A high-strength and slow-setting cementitious material applicable to 3D printing construction and its preparation method

Abstract

The present invention provides a high-strength and slow-setting gelling material applicable to 3D printing construction and a preparation method thereof. The raw materials include ultrafine tailings sand, fly ash, deionized water, sodium silicate and sodium hydroxide that constitute a gelling matrix, and also include a retarder, sodium tripolyphosphate. The whole process of the present invention is simple to operate, has low energy consumption, the prepared high-strength and slow-setting gelling material has excellent mechanical properties, a long initial setting time, a short time interval between the initial setting and the final setting, has certain economic value, and provides a reference for the development of green 3D printing building materials.

Description

Technical Field

[0001] The present invention belongs to the field of 3D printing buildings, and in particular relates to a gelling material suitable for 3D printing buildings. Background Art

[0002] Cementitious materials, as a new type of building material (hereinafter referred to as "building materials"), are increasingly being used in the construction industry to replace traditional cement or concrete due to their low energy consumption and low emissions. During the 3D building printing process, the initial setting time of the building materials must be extended to ensure a high level of fluidity during transportation through vehicles and pipelines, thereby ensuring a certain degree of fluidity before the building materials are ejected from the 3D printer pipeline to prevent pipeline blockage. Furthermore, the initial setting time must be no less than 45 minutes, and the final setting time no more than 600 minutes, while ensuring a compressive strength of no less than 30 MPa (C30) (low compressive strength can cause 3D-printed buildings to collapse). The time interval between initial and final setting must be minimized to ensure that the building materials solidify quickly after extrusion. However, existing building materials have a short initial setting time and a relatively long time between initial and final setting, which can lead to pipeline blockage before they are fully ejected. This can prevent the subsequent 3D-printed building from being successfully printed and irreversibly damage the 3D printer output pipeline, increasing the construction cost of 3D-printed buildings.

[0003] Currently, reports on 3D printing mainly focus on the fields of conventional 3D printing plastic materials and printer technology. For example, patent publication number CN113024740A discloses a 3D printing material and a 3D printing method, which synthesizes materials such as polyurethane acrylic resin and aluminum stearate in a certain proportion to form a thermoplastic material that effectively improves the efficiency of photopolymerization 3D printing. For example, patent publication number CN114801187A discloses a 3D printing device with a specific detection mode. In this detection mode, the light receiver can generate a light intensity signal of corresponding intensity based on the intensity of the received light and transmit the light intensity signal to the controller. The controller compares the received light intensity signal with a preset first threshold and adjusts the output power of the optical machine based on the comparison result. However, there are relatively few reports on the development of cementitious materials for use in 3D-printed buildings. For example, patent publication number CN 202011219142 discloses a 3D-printed geopolymer and a method for 3D-printing buildings. This invention involves uniformly mixing materials such as silicon-aluminum oxide, fillers, and carbonates at high speed, adding them to a concrete mixer and mixing with water to produce a fluid, paste-like geopolymer. This mixture is then combined with a printing method to construct 3D-printed buildings. However, the methods described in this invention fail to rationally regulate the material's compressive strength and setting time, failing to meet the basic requirement of an initial setting time of at least 45 minutes.

[0004] In summary, the existing 3D printing building materials have problems such as the collapse of 3D printed buildings due to low compressive strength, the blockage of the pipes of 3D printers due to short initial setting time, and the inability to print and form subsequent 3D printed buildings smoothly due to the long interval between initial setting and final setting time, resulting in low feasibility in practical applications. Summary of the Invention

[0005] To solve the problems existing in the above-mentioned prior art, the present invention provides a high-strength and slow-setting gelling material applicable to 3D printing buildings and a preparation method thereof. On the premise of meeting the mechanical property requirements of building materials, internal regulation of the setting time is achieved to help 3D printing buildings realize large-scale market application as soon as possible.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A high-strength and slow-setting gelling material applicable to 3D printing buildings, characterized in that: the raw materials of the gelling material include ultrafine tailings sand, fly ash, deionized water, sodium silicate and sodium hydroxide constituting the gelling matrix, and also include the retarder sodium tripolyphosphate.

