Recycled cement-based full-solid-waste cementitious material and preparation method

Abstract

The application provides a recycled cement-based full-solid-waste cementitious material and a preparation method, and belongs to the technical field of building materials. The recycled cement-based full-solid-waste cementitious material is a cementitious material made of a mixture containing the following components: recycled cement, activated silt lime, phosphogypsum, borax, water reducing agent and water. Among them, the amount of recycled cement is 150kg-270kg per cubic meter of recycled cement-based full-solid-waste cementitious material, the amount of activated silt lime is 30kg-150kg, the amount of phosphogypsum is 20kg-40kg, the amount of borax is 20kg-40kg, the amount of water reducing agent is 1kg-3kg, and the amount of water is 35%-45% of the total mass of recycled cement, activated silt lime and phosphogypsum. The recycled cement is recycled from waste cement slurry; and the activated silt lime is recycled from dredged silt.

Description

Technical Field

[0001] This application belongs to the field of building materials technology, specifically relating to a recycled cement-based all-solid waste cementitious material and its preparation method. Background Technology

[0002] Against the backdrop of the traditional cement industry facing dual pressures of energy conservation and emission reduction, and the accelerated pace of urban renewal, the disposal of bulk solid waste such as construction waste and dredged sludge is becoming increasingly prominent. Recycled cement, obtained by reactivating waste concrete, retains some incompletely hydrated clinker residue and a high alkali reserve; meanwhile, dredged sludge generated from large-scale water conservancy dredging has been proven to possess significant potential pozzolanic activity. Utilizing the alkaline environment of recycled cement to activate dredged sludge and synergistically prepare all-solid-waste cementitious materials not only achieves high-value resource utilization of waste but also represents an effective technological approach to replace traditional silicate cement and reduce environmental impact.

[0003] However, compared to virgin cement, recycled cement contains a large amount of hydrated calcium silicate (CSH) gel and other components generated from the crushing of old cement stone in its microstructure. These products have a large specific surface area and a loose, porous structure, exhibiting extremely strong water absorption properties. When preparing cementitious materials, this characteristic leads to poor initial fluidity and excessively rapid setting rates, severely restricting pumping and paving construction in practical engineering. Therefore, for recycled cement-based solid waste systems, effectively addressing the uncontrollable workability of the slurry and achieving precise control of workability while ensuring high performance has become the primary challenge for promoting the large-scale engineering application of this technology. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a recycled cement-based solid waste cementitious material and its preparation method, aiming to at least partially solve the above-mentioned technical problems. The specific technical solution provided by this application is as follows.

[0005] As a first aspect of this application, a recycled cement-based all-solid waste cementitious material is provided, which is a cementitious material made from a mixture comprising the following components: recycled cement, activated sludge ash, phosphogypsum, borax, water-reducing agent and water.

[0006] The composition of recycled cement-based solid waste cementitious materials per cubic meter includes: 150-270 kg of recycled cement, 30-150 kg of activated sludge ash, 20-40 kg of phosphogypsum, 20-40 kg of borax, 1-3 kg of water-reducing agent, and 35%-45% of the total mass of recycled cement, activated sludge ash, and phosphogypsum. The recycled cement is recovered from waste cement slurry; the activated sludge ash is recovered from dredged sludge.

[0007] As a second aspect of this application, a method for preparing the recycled cement-based solid waste cementitious material as described above is provided, comprising the following steps: mixing recycled cement, activated sludge ash, phosphogypsum, and borax evenly, adding a water-reducing agent and water, continuing to mix evenly, and then molding and curing to obtain the recycled cement-based solid waste cementitious material.

