A magnesium-based construction waste recycling material and its preparation method

Abstract

The present invention relates to the technical field of building materials, and discloses a magnesium-based construction waste recycling material and a preparation method thereof. It includes 10-25 parts of magnesium-based cementitious material and 65-80 parts of construction waste recycled aggregate; a composite modifier, including an inorganic modifier, an organic modifier and an interface enhancer, and the specific weight parts are: inorganic modifier: 0.2-0.9 parts of potassium dihydrogen phosphate. Through the synergistic effect of the composite modifier and the nano-enhanced system, the present invention significantly improves the mechanical strength and durability of the material. Combining the aggregate interface strengthening treatment with the intelligent self-healing microcapsule design, the function of autonomous crack repair is realized; at the same time, high-amount construction waste recycled aggregate and industrial solid waste are adopted to optimize the microstructure of the material and reduce the porosity, with excellent crack resistance, high resource utilization rate and environmental friendliness and other characteristics, breaking through the performance bottleneck of traditional recycled materials, and being applicable to the field of green building engineering with high durability requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly to a magnesium-based construction waste recycling material and a preparation method thereof. Background Art

[0002] With the acceleration of the urbanization process, the generation amount of construction waste is increasing day by day. Traditional treatment methods such as landfilling and open stacking not only occupy a large amount of land resources but also cause environmental pollution. For traditional construction waste recycling technologies, it is necessary to separate soil-like, wood-like, organic matter-like, and powder-like materials in construction waste, and use the selected materials with certain strength as construction waste recycled aggregates, and then carry out water washing or other dust removal methods for reuse. Nearly 50% of the remaining materials after separation are difficult to utilize.

[0003] Existing construction waste recycling materials mostly rely on portland cement, with high production energy consumption (accounting for 8% of the global CO2 emissions). Due to the high porosity and strong water absorption of recycled aggregates, the mechanical properties of traditional portland cement-based materials are insufficient, such as low strength and poor durability. They can only be incorporated into other concretes in a small proportion.

[0004] Magnesium-based cementitious materials have the advantages of good compatibility, fast setting, high strength, and good fire resistance. When applied to construction waste recycling materials, the construction waste does not need to be separated. The construction waste is crushed to a particle size of 0.5 - 3 cm and combined with magnesium-based cementitious materials. Through modifiers, the properties of magnesium-based cementitious materials are improved, and the water resistance and inhibition of brine return are enhanced, which is suitable for humid environments. By optimizing the magnesium-based cementitious system with additives and combining with solid waste-based materials, solid waste resource utilization and low-carbon preparation are realized, providing a construction waste recycling material with high strength, fast hardening, water resistance, and environmental protection characteristics. Therefore, we propose a magnesium-based construction waste recycling material and a preparation method thereof to solve the above problems. Summary of the Invention

[0005] A magnesium-based construction waste recycling material and a preparation method thereof proposed by the present invention solve the problem that existing construction waste recycling materials do not have the characteristics of high strength, fast hardening, water resistance, and environmental protection.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present application provides a magnesium-based construction waste recycling material, which, by weight, comprises:

[0008] 10 - 25 parts of magnesium-based cementitious material;

[0009] 65 - 80 parts of construction waste recycled aggregate;

[0010] Composite modifier, including inorganic modifier, organic modifier and interfacial enhancer, with specific weight parts as follows: inorganic modifier: 0.2 - 0.9 parts of potassium dihydrogen phosphate, 0.1 - 0.6 parts of borax; organic modifier: 0.1 - 0.5 parts of polycarboxylate water reducer, 0.05 - 0.3 parts of calcium lignosulfonate; interfacial enhancer: 0.05 - 0.4 parts of titanate coupling agent;

[0011] Mineral additive: 1 - 3 parts of silica fume, 1 - 2 parts of fly ash, 0.5 - 1 part of blast furnace slag;

[0012] Nano composite enhancer, compounded from 0.2 - 0.8 parts of nano silica (10 - 30nm) and 0.1 - 0.4 parts of nano alumina (20 - 50nm);

[0013] Functional auxiliary agent, including: 0.1 - 0.56 parts of sodium fluorosilicate, 0.06 - 0.4 parts of polyvinyl alcohol fiber;

[0014] 0.1 - 0.5 parts of self - healing microcapsules;

[0015] 8 - 18 parts of water.

[0016] Optionally, the magnesium - based cementitious material is a mixture of magnesium oxychloride cement and magnesium sulfate cement, where the mass ratio of magnesium oxide, magnesium chloride, and magnesium sulfate is 3:2:1;

[0017] The recycled construction waste aggregate is surface - pretreated, and the pretreatment method is: soaking the aggregate in phosphoric acid solution for 2 - 4 hours and then drying.

