A phosphogypsum-based breathable water-retaining lightweight concrete and its preparation method

Abstract

The present invention belongs to the field of vegetative concrete and relates to a phosphogypsum-based breathable and water-retaining lightweight concrete and a preparation method thereof. The phosphogypsum-based breathable and water-retaining lightweight concrete is composed of the following raw materials in parts by weight: 42-52 parts of phosphogypsum-based sulphoaluminate-iron-based cementitious clinker, 26-35 parts of raw phosphogypsum, 4-8 parts of auxiliary cementitious material, 13-20 parts of phosphogypsum-based fertilizer-loaded lightweight aggregate, 0.34-0.81 parts of functional admixture, 0.25-0.65 parts of chopped fiber, 30-40 parts of water, and 0.03-0.06 parts of physical foaming foam. The phosphogypsum-based breathable and water-retaining lightweight concrete has a density of 650-750 kg / m<supgt;3< / supgt;, a compressive strength of 3.5-5 MPa, a mass water absorption rate of 25%-35%, a pH value of 7.5-9.0, and a porosity of 50%-60%. The present invention prepares a green vegetative concrete with light weight, breathability, water retention, low alkalinity and long-acting slow-release fertilizer efficiency function, long service life, high weather resistance, low carbon footprint, while improving the plant survival rate and compatibility, and greatly reducing the later maintenance cost.

Description

Technical Field

[0001] The invention belongs to the field of vegetation concrete and relates to phosphogypsum-based breathable and water-retaining lightweight concrete and a preparation method thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] In the context of modern urbanization and the densification of transportation networks, the integrity of the ecosystem in high-density urban built-up areas has been destroyed and is in a fragmented state, which has led to the intensification of the urban heat island effect, the attenuation of carbon sink capacity, and the sharp decline in biodiversity. As linear space carriers, viaducts, urban roads, and highways have the potential to build continuous ecological corridors. Road greening can not only alleviate the heat island effect, improve air quality, and effectively reduce air pollution and noise pollution around the bridge, but also increase the green coverage rate and improve the beauty and comfort of the city. Therefore, actively developing urban viaduct greening is crucial to alleviating urban space pressure, improving urban ecological environment, and enhancing urban landscape quality.

[0004] The existing forms of urban road greening mainly include external hanging type (planting troughs are placed outside the crash wall), top-mounted type (planting troughs are placed on the crash wall) and built-in type (planting troughs are reserved when designing the bridge). External hanging type and top-mounted type usually use low-cost PVC (polyvinyl chloride) plastic planting boxes, but in use, due to the long-term wind, rain and light, there are problems such as easy aging, poor safety, poor practicality, high risk of waterlogging, airtight soil roots, low plant survival rate, and insufficient fertilizer retention capacity, which seriously reduce the greening effect. The built-in type can reduce the damage and safety hazards of the planting trough, but it requires preliminary design, and the soil is easy to compact and airtight, the plant growth is poor, and to a certain extent, the comprehensive cost of the bridge project is increased. However, traditional vegetation concrete has problems such as heavy weight, low water absorption, poor water retention, poor fertilizer slow-release performance, high internal alkalinity, and high material carbon emissions, which limit its application in viaduct greening. Therefore, there is an urgent need to develop a green vegetation concrete that is lightweight, water-retaining, breathable, low in alkalinity, and has a long-term slow-release function for fertilizer, which can be used for urban road greening, improve ecological benefits, achieve long-term operation and maintenance, reduce safety risks, and optimize the plant growth environment, thereby helping to achieve a balance between urban transportation and ecological sustainability. Summary of the invention

[0005] To solve the above problems, the present invention provides a phosphogypsum-based breathable water-retaining lightweight concrete and a preparation method thereof. By utilizing the characteristics that most of the sulfur-aluminum-iron-based gelling materials present open pores, through the three-stage combination of phosphogypsum-based clinker, phosphogypsum-based fertilizer-loaded lightweight aggregate, and phosphogypsum, with ettringite as the basic skeleton, a three-dimensional open pore network is constructed inside the matrix, realizing the three-effect synergistic control of water retention, air permeability, and water seepage of the product, completing the structural design integrating lightweight, water retention, air permeability, and long-term slow release of fertilizer efficiency, and significantly reducing the later maintenance cost.

