Phosphogypsum-based breathable water-retaining lightweight concrete and preparation method thereof

Abstract

The invention belongs to the field of vegetation concrete, and relates to ardealite-based breathable water-retaining lightweight concrete and a preparation method thereof. The phosphogypsum-based breathable water-retention lightweight concrete is prepared from the following raw materials in parts by weight: 42 to 52 parts of phosphogypsum-based sulfur aluminum iron series gelling clinker, 26 to 35 parts of undisturbed phosphogypsum, 4 to 8 parts of auxiliary gelling material, 13 to 20 parts of phosphogypsum-based fertilizer-loaded lightweight aggregate, 0.34 to 0.81 part of functional additive, 0.25 to 0.65 part of chopped fiber, 30 to 40 parts of water and 0.03 to 0.06 part of physical foaming foam. The density of the ardealite-based breathable 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%. The green plant-growing concrete which is light in weight, breathable, water-retaining, low in alkalinity and long-acting and slow-release in fertilizer efficiency is prepared, the green plant-growing concrete is long in service life, high in weather resistance and low in carbon footprint, meanwhile, the survival rate and compatibility of plants are improved, and the later maintenance cost is greatly reduced.

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] In order to solve the above problems, the present invention provides a phosphogypsum-based breathable and water-retaining lightweight concrete and a preparation method thereof. The present invention utilizes the characteristics that most of the sulfur-aluminum-iron gelling materials present open pores, and through the three-level combination of phosphogypsum-based clinker, phosphogypsum-based fertilizer-loaded lightweight aggregate, and phosphogypsum, with calcium sulfoxide as the basic skeleton, a three-dimensional open pore network is constructed inside the matrix, 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 later maintenance cost.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: The first aspect of the present invention provides a phosphogypsum-based breathable and water-retaining lightweight concrete, which 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.

[0007] The phosphogypsum-based ferro-aluminum-sulfur 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.

[0008] The present invention uses phosphogypsum in multiple stages to eventually synthesize ettringite from dihydrate gypsum in a targeted manner. The overlapping and interlacing of ettringite constitutes a microscopic skeleton network of the material, which is also the main source of the material's strength development.

[0009] The extended growth of calcium aluminate causes a large number of microchannels to appear in the pore wall structure, which provides a prerequisite for the air permeability of the material. At the same time, the present invention can form connectivity on the pore wall by regulating the surface tension of the fresh slurry, further increasing the air permeability. Finally, a hierarchical pore structure is formed, with a pore size gradient pattern of "macropores (100-400 μm) water storage-micropores (0.1-20 μm) water retention-gel pores (≤0.05 μm) water adsorption". The open macroporous pore 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-pores realize water infiltration, adsorption and storage to form secondary water storage. In the three-dimensional pore network of the foam substrate, the through-pore pores can be regulated to account for more than 70%, thereby forming a gas diffusion channel and achieving effective air permeability.

[0010] The invention has the performance of slow-release fertilizer. On the one hand, the multi-level and large-scale use of phosphogypsum makes the phosphorus in the phosphogypsum in different microstructures, which can slowly and continuously provide phosphorus elements. On the other hand, the invention utilizes the high water absorption of expanded perlite to adsorb urea well, and then forms a core-shell structure through the coating of phosphogypsum-based sulfur-aluminum-iron gelling material, so that urea is not easily diffused out, which also has a good slow-release effect.

[0011] In some embodiments, the mass ratio of the dry phosphogypsum to the calcium-silicon-aluminum-iron raw material is (24-35): (65-76).

[0012] 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 sulphur-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.

[0013] 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.

[0014] In some embodiments, 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.

[0015] In some embodiments, the density of the phosphogypsum-based air-permeable and water-retaining 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%.