[0018] Optionally, the specific surface area of the nano composite enhancer ≥ 200m² / g.

[0019] Optionally, the polyvinyl alcohol fiber has a length of 6 - 12mm and a diameter of 20 - 40μm.

[0020] Optionally, the surface of the polyvinyl alcohol fiber is pretreated with silane coupling agent.

[0021] Optionally, the self - healing microcapsules are composed of a polyurethane shell wrapping an epoxy resin core, with a particle size of 50 - 200μm.

[0022] In the second aspect, the present application provides a preparation method of a magnesium - based recycled construction waste material, including the following steps:

[0023] (1) Pretreat the recycled construction waste aggregate: soak the aggregate in a phosphoric acid solution with a mass fraction of 5 - 10% for 2 - 4 hours, and dry it to a moisture content ≤ 1%;

[0024] (2) Prepare the magnesium - based cementitious material: mix magnesium oxide, magnesium chloride, and magnesium sulfate according to a mass ratio of 3:2:1 to obtain the magnesium - based cementitious material;

[0025] (3) Stepwise mixing of raw materials: successively add 10 - 25 parts of magnesium - based cementitious material, 65 - 80 parts of pre - treated construction waste recycled aggregate, 1 - 3 parts of silica fume, 1 - 2 parts of fly ash, 0.5 - 1 part of blast furnace slag, and dry - mix for 2 - 5 minutes; then add the compound modifier, nano - composite reinforcing agent, and functional auxiliary agent prepared above, and continue stirring for 3 - 8 minutes;

[0026] (4) Final mixing and forming: add 8 - 18 parts of water and 0.1 - 0.5 parts of self - healing microcapsules, control the stirring speed at 200 - 400 r / min, stir for 5 - 15 minutes and then put into the mold, and cure for 7 - 28 days under the conditions of temperature 20 - 35 °C and humidity 60 - 85%.

[0027] Optionally, the preparation of the compound modifier includes:

[0028] Pre - mix 0.2 - 0.9 parts of potassium dihydrogen phosphate and 0.1 - 0.6 parts of borax to form an inorganic modifier; pre - mix 0.1 - 0.5 parts of polycarboxylate superplasticizer and 0.05 - 0.3 parts of calcium lignosulfonate to form an organic modifier; finally, compound with 0.05 - 0.4 parts of titanate coupling agent.

[0029] Optionally, the preparation method of the nano - composite reinforcing agent is:

[0030] Add 0.2 - 0.8 parts of nano - silica (10 - 30 nm) and 0.1 - 0.4 parts of nano - alumina (20 - 50 nm) into a ball mill, use ethanol as the dispersion medium, ball - mill for 1 - 3 hours, dry and then pass through a 200 - 400 - mesh sieve to obtain a composite powder with a specific surface area ≥ 200 m² / g.

[0031] Optionally, the preparation of the functional auxiliary agent includes:

[0032] Soak 0.06 - 0.4 parts of polyvinyl alcohol fiber in a 1 - 3% KH - 550 solution for 30 - 60 minutes, dry and then mix with 0.1 - 0.56 parts of sodium fluorosilicate.

[0033] The beneficial effects of the present invention are:

[0034] Through the synergistic effect of the compound modifier and the nano - reinforcement system, the mechanical properties of the material are significantly improved, achieving excellent compressive and flexural strengths, and at the same time, the freeze - thaw resistance and chloride ion erosion resistance are greatly enhanced.

[0035] Intelligent self - repair function: The unique micro - capsule design endows the material with self - repair ability, which can effectively restore crack damage, and cooperate with a stable cementitious system to ensure the long - term effectiveness of the repair agent.

[0036] Interface bonding enhancement: The synergistic effect of surface activation treatment of aggregates and interface enhancer significantly improves the bonding strength between aggregates and the matrix, and inhibits the generation of interface defects.

[0037] Resource recycling: High proportion utilization of recycled aggregates from construction waste and industrial solid waste significantly reduces raw material consumption, reflecting the characteristics of green environmental protection.

[0038] Optimization of structural compactness: The synergistic effect of nano-enhancer and step-by-step mixing process significantly improves the microstructure of the material, reduces harmful pores and enhances the overall compactness.

[0039] Enhanced crack resistance: The synergistic effect of modified fibers and functional additives effectively inhibits shrinkage cracking and improves the deformation adaptability of the material.