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

[0007] In the first aspect of the present invention, a phosphogypsum-based breathable water-retaining lightweight concrete is provided, which is composed of the following raw materials in parts by weight: 42-52 parts of phosphogypsum-based sulfur-aluminum-iron-based gelling clinker, 26-35 parts of raw phosphogypsum, 4-8 parts of auxiliary gelling material, 13-20 parts of phosphogypsum-based fertilizer-loaded lightweight aggregate, 0.34-0.81 parts of functional admixture, 0.25-0.65 parts of chopped fiber, 30-40 parts of water, and 0.03-0.06 parts of physical foaming foam.

[0008] The phosphogypsum-based sulfur-aluminum-iron-based gelling clinker is made by firing a mixture of dried phosphogypsum and calcium-silicon-aluminum-iron raw materials at 1150-1250 °C for 30-45 minutes and quenching in air.

[0009] Through the multi-level utilization of phosphogypsum, the present invention finally targets the synthesis of ettringite from gypsum dihydrate. The overlapping and interlacing of ettringite constitute the microscopic skeleton network of the material, which is also the main source of the material strength development.

[0010] The extended growth of ettringite causes a large number of micro-channels to appear in the pore wall structure, which provides the premise for the air permeability of the material. At the same time, by regulating the surface tension of the fresh paste, the present invention can form connectivity on the pore wall, further increasing the air permeability. Eventually, a hierarchical pore structure is formed, with a pore size gradient mode of "macropores (100-400 μm) storing water - micropores (0.1-20 μm) retaining water - gel pores (≤0.05 μm) adsorbing water". The open macropore network binds liquid water through surface tension, the micropores drive liquid penetration through capillary force, and the gel pores can further adsorb and fix water; at the same time, some closed pores form primary water storage to delay water loss; the lightweight aggregate shell structure, external micropores, and internal expanded perlite through-holes realize water infiltration, adsorption, and storage to form secondary water storage. In the three-dimensional pore network of the foam substrate, the adjustable through-pore porosity can be made to exceed 70%, thereby forming a gas diffusion channel to achieve effective air permeability.

[0011] The present invention has a fertilizer slow-release property. On the one hand, the multi-level and large-scale use of phosphogypsum enables the phosphorus in phosphogypsum to be in different microstructures, which can slowly and continuously provide phosphorus elements. On the other hand, the present invention utilizes the high water absorption of expanded perlite to well adsorb urea, and then through the coating of the phosphogypsum-based sulphoaluminate-ferrite cementitious material, a core-shell structure is formed, making it difficult for urea to diffuse out, which also achieves a good slow-release effect.

[0012] In some embodiments, the mass ratio of the dry phosphogypsum to the calcium-silicon-aluminum-iron raw material is (24 - 35):(65 - 76).

[0013] In some embodiments, the phosphogypsum-based fertilizer-loaded lightweight aggregate is composed of the following raw materials in parts by weight: 35 - 45 parts of phosphogypsum-based sulphoaluminate-ferrite cementitious clinker, 40 - 50 parts of phosphogypsum, 5 - 15 parts of auxiliary cementitious material, 5 - 8 parts of expanded perlite, 1 - 1.6 parts of urea, and 25 - 36 parts of water.

[0014] In some embodiments, the auxiliary cementitious material is selected from at least one of silica fume, limestone tailings powder, blast furnace slag powder, and fly ash.

[0015] In some embodiments, the functional admixture is composed of the following raw materials in parts by weight: 0.2 - 0.4 part of water reducer, 0.12 - 0.36 part of pore regulator, and 0.02 - 0.05 part of retarder.

[0016] In some embodiments, the density of the phosphogypsum-based breathable and water-retaining lightweight concrete is 650 - 750 kg / m 3 , the compressive strength is 3.5 - 5 MPa, the mass water absorption rate is 25% - 35%, the pH value is 7.5 - 9.0, and the porosity is 50% - 60%.