[0016] The second aspect of the present invention provides a method for preparing phosphogypsum-based air-permeable and water-retaining lightweight concrete, comprising: The phosphogypsum-based sulphur-aluminium-iron cementitious clinker, phosphogypsum and auxiliary cementitious materials are mixed evenly to prepare a mixture; The urea solution and the expanded perlite are mixed evenly, and the urea solution is fully absorbed to obtain the pretreated expanded perlite; Taking the pretreated expanded perlite for granulation, spraying the mixture, and spraying water to obtain phosphogypsum-based fertilizer-loaded lightweight aggregate; 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.

[0017] In some embodiments, the mass dispersion of the urea solution is 10%-16%.

[0018] In some embodiments, during the physical foaming foam preparation process, the mass ratio of the physical foaming agent to water is 1:(25-40).

[0019] Beneficial Effects of the Invention The present invention prepares a green vegetation concrete that is lightweight, breathable, water-retaining, low in alkalinity and has a long-term slow-release function for fertilizer. It has the advantages of long life, high weather resistance, and low carbon footprint. It also improves plant survival rate and compatibility, and greatly reduces later maintenance costs. The specific advantages are as follows: (1) The present invention has created a new multi-stage utilization model for phosphogypsum: in the first stage, low-alkalinity and low-carbon phosphogypsum-based clinker is prepared. The phosphogypsum provides the sulfur and calcium elements necessary for the sulphur-aluminum-iron clinker firing and reduces the alkalinity of the cementitious system; in the second stage, phosphogypsum-based fertilizer-loaded light aggregate is prepared. Through the synergistic hydration of phosphogypsum and sulphur-aluminum-iron clinker, the core-shell structure of the light aggregate is formed and the hydration strength is improved. In addition, the gel pores and microporous structures formed by the hydration of the internal expanded perlite and urea effectively delay the release rate of urea, achieving the purpose of slow release of fertilizer effect; in the third stage, phosphogypsum is further incorporated in the process of preparing the bio-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-stage 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 entire system, full utilization of the phosphorus element and acidic properties in phosphogypsum is achieved to enhance the product's slow-release fertilizer characteristics and improve plant survival rate and compatibility.

[0020] (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; (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.

[0021] 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

[0022] 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.

[0023] Figure 1 Process flow chart of the present invention; 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); Figure 3 Actual picture of the phosphogypsum-based breathable and water-retaining lightweight concrete prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0024] 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.

[0025] As described in the background technology, the current urban viaduct greening mainly faces the following problems: (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.

[0026] (2) Traditional green concrete has problems such as heavy weight, poor water retention, and high carbon emissions, and is not suitable for viaduct greening construction.

[0027] (3) Traditional vegetated concrete lacks fertilizer retention and slow-release properties, and is unable to regulate the plant growth environment and meet plant growth needs.

[0028] To this end, the present invention provides a method for preparing phosphogypsum-based air-permeable and water-retaining lightweight concrete, comprising: (1) Take 35-45 parts of phosphogypsum-based sulphur-aluminum-iron cementitious clinker, 40-50 parts of phosphogypsum, and 5-15 parts of auxiliary cementitious materials, mix the dry materials evenly to form a mixture, and set aside; (2) Weigh 1-1.6 parts of urea, dissolve it in 10 times the amount of water, mix well and pour it into a bucket containing 5-8 parts of expanded perlite, fully absorb the mixed liquid and set aside; (3) The pretreated expanded perlite prepared in step (2) is placed in a granulator, and the mixture prepared in step (1) is sprayed with 15-20 parts of water to complete the preparation of the phosphogypsum-based fertilizer loaded lightweight aggregate; (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 stir at high speed to fully disperse the original phosphogypsum and chopped fibers; (5) Take 42-52 parts of phosphogypsum-based sulphur-aluminum-iron cementitious clinker, 4-8 parts of auxiliary cementitious material, 0.12-0.36 parts of pore control agent, and 0.02-0.05 parts of retarder, mix them evenly, pour them into the first slurry prepared in step (4), and continue stirring at high speed; (6) Take 13-20 parts of the phosphogypsum-based fertilizer loaded with lightweight aggregate in step (3) and add it directly to the second slurry prepared in step (5), and stir it slowly for 2-4 minutes to prepare a third slurry for later use; (7) Take a physical foaming agent and mix it evenly with 25-40 times water, put it in a cement foaming machine to prepare physical foaming foam for later use; (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, pour into a mold and solidify, and demold after 6-8 hours, thereby completing the preparation of phosphogypsum-based breathable and water-retaining lightweight concrete.

