A recycled environmental protection aggregate based on construction waste and its preparation method

Abstract

The present invention relates to the technical field of recycled building materials, and discloses a recycled environmental protection aggregate based on construction waste and a preparation method thereof. In the present invention, waste concrete is crushed, screened, and washed to obtain pretreated recycled aggregate. Nano-silica is added to a modified acrylate emulsion and ultrasonically dispersed to obtain a composite emulsion. The composite emulsion is added to the pretreated recycled aggregate, stirred and mixed, and then dried by sunning to obtain a recycled environmental protection aggregate based on construction waste. The nitrogen atoms in the imidazole group and pyrrole group form hydrogen bonds with the hydroxyl groups on the surface of the aggregate, improving the mechanical properties of the aggregate; the silyl group reacts with the hydroxyl groups on the surface of the aggregate to form a hydrophobic film to block the penetration of water molecules and reduce the water absorption rate; the sulfonate group can form a stable calcium sulfonate complex with calcium ions in the cement hydration products, enhancing the chemical bonding between the aggregate and the cement matrix; the introduction of fluorine-containing monomers can improve the hydrophobic performance of the modified polyacrylate emulsion after film formation, thereby reducing the water absorption rate.

Description

Technical Field

[0001] The present invention relates to the technical field of recycled building materials, and specifically to a recycled environmental protection aggregate based on construction waste and a preparation method thereof. Background Art

[0002] Recycled aggregates are mainly made from construction solid wastes such as waste concrete and bricks through multiple processing links such as crushing and screening by professional recycling equipment. The treatment and recycling of recycled aggregates can not only solve the shortage problem of natural aggregates, but also reduce the pollution caused by natural aggregates to the environment, with huge economic and environmental benefits. The component sources of recycled aggregates are complex, with more angular particles and rough surfaces, and some also have microcracks. These factors lead to a higher water absorption rate of recycled aggregates, and their mechanical properties in cement-based materials are not stable, directly affecting the strength of recycled aggregate concrete. This defect has limited the wider application of recycled aggregates to a certain extent. Patent CN105884279B discloses carbon fiber reinforced recycled aggregate concrete, and the compressive and tensile abilities of this invention's concrete are significantly improved. And the raw materials are all common and the processing technology is simple, but the water absorption rate of the recycled aggregates therein has not been improved. Summary of the Invention

[0003] (I) Technical Problems to be Solved

[0004] Aiming at the deficiencies of the prior art, the present invention provides a recycled environmental protection aggregate based on construction waste and a preparation method thereof. The recycled environmental protection aggregate prepared by the present invention has good mechanical properties and a low water absorption rate.

[0005] (II) Technical Solutions

[0006] To achieve the above object, the present invention provides the following technical solutions: A recycled environmental protection aggregate based on construction waste, comprising the following weight components: 80-90 parts by weight of waste concrete, 20-24 parts by weight of modified acrylate emulsion, and 2-5 parts by weight of nano-silica.

[0007] Preferably, the preparation method of the modified acrylate emulsion includes the following steps:

[0008] (1) Add 11.5-11.8 g of 2-amino-1-methylimidazole to 80-100 mL of ethanol solvent, stir to dissolve, add 2.4-3.2 mL of concentrated hydrochloric acid to adjust the pH value, introduce nitrogen protection, heat up to 90-100 °C, add 10.4-11 mL of formaldehyde solution with a mass fraction of 35%-39%, 10.8-11.2 g of N-vinylpyrrolidone, and 0.05-0.08 g of hydroquinone inhibitor thereto, react for 5-7 h, after the reaction is completed, remove the solvent by rotary evaporation, wash and dry in vacuum to obtain a Mannich base intermediate;

[0009] (2) Under a nitrogen atmosphere, 2.3 - 2.5 g of Mannich base intermediate, 0.03 - 0.05 g of catalyst, and 0.02 - 0.04 g of hydroquinone inhibitor were added to 50 - 80 mL of tetrahydrofuran solvent, stirred and mixed. Then 2.8 - 3.2 g of acryloxypropyltrimethoxysilane was added thereto, and the temperature was raised to 30 - 45 °C for reaction for 2.5 - 4 h. After the reaction was completed, it was filtered, washed and dried to obtain a silane-modified Mannich base monomer;