[0017] In the second aspect of the present invention, a preparation method of phosphogypsum-based breathable and water-retaining lightweight concrete is provided, including:

[0018] Taking the phosphogypsum-based sulphoaluminate-ferrite cementitious clinker, phosphogypsum, and auxiliary cementitious material and mixing them evenly to form a mixture;

[0019] Mixing the urea solution with the expanded perlite evenly and fully absorbing the urea solution to obtain pretreated expanded perlite;

[0020] Taking the pretreated expanded perlite for granulation, spraying the mixture, and spraying water to obtain the phosphogypsum-based fertilizer-loaded lightweight aggregate;

[0021] Taking phosphogypsum, chopped fibers, water reducer, and water and mixing them evenly to obtain a first slurry;

[0022] Take the phosphogypsum-based sulphoaluminate-iron cement clinker, auxiliary cementitious material, pore regulator, and retarder, mix them evenly and pour them into the first slurry, mix evenly to obtain the second slurry;

[0023] Take the phosphogypsum-based fertilizer-loaded lightweight aggregate and add it to the second slurry, mix evenly to obtain the third slurry;

[0024] Add physical foamed foam to the third slurry, mix evenly, cast and form, stand still, and demold to obtain the product.

[0025] In some embodiments, the mass fraction of the urea solution is 10%-16%.

[0026] In some embodiments, during the preparation of the physical foamed foam, the mass ratio of the physical foaming agent to water is 1:(25-40).

[0027] Advantages of the present invention

[0028] The present invention prepares a green vegetative concrete with light weight, breathability, water retention, low alkalinity and long-acting slow-release fertilizer effect, which has the advantages of long life, high weather resistance, low carbon footprint, etc. At the same time, it improves the plant survival rate and compatibility, and greatly reduces the later maintenance cost. The specific advantages are as follows:

[0029] (1) The present invention has created a new model for multi-level utilization of phosphogypsum: at the first level, a low-alkalinity and low-carbon phosphogypsum-based clinker is prepared. Phosphogypsum provides the necessary sulfur and calcium elements for the firing of sulphoaluminate-iron clinker and reduces the alkalinity of the cementitious system; at the second level, a phosphogypsum-based fertilizer-loaded lightweight aggregate is prepared. Through the synergistic hydration of phosphogypsum and sulphoaluminate-iron clinker, a core-shell structure of the lightweight aggregate is formed and the hydration strength is improved. In addition, the gel pores and microporous structures formed by the internal expanded perlite and urea hydration effectively delay the urea release rate to achieve the purpose of slow-release fertilizer effect; at the third level, phosphogypsum is further incorporated during the preparation of vegetative concrete to provide sufficient calcium sulfate for the hydration of calcium sulfoaluminate in the clinker, so as to promote the hydration process and form a three-dimensional open pore network with a certain strength. Through the multi-level application of phosphogypsum, the comprehensive utilization rate of phosphogypsum in the present invention even exceeds 60%, while maximizing the excellent physical and chemical properties of the product. In the whole system, the phosphorus element and acidic characteristics in phosphogypsum are fully utilized to strengthen the slow-release characteristics of the fertilizer of the product and improve the plant survival rate and compatibility.

[0030] (2) Unlike the traditional silicate foam concrete, which mostly has a closed-pore structure, the present invention utilizes the characteristics of open pores in most of the sulfur-aluminum-iron gelling materials. Through the three-level combination of phosphogypsum-based clinker, phosphogypsum-based fertilizer-loaded lightweight aggregate, and phosphogypsum, a three-dimensional open-pore network is constructed inside the matrix with calcium sulfate as the basic skeleton, achieving the product's three-effect synergistic control of water retention, air permeability, and water seepage, completing a structural design that integrates lightweight, water retention, air permeability, and long-term slow release of fertilizer effect, which can greatly reduce the subsequent maintenance costs;

[0031] (3) The present invention uses low-carbon raw materials and low-carbon processes (wet mixing process, integral mold casting process), and has the advantages of long life, good durability, and greatly reduced carbon footprint over the entire life cycle of the product.