[0008] Further, in the gelling matrix, the dosage ratio of ultrafine tailings sand to fly ash is 60-100%: 0-40%. The most preferred is 80%: 20%.

[0009] Further, the water-solid ratio of the gelling matrix is 36-44%, the modulus of the alkali activator is 0.8-1.6, and the dosage of the alkali activator is 5-9%. Most preferably, the water-solid ratio of the gelling matrix is 38%, the modulus of the alkali activator is 1.0, and the dosage of the alkali activator is 6%.

[0010] Among them:

[0011] The water-solid ratio refers to the ratio of the mass of the liquid component to the mass of the solid component in the gelling matrix. The mass of the liquid component includes the sum of the solvent mass in sodium silicate and the added deionized water mass; the mass of the solid component includes the total mass of the ultrafine tailings sand and fly ash raw materials and the solid component mass in the activator. The solid component in the activator includes sodium hydroxide and Na2O and SiO2 in sodium silicate. The calculation method is shown in formula (1):

[0012] m = (M + y + x*a)*λ - x*(1 - a) (1)

[0013] The modulus of the alkali activator refers to the molar ratio of SiO2 and Na2O in the alkali activator. In the present invention, the activator uses a composite alkali activator of sodium silicate and sodium hydroxide. The sodium silicate product is produced by Yourui Refractory Materials Co., Ltd. in Jiashan County, China. The sodium silicate product itself has a modulus of 2.3, a Na2O content of 13.5%, a SiO2 content of 30%, and a water content of 56.5%.

[0014] The alkaline activator modulus is obtained by quantitative calculation of sodium silicate and sodium hydroxide. Suppose xg of sodium silicate is taken and the mass of added sodium hydroxide is yg. By adjusting the target modulus, a corresponding relationship between y and x can be obtained, for example, the target modulus is taken as 0.8.

[0015] n(SiO2)=30%x / 60 (2)

[0016] n(Na2O)=13.5%x / 62(Na2SiO3)+y / 80(NaOH) (3)

[0017] n(SiO2) / n(NaO2)=1314.4x / (648x+3720y)=0.8 (4)

[0018] The alkali activator dosage is the percentage of the mass of Na2O in the activator to the mass of the raw materials of ultrafine tailings sand and fly ash, expressed as Q%. The sources of alkali in the composite activator are sodium silicate and sodium hydroxide. The mass of Na2O in sodium silicate and sodium hydroxide are calculated respectively. The calculation process is as follows: Alkali content in sodium silicate: 13.5% x; Based on the Na in the system + According to the law of conservation, the alkali content in sodium hydroxide is converted into the mass of Na2O: 62y / 80. Then the equation is:

[0019] M*Q%=13.5%x+62y / 80 (5)

[0020] For example, if the alkali equivalent is 5% and the raw material is 500g, then:

[0021] 500*5%=13.5%x+62y / 80 (6)

[0022] 25=0.135x+0.775y (7)

[0023] In summary, by combining equations (4) and (7), the amounts of sodium silicate and sodium hydroxide used can be calculated.

[0024] In all the above formulas: M is the total mass of ultrafine tailings sand and fly ash raw materials, in g; m is the mass of added deionized water, in g; x is the mass of sodium silicate, in g; y is the mass of sodium hydroxide, in g; a is the solid mass fraction in sodium silicate, in %; λ is the water-solid ratio of the test, in %; Q is the dosage of alkali activator, in %.

[0025] Note: Sodium silicate used in the present invention is in gel state and sodium hydroxide is in solid state. The allowable error range of all raw materials in the calculation of water-solid ratio, modulus and alkali equivalent is ±0.3g.