[0010] (3) Under a nitrogen atmosphere, 2.5 - 4.2 g of sodium bisulfite was added to 20 - 40 mL of deionized water solvent and stirred until dissolved. 3.1 - 5.2 g of 2-(3,4-difluorophenyl)oxirane was dissolved in 30 - 50 mL of absolute ethanol. At the reaction temperature, it was added dropwise to the sodium bisulfite solution, and the dropping time was controlled within 1 - 1.5 h. After the dropping was completed, the reaction continued for 3 - 6 h. After the reaction was completed, the reaction solution was cooled in an ice-water bath, and the precipitated crystals after cooling were suction-filtered and recrystallized to obtain sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate;

[0011] (4) 2.2 - 2.9 g of sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate and 1.2 - 1.6 g of triethylamine acid-binding agent were added to 60 - 90 mL of tetrahydrofuran solvent and stirred until dissolved. Then 1 - 1.5 g of methacryloyl chloride was added dropwise thereto. After the dropping was completed, the reaction was carried out at 0 - 10 °C for 1 - 2 h, and then the temperature was raised to 20 - 28 °C for reaction for 4 - 8 h. After the reaction was completed, it was filtered and the solvent was removed by rotary evaporation to obtain a fluorosulfonate-modified methyl methacrylate monomer;

[0012] (5) 0.6 - 0.8 g of acrylic acid, 1.5 - 1.9 g of fluorosulfonate-modified methyl methacrylate monomer, 0.8 - 1.2 g of hydroxypropyl methacrylate, 2.1 - 2.3 g of silane-modified Mannich base monomer, and 0.04 - 0.08 g of emulsifier were added to 15 - 20 mL of deionized water and stirred and mixed to obtain a pre-emulsion. 4 - 8 mL of deionized water and 0.06 - 0.12 g of emulsifier were added to the reactor, and the temperature was raised to 60 - 80 °C. 10% - 20% of the pre-emulsion and 0.01 - 0.03 g of initiator were added thereto. After constant-temperature reaction for 15 - 30 min, the remaining pre-emulsion and 0.04 - 0.05 g of initiator were added, and the constant-temperature reaction continued for 1.5 - 2.5 h. After the reaction was completed, it was cooled and filtered to obtain a modified acrylate emulsion.

[0013] Preferably, in the step (1), the pH value is adjusted to 2 - 2.5.

[0014] Preferably, in the step (2), the catalyst is triethylamine.

[0015] Preferably, the reaction temperature in step (3) is 25 - 40 °C.

[0016] Preferably, the emulsifier in step (5) is sodium dodecyl sulfate.

[0017] Preferably, the initiator in step (5) is ammonium persulfate.

[0018] Preferably, the preparation method of the recycled environmental protection aggregate based on construction waste is as follows: crushing, screening, and washing waste concrete to obtain pretreated recycled aggregate; adding nano-silica into the modified acrylate emulsion and ultrasonically dispersing for 20 - 40 min to obtain a composite emulsion; adding the composite emulsion into the pretreated recycled aggregate, stirring and mixing for 10 - 15 min, and drying in the sun to obtain the recycled environmental protection aggregate based on construction waste.

[0019] (III) Beneficial technical effects

[0020] In the present invention, waste concrete is crushed, screened, and washed to obtain pretreated recycled aggregate; nano-silica is added into the modified acrylate emulsion and ultrasonically dispersed to obtain a composite emulsion; the composite emulsion is added into the pretreated recycled aggregate, stirred and mixed, and dried in the sun to obtain the recycled environmental protection aggregate based on construction waste.

[0021] The molecular chain of the modified acrylate emulsion can penetrate into the pores of the recycled environmental protection aggregate and form a dense polymer film after curing, reducing the porosity and improving the density and compressive strength of the aggregate; in the silane-modified Mannich base monomer, the nitrogen atoms in the imidazole group and pyrrole group form hydrogen bonds with the hydroxyl groups on the surface of the recycled environmental protection aggregate, further improving the bonding strength between the recycled environmental protection aggregate and the modified acrylate emulsion, and thus improving the mechanical properties of the recycled environmental protection aggregate; after hydrolysis, the silyl group reacts with the hydroxyl groups on the surface of the recycled environmental protection aggregate to form stable siloxane bonds, forming a hydrophobic film to block the penetration of water molecules and improving the denseness of the polymer film, thereby reducing the water absorption rate; the sulfonate group can form a stable calcium sulfonate complex with calcium ions in the cement hydration products, enhancing the chemical bonding between the recycled environmental protection aggregate and the cement matrix; the high electronegativity of fluorine atoms makes the surface energy of the fluorine-containing polymer low and not easily wetted by water. The introduction of fluorine-containing monomers can improve the hydrophobic performance of the modified acrylate emulsion film after film formation, thereby reducing the water absorption rate of the recycled environmental protection aggregate. Description of the drawings

