A method for designing and preparing 3D printed concrete with enhanced mixing efficiency

Abstract

The application discloses a 3D printing concrete design and preparation method for enhancing stirring efficiency, which comprises the following steps: according to material proportioning, cementing material, water reducing agent, water retention thickening agent, reinforcing fiber, water with a mass of W1 to be added for the first time, a surfactant and a solution formed by fully dissolving the surfactant are put into a stirring device; the surfactant solution is added into the stirring device, and primary stirring is carried out for t1; according to material proportioning, aggregate is put into the stirring device, water with a mass of W2 to be added for the second time is put into the device, and secondary stirring is carried out for t2; water with a mass of W3 to be added for the third time is put into the device, and tertiary stirring is carried out for t3. 2， By adjusting material proportioning at different temperatures and preparation methods for different stirring devices, the surface tension of water in the stirring process is reduced, the material stirring resistance can be effectively reduced, the material stirring efficiency is improved, and the stirring time is shortened.

Description

Technical Field

[0001] This invention relates to the field of 3D printing technology in construction, specifically to a method for designing and preparing 3D printed concrete with enhanced mixing efficiency. Background Technology

[0002] 3D printing technology is a novel construction technology. Its basic principle is to slice the digital model of a building, convert it into a path program, control the 3D printing equipment to move along the path, and extrude the material to achieve the building's outline. One of the materials used in 3D printing is 3D printed concrete, whose main components are cement-based binders and fine aggregates. Compared with traditional concrete or cement mortar, 3D printed concrete needs to have certain extrudability and constructability. Extrudability refers to the ability of the material to be continuously and stably extruded through the printing nozzle, while constructability refers to the ability of the material to not collapse or deform after being stacked in multiple layers.

[0003] To ensure the constructability of the material, 3D printed concrete typically requires the addition of thickening and viscous materials, resulting in greater resistance during mixing and necessitating higher mixing speeds or longer mixing times. Among the currently disclosed 3D printed concrete formulations and preparation methods, few studies focus on enhancing mixing efficiency. For example, the 3D printed concrete preparation method described in invention patent CN111499314B does not specify the mixing equipment or speed, and its required total mixing time is 26-44 minutes. The 3D printed concrete preparation method described in invention patent CN109942262B requires dry mixing at 120-150 rpm for 2-3 minutes, followed by mixing at 400-500 rpm for 1-2 minutes. As can be seen from the two technical examples above, the time required for 3D printing concrete mixing is related to the performance of the mixing equipment: if inefficient mixing equipment, such as a gravity mixer or a vertical single-shaft mixer (generally with a speed below 60 rpm), is used, a longer mixing time is required, which affects the printing construction progress and shortens the material open time; if more efficient mixing equipment, such as a planetary mixer, is used, or the mixing speed is increased, the mixing time can be shortened, but a greater mixing power is required.

[0004] The root cause of these problems lies in the fact that 3D-printed concrete, compared to conventional concrete or cement mortar, has higher viscosity and yield stress, resulting in a greater load on the mixing equipment. The key to the mixing process of 3D-printed concrete is to achieve the dispersion and wetting of powder particles by forcing the slurry to flow. The essence of this slurry flow process is the displacement of particles and the breaking and reconstruction of liquid bridges between particles. In this process, the surface tension of water is one of the main resistance factors. By adjusting the material ratio and preparation method, reducing the surface tension of water during mixing can effectively reduce the mixing resistance, improve mixing efficiency, and shorten the mixing time. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] Therefore, the purpose of this invention is to provide a 3D printed concrete design and preparation method that enhances mixing efficiency. By adjusting the material ratio at different temperatures and the preparation method for different mixing equipment, the surface tension of water during the mixing process can be reduced, thereby effectively reducing the material mixing resistance, improving the material mixing efficiency, and shortening the mixing time.

[0007] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0008] A method for designing and preparing 3D-printed concrete with enhanced mixing efficiency, comprising:

[0009] According to the material ratio, cementitious materials, water-reducing agents, water-retaining thickeners, and reinforcing fibers are added to the mixing equipment. The cementitious materials include cement, fly ash, and granulated blast furnace slag.

[0010] Weigh out water of mass W1 to be added first, add surfactant according to the material ratio and dissolve it completely to form a solution. When the water temperature is below 10℃, first dissolve the surfactant in a small amount of warm water at 40-60℃, and then mix it with cold water to ensure complete dissolution.

[0011] The surfactant solution is added to the stirring device and stirred once for a duration of t1.

[0012] According to the material ratio, put the aggregate into the mixing equipment, weigh out the water that needs to be added a second time (W2) and add it into the equipment for secondary mixing. The mixing time is t2.

