3D printing alkali-activated concrete with high printability and printing method thereof

Abstract

The invention discloses 3D printing alkali-activated concrete with high printability and a printing method thereof.The 3D printing alkali-activated concrete is prepared from, by weight, 600-900 parts of slag, 100-400 parts of fly ash, 50-100 parts of waste glass powder, 1000-1800 parts of river sand, 340-400 parts of water and 30-60 parts of exciting agent; the waste glass powder contains more than 80% by mass of silicon element. The printing method comprises the following steps that the slag, the fly ash, the waste glass powder and the river sand are stirred; adding water, and stirring to form precursor slurry; pumping the precursor slurry and an exciting agent into a stirring and extruding device, and stirring to obtain alkali-activated concrete; the alkali-activated concrete is extruded through a stirring and extruding device and stacked layer by layer to form a component; and spraying or watering for maintenance. According to the invention, on the premise of ensuring the pumpability and extrudability of the material, controllable condensation and rapid prototyping in the printing process can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to 3D printing concrete and its printing method, in particular to a 3D printing alkali-activated concrete with high printability and its printing method. BACKGROUND

[0002] As a new construction technology, 3D printing concrete has the advantages of no need for templates, rapid prototyping, printable special-shaped components, high design flexibility and high construction efficiency compared with traditional casting methods, and has obvious economic benefits in terms of material and labor cost saving, so it has attracted widespread attention in the field of construction. This technology is a digital and automated additive manufacturing method, which forms a three-dimensional structure or component by stacking concrete materials layer by layer according to the digital model path.

[0003] Although 3D printing concrete shows broad prospects in intelligent construction, compared with traditional casting methods, there are still some technical problems: (1) the printing concrete material must have low viscosity and yield stress during pumping to ensure smooth delivery, but it needs to develop strength quickly to maintain shape stability during forming, which is contradictory to the performance requirements; (2) existing methods improve the rheological properties by adding thixotropic materials or fast-hardening cementitious materials, but often significantly increase the viscosity of the paste, leading to pumping and extrusion difficulties; (3) the performance window of the printing material is limited, and problems such as pipe blockage, collapse or insufficient interlayer adhesion are prone to occur.

[0004] Alkali-activated concrete, as a cementitious material mainly using industrial by-products such as slag and fly ash as raw materials, can effectively reduce carbon dioxide emissions by significantly reducing the amount of cement clinker used in the preparation process, which meets the development trend of low-carbon building materials. At the same time, such materials also have high compressive strength, rapid setting and hardening characteristics, and excellent acid and alkali resistance, and are considered to be an ideal candidate material for 3D printing concrete.

[0005] Existing methods usually balance the pumpability, extrudability and build stability of alkali-activated concrete by adding retarders or reducing the amount of alkali. However, reducing the amount of alkali can improve pumpability, but it will lead to a decrease in late-stage strength; while the use of retarders prolongs the working time, but increases the construction cost. Therefore, the existing methods still have deficiencies in considering the printability and mechanical properties of the material. SUMMARY

[0006] The purpose of the present application is to overcome the deficiencies in the prior art, and to provide a 3D printing alkali-activated concrete with fast construction speed, high compressive strength and high printability, and a printing method for the 3D printing alkali-activated concrete with high interlayer component forming precision, low cost and high printability.

[0007] Technical solution: The 3D printing alkali-activated concrete with high printability provided by the application comprises the following components in parts by weight: slag 600-900 parts, fly ash 100-400 parts, waste glass powder 50-100 parts, river sand 1000-1800 parts, water 340-400 parts, and activator 30-60 parts; the waste glass powder contains more than 80% of silicon element in mass percentage.

[0008] Further, the slag is granulated blast furnace slag powder, which is a high-temperature molten slag generated during iron smelting in a steel plant, and is ground into a powder material after water quenching, with a specific surface area greater than 400 m 2 / kg to ensure sufficient reactivity and early strength development.