[0040] Through the synergistic effect of composite modifiers and nano-enhancement system, the present invention significantly improves the mechanical strength and durability of the material. Combining the aggregate interface strengthening treatment with the intelligent self-healing microcapsule design, the function of autonomous crack repair is realized. At the same time, high-ratio recycled aggregates from construction waste and industrial solid waste are used to optimize the microstructure of the material and reduce the porosity, with excellent crack resistance, high resource utilization rate and environmental friendliness. It breaks through the performance bottleneck of traditional recycled materials and is applicable to the field of green building engineering with high durability requirements. Brief description of the drawings

[0041] Figure 1 It is a flow chart of the preparation method of a magnesium-based construction waste recycled material of the present invention. Detailed implementation manners

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0043] Example 1, a magnesium-based construction waste recycled material, by weight, includes:

[0044] 10 parts of magnesium-based cementitious material;

[0045] 65 parts of recycled aggregates from construction waste;

[0046] Composite modifier, including inorganic modifier, organic modifier and interface enhancer. The specific parts by weight are: inorganic modifier: 0.2 parts of potassium dihydrogen phosphate, 0.1 part of borax; organic modifier: 0.1 part of polycarboxylate water reducer, 0.05 part of calcium lignosulfonate; interface enhancer: 0.05 part of titanate coupling agent;

[0047] Mineral additives: 1 part of silica fume, 1 part of fly ash, 0.5 part of blast furnace slag;

[0048] The nano-composite reinforcing agent is composed of 0.2 parts of nano-silica (10 - 30 nm) and 0.1 part of nano-aluminum oxide (20 - 50 nm) compounded together;

[0049] The functional auxiliary agent includes: 0.1 part of sodium fluorosilicate and 0.06 part of polyvinyl alcohol fiber; the length of the polyvinyl alcohol fiber is 6 - 12 mm, and the diameter is 20 - 40 μm;

[0050] 0.1 part of self-healing microcapsules, the self-healing microcapsules are composed of an epoxy resin core material wrapped with a polyurethane shell, and the particle size is 50 - 200 μm;

[0051] 8 parts of water.

[0052] Such as Figure 1 , the preparation method of the magnesium-based construction waste recycling material includes the following steps:

[0053] Prepare the composite modifier: premix 0.2 part of potassium dihydrogen phosphate and 0.1 part of borax to make an inorganic modifier; premix 0.1 part of polycarboxylate superplasticizer and 0.05 part of calcium lignosulfonate to make an organic modifier; finally compound with 0.05 part of titanate coupling agent.

[0054] Prepare the nano-composite reinforcing agent: add 0.2 part of nano-silica (10 - 30 nm) and 0.1 part of nano-aluminum oxide (20 - 50 nm) into a ball mill, use ethanol as the dispersion medium, ball mill for 1 hour, dry and then pass through a 200-mesh sieve to obtain a composite powder with a specific surface area ≥ 200 m² / g.

[0055] Prepare the functional auxiliary agent: soak 0.06 part of polyvinyl alcohol fiber in a 1% KH-550 solution for 30 minutes, dry and then mix with 0.1 part of sodium fluorosilicate;

[0056] Soak the aggregate in a 5% phosphoric acid solution by mass for 2 hours, and dry until the moisture content ≤ 1%;

[0057] Prepare the magnesium-based cementitious material: mix magnesium oxide, magnesium chloride, and magnesium sulfate in a mass ratio of 3:2:1 to obtain the magnesium-based cementitious material;

[0058] Mix the raw materials step by step: add 10 parts of the magnesium-based cementitious material, 65 parts of the pretreated construction waste recycled aggregate, 1 part of silica fume, 1 part of fly ash, and 0.5 part of blast furnace slag in sequence, and dry mix for 2 minutes; then add the above-prepared composite modifier, nano-composite reinforcing agent, and functional auxiliary agent, and continue to stir for 3 minutes;

[0059] Final mixing and molding: add 8 parts of water and 0.1 part of self-healing microcapsules, control the stirring speed at 200 r / min, stir for 5 minutes and then put into the mold, and cure for 7 days under the conditions of a temperature of 20 °C and a humidity of 60%.