[0022] Figure 1 is the synthesis reaction formula of the silane-modified Mannich base monomer.

[0023] Figure 2 is the fluorosulfonate-modified methyl methacrylate monomer. Specific embodiments

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] To better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments. Example 1

[0026] (1) Add 11.5 g of 2-amino-1-methylimidazole to 80 mL of ethanol solvent, stir to dissolve, add 2.4 mL of concentrated hydrochloric acid to adjust the pH value to 2, introduce nitrogen for protection, heat up to 90 °C, add 10.4 mL of formaldehyde solution with a mass fraction of 35%, 10.8 g of N-vinylpyrrolidone, and 0.05 g of hydroquinone inhibitor, react for 5 h. After the reaction is completed, remove the solvent by rotary evaporation, wash, and dry under vacuum to obtain the Mannich base intermediate.

[0027] (2) Under a nitrogen atmosphere, add 2.3 g of the Mannich base intermediate, 0.03 g of triethylamine catalyst, and 0.02 g of hydroquinone inhibitor to 50 mL of tetrahydrofuran solvent, stir and mix, add 2.8 g of acryloxypropyltrimethoxysilane thereto, heat up to 30 °C and react for 2.5 h. After the reaction is completed, filter, wash, and dry to obtain the silane-modified Mannich base monomer.

[0028] (3) Under a nitrogen atmosphere, add 2.5 g of sodium bisulfite to 20 mL of deionized water solvent, stir to dissolve, dissolve 3.1 g of 2-(3,4-difluorophenyl)oxirane in 30 mL of absolute ethanol, and at 25 °C, drop it into the sodium bisulfite solution. The dropping time is controlled within 1 h. After the dropping is completed, continue to react for 3 h. After the reaction is completed, cool the reaction solution in an ice-water bath, filter the precipitated crystals after cooling, and recrystallize to obtain 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonic acid sodium salt.

[0029] (4) Add 2.2 g of 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonic acid sodium salt and 1.2 g of triethylamine acid-binding agent to 60 mL of tetrahydrofuran solvent, stir to dissolve, dropwise add 1 g of methacryloyl chloride thereto. After the dropping is completed, react at 0 °C for 1 h, heat up to 20 °C and react for 4 h. After the reaction is completed, filter and remove the solvent by rotary evaporation to obtain the fluorosulfonate-modified methyl methacrylate monomer.

[0030] (5) Add 0.6 g of acrylic acid, 1.5 g of fluorosulfonate-modified methyl methacrylate monomer, 0.8 g of hydroxypropyl methacrylate, 2.1 g of silane-modified Mannich base monomer, and 0.04 g of sodium dodecyl sulfate emulsifier to 15 mL of deionized water, stir and mix to obtain a pre-emulsion. Add 4 mL of deionized water and 0.06 g of sodium dodecyl sulfate emulsifier to the reactor, heat up to 60 °C, add 10% of the pre-emulsion and 0.01 g of ammonium persulfate initiator, keep the temperature constant and react for 15 min, then add the remaining pre-emulsion and 0.04 g of ammonium persulfate initiator, continue to keep the temperature constant and react for 1.5 h. After the reaction is completed, cool and filter to obtain a modified acrylate emulsion;

[0031] (6) Crush, screen, and wash 80 parts by weight of waste concrete to obtain pretreated recycled aggregate. Add 2 parts by weight of nano-silica to 20 parts by weight of the modified acrylate emulsion, ultrasonically disperse for 20 min to obtain a composite emulsion. Add the composite emulsion to the pretreated recycled aggregate, stir and mix for 10 min, then dry in the sun to obtain recycled and environmentally friendly aggregate based on construction waste. Example 2

