All-solid waste phosphogypsum recycled concrete and preparation method thereof

Abstract

The invention discloses all-solid waste phosphogypsum recycled concrete and a preparation method thereof, and belongs to the field of solid waste resource utilization and green building material preparation. The concrete is prepared from the following components in parts by mass: 90 to 130 parts of semi-hydrated phosphogypsum, 280 to 320 parts of recycled concrete coarse aggregate, 140 to 160 parts of recycled concrete fine aggregate and 0.9 to 1.3 parts of water reducing agent, and the water-binder ratio is 0.36. The semi-hydrated phosphogypsum is prepared by air-drying, crushing and screening industrial by-product gypsum, drying at 150-170 DEG C for 2-4 hours, and carrying out sealed aging for 5-8 days; the recycled aggregate is prepared by crushing, screening, cleaning and shaping waste concrete blocks. The preparation method comprises the steps of raw material pretreatment, dry mixing, wet mixing, pouring compaction and maintenance. According to the invention, industrial by-product gypsum and construction waste are utilized, cement and other traditional cementing materials are not needed, the preparation process is free of burning and low in carbon, the 28-day compressive strength of the obtained concrete reaches 30-35 MPa, the requirements of common structural concrete are met, and the concrete has the advantages of environmental protection, economy and good performance.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and green building material preparation, and particularly to a whole solid waste phosphogypsum recycled concrete and its preparation method. Specifically, it is a method for preparing whole solid waste recycled concrete using hemihydrate phosphogypsum as a cementing material and recycled concrete coarse and fine aggregates as aggregates. Background Technology

[0002] With rapid industrialization and urbanization, the amount of solid waste generated is increasing daily, and how to achieve its resource utilization has become a focus of social concern. In the industrial sector, the production of phosphate fertilizers generates a large amount of byproduct phosphogypsum, with huge emissions and a massive accumulated stockpile. Long-term open-air stockpiling not only occupies land but may also lead to leakage and groundwater pollution, posing environmental and safety hazards. Meanwhile, in the construction industry, demolition and construction processes generate large amounts of waste concrete blocks. Direct landfilling of these blocks not only wastes resources but also exacerbates environmental pressure.

[0003] On the other hand, with the gradual scarcity of natural sand and gravel resources, how to utilize the aforementioned solid waste resources has become an urgent need for the development of a circular economy and green building materials. In recent years, the utilization of recycled concrete aggregates has gradually attracted attention, but due to the porous surface and high paste content of recycled aggregates, the concrete prepared from them has shortcomings in terms of mechanical properties and durability. In addition, phosphogypsum-based materials have been researched and applied to some extent, but they usually need to be combined with cement, fly ash, or slag and other cementing materials, making it difficult to achieve a truly "all-solid-waste" solution. Existing utilization methods generally suffer from complex processes, high costs, and insufficient green environmental protection.

[0004] For example, existing research has involved the co-utilization of phosphogypsum and waste aggregates, but these generally require the addition of cement or alkaline additives, which not only increases costs but also reduces environmental benefits. Therefore, developing a fully recycled solid waste concrete that requires no traditional cementitious materials, has a simple process, and is inexpensive is of great significance for solving the above problems.

[0005] In existing technologies, the main methods for treating phosphogypsum include stockpiling and partial utilization in cement retarders and gypsum board, but the utilization rate is low and large-scale disposal is not feasible. The recycling of construction waste concrete is also mostly limited to non-structural components or requires mixing with large quantities of fresh cement concrete, failing to achieve true full utilization of solid waste. Furthermore, existing phosphogypsum-based building materials often require high-temperature calcination or the addition of chemical activators, increasing energy consumption and cost, and the processes are complex.