[0026] The present invention also provides a preparation method of the high-strength and slow-setting gelling material applicable to 3D printing construction, specifically as follows:

[0027] Add sodium silicate into deionized water and stir to obtain an aqueous sodium silicate solution; then add sodium hydroxide and stir to completely dissolve sodium hydroxide in the aqueous sodium silicate solution to obtain a mixed solution; then add sodium tripolyphosphate to the mixed solution and mix evenly by ultrasonic wave to obtain a composite alkali activator solution;

[0028] Pour ultrafine tailings sand and fly ash into a blender in sequence and mix evenly. Add the composite alkali activator solution to the mixed solid-phase system and stir until it reaches a flowable plastic state to obtain the high-strength and slow-setting gelling material applicable to 3D printing construction.

[0029] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0030] Through raw material screening and exploration of the optimal water-solid ratio, modulus of the alkali activator, and dosage of the alkali activator, the present invention obtains a high-strength and slow-setting gelling material applicable to 3D printing construction. Its 28-day compressive strength meets the requirements of C30, and it has a long initial setting time and a small interval between the initial setting time and the final setting time, without causing pipeline blockage and non-forming after extrusion. The preparation process of the gelling material of the present invention is simple, with low energy consumption and cost. Brief Description of the Drawings

[0031] Figure 1 It is a trend chart of the influence of different fly ash dosages on the compressive strength of the high-strength and slow-setting gelling material.

[0032] Figure 2 It is a trend chart of the influence of different water-solid ratios on the compressive strength of the high-strength and slow-setting gelling material.

[0033] Figure 3 It is a trend chart of the influence of different moduli of the alkali activator on the compressive strength of the high-strength and slow-setting gelling material.

[0034] Figure 4 It is a trend chart of the influence of different dosages of the alkali activator on the compressive strength of the high-strength and slow-setting gelling material.

[0035] Figure 5 It is a trend chart of the influence of the dosage of sodium tripolyphosphate retarder on the fluidity of the high-strength and slow-setting gelling material.

[0036] Figure 6 It is a trend chart of the influence of the dosage of sodium tripolyphosphate retarder on the setting time of the high-strength and slow-setting gelling material. Specific Embodiments

[0037] In order to further illustrate the features and advantages of the present invention, the technical solutions of the present invention will be described below in combination with embodiments. Obviously, the described embodiments are only a part of the present invention, and the protection scope of the present invention is not limited to the following embodiments.

[0038] Example 1

[0039] This example explored the effect of different fly ash dosages on the compressive strength of high-strength and slow-setting cementitious materials, and the specific steps were as follows:

[0040] S1: Preparation of high-strength and slow-setting cementitious materials

[0041] The raw materials used for preparing the cementitious materials were: 300 - 500 g of ultrafine tailings sand, 0 - 200 g of fly ash, 161.3 g of deionized water, 64.4 g of sodium silicate, 21 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate was 0 g. Among them, with the total amount of ultrafine tailings sand and fly ash being 500 g, the dosage of fly ash was regulated (that is, the mass percentage of fly ash in the total mass of ultrafine tailings sand and fly ash).

[0042] Add sodium silicate to deionized water and stir at a speed of 100 rmp for 1 min to prevent sodium silicate crystallization, obtaining a sodium silicate aqueous solution; then add sodium hydroxide and stir at a speed of 200 rmp for 1 min, and use the principle of heat release of alkaline water to completely dissolve sodium hydroxide in the sodium silicate aqueous solution, obtaining a mixed solution; then add sodium tripolyphosphate to the mixed solution and place it in a JK-2200 type ultrasonic device, set the ultrasonic power to 1200 W, and perform ultrasonic mixing and stirring for 5 min to obtain a composite alkali activator solution.

[0043] Pour ultrafine tailings sand and fly ash into a JJ-5 type cement mortar mixer in sequence for uniform mixing, add the composite alkali activator solution to the mixed solid phase system, start the mixer and stir at a slow speed of 140 rmp for 2 min, stop for 15 s, and then stir at a fast speed of 285 rmp for 2 min. After stirring to a fluidized state, a high-strength and slow-setting cementitious material is formed.

