris helps to remove organic impurities therein, and at the same time makes the surface of the raw materials rough and porous, which is conducive to the loading of subsequent substances. Shell powder has a porous structure, and shell powder can adhere to the gaps or rough surfaces of pulp, cotton linter, and straw debris, which is beneficial to enhancing the structural strength of subsequent recycled concrete. Sugarcane pulp fibers have strong tensile toughness, and after incorporation, they can transfer the shrinkage stress during the hardening of recycled concrete. The prepared recycled concrete has high strength, good toughness, and excellent durability, and can effectively prevent concrete cracking. At the same time, due to the good adsorption performance of shell powder, when shell powder is added to recycled concrete, it can adsorb other components, making the various components in the recycled concrete raw material system combine more tightly, so it is not easy to crack. Peach gum has good adhesiveness, which not only fills the gaps between pulp, cotton linter, and straw debris and the pores of shell powder, but also further bonds various components, making pulp, cotton linter, and straw debris, shell powder, and sugarcane pulp fibers bond to each other, thereby enhancing the structural strength, mechanical properties, and anti-cracking performance of the composite fiber pulp.

[0032] Preferably, the mass ratio of the mixed fragments, shell powder, and sugarcane pulp fibers is 1:0.5 - 0.9:1.3 - 1.8.

[0033] By adopting the above technical solution, controlling the mass ratio of the mixed fragments, shell powder, and sugarcane pulp fibers within a certain range can obtain a composite fiber pulp with better anti-cracking performance and stronger structural strength. Shell powder can be loaded into the structural gaps and surface pores of the mixed fragments, increasing the structural strength of the mixed fragments. Sugarcane pulp fibers further connect shell powder and the mixed fragments, enhancing the adhesiveness between shell powder and the mixed fragments, which helps to reduce the cracking probability between the mixed fragments.

[0034] Preferably, the mass ratio of the mixed crushed materials to the peach gum is 1:0.1 - 0.3.

[0035] By adopting the above technical solution, controlling the mass ratio of the mixed crushed materials to the peach gum within a certain range, the peach gum has excellent adhesive properties, which can bond the pulp, cotton linter, straw debris, shell powder and sugarcane pulp fibers to each other, thereby enhancing the structural strength, mechanical properties and anti-cracking properties of the composite fiber pulp.

[0036] Preferably, the particle size range of the silica sol is 60 - 80 nm, and the silica content is 20 - 30%.

[0037] By adopting the above technical solution, the silica sol has good penetration, can fill the gaps in the recycled concrete, and at the same time improve the compressive strength, flexural strength and durability of the recycled concrete, extend the curing period of the concrete, and improve the use of the concrete to a greater extent.

[0038] In a second aspect, the present application also provides a preparation method of low-shrinkage recycled concrete, including the following steps: mixing construction waste, cement and fly ash, stirring for 30 - 60 min, then adding fine aggregate, sepiolite fiber, polycarboxylate water reducer and water, continuing to stir and mix for 60 - 90 min, and then adding composite fiber pulp thereto, continuing to stir for 1 - 3 h to obtain low-shrinkage recycled concrete.

[0039] By adopting the above technical solution, using the above preparation method, the operation is simple and the process time is short, which helps to improve the preparation efficiency.

[0040] In summary, the present application has the following beneficial effects:

[0041] 1. In the present application, the construction waste materials are recycled, saving resources. However, a large number of fine cracks will appear during the crushing process of the construction waste materials, resulting in low strength, low compactness and large shrinkage of the concrete. The cement slurry formed by dissolving cement wraps the surface of the construction waste materials and fine aggregate and fills part of the voids in the construction waste materials, while fly ash can further fill the gaps between the construction waste materials and fine aggregate and the voids in the construction waste materials, improve the structural strength of the construction waste materials, increase the slump of the concrete, improve the strength. The mixture of fly ash and cement can play a lubricating role, help the components of the concrete to be mixed evenly, have good workability, and reduce the shrinkage during the hardening process of the concrete.