[0013] Weigh out W3 of the water to be added for the third time and add it to the equipment. Stir three times for a total stirring time of t3.

[0014] The mass of the water-reducing agent ;

[0015] The mass of the water-retaining and thickening agent ;

[0016] The amount of surfactant ;

[0017] In the formula, m 减 , m保 , m 表 These represent the amounts of water-reducing agent, water-retaining thickener, and surfactant in the material, in kg and m, respectively. C , m F , m S , m A These represent the mass (kg) of cement, fly ash, granulated blast furnace slag, and aggregate used in the material; ρ C ,ρ F , ρ S , ρ A These represent the densities (kg / m³) of the cement, fly ash, granulated blast furnace slag, and aggregates used in the material. 3 T represents the ambient temperature during construction, and 0℃≤T≤30℃.

[0018] As a preferred embodiment of the 3D-printed concrete design and preparation method for enhancing mixing efficiency described in this invention, wherein,

[0019] The quality of the cement, fly ash, and granulated blast furnace slag meets the requirements of m. C ≥ (m F +m S );

[0020] The mass of the reinforcing fiber accounts for 0-0.2% of the total mass of the cementitious material and aggregate;

[0021] The cement, fly ash, granulated blast furnace slag, and aggregates satisfy the following formula:

[0022]

[0023] In the formula, m C , m F , m S , m A These represent the mass (kg) of cement, fly ash, granulated blast furnace slag, and aggregate used in the material; ρ A The density of the aggregate used, kg / m³ 3 .

[0024] As a preferred embodiment of the 3D-printed concrete design and preparation method for enhancing mixing efficiency described in this invention, wherein,

[0025] ;

[0026] ;

[0027] ;

[0028] In the formula, W1, W2, and W3 represent the amounts of water added in the first, second, and third tertiary applications, respectively, in kg; mC , m F , m S , m A The quantities are: cement, fly ash, granulated blast furnace slag, and aggregate, respectively, in kg; ρ A The density of the aggregate is expressed in kg / m³. 3 w represents the moisture content of the aggregate; W / B represents the water-cement ratio of the material.

[0029] As a preferred embodiment of the 3D-printed concrete design and preparation method for enhancing mixing efficiency described in this invention, wherein,

[0030]

[0031]

[0032]

[0033] In the formula, t1, t2, and t3 are the durations of the first, second, and third stirring operations, respectively, in minutes; R is the spindle speed of the stirring equipment, in rpm; and k is an empirical efficiency coefficient related to the type of stirring equipment.

[0034] As a preferred embodiment of the 3D-printed concrete design and preparation method for enhancing mixing efficiency described in this invention, the specific steps for determining the water-cement ratio (W / B) of the material are as follows:

[0035] Weigh the cementitious materials, dried aggregates, reinforcing fibers, water-reducing agents, water-retaining thickeners, and surfactants required for 0.5L of material;

[0036] Add the weighed raw materials to the cement mortar mixer, add 100-120g of water, and mix at low speed for 3 minutes. Measure the flowability of the material on the mixing table. If the flowability is less than 180mm, return the material to the mixer, add 5g of water, and continue mixing for 30 seconds. Measure the flowability again. Repeat this step until the flowability reaches 180mm. Record the total amount of water added, W0. Calculate the water-cement ratio of the material using the following formula:

[0037]

[0038] In the formula, W / B is the water-cement ratio of the material; W0 is the total amount of water added to achieve a flowability of 180 mm, in grams; , The values ​​are the masses (g) of cement, fly ash, and granulated blast furnace slag used in this fluidity test.

[0039] As a preferred embodiment of the 3D printed concrete design and preparation method for enhancing mixing efficiency described in this invention, the aggregate moisture content w is specifically determined as follows: a small amount of aggregate is taken and dried in an oven at 105°C for 6 hours, and the aggregate moisture content w is calculated based on the weight change before and after drying.

[0040] As a preferred embodiment of the 3D printed concrete design and preparation method for enhancing mixing efficiency described in this invention, the cement is silicate cement, specifically one of type I silicate cement, type II silicate cement, ordinary silicate cement, and composite silicate cement.

[0041] As a preferred embodiment of the 3D printed concrete design and preparation method for enhancing mixing efficiency described in this invention, the fly ash is required to be Grade I or Grade II fly ash, and the activity index of the granulated blast furnace slag is S95 or S105.