[0044] S2: Maintenance of high-strength and slow-setting cementitious materials: Pour the fluidized cementitious material into a 10*10*10 mm stainless steel mold, place the mold on a HZJ-0.5 type vibrating table and keep the vibration frequency at 50 Hz until the high-strength and slow-setting cementitious material is vibrated solid inside and the bubbles are discharged. After vibration, place the mold in an environment with a temperature of 40 °C for molding and maintenance for 24 h. After the test block is molded, demold it and perform normal temperature maintenance. The time of water-solid mixing is used as the starting time of maintenance and the maintenance age is calculated as 3, 7, and 28 d.

[0045] S3: Compressive strength test of high-strength and slow-setting cementitious materials: Put the high-strength and slow-setting cementitious material test blocks with a maintenance age of 3, 7, and 28 d into a universal testing machine, and perform compressive strength determination at a loading rate of 0.5 N / s. The compressive strength takes the average value of 6 tests as the final result. The compressive strength is defined as: F ccrefers to the compressive strength value (unit: MPa), F refers to the failure load of the test block (unit: N), and b 2 is the bearing surface area (unit: mm 2 ).

[0046] Figure 1 Figure 8 shows the influence trend of different fly ash dosages on the compressive strength of high-strength and slow-setting cementitious materials. The specific data are shown in Table 1. The results show that the compressive strength of high-strength and slow-setting cementitious materials generally shows a trend of first increasing and then decreasing. Under the condition that other conditions are the same, the compressive strength of high-strength and slow-setting cementitious materials with 20% fly ash reaches the maximum at 3, 7, and 28 days. This shows that the incorporation of a small amount of fly ash will not cause obvious changes in the internal structure of the cementitious material, while the incorporation of excessive fly ash will lead to cracks on the surface of the cementitious material and reduce the compressive strength. When the fly ash dosage is 20%, the compressive strength of high-strength and slow-setting cementitious materials is relatively the highest.

[0047] Table 1 Influence of different fly ash dosages on the compressive strength of high-strength and slow-setting cementitious materials

[0048]

[0049]

[0050] Example 2

[0051] This example explores the influence of different water-solid ratios on the compressive strength of high-strength and slow-setting cementitious materials, and the specific steps are as follows:

[0052] S1: Preparation of high-strength and slow-setting cementitious materials:

[0053] The raw materials used for the preparation of high-strength and slow-setting cementitious materials are: 400 g of ultra-fine tailings sand, 100 g of fly ash, 161.3 - 205.2 g of deionized water, 64.4 g of sodium silicate, 21 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate is 0 g. The remaining steps are the same as those in step S1 of Example 1.

[0054] S2: The same as step S2 in Example 1.

[0055] S3: The same as step S3 in Example 1.

[0056] Figure 2It is a graph showing the influence trend of different water-solid ratios on the compressive strength of high-strength and slow-setting cementitious materials. The specific data are shown in Table 2. The results show that during the process of the water-solid ratio increasing from 36% to 44%, the overall trend of the compressive strength of high-strength and slow-setting cementitious materials with different curing times first increases and then decreases. When the water-solid ratio is 38%, the compressive strengths of high-strength and slow-setting cementitious materials at 3, 7, and 28 days are all at the peak state, which are 14.18, 15.11, and 21.42 MPa respectively. When the water-solid ratio is small, a large number of silicate ions and aluminate ions in ultrafine tailings sand and fly ash are dissolved, resulting in a relatively high alkalinity of high-strength and slow-setting cementitious materials. At the same time, the decrease in water content at a low water-solid ratio will inevitably lead to a decrease in the migration ability of water inside high-strength and slow-setting cementitious materials, and the mobility of dissolved silicate ions and aluminate ions is restricted, hindering the polycondensation reaction process, and ultimately resulting in a relatively low compressive strength of high-strength and slow-setting cementitious material specimens. When the water-solid ratio is too large, the alkalinity of high-strength and slow-setting cementitious materials decreases, making it difficult for silicate ions and aluminate ions in ultrafine tailings sand and fly ash to form silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons, ultimately resulting in a decrease in the compressive strength of high-strength and slow-setting cementitious material specimens. In addition, the addition of excessive water will increase the porosity of high-strength and slow-setting cementitious materials, indirectly causing a decrease in compressive strength. When the water-solid ratio is 38%, the compressive strength of high-strength and slow-setting cementitious material specimens reaches a stage peak. Therefore, a water-solid ratio of 38% is selected as the optimal water-solid ratio.

