Low-carbon regenerated salt-corrosion-resistant cement concrete and preparation method thereof

Abstract

The invention belongs to the technical field of recycled concrete, and discloses low-carbon recycled salt-corrosion-resistant cement concrete and a preparation method thereof. The concrete comprises cement, modified recycled coarse aggregate, recycled fine aggregate, modified fiber, fly ash, mineral powder, a water reducing agent and water. The preparation method comprises the following steps: replacing natural aggregate with recycled aggregate, firstly soaking recycled coarse aggregate with carbon nanotube dispersion liquid to enable carbon nanotubes to be adsorbed on the surface and in internal pores, then soaking the recycled coarse aggregate in hydrophobic epoxy resin emulsion, and then heating and curing the recycled coarse aggregate. Through the modification of the carbon nanotubes and the hydrophobic epoxy resin, gaps of the recycled coarse aggregate are filled, the compactness is improved, the porosity is reduced, the outer cured hydrophobic epoxy resin layer can reduce the invasion of moisture and resist the corrosion of salt, and the carbon nanotubes can be further prevented from falling off. The epoxy resin can also enhance the strength of the concrete, and the problems that the concrete is low in strength and is not resistant to sulfate corrosion during resource utilization of the traditional recycled coarse aggregate are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of recycled concrete, and particularly to a low-carbon recycled sulfate-resistant cement concrete and a preparation method thereof. Background Art

[0002] Recycled concrete refers to new concrete prepared by crushing, cleaning, and grading waste concrete blocks, mixing them in a certain proportion and gradation, partially or completely replacing natural aggregates such as sand and gravel, and then adding cement, water, etc. Recycling waste concrete not only reduces the consumption of natural resources such as sand and gravel, but also realizes the resource recycling of construction waste, reduces the stockpiling of construction waste, and is more in line with the current low-carbon environmental protection trend. Therefore, recycled concrete has received extensive attention in the construction industry.

[0003] However, the composition of recycled aggregates includes not only a small amount of stones separated from mortar, some stones wrapped with mortar, but also a small amount of independent cement mortar blocks. Because the surface of cement mortar is rough, has many edges and corners, and a large number of microcracks appear inside the aggregates during the destruction of concrete structures and the production of aggregates, the porosity of recycled aggregates is large. When there are a large number of microcracks and a large porosity inside the recycled aggregates, the internal stress of the prepared recycled concrete is uneven after being subjected to temperature stress and other effects, the concrete strength decreases significantly, and affected by the use environment, the recycled concrete is easily eroded and damaged by sulfates, resulting in the shedding and crystallization of the concrete surface, and the durability is poor. This seriously limits the large-scale resource utilization of recycled aggregates.

[0004] Therefore, how to improve the sulfate resistance and durability of recycled concrete is an urgent problem to be solved at present. Summary of the Invention

[0005] The purpose of the present invention is to provide a low-carbon recycled sulfate-resistant cement concrete and a preparation method thereof, so as to solve the problem that the existing recycled concrete is easily eroded by sulfates and affects its performance.

[0006] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a low-carbon recycled sulfate-resistant cement concrete, which comprises the following raw materials in parts by mass: 60-100 parts of cement, 100-200 parts of modified recycled coarse aggregates, 50-150 parts of recycled fine aggregates, 10-25 parts of modified fibers, 40-80 parts of fly ash, 20-50 parts of mineral powder, 1-10 parts of water reducing agent, and 40-120 parts of water.

[0008] Preferably, in the above-mentioned low-carbon recycled sulfate-resistant cement concrete, the particle size of the modified recycled coarse aggregates is 5-10 mm; the particle size of the recycled fine aggregates is 0.1-0.5 mm.

[0009] Preferably, in the above-mentioned low-carbon recycled salt-resistant cement concrete, the preparation method of the modified recycled coarse aggregate is as follows: soaking the recycled coarse aggregate in a carbon nanotube dispersion liquid to obtain a pre-modified aggregate; soaking the pre-modified aggregate in a fluorosilicon-modified epoxy resin emulsion, and then heating and curing to obtain the modified recycled coarse aggregate.

[0010] Preferably, in the above-mentioned low-carbon recycled salt-resistant cement concrete, the mass ratio of the recycled coarse aggregate to the carbon nanotubes in the carbon nanotube dispersion liquid is 100:0.1-1.