[0008] In this application, a recycled cement-based all-solid waste cementitious material and its preparation method are provided. Through a specific combination and dosage ratio of recycled cement, activated sludge ash, phosphogypsum, borax, water-reducing agent, and water, the prepared recycled cement-based all-solid waste cementitious material achieves precise and controllable workability. Borax and phosphogypsum work synergistically to effectively inhibit the excessively rapid early hydration rate of recycled cement, improving the dry and thick problem of the cementitious material caused by the high water absorption rate of recycled cement. This results in a cementitious material with good initial fluidity and a suitable setting time, meeting the requirements for pumping and paving construction. Simultaneously, the sulfate ions provided by phosphogypsum react with the active aluminates in the recycled cement to generate interwoven needle-like columnar ettringite crystals, filling pores and enhancing density, thereby achieving high mechanical strength while ensuring excellent workability. Furthermore, this recycled cement-based all-solid waste cementitious material uses waste cement slurry, dredged sludge, and phosphogypsum as raw materials, realizing the synergistic high-value utilization of multiple waste sources, exhibiting significant environmental friendliness and resource recycling benefits. Attached Figure Description

[0009] Figure 1 A comparison diagram of the flowability of recycled cement-based solid waste cementitious materials prepared in the embodiments and comparative examples of this application;

[0010] Figure 2 A comparison diagram of the setting time of the recycled cement-based solid waste cementitious materials prepared in the embodiments and comparative examples of this application;

[0011] Figure 3 This is a comparison diagram of the compressive strength of the recycled cement-based solid waste cementitious materials prepared in the embodiments and comparative examples of this application;

[0012] Figure 4 The X-ray diffraction pattern of the recycled cement-based solid waste cementitious material in Example 7 of this application after 28 days;

[0013] Figure 5 This is a scanning electron microscope image of the recycled cement-based solid waste cementitious material in Example 7 of this application after 28 days. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0015] In realizing the concept of this application, it was discovered that traditional cement production has a high environmental impact, low resource utilization rate of dredged sludge and recycled cement, and poor workability of recycled cement-based materials due to high water absorption and rapid hydration rate. Based on this, this application provides a recycled cement-based all-solid-waste cementitious material and its preparation method. Through a specific synergistic ratio of recycled cement, activated sludge ash, phosphogypsum, borax, water-reducing agent, and water, the cementitious material achieves controllable setting time, high fluidity retention, and excellent workability. It precisely regulates early hydration behavior and synergistically enhances the microstructure, significantly improving structural crack resistance while solving construction problems and increasing the resource recycling efficiency of multi-source bulk solid waste.

[0016] As a first aspect of this application, a recycled cement-based all-solid waste cementitious material is provided, which is a cementitious material made from a mixture comprising the following components: recycled cement, activated sludge ash, phosphogypsum, borax, water-reducing agent and water.

[0017] The composition of recycled cement-based solid waste cementitious materials per cubic meter includes: 150-270 kg of recycled cement, 30-150 kg of activated sludge ash, 20-40 kg of phosphogypsum, 20-40 kg of borax, 1-3 kg of water-reducing agent, and 35%-45% of the total mass of recycled cement, activated sludge ash, and phosphogypsum. The recycled cement is recovered from waste cement slurry; the activated sludge ash is recovered from dredged sludge.

[0018] In this embodiment, through a specific combination and dosage ratio of recycled cement, activated sludge ash, phosphogypsum, borax, water-reducing agent, and water, the recycled cement-based all-solid waste cementitious material achieves a synergistic unity of workability and mechanical properties. The introduction of borax and phosphogypsum effectively regulates the hydration process of the system, overcoming the problem of rapid drying and thickening of the cementitious material caused by the high water absorption rate of recycled cement. This endows the cementitious material with good initial fluidity and adjustable setting time, meeting the requirements for engineering pumping and paving. Simultaneously, the interaction between phosphogypsum and the active components in the recycled cement promotes the densification of the microstructure, thereby achieving stable strength development while ensuring excellent workability. The recycled cement-based all-solid waste cementitious material provided in this application uses waste cement slurry, dredged sludge, and phosphogypsum as raw materials, without the need for traditional cement, significantly improving the recycling level of solid waste resources and demonstrating outstanding environmental benefits and engineering applicability.

[0019] In some embodiments, recycled cement is produced from waste cement slurry through crushing, ball milling, calcination, and secondary ball milling.

[0020] Specifically, when preparing recycled cement, the calcination temperature is 650-750℃, for example, 650℃, 700℃, or 750℃; the calcination time is 1.5-2.5h, for example, 1.5h, 2h, or 2.5h.

