A fast-curing magnesium hydroxide sulphate cement 3D printing concrete

Abstract

The application relates to the technical field of building materials, and specifically discloses a kind of quick solidification alkali magnesium sulfate cement 3D printing concrete.The concrete is made of raw materials containing the following weight parts: salt lake potassium extraction byproduct 30-50 parts, Portland cement 20-40 parts, metakaolin 5-15 parts, quartz sand 10-25 parts, composite activator 3-8 parts, polycarboxylate superplasticizer 0.5-2 parts, water retaining agent 0.1-0.5 parts and defoaming agent 0.05-0.2 parts;The preparation method is as follows: S1, raw material pretreatment: the salt lake potassium extraction byproduct is dried, then crushed and sieved to obtain the pretreated byproduct;S2, active activation calcination;S3, dry powder preparation;S4, printing construction.The concrete can be used for rapid construction components, special-shaped templates, decorative parts and reinforcement repair layers in the field of building 3D printing, and has the advantages of quick solidification forming, high interlayer bonding strength, high rheological property and constructability.

Description

Technical Field

[0001] This application relates to the field of building materials technology, and more specifically, it relates to a rapidly curing basic magnesium sulfate cement 3D printed concrete. Background Technology

[0002] As an emerging digital construction method, 3D printing technology has significant advantages such as moldlessness, automation, high design freedom, and labor saving, and has broad application prospects in the construction field. This technology places requirements on printing materials, which must simultaneously meet the following requirements: good extrudability and flowability to ensure smooth pumping and extrusion; excellent shape retention to prevent collapse after extrusion; rapid solidification characteristics to achieve support between lower and upper layers; and excellent interlayer bond strength to ensure the overall integrity of the structure.

[0003] Currently, most mainstream 3D printed concrete uses silicate cement as the main cementing material. However, this type of material has inherent defects: First, the setting and curing speed is relatively slow, especially in low-temperature environments, the early strength build-up is difficult to meet the requirements of 3D printing, resulting in low printing efficiency and the risk of collapse; Second, the interlayer bonding performance is poor. Due to the printing interval, after the lower layer material initially sets, it is easy to form cold joints with the upper layer of new material, which weakens the interlayer bonding force and affects the overall mechanical properties of the component; Third, the carbon emissions are high. The production process of silicate cement has high energy consumption and large carbon emissions, which is contrary to the concept of green building development. Summary of the Invention

[0004] To address the problem that 3D printed concrete using silicate cement as a binder cannot meet the requirements of 3D printing, this application provides a rapidly curing basic magnesium sulfate cement 3D printed concrete.

[0005] In the first aspect, this application provides a rapidly curing basic magnesium sulfate cement 3D printed concrete, employing the following technical solution: A rapidly curable basic magnesium sulfate cement 3D printed concrete is made from the following raw materials in parts by weight: 30-50 parts of potassium extraction byproducts from salt lakes, 20-40 parts of silicate cement, 5-15 parts of metakaolin, 10-25 parts of quartz sand, 3-8 parts of composite activator, 0.5-2 parts of polycarboxylate-based high-efficiency water-reducing agent, 0.1-0.5 parts of water-retaining agent, and 0.05-0.2 parts of defoamer.

[0006] By adopting the above technical solution, the use of potassium extraction byproducts from salt lakes as one of the main raw materials realizes the utilization of industrial solid waste and reduces raw material costs. Through the synergistic effect of composite activators and medium-temperature calcination, the activity of magnesium oxide in the byproducts is activated, causing it to react with magnesium sulfate components in the system to form a basic magnesium sulfate cement phase, thereby constructing a fast-hardening cementitious system. Silicate cement and metakaolin supplement the cementitious components and improve the microstructure. Quartz sand serves as aggregate to provide skeletal support. Polycarboxylate-based high-efficiency water-reducing agents, water-retaining agents, and defoamers jointly optimize the rheological properties, water retention, and homogeneity of the slurry. Therefore, the obtained concrete has good extrudability, rapid early strength development, excellent interlayer bonding performance, and the convenience of single-component construction, meeting the core requirements of 3D printing.

[0007] Preferably, the composite activator is prepared by compounding sodium sulfate, calcium aluminate powder and gypsum in a weight ratio of 1.8-2.2:0.9-1.1:0.9-1.1.

[0008] By adopting the above technical solution, due to the use of this specific ratio of composite activator, sodium sulfate plays an activating role in the calcination and subsequent hydration process, promoting the active release of magnesium oxide and silicate components in the potassium extraction by-products from salt lakes; calcium aluminate powder provides the early aluminate phase, which works synergistically with gypsum to regulate the setting time and promote early strength development; gypsum further participates in the hydration reaction, stabilizing the sulfoaluminate phase and optimizing the pore structure. Therefore, the activating effect on the active components of industrial solid waste is achieved, ensuring that the gelation system can establish early strength and providing a guarantee for the bearing capacity of the printing layer.

