Preparation method of low-alkali vegetation concrete with full-doping amount of phosphogypsum and recycled aggregate

Abstract

The invention discloses a preparation method of low-alkali plant-growing concrete with full-dosage phosphogypsum and recycled aggregate, and belongs to the technical field of resource utilization of industrial solid waste and building solid waste and ecological building materials. The low-alkali plant-growing concrete containing the full-dosage phosphogypsum and the recycled aggregate is prepared from the following raw materials in parts by weight: 180 to 190 parts of semi-hydrated phosphogypsum, 1365 to 1375 parts of the recycled aggregate, 55 to 65 parts of cement, 17 to 22 parts of fly ash, 0.4 to 0.6 part of a water-retaining agent, 32 parts of electrolytic manganese residues and 0.8 to 1.2 parts of a water reducing agent. The low-alkali plant-growing concrete prepared by the invention realizes full utilization of solid wastes, construction of a low-alkali environment and cooperation of a suitable pore structure and plant nutrition supply, and the comprehensive performance meets ecological engineering requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of industrial solid waste and construction solid waste and ecological building materials, and in particular to a method for preparing low-alkali bioremediation concrete containing full dosage of phosphogypsum and recycled aggregate. Background Art

[0002] Currently, large-scale utilization of industrial solid waste and construction waste has become a core goal in the building materials sector. Phosphogypsum is a byproduct of wet-process phosphoric acid production. For every ton of phosphoric acid produced, 4.5 to 5 tons of phosphogypsum are emitted. Its main components are calcium sulfate dihydrate (CaSO4·2H2O, CaSO4·0.5H2O), soluble phosphorus (P2O3), and trace elements (Mg, K, Fe). Currently, phosphogypsum is primarily disposed of by direct stacking, which carries the risk of releasing acidic substances and polluting the environment. Waste concrete from building demolition accounts for over 60% of total construction waste, generating a large amount of solid construction waste annually. Most of this waste is disposed of in outdoor landfills, which consumes land resources and pollutes the environment.

[0003] Traditional vegetative concrete has the following drawbacks: (1) excessively high alkalinity (pH > 9), which inhibits plant growth; (2) low solid waste content (usually < 30%), which makes it impossible to absorb large amounts of solid waste; and (3) single function, lacking nutrient supply for plant growth. In the prior art, although there are methods of lowering pH by adding acidic admixtures, this increases costs and may introduce harmful components. Research on lowering alkalinity by modifying recycled aggregates also has problems such as complex processes and low nutrient retention. Therefore, there is an urgent need to find a vegetative concrete with low alkalinity, suitable for plant growth, that can provide nutrients required for plant growth, and that can absorb large amounts of solid waste. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing low-alkali bioremediation concrete with full dosage of phosphogypsum and recycled aggregate, so as to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a low-alkali bioremediation concrete with full dosage of phosphogypsum and recycled aggregate, comprising the following raw materials in parts by weight: 180-190 parts of hemihydrate phosphogypsum, 1365-1375 parts of recycled aggregate, 55-65 parts of cement, 17-22 parts of fly ash, 0.4-0.6 parts of water retaining agent, 32 parts of electrolytic manganese slag and 0.8-1.2 parts of water reducing agent.

[0007] Use recycled aggregate to replace all natural aggregates; use hemihydrate phosphogypsum to replace part of the cement.

[0008] Hemihydrated phosphogypsum can be hydrated to produce a gelling effect, ensuring the bond strength between the raw materials. The rough surface of the recycled aggregate can enhance the mechanical bond with the phosphogypsum slurry, compensating for the lack of phosphogypsum's bonding strength.

[0009] Furthermore, the water-cement ratio of the low-alkali vegetation concrete is 0.32 to 0.35.

[0010] Furthermore, the particle size of the electrolytic manganese slag is less than 0.075 mm.

[0011] The natural acidic substances contained in the hemihydrate phosphogypsum in the low-alkali vegetation concrete of the present invention can neutralize the alkaline substances in the recycled aggregate and cement, so that the vegetation concrete has low-alkali properties (pH is in the range of 6.5 to 9); at the same time, it can provide plants with nutrients such as phosphorus and other trace elements, which is suitable for plant growth.