[0042] As a preferred embodiment of the 3D-printed concrete design and preparation method for enhancing mixing efficiency described in this invention, the water-reducing agent is a polycarboxylate water-reducing agent; the water-retaining and thickening agent is a nonionic cellulose ether, such as hydroxyethyl methyl cellulose or hydroxypropyl methyl cellulose, requiring a standard viscosity of less than 40,000 mPa·s; and the surfactant is sodium dodecyl sulfate.

[0043] As a preferred embodiment of the 3D printed concrete design and preparation method for enhancing mixing efficiency described in this invention, the aggregate is one or more of river sand, manufactured sand, quartz sand, tailings sand, coal gangue, slag, recycled concrete, and lightweight aggregate, with an aggregate particle size range of 0.075-2.5 mm and a moisture content of less than 10%.

[0044] As a preferred embodiment of the 3D printed concrete design and preparation method for enhancing mixing efficiency described in this invention, the reinforcing fiber may be selected from basalt fiber, polypropylene fiber, or glass fiber.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] (1) In this technical solution, a surfactant is added to the water for mixing 3D printed concrete. During the mixing process, the surface tension of the water can be reduced, the capillary action between particles can be suppressed, and the material will not become "dry and hard" or shear thickening in the early stage of mixing. This effectively reduces the mixing resistance, promotes particle wetting, and improves the mixing efficiency.

[0047] (2) During the material mixing process, the presence of surfactants can promote the production of a large number of microbubbles in the slurry. These bubbles can reduce the viscosity of the slurry and provide support. In addition, surfactants reduce the surface tension of free water in the slurry, thereby reducing the capillary action between particles during the flow process. The macroscopic effect of surfactants is that the kinematic viscosity of the material decreases while the yield stress increases, which improves the extrudability and constructability of the material.

[0048] (3) Since the effect of surfactants is sensitive to temperature, this technical solution summarizes and fits the experimental phenomena at different temperatures and obtains the expression of temperature-related correction coefficient. The appropriate amount of surfactant can be calculated by temperature within the range of 0-30℃.

[0049] (4) This invention proposes a three-stage mixing process to enhance mixing efficiency. Since the wetting and dispersion of cementitious materials are the most difficult, only the cementitious materials are mixed in the first stage of mixing, and a surfactant solution is added to quickly disperse and wet the cement particles, forming a uniform paste. Aggregates are added in the second stage of mixing to quickly disperse and coat the paste. Water is added in the third stage of mixing to achieve the final required fluidity. Adding water in stages during the three-stage mixing process allows the material to have suitable fluidity in the first and second stages of mixing, ensuring that the mixing equipment can effectively shear and knead the material, further improving the mixing efficiency. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0051] Figure 1 This is a flowchart illustrating a method for designing and preparing 3D-printed concrete to enhance mixing efficiency, as described in this invention. Detailed Implementation

[0052] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0053] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0054] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0055] This invention provides a design and preparation method for 3D printed concrete that enhances mixing efficiency. By adjusting the material ratio and preparation method, the surface tension of water during the mixing process is reduced, which can effectively reduce the mixing resistance of the material, improve the mixing efficiency, and shorten the mixing time.

[0056] A method for designing and preparing 3D-printed concrete with enhanced mixing efficiency, comprising:

[0057] According to the material ratio, cementitious materials, water-reducing agents, water-retaining thickeners, and reinforcing fibers are added to the mixing equipment. The cementitious materials include cement, fly ash, and granulated blast furnace slag.

[0058] Weigh out water of mass W1 to be added first, add surfactant according to the material ratio and dissolve it completely to form a solution. When the water temperature is below 10℃, first dissolve the surfactant in a small amount of warm water at 40-60℃, and then mix it with cold water to ensure complete dissolution.

[0059] The surfactant solution is added to the stirring device and stirred once for a duration of t1.

[0060] According to the material ratio, put the aggregate into the mixing equipment, weigh out the water that needs to be added a second time (W2) and add it into the equipment for secondary mixing. The mixing time is t2.

[0061] Weigh out W3 of the water to be added for the third time and add it to the equipment. Stir three times for a total stirring time of t3.

[0062] The mass of the water-reducing agent ;

[0063] The mass of the water-retaining and thickening agent ;

[0064] The amount of surfactant ;

[0065] In the formula, m 减 , m 保 , m 表 These represent the amounts of water-reducing agent, water-retaining thickener, and surfactant in the material, in kg and m, respectively. C , m F , m S , m A These represent the mass (kg) of cement, fly ash, granulated blast furnace slag, and aggregate used in the material; ρ C ,ρ F , ρ S, ρ A These represent the densities (kg / m³) of the cement, fly ash, granulated blast furnace slag, and aggregates used in the material. 3 T represents the ambient temperature during construction, and 0℃≤T≤30℃.