[0006] Therefore, in view of the above-mentioned problems in the existing technology, there is an urgent need to develop a new type of all-solid-waste recycled concrete and its preparation method, which can simultaneously solve the resource utilization problem of phosphogypsum and construction waste concrete, and realize a truly green and low-carbon building material. Summary of the Invention

[0007] The main objective of this invention is to address the shortcomings of existing technologies by providing a recycled concrete made entirely from solid waste phosphogypsum and its preparation method. This method fully utilizes industrial by-product gypsum and construction waste concrete resources, eliminates the need for high-temperature calcination during the preparation process, reduces energy consumption and costs, and ensures that the concrete has sufficient strength and good durability.

[0008] To achieve the above objectives, the present invention provides the following technical solution: On the one hand, the present invention provides a whole solid waste phosphogypsum recycled concrete, which comprises the following components by weight: 90-130 parts hemihydrate phosphogypsum; 280-320 parts recycled concrete coarse aggregate; 140-160 parts recycled concrete fine aggregate; 0.9-1.3 parts water-reducing agent; wherein the water-cement ratio is 0.36.

[0009] Preferably, the hemihydrate phosphogypsum is derived from industrial by-product gypsum, which is obtained by natural air drying, crushing, sieving, drying at 150-170℃ for 2-4 hours and then aged in a sealed container for 5-8 days.

[0010] Preferably, the industrial by-product gypsum includes phosphogypsum, desulfurized gypsum, natural anhydrite, or natural dihydrate gypsum.

[0011] Preferably, the recycled concrete coarse aggregate and recycled concrete fine aggregate are derived from waste concrete blocks and are obtained through crushing, screening, washing, and shaping.

[0012] Preferably, the coarse aggregate of the recycled concrete has a particle size of 5-25 mm, and the fine aggregate of the recycled concrete has a particle size of less than 5 mm.

[0013] Preferably, the recycled concrete coarse aggregate and recycled concrete fine aggregate meet the following technical indicators: mud content ≤ 5.0%; chloride ion content ≤ 0.06%; sulfate content ≤ 1.0%; needle-like and flaky content ≤ 15%; Los Angeles abrasion ≤ 35%; crushing value ≤ 30%; apparent density: recycled concrete coarse aggregate ≥ 2400 kg / m³ 3 Recycled concrete fine aggregate ≥2300kg / m³ 3 24h water absorption rate: recycled concrete coarse aggregate ≤8.0%, recycled concrete fine aggregate ≤10.0%.

[0014] Preferably, the water-reducing agent is a melamine-based water-reducing agent.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned recycled concrete from all-solid waste phosphogypsum, comprising the following steps: S1. Raw material pretreatment: Industrial by-product gypsum is used to prepare hemihydrate phosphogypsum; waste concrete blocks are used to prepare recycled concrete coarse aggregate and recycled concrete fine aggregate. S2. Dry mixing: Weigh out the hemihydrate phosphogypsum, recycled concrete coarse aggregate and recycled concrete fine aggregate according to the mix proportion, and add them to the concrete mixer and dry mix for 1-3 minutes. S3. Wet mixing: Add water containing water-reducing agent to the dry-mixed mixture, and wet mix for 4-8 minutes to obtain concrete mixture; S4. Pouring and curing: Pour the concrete mixture into the mold and vibrate it to compact it. After standing, remove it from the mold and then cure it for 28 days.

[0016] Further, in step S1, industrial by-product gypsum is naturally air-dried, crushed, and screened, then dried at 150-170℃ for 2-4 hours and aged in a sealed environment for 5-8 days to obtain hemihydrate phosphogypsum; waste concrete blocks are crushed and mixed with steel nails in a horizontal forced mixer for 3-5 minutes, and coarse and fine aggregates are obtained by particle size screening, and the coarse and fine aggregates are washed to obtain recycled concrete coarse aggregate and recycled concrete fine aggregate.

[0017] Furthermore, in step S4, the mold is removed after standing for 72 hours; the curing conditions are an ambient temperature of 25°C and a relative humidity of 75%.

[0018] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: (1) The raw materials are environmentally friendly and widely available: the hemihydrate phosphogypsum and recycled aggregates used are all industrial by-products or construction wastes, avoiding traditional cementitious materials such as cement, which is in line with the concept of full solid waste reuse, saving natural resources and reducing raw material costs. (2) Green and low carbon: The preparation process is free from high-temperature calcination and only requires low-temperature drying, which has low energy consumption and significantly reduces CO2 emissions.