[0032] (1) Add 11.8 g of 2-amino-1-methylimidazole to 100 mL of ethanol solvent, stir to dissolve, add 3.2 mL of concentrated hydrochloric acid to adjust the pH value to 2.5, introduce nitrogen protection, heat up to 100 °C, add 11 mL of formaldehyde solution with a mass fraction of 39%, 11.2 g of N-vinylpyrrolidone, and 0.08 g of hydroquinone inhibitor, react for 7 h. After the reaction is completed, remove the solvent by rotary evaporation, wash and dry in vacuum to obtain a Mannich base intermediate;

[0033] (2) Under a nitrogen atmosphere, add 2.5 g of the Mannich base intermediate, 0.05 g of triethylamine catalyst, and 0.04 g of hydroquinone inhibitor to 80 mL of tetrahydrofuran solvent, stir and mix, add 3.2 g of acryloxypropyltrimethoxysilane, heat up to 45 °C and react for 4 h. After the reaction is completed, filter, wash and dry to obtain a silane-modified Mannich base monomer;

[0034] (3) Under a nitrogen atmosphere, add 4.2 g of sodium bisulfite to 40 mL of deionized water solvent, stir to dissolve. Dissolve 5.2 g of 2-(3,4-difluorophenyl)oxirane in 50 mL of absolute ethanol, and drop it into the sodium bisulfite solution at 40 °C. Control the dropping time within 1.5 h. After the dropping is completed, continue to react for 6 h. After the reaction is completed, cool the reaction solution in an ice-water bath, filter the precipitated crystals after cooling, and recrystallize to obtain 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate;

[0035] (4) Add 2.9 g of sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate and 1.6 g of triethylamine as an acid-binding agent to 90 mL of tetrahydrofuran solvent, stir to dissolve, and add 1.5 g of methacryloyl chloride dropwise thereto. After the addition is complete, react at 10 °C for 2 h, then raise the temperature to 28 °C and react for 8 h. After the reaction is completed, filter and remove the solvent by rotary evaporation to obtain a methyl methacrylate monomer modified with fluorosulfonate;

[0036] (5) Add 0.8 g of acrylic acid, 1.9 g of methyl methacrylate monomer modified with fluorosulfonate, 1.2 g of hydroxypropyl methacrylate, 2.3 g of silane-modified Mannich base monomer, and 0.08 g of sodium dodecyl sulfate emulsifier to 20 mL of deionized water, stir and mix to obtain a pre-emulsion. Add 8 mL of deionized water and 0.12 g of sodium dodecyl sulfate emulsifier to the reactor, heat up to 80 °C, add 20% of the pre-emulsion and 0.03 g of ammonium persulfate initiator thereto, react at a constant temperature for 30 min, then add the remaining pre-emulsion and 0.05 g of ammonium persulfate initiator, and continue to react at a constant temperature for 2.5 h. After the reaction is completed, cool and filter to obtain a modified acrylate emulsion;

[0037] (6) Crush, screen, and wash 90 parts by weight of waste concrete to obtain pretreated recycled aggregate. Add 5 parts by weight of nano-silica to 24 parts by weight of the modified acrylate emulsion, disperse ultrasonically for 40 min to obtain a composite emulsion. Add the composite emulsion to the pretreated recycled aggregate, stir and mix for 15 min, then air dry to obtain recycled and environmentally friendly aggregate based on construction waste. Example 3

[0038] (1) Add 11.65 g of 2-amino-1-methylimidazole to 90 mL of ethanol solvent, stir to dissolve, add 2.8 mL of concentrated hydrochloric acid to adjust the pH value to 2.3, protect with nitrogen, heat up to 95 °C, and add 10.7 mL of formaldehyde solution with a mass fraction of 37%, 11 g of N-vinylpyrrolidone, and 0.065 g of hydroquinone as a polymerization inhibitor. React for 6 h. After the reaction is completed, remove the solvent by rotary evaporation, wash, and dry in vacuo to obtain a Mannich base intermediate;

[0039] (2) Under a nitrogen atmosphere, add 2.4 g of the Mannich base intermediate, 0.04 g of triethylamine catalyst, and 0.03 g of hydroquinone as a polymerization inhibitor to 65 mL of tetrahydrofuran solvent, stir and mix, add 3 g of acryloxypropyltrimethoxysilane thereto, heat up to 38 °C and react for 3.2 h. After the reaction is completed, filter, wash, and dry to obtain a silane-modified Mannich base monomer;