[0009] Further, the fly ash is collected during the coal combustion process in a thermal power plant, with an activity index greater than or equal to 70%, and the fly ash particles are mostly spherical glass bodies with smooth surfaces, good micro-aggregate filling effect and potential pozzolanic reactivity, and the fineness meets the requirements of GB / T 1596-2017 standard.

[0010] Further, the waste glass powder is subjected to alkali pretreatment, mechanical activation treatment or silane coupling agent surface treatment to enhance its activity and interfacial bonding capacity, thereby significantly improving the printability and layer forming quality of the 3D printing alkali-activated concrete.

[0011] Further, the alkali pretreatment is: soaking the glass powder in a 0.5-2 wt% sodium hydroxide solution for 0.5-2 hours, drying at 60-80 ℃ and grinding to D50 of 10-40 μm. The sodium hydroxide solution slightly etches the glass powder surface to generate more silicon-oxygen defect sites, improving the solubility and reactivity of the waste glass powder. Grinding allows it to participate in the formation of a denser gel during the extrusion activation stage, improving the structural stability between the printed layers.

[0012] Further, the mechanical activation treatment is: ball milling the glass powder for 30-120 min to control the particle size to D50 of 5-20 μm. The mechanical activation further improves the reactivity and shear thickening properties of the waste glass powder. Ball milling causes the waste glass powder to produce a large number of broken bond structures, improving the amorphous degree. Particle size control significantly improves the thixotropy, yield stress growth rate and early strength of the alkali-activated concrete.

[0013] Further, the silane coupling agent surface treatment is: the glass powder is added into the ethanol solution containing 0.5-1 wt% silane coupling agent and mixed for 15-60 min, and then dried and ground. The interface bonding capacity between the waste glass powder and the gel structure of the alkali-activated system is enhanced by the silane coupling agent surface modification method. The coupling agent forms a Si-O-Si chemical bonding layer on the surface of the glass powder; after drying and fine grinding, the interlayer bonding strength of the 3D printed alkali-activated concrete can be significantly improved, and the forming stability is improved.

[0014] Further, the activator is solid sodium silicate, which is anhydrous sodium silicate, white powder, good solubility, strong alkaline, can quickly react with the active components in slag and fly ash to form a gel product with strength. The modulus of the solid sodium silicate can be selected as 0.5, 1.0, 1.5 or 2.0 according to the need, the purity is greater than 99%, has good storage stability and controllable release characteristics, can realize rapid dissolution and reaction activation at the stirring and extruding device, and the modulus of the solid sodium silicate used in the application is 1.0.

[0015] Further, the river sand is natural fine sand, the particle size range is 0.25-0.5 mm, the clay content is less than 2%, and the particle size distribution meets the standard of GB / T 14684-2011 "Construction Sand". The fine sand particle morphology is relatively round, the surface is clean, can play a skeleton role in the slurry, at the same time, improve the fluidity and pumpability of the mixed material, and improve the forming stability of the printing interlayer and the surface precision of the component.

[0016] The printing method of the 3D printed alkali-activated concrete with high printability provided by the application comprises the following steps:

[0017] Step one, the slag, fly ash, waste glass powder and river sand are stirred according to the proportion;

[0018] Step two, water is added to the dry material obtained in step one to form a precursor slurry by stirring;

[0019] Step three, the precursor slurry obtained in step two and the activator are pumped into the stirring and extruding device, and are uniformly stirred at a speed of 60-240 rpm to obtain the alkali-activated concrete;

[0020] Step four, the alkali-activated concrete is extruded through the stirring and extruding device to form a component by layer stacking, the single-layer height of the component is 12-20 mm, the rotation speed of the extruding screw is 60-120 rpm, the diameter of the extruding nozzle is 20-40 mm, and the printing speed is 40-120 mm / s;

[0021] Step five, after printing, spray or water conservation is adopted, and the conservation time is greater than or equal to 7 days.

[0022] Furthermore, the stirring extrusion device includes a stirring chamber and an extrusion chamber arranged perpendicularly to each other. The stirring chamber includes a stirring motor and stirring blades, and the extrusion chamber includes an extrusion motor and extrusion blades. The stirring chamber is provided with an inlet one for pumping in the precursor slurry and an inlet two for pumping in the activator.