[0009] Preferably, the potassium extraction byproduct from the salt lake is made from the following raw materials by weight percentage: 30-40% magnesium oxide, 15-25% calcium oxide, 20-30% silicon dioxide, and impurity content satisfying ≤5% ferric oxide, ≤1% chloride ions and ≤3% sulfate ions.

[0010] By adopting the above technical solution, the chemical composition of the potassium extraction by-products from salt lakes is limited, ensuring that the main component is active magnesium oxide, which can be used to form the basic magnesium sulfate cement phase. At the same time, the content of calcium oxide and silicon dioxide is controlled to participate in the auxiliary cementitious reaction. The content of impurities such as ferric oxide, chloride ions and sulfate ions is limited to avoid impurities interfering with the main hydration reaction, corroding steel bars or causing volume instability. Therefore, core raw materials with stable composition and controllable activity are obtained, which is the material basis for achieving repeatable concrete performance, high strength and durability.

[0011] Preferably, the particle size range of the quartz sand is 0.15-0.6 mm.

[0012] By adopting the above technical solution, the use of quartz sand with a particle size range of 0.15 to 0.6 mm provides aggregate with a gradation that can support the slurry and reduce plastic deformation without increasing the slurry viscosity, thus providing shape retention capability, i.e., mold stability, for the printed structure. At the same time, the finer particle size is conducive to uniform distribution in the slurry, avoiding blockage in the printing nozzle or pipeline. Therefore, printing smoothness and extrusion molding stability are achieved, ensuring the geometric accuracy of the printed components.

[0013] Preferably, the slump spread of the concrete is 180-220mm, the slump loss after 1 hour is ≤10mm, the compressive strength after 28 days is ≥40MPa, and the interlayer bond strength is ≥3.5MPa.

[0014] By adopting the above technical solution, the concrete slurry has slump expansion in the initial stage due to the optimization of raw material ratio and preparation process, which ensures its good fluidity and pumpability; the expansion loss within 1 hour does not exceed a certain range, indicating that the slurry has long-term stability and can support long-term continuous printing operations without performance degradation; the 28-day compressive strength and interlayer bond strength directly reflect that the final component formed by the material has load-bearing capacity and integrity, overcoming the cold joint problem of weak interlayer bond in traditional materials. Therefore, high-performance concrete that meets the comprehensive performance requirements of 3D printed building construction is obtained.

[0015] Secondly, this application provides a method for preparing rapidly curing basic magnesium sulfate cement 3D printed concrete, using the following technical solution: A method for preparing rapidly curing basic magnesium sulfate cement 3D printed concrete includes the following steps: S1. Raw material pretreatment: The potassium extraction by-product from the salt lake is dried, then crushed and sieved to obtain the pretreated by-product; S2. Activation-activated calcination: The pretreatment by-products, metakaolin and composite activator are mixed evenly according to the ratio, calcined and naturally cooled to obtain the active mixed powder. S3. Preparation of dry powder: The active mixed powder is mixed with silicate cement and quartz sand in proportion and then dry-mixed. Polycarboxylate superplasticizer, water-retaining agent and defoamer are added and stirred to obtain single-component 3D printing concrete dry powder. S4. Printing Construction: Mix the obtained single-component 3D printing concrete dry powder with water at a certain powder-to-water ratio and stir to form a slurry for 3D printing.

[0016] By adopting the above technical solution, a systematic preparation process including pretreatment, calcination activation, dry mixing, and on-site mixing is employed. The raw material pretreatment removes moisture from the by-products and homogenizes the particles, creating uniform conditions for subsequent calcination activation. The activation calcination step enhances the gelling activity of the potassium extraction by-products from the salt lake through a thermochemical process, which is a precursor to form a rapid curing system. The dry powder preparation step premixes all solid components uniformly and ensures uniform dispersion of chemical additives through stepwise feeding, forming a stable single-component product. The final printing and construction step only requires the addition of water to obtain a ready-to-use slurry. Therefore, a convenient, stable, and controllable preparation method is obtained, solving the problems of large errors and complex processes in multi-component on-site batching, and ensuring the rapid curing and high-strength bonding performance of concrete.

[0017] Preferably, in step S1, the drying temperature is 90-120℃, the drying time is 2-3 hours, and the sieve mesh size is 70-90 mesh.

[0018] By adopting the above technical solution, the drying temperature and time used in the raw material pretreatment step can remove the free water adsorbed by potassium extraction byproducts from salt lakes, avoiding the water causing vapor pressure during subsequent calcination, which could lead to material splashing or affect heat transfer efficiency. It also prevents pre-hydration of the dry powder during storage. After drying, the material is crushed and passed through a sieve to pulverize it to a suitable fineness, increasing the specific surface area to facilitate the full solid-phase reaction during subsequent calcination and ensuring uniform mixing with other powder raw materials. Therefore, a dry, pure, and appropriately sized pretreated raw material is obtained, laying the foundation for the efficiency and consistency of the subsequent activation step.