[0060] Example 2. A magnesium-based recycled construction waste material, by weight, includes:

[0061] 13 parts of magnesium-based cementitious material;

[0062] 68 parts of recycled construction waste aggregate;

[0063] Composite modifier, including inorganic modifier, organic modifier and interfacial enhancer. The specific weight parts are: inorganic modifier: 0.4 part of potassium dihydrogen phosphate, 0.2 part of borax; organic modifier: 0.2 part of polycarboxylate superplasticizer, 0.08 part of calcium lignosulfonate; interfacial enhancer: 0.1 part of titanate coupling agent;

[0064] Mineral additives: 1.5 parts of silica fume, 1.2 parts of fly ash, 0.6 part of blast furnace slag;

[0065] Nano composite enhancer, composed of 0.3 part of nano-silica (10 - 30nm) and 0.2 part of nano-alumina (20 - 50nm) compounded;

[0066] Functional auxiliary agent, including: 0.2 part of sodium fluorosilicate, 0.1 part of polyvinyl alcohol fiber; the polyvinyl alcohol fiber has a length of 6 - 12mm and a diameter of 20 - 40μm;

[0067] 0.2 part of self-healing microcapsule, the self-healing microcapsule is composed of a polyurethane shell wrapped around an epoxy resin core material, and the particle size is 50 - 200μm;

[0068] 10 parts of water.

[0069] The preparation method of the magnesium-based recycled construction waste material includes the following steps:

[0070] Prepare the composite modifier: Premix 0.4 part of potassium dihydrogen phosphate and 0.2 part of borax to make an inorganic modifier; Premix 0.2 part of polycarboxylate superplasticizer and 0.08 part of calcium lignosulfonate to make an organic modifier; finally compound with 0.1 part of titanate coupling agent.

[0071] Prepare the nano composite enhancer: Add 0.3 part of nano-silica (10 - 30nm) and 0.2 part of nano-alumina (20 - 50nm) into a ball mill, use ethanol as the dispersion medium, ball mill for 1.5 hours, dry and then pass through a 250-mesh sieve to obtain a composite powder with a specific surface area ≥ 200m² / g.

[0072] Prepare the functional auxiliary agent: Immerse 0.1 part of polyvinyl alcohol fiber in a 1.5% KH-550 solution for 35 minutes, dry and then mix with 0.2 part of sodium fluorosilicate;

[0073] Immerse the aggregate in a 6% phosphoric acid solution by mass for 2.5 hours, dry until the moisture content ≤ 1%;

[0074] Prepare the magnesium-based cementitious material: Mix magnesium oxide, magnesium chloride, and magnesium sulfate in a mass ratio of 3:2:1 to obtain the magnesium-based cementitious material;

[0075] Mix the raw materials step by step: Add 13 parts of the magnesium-based cementitious material, 68 parts of the pretreated construction waste recycled aggregate, 1.5 parts of silica fume, 1.2 parts of fly ash, and 0.6 parts of blast furnace slag in sequence, and dry mix for 3 minutes; Then add the above-prepared composite modifier, nano-composite reinforcing agent, and functional auxiliary agent, and continue stirring for 4 minutes;

[0076] Final mixing and forming: Add 10 parts of water and 0.2 parts of self-healing microcapsules, control the stirring speed at 250 r / min, stir for 8 minutes and then put into the mold, and cure for 10 days under the conditions of a temperature of 25 °C and a humidity of 65%.

[0077] Example 3, a magnesium-based construction waste recycled material, by weight, includes:

[0078] 18 parts of magnesium-based cementitious material;

[0079] 72 parts of construction waste recycled aggregate;

[0080] Composite modifier, including inorganic modifier, organic modifier, and interface reinforcing agent. The specific weight parts are: Inorganic modifier: 0.55 parts of potassium dihydrogen phosphate, 0.35 parts of borax; Organic modifier: 0.3 parts of polycarboxylate water reducer, 0.18 parts of calcium lignosulfonate; Interface reinforcing agent: 0.23 parts of titanate coupling agent;

[0081] Mineral additives: 2 parts of silica fume, 1.5 parts of fly ash, 0.8 parts of blast furnace slag;

[0082] Nano-composite reinforcing agent, composed of 0.5 parts of nano-silica (10 - 30 nm) and 0.25 parts of nano-alumina (20 - 50 nm) compounded;

[0083] Functional auxiliary agent, including: 0.33 parts of sodium fluorosilicate, 0.23 parts of polyvinyl alcohol fiber; The polyvinyl alcohol fiber has a length of 6 - 12 mm and a diameter of 20 - 40 μm;

[0084] 0.3 parts of self-healing microcapsules, the self-healing microcapsules are composed of a polyurethane shell wrapping an epoxy resin core material, and the particle size is 50 - 200 μm;

[0085] 13 parts of water.

[0086] The preparation method of the magnesium-based construction waste recycled material includes the following steps:

[0087] Prepare the composite modifier: Premix 0.55 parts of potassium dihydrogen phosphate and 0.35 parts of borax to form an inorganic modifier; premix 0.3 parts of polycarboxylate superplasticizer and 0.18 parts of calcium lignosulfonate to form an organic modifier; finally, compound it with 0.23 parts of titanate coupling agent.