[0029] The present invention has the following advantages: (1) It greatly adapts to the needs of urban road greening, realizes a structural design that integrates lightweight, breathable, water-retaining, and long-term slow-release of fertilizer, improves plant survival rate and compatibility, and greatly reduces subsequent maintenance costs; (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. (3) The internal open-pore structure is constructed to achieve the product's three effects of water retention, air permeability, and water seepage; (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.

[0030] 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.

[0031] In the present invention, the specific surface area of ​​the auxiliary gelling material is not less than 400 m2 / kg.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The auxiliary cementitious material is blast furnace slag powder with a specific surface area of ​​not less than 400 m² / kg.

[0037] 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.

[0038] The pore control agent is obtained by mixing dodecyl polyoxyethylene ether sulfate and polyvinyl alcohol in a ratio of 1:5; The water reducer is a polycarboxylate water reducer with a water reduction rate of ≥25%, a commercially available product; The retarder is boric acid.

[0039] Example 1 The present invention proposes a phosphogypsum-based air-permeable and water-retaining lightweight concrete and a preparation method thereof, comprising the following steps: (1) Take 35 parts of phosphogypsum-based sulphur-aluminum-iron cementitious clinker, 50 parts of phosphogypsum, and 15 parts of auxiliary cementitious materials, mix the materials evenly to form a mixture, and set aside; (2) Weigh 1.0 part of urea, dissolve it in 10 times the amount of water, mix well and pour it into a bucket containing 5 parts of expanded perlite. Allow the mixture to fully absorb and set aside. (3) The pretreated expanded perlite prepared in step (2) is placed in a granulator, and the mixture prepared in step (1) is sprayed with 15 parts of water to complete the preparation of the phosphogypsum-based fertilizer-loaded lightweight aggregate; (4) Take 26 parts of phosphogypsum, 0.4 parts of chopped fibers, 0.2 parts of water reducer and 32 parts of water, and stir at high speed to fully disperse the original phosphogypsum and chopped fibers; (5) Take 52 parts of phosphogypsum-based sulphur-aluminum-iron cementitious clinker, 8 parts of auxiliary cementitious material, 0.18 parts of pore control agent, and 0.02 parts of retarder, mix them evenly, pour them into the first slurry prepared in step (4), and continue stirring at high speed; (6) Take 14 parts of the phosphogypsum-based fertilizer loaded with lightweight aggregate in step (3) and add it directly to the second slurry prepared in step (5), and stir it slowly for 4 minutes to prepare a third slurry for later use; (7) Take a physical foaming agent and mix it evenly with 25 times water, put it in a cement foaming machine to prepare physical foaming foam, and set it aside; (8) Add 0.04 parts of the physical foaming foam in step (7) to the third slurry prepared in step (6), stir slowly for 4 minutes, pour into a mold and solidify, and demold after 6 hours, thereby completing the preparation of phosphogypsum-based breathable and water-retaining lightweight concrete.