[0019] Preferably, in step S2, the calcination temperature is 630-680℃ and the calcination time is 2.3-2.7 hours.

[0020] By adopting the above technical solution, the pretreated mixture is calcined for a certain time within a set temperature range during the activation calcination step. This temperature and time window are optimized process parameters, which are sufficient to allow the composite activator to undergo a solid-phase reaction with the amorphous or low-activity components in the potassium extraction by-products from the salt lake and metakaolin, transforming substances such as magnesium oxide into reactive forms, but without causing sintering or the formation of unfavorable crystal phases due to excessively high temperatures. The reasonable calcination time ensures uniform heat transfer and complete reaction. Therefore, a mixed powder with cementitious activity is obtained, which is a precursor that imparts rapid hardening and early strength characteristics to concrete.

[0021] Preferably, in step S3, the dry mixing time is 10-15 minutes, and the stirring time is 5-8 minutes.

[0022] By adopting the above technical solution, in the dry powder preparation step, the active mixed powder is first dry-mixed with silicate cement and quartz sand for a certain period of time. This period of time is sufficient to achieve macroscopic uniform mixing of various powders and aggregates with different densities and particle sizes, forming a homogeneous basic dry powder. Subsequently, chemical additives such as polycarboxylate-based high-efficiency water-reducing agents, water-retaining agents, and defoamers are added and stirred for a period of time. This step ensures that trace amounts of additives can be fully dispersed in the dry powder and coated on the particle surface, avoiding clumping or uneven distribution when water is added and stirred later. Therefore, a single-component dry powder with uniformly dispersed chemical additives and highly homogeneous components is obtained, ensuring the uniformity and stability of the final slurry performance.

[0023] Preferably, in step S4, the powder-to-water ratio is 1:0.25-0.35, and the mixing time is 3-5 minutes; it also includes adjusting printing parameters according to different climatic environments. In high-temperature environments with temperatures >35℃ and relative humidity <40%, the powder-to-water ratio should be adjusted to 1:0.32-0.35, and the printing speed should be adjusted to 25-35mm / s. In a low-temperature environment of 5-15℃, the powder-to-water ratio should be adjusted to 1:0.25-0.28, and warm water at 20-30℃ should be used to mix the slurry; In high humidity environments with relative humidity >70%, adjust the powder-to-water ratio to 1:0.25-0.28 and extend the printing interval between each layer by 3-5 minutes; In a dry environment with relative humidity <50%, the powder-to-water ratio should be adjusted to 1:0.30-0.35, and a moisturizing film should be used for curing after printing.

[0024] By adopting the above technical solution, by setting a baseline powder-to-water ratio and stirring for a certain time during the printing process, the water consumption range can reduce the free water content while ensuring the fluidity of the slurry, which is conducive to rapid setting and strength development. The stirring time ensures the formation of a uniform slurry. Furthermore, specific parameter adjustment schemes are formulated for different climatic environments. In high-temperature and dry environments, the water consumption is appropriately increased and the printing speed is reduced to compensate for water evaporation and prevent the slurry from losing its workability prematurely. In low-temperature environments, a lower water-to-cement ratio and warm water are used for mixing, and the printing speed is increased to reduce heat loss and promote early hydration. In high-humidity environments, a low water-to-cement ratio is used and the interlayer interval is extended to facilitate the evaporation of surface moisture and avoid excessive load. In dry environments, the water consumption is appropriately increased and moisturizing is strengthened to prevent plastic shrinkage cracking. Therefore, a complete set of construction adaptability strategies is obtained, which can offset the impact of environmental temperature and humidity fluctuations on printing operations and the quality of the final components, ensuring stable and reliable printing results under different climatic conditions.

[0025] In summary, this application has the following beneficial effects: 1. Since this application adopts a scheme that uses potassium extraction by-products from salt lakes as the main raw material and combines a composite activator with the synergistic effect of medium-temperature calcination, this scheme can efficiently activate the gelling activity of industrial solid waste, forming a rapid hardening system mainly composed of basic magnesium sulfate cement phase. At the same time, silicate cement and metakaolin are used to optimize the microstructure, and additives are used to regulate the slurry properties. Therefore, the scheme achieves the effect of high-value utilization of industrial solid waste, material with rapid curing and interlayer bonding strength, and meets the requirements of 3D printing construction.

[0026] 2. In this application, a composite activator made of sodium sulfate, calcium aluminate powder and gypsum in a specific mass ratio is preferred. The components of this composite activator can work synergistically during calcination and hydration to effectively activate the activity of raw materials, regulate the setting time and stabilize the hydration products. Therefore, it can efficiently activate the effective components in the potassium extraction by-products of salt lakes and ensure the rapid establishment and stable development of the early strength of the gelation system.