[0088] Prepare the nano-composite reinforcing agent: Add 0.5 parts of nano-silica (10 - 30 nm) and 0.25 parts of nano-alumina (20 - 50 nm) into a ball mill, use ethanol as the dispersion medium, ball mill for 2 hours, dry and then pass through a 300-mesh sieve to obtain a composite powder with a specific surface area ≥ 200 m² / g.

[0089] Prepare the functional auxiliary agent: Immerse 0.23 parts of polyvinyl alcohol fiber in a 2% KH-550 solution for 45 minutes, dry and then mix with 0.33 parts of sodium fluorosilicate;

[0090] Immerse the aggregate in a 7.5% phosphoric acid solution by mass for 3 hours, dry until the moisture content ≤ 1%;

[0091] Prepare the magnesium-based cementitious material: Mix magnesium oxide, magnesium chloride, and magnesium sulfate in a mass ratio of 3:2:1 to obtain the magnesium-based cementitious material;

[0092] Mix the raw materials step by step: Add 18 parts of the magnesium-based cementitious material, 72 parts of pretreated construction waste recycled aggregate, 2 parts of silica fume, 1.5 parts of fly ash, and 0.8 parts of blast furnace slag in sequence, and dry mix for 3.5 minutes; then add the composite modifier, nano-composite reinforcing agent, and functional auxiliary agent prepared above, and continue to stir for 3 - 8 minutes;

[0093] Final mixing and molding: Add 13 parts of water and 0.3 parts of self-healing microcapsules, control the stirring speed at 300 r / min, stir for 10 minutes and then put into the mold, and cure for 18 days under the conditions of a temperature of 22.5 °C and a humidity of 72%.

[0094] Example 4, a magnesium-based construction waste recycled material, by weight, includes:

[0095] 20 parts of magnesium-based cementitious material;

[0096] 75 parts of construction waste recycled aggregate;

[0097] The composite modifier, including an inorganic modifier, an organic modifier, and an interface enhancer, with specific weights as follows: Inorganic modifier: 0.7 parts of potassium dihydrogen phosphate, 0.5 parts of borax; Organic modifier: 0.3 parts of polycarboxylate superplasticizer, 0.25 parts of calcium lignosulfonate; Interface enhancer: 0.35 parts of titanate coupling agent;

[0098] Mineral additives: 2.5 parts of silica fume, 1.8 parts of fly ash, 0.8 parts of blast furnace slag;

[0099] Nano-composite reinforcing agent, which is prepared by compounding 0.7 parts of nano-silica (10 - 30 nm) and 0.3 parts of nano-alumina (20 - 50 nm);

[0100] Functional auxiliary agent, including: 0.50 parts of sodium fluorosilicate and 0.35 parts of polyvinyl alcohol fiber; the length of the polyvinyl alcohol fiber is 6 - 12 mm, and the diameter is 20 - 40 μm;

[0101] 0.4 parts of self-healing microcapsules, which are composed of an epoxy resin core material wrapped in a polyurethane shell, and the particle size is 50 - 200 μm;

[0102] 16 parts of water.

[0103] The preparation method of the magnesium-based construction waste recycling material includes the following steps:

[0104] Prepare the composite modifier: Premix 0.7 parts of potassium dihydrogen phosphate and 0.5 parts of borax to make an inorganic modifier; premix 0.3 parts of polycarboxylate superplasticizer and 0.25 parts of calcium lignosulfonate to make an organic modifier; finally, compound with 0.35 parts of titanate coupling agent.

[0105] Prepare the nano-composite reinforcing agent: Add 0.7 parts of nano-silica (10 - 30 nm) and 0.3 parts of nano-alumina (20 - 50 nm) into a ball mill, use ethanol as the dispersion medium, ball mill for 2.5 hours, dry and then pass through a 350-mesh sieve to obtain a composite powder with a specific surface area ≥ 200 m² / g.