[0012] Electrolytic manganese slag contains active ingredients such as calcium oxide, silicon dioxide, and aluminum oxide. Hemihydrated phosphogypsum undergoes hydration under certain conditions to produce dihydrated gypsum. In concrete systems, the active calcium oxide and other components in the electrolytic manganese slag react with the calcium sulfate produced by the hydration of hemihydrated phosphogypsum and calcium hydroxide, a product of cement hydration, to produce hydration products such as ettringite. These reactions promote the gelation of electrolytic manganese slag and hemihydrated phosphogypsum in concrete, helping to improve the strength, durability, and mechanical properties of concrete.

[0013] Furthermore, the hemihydrate phosphogypsum has a hemihydrate calcium sulfate content of ≥80 wt.%, a soluble phosphorus content of 0.8-1.2 wt.%, a pH of 3-5, and a particle size of ≤5 mm.

[0014] Furthermore, the preparation method of the hemihydrate phosphogypsum comprises: dehydrating the phosphogypsum at high temperature and then screening the dehydrated phosphogypsum to obtain the hemihydrate phosphogypsum.

[0015] Furthermore, the recycled aggregate includes waste concrete with a particle size of 10 to 20 mm.

[0016] Further, the cement comprises Portland cement;

[0017] The fly ash includes Class II fly ash;

[0018] The water-retaining agent includes hydroxypropyl methylcellulose;

[0019] The water reducing agent includes a polycarboxylic acid high-performance water reducing agent with a water reducing rate of ≥25%.

[0020] In the present invention, hemihydrate phosphogypsum is the main solid waste admixture, providing acidic components (to neutralize alkalinity) and phosphorus-containing nutrients (to promote plant growth);

[0021] Recycled aggregate is the main aggregate, and the single particle size structure forms the initial pore skeleton;

[0022] Cement provides basic gel strength;

[0023] Fly ash reduces the alkalinity of the cementitious system and improves the fluidity of the slurry;

[0024] The function of water retaining agent is to reduce water loss and stabilize the pore structure;

[0025] The function of water reducer is to reduce the water-cement ratio and improve the encapsulation of the slurry.

[0026] Phosphogypsum is often used in concrete as a partial replacement for cement (e.g., a replacement rate ≤ 20%) or as an activator / modifier (e.g., in geopolymers or foamed lightweight soils). For example, studies have found that a 7% replacement rate can optimize pore structure, but this does not overcome the limitations of cement-based systems. This invention, through the selection of raw materials and their synergistic effects, increases the amount of cement that can be replaced by phosphogypsum to over 70%, forming an independent cementitious system and resolving the issue of phosphogypsum being a "supporting role" in existing research.

[0027] The alkalinity control of low-alkali vegetation concrete mainly relies on dilution of external admixtures (such as adding a large amount of fly ash, which can react with alkaline HO - Reaction (i.e., secondary hydration reaction) to reduce the alkalinity of the vegetation concrete), slag) or chemical neutralization (such as adding acidic substances), but it may introduce new environmental risks (such as heavy metal dissolution). The present invention takes advantage of the low pH value of phosphogypsum itself and uses it as a cementitious system to directly reduce the alkalinity of the vegetation concrete. It can adapt to plant growth without the need for additional alkalinity-reducing agents, avoiding the complexity of external admixtures.

[0028] Recycled aggregates are often used to partially replace natural aggregates in bio-concrete (e.g., replacement rate ≤ 50%) and are often compounded with natural sand. For example, recycled aggregates can be mixed with fertile soil, but cement remains the primary binder.

[0029] Recycled aggregate is processed from concrete and is alkaline. Excessive addition will make the alkalinity of the vegetation concrete too high, which is not conducive to plant growth. In addition, the physical properties of the recycled aggregate are not as good as those of natural crushed stone. Excessive addition will affect the final strength. The present invention uses a large amount of phosphogypsum to adjust the pH value, and combines it with the addition of admixtures to enhance the strength of the vegetation concrete, thereby achieving the goal of completely replacing natural crushed stone with recycled aggregate and solving the problem of "limited addition" of recycled aggregate in existing research. In addition, the use of recycled aggregate can make the vegetation concrete have larger pores, which can promote air circulation and rainwater infiltration, further dilute alkaline substances, and form a technical effect of material-structure dual control of alkalinity.

[0030] The hemihydrate phosphogypsum and recycled aggregate in the present invention can form a cementitious-aggregate double circulation chain, which is different from the utilization of a single solid waste (such as only using phosphogypsum or only using recycled aggregate) in existing research.