[0019] (3) Good structural performance: The 28-day compressive strength of the concrete prepared under reasonable proportion is in the range of 30-35MPa, which can meet the strength grade requirements of general building concrete; at the same time, the hydration products of phosphogypsum are firmly bonded, and the water-reducing agent improves the fluidity and density, making the internal structure of the concrete dense and having excellent mechanical properties and durability.

[0020] (4) Good economic efficiency: The raw materials are industrial by-products and construction waste, and the cost is significantly lower than that of traditional concrete. Comprehensive utilization of solid waste and recycling of phosphogypsum and waste concrete into concrete cementitious materials reduces the environmental burden and has important significance for resource utilization. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 The flowchart shows the preparation method of recycled concrete from solid waste phosphogypsum provided by the present invention. Figure 2 This is a schematic diagram of the preparation method of coarse and fine aggregates for recycled concrete in this invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 This embodiment demonstrates the mix proportioning and preparation of a fully recycled solid waste phosphogypsum concrete. The test concrete was prepared according to the following mass proportions: 90 parts of hemihydrate phosphogypsum; 280 parts of recycled concrete coarse aggregate; 140 parts of recycled concrete fine aggregate; The admixture is 0.9 parts of melamine water-reducing agent; the water-to-binder ratio is 0.36.

[0025] The production method is as follows: After the phosphogypsum is naturally air-dried, it is crushed, sieved, and then dried at 150℃ for 2 hours. After being aged in a sealed container for 6 days, hemihydrate phosphogypsum is obtained.

[0026] After crushing and screening waste concrete blocks, they are added to a horizontal forced mixer along with steel nails and mixed for 3-5 minutes. Coarse and fine aggregates are obtained through particle size screening. These aggregates are then washed to produce recycled concrete coarse and fine aggregates. The recycled concrete coarse aggregate has a particle size of 5-25 mm, and the recycled concrete fine aggregate has a particle size less than 5 mm. In this embodiment, the purpose of adding steel nails during mixing is to create an irregular pitted structure on the aggregate surface, improving adhesion. The recycled concrete coarse and fine aggregates meet the following technical specifications: mud content ≤ 5.0%; chloride ion content ≤ 0.06%; sulfate (as SO3) content ≤ 1.0%; needle-like and flaky content ≤ 15%; Los Angeles abrasion ≤ 35%; crushing value ≤ 30%; apparent density: recycled concrete coarse aggregate ≥ 2400 kg / m³. 3 Recycled concrete fine aggregate ≥2300kg / m³ 3 24h water absorption rate: recycled concrete coarse aggregate ≤8.0%, recycled concrete fine aggregate ≤10.0%.

[0027] The hemihydrate phosphogypsum, recycled concrete coarse aggregate, and recycled concrete fine aggregate were added to a concrete mixer at the above mass ratio and dry-mixed for 1-3 minutes. Then, water containing a water-reducing agent (the water-reducing agent was first dissolved in the water) was added and wet-mixed for another 4 minutes. The well-mixed concrete slurry was quickly poured into a standard mold and compacted. After the cast test blocks were cured at room temperature (25℃) and relative humidity of 75% for 72 hours, they were demolded. After curing for 7 days and 28 days, the compressive strength of the concrete was measured. The 7-day compressive strength was 25.5 MPa, the 28-day compressive strength was 30.2 MPa, and the slump was 135 mm.

[0028] Example 2 This embodiment demonstrates the mix proportioning and preparation of recycled concrete made entirely from solid waste phosphogypsum. It is prepared according to the following mass proportions: 100 parts of hemihydrate phosphogypsum; 290 parts of recycled concrete coarse aggregate; 145 parts of recycled concrete fine aggregate; The admixture is 1 part melamine water-reducing agent; the water-to-binder ratio is 0.36.