[0106] Prepare the functional auxiliary agent: Immerse 0.35 parts of polyvinyl alcohol fiber in a 2.5% KH-550 solution for 50 minutes, dry and then mix with 0.50 parts of sodium fluorosilicate;

[0107] Immerse the aggregate in a 9% phosphoric acid solution by mass for 3.5 hours, and dry until the moisture content ≤ 1%;

[0108] Prepare the magnesium-based cementitious material: Mix magnesium oxide, magnesium chloride, and magnesium sulfate in a mass ratio of 3:2:1 to obtain the magnesium-based cementitious material;

[0109] Mix the raw materials step by step: Add 20 parts of the magnesium-based cementitious material, 75 parts of the pretreated construction waste recycled aggregate, 2.5 parts of silica fume, 1.8 parts of fly ash, and 0.8 parts of blast furnace slag in sequence, and dry mix for 4.5 minutes; then add the above-prepared composite modifier, nano-composite reinforcing agent, and functional auxiliary agent, and continue to stir for 7 minutes;

[0110] Final mixing and molding: Add 16 parts of water and 0.4 parts of self-healing microcapsules, control the stirring speed at 350 r / min, stir for 12 minutes and then put into the mold, and cure at a temperature of 30 °C and a humidity of 80% for 22 days.

[0111] Example 5. A magnesium-based recycled construction waste material, by weight, includes:

[0112] 25 parts of magnesium-based cementitious material;

[0113] 80 parts of recycled construction waste aggregate;

[0114] Compound modifier, including inorganic modifier, organic modifier and interfacial enhancer. The specific weight parts are: inorganic modifier: 0.9 part of potassium dihydrogen phosphate and 0.6 part of borax; organic modifier: 0.5 part of polycarboxylate superplasticizer and 0.3 part of calcium lignosulfonate; interfacial enhancer: 0.4 part of titanate coupling agent;

[0115] Mineral additive: 3 parts of silica fume, 2 parts of fly ash, 1 part of blast furnace slag;

[0116] Nano composite enhancer, composed of 0.8 part of nano-silica (10 - 30nm) and 0.4 part of nano-alumina (20 - 50nm) by compounding;

[0117] Functional auxiliary agent, including: 0.56 part of sodium fluorosilicate and 0.4 part of polyvinyl alcohol fiber; the polyvinyl alcohol fiber has a length of 6 - 12mm and a diameter of 20 - 40μm;

[0118] 0.5 part of self-healing microcapsule, the self-healing microcapsule is composed of a polyurethane shell wrapping an epoxy resin core material, and the particle size is 200μm;

[0119] 18 parts of water.

[0120] The preparation method of the magnesium-based recycled construction waste material includes the following steps:

[0121] Prepare the compound modifier: Premix 0.9 part of potassium dihydrogen phosphate and 0.6 part of borax to make an inorganic modifier; premix 0.5 part of polycarboxylate superplasticizer and 0.3 part of calcium lignosulfonate to make an organic modifier; finally, compound with 0.4 part of titanate coupling agent.

[0122] Prepare the nano composite enhancer: Add 0.8 part of nano-silica (10 - 30nm) and 0.4 part of nano-alumina (20 - 50nm) into a ball mill, use ethanol as a dispersion medium, ball mill for 3 hours, dry and then pass through a 400-mesh sieve to obtain a composite powder with a specific surface area ≥200m² / g.

[0123] Prepare the functional auxiliary agent: Immerse 0.4 part of polyvinyl alcohol fiber in a 3% KH-550 solution for 60 minutes, dry and then mix with 0.56 part of sodium fluorosilicate;

[0124] Immerse the aggregate in a 10% phosphoric acid solution by mass for 4 hours, dry until the moisture content ≤1%;

[0125] Preparation of magnesium-based cementitious material: Mix magnesium oxide, magnesium chloride, and magnesium sulfate in a mass ratio of 3:2:1 to obtain the magnesium-based cementitious material;

[0126] Mix raw materials step by step: Add 25 parts of the magnesium-based cementitious material, 80 parts of pretreated construction waste recycled aggregate, 3 parts of silica fume, 2 parts of fly ash, and 1 part of blast furnace slag in sequence, and dry mix for 5 minutes; then add the composite modifier, nano-composite reinforcing agent, and functional auxiliary agent prepared above, and continue to stir for 8 minutes;

[0127] Final mixing and forming: Add 18 parts of water and 0.5 part of self-healing microcapsules, control the stirring speed at 400 r / min, stir for 15 minutes and then pour into the mold, and cure at a temperature of 35 °C and a humidity of 85% for 28 days.

[0128] Comparative Example 1

[0129] The difference between this comparative example and Example 1 is only that: the interfacial reinforcing agent (titanate coupling agent) in the composite modifier is removed, and only the inorganic modifier and organic modifier are retained, and the other components are the same as those in Example 1.

[0130] Comparative Example 2

[0131] The difference between this comparative example and Example 2 is only that: the nano-composite reinforcing agent is changed to single nano-silica (0.3 part), and the nano-aluminum oxide component is removed, and the other components are the same as those in Example 2.