[0032] The entire process of the present invention focuses on improving the compatibility and survival rate of plants in lightweight concrete, greatly improving the practicality of vegetation concrete from the perspectives of alkalinity control, pore regulation, and long-term slow release of fertilizer effect. At the same time, it takes into account the large-scale use of phosphogypsum and the low carbonization of the preparation process. Finally, the development of green vegetation concrete that integrates lightweight, water retention, air permeability, low alkalinity, and long-term slow release of fertilizer effect is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] Figure 1 Process flow chart of the present invention;

[0035] Figure 2 Internal pore diagram of the phosphogypsum-based breathable and water-retaining lightweight concrete prepared in Example 3 of the present invention (10 times magnified);

[0036] Figure 3 Actual picture of the phosphogypsum-based breathable and water-retaining lightweight concrete prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0037] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0038] As described in the background technology, the current urban viaduct greening mainly faces the following problems:

[0039] (1) Traditional elevated bridge PVC flower boxes have problems such as easy aging, heat resistance, airtightness, high risk of waterlogging, low plant survival rate, and poor safety, resulting in high subsequent maintenance costs.

[0040] (2) Traditional vegetative concrete has problems such as high self-weight, poor water retention, and high material carbon emissions, and is not suitable for viaduct greening construction.

[0041] (3) Traditional vegetative concrete lacks fertilizer retention and slow-release fertilizer efficiency, and cannot regulate the plant growth environment and meet the growth needs of plants.

[0042] For this reason, the present invention provides a preparation method of phosphogypsum-based breathable and water-retaining lightweight concrete, including:

[0043] (1) Take 35-45 parts of phosphogypsum-based sulphoaluminate-ferrite cementitious clinker, 40-50 parts of phosphogypsum, and 5-15 parts of auxiliary cementitious material, mix the dry materials evenly to form a mixture for standby;

[0044] (2) Weigh 1-1.6 parts of urea, dissolve it in 10 times of water, mix evenly and pour it into a bucket containing 5-8 parts of expanded perlite, and let it fully absorb the mixed solution for standby;

[0045] (3) Take the pretreated expanded perlite in step (2) and place it in a granulator, and complete the preparation of phosphogypsum-based fertilizer-loaded lightweight aggregate by spraying the mixture in step (1) and 15-20 parts of water at the same time;

[0046] (4) Take 26-35 parts of phosphogypsum, 0.25-0.65 parts of chopped fibers, 0.2-0.4 parts of water reducer and 30-40 parts of water, and disperse the original phosphogypsum and chopped fibers fully by high-speed stirring;

[0047] (5) Take 42-52 parts of phosphogypsum-based sulphoaluminate-ferrite cementitious clinker, 4-8 parts of auxiliary cementitious material, 0.12-0.36 parts of pore regulator, and 0.02-0.05 parts of retarder, mix evenly and pour them into the first slurry prepared in step (4), and continue high-speed stirring;

[0048] (6) Take 13-20 parts of the phosphogypsum-based fertilizer-loaded lightweight aggregate in step (3) and directly add it to the second slurry prepared in step (5), stir slowly for 2-4 minutes to form a third slurry for standby;

[0049] (7) Mix the physical foaming agent evenly with 25-40 times of water, place it in a cement foaming machine to prepare physical foaming foam for standby;

[0050] (8) Add 0.03-0.06 parts of the physical foaming foam in step (7) to the third slurry in step (6), stir slowly for 2-4 minutes, then pour it into a mold for curing, and demold it after 6-8 hours to complete the preparation of phosphogypsum-based breathable and water-retaining lightweight concrete.

[0051] The present invention has the following advantages:

[0052] (1) It is highly adaptable to the needs of urban road greening, and realizes a structural design that integrates lightweight, breathable, water-retaining, and long-term slow-release fertilizer effects, thereby improving plant survival rate and compatibility and significantly reducing subsequent maintenance costs;

[0053] (2) The problem of phosphogypsum being difficult to utilize on a large scale was solved. The concept of "using waste to treat pollution" was proposed. A large amount of phosphogypsum was used to fully utilize the phosphorus element in phosphogypsum to provide fertilizer for plants. At the same time, the alkalinity of the pore solution of the material was reasonably controlled to adapt to plant growth.