[0021] Furthermore, the recycled cement prepared by the above method has the following physical properties: the particle size range of the recycled cement is 0.2μm-12μm, for example, 0.2μm, 0.5μm, 1μm, 3μm, 5μm, 7μm, 10μm, 12μm; the strength activity index is 0.80-0.85, for example, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85; and the apparent density is 3 g / cm³. 3 -3.5 g / cm 3 For example, it can be 3 g / cm 3 3.1 g / cm 3 3.2 g / cm 3 3.3 g / cm 3 3.4 g / cm 3 3.5 g / cm 3 .

[0022] In this embodiment, waste cement slurry is sequentially crushed, ball-milled, calcined, and then ball-milled again. With appropriate calcination temperature and time controlled, the resulting recycled cement exhibits fine and uniformly distributed particle size, a good strength activity index, and suitable apparent density. When used in all-solid-waste cementitious materials, this recycled cement provides sufficient alkali reserves and active components, facilitating synergistic reactions with activated sludge ash, phosphogypsum, and other components. Simultaneously, its fine particles effectively fill the pores of the system, improving the compactness of the recycled cement-based all-solid-waste cementitious material, thereby enhancing mechanical properties and structural stability while ensuring workability.

[0023] In some embodiments, activated sludge ash is obtained from dredged sludge through dehydration, drying, ball milling, calcination, and secondary ball milling.

[0024] Specifically, when preparing activated sludge ash, the calcination temperature is 750-850℃, for example, 750℃, 800℃, or 850℃; the calcination time is 1.5-2.5h, for example, 1.5h, 2h, or 2.5h.

[0025] Furthermore, the activated sludge ash prepared by the above method has the following physical properties: the particle size range of the activated sludge ash is 0.1μm-8.5μm, for example, 0.1μm, 0.5μm, 1μm, 3μm, 5μm, 7μm, 8μm, 8.5μm; the strength activity index is 1.11-1.20, for example, 1.11, 1.13, 1.15, 1.17, 1.20; and the apparent density is 2 g / cm³. 3 -2.5g / cm 3 For example, it can be 2 g / cm 3 2.1 g / cm 3 2.2 g / cm 3 2.3 g / cm 3 2.4 g / cm 3 2.5 g / cm 3 .

[0026] In this embodiment, the dredged sludge is subjected to dehydration, drying, ball milling, calcination, and secondary ball milling in sequence, with appropriate calcination temperature and time controlled. The resulting activated sludge ash possesses fine and uniformly distributed particle size, a high strength activity index, and suitable apparent density. When used in solid waste cementitious materials, this activated sludge ash fully utilizes its pozzolanic activity, reacting efficiently with alkaline components in the system to promote the formation and densification of hydration products. This effectively improves the mechanical properties and durability of recycled cement-based solid waste cementitious materials, while simultaneously achieving high-value utilization of dredged sludge.

[0027] In some embodiments, the apparent density of the recycled cement-based all-solid waste cementitious material is 480 kg / m³. 3 -485 kg / m 3 For example, it can be 480 kg / m 3 481 kg / m 3 482 kg / m 3 483 kg / m 3 484 kg / m 3 485 kg / m 3 .

[0028] In this embodiment, through specific proportions of each component and preparation process, the recycled cement-based all-solid waste cementitious material obtained has a low apparent density, falling into the category of lightweight cementitious materials. While maintaining good mechanical properties and structural stability, this cementitious material significantly reduces its unit volume weight, which is beneficial for reducing structural loads, transportation, and construction costs, making it suitable for engineering components requiring lightweighting. Furthermore, the low apparent density reflects the rational control of the internal pore structure of the cementitious material, synergistically matching its workability and strength development, further expanding the application scenarios of all-solid waste cementitious materials.

[0029] In some embodiments, the main component of the phosphogypsum used in this application is calcium sulfate dihydrate (CaSO4·2H2O), which also contains impurities such as free phosphoric acid and fluorides. It is a solid waste generated in the wet phosphoric acid process and is incorporated as an internally added gelling component.

[0030] In some embodiments, the borax used in this application is sodium tetraborate decahydrate (Na2B4O7·10H2O), which is a white or colorless crystal and is incorporated as an external cementitious component into recycled cement-based solid waste cementitious materials.