[0066] As a preferred embodiment of the 3D-printed concrete design and preparation method for enhancing mixing efficiency described in this invention, wherein,

[0067] The quality of the cement, fly ash, and granulated blast furnace slag meets the requirements of m. C ≥ (m F +m S );

[0068] The mass of the reinforcing fiber accounts for 0-0.2% of the total mass of the cementitious material and aggregate;

[0069] The cement, fly ash, granulated blast furnace slag, and aggregates satisfy the following formula:

[0070]

[0071] In the formula, m C , m F , m S , m A These represent the mass (kg) of cement, fly ash, granulated blast furnace slag, and aggregate used in the material; ρ A The density of the aggregate used, kg / m³ 3 .

[0072] As a preferred embodiment of the 3D-printed concrete design and preparation method for enhancing mixing efficiency described in this invention, wherein,

[0073] ;

[0074] ;

[0075] ;

[0076] In the formula, W1, W2, and W3 represent the water volume added in the first, second, and third tertiary applications, respectively, in kg; m C , m F , m S , m A The quantities are: cement, fly ash, granulated blast furnace slag, and aggregate, respectively, in kg; ρ A The density of the aggregate is expressed in kg / m³. 3 w represents the moisture content of the aggregate; W / B represents the water-cement ratio of the material.

[0077] As a preferred embodiment of the 3D-printed concrete design and preparation method for enhancing mixing efficiency described in this invention, wherein,

[0078]

[0079]

[0080]

[0081] In the formula, t1, t2, and t3 are the durations of the first, second, and third stirring operations, respectively, in minutes; R is the spindle speed of the stirring equipment, in rpm; and k is an empirical efficiency coefficient related to the type of stirring equipment.

[0082] The empirical efficiency coefficient k of several typical mixing devices can be found in Table 1 below:

[0083] Table 1 Empirical efficiency coefficients of typical mixing equipment

[0084] Types of mixing equipment Equipment details Speed ​​range k value Single-shaft vertical blade type Number of blades: 3-5; blade angle: 45° 20-60 rpm 1 Single-shaft vertical blade type Number of blades: 3-5; blade angle: 90° 20-60 rpm 1.15 Single-shaft vertical ribbon type 20-60 rpm 0.85 Self-falling (roller type) Volume 300-1000 L 10-30 rpm 2.25 Self-falling (roller type) Volume 1000-3000 L 10-30 rpm 2.6 Vertical shaft double blade type Equipped with low-speed side scraper blades, or a self-rotating bucket with a scraper. High-speed blade speed 60-120 rpm 0.8 Planetary With 1 planetary axis Revolution speed 60-120 rpm 0.55 Single-axis horizontal 20-60 rpm 0.9 Twin-axis horizontal 20-60 rpm 0.5

[0085] The specific steps for determining W / B are as follows:

[0086] Weigh the cementitious materials, dried aggregates, reinforcing fibers, water-reducing agents, water-retaining thickeners, and surfactants required for 0.5L of material;

[0087] Add the weighed raw materials to the cement mortar mixer, add 100-120g of water, and mix at low speed for 3 minutes. Measure the flowability of the material on the mixing table. If the flowability is less than 180mm, return the material to the mixer, add 5g of water, and continue mixing for 30 seconds. Measure the flowability again. Repeat this step until the flowability reaches 180mm. Record the total amount of water added, W0. Calculate the water-cement ratio of the material using the following formula:

[0088]

[0089] In the formula, W / B is the water-cement ratio of the material; W0 is the total amount of water added to achieve a flowability of 180 mm, in grams; , The values ​​are the masses (g) of cement, fly ash, and granulated blast furnace slag used in this fluidity test.

[0090] The specific determination of the aggregate moisture content w is as follows: Take a small amount of aggregate and dry it in an oven at 105℃ for 6 hours. Calculate the aggregate moisture content w by the weight change before and after drying.

[0091] The cement is silicate cement, specifically one of type I silicate cement, type II silicate cement, ordinary silicate cement, or composite silicate cement.

[0092] The fly ash must be either Grade I or Grade II fly ash.

[0093] The activity index of the granulated blast furnace slag is S95 or S105.

[0094] The water-reducing agent is a polycarboxylate water-reducing agent; the water-retaining and thickening agent is a non-ionic cellulose ether, such as hydroxyethyl methyl cellulose or hydroxypropyl methyl cellulose, requiring a standard viscosity of less than 40,000 mPa·s; the surfactant is sodium dodecyl sulfate.