[0027] 3. The method of this application includes a process that includes raw material pretreatment, activation calcination, dry powder preparation, and climate-adaptive printing construction. The pretreatment lays the foundation for subsequent activation, the calcination step is the activation step, the dry mixing preparation ensures the homogeneity and stability of the single-component product, and the parameter adjustment for different environments offsets the influence of external condition fluctuations. Therefore, the method achieves the effect of a clear process flow, stable preparation of 3D printed concrete products that are easy to construct, reliable in performance, and highly adaptable to the environment. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating a method for preparing rapidly curable basic magnesium sulfate cement 3D printed concrete, as proposed in this application. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Technical concept: Most 3D printed concrete uses silicate cement as the main binder. However, this type of material has inherent defects: First, the setting and curing speed is relatively slow, especially in low-temperature environments, and the early strength build-up is difficult to meet the requirements of 3D printing, resulting in low printing efficiency and the risk of collapse; Second, the interlayer bonding performance is poor. Due to the printing interval, cold joints are easily formed between the lower layer material and the upper layer after the initial setting, which weakens the interlayer bonding force and affects the overall mechanical properties of the component; Third, the carbon emissions are high. The production process of silicate cement is energy-intensive and has a large amount of carbon emissions, which is contrary to the concept of green building development.

[0031] This application discloses a rapidly curable basic magnesium sulfate cement 3D printed concrete. It is made from raw materials comprising the following parts by weight: 30-50 parts of potassium extraction byproducts from salt lakes, 20-40 parts of silicate cement, 5-15 parts of metakaolin, 10-25 parts of quartz sand, 3-8 parts of composite activator, 0.5-2 parts of polycarboxylate-based high-efficiency water-reducing agent, 0.1-0.5 parts of water-retaining agent, and 0.05-0.2 parts of defoamer. The preparation method is as follows: S1, raw material pretreatment: drying the potassium extraction byproducts from salt lakes, followed by crushing and sieving to obtain pretreated byproducts; S2, activation calcination; S3, dry powder preparation; S4, printing construction.

[0032] This application adopts a scheme that uses potassium extraction by-products from salt lakes as the main raw material, combined with a composite activator and medium-temperature calcination. This scheme can efficiently activate the gelling activity of industrial solid waste, forming a rapid hardening system mainly composed of basic magnesium sulfate cement phase. At the same time, silicate cement and metakaolin are used to optimize the microstructure, and additives are used to regulate the slurry properties. Therefore, it achieves the effect of high-value utilization of industrial solid waste, material with rapid curing and interlayer bonding strength, and meets the requirements of 3D printing construction.

[0033] Example 1: This example provides a fast-curing basic magnesium sulfate cement 3D printed concrete, which is made from the following raw materials in parts by weight: 30 parts of potassium extraction byproducts from salt lakes, 20 parts of silicate cement, 5 parts of metakaolin, 10 parts of quartz sand, 3 parts of composite activator, 0.5 parts of polycarboxylate-based high-efficiency water-reducing agent, 0.1 parts of water-retaining agent, and 0.05 parts of defoamer.

[0034] The composite activator is composed of sodium sulfate, calcium aluminate powder and gypsum in a weight ratio of 1.8:0.9:0.9.

[0035] Among them, the by-products of potassium extraction from salt lakes contain 30% magnesium oxide, 15% calcium oxide, and 20% silicon dioxide, with the remainder being impurities. Among the impurities, the content of ferric oxide is 4.5%, chloride ion content is 0.8%, and sulfate ion content is 2.5%.

[0036] The particle size of the quartz sand is 0.15 mm.

[0037] The concrete has a slump spread of 180 mm, a 1-hour time loss of 9 mm, a 28-day compressive strength of 42 MPa, and an interlayer bond strength of 3.6 MPa.

[0038] The above-mentioned method for preparing rapidly curing basic magnesium sulfate cement 3D printed concrete includes the following steps: S1. Raw material pretreatment: The potassium extraction by-product from the salt lake is dried, then crushed and sieved to obtain the pretreated by-product.

[0039] The drying temperature is 90℃, the drying time is 2 hours, and the sieve mesh size is 70 mesh.

[0040] S2. Activation-activated calcination: The pretreatment by-products, metakaolin, and composite activator are mixed evenly according to the ratio, calcined, and naturally cooled to obtain the activated mixed powder.

[0041] The calcination temperature was 630℃ and the calcination time was 2.3 hours.

[0042] S3. Dry powder preparation: The active mixed powder is mixed with silicate cement and quartz sand in proportion and then dry-mixed. Polycarboxylate-based high-efficiency water-reducing agent, water-retaining agent and defoamer are added and stirred to obtain single-component 3D printing concrete dry powder.

[0043] The mixing time is 10 minutes, followed by 5 minutes of continued stirring.

[0044] S4. Printing Construction: Mix the obtained single-component 3D printing concrete dry powder with clean water at a powder-to-water ratio of 1:0.32 and stir to form a slurry for 3D printing.

[0045] The mixing time was 3 minutes; printing was carried out in a high-temperature environment of 36℃ and 35% relative humidity, and the printing speed was set to 25mm / s.