[0040] (3) Under a nitrogen atmosphere, 3.35 g of sodium bisulfite was added to 30 mL of deionized water solvent and stirred until dissolved. 4.15 g of 2-(3,4-difluorophenyl)oxirane was dissolved in 40 mL of absolute ethanol. At 32 °C, it was added dropwise to the sodium bisulfite solution, and the dropping time was controlled within 1.2 h. After the dropping was completed, the reaction continued for 4.5 h. After the reaction ended, the reaction solution was cooled in an ice-water bath, and the crystals precipitated after cooling were filtered by suction and recrystallized to obtain sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate;

[0041] (4) 2.55 g of sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate and 1.4 g of triethylamine as an acid-binding agent were added to 75 mL of tetrahydrofuran solvent and stirred until dissolved. 1.25 g of methacryloyl chloride was added dropwise thereto. After the dropping was completed, the reaction was carried out at 5 °C for 1.5 h and then heated to 24 °C for 6 h. After the reaction ended, it was filtered, and the solvent was removed by rotary evaporation to obtain a fluorosulfonate-modified methyl methacrylate monomer;

[0042] (5) 0.7 g of acrylic acid, 1.7 g of fluorosulfonate-modified methyl methacrylate monomer, 1 g of hydroxypropyl methacrylate, 2.2 g of silane-modified Mannich base monomer, and 0.06 g of sodium dodecyl sulfate emulsifier were added to 18 mL of deionized water and stirred and mixed to obtain a pre-emulsion. 6 mL of deionized water and 0.09 g of sodium dodecyl sulfate emulsifier were added to the reactor, and the temperature was raised to 70 °C. 15% of the pre-emulsion and 0.02 g of ammonium persulfate initiator were added thereto. After reacting at a constant temperature for 22 min, the remaining pre-emulsion and 0.045 g of ammonium persulfate initiator were added, and the reaction continued at a constant temperature for 2 h. After the reaction ended, it was cooled and filtered to obtain a modified acrylate emulsion;

[0043] (6) 85 parts by weight of waste concrete was crushed, screened, and washed to obtain pretreated recycled aggregate. 3.5 parts by weight of nano-silica was added to 22 parts by weight of the modified acrylate emulsion and ultrasonically dispersed for 30 min to obtain a composite emulsion. The composite emulsion was added to the pretreated recycled aggregate, stirred and mixed for 12 min, and then dried by sunning to obtain a recycled environmental protection aggregate based on construction waste. Example 4

[0044] (1) 11.5 g of 2-amino-1-methylimidazole was added to 80 mL of ethanol solvent and stirred until dissolved. 2.4 mL of concentrated hydrochloric acid was added to adjust the pH value to 2. Nitrogen protection was introduced, and the temperature was raised to 90 °C. 10.4 mL of formaldehyde solution with a mass fraction of 35%, 10.8 g of N-vinylpyrrolidone, and 0.05 g of hydroquinone inhibitor were added thereto, and the reaction was carried out for 5 h. After the reaction ended, the solvent was removed by rotary evaporation, washed, and dried in vacuo to obtain a Mannich base intermediate;

[0045] (2) Under a nitrogen atmosphere, 2.3 g of a Mannich base intermediate, 0.03 g of a triethylamine catalyst, and 0.02 g of a hydroquinone inhibitor were added to 50 mL of a tetrahydrofuran solvent, stirred and mixed, 2.8 g of acryloxypropyltrimethoxysilane was added thereto, the temperature was raised to 30 °C and reacted for 2.5 h. After the reaction was completed, it was filtered, washed and dried to obtain a silane-modified Mannich base monomer;

[0046] (3) Under a nitrogen atmosphere, 4.2 g of sodium bisulfite was added to 40 mL of a deionized water solvent, stirred and dissolved. 5.2 g of 2-(3,4-difluorophenyl)oxirane was dissolved in 50 mL of absolute ethanol. At 40 °C, it was added dropwise to the sodium bisulfite solution, and the dropping time was controlled within 1.5 h. After the dropping was completed, the reaction was continued for 6 h. After the reaction was completed, the reaction solution was cooled in an ice-water bath, and the crystals precipitated after cooling were filtered by suction and recrystallized to obtain sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate;