[0095] The aggregate is one or more of river sand, manufactured sand, quartz sand, tailings sand, coal gangue, slag, recycled concrete, and lightweight aggregate, with a particle size range of 0.075-2.5mm and a moisture content of less than 10%.

[0096] The reinforcing fiber can be selected from basalt fiber, polypropylene fiber, or glass fiber.

[0097] Example 1

[0098] The cementing materials used are 42.5MPa ordinary Portland cement, S95 granulated blast furnace slag, and Class I fly ash; the aggregate used is fine river sand with a measured moisture content of 2%; the reinforcing fiber used is 15mm long basalt fiber; the water-reducing agent used is polycarboxylate superplasticizer; the water-retaining thickener is 25000mPa·s viscosity hydroxypropyl methylcellulose; and the surfactant is sodium dodecyl sulfate.

[0099] The density ρ of the cement used C = 3120 kg / m 3 fly ash density ρ F = 2450 kg / m 3 granulated blast furnace slag density ρ S = 2810 kg / m 3 Density ρ of fine river sand A = 2570 kg / m 3 .

[0100] The mixing equipment used is a single-shaft vertical mixer, which can mix 100-200L at a time, with a selected speed of 40 rpm and an ambient temperature of 5℃.

[0101] The dry mix ratio of the 3D printed concrete to be mixed each time is set as follows: 75kg cement, 20kg blast furnace granulated slag, 25kg fly ash, 180kg river sand, and 0.45kg basalt fiber.

[0102] The calculated dosages based on the formula are: 360g of water-reducing agent, 75.8g of water-retaining and thickening agent, and 29.2g of surfactant.

[0103] The measured moisture content of the aggregate was w=2%.

[0104] Weigh out 250g of cement, 66.7g of blast furnace granulated slag, 83.3g of fly ash, 600g of dried river sand, 1.2g of water-reducing agent, 0.253g of water-retaining thickener, 0.097g of surfactant, and 1.5g of reinforcing fiber.

[0105] The weighed raw materials were added to the cement mortar mixer for mixing and a flowability test. When 140g of water was added, the flowability reached 180mm. According to the formula... The calculated water-to-binder ratio is 0.35.

[0106] According to the formula ;

[0107] ;

[0108] ;

[0109] The calculations show that the amount of water added once is 30 kg, the amount added twice is 6.3 kg, and the amount added three times is 2.1 kg.

[0110] Based on the fact that the mixing equipment is a single-shaft vertical mixer, the empirical coefficient is determined to be 1. The calculated mixing time is 7.9 min for the first mixing, 4.7 min for the second mixing, and 3.2 min for the third mixing.

[0111] Add 75 kg of cement, 20 kg of blast furnace granulated slag, 25 kg of fly ash, 0.45 kg of basalt fiber, 360 g of water-reducing agent, 75.8 kg of water-retaining thickener, 29.2 kg of surfactant, and 30 kg of water to a single-shaft vertical mixer. Mix for 8 minutes.

[0112] Continue adding 180 kg of river sand and 6.3 kg of water to the mixer, and continue mixing for 4 minutes and 40 seconds.

[0113] Add another 2.1 kg of water to the mixer and continue mixing for 3 minutes and 10 seconds. The resulting 3D-printed concrete is now ready.

[0114] Example 2

[0115] The cementing materials used are 42.5MPa ordinary Portland cement, S95 granulated blast furnace slag, and Class I fly ash; the aggregate used is fine river sand with a measured moisture content of 4.1%; the reinforcing fiber used is 15mm long basalt fiber; the water-reducing agent used is polycarboxylate superplasticizer; the water-retaining thickener is 25000mPa·s viscosity hydroxypropyl methylcellulose; and the surfactant is sodium dodecyl sulfate.

[0116] The density ρ of the cement used C = 3120 kg / m 3 fly ash density ρ F = 2450 kg / m 3 granulated blast furnace slag density ρ S = 2810 kg / m 3 Density ρ of fine river sand A = 2570 kg / m 3 .

[0117] The mixing equipment used is a vertical shaft double-stage mixer, which has a mixing shaft, a rotating cylinder with a scraper, and can mix 5-10L at a time. The selected speed is 60 rpm and the ambient temperature is 25℃.

[0118] The dry mix ratio of the 3D printed concrete to be mixed each time is set as follows: 3kg cement, 0.8kg granulated blast furnace slag, 1.2kg fly ash, 5kg river sand, and 0.015kg basalt fiber.

[0119] The calculated dosage of water-reducing agent is 14.6g, water-retaining and thickening agent is 2.5g, and surfactant is 0.8g.

[0120] The measured moisture content of the aggregate was w=4.1%.