[0054] (3) The internal open-pore structure is constructed to achieve the product's three effects of water retention, air permeability, and water seepage;

[0055] (4) The use of low-carbon raw materials and low-carbon processes (wet mixing process, integral mold casting process) has the advantages of long life, good durability, and significantly reduced carbon footprint over the entire life cycle of the product.

[0056] It should be noted that the "calcium-silicon-aluminum-iron raw materials" in the present invention are a mixture of calcium raw materials, silicon raw materials, aluminum raw materials, and iron raw materials, among which calcium raw materials are such as carbide slag, limestone, etc.; silicon raw materials are such as coal gangue, various tailings, etc.; aluminum raw materials are such as aluminum ash, bauxite, etc.; iron raw materials are such as red mud, steel slag, iron bauxite, etc.

[0057] In the present invention, the specific surface area of ​​the auxiliary gelling material is not less than 400 m2 / kg.

[0058] In the present invention, the pore regulating agent is formed by mixing component A and component B in a mass ratio of 1:5-8, wherein component A is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and dodecyl polyoxyethylene ether sulfate; and component B is selected from at least one of hydroxypropyl methylcellulose ether, xanthan gum, starch, and polyvinyl alcohol.

[0059] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0060] In the following embodiments, the calcium-silicon-aluminum-iron raw material is a mixture of carbide slag, coal gangue, aluminum ash, and red mud, with a mass ratio of 1:1:2:1.

[0061] The phosphogypsum-based ferro-aluminum-sulfur cementitious clinker is prepared by heating a mixture of dry phosphogypsum and calcium-silicon-aluminum-iron raw materials at 1250°C for 30 minutes and rapidly cooling in air.

[0062] The auxiliary cementitious material is blast furnace slag powder with a specific surface area of ​​not less than 400 m² / kg.

[0063] The functional admixture is composed of the following raw materials in parts by weight: 0.2 parts of water reducing agent, 0.36 parts of pore regulating agent, and 0.02 parts of retarder.

[0064] The pore regulator is obtained by mixing dodecyl polyoxyethylene ether sulfate and polyvinyl alcohol in a ratio of 1:5;

[0065] The water reducer is a polycarboxylate water reducer with a water reduction rate of ≥25%, which is a commercially available product;

[0066] The retarder is boric acid.

[0067] Example 1

[0068] The present invention provides a phosphogypsum-based breathable water-retaining lightweight concrete and a preparation method thereof, comprising the following steps:

[0069] (1) Take 35 parts of phosphogypsum-based sulphoaluminate ferrite cementitious clinker, 50 parts of phosphogypsum, and 15 parts of auxiliary cementitious material, mix the materials evenly to form a mixture, and set aside;

[0070] (2) Weigh 1.0 part of urea, dissolve it in 10 times the amount of water, mix evenly, and pour it into a bucket containing 5 parts of expanded perlite, and let it fully absorb the mixed solution, and set aside;

[0071] (3) Take the pretreated expanded perlite in step (2) and place it in a granulator, and complete the preparation of the phosphogypsum-based fertilizer-loaded lightweight aggregate by spraying the mixture in step (1) and 15 parts of water at the same time;

[0072] (4) Take 26 parts of phosphogypsum, 0.4 part of chopped fiber, 0.2 part of water reducer and 32 parts of water, and disperse the original phosphogypsum and chopped fiber by high-speed stirring;

[0073] (5) Take 52 parts of phosphogypsum-based sulphoaluminate ferrite cementitious clinker, 8 parts of auxiliary cementitious material, 0.18 part of pore regulator, and 0.02 part of retarder, mix evenly and pour them into the first slurry prepared in step (4), and continue high-speed stirring;

[0074] (6) Take 14 parts of the phosphogypsum-based fertilizer-loaded lightweight aggregate in step (3) and directly add it to the second slurry prepared in step (5), stir slowly for 4 minutes to form a third slurry, and set aside;

[0075] (7) Mix the physical foaming agent with 25 times the amount of water evenly, and place it in a cement foaming machine to prepare physical foamed foam, and set aside;

[0076] (8) Add 0.04 part of the physical foamed foam in step (7) to the third slurry prepared in step (6), stir slowly for 4 minutes, then pour it into a mold for curing, and demold after 6 hours to complete the preparation of the phosphogypsum-based breathable water-retaining lightweight concrete.