[0046] Example 2: This example provides a fast-curing basic magnesium sulfate cement 3D printed concrete, which is made from the following raw materials in parts by weight: 40 parts of potassium extraction byproducts from salt lakes, 30 parts of silicate cement, 10 parts of metakaolin, 17.5 parts of quartz sand, 5.5 parts of composite activator, 1.3 parts of polycarboxylate-based high-efficiency water-reducing agent, 0.3 parts of water-retaining agent, and 0.13 parts of defoamer.

[0047] The composite activator is composed of sodium sulfate, calcium aluminate powder and gypsum in a weight ratio of 2.0:1.0:1.0.

[0048] Among them, the by-products of potassium extraction from salt lakes contain 35% magnesium oxide, 20% calcium oxide, and 25% silicon dioxide, with the remainder being impurities. Among the impurities, the content of ferric oxide is 2.0%, chloride ion content is 0.5%, and sulfate ion content is 1.5%.

[0049] The particle size of the quartz sand is 0.38 mm.

[0050] The concrete has a slump extension of 200 mm, a 1-hour time loss of 5 mm, a 28-day compressive strength of 50 MPa, and an interlayer bond strength of 4.0 MPa.

[0051] The above-mentioned method for preparing rapidly curing basic magnesium sulfate cement 3D printed concrete includes the following steps: S1. Raw material pretreatment: The potassium extraction by-product from the salt lake is dried, then crushed and sieved to obtain the pretreated by-product.

[0052] The drying temperature is 105℃, the drying time is 2.5 hours, and the sieve mesh size is 80 mesh.

[0053] S2. Activation-activated calcination: The pretreatment by-products, metakaolin, and composite activator are mixed evenly according to the ratio, calcined, and naturally cooled to obtain the activated mixed powder.

[0054] The calcination temperature was 655℃ and the calcination time was 2.5 hours.

[0055] S3. Dry powder preparation: The active mixed powder is mixed with silicate cement and quartz sand in proportion and then dry-mixed. Polycarboxylate-based high-efficiency water-reducing agent, water-retaining agent and defoamer are added and stirred to obtain single-component 3D printing concrete dry powder.

[0056] The dry mixing time is 12.5 minutes, and the continued mixing time is 6.5 minutes.

[0057] S4. Printing Construction: Mix the obtained single-component 3D printing concrete dry powder with 25°C warm water at a powder-to-water ratio of 1:0.28 and stir to form a slurry for 3D printing.

[0058] The stirring time was 4 minutes; printing was carried out at a low temperature of 10℃.

[0059] Example 3: This example provides a fast-curing basic magnesium sulfate cement 3D printed concrete, which is made from the following raw materials in parts by weight: 45 parts of potassium extraction byproducts from salt lakes, 35 parts of silicate cement, 12.5 parts of metakaolin, 20 parts of quartz sand, 6.5 parts of composite activator, 1.8 parts of polycarboxylate-based high-efficiency water-reducing agent, 0.4 parts of water-retaining agent, and 0.18 parts of defoamer.

[0060] The composite activator is composed of sodium sulfate, calcium aluminate powder and gypsum in a weight ratio of 2.1:1.05:0.95.

[0061] Among them, the by-products of potassium extraction from salt lakes contain 38% magnesium oxide, 22% calcium oxide, and 28% silicon dioxide, with the remainder being impurities. Among the impurities, the content of ferric oxide is 1.0%, chloride ion content is 0.3%, and sulfate ion content is 2.0%.

[0062] The particle size of the quartz sand is 0.5 mm.

[0063] The concrete slump extension is 210 mm, the slump loss over 1 hour is 8 mm, the compressive strength over 28 days is 55 MPa, and the interlayer bond strength is 4.2 MPa.

[0064] The above-mentioned method for preparing rapidly curing basic magnesium sulfate cement 3D printed concrete includes the following steps: S1. Raw material pretreatment: The potassium extraction by-product from the salt lake is dried, then crushed and sieved to obtain the pretreated by-product.

[0065] The drying temperature is 115℃, the drying time is 2.8 hours, and the sieve mesh size is 85 mesh.

[0066] S2. Activation-activated calcination: The pretreatment by-products, metakaolin, and composite activator are mixed evenly according to the ratio, calcined, and naturally cooled to obtain the activated mixed powder.

[0067] The calcination temperature was 670℃ and the calcination time was 2.6 hours.

[0068] S3. Dry powder preparation: The active mixed powder is mixed with silicate cement and quartz sand in proportion and then dry-mixed. Polycarboxylate-based high-efficiency water-reducing agent, water-retaining agent and defoamer are added and stirred to obtain single-component 3D printing concrete dry powder.

[0069] The mixing time is 14 minutes, and the stirring time is 7.5 minutes.

[0070] S4. Printing Construction: Mix the obtained single-component 3D printing concrete dry powder with clean water at a powder-to-water ratio of 1:0.26 and stir to form a slurry for 3D printing.