[0031] The phosphorus, sulfur, and other elements contained in the phosphogypsum of this invention are slowly released, providing long-lasting nutrients to plants. This differs from existing approaches that rely on fertile soil for nutritional supplementation. The synergy between the phosphogypsum's gelling system and the pore structure of recycled aggregates achieves the dual ecological adaptability of "low-alkaline environment + nutrient supply."

[0032] Phosphogypsum-based materials generally suffer from insufficient strength (e.g., 7-day compressive strength of 9.0 MPa) and poor water resistance, while recycled aggregate concrete suffers from high water absorption and weak freeze-thaw resistance. This invention uses phosphogypsum and recycled aggregate to prepare bioremediation concrete. The calcium sulfate in the phosphogypsum reacts with residual Ca(OH)2 on the surface of the recycled aggregate to generate ettringite, which fills the pores. This improves the density of the bioremediation concrete, while maintaining its low-alkali properties while enhancing its early strength, thus overcoming the "high-alkali, low-strength" technical bottleneck in existing research.

[0033] Phosphogypsum-based materials are mostly used in non-load-bearing components such as indoor partition boards and plaster, while recycled aggregate vegetated concrete is mainly used in low-load scenarios such as slope protection and permeable pavements. The present invention optimizes the mix ratio (such as the phosphogypsum / cement ratio and aggregate grading) so that the material can meet both mechanical strength (such as 28-day compressive strength ≥10MPa) and ecological requirements. It can be used in scenarios with higher strength requirements such as ecological retaining walls and vegetated sidewalks. The design of phosphogypsum content ≥70% and full replacement of recycled aggregates allows one cubic meter of concrete to absorb about 1.2 tons of solid waste, far exceeding the absorption level of a single solid waste in existing research (such as phosphogypsum only used for filling soil).

[0034] The bioremediation concrete of the present invention can be hardened at room temperature, has lower energy consumption than geopolymer, and is more in line with low-carbon requirements.

[0035] The second technical solution of the present invention is a method for preparing the above-mentioned low-alkali bioremediation concrete containing full dosage of phosphogypsum and recycled aggregate, comprising the following steps:

[0036] Evenly mixing hemihydrate phosphogypsum, recycled aggregate, cement, fly ash and electrolytic manganese slag to obtain a dry mix;

[0037] dissolving a water reducing agent and a water retaining agent in water to obtain a mixed solution;

[0038] The mixed solution is added to the dry mix, mixed evenly, and then formed and cured to obtain the low-alkali vegetation concrete.

[0039] The third technical solution of the present invention: an application of the above-mentioned low-alkali vegetation concrete with full dosage of phosphogypsum and recycled aggregate in mine restoration, slope greening or urban sponge facility construction.

[0040] The fourth technical solution of the present invention: A slope greening method, comprising the following steps: laying nutrient soil on the low-alkali vegetation concrete prepared by the above preparation method and sowing plant seeds, and spraying water for maintenance.

[0041] Furthermore, the plant seeds include seeds of herbaceous plants or shrubs.

[0042] The present invention discloses the following technical effects:

[0043] (1) The low-alkali bioremediation concrete of the present invention uses industrial by-product phosphogypsum and recycled aggregates from waste concrete from building demolition as main raw materials (absorbing a large amount of industrial solid waste and construction waste, and the comprehensive utilization rate of solid waste can reach about 90%), which significantly reduces the environmental load of industrial solid waste and construction waste.

[0044] (2) The low-alkali vegetation concrete of the present invention has low-alkali properties (pH is in the range of 6.5 to 9.0, which is suitable for the growth of plant roots).

[0045] The semi-hydrated phosphogypsum used in the present invention contains soluble acidic components (H3PO4, HF) with a pH of 3 to 5. It can react with the alkaline product Ca(OH)2 of cement hydration and alkaline substances (such as Ca(OH)2) remaining on the surface of concrete recycled aggregate to generate insoluble salts such as Ca3(PO4)2 and CaF2. By optimizing the mix ratio, low-alkali vegetation concrete suitable for plant growth (with a pH in the range of 6.5 to 9.0, which is suitable for plant root growth) can be prepared to meet the growth requirements of most plants (such as ryegrass and tall fescue).

[0046] (3) The low-alkali vegetation concrete of the present invention has a suitable pore structure (the porosity is in the range of 25-30%, which meets the air and water permeability required for vegetation).