[0031] In some embodiments, the water-reducing agent used in this application is a liquid polycarboxylate-based water-reducing agent with a water reduction rate of 28%.

[0032] In some embodiments, the mixing water used in this application is tap water, which is weakly alkaline.

[0033] In this embodiment, by selecting phosphogypsum with a specific composition as an internal cementitious component and borax as an external cementitious component, combined with liquid polycarboxylate superplasticizer and weakly alkaline mixing water, the components work synergistically in the system. Borax and phosphogypsum can effectively slow down the early hydration rate of the system and improve the workability of the cementitious material; phosphogypsum provides sulfate ions, promotes the formation of hydration products, and enhances the density of the cementitious material; the superplasticizer optimizes the fluidity of the cementitious material, ensuring workability during construction; and the weakly alkaline mixing water helps to activate the activity of the cementitious components. The above combined effects enable the all-solid waste cementitious material to have controllable setting time, good fluidity, and stable mechanical properties without the addition of traditional cement, achieving efficient synergistic utilization of multi-source solid waste.

[0034] As a second aspect of this application, a method for preparing the recycled cement-based solid waste cementitious material as described above is provided, comprising the following steps: mixing recycled cement, activated sludge ash, phosphogypsum, and borax evenly, adding a water-reducing agent and water, continuing to mix evenly, and then molding and curing to obtain the recycled cement-based solid waste cementitious material.

[0035] In this embodiment, recycled cement, activated sludge ash, phosphogypsum, and borax are first dry-mixed until uniform, then water-reducing agent and water are added for further mixing. This stepwise feeding method facilitates full dispersion and contact of the components, ensuring the uniformity of subsequent hydration reactions. After molding and curing, a dense and stable solid waste cementitious material can be obtained. This method is simple to operate, requires no special equipment, is suitable for large-scale production, and can effectively guarantee the working performance and mechanical properties of the cementitious material, achieving efficient resource utilization of multi-source solid waste.

[0036] In summary, this application provides a high-performance recycled cement-based all-solid waste cementitious material with controllable performance and its preparation method, which can precisely control the early hydration kinetics of the recycled cement-based all-solid waste cementitious material, achieving a synergistic unity of maintaining high fluidity and high strengthening in the later stage. Specifically, the recycled cement-based all-solid waste cementitious material and its preparation method provided in this application have the following beneficial effects.

[0037] (1) Performance regulation: Compared with conventional solid waste cementitious materials, this application achieves an organic combination of retarding regulation and activation enhancement through the synergistic incorporation of borax and phosphogypsum. Among them, borax can effectively inhibit the early rapid hydration of active components in recycled cement, thereby solving the industry problem of easy drying and thickening of slurry and short construction window caused by the loose and porous nature and high water absorption of recycled cement, and ensuring the precise control of the working performance of cementitious materials.

[0038] (2) In terms of strength enhancement: Under the premise of ensuring good workability, the sulfate ions provided by phosphogypsum react with the active aluminates in recycled cement to induce the formation of a large number of interwoven needle-like columnar ettringite crystals in the matrix. This microscopic "bridging" effect significantly improves the density of the material, thereby greatly enhancing the mechanical properties of the system.

[0039] (3) In terms of resources and environmental protection: This application realizes the synergistic high-value utilization of various bulk solid wastes such as dredged sludge, recycled cement and phosphogypsum, effectively reducing production costs and environmental burden, and providing an efficient and low-carbon disposal path for multi-source waste generated by urban renewal and water conservancy projects.

[0040] The present application is further illustrated below through embodiments and related test experiments. In the detailed description below, numerous specific details are set forth for ease of explanation to provide a comprehensive understanding of the embodiments of the present application. However, it is apparent that one or more embodiments may be implemented without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict. All instruments, consumables, and reagents used in the following embodiments are commercially available unless otherwise specified.

[0041] The recycled cement used in the following examples and comparative examples was prepared by the following method.

[0042] (1) Use a jaw crusher to crush waste cement slurry into blocks that can pass through a 4.75cm square hole screen;

[0043] (2) Place the above block into a cement test mill and ball mill for 10 minutes to obtain waste cement powder;

[0044] (3) Put the waste cement powder into a box-type resistance furnace and calcine it at a constant temperature of 700℃ for 2 hours. After taking it out, place it outdoors to cool naturally.