[0071] The mixing time is 5 minutes; printing is carried out in a high humidity environment with a relative humidity of 75%, and the interval between each layer is extended by 4 minutes.

[0072] Example 4: This example provides a fast-curing basic magnesium sulfate cement 3D printed concrete, which is made from the following raw materials in parts by weight: 50 parts of potassium extraction byproducts from salt lakes, 40 parts of silicate cement, 15 parts of metakaolin, 25 parts of quartz sand, 8 parts of composite activator, 2 parts of polycarboxylate-based high-efficiency water-reducing agent, 0.5 parts of water-retaining agent and 0.2 parts of defoamer.

[0073] The composite activator is composed of sodium sulfate, calcium aluminate powder and gypsum in a weight ratio of 2.2:1.1:1.1.

[0074] Among them, the by-products of potassium extraction from salt lakes contain 40% magnesium oxide, 25% calcium oxide, and 30% silicon dioxide, with the remainder being impurities. Among the impurities, the content of ferric oxide is 0.5%, chloride ion content is 0.1%, and sulfate ion content is 1.0%.

[0075] The particle size of the quartz sand is 0.6 mm.

[0076] The concrete slump extension is 220 mm, the slump loss over 1 hour is 3 mm, the compressive strength over 28 days is 60 MPa, and the interlayer bond strength is 4.5 MPa.

[0077] The above-mentioned method for preparing rapidly curing basic magnesium sulfate cement 3D printed concrete includes the following steps: S1. Raw material pretreatment: The potassium extraction by-product from the salt lake is dried, then crushed and sieved to obtain the pretreated by-product.

[0078] The drying temperature is 120℃, the drying time is 3 hours, and the sieve mesh size is 90 mesh.

[0079] S2. Activation-activated calcination: The pretreatment by-products, metakaolin, and composite activator are mixed evenly according to the ratio, calcined, and naturally cooled to obtain the activated mixed powder.

[0080] The calcination temperature was 680℃ and the calcination time was 2.7 hours.

[0081] S3. Dry powder preparation: The active mixed powder is mixed with silicate cement and quartz sand in proportion and then dry-mixed. Polycarboxylate-based high-efficiency water-reducing agent, water-retaining agent and defoamer are added and stirred to obtain single-component 3D printing concrete dry powder.

[0082] The mixing time is 15 minutes, followed by 8 minutes of continued stirring.

[0083] S4. Printing Construction: Mix the obtained single-component 3D printing concrete dry powder with clean water at a powder-to-water ratio of 1:0.33 and stir to form a slurry for 3D printing.

[0084] The stirring time is 4 minutes; printing is carried out in a dry environment with a relative humidity of 45%, and a moisturizing film is used for curing after printing.

[0085] Comparative Example 1: This comparative example is based on the content of Example 1, except that the amount of potassium extraction byproduct from the salt lake is changed from 30 parts to 20 parts, and the amount of silicate cement is changed to 10 parts. The rest of the content is the same as that of Example 1.

[0086] Comparative Example 2: This comparative example is based on the content of Example 1, except that the amount of potassium extraction byproduct from the salt lake is changed from 30 parts to 65 parts, and the amount of silicate cement is changed to 50 parts. The rest of the content is the same as that of Example 1.

[0087] Comparative Example 3: This comparative example is based on the content of Example 1, except that the amount of composite activator is changed from 3 parts to 1.5 parts, and the rest is the same as Example 1.

[0088] Comparative Example 4: This comparative example is the same as that in Example 1, except that the weight ratio of sodium sulfate, calcium aluminate powder and gypsum in the composite activator is changed from 1.8:0.9:0.9 to 1.0:2.0:1.0. The rest of the contents are the same as those in Example 1.

[0089] Comparative Example 5: This comparative example refers to the content of Example 1, except that the calcination temperature in step S2 is changed from 630°C to 500°C, and the rest is the same as Example 1.

[0090] Comparative Example 6: This comparative example refers to the content of Example 1, except that the powder-to-water ratio in step S4 is changed from 1:0.32 to 1:0.20, and the rest is the same as Example 1.

[0091] Performance testing Sample preparation: Performance test samples were prepared according to the proportions and preparation methods disclosed in the examples and comparative examples: all specimens were cured at a temperature of 36°C and a relative humidity of 35% until the specified age.

[0092] Slump spread and time loss test: Freshly mixed slurry is filled into a standard slump cone. After lifting the cone, the maximum diameter of the slurry after horizontal diffusion and the vertical diameter are measured, and the average value is taken as the slump spread. This value directly reflects the fluidity and extrudability of the slurry. After mixing, the mixture is allowed to stand for 1 hour, and its spread is tested again. The loss of spread within 1 hour, i.e., the time loss, is calculated to evaluate the slump's ability to retain workability. This is crucial for ensuring smooth delivery and accurate stacking during continuous printing. This test is conducted in accordance with the standard GB / T50080 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures".