[0121] Weigh out 300g of cement, 80g of granulated blast furnace slag, 120g of fly ash, 500g of dried river sand, 1.46g of water-reducing agent, 0.25g of water-retaining thickener, 0.08g of surfactant, and 1.5g of reinforcing fiber.

[0122] The weighed raw materials were added to the cement mortar mixer for mixing and a flowability test on a mixing table. When 165g of water was added, the flowability on the mixing table reached 180mm. According to the formula... The calculated water-to-binder ratio is 0.33.

[0123] According to the formula ;

[0124] ;

[0125] ;

[0126] The calculations show that the amount of water added once is 1320g, the amount added twice is 42.5g, and the amount added three times is 82.5g.

[0127] Based on the fact that the mixing equipment is a vertical shaft re-mixing mixer, and the empirical coefficient is determined to be 0.8, the calculated mixing time is 5.16 min for the first mixing, 3.10 min for the second mixing, and 2.07 min for the third mixing.

[0128] Add 3 kg of cement, 0.8 kg of blast furnace granulated slag, 1.2 kg of fly ash, 0.015 kg of basalt fiber, 14.6 g of water-reducing agent, 2.5 g of water-retaining thickener, and 0.8 g of surfactant to a single-shaft vertical mixer, and add 1320 kg of water. Mix for 5 min 10 s.

[0129] Continue adding 5 kg of river sand and 42.5 kg of water to the mixer, and continue mixing for 3 minutes and 10 seconds.

[0130] Add another 82.5g of water to the mixer and continue mixing for 2 minutes. The resulting 3D-printed concrete is now ready.

[0131] Example 3

[0132] The cementing materials used are 42.5MPa ordinary Portland cement, S95 granulated blast furnace slag, and Class I fly ash; the aggregate used is fine river sand with a measured moisture content of 4.1%; the reinforcing fiber used is 15mm long basalt fiber; the water-reducing agent used is polycarboxylate superplasticizer; the water-retaining thickener is 25000mPa·s viscosity hydroxypropyl methylcellulose; and the surfactant is sodium dodecyl sulfate.

[0133] The density ρ of the cement used C = 3120 kg / m 3 fly ash density ρ F = 2450 kg / m 3 granulated blast furnace slag density ρ S = 2810 kg / m 3 Density ρ of fine river sand A = 2570 kg / m 3 .

[0134] The mixing equipment used is a planetary mixer with one planetary shaft, which can mix 50-100L at a time. The selected planetary shaft speed is 90 rpm, and the ambient temperature is 25℃.

[0135] The dry mix ratio of the 3D printed concrete to be mixed each time is set as follows: 18 kg of cement, 4 kg of blast furnace granulated slag, 8 kg of fly ash, 70 kg of river sand, and 0.1 kg of basalt fiber.

[0136] The calculated dosage of water-reducing agent is 86.4g, the calculated dosage of water-retaining and thickening agent is 24.5g, and the calculated dosage of surfactant is 4.84g.

[0137] The measured moisture content of the aggregate was w=4.1%.

[0138] Weigh out 180g of cement, 40g of granulated blast furnace slag, 80g of fly ash, 500g of dried river sand, 0.864g of water-reducing agent, 0.245g of water-retaining thickener, 0.048g of surfactant, and 1g of reinforcing fiber.

[0139] The weighed raw materials were added to the cement mortar mixer for mixing and a flowability test. When 105g of water was added, the flowability reached 180mm. According to the formula... The calculated water-to-binder ratio is 0.35.

[0140] According to the formula ;

[0141] ;

[0142] ;

[0143] The calculations show that the amount of water added once is 6623g, the amount added twice is 482g, and the amount added three times is 525g.

[0144] Based on the fact that the mixing equipment is a planetary mixer, the empirical coefficient is determined to be 0.75, and the calculated mixing time is 2.9 min for the first mixing, 1.7 min for the second mixing, and 1.2 min for the third mixing.

[0145] Add 18 kg of cement, 4 kg of blast furnace granulated slag, 8 kg of fly ash, 0.1 kg of basalt fiber, 84.4 g of water-reducing agent, 2.45 g of water-retaining thickener, 4.84 g of surfactant, and 6623 kg of water to a single-shaft vertical mixer. Mix for 3 minutes.

[0146] Continue adding 70 kg of river sand and 482 kg of water to the mixer, and continue mixing for 1 minute and 40 seconds.

[0147] Add another 52.5g of water to the mixer and continue mixing for 1 minute and 10 seconds. The resulting 3D-printed concrete is now ready.