[0045] (4) The cooled sintered waste cement is put into a cement test mill and ball-milled for 1 minute to obtain recycled cement.

[0046] Testing revealed that the recycled cement prepared using the above method had a particle size range of 0.2 μm-12 μm, with a median particle size of 3.3 μm. According to the methods specified in the national standard "Technical Specification for Application of Mineral Admixtures" (GB / T 51003-2014), its strength activity index was measured to be 0.80-0.85, and its apparent density was 3.2 g / cm³. 3 Its main chemical components are CaO, SiO2, Al2O3, MgO, Fe2O3, etc.

[0047] The activated sludge ash used in the following examples and comparative examples was prepared by the following method.

[0048] (1) The dredged sludge was dehydrated and dried using a blower-type drying oven until the difference between two weighings of the sludge was less than 1%;

[0049] (2) Place the dehydrated sludge blocks into a cement test mill and ball mill for 5 minutes to obtain dehydrated sludge ash;

[0050] (3) Place the dehydrated sludge ash into a box-type resistance furnace and calcine it at a constant temperature of 800℃ for 2 hours. After taking it out, place it outdoors to cool naturally.

[0051] (4) The cooled sintered sludge was placed in a cement test mill and ball-milled for 1 minute to obtain activated sludge ash.

[0052] Testing revealed that the activated sludge ash prepared using the above method had a particle size range of 0.1 μm to 8.5 μm, with a median particle size of 1.2 μm. According to the methods specified in the national standard "Technical Specification for Application of Mineral Admixtures" (GB / T 51003-2014), its strength activity index was measured to be 1.11-1.20, and its apparent density was 2.1 g / cm³. 3 Its main chemical components are SiO2, Al2O3, CaO, MgO, Fe2O3, etc.

[0053] Example 1

[0054] This embodiment describes the preparation of a recycled cement-based solid waste cementitious material using the following method, the specific process of which is as follows.

[0055] Weigh out 270 kg of recycled cement, 30 kg of activated sludge, 40 kg of phosphogypsum, 20 kg of borax, 120 kg of water, and 1.0 kg of water-reducing agent per cubic meter of cementitious material. Mix the recycled cement, activated sludge, phosphogypsum, and borax evenly. Add water and water-reducing agent and continue stirring until the slurry is homogeneous, obtaining a cementitious slurry. Pour the cementitious slurry into a cubic mold with a side length of 40 mm, cure at room temperature for 24 hours, demold, and place in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days to obtain an apparent density of 481 kg / m³. 3 Recycled cement-based solid waste cementitious materials.

[0056] Example 2

[0057] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 1, except that the amount of phosphogypsum used in this embodiment is 30 kg and the amount of borax used is 30 kg.

[0058] Example 3

[0059] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 1, except that the amount of phosphogypsum used in this embodiment is 20 kg and the amount of borax used is 40 kg.

[0060] Example 4

[0061] This embodiment describes the preparation of a recycled cement-based solid waste cementitious material using the following method, the specific process of which is as follows.

[0062] Weigh out 240 kg of recycled cement, 60 kg of activated sludge, 40 kg of phosphogypsum, 20 kg of borax, 120 kg of water, and 1.5 kg of water-reducing agent per cubic meter of cementitious material. Mix the recycled cement, activated sludge, phosphogypsum, and borax evenly. Add water and water-reducing agent and continue stirring until the slurry is homogeneous, obtaining a cementitious slurry. Pour the cementitious slurry into a cubic mold with a side length of 40 mm, cure at room temperature for 24 hours, demold, and place in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days to obtain an apparent density of 481.5 kg / m³. 3 Recycled cement-based solid waste cementitious materials.

[0063] Example 5

[0064] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 4, except that the amount of phosphogypsum used in this embodiment is 30 kg and the amount of borax used is 30 kg.

[0065] Example 6

[0066] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 4, except that the amount of phosphogypsum used in this embodiment is 20 kg and the amount of borax used is 40 kg.

[0067] Example 7

[0068] This embodiment describes the preparation of a recycled cement-based solid waste cementitious material using the following method, the specific process of which is as follows.