[0011] Preferably, in the above-mentioned low-carbon recycled salt-resistant cement concrete, the carbon nanotube dispersion liquid is an aqueous solution of carbon nanotubes; the mass fraction of carbon nanotubes in the carbon nanotube dispersion liquid is 0.5-1%.

[0012] Preferably, in the above-mentioned low-carbon recycled salt-resistant cement concrete, the dosage ratio of the pre-modified aggregate to the fluorosilicon-modified epoxy resin emulsion is 1-10 g:20-50 mL.

[0013] Preferably, in the above-mentioned low-carbon recycled salt-resistant cement concrete, the soaking time in the carbon nanotube dispersion liquid is 0.5-3 h; the soaking time in the fluorosilicon-modified epoxy resin emulsion is 1-2 h.

[0014] Preferably, in the above-mentioned low-carbon recycled salt-resistant cement concrete, the heating and curing temperature is 200-300 °C; the heating and curing time is 1-5 h.

[0015] Preferably, in the above-mentioned low-carbon recycled salt-resistant cement concrete, the modified fiber is a silane coupling agent-modified polypropylene fiber.

[0016] The present invention also provides a preparation method of a low-carbon recycled salt-resistant cement concrete, comprising the following steps:

[0017] Mixing cement, fly ash, and mineral powder to obtain a powder material; mixing the powder material, modified recycled coarse aggregate, recycled fine aggregate, modified fiber, water, and water reducer to obtain a low-carbon recycled salt-resistant cement concrete.

[0018] Through the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The low-carbon recycled salt-resistant cement concrete of the present invention uses recycled aggregates to replace natural aggregates, and then modifies the recycled coarse aggregates. First, soak them in a carbon nanotube dispersion liquid so that the carbon nanotubes are adsorbed on the surface and inside the pores of the recycled coarse aggregates, and then soak them in a fluorosilicon-modified epoxy resin emulsion, and then heat and cure. By modifying the recycled coarse aggregates with the above carbon nanotubes and hydrophobic epoxy resin, the gaps of the recycled coarse aggregates are filled, the density is increased, the porosity is reduced, and the outer cured hydrophobic epoxy resin layer can reduce the intrusion of moisture, resist the erosion of salts, and further prevent the shedding of carbon nanotubes. At the same time, the epoxy resin can also enhance the strength of the concrete, effectively solving the problems of low concrete strength and poor sulfate erosion resistance existing in the resource utilization of traditional recycled coarse aggregates.

[0020] (2) The present invention also adds silane-coupled modified polypropylene fibers. After modification, the fibers are tightly connected to the concrete skeleton and can also fill the recycled coarse aggregates to ensure the strength of the concrete. Specific embodiments

[0021] The present invention provides a low-carbon recycled salt-resistant cement concrete, which comprises the following raw materials in parts by mass: 60-100 parts of cement, 100-200 parts of modified recycled coarse aggregates, 50-150 parts of recycled fine aggregates, 10-25 parts of modified fibers, 40-80 parts of fly ash, 20-50 parts of mineral powder, 1-10 parts of water reducer, and 40-120 parts of water.

[0022] In the present invention, the cement is preferably 42.5-grade portland cement.

[0023] In the present invention, the recycled coarse aggregates and recycled fine aggregates are preferably obtained by crushing, impurity removal, screening, and grading of waste concrete.

[0024] In the present invention, the particle size of the modified recycled coarse aggregates is preferably 5-10 mm; the particle size of the recycled fine aggregates is preferably 0.1-0.5 mm.

[0025] In the present invention, the preparation method of the modified recycled coarse aggregates is: soak the recycled coarse aggregates in a carbon nanotube dispersion liquid to obtain pre-modified aggregates; soak the pre-modified aggregates in a fluorosilicon-modified epoxy resin emulsion, and then heat and cure to obtain modified recycled coarse aggregates.

[0026] In the present invention, the mass ratio of the recycled coarse aggregates to the carbon nanotubes in the carbon nanotube dispersion liquid is preferably 100:0.1-1, more preferably 100:0.5-1, and still more preferably 100:0.8.

[0027] In the present invention, the carbon nanotube dispersion is preferably an aqueous solution of carbon nanotubes; the mass fraction of carbon nanotubes in the carbon nanotube dispersion is preferably 0.5 to 1%, more preferably 0.7 to 1%, and still more preferably 1%; the carbon nanotubes are preferably multi-walled carbon nanotubes, purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd., with the model number XFM34.