[0047] The recycled aggregate used in the present invention is a single-size graded aggregate of 10 to 20 mm, without fine aggregate filling, and is used to form an initial porous skeleton. Then, the amount of coarse aggregate and the amount of cementitious material can be calculated according to the designed porosity (25 to 30%) and the bulk density of the coarse aggregate (i.e., recycled aggregate). The cementitious slurry is used to fill part of the pores, and the final porosity is 25 to 30% (tested by drainage method) combined with the control of vibration time (e.g., 15 seconds), and the permeability coefficient is ≥1.2×10 -2 cm / s, ensuring water and air exchange.

[0048] (4) The low-alkali vegetation concrete of the present invention can provide nutrients required for plant growth.

[0049] Phosphogypsum contains soluble phosphorus (P2O5) and trace elements (Mg, K, Fe), which can be slowly released during plant growth, providing continuous nutrients for plants (the effective phosphorus content of low-alkali vegetation concrete in 28 days is ≥50 mg / kg).

[0050] (5) The low-alkali vegetation concrete of the present invention has good mechanical properties and can meet the requirements of non-load-bearing ecological engineering.

[0051] On the one hand, the hydration of CaSO4·0.5H2O in phosphogypsum produces a gelling effect, ensuring the bonding strength. On the other hand, because the surface of recycled aggregate is rougher and more irregular than that of natural crushed stone, its rough surface can enhance the mechanical bite with the phosphogypsum slurry and improve the bonding strength with the phosphogypsum. The 28d compressive strength is greater than 10MPa, which meets the needs of non-load-bearing projects such as grass bricks and ecological slope protection.

[0052] (6) The low-alkali vegetation concrete of the present invention has good low-alkali properties (pH in the range of 6.5 to 9.0), suitable pore structure (porosity in the range of 25 to 30%) and plant nutrition function (providing phosphorus nutrients necessary for plants, with effective phosphorus ≥ 50 mg / kg), and is suitable for engineering scenarios such as mine restoration, ecological slope protection, bank protection, grass-planted roadbed, and sponge city vegetation concrete layer. DETAILED DESCRIPTION

[0053] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0054] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0055] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0056] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0057] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0058] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0059] In a first aspect, the present invention provides a low-alkali bioremediation concrete with full dosage of phosphogypsum and recycled aggregate, comprising the following raw materials in parts by weight: 187 parts of hemihydrate phosphogypsum, 1372 parts of recycled aggregate, 62 parts of cement, 20 parts of fly ash, 0.5 parts of water retaining agent, 32 parts of electrolytic manganese slag and 1.0 part of water reducing agent.

[0060] In a specific embodiment of the present invention, the water-cement ratio of the low-alkali vegetation concrete is 0.32-0.35 (ie, the ratio of the mass of water to the total mass of cement, hemihydrate phosphogypsum, fly ash and electrolytic manganese slag).

[0061] In a specific embodiment of the present invention, the preparation method of hemihydrate phosphogypsum comprises the following steps:

[0062] Phosphogypsum, a by-product of wet-process phosphoric acid, is selected and dehydrated at high temperature (120-150° C.) and then passed through a 5 mm vibrating screen to remove large particle impurities to obtain hemihydrate phosphogypsum with a particle size of ≤5 mm (hemihydrate calcium sulfate content ≥80 wt.%, soluble phosphorus (P2O5) content of 0.8-1.2 wt.%, pH 3-5).

[0063] In a specific embodiment of the present invention, the method for preparing recycled aggregate comprises the following steps:

[0064] The waste concrete from building demolition (original concrete strength grade is C25-C35) is crushed by jaw crusher and screened by vibrating screen, and 10-20mm single-particle aggregate is taken (15-20mm accounts for ≥90wt.%), and impurities such as metal and plastic are removed;

[0065] Use a high-pressure water gun to rinse the surface (water pressure 0.5MPa) to remove floating dust and loose cement paste (retain the dense old cement mortar layer on the surface, containing alkaline substances Ca(OH)2, for reacting with the acidic components of phosphogypsum), and dry it naturally until the surface is dry (water content ≤2%) to obtain recycled aggregate;

[0066] The bulk porosity of the recycled aggregate is approximately 38%.