[0042] 2. In the present application, the sepiolite fibers are three-dimensionally distributed in the concrete, playing a role of skeleton support, increasing the compressive and flexural strengths and the bonding strength of the concrete, being uniformly mixed with construction waste materials, fine aggregates, and fly ash. The sepiolite fibers can not only fill the microcracks in the construction waste materials, but also reduce the stress that generates microcracks, enabling the tensile stress caused by dry shrinkage of the concrete to be weakened or eliminated, thereby reducing the probability of microcracks occurring.

[0043] 3. In the present application, the composite fiber pulp plays the role of a secondary reinforcing bar in the concrete, improving the compactness of the concrete, having good crack resistance, further reducing the probability of crack generation in combination with the sepiolite fibers, and in combination with other components of the concrete, thereby improving the compactness and strength of the recycled concrete and reducing the shrinkage of the recycled concrete. Specific Embodiments

[0044] The following further elaborates on the present application in conjunction with embodiments.

[0045] The raw materials used in the embodiments and comparative examples can all be obtained commercially. Among them, the particle size range of the silica sol is 60 - 80 nm, and the silica content is 20 - 30%.

[0046] Preparation Example of Chitosan Microcapsules

[0047] Preparation Example 1 - 1

[0048] The preparation method of chitosan microcapsules includes the following steps:

[0049] (1) Dissolve 1.2 kg of chitosan in 2 L of 0.05 - 1 mol / L citric acid, then add 0.2 kg of sodium dodecyl sulfate and 0.1 kg of glutaraldehyde, stir for 2 h, and then add 0.05 kg of graphene, and ultrasonicate for 4 h at a temperature of 55°C to obtain a wall material mixture;

[0050] (2) Disperse 0.5 kg of soy protein isolate in 1.5 L of water, add 0.2 kg of galangal essential oil, 0.2 kg of polyacrylamide, and 0.09 kg of emulsifier, and homogenize and emulsify to form an emulsion;

[0051] (3) Add the wall material mixture obtained in step (1) to the emulsion obtained in step (2), carry out a complex coacervation reaction by stirring in a constant temperature water bath at 65°C for 2 h, then add tannic acid, continue to stir and react for 3 h, and spray dry to obtain chitosan microcapsules; among them, spray drying is carried out by air - flow spray drying method, the inlet air temperature is 120°C, the outlet air temperature is 90°C, and the atomization pressure is 0.8 MPa.

[0052] Preparation Example 1 - 2

[0053] The difference from Preparation Example 1-1 is that in step (1), graphene is not added.

[0054] Preparation Example 1-3

[0055] The difference from Preparation Example 1-1 is that in step (2), polyacrylamide is not added.

[0056] Preparation Examples of Composite Fiber Pulp

[0057] Preparation Example 2-1

[0058] A method for preparing composite fiber pulp, comprising the following steps:

[0059] (1) Stir and mix 1.8 kg of papermaking pulp, cotton linter, and straw debris, then add 2.5 L of sodium hydroxide solution with a mass fraction of 20%, soak at 80 °C for 50 min, wash with water, filter, dry, and then pulverize to obtain mixed fragments;

[0060] (2) Mix the mixed fragments obtained in step (1) with shell powder and sugarcane pulp fibers, stir for 2 h, freeze-dry, grind, and pass through a 50-mesh sieve to obtain a mixture for standby;

[0061] (3) Dissolve peach gum in water, stir at 95 °C, then add the mixture obtained in step (2), and continue to stir for 5 h to obtain composite fiber pulp, wherein the mass ratio of the mixed fragments, shell powder, and sugarcane pulp fibers is 1:0.5:1.3; the mass ratio of the mixed fragments and peach gum is 1:0.1.

[0062] Preparation Example 2-2

[0063] The difference from Preparation Example 2-1 is that in step (1), sodium hydroxide solution is not added.

[0064] Preparation Example 2-3

[0065] The difference from Preparation Example 2-1 is that in step (2), shell powder is not added.