[0057] Table 2 Influence of different water-solid ratios on the compressive strength of high-strength and slow-setting cementitious materials

[0058]

[0059] Example 3

[0060] This example explores the influence of different alkali activator moduli on the compressive strength of high-strength and slow-setting cementitious materials, and the specific steps are as follows:

[0061] S1: Preparation of high-strength and slow-setting cementitious materials:

[0062] When the alkali activator modulus is 0.8, the raw materials used for the preparation of high-strength and slow-setting cementitious materials are: 400 g of ultrafine tailings sand, 100 g of fly ash, 172.2 g of deionized water, 64.4 g of sodium silicate, 21 g of sodium hydroxide, and the dosage of retarder sodium tripolyphosphate is 0 g.

[0063] When the alkali activator modulus is 1.0, the raw materials used for the preparation of high-strength and slow-setting cementitious materials are: 400 g of ultrafine tailings sand, 100 g of fly ash, 164.7 g of deionized water, 80.5 g of sodium silicate, 18.2 g of sodium hydroxide, and the dosage of retarder sodium tripolyphosphate is 0 g.

[0064] When the modulus of the alkali activator is 1.2, the raw materials used for preparing the high-strength and slow-setting cementitious material are: 400 g of ultra-fine tailings sand, 100 g of fly ash, 157.2 g of deionized water, 96.6 g of sodium silicate, 15.4 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate is 0 g.

[0065] When the modulus of the alkali activator is 1.4, the raw materials used for preparing the high-strength and slow-setting cementitious material are: 400 g of ultra-fine tailings sand, 100 g of fly ash, 149.7 g of deionized water, 112.7 g of sodium silicate, 12.6 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate is 0 g.

[0066] When the modulus of the alkali activator is 1.6, the raw materials used for preparing the high-strength and slow-setting cementitious material are: 400 g of ultra-fine tailings sand, 100 g of fly ash, 142.2 g of deionized water, 128.8 g of sodium silicate, 9.8 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate is 0 g.

[0067] All the remaining steps are the same as those in step S1 of Example 1.

[0068] S2: The same as step S2 in Example 1.

[0069] S3: The same as step S3 in Example 1.

[0070] Figure 3 It is a trend chart of the influence of different alkali activator moduli on the compressive strength of the high-strength and slow-setting cementitious material. The specific data are shown in Table 3. The results show that: the increase in the modulus of the alkali activator leads to a trend of first increasing and then decreasing in the compressive strength of the high-strength and slow-setting cementitious material. When the modulus of the alkali activator is 1, the compressive strengths of the high-strength and slow-setting cementitious material after 3, 7, and 28 days of curing reach the peak values, which are 17.06, 19.61, and 29.82 MPa respectively; through internal comparison, it is found that the compressive strength of the high-strength and slow-setting cementitious material cured for 3 days can reach 57% of the compressive strength cured for 28 days, which conforms to the characteristic of high early strength of the high-strength and slow-setting cementitious material. In the composite alkali activator system, when the modulus of the alkali activator is relatively low, the mass of solid sodium hydroxide in the cementitious system will be relatively large. Too high alkali content will cause obvious efflorescence phenomenon inside the high-strength and slow-setting cementitious material, which is not conducive to the progress of the geopolymerization reaction, and finally less aluminosilicate gel is generated, resulting in lower compressive strength. However, if the modulus of the alkali activator is continuously increased, it will be found that the compressive strength shows a continuous downward trend after reaching the peak value. A high modulus means a relatively high SiO2 content in the composite alkali activator system, resulting in the abnormal dissolution of Si and Al ions, and a significant reduction in the amount of aluminosilicate gel. Therefore, it is optimal to control the modulus of the alkali activator to 1.