[0148] Example 4

[0149] The cementing material used is 32.5MPa ordinary Portland cement and Class I fly ash; the aggregate used is fine river sand with a measured moisture content of 1.7%; the water-reducing agent used is polycarboxylate superplasticizer, the water-retaining and thickening agent is 25000mPa·s viscosity hydroxypropyl methylcellulose, and the surfactant is sodium dodecyl sulfate.

[0150] The density of the materials used is based on the density ρ of cement. C = 3100 kg / m 3 fly ash density ρ F = 2500 kg / m 3 Density ρ of fine river sand A = 2600 kg / m 3 .

[0151] The mixing equipment used was a free-fall mixer with a maximum capacity of 2000L, a selected speed of 20 rpm, and an ambient temperature of 12℃.

[0152] The dry mix ratio of the 3D printed concrete to be mixed each time is set as follows: 300 kg of cement, 100 kg of fly ash, and 600 kg of river sand.

[0153] The calculation based on the formula shows that the amount of water-reducing agent is 1240g, and the amount of water-retaining thickener is 250g.

[0154] The measured moisture content of the aggregate was w=1.7%.

[0155] Weigh out 300g of cement, 100g of fly ash, 600g of dried river sand, 1.24g of water-reducing agent, 0.25g of water-retaining thickener, and 0.072g of surfactant.

[0156] The weighed raw materials were added to the cement mortar mixer for mixing and a flowability test. When 135g of water was added, the flowability reached 180mm. According to the formula... The calculated water-to-binder ratio is 0.3375.

[0157] According to the formula ;

[0158] ;

[0159] ;

[0160] The calculations show that the amount of water added once is 96.58 kg, the amount added twice is 21.47 kg, and the amount added three times is 6.75 kg.

[0161] Based on the fact that the mixing equipment is a free-fall type, the empirical coefficient is determined to be 2.6. The calculated mixing time is 29 minutes for the first mixing, 17.4 minutes for the second mixing, and 11.6 minutes for the third mixing.

[0162] Add 300 kg of cement, 100 kg of fly ash, 1240 g of water-reducing agent, 250 g of water-retaining thickener, 72.2 g of surfactant, and 96.58 kg of water to a single-shaft vertical mixer. Mix for 29 minutes.

[0163] Continue adding 600 kg of river sand and 21.47 kg of water to the mixer, and continue mixing for 17 minutes and 30 seconds.

[0164] Add another 6.75g of water to the mixer and continue mixing for 11 minutes and 30 seconds. The resulting 3D-printed concrete is now ready.

[0165] Comparative Example 1

[0166] Comparative Example 1 is based on the material ratio and preparation method of Example 2, but without adding surfactants to the materials.

[0167] Comparative Example 2

[0168] Comparative Example 2 is based on the material ratio of Example 2. All materials were put into a mixer at once, 1445g of water was added, and the mixture was stirred for 10min20s.

[0169] Results Comparison and Analysis

[0170] According to the 3D printed concrete design and preparation methods of Examples 1 to 4 above, the material reaches a uniformly mixed state after mixing, and has good extrudability and constructability, and can be directly used for 3D printing construction.

[0171] The 3D printed concrete prepared according to Comparative Example 1 was not effectively dispersed after mixing and remained in a dry and hard state. The particles were not fully wetted and could not be used for 3D printing construction.

[0172] According to the 3D printed concrete preparation of Comparative Example 2, the material was relatively dry and hard in the early stage of the mixing process, and it would be spilled out of the mixing bucket when it was stirred by the mixing paddle; in the later stage of mixing, the material gradually softened, and when the mixing was finished, the material was basically dispersed, but there were still lumps in the slurry.

[0173] Examples 1-4 above demonstrate that the 3D printed concrete design and preparation method proposed in this technical solution has good applicability to different material ratios, different mixing equipment, and different temperatures.

[0174] The comparison between Example 2 and Comparative Example 1 shows that by adding surfactants, the mixing efficiency of materials can be effectively improved, and the extrudability and workability of materials can be improved.

[0175] The comparison between Example 2 and Comparative Example 2 shows that the 3D printing concrete preparation method proposed in this technical solution can effectively shorten the mixing time and improve the mixing efficiency.