[0047] (4) 2.9 g of sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate and 1.6 g of a triethylamine acid-binding agent were added to 90 mL of a tetrahydrofuran solvent, stirred and dissolved, 1.5 g of methacryloyl chloride was added dropwise thereto. After the dropping was completed, the reaction was carried out at 10 °C for 2 h, and the temperature was raised to 28 °C and reacted for 8 h. After the reaction was completed, it was filtered and the solvent was removed by rotary evaporation to obtain a fluorosulfonate-modified methyl methacrylate monomer;

[0048] 0.7 g of acrylic acid, 1.7 g of the fluorosulfonate-modified methyl methacrylate monomer, 1 g of hydroxypropyl methacrylate, 2.2 g of the silane-modified Mannich base monomer, and 0.06 g of sodium dodecyl sulfate emulsifier were added to 18 mL of deionized water, stirred and mixed to obtain a pre-emulsion. 6 mL of deionized water and 0.09 g of sodium dodecyl sulfate emulsifier were added to the reactor, the temperature was raised to 70 °C, 15% of the pre-emulsion and 0.02 g of ammonium persulfate initiator were added thereto, and after reacting at a constant temperature for 22 min, the remaining pre-emulsion and 0.045 g of ammonium persulfate initiator were added, and the reaction was continued at a constant temperature for 2 h. After the reaction was completed, it was cooled and filtered to obtain a modified acrylate emulsion;

[0049] (6) 85 parts by weight of waste concrete was crushed, screened and washed to obtain pretreated recycled aggregate. 3.5 parts by weight of nano-silica was added to 22 parts by weight of the modified acrylate emulsion, ultrasonically dispersed for 30 min to obtain a composite emulsion. The composite emulsion was added to the pretreated recycled aggregate, stirred and mixed for 12 min, and then dried by airing to obtain a recycled environmental protection aggregate based on construction waste. Example 5

[0050] (1) Add 11.8 g of 2-amino-1-methylimidazole to 100 mL of ethanol solvent, stir to dissolve, add 3.2 mL of concentrated hydrochloric acid to adjust the pH value to 2.5, introduce nitrogen for protection, heat up to 100 °C, add 11 mL of formaldehyde solution with a mass fraction of 39%, 11.2 g of N-vinylpyrrolidone, and 0.08 g of hydroquinone inhibitor, react for 7 h. After the reaction, remove the solvent by rotary evaporation, wash and dry in vacuum to obtain the Mannich base intermediate;

[0051] (2) Under a nitrogen atmosphere, add 2.5 g of the Mannich base intermediate, 0.05 g of triethylamine catalyst, and 0.04 g of hydroquinone inhibitor to 80 mL of tetrahydrofuran solvent, stir and mix, add 3.2 g of acryloxypropyltrimethoxysilane to it, heat up to 45 °C and react for 4 h. After the reaction, filter, wash and dry to obtain the silane-modified Mannich base monomer;

[0052] (3) Under a nitrogen atmosphere, add 3.35 g of sodium bisulfite to 30 mL of deionized water solvent, stir to dissolve, dissolve 4.15 g of 2-(3,4-difluorophenyl)oxirane in 40 mL of absolute ethanol, and at 32 °C, drop it into the sodium bisulfite solution. The dropping time is controlled within 1.2 h. After dropping, continue to react for 4.5 h. After the reaction, cool the reaction solution in an ice-water bath, filter the precipitated crystals by suction, and recrystallize to obtain sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate;

[0053] (4) Add 2.55 g of sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate and 1.4 g of triethylamine acid-binding agent to 75 mL of tetrahydrofuran solvent, stir to dissolve, drop 1.25 g of methacryloyl chloride into it. After dropping, react at 5 °C for 1.5 h, then heat up to 24 °C and react for 6 h. After the reaction, filter and remove the solvent by rotary evaporation to obtain the fluorosulfonate-modified methyl methacrylate monomer;