[0067] In a specific embodiment of the present invention, the cement is ordinary Portland cement, grade 42.5;

[0068] The fly ash is Class II fly ash, and the water requirement ratio is ≤105%;

[0069] The water-retaining agent is hydroxypropyl methylcellulose with a viscosity of 60,000 mPa·s;

[0070] The particle size of electrolytic manganese slag is less than 0.075mm;

[0071] The water reducer is a polycarboxylic acid high-performance water reducer with a water reduction rate of ≥25%;

[0072] The water is tap water.

[0073] In a second aspect, the present invention provides a method for preparing the low-alkali bioremediation concrete containing the full amount of phosphogypsum and recycled aggregate, comprising the following steps:

[0074] (1) Dry mixing and dispersion: Add hemihydrated phosphogypsum, recycled aggregate, cement, fly ash and electrolytic manganese slag into a forced mixer and dry mix at low speed (15 r / min) for 2 min to preliminarily mix the aggregate and cementitious material (to avoid pH fluctuation caused by local enrichment of hemihydrated phosphogypsum) to obtain a dry mix;

[0075] (2) Wet mixing film formation: dissolve the water reducing agent and water retaining agent in water to make a mixed solution;

[0076] Add the slurry into the mixer containing the dry mix at a flow rate of 2.5 L / min, increase the speed to 25 r / min, and stir for 4 minutes (so that the slurry is evenly wrapped on the surface of the aggregate to form a 0.2-0.5 mm thick "gel film", which fills some pores and retains air permeability channels);

[0077] (3) Static pore stabilization: Stop stirring for 1 minute and use the slurry's own weight to fill the gaps between the aggregates (avoid excessive stirring to damage the pore structure), then remix at a low speed (10 r / min) for 1 minute to ensure uniformity, and obtain low-alkali vegetation concrete slurry;

[0078] (4) Molding and curing (neutralization reaction and nutrient release)

[0079] A. Vibration molding: Pour the low-alkali biomass concrete slurry into a 150mm×150mm×150mm mold and vibrate it for 15 seconds using a flat vibrator (frequency 50Hz, amplitude 0.2mm). After scraping the surface flat, cover it with a breathable film (PE film, pore size 0.1μm).

[0080] B. Initial curing and neutralization: Curing for 48 hours in an environment with a temperature of 20±2℃ and a relative humidity of 60-70% (to promote the reaction of soluble acidic components of phosphogypsum (H3PO4, HF) with cement hydration product Ca(OH)2 and Ca(OH)2 remaining on the surface of recycled aggregate to generate insoluble salts such as Ca3(PO4)2 and CaF2, lower the pH and release phosphorus (P) nutrients).

[0081] C. Standard curing: After demolding, place the concrete in a standard curing room (temperature 20±2°C, relative humidity ≥95%) for 28 days (to complete the hydration reaction, form cementitious products such as calcium silicate (CSH) and ettringite (AFt), and improve the strength) to obtain low-alkali bioremediation concrete.

[0082] The third aspect of the present invention provides an application of the above-mentioned low-alkali vegetation concrete with full dosage of phosphogypsum and recycled aggregate in mine restoration, slope greening or urban sponge facility construction.

[0083] The fourth aspect of the present invention provides a slope greening method (i.e., plant adaptability test of low-alkali vegetation concrete), comprising the following steps: laying 3 to 5 cm thick nutrient soil on the low-alkali vegetation concrete prepared by the above preparation method and sowing plant seeds, and regularly spraying water for maintenance.

[0084] Observe the plant germination rate (germination rate ≥ 85%), seedling growth height and root penetration depth (at 30 days, the target root depth ≥ 5 cm).

[0085] In a specific embodiment of the present invention, the plant seeds include seeds of herbaceous plants (such as Bermuda grass and tall fescue) or shrubs (such as Amorpha fruticosa).

[0086] In a specific embodiment of the present invention, the method for testing the vegetation performance is as follows:

[0087] (1) Porosity: After curing, the porosity of low-alkali vegetation concrete is tested using the drainage method (CJJ / T 253-2016 Technical Specification for Application of Recycled Aggregate Permeable Concrete) (the target porosity is 25-30%) to ensure that plant roots can penetrate and grow.

[0088] (2) pH value detection: NY / T 1377-2007 was used to determine the pH value of the bio-concrete (the target pH value was 6.5-9.0) to verify the neutralization effect of phosphogypsum and alkaline substances.

[0089] (3) Compressive strength: The compressive strength is tested according to GB / T 50081-2019. The target compressive strength after 28 days of curing is >10 MPa.

[0090] (4) Water permeability coefficient: tested in accordance with GB / T 25993-2010.