[0069] Weigh out 210 kg of recycled cement, 90 kg of activated sludge, 40 kg of phosphogypsum, 20 kg of borax, 120 kg of water, and 2.0 kg of water-reducing agent per cubic meter of cementitious material. Mix the recycled cement, activated sludge, phosphogypsum, and borax evenly. Add water and water-reducing agent and continue stirring until the slurry is homogeneous, obtaining a cementitious slurry. Pour the cementitious slurry into a cubic mold with a side length of 40 mm, cure at room temperature for 24 hours, demold, and place in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days to obtain an apparent density of 482 kg / m³. 3 Recycled cement-based solid waste cementitious materials.

[0070] Example 8

[0071] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 7, except that the amount of phosphogypsum used in this embodiment is 30 kg and the amount of borax used is 30 kg.

[0072] Example 9

[0073] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 7, except that the amount of phosphogypsum used in this embodiment is 20 kg and the amount of borax used is 40 kg.

[0074] Example 10

[0075] This embodiment describes the preparation of a recycled cement-based solid waste cementitious material using the following method, the specific process of which is as follows.

[0076] Weigh out 180 kg of recycled cement, 120 kg of activated sludge, 40 kg of phosphogypsum, 20 kg of borax, 120 kg of water, and 2.5 kg of water-reducing agent per cubic meter of cementitious material. Mix the recycled cement, activated sludge, phosphogypsum, and borax evenly. Add water and water-reducing agent and continue stirring until the slurry is homogeneous, obtaining a cementitious slurry. Pour the cementitious slurry into a cubic mold with a side length of 40 mm, cure at room temperature for 24 hours, demold, and place in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days to obtain an apparent density of 482.5 kg / m³. 3 Recycled cement-based solid waste cementitious materials.

[0077] Example 11

[0078] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 10, except that the amount of phosphogypsum used in this embodiment is 30 kg and the amount of borax used is 30 kg.

[0079] Example 12

[0080] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 10, except that the amount of phosphogypsum used in this embodiment is 20 kg and the amount of borax used is 40 kg.

[0081] Example 13

[0082] This embodiment describes the preparation of a recycled cement-based solid waste cementitious material using the following method, the specific process of which is as follows.

[0083] Weigh out 150 kg of recycled cement, 150 kg of activated sludge, 40 kg of phosphogypsum, 20 kg of borax, 120 kg of water, and 3.0 kg of water-reducing agent per cubic meter of cementitious material. Mix the recycled cement, activated sludge, phosphogypsum, and borax evenly. Add water and water-reducing agent and continue stirring until the slurry is homogeneous, obtaining a cementitious slurry. Pour the cementitious slurry into a cubic mold with a side length of 40 mm, cure at room temperature for 24 hours, demold, and place in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days to obtain an apparent density of 483 kg / m³. 3 Recycled cement-based solid waste cementitious materials.

[0084] Example 14

[0085] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 13, except that the amount of phosphogypsum used in this embodiment is 30 kg and the amount of borax used is 30 kg.

[0086] Example 15

[0087] The recycled cement-based solid waste cementitious material in this embodiment is the same as that in Example 13, except that the amount of phosphogypsum used in this embodiment is 20 kg and the amount of borax used is 40 kg.

[0088] Comparative Example 1

[0089] This comparative example prepared a recycled cement-based all-solid waste cementitious material by the following method, the specific process of which is described below.

[0090] Weigh out 270 kg of recycled cement, 30 kg of activated sludge, 120 kg of water, and 2.0 kg of water-reducing agent per cubic meter of cementitious material. Mix the recycled cement and activated sludge evenly, add water and water-reducing agent, and continue stirring until the slurry is homogeneous to obtain a cementitious slurry. Pour the cementitious slurry into a cubic mold with a side length of 40 mm, cure at room temperature for 24 hours, demold, and place in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days to obtain an apparent density of 422 kg / m³. 3 Recycled cement-based solid waste cementitious materials.

[0091] Comparative Example 2

[0092] This comparative example prepared a recycled cement-based all-solid waste cementitious material by the following method, the specific process of which is described below.