[0054] (5) Add 0.6 g of acrylic acid, 1.5 g of the fluorosulfonate-modified methyl methacrylate monomer, 0.8 g of hydroxypropyl methacrylate, 2.1 g of the silane-modified Mannich base monomer, and 0.04 g of sodium dodecyl sulfate emulsifier to 15 mL of deionized water, stir and mix to obtain a pre-emulsion. Add 4 mL of deionized water and 0.06 g of sodium dodecyl sulfate emulsifier to the reactor, heat up to 60 °C, add 10% of the pre-emulsion and 0.01 g of ammonium persulfate initiator, keep the temperature constant and react for 15 min, then add the remaining pre-emulsion and 0.04 g of ammonium persulfate initiator, and continue to keep the temperature constant and react for 1.5 h. After the reaction, cool and filter to obtain the modified acrylate emulsion;

[0055] (6) Crush, screen, and wash 80 parts by weight of waste concrete to obtain pretreated recycled aggregate. Add 2 parts by weight of nano-silica to 20 parts by weight of modified acrylate emulsion, and ultrasonically disperse for 20 min to obtain a composite emulsion. Add the composite emulsion to the pretreated recycled aggregate, stir and mix for 10 min, and then air dry to obtain recycled environmental protection aggregate based on construction waste.

[0056] Comparative Example 1

[0057] Compared with Example 5, the difference in this comparative example is that the fluorosulfonate-modified methyl methacrylate monomer is not included in step (5).

[0058] Comparative Example 2

[0059] Compared with Example 5, the difference in this comparative example is that the silane-modified Mannich base monomer is not included in step (5).

[0060] Prepare concrete from the recycled environmental protection aggregates in Examples 1-5 and Comparative Examples 1-2 of the present invention according to the following formula: 350 kg of portland cement, 70 kg of Class II fly ash, 825 kg of recycled environmental protection aggregate, 720 kg of river sand, 7.5 kg of polycarboxylate water reducer, and 189 kg of water.

[0061] Refer to GB / T50081-2019 "Standard Test Method for Physical and Mechanical Properties of Concrete" to conduct compressive strength tests on the above-prepared concrete. The test results are shown in Table 1.

[0062] Table 1: Compressive strength test.

[0063] Item 28d Compressive Strength (MPa) 56d Compressive Strength (MPa) Example 1 39.8 45.6 Example 2 40.4 46.3 Example 3 41.5 46.9 Example 4 38.9 44.8 Example 5 42.0 46.1 Comparative Example 1 30.6 37.8 Comparative Example 2 26.4 34.1

[0064] As can be seen from Table 1, the recycled environmental protection aggregates in Examples 1-5 of the present invention have better mechanical properties than those in Comparative Examples 1-2, which is reflected in that the concrete prepared from the recycled environmental protection aggregates in Examples 1-5 of the present invention has better compressive strength than the concrete prepared from the recycled environmental protection aggregates in Comparative Examples 1-2.

[0065] Weigh 1.5 kg of the dry weight of the recycled environmental protection aggregates in Examples 1-5 and Comparative Examples 1-2 respectively, store them under indoor conditions with a humidity of 50% for 7 d, take out the recycled environmental protection aggregates, weigh the wet weight, and calculate the water absorption rate. The test results are shown in Table 2.

[0066] Table 2: Water absorption rate test.

[0067] Item Water Absorption Rate (%) Example 1 3.8 Example 2 3.4 Example 3 3.7 Example 4 3.5 Example 5 3.3 Comparative Example 1 5.8 Comparative Example 2 6.2

[0068] As can be seen from Table 2, the recycled environmental protection aggregates in Examples 1-5 of the present invention have lower water absorption rates than those in Comparative Examples 1-2.

[0069] It should be noted that, in this document, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0071] Those skilled in the art should understand that the above are only several specific embodiments of the present invention, rather than all embodiments. It should be pointed out that many variations and improvements can be made for those of ordinary skill in the art, and all variations or improvements that do not exceed the scope of the claims should be regarded as the protection scope of the present invention.