[0132] Comparative Example 3

[0133] The difference between this comparative example and Example 3 is only that: the self-healing microcapsules are not added, and the water consumption is increased by 0.2 part correspondingly to keep the total liquid volume, and the other components are the same as those in Example 3.

[0134] Comparative Example 4

[0135] The difference between this comparative example and Example 4 is only that: the construction waste recycled aggregate is not pretreated with phosphoric acid solution, and the original water content (about 5%) aggregate is directly used, and the other preparation processes are the same as those in Example 4.

[0136] Comparative Example 5

[0137] The difference between this comparative example and Example 5 is only that: the magnesium-based cementitious material only uses magnesium oxide + magnesium chloride (mass ratio 3:2), and the magnesium sulfate component is removed, and the other components are the same as those in Example 5.

[0138] In order to verify the technical effects of the present invention, the magnesium-based construction waste recycled materials prepared in Examples 1-5 and Comparative Examples 1-5 were tested.

[0139] Verification experiment design

[0140] Test items and standards:

[0141] 1. Mechanical properties (GB / T50081-2019): 7 / 28-day compressive strength, 28-day flexural strength;

[0142] 2. Durability (GB / T50082-2009): Strength loss rate after 50 freeze-thaw cycles, chloride ion penetration coefficient (coulometric method);

[0143] 3. Self-healing performance: Strength recovery rate after 30 days with a pre-crack of 0.3 mm, SEM observation of crack healing;

[0144] 4. Microstructure: Porosity measured by mercury intrusion porosimetry, XRD analysis of hydration products;

[0145] 5. Interface characteristics: Microhardness of the aggregate-matrix interface, aggregate peel strength test.

[0146] The test results are shown in the following table:

[0147] Table 1 Test data of Examples 1-5 and Comparative Examples 1-5

[0148]

[0149] In Table 1, the self-healing microcapsules were uniquely removed: Only in Comparative Example 3 were the self-healing microcapsules clearly removed (replaced with an equal amount of water), so its recovery rate (12.5%) reflects the natural healing ability without a repair system (such as carbonation healing of cement-based materials). The other comparative examples retained the microcapsules: Although the remaining comparative examples (1 / 2 / 4 / 5) retained the microcapsules, the microcapsules could not function properly due to the lack of key synergistic components.

[0150] Through the collaborative optimization of technical features, the present invention significantly improves the comprehensive performance of recycled construction waste materials. The interfacial enhancer (titanate coupling agent) in the composite modifier increases the hardness of the aggregate-matrix interface by 35%-45%. The comparison between Example 1 and Comparative Example 1 shows that the 28-day compressive strength increases from 38.7 MPa to 52.3 MPa, and the freeze-thaw loss rate decreases by 124%, verifying the key role of interfacial modification. The compounding of nano-Al2O3 / SiO2 optimizes the pore structure through the synergistic filling effect. The chloride ion penetration coefficient of Example 2 is reduced by 72% compared with Comparative Example 2 with single nano-SiO2, and the proportion of harmless pores below 100 nm increases by 62%. The self-healing microcapsule system realizes intelligent repair under the support of a complete technical chain. The crack recovery rate of Example 3 reaches 82.4%, far exceeding 12.5% of Comparative Example 3 without capsules; while in Comparative Example 5 where magnesium sulfate is missing in the gelling system, the microcapsules fail prematurely due to pH imbalance, and the repair rate is less than 5%, highlighting the necessity of the ternary gelling system (MgO-MgCl2-MgSO4) for maintaining the stability of the repair agent. In addition, 5%-10% phosphoric acid pretreatment increases the aggregate stripping strength by 68%. The comparison between Example 4 and Comparative Example 4 without treatment shows that the freeze-thaw loss rate decreases by 280%, and the porosity is optimized from 20.3% to 9.7%. Through the four mechanisms of interfacial strengthening, structural densification, self-healing synergy, and stable hydration, each technical feature enables the example to form significant advantages in terms of mechanical strength, durability, and intelligent repair. The compressive strength (52.3-68.9 MPa) and flexural strength (6.8-8.7 MPa) comprehensively exceed those of the comparative examples, and the chloride ion penetration coefficient (720-1280 Coulombs) is reduced by 42%-72% compared with the comparative examples, fully demonstrating the synergistic effect of component optimization and process innovation.