[0066] Preparation Example 2-4

[0067] The difference from Preparation Example 2-1 is that in step (2), sugarcane pulp fibers are not added.

[0068] Preparation Example 2-5

[0069] The difference from Preparation Example 2-1 is that in step (3), peach gum is not added.

[0070] Preparation Example 2-6

[0071] The difference from Preparation Example 2-1 is that the mass ratio of the mixed fragments, shell powder, and sugarcane pulp fibers is 1:0.9:1.8.

[0072] Preparation Example 2-7

[0073] It is different from Preparation Example 2-1 in that the mass ratio of the mixed broken materials, shell powder and sugarcane pulp fiber is 1:1.3:0.8.

[0074] Preparation Example 2-8

[0075] It is different from Preparation Example 2-1 in that the mass ratio of the mixed broken materials and peach gum is 1:0.3.

[0076] Preparation Example 2-9

[0077] It is different from Preparation Example 2-1 in that the mass ratio of the mixed broken materials and peach gum is 1:0.6.

[0078] Examples

[0079] Example 1

[0080] A low-shrinkage recycled concrete, by weight, comprises the following raw materials: 150 kg of cement, 90 kg of construction waste materials, 30 kg of composite fiber pulp, 40 kg of fly ash, 50 kg of fine aggregate, 12 kg of sepiolite fiber, 2 kg of polycarboxylate water reducer and 180 kg of water; the construction waste materials comprise the following raw materials by weight: 60 kg of waste building bricks, 30 kg of gypsum, 15 kg of waterborne epoxy resin, 15 kg of carbon fiber, 20 kg of chitosan microcapsules, 30 kg of silica sol and 150 kg of water.

[0081] Among them, the preparation method of the construction waste materials comprises the following steps:

[0082] (1) Crush the waste building bricks into pieces with a particle size not greater than 20 mm, then soak them in hydrochloric acid for 4 h, wash them with water, dry them, and then add gypsum, stir evenly, and crush them twice to obtain pieces not greater than 10 mm;

[0083] (2) Mix the waterborne epoxy resin, carbon fiber, chitosan microcapsules, silica sol and water, stir for 3 h, and then add the pieces obtained in step (1), and continue to stir for 4 h to obtain the construction waste materials.

[0084] The preparation method of the above low-shrinkage recycled concrete comprises the following steps: Blend the construction waste, cement and fly ash, stir for 40 min, then add the fine aggregate, sepiolite fiber, polycarboxylate water reducer and water, continue to stir and mix for 80 min, and then add the composite fiber pulp to it, and continue to stir for 1-3 h to obtain the low-shrinkage recycled concrete.

[0085] The chitosan microcapsules are prepared by Preparation Example 1-1; the composite fiber pulp is prepared by Preparation Example 2-1.

[0086] Example 2

[0087] A low-shrinkage recycled concrete, different from Example 1 in that the chitosan microcapsules are prepared by Preparation Example 1-2.

[0088] Example 3

[0089] A low-shrinkage recycled concrete, different from Example 1 in that the chitosan microcapsules are prepared by Preparation Example 1-3.

[0090] Example 4

[0091] A low-shrinkage recycled concrete, different from Example 1 in that the composite fiber pulp is prepared by Preparation Example 2-2.

[0092] Example 5

[0093] A low-shrinkage recycled concrete, different from Example 1 in that the composite fiber pulp is prepared by Preparation Example 2-3.

[0094] Example 6

[0095] A low-shrinkage recycled concrete, different from Example 1 in that the composite fiber pulp is prepared by Preparation Example 2-4.

[0096] Example 7

[0097] A low-shrinkage recycled concrete, different from Example 1 in that the composite fiber pulp is prepared by Preparation Example 2-5.

[0098] Example 8

[0099] A low-shrinkage recycled concrete, different from Example 1 in that the composite fiber pulp is prepared by Preparation Example 2-6.

[0100] Example 9

[0101] A low-shrinkage recycled concrete, different from Example 1 in that the composite fiber pulp is prepared by Preparation Example 2-7.