[0093] Compressive strength test: The grout is cast into prism specimens of 40mm×40mm×160mm, cured under standard curing conditions or specified environmental conditions, and the compressive strength is tested to evaluate its final mechanical properties and strength development stability; this test is carried out in accordance with the standard GB / T17671 "Test method for strength of cement mortar (ISO method)".

[0094] Interlayer bond strength testing: First, print the first layer of concrete strips. After the set interlayer interval, print the second layer of strips on top of it. After curing for the specified age, test the bond strength between the two layers of concrete using shear or splitting tensile strength methods. The testing method can refer to ASTM C1583 "Test Method for Bond Strength between Concrete Repair Materials and Matrix Concrete" or the industry-standard guideline for testing interlayer bond strength of 3D printed concrete.

[0095] To elucidate the synergistic mechanism of composite activators and medium-temperature calcination in activating the activity and optimizing the microstructure of industrial solid waste, microstructural analysis is necessary. X-ray diffraction analysis was used to identify the phase composition of hydration products at different curing ages (e.g., 1 day, 28 days), clarifying the appearance and evolution of characteristic peaks such as basic magnesium sulfate cement phase and ettringite, thus confirming the formation of the expected hydration products. Scanning electron microscopy was used to observe the morphology, distribution, and pore structure of the hydration products, analyzing the quality of the interfacial transition zone to explain the high mechanical properties and interlayer bond strength of the material at the microscopic level. This analysis provides scientific evidence to confirm the technical effectiveness and is crucial experimental data supporting the mechanism claims in the patent application.

[0096] Table 1: Performance Comparison Table

[0097] Example Conclusion: Based on Examples 1-4 and Comparative Example 1, and in conjunction with Table 1, it can be seen that the ratio of potassium extraction by-products from salt lakes to silicate cement needs to be maintained within a suitable range. When the ratio of main materials is unbalanced, the total amount of effective components used to form the cementitious network will be insufficient or the system will be unbalanced. This will cause the cohesiveness and fluidity of the freshly mixed slurry to deteriorate, the workability to deteriorate, and the amount and degree of interweaving of hydration products to decrease. Ultimately, this will result in a loose overall structure of the hardened body and a decrease in mechanical properties and interlayer bonding performance. Therefore, an optimized ratio of main materials is the foundation for ensuring that the material achieves printability and final structural strength.

[0098] Based on Examples 1-4 and Comparative Example 2, and referring to Table 1, it can be seen that the potassium extraction by-products from salt lakes and silicate cement need to be maintained within a suitable ratio range. When the proportion of main materials is unbalanced, it will also disrupt the material gradation and chemical equilibrium of the system. Excessive components cannot be fully hydrated or will produce adverse volume changes, interfering with the formation of dense microstructures. This will lead to a decrease in the homogeneity of the slurry, an increase in flow resistance, and the introduction of more defects after hardening, thereby impairing the rheological properties, strength development, and effective bonding between layers of the material. Therefore, an optimized ratio of main materials is necessary to coordinate the workability and mechanical properties of the material.

[0099] As can be seen from Examples 1-4 and Comparative Example 3, and Table 1, the amount of composite activator must be sufficient. Sufficient activator is a necessary condition to ensure that the active components in the potassium extraction by-products from salt lakes are fully activated during calcination and hydration. Insufficient activator will result in incomplete activation reaction, leading to slow early hydration reaction and insufficient amount of effective gelling products. This will result in slow slurry setting and hardening, poor structural strength establishment, rapid loss of fluidity, short construction time, and low strength and interlayer bonding of the final structure. Therefore, sufficient composite activator is the guarantee for achieving rapid curing and high strength performance of the material.

[0100] Based on Examples 1-4 and Comparative Example 4, and referring to Table 1, it can be seen that the proportions of each component in the composite activator need to be improved. Sodium sulfate, calcium aluminate powder, and gypsum play the roles of activating, promoting coagulation, and stabilizing the product in the system. An imbalance in the proportions of the three components will destroy the synergistic effect, leading to disorder in the hydration process. This, in turn, affects the workability retention of the freshly mixed slurry and hinders the formation of a uniform, dense, and high-strength hydration product structure, thus having a comprehensive negative impact on the material's flow properties, final strength, and interlayer bonding. Therefore, an optimized activator ratio is essential to achieve efficient synergy and stable performance of each component.

[0101] Based on Examples 1-4 and Comparative Example 5, and in conjunction with Table 1, it can be seen that calcining the pretreatment by-products at a suitable temperature is the step to activate their gelling activity. The optimized calcination temperature can provide reaction energy for the activator and the effective components in the by-products, promoting the formation of highly active precursors. If the calcination temperature is insufficient, the activation reaction will be incomplete, the precursor activity will be low, resulting in weak hydration reaction kinetics and slow speed. As a result, the slurry hardens slowly, has low early strength, insufficient development of overall mechanical properties, and difficulty in establishing interlayer bonding. Therefore, a suitable calcination process is the key to fully releasing the potential of solid waste raw materials.