[0091] (5) Nutrient release analysis: The available phosphorus (P2O5) content in the leachate was determined to be ≥50 mg / kg by water extraction test (NY / T 1121.7-2014) for low-alkali vegetation concrete to evaluate its nutrient supply capacity for plant growth.

[0092] (6) Plant adaptability test: Lay 3 to 5 cm thick nutrient soil (containing humus ≥ 15%) on the low-alkali vegetation concrete and sow plant seeds, and spray water regularly for maintenance.

[0093] Composition of electrolytic manganese slag: silicon dioxide (SiO2, 30-40%), calcium oxide (CaO, 20-30%), sulfate (CaSO4, MnSO4, etc., 10-20%), aluminum oxide (Al2O3, 5-15%), magnesium oxide (MgO, 5-15%), manganese oxide (MnO, 1%-5%), other components (Fe2O3, FeO, etc., 1-5%)

[0094] Example 1

[0095] A method for preparing low-alkali bioremediation concrete containing full dosage of phosphogypsum and recycled aggregate:

[0096] (1) Raw material pretreatment

[0097] A. Preparation of Hemihydrate Phosphogypsum: Phosphogypsum (soluble phosphorus 1.1%, pH 4.5) produced as a wet process byproduct of a phosphate fertilizer plant was selected and dehydrated at high temperature (130°C). Large particles of impurities were removed through a 5 mm vibrating sieve to obtain hemihydrate phosphogypsum with a particle size of ≤5 mm (calcium sulfate hemihydrate content = 92 wt.%, soluble phosphorus (P2O5) content = 0.9 wt.%, pH 4.7).

[0098] B. The waste concrete from building demolition (when newly prepared, the concrete strength grade is C30) is crushed by a jaw crusher and screened by a vibrating screen. 10-20mm single-particle aggregate is taken (15-20mm accounts for 93wt.%), and impurities such as metal and plastic are removed.

[0099] The surface was rinsed with a high-pressure water gun (water pressure 0.5 MPa) to remove floating dust and loose cement slurry (retaining the dense old cement mortar layer on the surface, containing alkaline substance Ca(OH)2, for reacting with the acidic components of phosphogypsum), and then naturally dried until the surface was dry (water content was 1.8%) to obtain recycled aggregate.

[0100] The bulk porosity of the recycled aggregate is approximately 38%.

[0101] (2) Mix ratio

[0102] Low-alkali vegetation concrete is composed of the following raw materials: 187 kg of hemihydrate phosphogypsum, 1372 kg of recycled aggregate, 62 kg of cement, 20 kg of fly ash, 0.5 kg of water retaining agent, 32 kg of electrolytic manganese slag, 1.0 kg of water reducing agent and 97 kg of water.

[0103] Among them, cement is ordinary Portland cement, grade 42.5;

[0104] The fly ash is Class II fly ash, and the water requirement ratio is 102%;

[0105] The water-retaining agent is hydroxypropyl methylcellulose with a viscosity of 60,000 mPa·s;

[0106] The water reducer is a polycarboxylic acid high-performance water reducer with a water reduction rate of 227%.

[0107] The particle size of electrolytic manganese slag is less than 0.075mm;

[0108] The water is tap water;

[0109] The total solid waste content accounts for approximately 90% ((187+1372+32) / (187+1372+62+20+0.5+1.0+97+32)≈90%).

[0110] (3) Preparation method of low-alkali vegetation concrete

[0111] A. Dry mixing and dispersion: Add hemihydrate phosphogypsum, recycled aggregate, cement and fly ash into a forced mixer and dry mix at a speed of 15 r / min for 2 minutes to obtain a dry mix;

[0112] B. Wet-mix film formation: dissolve the water-reducing agent and water-retaining agent in water to make a mixed solution;

[0113] Add the mixture into the mixer containing the dry mix at a flow rate of 2.5 L / min, increase the speed to 25 r / min, and stir for 4 minutes;

[0114] C. Let the mixture stand for 1 minute to stabilize the hole: stop stirring for 1 minute, then re-stir at a speed of 10 r / min for 1 minute to obtain low-alkali vegetation concrete slurry.

[0115] (4) Molding and curing (neutralization reaction and nutrient release)

[0116] A. Vibration molding: Pour the low-alkali biomass concrete slurry into a 150mm×150mm×150mm mold and vibrate it for 15 seconds using a flat vibrator (frequency 50Hz, amplitude 0.2mm). After scraping the surface flat, cover it with a breathable film (PE film, pore size 0.1μm).