[0093] Weigh out 270 kg of recycled cement, 30 kg of activated sludge ash, 30 kg of phosphogypsum, 120 kg of water, and 2.0 kg of water-reducing agent per cubic meter of cementitious material. Mix the recycled cement, activated sludge ash, and phosphogypsum evenly, add water and water-reducing agent, and continue stirring until the slurry is homogeneous to obtain a cementitious slurry. Pour the cementitious slurry into a cubic mold with a side length of 40 mm, cure at room temperature for 24 hours, demold, and place in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days to obtain an apparent density of 452 kg / m³. 3 Recycled cement-based solid waste cementitious materials.

[0094] Comparative Example 3

[0095] This comparative example prepared a recycled cement-based all-solid waste cementitious material by the following method, the specific process of which is described below.

[0096] Weigh out 270 kg of recycled cement, 30 kg of activated sludge, 30 kg of borax, 120 kg of water, and 2.0 kg of water-reducing agent per cubic meter of cementitious material. Mix the recycled cement, activated sludge, and borax evenly, then add water and water-reducing agent and continue stirring until the slurry is homogeneous, obtaining a cementitious slurry. Pour the cementitious slurry into a cubic mold with a side length of 40 mm, cure at room temperature for 24 hours, then demold and place in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days, yielding an apparent density of 452 kg / m³. 3 Recycled cement-based solid waste cementitious materials.

[0097] The aforementioned waste cement slurry originated from a discarded concrete building in Jinnan District, Tianjin.

[0098] The aforementioned dredged silt originated from Baiyangdian Lake in Hebei Province;

[0099] The aforementioned phosphogypsum originated from a phosphogypsum stockpile at a chemical plant in Tianjin;

[0100] The aforementioned borax originated from Tianjin Beichen Fangzheng Reagent Factory;

[0101] The aforementioned water-reducing agent is a liquid polycarboxylate-based high-performance water-reducing agent, sourced from Shanxi Feike New Material Technology Co., Ltd.

[0102] Furthermore, the recycled cement-based solid waste cementitious materials prepared in the above embodiments and comparative examples were subjected to structural characterization and performance testing.

[0103] Flowability test method: According to national standard GB / T8077–2012, the gelatinous slurries with different mix proportions according to the above examples and comparative examples are filled into a truncated conical mold and leveled with a scraper. After lifting the mold, wait for 30 seconds and measure the diameter of free diffusion of the gelatinous slurry on the plane. The test is repeated three times for each mix proportion, and the average value is recorded.

[0104] Setting time test method: Referring to the national standard GB / T1346-2024, the initial setting and final setting times of the recycled cement-based solid waste cementitious materials prepared according to the above examples and comparative examples were determined using a Vicat apparatus.

[0105] Compressive strength test method: The compressive strength of the specimens at 28 days of age was tested according to national standard GB / T 17671-2021. Three cubic specimens with a side length of 40 mm were prepared for the recycled cement-based solid waste cementitious materials prepared according to the above examples and comparative examples, and cured under standard curing conditions. The loading rate for the compressive strength test was 2.4 kN / s, and the average strength was taken.

[0106] Figure 1 A comparison diagram of the flowability of recycled cement-based solid waste cementitious materials prepared in the embodiments and comparative examples of this application; Figure 2 A comparison diagram of the setting time of the recycled cement-based solid waste cementitious materials prepared in the embodiments and comparative examples of this application; Figure 3 This is a comparison diagram of the compressive strength of the recycled cement-based solid waste cementitious materials prepared in the embodiments and comparative examples of this application.

[0107] Depend on Figures 1 to 3 It can be seen that in Comparative Example 1, the all-solid waste cementitious material composed solely of recycled cement and activated sludge ash exhibits characteristics of low fluidity, rapid setting and hardening, and low compressive strength, which is unfavorable for on-site construction and has insufficient mechanical properties. A comparison of Comparative Examples 2 and 3 with Examples 1-15 shows that while adding phosphogypsum alone can improve compressive strength, its effect on improving workability is limited; adding borax alone can significantly improve workability, but it has almost no effect on compressive strength; however, when the two are used in combination, a dual enhancement of workability and compressive strength is achieved, producing a significant synergistic effect.