[0102] As can be seen from Examples 1-4 and Comparative Example 6, and Table 1, the appropriate water-to-material ratio has a significant impact on the preparation of the slurry. A suitable amount of water ensures the activator and hydration reaction proceed fully, resulting in high fluidity and lubricity of the slurry, facilitating printing extrusion and interlayer bonding. Insufficient water leads to a slurry that is too dry and viscous, increasing flow and extrusion resistance and resulting in poor printability. Furthermore, insufficient water limits the degree of hydration reaction in the cementitious material, reducing the amount of hydration products generated, resulting in a less dense structure, and weakening the material's mechanical properties and interlayer bonding performance. Therefore, an improved water-to-material ratio is the key to balancing the workability and final performance of the material.

[0103] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A rapidly curing basic magnesium sulfate cement 3D-printed concrete, characterized in that, It is made from the following raw materials in parts by weight: 30-50 parts potassium extraction byproducts from salt lakes, 20-40 parts silicate cement, 5-15 parts metakaolin, 10-25 parts quartz sand, 3-8 parts composite activator, 0.5-2 parts polycarboxylate-based high-efficiency water-reducing agent, 0.1-0.5 parts water-retaining agent, and 0.05-0.2 parts defoamer.

2. The rapidly curable basic magnesium sulfate cement 3D printed concrete according to claim 1, characterized in that, The composite activator is prepared by compounding sodium sulfate, calcium aluminate powder and gypsum in a weight ratio of 1.8-2.2:0.9-1.1:0.9-1.

1.

3. The rapidly curable basic magnesium sulfate cement 3D printed concrete according to claim 1, characterized in that, The potassium extraction byproduct from the salt lake is made from the following raw materials by weight percentage: 30-40% magnesium oxide, 15-25% calcium oxide, 20-30% silicon dioxide, and impurity content of ≤5% ferric oxide, ≤1% chloride ions and ≤3% sulfate ions.

4. The rapidly curable basic magnesium sulfate cement 3D printed concrete according to claim 1, characterized in that, The particle size range of the quartz sand is 0.15-0.6 mm.

5. The rapidly curable basic magnesium sulfate cement 3D printed concrete according to claim 1, characterized in that, The concrete has a slump spread of 180-220mm, a 1-hour time loss of ≤10mm, a 28-day compressive strength of ≥40MPa, and an interlayer bond strength of ≥3.5MPa.

6. A method for preparing rapidly curing basic magnesium sulfate cement 3D printed concrete, characterized in that, The method for using a rapidly curing basic magnesium sulfate cement 3D printing concrete according to any one of claims 1-5 includes the following steps: S1. Raw material pretreatment: The potassium extraction by-product from the salt lake is dried, then crushed and sieved to obtain the pretreated by-product; S2. Activation-activated calcination: The pretreatment by-products, metakaolin and composite activator are mixed evenly according to the ratio, calcined and naturally cooled to obtain the active mixed powder. S3. Preparation of dry powder: The active mixed powder is mixed with silicate cement and quartz sand in proportion and then dry-mixed. Polycarboxylate superplasticizer, water-retaining agent and defoamer are added and stirred to obtain single-component 3D printing concrete dry powder. S4. Printing Construction: Mix the obtained single-component 3D printing concrete dry powder with water at a certain powder-to-water ratio and stir to form a slurry for 3D printing.

7. The method for preparing rapidly curable basic magnesium sulfate cement 3D printed concrete according to claim 6, characterized in that, In step S1, the drying temperature is 90-120℃, the drying time is 2-3 hours, and the sieve mesh size is 70-90 mesh.

8. The method for preparing rapidly curable basic magnesium sulfate cement 3D printed concrete according to claim 6, characterized in that, In step S2, the calcination temperature is 630-680℃ and the calcination time is 2.3-2.7 hours.

9. The method for preparing rapidly curable basic magnesium sulfate cement 3D printed concrete according to claim 6, characterized in that, In step S3, the dry mixing time is 10-15 minutes, and the stirring time is 5-8 minutes.

10. The method for preparing rapidly curable basic magnesium sulfate cement 3D printed concrete according to claim 6, characterized in that, In step S4, the powder-to-water ratio is 1:0.25-0.35, and the mixing time is 3-5 minutes; it also includes adjusting printing parameters according to different climate environments. In high-temperature environments with temperatures >35℃ and relative humidity <40%, the powder-to-water ratio should be adjusted to 1:0.32-0.35, and the printing speed should be adjusted to 25-35mm / s. In a low-temperature environment of 5-15℃, the powder-to-water ratio should be adjusted to 1:0.25-0.28, and warm water at 20-30℃ should be used to mix the slurry. In high humidity environments with relative humidity >70%, adjust the powder-to-water ratio to 1:0.25-0.28 and extend the printing interval between each layer by 3-5 minutes; In a dry environment with relative humidity <50%, the powder-to-water ratio should be adjusted to 1:0.30-0.35, and a moisturizing film should be used for curing after printing.

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