[0040] Example 2 The present invention proposes a phosphogypsum-based air-permeable and water-retaining lightweight concrete and a preparation method thereof, comprising the following steps: step: (1) Take 45 parts of phosphogypsum-based sulphur-aluminium-iron cementitious clinker, 50 parts of phosphogypsum, and 5 parts of auxiliary cementitious materials, mix the dry materials evenly to form a mixture, and set aside; (2) Weigh 1.6 parts of urea, dissolve it in 10 times the amount of water, mix well and pour it into a bucket containing 8 parts of expanded perlite. Allow the mixture to fully absorb and set aside. (3) The pretreated expanded perlite prepared in step (2) is placed in a granulator, and the mixture prepared in step (1) is sprayed with 20 parts of water to complete the preparation of the phosphogypsum-based fertilizer loaded lightweight aggregate; (4) Take 35 parts of phosphogypsum, 0.65 parts of chopped fibers, 0.4 parts of water reducer and 40 parts of water, and stir at high speed to fully disperse the original phosphogypsum and chopped fibers; (5) Take 43 parts of phosphogypsum-based sulphur-aluminum-iron cementitious clinker, 4 parts of auxiliary cementitious material, 0.36 parts of pore control agent, and 0.05 parts of retarder, mix them evenly, pour them into the first slurry prepared in step (4), and continue stirring at high speed; (6) Take 19 parts of the phosphogypsum-based fertilizer loaded with lightweight aggregate in step (3) and add it directly to the second slurry prepared in step (5), and stir it slowly for 4 minutes to prepare a third slurry for later use; (7) Take a physical foaming agent and mix it evenly with 40 times water, put it in a cement foaming machine to prepare physical foaming foam, and set it aside; (8) Add 0.06 parts of the physical foaming foam in step (7) to the third slurry prepared in step (6), stir slowly for 2 minutes, pour into a mold and solidify, and demold after 8 hours, thereby completing the preparation of phosphogypsum-based breathable and water-retaining lightweight concrete.

[0041] Example 3 The present invention proposes a phosphogypsum-based air-permeable and water-retaining lightweight concrete and a preparation method thereof, comprising the following steps: (1) Take 45 parts of phosphogypsum-based sulphur-aluminum-iron cementitious clinker, 45 parts of phosphogypsum, and 10 parts of auxiliary cementitious materials, mix the dry materials evenly to form a mixture, and set aside; (2) Weigh 1.3 parts of urea, dissolve it in 10 times the amount of water, mix well and pour it into a bucket containing 7 parts of expanded perlite. Allow the mixture to fully absorb and set aside. (3) The pretreated expanded perlite prepared in step (2) is placed in a granulator, and the mixture prepared in step (1) is sprayed with 18 parts of water to complete the preparation of the phosphogypsum-based fertilizer loaded lightweight aggregate; (4) Take 31 parts of phosphogypsum, 0.45 parts of chopped fibers, 0.3 parts of water reducer and 35 parts of water, and stir at high speed to fully disperse the original phosphogypsum and chopped fibers; (5) Take 46 parts of phosphogypsum-based sulphur-aluminum-iron cementitious clinker, 6 parts of auxiliary cementitious material, 0.24 parts of pore control agent, and 0.03 parts of retarder, mix them evenly, pour them into the first slurry prepared in step (4), and continue stirring at high speed; (6) Take 17 parts of the phosphogypsum-based fertilizer loaded with lightweight aggregate in step (3) and add it directly to the second slurry prepared in step (5), and stir it slowly for 3 minutes to prepare a third slurry for later use; (7) Take a physical foaming agent and mix it evenly with 32 times water, put it in a cement foaming machine to prepare physical foaming foam, and set it aside; (8) Add 0.05 parts of the physical foaming foam in step (7) to the third slurry prepared in step (6), stir slowly for 3 minutes, pour into a mold and solidify, and demold after 7 hours, thereby completing the preparation of phosphogypsum-based breathable and water-retaining lightweight concrete.

[0042] Comparative Example 1 The difference from Example 1 is that in step (5), ordinary sulfide-aluminum-iron cementitious clinker is used instead of phosphogypsum-based sulfide-aluminum-iron cementitious clinker.

[0043] Comparative Example 2 The difference from Example 1 is that in step (3), the mixed material is not sprayed during the granulation process to produce lightweight aggregate.

[0044] Comparative Example 3 The difference from Example 1 is that in step (4), natural gypsum is used instead of phosphogypsum.