[0077] Example 2

[0078] The present invention provides a phosphogypsum-based breathable water-retaining lightweight concrete and a preparation method thereof, including the following

[0079] steps:

[0080] (1) Take 45 parts of phosphogypsum-based sulphoaluminate-ferrite cementitious clinker, 50 parts of phosphogypsum, and 5 parts of auxiliary cementitious material. Mix the dry materials evenly to form a mixture for standby;

[0081] (2) Weigh 1.6 parts of urea, dissolve it in 10 times the amount of water, mix evenly, and pour it into a bucket containing 8 parts of expanded perlite. Let it fully absorb the mixed liquid for standby;

[0082] (3) Take the pretreated expanded perlite in step (2) and place it in a granulator. By spraying the mixture in step (1) and 20 parts of water simultaneously, complete the preparation of the phosphogypsum-based fertilizer-loaded lightweight aggregate;

[0083] (4) Take 35 parts of phosphogypsum, 0.65 parts of chopped fiber, 0.4 parts of water reducer, and 40 parts of water. Stir at high speed to fully disperse the as-received phosphogypsum and chopped fiber;

[0084] (5) Take 43 parts of phosphogypsum-based sulphoaluminate-ferrite cementitious clinker, 4 parts of auxiliary cementitious material, 0.36 parts of pore regulator, and 0.05 parts of retarder. Mix evenly and pour it into the first slurry prepared in step (4), and continue to stir at high speed;

[0085] (6) Take 19 parts of the phosphogypsum-based fertilizer-loaded lightweight aggregate in step (3) and directly add it to the second slurry prepared in step (5). Stir slowly for 4 minutes to form a third slurry for standby;

[0086] (7) Mix the physical foaming agent evenly with 40 times the amount of water, and place it in a cement foaming machine to prepare physical foamed foam for standby;

[0087] (8) Add 0.06 parts of the physical foamed foam in step (7) to the third slurry prepared in step (6). After stirring slowly for 2 minutes, pour it into a mold for curing, and demold it after 8 hours to complete the preparation of the phosphogypsum-based breathable water-retaining lightweight concrete.

[0088] Example 3

[0089] The present invention provides a phosphogypsum-based breathable water-retaining lightweight concrete and a preparation method thereof, including the following steps:

[0090] (1) Take 45 parts of phosphogypsum-based sulphoaluminate-ferrite cementitious clinker, 45 parts of phosphogypsum, and 10 parts of auxiliary cementitious material. Mix the dry materials evenly to form a mixture for standby;

[0091] (2) Weigh 1.3 parts of urea, dissolve it in 10 times the amount of water, mix evenly and pour it into a bucket containing 7 parts of expanded perlite. Let it fully absorb the mixed solution and set aside for later use.

[0092] (3) Take the pretreated expanded perlite in step (2) and place it in a granulator. By spraying the mixture in step (1) and 18 parts of water simultaneously, the preparation of lightweight aggregate loaded with phosphogypsum-based fertilizer is completed.

[0093] (4) Take 31 parts of phosphogypsum, 0.45 parts of chopped fiber, 0.3 parts of water reducer and 35 parts of water. Stir at high speed to fully disperse the raw phosphogypsum and chopped fiber.

[0094] (5) Take 46 parts of phosphogypsum-based sulphoaluminate ferrite cementitious clinker, 6 parts of auxiliary cementitious material, 0.24 parts of pore regulator and 0.03 parts of retarder. Mix them evenly and pour them into the first slurry prepared in step (4), and continue to stir at high speed.

[0095] (6) Take 17 parts of the phosphogypsum-based fertilizer-loaded lightweight aggregate in step (3) and directly add it to the second slurry prepared in step (5). Stir slowly for 3 minutes to make the third slurry and set aside for later use.

[0096] (7) Mix the physical foaming agent evenly with 32 times the amount of water, place it in a cement foaming machine to prepare physical foaming foam and set aside for later use.