[0151] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A magnesium-based construction waste recycling material, characterized in that, By weight parts, it includes: 10 - 25 parts of magnesium - based cementitious material, where the magnesium - based cementitious material is a mixture of magnesium oxychloride cement and magnesium sulfate cement, and the mass ratio of magnesium oxide, magnesium chloride, and magnesium sulfate is 3:2:1; 65 - 80 parts of recycled construction waste aggregate; Compound modifier, including inorganic modifier, organic modifier, and interfacial enhancer. The specific weight parts are: inorganic modifier: 0.2 - 0.9 parts of potassium dihydrogen phosphate, 0.1 - 0.6 parts of borax; organic modifier: 0.1 - 0.5 parts of polycarboxylate superplasticizer, 0.05 - 0.3 parts of calcium lignosulfonate; interfacial enhancer: 0.05 - 0.4 parts of titanate coupling agent; Mineral additives: 1 - 3 parts of silica fume, 1 - 2 parts of fly ash, 0.5 - 1 part of blast furnace slag; Nano - composite enhancer, which is compounded by 0.2 - 0.8 parts of nano - silica and 0.1 - 0.4 parts of nano - alumina, and the specific surface area of the nano - composite enhancer ≥ 200 m² / g; Functional auxiliary agent, including: 0.1 - 0.56 parts of sodium fluorosilicate, 0.06 - 0.4 parts of polyvinyl alcohol fiber; 0.1 - 0.5 parts of self - healing microcapsules; 8 - 18 parts of water; The recycled construction waste aggregate is subjected to surface pretreatment. The pretreatment method is: soaking the aggregate in phosphoric acid solution for 2 - 4 hours and then drying.

2. The magnesium-based construction waste recycling material according to claim 1, wherein The polyvinyl alcohol fiber has a length of 6 - 12 mm and a diameter of 20 - 40 μm.

3. The magnesium-based construction waste recycling material according to claim 2, characterized in that, The surface of the polyvinyl alcohol fiber is pretreated with silane coupling agent.

4. A magnesium-based construction waste recycling material according to claim 1, wherein, The self - healing microcapsules are composed of a polyurethane shell wrapping an epoxy resin core material, and the particle size is 50 - 200 μm.

5. A preparation method of the magnesium-based construction waste recycled material according to any one of claims 1-4, characterized in that, It includes the following steps: (1) Pretreat the recycled construction waste aggregate: soak the aggregate in a phosphoric acid solution with a mass fraction of 5 - 10% for 2 - 4 hours and dry it to a moisture content ≤ 1%; (2) Prepare the magnesium - based cementitious material: mix magnesium oxide, magnesium chloride, and magnesium sulfate according to the mass ratio of 3:2:1 to obtain the magnesium - based cementitious material; (3) Mix the raw materials step by step: add 10 - 25 parts of magnesium - based cementitious material, 65 - 80 parts of pretreated recycled construction waste aggregate, 1 - 3 parts of silica fume, 1 - 2 parts of fly ash, and 0.5 - 1 part of blast furnace slag in sequence, and dry - mix for 2 - 5 minutes; then add the above - prepared compound modifier, nano - composite enhancer, and functional auxiliary agent, and continue to stir for 3 - 8 minutes; (4) Final mixing and molding: add 8 - 18 parts of water and 0.1 - 0.5 parts of self - healing microcapsules, control the stirring speed at 200 - 400 r / min, stir for 5 - 15 minutes and then put it into the mold, and cure it for 7 - 28 days under the conditions of temperature 20 - 35°C and humidity 60 - 85%.

6. The preparation method of a magnesium-based construction waste recycling material according to claim 5, characterized in that, The preparation of the compound modifier includes: Pre - mix 0.2 - 0.9 parts of potassium dihydrogen phosphate and 0.1 - 0.6 parts of borax to prepare the inorganic modifier; pre - mix 0.1 - 0.5 parts of polycarboxylate superplasticizer and 0.05 - 0.3 parts of calcium lignosulfonate to prepare the organic modifier; finally, compound it with 0.05 - 0.4 parts of titanate coupling agent.

7. The preparation method of a magnesium-based construction waste recycling material according to claim 5, characterized in that, The preparation method of the nano - composite enhancer is: Add 0.2 - 0.8 parts of nano - silica and 0.1 - 0.4 parts of nano - alumina into a ball mill, use ethanol as the dispersion medium, ball - mill for 1 - 3 hours, dry and then pass through a 200 - 400 - mesh sieve to obtain a composite powder with a specific surface area ≥ 200 m² / g.

8. The preparation method of a magnesium-based construction waste recycling material according to claim 5, characterized in that, The preparation of the functional auxiliary agent includes: Soak 0.06 - 0.4 parts of polyvinyl alcohol fiber in a KH - 550 solution with a concentration of 1 - 3% for 30 - 60 minutes, dry and then mix with 0.1 - 0.56 parts of sodium fluorosilicate.

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