[0102] Example 10

[0103] A low-shrinkage recycled concrete, different from Example 1 in that the composite fiber pulp is prepared by Preparation Example 2-8.

[0104] Example 11

[0105] A low-shrinkage recycled concrete, different from Example 1 in that the composite fiber pulp is prepared by Preparation Example 2-9.

[0106] Example 12

[0107] A low-shrinkage recycled concrete, which is different from that of Example 1, comprises the following raw materials by weight: 120 kg of cement, 60 kg of construction waste materials, 35 kg of composite fiber pulp, 30 kg of fly ash, 30 kg of fine aggregate, 10 kg of sepiolite fiber, 1 kg of polycarboxylate water reducer and 150 kg of water.

[0108] Example 13

[0109] A low-shrinkage recycled concrete, which is different from that of Example 1, comprises the following raw materials by weight: 180 kg of cement, 120 kg of construction waste materials, 20 kg of composite fiber pulp, 50 kg of fly ash, 80 kg of fine aggregate, 15 kg of sepiolite fiber, 3 kg of polycarboxylate water reducer and 200 kg of water.

[0110] Example 14

[0111] A low-shrinkage recycled concrete, which is different from that of Example 1, in which the construction waste materials comprise the following raw materials by weight: 40 kg of waste building bricks, 15 kg of gypsum, 10 kg of waterborne epoxy resin, 6 kg of carbon fiber, 30 kg of chitosan microcapsules, 20 kg of silica sol and 100 kg of water.

[0112] Example 15

[0113] A low-shrinkage recycled concrete, which is different from that of Example 1, in which the construction waste materials comprise the following raw materials by weight: 80 kg of waste building bricks, 45 kg of gypsum, 20 kg of waterborne epoxy resin, 25 kg of carbon fiber, 15 kg of chitosan microcapsules, 40 kg of silica sol and 200 kg of water.

[0114] Comparative example

[0115] Comparative example 1

[0116] A low-shrinkage recycled concrete, which is different from that of Example 1, comprises the following raw materials by weight: 100 kg of cement, 150 kg of construction waste materials, 39 kg of composite fiber pulp, 20 kg of fly ash, 100 kg of fine aggregate, 5 kg of sepiolite fiber, 0.5 kg of polycarboxylate water reducer and 220 kg of water.

[0117] Comparative example 2

[0118] A low-shrinkage recycled concrete, which is different from that of Example 1, in which the construction waste materials comprise the following raw materials by weight: 100 kg of waste building bricks, 10 kg of gypsum, 35 kg of waterborne epoxy resin, 45 kg of carbon fiber, 10 kg of chitosan microcapsules, 10 kg of silica sol and 80 kg of water.

[0119] Comparative example 3

[0120] A low-shrinkage recycled concrete, which is different from that of Example 1 in that no composite fiber pulp is added.

[0121] Comparative Example 4

[0122] A low-shrinkage recycled concrete, which is different from that of Example 1 in that no sepiolite fiber is added.

[0123] Comparative Example 5

[0124] A low-shrinkage recycled concrete, which is different from that of Example 1 in that no chitosan microcapsules are added.

[0125] Performance detection test: The low-shrinkage recycled concretes prepared in Examples 1-15 and Comparative Examples 1-5 were subjected to performance tests. The compressive strength was tested by the compressive strength test method T0551-2020, and the specification was "Test Procedures for Cement and Concrete in Highway Engineering"; the shrinkage rate was tested by "Test Procedures for Cement and Concrete in Highway Engineering" T0575-2020, and the non-contact method was used to test the shrinkage rate for 7 days; the test results are shown in Table 1.

[0126] Table 1 Test data of examples and comparative examples

[0127]

[0128]

[0129] As can be seen from Table 1, the concretes prepared in Examples 1, 8, 10, and 12-15 of the present application have good mechanical properties and low shrinkage rates. The 7-day compressive strength reaches 45.3 MPa, the 28-day compressive strength reaches 72.6 MPa, the water absorption rate is 6.1%, and the 7-day shrinkage rate is 22×10 -6 , indicating that the prepared concrete has good compressive strength, low water absorption rate and shrinkage rate at the same time, indicating that the prepared recycled concrete has good compactness, small porosity, good impermeability and small shrinkage, and has a good service life.