[0097] (8) Add 0.05 parts of the physical foaming foam in step (7) to the third slurry prepared in step (6). After stirring slowly for 3 minutes, pour it into a mold for curing. Demolding can be done after 7 hours to complete the preparation of phosphogypsum-based breathable and water-retaining lightweight concrete.

[0098] Comparative Example 1

[0099] The difference from Example 1 is that in step (5), ordinary sulphoaluminate ferrite cementitious clinker is used to replace the phosphogypsum-based sulphoaluminate ferrite cementitious clinker.

[0100] Comparative Example 2

[0101] The difference from Example 1 is that in step (3), the mixture is not sprayed during the granulation process to obtain the lightweight aggregate.

[0102] Comparative Example 3

[0103] The difference from Example 1 is that in step (4), natural gypsum is used to replace phosphogypsum.

[0104] Comparative Example 4

[0105] The difference from Example 1 is that in step (1), phosphogypsum is not added. The mixture consists of 45 parts of phosphogypsum-based sulphoaluminate ferrite cementitious clinker and 55 parts of auxiliary cementitious material.

[0106] Comparative Example 5

[0107] The difference from Example 1 is that in step (1), no auxiliary cementitious material was added. The mixture is composed of 45 parts of phosphogypsum-based sulfoaluminate-ferrite cement clinker and 55 parts of phosphogypsum.

[0108] The properties of the phosphogypsum-based breathable and water-retaining lightweight concrete prepared in the examples and comparative examples were tested. Among them, the test methods for apparent density, compressive strength, and water absorption follow "GB / T 43487—2023 - Test Methods for Foamed Concrete and Its Products"; the test method for water retention rate is: place the saturated water-absorbed specimen at 20 ± 2°C and relative humidity of 45% ± 5%, and measure its mass at regular intervals to calculate its moisture retention rate; the test methods for water permeability coefficient and pH value follow "JC / T 2557—2020 - Vegetative Concrete" and "T / ZACA 001-2018 - Test Method for Water Permeability Coefficient of Permeable Cement Concrete"; the test method for urea release rate is: soak the test block in deionized water, measure the urea content in the aqueous solution at regular intervals, and replace the deionized water for continuous soaking each time, and calculate the urea release rate. The test method for urea content in the aqueous solution adopts dimethylaminobenzaldehyde spectrophotometry; the porosity is obtained by X-CT three-dimensional reconstruction.

[0109] Table 1 Test Results of the Properties of Phosphogypsum-Based Breathable and Water-Retaining Lightweight Concrete

[0110]

[0111] It can be seen from the comparison between Example 1 and Comparative Example 1 that replacing the phosphogypsum-based sulfoaluminate-ferrite cement clinker with ordinary sulfoaluminate-ferrite cement clinker will cause the alkalinity of the material to be on the high side, and the mechanical properties and fertilizer efficiency slow-release properties will decrease slightly;

[0112] It can be seen from the comparison between Example 1 and Comparative Example 2 that without adding the mixture during the granulation process, the mechanical strength of the lightweight aggregate cannot be guaranteed. Especially due to the lack of the protection of the shell layer, the product strength decreases significantly, and at the same time, the slow-release effect of urea is lost;

[0113] It can be seen from the comparison between Example 1 and Comparative Example 3 that after replacing phosphogypsum with natural gypsum, the water absorption rate and porosity decrease slightly;

[0114] It can be seen from the comparison between Example 1 and Comparative Example 4 that not adding phosphogypsum during the granulation process will directly affect the density and mechanical strength of the lightweight aggregate, thereby increasing the product density, affecting the slow-release effect of urea, and at the same time, the alkalinity also increases further;

[0115] It can be seen from the comparison between Example 1 and Comparative Example 5 that the non-addition of auxiliary cementitious materials during the granulation process will affect the mechanical properties of the lightweight aggregate and have a negative impact on the mechanical strength of the product. Therefore, through the synergistic cooperation of phosphogypsum-based sulphoaluminate-ferrite cement clinker, phosphogypsum and auxiliary cementitious materials, the performance requirements such as the mechanical strength, density and alkalinity of the lightweight aggregate can be better met.