[0023] Furthermore, the time interval between two adjacent deposition layers should be less than the initial setting time of the alkali-activated concrete mixture to ensure the interlayer bonding strength.

[0024] Preparation principle: Based on the characteristic that alkali-activated concrete can quickly solidify and harden within minutes when the activator ratio is appropriate, the precursor slurry and the activator solid sodium silicate are innovatively mixed online at the extrusion device. This allows the material to maintain good pumpability and fluidity before extrusion, and quickly obtain structural stability after extrusion, thereby meeting the performance requirements of 3D printing for the entire process of "pumpable-extrudable-constructable".

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0026] 1. It can achieve controllable solidification and rapid molding during the printing process while ensuring the pumpability and extrudability of the material, thus avoiding the drawback of the traditional method of improving construction performance by reducing the amount of alkali, which leads to a decrease in material strength.

[0027] 2. By achieving online mixing of the precursor slurry and the activator solid sodium silicate at the stirring extrusion device, the equipment complexity and safety hazards caused by traditional heating methods such as microwave are avoided;

[0028] 3. It extends the printing time window, significantly improves interlayer bond strength and component forming accuracy, reduces construction complexity and additional costs, and overall promotes the efficient application and promotion of alkali-activated concrete in 3D printing engineering.

[0029] 4. Since alkali-activated concrete uses industrial by-products such as fly ash, slag, and waste glass powder as its main raw materials and has been calcined at high temperatures, it has lower carbon emissions compared to traditional cement-based materials. This invention not only breaks through the printability bottleneck of 3D printed concrete in terms of performance, but also has significant advantages in terms of environmental sustainability, and can provide important technical support for the green and low-carbon development of water conservancy projects, construction projects and other fields. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the stirring extrusion device of the present invention;

[0031] Figure 2 This is a process flow diagram of the online excitation and printing of the present invention. Detailed Implementation

[0032] Unless otherwise specified, all materials and reagents used in the following embodiments are commercially available. Experimental methods not specifically described in the embodiments are generally performed under standard conditions or as recommended by the manufacturer. The slag is granulated blast furnace slag powder, a powder material produced by rapidly cooling high-temperature molten slag during ironmaking in steel plants, after water quenching. Its main chemical components include silicon dioxide, calcium oxide, and aluminum oxide. It has a high glass content and a specific surface area greater than 400 m². 2 / kg, to ensure sufficient reactivity and early strength development. Fly ash is collected during the combustion of coal in thermal power plants, and its main components are silicon dioxide, alumina, and calcium oxide. It has good micro-aggregate filling effect and potential pozzolanic reactivity, with an activity index of not less than 70%. Waste glass powder is collected during the demolition or renovation of buildings. Its main component is silicon dioxide, which can provide a large amount of silicon source required for the alkali-activated reaction, with a silicon content of not less than 80%. The activator is solid sodium silicate powder, which is anhydrous sodium silicate. It has good solubility and strong alkalinity, and can react rapidly with the active components in slag, fly ash, and waste glass powder to form a strong gel product with a purity greater than 99%. It has good storage stability and controllable release characteristics, and can achieve rapid dissolution and reaction activation at the stirring extrusion device.

[0033] To evaluate the initial pumpability and extrudability of the alkali-activated concrete of this invention, the workability of the mixture was characterized using rheological parameters in accordance with relevant literature. Rheological performance tests were conducted using an RST-SST rotational rheometer with a paddle rotor inner diameter of 10 mm and an outer diameter of 20 mm. The experimental conditions were set as follows: temperature (25±2)℃ and relative humidity (70±3)%. During the pumpability test, the static yield stress of the freshly mixed mortar was determined using a low-speed shear mode with a shear rate of 0.1 r / s for 60 s to obtain the static yield stress of the mortar under low shear conditions. During the extrudability test, the shear rate was linearly increased from 0 r / s to 50 r / s within 30 seconds, and then linearly decreased from 50 r / s to 0 r / s within 30 seconds, while continuously recording the changes in dynamic yield stress and plastic viscosity.