[0028] In the present invention, the dosage ratio of the pre-modified aggregate to the fluorosilicon-modified epoxy resin emulsion is preferably 1 to 10 g: 20 to 50 mL, more preferably 5 to 10 g: 25 to 40 mL, and still more preferably 10 g: 30 mL.

[0029] In the present invention, the soaking time in the carbon nanotube dispersion is preferably 0.5 to 3 h, more preferably 0.5 to 2 h, and still more preferably 1 h; the soaking time in the fluorosilicon-modified epoxy resin emulsion is preferably 1 to 2 h, more preferably 1.5 to 2 h, and still more preferably 2 h.

[0030] In the present invention, the heating and curing temperature is preferably 200 to 300 °C, more preferably 220 to 280 °C, and still more preferably 250 °C; the heating and curing time is preferably 1 to 5 h, more preferably 2 to 4 h, and still more preferably 3 h.

[0031] In the present invention, the preparation method of the fluorosilicon-modified epoxy resin emulsion refers to Example 1 of Patent 201610996580.3, specifically: 50 g of epoxy E-44, 20 g of hydroxyl-terminated fluorosilicon polymer (octamethylcyclotetrasiloxane-methyltrifluoropropylcyclotrisiloxane copolymer, hydroxyl content 0.1%, number average molecular weight 40000, weight average molecular weight 60000) and 0.07 g of dibutyltin dilaurate are added to a 250 mL three-necked flask equipped with a thermometer, a stirring device and a reflux condenser, 100 mL of ethyl acetate is added and completely dissolved, the temperature is raised to 120 °C, and the mixture is stirred and refluxed for 1 h. The obtained clear and transparent liquid is distilled under reduced pressure to remove ethyl acetate to obtain the fluorosilicon-modified epoxy resin emulsion.

[0032] In the present invention, the modified fiber is a silane coupling agent-modified polypropylene fiber; the silane coupling agent is preferably KH550 and / or KH560, more preferably KH550 or KH560, and still more preferably KH560; the preparation method of the modified fiber is: mixing polypropylene fiber, silane coupling agent and water in a mass ratio of 1: 0.5: 50, reacting at 70 °C for 2 h to obtain the modified fiber.

[0033] In the present invention, the fly ash is preferably secondary fly ash.

[0034] In the present invention, the mineral powder is preferably S95 grade mineral powder.

[0035] In the present invention, the water reducing agent is preferably a polycarboxylate water reducing agent.

[0036] The present invention also provides a method for preparing a low-carbon recycled salt-resistant cement concrete, comprising the following steps:

[0037] Mix cement, fly ash, and mineral powder to obtain a powder material; mix the powder material, modified recycled coarse aggregate, recycled fine aggregate, modified fiber, water, and water reducing agent to obtain a low-carbon recycled salt-resistant cement concrete.

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0039] Example 1

[0040] This example provides a low-carbon recycled salt-resistant cement concrete, containing the following raw materials in parts by mass: 85 parts of cement, 140 parts of modified recycled coarse aggregate with a particle size of 5 - 10 mm, 70 parts of recycled fine aggregate with a particle size of 0.1 - 0.5 mm, 18 parts of KH560 modified fiber, 60 parts of fly ash, 35 parts of mineral powder, 7 parts of water reducing agent, and 80 parts of water.

[0041] The preparation method of the above low-carbon recycled salt-resistant cement concrete comprises the following steps:

[0042] (1) Immerse the recycled coarse aggregate in a 1% carbon nanotube aqueous dispersion for 1 h, with the mass ratio of the recycled coarse aggregate to the carbon nanotube being 100:0.8. After drying, obtain a pre-modified aggregate; immerse the pre-modified aggregate in a fluorosilicon-modified epoxy resin emulsion for 2 h, with the dosage ratio of the pre-modified aggregate to the fluorosilicon-modified epoxy resin emulsion being 10 g:30 mL. After drying, heat and cure at 250 °C for 3 h to obtain a modified recycled coarse aggregate;

[0043] (2) Mix cement, fly ash, and mineral powder evenly by stirring to obtain a powder material;

[0044] (3) Mix the powder material, modified recycled coarse aggregate, recycled fine aggregate, and KH560 modified fiber evenly by stirring, and then add water and water reducing agent and mix evenly by stirring to obtain a low-carbon recycled salt-resistant cement concrete.