[0116] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. 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 phosphogypsum-based air-permeable and water-retaining lightweight concrete, characterized in that: The method is composed of the following raw materials in parts by weight: 42-52 parts of phosphogypsum-based sulfur-aluminum-iron cementitious clinker, 26-35 parts of original phosphogypsum, 4-8 parts of auxiliary cementitious materials, 13-20 parts of phosphogypsum-based fertilizer-loaded lightweight aggregate, 0.34-0.81 parts of functional admixtures, 0.25-0.65 parts of chopped fibers, 30-40 parts of water, and 0.03-0.06 parts of physical foaming foam; The phosphogypsum-based sulphur-aluminum-iron cementitious clinker is prepared by firing a mixture of dry phosphogypsum and calcium-silicon-aluminum-iron raw materials at 1150-1250° C. for 30-45 minutes and rapidly cooling in air; The phosphogypsum-based fertilizer-loaded lightweight aggregate is composed of the following raw materials in parts by weight: 35-45 parts of phosphogypsum-based sulfur-aluminum-iron cementitious clinker, 40-50 parts of phosphogypsum, 5-15 parts of auxiliary cementitious materials, 5-8 parts of expanded perlite, 1-1.6 parts of urea, and 25-36 parts of water; The preparation method of the phosphogypsum-based fertilizer loaded with lightweight aggregate is as follows: The phosphogypsum-based sulphur-aluminum-iron cementitious clinker, phosphogypsum and auxiliary cementitious materials are mixed evenly to prepare a mixture; the urea solution and expanded perlite are mixed evenly, and the urea solution is fully absorbed to obtain pretreated expanded perlite; the pretreated expanded perlite is granulated, and the mixture is sprayed, and water is sprayed to obtain phosphogypsum-based fertilizer-loaded lightweight aggregate.

2. The phosphogypsum-based air-permeable and water-retaining lightweight concrete according to claim 1, characterized in that: The mass ratio of the dry phosphogypsum to the calcium-silicon-aluminum-iron raw material is (24-35): (65-76).

3. The phosphogypsum-based air-permeable and water-retaining lightweight concrete according to claim 1, characterized in that: The auxiliary cementitious material is selected from at least one of silica fume, limestone tailings powder, blast furnace slag powder and fly ash.

4. The phosphogypsum-based air-permeable and water-retaining lightweight concrete according to claim 1, characterized in that: The functional admixture is composed of the following raw materials in parts by weight: 0.2-0.4 parts of water reducing agent, 0.12-0.36 parts of pore regulating agent, and 0.02-0.05 parts of retarder.

5. The phosphogypsum-based air-permeable and water-retaining lightweight concrete according to claim 1, characterized in that: The density of the phosphogypsum-based water-retaining and breathable lightweight concrete is 650-750 kg / m 3 , compressive strength is 3.5-5 MPa, mass water absorption is 25%-35%, pH value is 7.5-9.0, and porosity is 50%-60%.

6. A method for preparing the phosphogypsum-based breathable and water-retaining lightweight concrete according to any one of claims 1 to 5, characterized in that: include: Mix phosphogypsum, chopped fibers, a water reducer and water to obtain a first slurry; Taking phosphogypsum-based sulphur-aluminum-iron cementitious clinker, auxiliary cementitious material, pore control agent, and retarder, mix them evenly, pour them into the first slurry, mix them evenly, and obtain a second slurry; Add the phosphogypsum-based fertilizer loaded with lightweight aggregate to the second slurry, mix well, and obtain a third slurry; Add the physical foaming foam into the third slurry, mix evenly, cast into shape, let stand, and demould to obtain the product.

7. The method for preparing phosphogypsum-based air-permeable and water-retaining lightweight concrete according to claim 6, characterized in that: The mass dispersion of the urea solution is 10%-16%.

8. The method for preparing phosphogypsum-based air-permeable and water-retaining lightweight concrete according to claim 6, characterized in that: During the physical foaming foam preparation process, the mass ratio of physical foaming agent to water is 1:(25-40).

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