[0117] B. Initial curing and neutralization: Curing in an environment with a temperature of 20°C and a relative humidity of 65% for 48 hours before demoulding;

[0118] C. Standard curing: After demolding, place the concrete in a standard curing room (temperature 20°C, relative humidity 95%) for 28 days to obtain low-alkali vegetation concrete.

[0119] (5) Performance testing

[0120] The porosity, pH value, 28d compressive strength, water permeability coefficient, available phosphorus content, and plant adaptability test of the low-alkali vegetation concrete prepared in step (4) were performed (5 cm thick nutrient soil was laid on the low-alkali vegetation concrete and 25 g / m2 of tall fescue seeds were sown and regularly sprayed with water for maintenance). The results are as follows:

[0121] Porosity: 28.1% (water drainage method);

[0122] pH value: 7.6 (28 days old, measured according to NY / T 1377-2007);

[0123] 28d compressive strength: 15.0MPa (GB / T 50081-2019);

[0124] Permeability coefficient: 1.6×10 -2 cm / s (GB / T 25993-2010);

[0125] Available phosphorus content: 65 mg / kg (NY / T 1121.7-2014);

[0126] Plant adaptability: The germination rate of tall fescue seeds is 91% after 20 days.

[0127] The above results show that the low-alkali vegetation concrete prepared by the present invention realizes the full utilization of solid waste, the creation of a low-alkali environment, the coordination of suitable pore structure and plant nutrition supply, and its comprehensive performance meets the needs of ecological engineering.

[0128] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A low-alkali bioremediation concrete containing full dosage of phosphogypsum and recycled aggregate, characterized in that: The invention comprises the following raw materials in parts by weight: 180-190 parts of hemihydrate phosphogypsum, 1365-1375 parts of recycled aggregate, 55-65 parts of cement, 17-22 parts of fly ash, 0.4-0.6 parts of water retaining agent, 32 parts of electrolytic manganese slag and 0.8-1.2 parts of water reducing agent.

2. The low-alkali vegetation concrete according to claim 1, characterized in that: The water-cement ratio of the low-alkali vegetation concrete is 0.32-0.

35.

3. The low-alkali vegetation concrete according to claim 1, characterized in that: The hemihydrate phosphogypsum has a hemihydrate calcium sulfate content of ≥80 wt.%, a soluble phosphorus content of 0.8-1.2 wt.%, a pH of 3-5, and a particle size of ≤5 mm.

4. The low-alkali vegetation concrete according to claim 3, characterized in that: The preparation method of the hemihydrate phosphogypsum comprises: dehydrating the phosphogypsum at high temperature and then screening the dehydrated phosphogypsum to obtain the hemihydrate phosphogypsum.

5. The low-alkali vegetation concrete according to claim 1, characterized in that: The recycled aggregate comprises waste concrete and has a particle size of 10 to 20 mm.

6. The low-alkali vegetation concrete according to claim 1, characterized in that: The cement comprises Portland cement; and / or, the fly ash comprises Class II fly ash; and / or, the water-retaining agent comprises hydroxypropyl methylcellulose; And / or, the water reducer includes a polycarboxylic acid high-performance water reducer with a water reduction rate of ≥25%.

7. A method for preparing low-alkali bioremediation concrete containing full dosage of phosphogypsum and recycled aggregate according to any one of claims 1 to 6, characterized in that: The following steps are involved: Evenly mixing hemihydrate phosphogypsum, recycled aggregate, cement, fly ash and electrolytic manganese slag to obtain a dry mix; dissolving a water reducing agent and a water retaining agent in water to obtain a mixed solution; The mixed solution is added to the dry mix, mixed evenly, and then formed and cured to obtain the low-alkali vegetation concrete.

8. Use of the low-alkali vegetation concrete containing full dosage of phosphogypsum and recycled aggregate according to any one of claims 1 to 6 in mine restoration, slope greening or urban sponge facility construction.

9. A slope greening method, characterized in that: The method comprises the following steps: laying nutrient soil on the low-alkali vegetation concrete prepared by the preparation method according to claim 7, sowing plant seeds, and spraying water for maintenance.

10. The slope greening method according to claim 9, characterized in that: The plant seeds include seeds of herbaceous plants or shrubs.