[0130] In the preparation method of chitosan microcapsules in Example 2, no graphene is added. In the preparation method of chitosan microcapsules in Example 3, no polyacrylamide is added. As can be seen from Table 1, compared with Example 1, the values of shrinkage rate and water absorption rate increase significantly, and the compressive strength at 7 days and 28 days decreases significantly, indicating that graphene affects the mechanical properties of chitosan microcapsules. Graphene and chitosan are crosslinked to improve the flexibility, mechanical strength and thermal stability of chitosan. Polyacrylamide has good water retention, adhesiveness and impermeability. Subsequently, when the chitosan wall material ruptures, polyacrylamide enters the structure of the concrete to fill the cracks in the concrete, thereby enhancing the interlayer bonding strength and durability of the recycled concrete.

[0131] In the preparation methods of the composite fiber slurries of Examples 4 - 7, sodium hydroxide solution, shell powder, sugarcane pulp fiber, and peach gum were not added respectively. It can be seen from Table 1 that compared with Example 1, the values of shrinkage rate and water absorption rate increased significantly, and the compressive strengths at 7d and 28d decreased significantly, indicating that sodium hydroxide made the surfaces of the pulp, cotton linter, and straw debris rough and porous, which was helpful for the loading of subsequent substances. The shell powder could adhere to the gaps or rough surfaces of the pulp, cotton linter, and straw debris, which was beneficial to enhancing the structural strength of the subsequent recycled concrete. The sugarcane pulp fiber had strong tensile toughness, and after being incorporated, it could transfer the shrinkage stress during the hardening of the recycled concrete. The prepared recycled concrete had high strength, good toughness, and excellent durability, and could effectively prevent concrete cracking. The peach gum had good adhesiveness. It not only filled the gaps between the pulp, cotton linter, and straw debris and the pores of the shell powder, but also further bonded various components, making the pulp, cotton linter, straw debris, shell powder, and sugarcane pulp fiber bond to each other, thereby enhancing the structural strength, mechanical properties, and anti - cracking properties of the composite fiber slurry.

[0132] In Example 9, the mass ratios of the mixed scraps, shell powder, and sugarcane pulp fiber were changed. In Example 11, the mass ratio of the mixed scraps and peach gum was changed. In Comparative Examples 1 - 2, the raw material ratios of the recycled concrete and the raw material ratios of the construction waste materials were changed respectively. It can be seen from Table 1 that compared with Example 1, the values of shrinkage rate and water absorption rate increased significantly, and the compressive strengths at 7d and 28d decreased significantly, indicating that each raw material component made the recycled concrete have good comprehensive performance according to a certain content ratio, and the change in the dosage of each raw material affected the mechanical properties such as the strength, shrinkage rate, and water absorption rate of the low - shrinkage recycled concrete.

[0133] In Comparative Examples 3 - 5, the composite fiber slurry, sepiolite fiber, and chitosan microcapsules were not added respectively. It can be seen from Table 1 that compared with Example 1, the values of shrinkage rate and water absorption rate increased significantly, and the compressive strengths at 7d and 28d decreased significantly, indicating that the composite fiber slurry improved the compactness of the concrete and had good crack resistance. The sepiolite fiber played a role in skeleton support, increasing the compressive and flexural strengths and bonding strength of the concrete. The chitosan microcapsules had certain viscoelasticity, were evenly mixed with the waste building bricks and gypsum, increasing the compactness, water retention, and cohesiveness of the subsequent recycled concrete. The components of the recycled concrete cooperated with each other, improving the compactness and strength of the recycled concrete and reducing the shrinkage of the recycled concrete.