[0176] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for designing and preparing 3D-printed concrete with enhanced mixing efficiency, characterized in that, include: According to the material ratio, cementitious materials, water-reducing agents, water-retaining thickeners, and reinforcing fibers are added to the mixing equipment. The cementitious materials include cement, fly ash, and granulated blast furnace slag. Weigh out water of mass W1 to be added first, add surfactant according to material ratio and dissolve it completely to form a solution. When the water temperature is below 10℃, first dissolve the surfactant in a small amount of warm water at 40-60℃, and then mix it with cold water to ensure complete dissolution. The surfactant solution is added to the stirring device and stirred once for a duration of t1. According to the material ratio, put the aggregate into the mixing equipment, weigh out the water that needs to be added a second time (W2) and add it into the equipment for secondary mixing. The mixing time is t2. Weigh out water of mass W3 to be added for the third time and add it to the equipment. Stir three times for a total stirring time of t3. The mass of the water-reducing agent ; The mass of the water-retaining and thickening agent ; The amount of surfactant ; In the formula, m 减 , m 保 , m 表 These represent the amounts of water-reducing agent, water-retaining thickener, and surfactant in the material, in kg; m C , m F , m S , m A These represent the mass of cement, fly ash, granulated blast furnace slag, and aggregate used in the material, in kg; ρ C , ρ F , ρ S , ρ A These are the densities of the cement, fly ash, granulated blast furnace slag, and aggregates used in the material, respectively, in kg / m³. 3 T represents the ambient temperature during construction, and 0℃≤T≤30℃; ； ； ； In the formula, W1, W2, and W3 represent the water addition amounts for the first, second, and third additions, respectively, in kg; m C , m F , m S , m A These represent the mass of cement, fly ash, granulated blast furnace slag, and aggregate, respectively, in kg; ρ A This refers to the density of the aggregate, expressed in kg / m³. 3 w represents the aggregate moisture content, expressed as %; W / B represents the water-cement ratio of the material. The specific steps for determining the water-cement ratio (W / B) of the material are as follows: Weigh the cementitious materials, dried aggregates, reinforcing fibers, water-reducing agents, water-retaining thickeners, and surfactants required for 0.5L of material; Add the weighed raw materials to the cement mortar mixer, add 100-120g of water, and mix at low speed for 3 minutes. Measure the flowability of the material on the mixing table. If the flowability is less than 180mm, return the material to the mixer, add 5g of water, and continue mixing for 30 seconds. Measure the flowability again. Repeat this step until the flowability reaches 180mm. Record the total amount of water added, W0. Calculate the water-cement ratio of the material using the following formula: ； In the formula, W / B is the water-cement ratio of the material; W0 is the total amount of water added to achieve a flowability of 180 mm, in grams. , These represent the masses of cement, fly ash, and granulated blast furnace slag used in this fluidity test, in grams.

2. The method for designing and preparing 3D-printed concrete with enhanced mixing efficiency according to claim 1, characterized in that: The quality of the cement, fly ash, and granulated blast furnace slag meets the requirements of m. C ≥ (m F +m S ); The mass of the reinforcing fiber accounts for 0-0.2% of the total mass of the cementitious material and aggregate; The cement, fly ash, granulated blast furnace slag, and aggregates satisfy the following formula: ； In the formula, m C , m F , m S , m A These represent the mass of cement, fly ash, granulated blast furnace slag, and aggregate used in the material, in kg; ρ A The density of the aggregate used, in kg / m³ 3 .

3. The method for designing and preparing 3D-printed concrete with enhanced mixing efficiency according to claim 1, characterized in that, ； ； ； In the formula, t1, t2, and t3 are the durations of the first, second, and third stirring operations, respectively, in minutes; R is the spindle speed of the stirring equipment, in rpm; and k is an empirical efficiency coefficient related to the type of stirring equipment.

4. The method for designing and preparing 3D-printed concrete with enhanced mixing efficiency according to claim 1, characterized in that, The specific determination of the aggregate moisture content w is as follows: Take a small amount of aggregate and dry it in an oven at 105℃ for 6 hours. Calculate the aggregate moisture content w by the weight change before and after drying.

5. The method for designing and preparing 3D-printed concrete with enhanced mixing efficiency according to claim 1, characterized in that: The cement is silicate cement; the fly ash is required to be Grade I or Grade II fly ash; the granulated blast furnace slag has an activity index of S95 or S105. The water-reducing agent is a polycarboxylate water-reducing agent; the water-retaining and thickening agent is a nonionic cellulose ether, specifically hydroxyethyl methylcellulose or hydroxypropyl methylcellulose, requiring a standard viscosity of less than 40,000 mPa·s; the surfactant is sodium dodecyl sulfate. The aggregate is one or more of the following: river sand, manufactured sand, quartz sand, tailings sand, coal gangue, slag, recycled concrete, and lightweight aggregate. The aggregate particle size range is 0.075-2.5mm, and the moisture content is less than 10%. The reinforcing fiber is one of basalt fiber, polypropylene fiber, or glass fiber.

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