[0045] Example 2

[0046] This embodiment provides a low-carbon recycled salt-resistant cement concrete, which comprises the following raw materials in parts by mass: 68 parts of cement, 110 parts of modified recycled coarse aggregate with a particle size of 5 - 10 mm, 55 parts of recycled fine aggregate with a particle size of 0.1 - 0.5 mm, 12 parts of KH560 modified fiber, 52 parts of fly ash, 20 parts of mineral powder, 4 parts of water reducer, and 56 parts of water.

[0047] The preparation method of the above low-carbon recycled salt-resistant cement concrete comprises the following steps:

[0048] (1) Immerse the recycled coarse aggregate in an aqueous dispersion of carbon nanotubes with a mass fraction of 0.5% for 0.5 h. The mass ratio of the recycled coarse aggregate to the carbon nanotubes is 100:0.5. After drying, obtain pre-modified aggregate; Immerse the pre-modified aggregate in a fluorosilicon-modified epoxy resin emulsion for 1 h. The dosage ratio of the pre-modified aggregate to the fluorosilicon-modified epoxy resin emulsion is 1 g:20 mL. After drying, heat and cure at 220 °C for 2 h to obtain modified recycled coarse aggregate;

[0049] (2) Mix the cement, fly ash, and mineral powder evenly to obtain a powder material;

[0050] (3) Mix the powder material, modified recycled coarse aggregate, recycled fine aggregate, and KH560 modified fiber evenly, and then add water and water reducer and mix evenly to obtain the low-carbon recycled salt-resistant cement concrete.

[0051] Example 3

[0052] This embodiment provides a low-carbon recycled salt-resistant cement concrete, which comprises the following raw materials in parts by mass: 60 parts of cement, 150 parts of modified recycled coarse aggregate with a particle size of 5 - 10 mm, 50 parts of recycled fine aggregate with a particle size of 0.1 - 0.5 mm, 20 parts of KH550 modified fiber, 60 parts of fly ash, 40 parts of mineral powder, 5 parts of water reducer, and 60 parts of water.

[0053] The preparation method of the above low-carbon recycled salt-resistant cement concrete comprises the following steps:

[0054] (1) Immerse the recycled coarse aggregate in an aqueous dispersion of carbon nanotubes with a mass fraction of 0.8% for 2 h. The mass ratio of the recycled coarse aggregate to the carbon nanotubes is 100:0.2. After drying, obtain pre-modified aggregate; Immerse the pre-modified aggregate in a fluorosilicon-modified epoxy resin emulsion for 1 h. The dosage ratio of the pre-modified aggregate to the fluorosilicon-modified epoxy resin emulsion is 5 g:30 mL. After drying, heat and cure at 240 °C for 4 h to obtain modified recycled coarse aggregate;

[0055] (2) Mix the cement, fly ash, and mineral powder evenly to obtain a powder material;

[0056] (3) Mix the powder, modified recycled coarse aggregate, recycled fine aggregate, and KH550 modified fiber evenly, then add water and water reducer and mix evenly to obtain low-carbon recycled salt-resistant cement concrete.

[0057] Example 4

[0058] This example provides a low-carbon recycled salt-resistant cement concrete, which contains the following raw materials in parts by mass: 100 parts of cement, 180 parts of modified recycled coarse aggregate with a particle size of 5 - 10 mm, 100 parts of recycled fine aggregate with a particle size of 0.1 - 0.5 mm, 22 parts of KH560 modified fiber, 80 parts of fly ash, 20 parts of mineral powder, 8 parts of water reducer, and 100 parts of water.

[0059] The preparation method of the above low-carbon recycled salt-resistant cement concrete includes the following steps:

[0060] (1) Immerse the recycled coarse aggregate in an aqueous dispersion of carbon nanotubes with a mass fraction of 0.7% for 3 h. The mass ratio of the recycled coarse aggregate to the carbon nanotubes is 100:1. After drying, obtain pre-modified aggregate; immerse the pre-modified aggregate in a fluorosilicon-modified epoxy resin emulsion for 2 h. The dosage ratio of the pre-modified aggregate to the fluorosilicon-modified epoxy resin emulsion is 1 g:50 mL. After drying, heat and cure at 300 °C for 1 h to obtain the modified recycled coarse aggregate;

[0061] (2) Mix the cement, fly ash, and mineral powder evenly to obtain the powder;

[0062] (3) Mix the powder, modified recycled coarse aggregate, recycled fine aggregate, and KH560 modified fiber evenly, then add water and water reducer and mix evenly to obtain low-carbon recycled salt-resistant cement concrete.