[0029] The production method is as follows: After the phosphogypsum is naturally air-dried, it is crushed, sieved, and then dried at 155℃ for 3 hours and aged in a sealed container for 7 days to obtain hemihydrate phosphogypsum.

[0030] After crushing and screening waste concrete blocks, they are mixed with steel nails in a horizontal forced mixer for 3-5 minutes. The mixture is then screened to obtain coarse and fine aggregates. These aggregates are then washed to produce recycled concrete coarse aggregate and recycled concrete fine aggregate. The recycled concrete coarse aggregate has a particle size of 5-25 mm, and the recycled concrete fine aggregate has a particle size of less than 5 mm. The recycled concrete coarse aggregate and recycled concrete fine aggregate meet the same technical specifications as in Example 1.

[0031] The hemihydrate phosphogypsum, recycled concrete coarse aggregate, and recycled concrete fine aggregate were added to a concrete mixer at the above mass ratio and dry-mixed for 1-3 minutes. Then, water containing a water-reducing agent (the water-reducing agent was first dissolved in the water) was added and wet-mixed for another 5 minutes. The well-mixed concrete paste was quickly poured into a standard mold and compacted. The poured test blocks were cured at room temperature (25℃) and relative humidity for 72 hours before demolding. After curing for 7 days and 28 days, the compressive strength of the concrete was measured: 7-day compressive strength was 26.8 MPa, 28-day compressive strength was 31.7 MPa, and the slump was 140 mm.

[0032] Example 3 This embodiment demonstrates the mix proportioning and preparation of recycled concrete made entirely from solid waste phosphogypsum. It is prepared according to the following mass proportions: 110 parts of hemihydrate phosphogypsum; 300 parts of recycled concrete coarse aggregate; 150 parts of recycled concrete fine aggregate; The admixture is 1.1 parts melamine water-reducing agent, and the water-to-binder ratio is 0.36.

[0033] The production method is as follows: After air-drying phosphogypsum, it is crushed, sieved, and then dried at 160℃ for 4 hours, followed by sealed aging for 7 days to obtain hemihydrate phosphogypsum. Waste concrete blocks are crushed and sieved, then mixed with steel nails in a horizontal forced mixer for 3-5 minutes. After particle size separation, coarse and fine aggregates are obtained. These aggregates are then washed to produce recycled concrete coarse aggregate and recycled concrete fine aggregate. The recycled concrete coarse aggregate has a particle size of 5-25mm, and the recycled concrete fine aggregate has a particle size of less than 5mm. The recycled concrete coarse aggregate and recycled concrete fine aggregate meet the same technical specifications as in Example 1.

[0034] The hemihydrate phosphogypsum, recycled concrete coarse aggregate, and recycled concrete fine aggregate were added to a concrete mixer at the above mass ratio and dry-mixed for 1-3 minutes. Then, water containing a water-reducing agent (the water-reducing agent was first dissolved in the water) was added and wet-mixed for another 6 minutes. The well-mixed concrete paste was quickly poured into a standard mold and compacted. The poured test blocks were cured at room temperature (25℃) and relative humidity for 72 hours before demolding. After curing for 7 days and 28 days, the compressive strength of the concrete was measured: 7-day compressive strength 27.9 MPa, 28-day compressive strength 32.8 MPa, and slump 155 mm.

[0035] Example 4 This embodiment demonstrates the mix proportioning and preparation of recycled concrete made entirely from solid waste phosphogypsum. It is prepared according to the following mass proportions: 120 parts of hemihydrate phosphogypsum; 310 parts of recycled concrete coarse aggregate; 155 parts of recycled concrete fine aggregate; The admixture is 1.2 parts melamine water-reducing agent, with a water-to-binder ratio of 0.36.