[0071] Table 3 Influence of different alkali activator moduli on the compressive strength of the high-strength and slow-setting cementitious material

[0072]

[0073]

[0074] Example 4

[0075] This example explored the influence of different dosages of alkali activators on the compressive strength of high-strength and slow-setting cementitious materials, and the specific steps were as follows:

[0076] S1: Preparation of high-strength and slow-setting cementitious materials:

[0077] When the dosage of the alkali activator was 5%, the raw materials used for the preparation of the high-strength and slow-setting cementitious materials were: 400 g of ultrafine tailings sand, 100 g of fly ash, 164.7 g of deionized water, 80.5 g of sodium silicate, 18.2 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate was 0 g.

[0078] When the dosage of the alkali activator was 6%, the raw materials used for the preparation of the high-strength and slow-setting cementitious materials were: 400 g of ultrafine tailings sand, 100 g of fly ash, 159.7 g of deionized water, 96.6 g of sodium silicate, 21.9 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate was 0 g.

[0079] When the dosage of the alkali activator was 7%, the raw materials used for the preparation of the high-strength and slow-setting cementitious materials were: 400 g of ultrafine tailings sand, 100 g of fly ash, 154.6 g of deionized water, 112.7 g of sodium silicate, 25.5 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate was 0 g.

[0080] When the dosage of the alkali activator was 8%, the raw materials used for the preparation of the high-strength and slow-setting cementitious materials were: 400 g of ultrafine tailings sand, 100 g of fly ash, 149.6 g of deionized water, 128.8 g of sodium silicate, 29.2 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate was 0 g.

[0081] When the dosage of the alkali activator was 9%, the raw materials used for the preparation of the high-strength and slow-setting cementitious materials were: 400 g of ultrafine tailings sand, 100 g of fly ash, 144.5 g of deionized water, 144.9 g of sodium silicate, 32.8 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate was 0 g.

[0082] All the remaining steps were the same as those in step S1 of Example 1.

[0083] S2: The same as step S2 in Example 1.

[0084] S3: The same as step S3 in Example 1.

[0085] Figure 4It is a graph showing the influence trend of different dosages of alkali activators on the compressive strength of high-strength and retarder-containing cementitious materials. The specific data are shown in Table 4. Overall, as the dosage of the composite activator increases, the compressive strength of the high-strength and retarder-containing cementitious materials shows a trend of increasing first and then decreasing. When the dosage of the composite activator reaches 6%, after curing for 3, 7, and 28 days, it is found that the compressive strengths reach the peak values of 22.29, 25.75, and 33.07 MPa respectively at the same period. Because of the increase in the dosage of the composite activator, the concentrations of OH - and SiO3 2- inside the high-strength and retarder-containing cementitious materials increase, which is beneficial to the dissolution of silicon and aluminum oxides in ultrafine tailings sand and fly ash, promotes the forward progress of the polycondensation reaction, a large amount of silicon-aluminate colloid will be generated inside the system, and then enhances the compressive strength of the high-strength and retarder-containing cementitious materials. However, when the dosage of the alkali activator is too high, CO2 in the air will react with the excessive alkaline substances inside the system to form carbonates, resulting in a decrease in the strength of the high-strength and retarder-containing cementitious materials. Therefore, when the dosage of the composite alkali activator is 6%, the alkali activation effect is the best and the compressive strength is the highest.