Claims

1. A recycled environmentally friendly aggregate based on construction waste, characterized in that: The invention comprises the following components by weight: 80-90 parts by weight of waste concrete, 20-24 parts by weight of modified acrylic emulsion, and 2-5 parts by weight of nano silicon dioxide; The preparation method of the modified acrylic ester emulsion comprises the following steps: (1) Add 11.5-11.8 g of 2-amino-1-methylimidazole to 80-100 mL of ethanol solvent, stir to dissolve, add 2.4-3.2 mL of concentrated hydrochloric acid to adjust the pH value, introduce nitrogen protection, heat to 90-100 ° C, add 10.4-11 mL of 35%-39% formaldehyde solution, 10.8-11.2 g of N-vinyl pyrrolidone, and 0.05-0.08 g of hydroquinone inhibitor, react for 5-7 hours, and after the reaction is completed, remove the solvent by rotary evaporation, wash and vacuum dry to obtain a Mannich base intermediate; (2) Under a nitrogen atmosphere, add 2.3-2.5 g of a Mannich base intermediate, 0.03-0.05 g of a catalyst, and 0.02-0.04 g of a hydroquinone inhibitor to 50-80 mL of a tetrahydrofuran solvent, stir and mix, add 2.8-3.2 g of acryloxypropyltrimethoxysilane, raise the temperature to 30-45° C. and react for 2.5-4 h. After the reaction is completed, filter, wash and dry to obtain a silane-modified Mannich base monomer; (3) Under a nitrogen atmosphere, add 2.5-4.2 g of sodium bisulfite to 20-40 mL of deionized water solvent, stir to dissolve, dissolve 3.1-5.2 g of 2-(3,4-difluorophenyl)ethylene oxide in 30-50 mL of anhydrous ethanol, and add it dropwise to the sodium bisulfite solution at the reaction temperature. The addition time is controlled to be 1-1.5 h. After the addition is completed, continue the reaction for 3-6 h. After the reaction is completed, cool the reaction solution in an ice water bath, filter the crystals precipitated after cooling, and recrystallize to obtain sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate; (4) Add 2.2-2.9 g of sodium 2-(3,4-difluorophenyl)-2-hydroxyethanesulfonate and 1.2-1.6 g of triethylamine acid binding agent to 60-90 mL of tetrahydrofuran solvent, stir to dissolve, add 1-1.5 g of methacryloyl chloride dropwise thereto, react at 0-10° C. for 1-2 h, heat to 20-28° C. for 4-8 h, filter after the reaction, and remove the solvent by rotary evaporation to obtain a fluorinated sulfonate-modified methyl methacrylate monomer; (5) Add 0.6-0.8 g of acrylic acid, 1.5-1.9 g of fluorinated sulfonate-modified methyl methacrylate monomer, 0.8-1.2 g of hydroxypropyl methacrylate, 2.1-2.3 g of silane-modified Mannich base monomer, and 0.04-0.08 g of emulsifier to 15-20 mL of deionized water, stir and mix to obtain a pre-emulsion, add 4-8 mL of deionized water and 0.06-0.12 g of emulsifier to the reactor, heat to 60-80° C., add 10%-20% of the pre-emulsion and 0.01-0.03 g of initiator, react at constant temperature for 15-30 min, then add the remaining pre-emulsion and 0.04-0.05 g of initiator, continue the constant temperature reaction for 1.5-2.5 h, cool and filter after the reaction to obtain a modified acrylic ester emulsion.

2. The recycled environmentally friendly aggregate based on construction waste according to claim 1 is characterized in that: In the step (1), the pH value is adjusted to 2-2.

5.

3. The recycled environmentally friendly aggregate based on construction waste according to claim 1 is characterized in that: The catalyst in step (2) is triethylamine.

4. The recycled environmentally friendly aggregate based on construction waste according to claim 1 is characterized in that: The reaction temperature in step (3) is 25-40°C.

5. The recycled environmentally friendly aggregate based on construction waste according to claim 1 is characterized in that: The emulsifier in step (5) is sodium lauryl sulfate.

6. The recycled environmentally friendly aggregate based on construction waste according to claim 1 is characterized in that: The initiator in step (5) is ammonium persulfate.

7. A method for preparing recycled environmentally friendly aggregate based on construction waste as claimed in any one of claims 1 to 6, characterized in that: The preparation method of the recycled environmentally friendly aggregate based on construction waste is as follows: waste concrete is crushed, screened and cleaned to obtain pre-treated recycled aggregate, nano silicon dioxide is added to a modified acrylic ester emulsion, ultrasonically dispersed for 20-40 minutes to obtain a composite emulsion, the composite emulsion is added to the pre-treated recycled aggregate, stirred and mixed for 10-15 minutes, and dried in the sun to obtain the recycled environmentally friendly aggregate based on construction waste.

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