[0045] Comparative Example 4 The difference from Example 1 is that in step (1), phosphogypsum is not added. The mixture consists of 45 parts of phosphogypsum-based sulphur-aluminium-iron cementitious clinker and 55 parts of auxiliary cementitious materials.

[0046] Comparative Example 5 The difference from Example 1 is that in step (1), no auxiliary cementitious material is added. The mixture consists of 45 parts of phosphogypsum-based sulphur-aluminium-iron cementitious clinker and 55 parts of phosphogypsum.

[0047] The performance of the phosphogypsum-based breathable and water-retaining lightweight concrete prepared in the embodiment and the comparative example was tested, wherein the apparent density, compressive strength, and water absorption rate tests followed the "GB / T 43487-2023-Test Methods for Foamed Concrete and Products"; the test method for water retention rate was: the saturated water-absorbed sample was placed at 20±2°C and a relative humidity of 45%±5%, and its mass was measured at intervals to calculate its water retention rate; the water permeability coefficient and pH value were measured according to "JC / T 2557-2020-Vegetation Concrete" and "T / ZACA 001-2018-Test Method for Water Permeability Coefficient of Permeable Cement Concrete"; the test method for urea release rate was: the test block was immersed in deionized water, and the urea content in the aqueous solution was measured at intervals. After each measurement, the deionized water needed to be replaced and continued to be immersed, and the urea release rate was calculated. The test method for urea content in the aqueous solution adopts dimethylaminobenzaldehyde spectrophotometry; the porosity was obtained by X-CT three-dimensional reconstruction.

[0048] Table 1 Performance test results of phosphogypsum-based air-permeable and water-retaining lightweight concrete

[0049] From the comparison between Example 1 and Comparative Example 1, it can be seen that replacing the phosphogypsum-based sulphur-aluminum-iron cementitious clinker with ordinary sulphur-aluminum-iron cementitious clinker will cause the basicity of the material to be higher, and the mechanical properties and fertilizer efficiency slow-release performance will be slightly reduced; From the comparison between Example 1 and Comparative Example 2, it can be seen that if no mixed material is added during the granulation process, the mechanical strength of the lightweight aggregate cannot be guaranteed. In particular, due to the lack of the protection of the shell layer, the product strength is significantly reduced, and the slow-release effect of urea is lost; From the comparison of Example 1 and Comparative Example 3, it can be seen that after replacing phosphogypsum with natural gypsum, the water absorption and porosity are slightly reduced; From the comparison of Example 1 and Comparative Example 4, it can be seen 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 further increasing the alkalinity; It can be seen from the comparison between Example 1 and Comparative Example 5 that not adding auxiliary cementitious materials during the granulation process will affect the mechanical properties of lightweight aggregate and have a negative impact on the mechanical strength of the product. Therefore, the phosphogypsum-based sulphur-aluminum-iron cementitious clinker, phosphogypsum, and auxiliary cementitious materials can better meet the performance requirements of lightweight aggregate such as mechanical strength, density, and alkalinity.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in 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 ferro-aluminum-sulfur 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.

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 phosphogypsum-based fertilizer-loaded lightweight aggregate is composed of the following raw materials in parts by weight: 35-45 parts of phosphogypsum-based sulphur-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.

4. 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.

5. 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.

6. 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%.

7. A method for preparing the phosphogypsum-based breathable and water-retaining lightweight concrete according to any one of claims 1 to 6, characterized in that: include: The phosphogypsum-based sulphur-aluminium-iron cementitious clinker, phosphogypsum and auxiliary cementitious materials are mixed evenly to prepare a mixture; The urea solution and the expanded perlite are mixed evenly, and the urea solution is fully absorbed to obtain the pretreated expanded perlite; Taking the pretreated expanded perlite for granulation, spraying the mixture, and spraying water to obtain phosphogypsum-based fertilizer-loaded lightweight aggregate; 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.

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

9. The method for preparing phosphogypsum-based air-permeable and water-retaining lightweight concrete according to claim 7, 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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