[0063] Comparative Example 1

[0064] This comparative example provides a low-carbon recycled salt-resistant cement concrete. For details, refer to Example 1. The difference is that the recycled coarse aggregate is not modified.

[0065] Comparative Example 2

[0066] This comparative example provides a low-carbon recycled salt-resistant cement concrete. For details, refer to Example 1. The difference is that the recycled coarse aggregate is only modified with carbon nanotubes and not modified with the fluorosilicon-modified epoxy resin emulsion.

[0067] Test the 28-day compressive strength and 28-day splitting tensile strength of the low-carbon recycled salt-resistant cement concretes prepared in Examples 1 - 4 and Comparative Examples 1 - 2 according to GB / T50081 - 2019, and test the compressive strength after sulfate attack according to GB / T50082 - 2024. The results are shown in Table 1.

[0068] Table 1 Performance test results of low-carbon recycled sulfate-resistant cement concrete

[0069]

[0070] As can be seen from Table 1, the concrete prepared by the present invention uses recycled aggregates, has excellent mechanical properties, the compressive strength can reach 54.7 MPa, and the splitting tensile strength can reach 3.82 MPa. At the same time, it also has good sulfate erosion resistance. By comparing the examples with the comparative examples, it can be seen that the recycled coarse aggregates modified by carbon nanotubes and hydrophobic epoxy resin can significantly improve the sulfate erosion resistance, while the modification with only carbon nanotubes does not significantly improve the sulfate erosion resistance, and the combined modification of the two can significantly improve the salt erosion resistance.

[0071] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A low-carbon recycled salt-resistant cement concrete, characterized in that, The raw materials include the following parts by mass: 60 - 100 parts of cement, 100 - 200 parts of modified recycled coarse aggregate, 50 - 150 parts of recycled fine aggregate, 10 - 25 parts of modified fiber, 40 - 80 parts of fly ash, 20 - 50 parts of slag powder, 1 - 10 parts of water reducing agent, and 40 - 120 parts of water.

2. A low-carbon recycled salt-resistant cement concrete according to claim 1, characterized in that, The particle size of the modified recycled coarse aggregate is 5 - 10 mm; the particle size of the recycled fine aggregate is 0.1 - 0.5 mm.

3. A low-carbon recycled salt-resistant cement concrete according to claim 2, characterized in that, The preparation method of the modified recycled coarse aggregate is as follows: soak the recycled coarse aggregate in a carbon nanotube dispersion liquid to obtain a pre-modified aggregate; soak the pre-modified aggregate in a fluorosilicon-modified epoxy resin emulsion, and then heat and cure to obtain the modified recycled coarse aggregate.

4. A low-carbon recycled salt-resistant cement concrete according to claim 3, characterized in that, The mass ratio of the recycled coarse aggregate to the carbon nanotubes in the carbon nanotube dispersion liquid is 100:0.1 - 1.

5. A low-carbon recycled salt-resistant cement concrete according to claim 4, characterized in that The carbon nanotube dispersion liquid is an aqueous solution of carbon nanotubes; the mass fraction of carbon nanotubes in the carbon nanotube dispersion liquid is 0.5 - 1%.

6. A low-carbon recycled salt-resistant cement concrete according to claim 3, characterized in that, The dosage ratio of the pre-modified aggregate to the fluorosilicon-modified epoxy resin emulsion is 1 - 10 g:20 - 50 mL.

7. A low-carbon recycled salt-resistant cement concrete according to claim 3, characterized in that, The soaking time in the carbon nanotube dispersion liquid is 0.5 - 3 h; the soaking time in the fluorosilicon-modified epoxy resin emulsion is 1 - 2 h.

8. A low-carbon recycled salt-resistant cement concrete according to claim 7, characterized in that The temperature of the heat curing is 200 - 300 °C; the time of the heat curing is 1 - 5 h.

9. A low-carbon recycled salt-resistant cement concrete according to claim 1, characterized in that The modified fiber is a silane coupling agent-modified polypropylene fiber.

10. A method for preparing a low-carbon recycled salt-resistant cement concrete according to any one of claims 1 to 9, characterized in that, It includes the following steps: Mix the cement, fly ash, and slag powder to obtain a powder; mix the powder, modified recycled coarse aggregate, recycled fine aggregate, modified fiber, water, and water reducing agent to obtain a low-carbon recycled salt-resistant cement concrete.

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