[0036] The production method is as follows: After air-drying phosphogypsum, it is crushed, sieved, and then dried at 165℃ for 4 hours, followed by sealed aging for 8 days to obtain hemihydrate phosphogypsum. Waste concrete blocks are crushed and sieved, then mixed with steel nails in a horizontal forced mixer for 3-5 minutes. After particle size separation, coarse and fine aggregates are obtained. These aggregates are then washed to produce recycled concrete coarse aggregate and recycled concrete fine aggregate. The recycled concrete coarse aggregate has a particle size of 5-25mm, and the recycled concrete fine aggregate has a particle size of less than 5mm. The recycled concrete coarse aggregate and recycled concrete fine aggregate meet the same technical specifications as in Example 1.

[0037] The hemihydrate phosphogypsum, recycled concrete coarse aggregate, and recycled concrete fine aggregate were added to a concrete mixer at the above mass ratio and dry-mixed for 1-3 minutes. Then, water containing a water-reducing agent (the water-reducing agent was first dissolved in the water) was added and wet-mixed for another 7 minutes. The well-mixed concrete paste was quickly poured into a standard mold and compacted. The poured test blocks were cured at room temperature (25℃) and relative humidity for 72 hours before demolding. After curing for 7 days and 28 days, the compressive strength of the concrete was measured: 7-day compressive strength 28.9 MPa, 28-day compressive strength 33.6 MPa, and slump 160 mm.

[0038] Example 5 This embodiment demonstrates the mix proportioning and preparation of recycled concrete made entirely from solid waste phosphogypsum. It is prepared according to the following mass proportions: 130 parts of hemihydrate phosphogypsum; 320 parts of recycled concrete coarse aggregate; 160 parts of recycled concrete fine aggregate; The admixture is 1.3 parts melamine water-reducing agent; the water-to-binder ratio is 0.36.

[0039] The production method is as follows: After air-drying phosphogypsum, it is crushed, sieved, and then dried at 170℃ for 4 hours, followed by sealed aging for 8 days to obtain hemihydrate phosphogypsum. Waste concrete blocks are crushed and sieved, then mixed with steel nails in a horizontal forced mixer for 3-5 minutes. After particle size separation, coarse and fine aggregates are obtained. These aggregates are then washed to produce recycled concrete coarse aggregate and recycled concrete fine aggregate. The recycled concrete coarse aggregate has a particle size of 5-25mm, and the recycled concrete fine aggregate has a particle size of less than 5mm. The recycled concrete coarse aggregate and recycled concrete fine aggregate meet the same technical specifications as in Example 1.

[0040] The hemihydrate phosphogypsum, recycled concrete coarse aggregate, and recycled concrete fine aggregate were added to a concrete mixer at the above mass ratio and dry-mixed for 1-3 minutes. Then, water containing a water-reducing agent (the water-reducing agent was first dissolved in the water) was added and wet-mixed for another 8 minutes. The well-mixed concrete paste was quickly poured into a standard mold and compacted. The poured test blocks were cured at room temperature (25℃) and relative humidity for 72 hours before demolding. After curing for 7 days and 28 days, the compressive strength of the concrete was measured: 7-day compressive strength 29.5 MPa, 28-day compressive strength 35.1 MPa, and slump 175 mm.

[0041] The concrete samples from Examples 1 to 5 above exhibited compressive strengths of 25-30 MPa at 7 days and 30-35 MPa at 28 days, meeting the performance requirements for general structural concrete. The slump of specimens with different mix proportions remained between 135-175 mm, demonstrating good fluidity. Details are shown in the table below. Table 1. Mix proportions and corresponding mechanical property data for each embodiment. Note: The water-to-binder ratio is 0.36; the water-reducing agent is melamine water-reducing agent; and the measurement basis is the dry weight of the finished product.

[0042] The data in the table show that the recycled phosphogypsum concrete prepared by this invention exhibits good mechanical properties under different mix proportions, and the concrete slump is moderate, making it easy to construct. With the increase of hemihydrate phosphogypsum content, the 28-day compressive strength shows an upward trend, indicating that a higher amount of cementitious material helps to improve strength.

[0043] The overall formula and process of this invention conform to the concept of "all-solid waste," and the hemihydrate phosphogypsum and recycled aggregates used are all industrial by-products or construction wastes, eliminating the need for traditional cementitious materials such as cement, fly ash, and slag. The resulting concrete has the advantages of high compressive strength, good durability, low cost, and environmental friendliness, and can be pumped for construction, making it suitable for various building and infrastructure projects.