[0134] This specific embodiment is only an interpretation of the present application, and it is not a limitation of the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A low-shrinkage recycled concrete, characterized in that, Composed of the following raw materials by weight parts: 120 - 180 parts of cement, 60 - 120 parts of construction waste materials, 20 - 35 parts of composite fiber pulp, 30 - 50 parts of fly ash, 30 - 80 parts of fine aggregate, 10 - 15 parts of sepiolite fiber, 1 - 3 parts of polycarboxylate water reducer, and 150 - 200 parts of water; The construction waste materials include the following raw materials by weight parts: 40 - 80 parts of waste building bricks, 15 - 45 parts of gypsum, 10 - 20 parts of waterborne epoxy resin, 6 - 25 parts of carbon fiber, 15 - 30 parts of chitosan microcapsules, 20 - 40 parts of silica sol, and 100 - 200 parts of water; The preparation method of the chitosan microcapsules includes the following steps: (1) Dissolve chitosan in citric acid with a concentration of 0.05 - 1mol / L, then add sodium dodecyl sulfate and glutaraldehyde, stir for 1 - 2h, and then add graphene, and ultrasonicate for 3 - 5h at a temperature of 50 - 60°C to obtain a wall material mixture; (2) Disperse soy protein isolate in water, add galangal essential oil, polyacrylamide, and an emulsifier, and homogenize and emulsify to form an emulsion; (3) Add the wall material mixture obtained in step (1) to the emulsion obtained in step (2), carry out a complex coacervation reaction by stirring in a constant temperature water bath at 60 - 70°C for 1 - 2h, then add a curing agent, continue to stir and react for 2 - 3h, and spray dry to obtain chitosan microcapsules; The preparation method of the construction waste materials includes the following steps: (1) Crush the waste building bricks into fragments with a particle size not greater than 20mm, then soak them in hydrochloric acid for 3 - 5h, wash with water, dry, then add gypsum, stir evenly, and crush them twice to obtain fragments not greater than 10mm; (2) Mix waterborne epoxy resin, carbon fiber, chitosan microcapsules, silica sol, and water, stir for 1 - 3h, then add the fragments obtained in step (1), and continue to stir for 3 - 5h to obtain construction waste materials; The preparation method of the composite fiber pulp includes the following steps: (1) Stir and mix pulp, cotton linters, and straw debris, then add sodium hydroxide solution, soak at a temperature of 75 - 85°C for 30 - 60min, wash with water, filter, dry, and then crush to obtain a mixed crushed material; (2) Mix the mixed crushed material obtained in step (1) with shell powder and sugarcane pulp fiber, stir for 1 - 2h, freeze-dry, grind, and pass through a 50-mesh sieve to obtain a mixture for standby; (3) Dissolve peach gum in water, stir at a temperature of 90 - 95°C, then add the mixture obtained in step (2), and continue to stir for 3 - 5h to obtain composite fiber pulp; The mass ratio of the mixed crushed material, shell powder, and sugarcane pulp fiber is 1:0.5 - 0.9:1.3 - 1.8; The mass ratio of the mixed crushed material and peach gum is 1:0.1 - 0.

3.

2. The low-shrinkage recycled concrete according to claim 1, wherein The spray drying adopts pneumatic spray drying method, the inlet air temperature is 110 - 120°C, the outlet air temperature is 80 - 90°C, and the atomization pressure is 0.6 - 0.8MPa.

3. A low-shrinkage recycled concrete according to claim 1, characterized in that, The curing agent is genipin and / or tannic acid.

4. A low-shrinkage recycled concrete according to claim 1, characterized in that, The particle size range of the silica sol is 60 - 80 nm, and the silica content is 20 - 30%.

5. A preparation method of a low-shrinkage recycled concrete according to any one of claims 1-4, characterized in that, It includes the following steps: Blend construction waste materials, cement, and fly ash, and stir for 30 - 60 min. Then add fine aggregate, sepiolite fiber, polycarboxylate water reducer, and water, and continue to stir and mix for 60 - 90 min. Then add composite fiber slurry thereto, and continue to stir for 1 - 3 h to obtain low-shrinkage recycled concrete.

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