[0086] Table 4 Influence of different dosages of alkali activators on the compressive strength of high-strength and retarder-containing cementitious materials

[0087]

[0088] Example 5

[0089] This example explores the comprehensive performance effects of different dosages of the retarder sodium tripolyphosphate on the compressive strength, fluidity, and setting time of high-strength and retarder-containing cementitious materials, and the specific steps are as follows:

[0090] S1: Preparation of high-strength and retarder-containing cementitious materials:

[0091] The raw materials used for the preparation of high-strength and retarder-containing cementitious materials are: 400 g of ultrafine tailings sand, 100 g of fly ash, 159.7 g of deionized water, 96.6 g of sodium silicate, 21.9 g of sodium hydroxide, and the dosage of the retarder sodium tripolyphosphate is 0 - 5 g. At this time, the water-solid ratio of the system is 38%, the modulus of the alkali activator is 1.0, the dosage of the alkali activator is 6%, and when the dosage of the retarder sodium tripolyphosphate is 0, 1, 2, 3, 4, and 5 g, they account for 0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% of the total mass of ultrafine tailings sand and fly ash respectively.

[0092] [[ID=2�]]The remaining steps are the same as those in step S1 of Example 1.

[0093] S2: The same as step S2 in Example 1.

[0094] S3: The same as step S3 in Example 1.

[0095] S4: Fluidity test of high-strength retarded cementing material: The fluidity of high-strength retarded cementing material was tested in accordance with GB / T 2419-2005 Determination of fluidity of cement mortar. The instrument was kept at a vertical vibration frequency of 0.04 Hz.

[0096] S5: Determination of setting time of high-strength retarded gelling material: The setting time of high-strength retarded gelling material is determined in accordance with GB / T 1346-2011 Test method for water content, setting time and stability of cement of standard consistency.

[0097] Experiments optimizing the synthesis of high-strength retarded gelling materials revealed that when the mass ratio of fly ash to ultrafine tailings sand was 1:4, the corresponding water-to-solid ratio, modulus, and alkali activator dosages of 38%, 1%, and 6%, respectively, resulted in a maximum 28-day compressive strength of 33.07 MPa. Therefore, given the inherent characteristics of 3D-printed building materials, maintaining a high degree of fluidity is essential. Therefore, the incorporation of retarders in varying proportions was necessary to enhance their fluidity. The experiments found that the incorporation of sodium tripolyphosphate (STP) as a retarder effectively improved the fluidity of the STP. The fluidity of the STP increased with increasing STP dosage, initially increasing before gradually reaching equilibrium. When the STP dosage exceeded 0.8%, the fluidity of the STP reached over 190 mm, a fluidity increase of over 15%. This suggests that the addition of retarders also improves the workability of the STP.

[0098] Figure 6 The graph shows the trend of the effect of different sodium tripolyphosphate dosages on the setting time (initial setting time and final setting time) of high-strength retarded gelling materials. As the amount of sodium tripolyphosphate added increases, the initial setting time and final setting time of the high-strength retarded gelling materials are significantly improved. When no sodium tripolyphosphate is added, the time for the high-strength retarded gelling materials to reach initial setting is 514 minutes, and the time for reaching final setting is 552 minutes. When the sodium tripolyphosphate dosage is 0.6%, the time for the high-strength retarded gelling materials to reach initial setting is 586 minutes, and the time for reaching final setting is 615 minutes. After that, it is found that the initial setting and final setting times tend to be balanced by increasing the sodium tripolyphosphate dosage. According to GB 175-2020, the "General Portland Cement Standard," the initial setting time must not be less than 45 minutes, and the final setting time must not exceed 600 minutes. This indicates that the addition of 0.4% sodium tripolyphosphate (STP) as a retarder can delay the initial setting time of high-strength retarded cement and shorten the interval between initial and final setting, while having virtually no negative impact on the material's 28-day compressive strength. This increase in initial and final setting time provides a high-flowability guarantee for the development of high-strength retarded cement as a 3D printing building material.