[0044] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A type of recycled concrete made entirely from solid waste phosphogypsum, characterized in that, The following components are included by mass: 90-130 parts of hemihydrate phosphogypsum; 280-320 parts of recycled concrete coarse aggregate; 140-160 parts of recycled concrete fine aggregate; Water-reducing agent: 0.9-1.3 parts; The water-to-binder ratio is 0.

36.

2. The recycled concrete made from all-solid waste phosphogypsum according to claim 1, characterized in that, The hemihydrate phosphogypsum is derived from industrial by-product gypsum, which is obtained by natural air drying, crushing, sieving, drying at 150-170℃ for 2-4 hours and then aging in a sealed environment for 5-8 days.

3. The recycled concrete made from all-solid waste phosphogypsum according to claim 2, characterized in that, The industrial by-product gypsum includes phosphogypsum, desulfurized gypsum, natural anhydrite, or natural dihydrate gypsum.

4. The recycled concrete made from all-solid waste phosphogypsum according to claim 1, characterized in that, The recycled concrete coarse aggregate and recycled concrete fine aggregate are derived from waste concrete blocks and are obtained through crushing, screening, washing, and shaping.

5. The recycled concrete made from all-solid waste phosphogypsum according to claim 1, characterized in that, The coarse aggregate of the recycled concrete has a particle size of 5-25mm, and the fine aggregate of the recycled concrete has a particle size of less than 5mm.

6. The recycled concrete made from all-solid waste phosphogypsum according to claim 1, characterized in that, The recycled concrete coarse aggregate and recycled concrete fine aggregate meet the following technical specifications: Mud content ≤ 5.0%; Chloride ion content ≤0.06%, sulfate content ≤1.0%; Needle-like and flaky content ≤15%, Los Angeles abrasion ≤35%, crushing value ≤30%; Apparent density: Coarse aggregate in recycled concrete ≥2400 kg / m³ 3 Recycled concrete fine aggregate ≥2300kg / m³ 3 ; 24-hour water absorption rate: Coarse aggregate of recycled concrete ≤8.0%, Fine aggregate of recycled concrete ≤10.0%.

7. The recycled concrete made from all-solid waste phosphogypsum according to claim 1, characterized in that, The water-reducing agent is a melamine-based water-reducing agent.

8. A method for preparing recycled concrete from all-solid waste phosphogypsum as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Raw material pretreatment: Industrial by-product gypsum is used to prepare hemihydrate phosphogypsum; waste concrete blocks are used to prepare recycled concrete coarse aggregate and recycled concrete fine aggregate. S2. Dry mixing: Weigh out the hemihydrate phosphogypsum, recycled concrete coarse aggregate and recycled concrete fine aggregate according to the mix proportion, and add them to the concrete mixer and dry mix for 1-3 minutes. S3. Wet mixing: Add water containing water-reducing agent to the dry-mixed mixture, and wet mix for 4-8 minutes to obtain concrete mixture; S4. Pouring and curing: Pour the concrete mixture into the mold and vibrate it to compact it. After standing, remove it from the mold and then cure it for 28 days.

9. The preparation method according to claim 8, characterized in that, In step S1, industrial by-product gypsum is naturally air-dried, crushed, and screened, then dried at 150-170℃ for 2-4 hours and aged in a sealed environment for 5-8 days to obtain hemihydrate phosphogypsum; waste concrete blocks are crushed and mixed with steel nails in a horizontal forced mixer for 3-5 minutes, and coarse and fine aggregates are obtained by particle size screening. The coarse and fine aggregates are then washed to obtain recycled concrete coarse aggregate and recycled concrete fine aggregate.

10. The preparation method according to claim 8, characterized in that, In step S4, the mold is removed after standing for 72 hours; the curing conditions are an ambient temperature of 25°C and a relative humidity of 75%.

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