[0108] Figure 4 The X-ray diffraction pattern of the recycled cement-based solid waste cementitious material in Example 7 of this application after 28 days; Figure 5 This is a scanning electron microscope image of the recycled cement-based solid waste cementitious material in Example 7 of this application after 28 days.

[0109] Depend on Figure 4 and Figure 5 It can be seen that the incorporation of borax can adsorb onto the surface of the active particles in recycled cement, forming an inert protective film. This effectively inhibits the early rapid hydration of dicalcium silicate (C2S), delays the precipitation of calcium hydroxide and the disordered formation of hydrated calcium silicate gel, and avoids the loose structure of the cementitious material caused by excessively rapid hydration, thus reserving sufficient space for the subsequent sulfate activation and crystal growth of phosphogypsum. In the borax-retarded system, the sulfate ions released by phosphogypsum fully react with the active aluminates in the alkaline environment of recycled cement, inducing the formation of a large number of acicular ettringite (AFt) crystals by 28 days. Scanning electron microscopy images further show that the cementitious material matrix has no obvious pores or microcracks, and the acicular ettringite crystals are evenly distributed and overlap each other, forming a continuous spatial network. The hydrated calcium silicate gel is tightly attached to the crystal surface and gaps. The microstructure constructed by the retardation regulation of borax and the crystal phase reinforcement of phosphogypsum is the fundamental reason why this all-solid waste cementitious material has both excellent workability and high mechanical strength.

[0110] By adopting the above technical solution, the recycled cement-based solid waste cementitious material of this application has a large controllable range in terms of fluidity and setting time. The fluidity can be adjusted within the range of 43mm-240mm, and the setting time can be controlled within 3.5-8.5h. In addition, the cementitious material also has good compressive strength.

[0111] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A recycled cement-based solid waste cementitious material, characterized in that, A cementitious material made from a mixture comprising the following components: recycled cement, activated sludge, phosphogypsum, borax, water-reducing agent, and water; Specifically, per cubic meter of the recycled cement-based solid waste cementitious material, the amount of recycled cement is 150kg-270kg, the amount of activated sludge ash is 30kg-150kg, the amount of phosphogypsum is 20kg-40kg, the amount of borax is 20kg-40kg, the amount of water-reducing agent is 1kg-3kg, and the amount of water is 35%-45% of the total mass of the recycled cement, the activated sludge ash, and the phosphogypsum. The recycled cement is recycled from waste cement paste, the particle size of the activated lime mud ranges from 0.1 μm to 8.5 μm, the strength activity index ranges from 1.11 to 1.20, and the apparent density is 2 g / cm 3 -2.5 g / cm 3 ; The activated silt ash is recovered from dredged silt, the particle size of the activated silt ash ranges from 0.1 μm to 8.5 μm, the strength activity index is 1.11-1.20, and the apparent density is 2 g / cm 3 -2.5 g / cm 3 ; The apparent density of the recycled cement-based solid waste cementitious material is 480 kg / m³. 3 -485 kg / m 3 .

2. The recycled cement-based solid waste cementitious material according to claim 1, characterized in that, The recycled cement is produced from waste cement slurry through crushing, ball milling, calcination, and secondary ball milling.

3. The recycled cement-based solid waste cementitious material according to claim 2, characterized in that, In preparing the recycled cement, the calcination temperature is 650-750℃ and the calcination time is 1.5-2.5h.

4. The recycled cement-based solid waste cementitious material according to claim 1, characterized in that, The activated sludge ash is obtained by dehydrating and drying dredged sludge, ball milling, calcining, and ball milling twice.

5. The recycled cement-based solid waste cementitious material according to claim 4, characterized in that, In preparing the activated sludge ash, the calcination temperature is 750-850℃ and the calcination time is 1.5-2.5h.

6. The recycled cement-based solid waste cementitious material according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate-based water-reducing agent.

7. A method for preparing a recycled cement-based all-solid waste cementitious material as described in any one of claims 1-6, characterized in that, Includes the following steps: After uniformly mixing recycled cement, activated sludge ash, phosphogypsum, and borax, water-reducing agent and water are added, and the mixture is further mixed evenly. After molding and curing, recycled cement-based solid waste cementitious material is obtained.

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