[0099] Table 5 Effect of different addition amounts of sodium tripolyphosphate on the comprehensive properties of high-strength retarded gelling materials

[0100] Content of sodium tripolyphosphate 0％ 0.2％ 0.4％ 0.6％ 0.8％ 1％ Flowability (mm) 165 173 182 190 194 196 Initial setting time (min) 514 542 565 586 603 615 Final setting time (min) 552 578 597 615 629 638 28-day compressive strength (Mpa) 33.07 32.34 33.19 31.75 31.73 32.52

[0101] In summary, through the optimization of the dosages of the main and auxiliary materials in the present invention, the 28-day compressive strength of the obtained high-strength and slow-setting cementitious material can reach up to 33.07 Mpa, which can meet the requirement of the "Code for Design of Concrete Structures" GB 50010-2020 that the strength grade of building materials used for structural 3D printing should be greater than C30 (i.e., the compressive strength is greater than 30 Mpa). At the same time, the addition of the retarder effectively prolongs the initial setting time of the high-strength and slow-setting cementitious material and shortens the time interval between the initial setting and the final setting. The high-strength and slow-setting cementitious material obtained in the present invention can be used as the building material for 3D printing buildings. [[ID=,7]]

[0102] The present invention solves the problems that the compressive strength of ordinary cementitious materials used in 3D printing buildings does not meet the standard, the initial setting time is less than 45 minutes, and the time interval between the initial setting and the final setting is long, which are specifically reflected in:

[0103] First: It improves the qualification rate of the compressive strength of the high-strength and slow-setting cementitious material applied in the field of 3D printing buildings to ensure that the material does not slump after being output;

[0104] Second: It solves the problem of printer pipeline blockage caused by traditional cementitious materials;

[0105] Third: It realizes the replacement of conventional 3D printing building materials with the high-strength and slow-setting cementitious material.

[0106] The whole process of the present invention is easy to operate, has low energy consumption, the prepared high-strength and slow-setting cementitious material has excellent mechanical properties, a long initial setting time, and a short time interval between the initial setting and the final setting, and has certain economic value, providing a reference for the development of green 3D printing building materials.

Claims

1. A high-strength slow-gelling material suitable for 3D printing buildings, characterized by: The raw materials of the cementitious material include ultrafine tailings, fly ash, deionized water, sodium silicate and sodium hydroxide constituting a cementitious matrix, and also include sodium tripolyphosphate as a retarder; in the cementitious matrix, the ultrafine tailings and fly ash are used in a ratio of 80%:20%; the water-solid ratio of the cementitious matrix is 38%, the alkali activator modulus is 1.0, and the alkali activator dosage is 6%; the amount of sodium tripolyphosphate as a retarder is 0.4% of the total mass of the ultrafine tailings and fly ash; the alkali activator dosage is the percentage of the mass of Na2O in the activators sodium silicate and sodium hydroxide to the mass of the raw materials of the ultrafine tailings and fly ash; The high-strength slow-setting gel material has a fluidity of 182 mm, an initial setting time of 565 min, a final setting time of 597 min, and a 28-day compressive strength of 33.19 MPa.

2. A method for preparing the high-strength slow-gelling gelling material suitable for 3D printing buildings according to claim 1, characterized in that: adding sodium silicate to deionized water and stirring to obtain a sodium silicate aqueous solution; then adding sodium hydroxide and stirring to completely dissolve the sodium hydroxide in the sodium silicate aqueous solution to obtain a mixed solution; then adding sodium tripolyphosphate to the mixed solution and ultrasonically mixing to obtain a composite alkali activator solution; Ultrafine tailings sand and fly ash are poured into a mixer in sequence and evenly mixed. A composite alkali activator solution is added to the mixed solid phase system and stirred until it reaches a fluid plastic state to obtain a high-strength slow-gelling gel material suitable for 3D printing buildings.

Images