[0034] To evaluate the constructability of the alkali-activated concrete of the present invention, after extrusion for 20 minutes, a mechanical testing system connected to a conical needle was gradually inserted into the alkali-activated concrete to measure the penetration resistance. The static yield strength was calculated to assess the development of bearing capacity and constructability.

[0035] Mechanical property testing was conducted according to the "Test Methods for Basic Mechanical Properties of 3D Printed Concrete" (T / CBMF183-2022 / T / CCPA33-2022). After 28 days of standard curing, the alkali-activated concrete specimens printed in the example were cut into standard sizes, and the compressive strength in the Z direction was tested to systematically evaluate the load-bearing capacity of the alkali-activated concrete after printing.

[0036] The stirring extrusion device used, such as Figure 1 The system includes a mixing chamber 1 and an extrusion chamber 2 arranged perpendicularly to each other. The mixing chamber 1 includes a stirring motor 11 and stirring blades 12, and the extrusion chamber 2 includes an extrusion motor 21 and extrusion blades 22. The mixing chamber 1 is provided with an inlet 13 for pumping in the precursor slurry and an inlet 14 for pumping in the activator. The stirring motor 11 and the extrusion motor 21 control the stirring blades 12 and the extrusion blades 22, respectively. The entire chamber is divided into the mixing chamber 1 and the extrusion chamber 2.

[0037] Example 1

[0038] like Figure 2 A 3D-printable alkali-activated concrete with improved printability comprises, by weight, the following components: 800 parts slag, 150 parts fly ash, 50 parts waste glass powder, 1600 parts river sand, 360 parts water, and 45 parts sodium silicate. The waste glass powder undergoes alkali pretreatment by immersing it in a 1wt% sodium hydroxide solution for 1 hour, followed by drying at 80 ℃ and grinding to a particle size of 10–40 μm.

[0039] The above-mentioned online activation printing process for alkali-activated concrete, which improves printability, includes the following steps:

[0040] (1) Raw material preparation and dry mixing: Weigh out slag, fly ash, waste glass powder and river sand according to the proportion, put them into a 50 L horizontal mixer, and mix at a mixing speed of 50 rpm for 3 minutes to obtain a uniformly mixed dry material.

[0041] (2) Preparation of precursor slurry: Add water to the dry material obtained in step (1), continue stirring at 50 rpm for 5 min to form a uniform precursor slurry, and let it stand for 10 min.

[0042] (3) Precursor slurry and activator are mixed and activated as needed: the precursor slurry and the activator solid sodium silicate powder are respectively pumped to the stirring extrusion device through the pumping system. After the mixing chamber is filled, the stirring blades are started and stirred at 180 rpm for 45s to achieve full mixing and activation.

[0043] (4) Extrusion and printing: The alkali-activated concrete after being mixed evenly is extruded through the print head and stacked layer by layer to form a component. The single-layer printing height is set to 12 mm, the rotation speed of the extrusion blade is 60 rpm, the diameter of the extrusion nozzle is 20 mm, and the printing speed is 40 mm / s.

[0044] (5) Molding and curing: After printing, spray moisturizing measures are taken for components that have not yet set. After the components have set, water curing is carried out for 14 days.

[0045] Example 2

[0046] A type of alkali-activated concrete for 3D printing that improves printability comprises the following components by weight: 800 parts slag, 200 parts fly ash, 75 parts waste glass powder, 1000 parts river sand, 340 parts water, and 60 parts sodium silicate. The waste glass powder undergoes alkali pretreatment by immersing it in a 1wt% sodium hydroxide solution for 1 hour, followed by drying at 80 °C and grinding to a particle size of 10–40 μm.

[0047] The above-mentioned online activation printing process for alkali-activated concrete, which improves printability, includes the following steps:

[0048] (1) Raw material preparation and dry mixing: Weigh out slag, fly ash, waste glass powder and river sand according to the proportion, put them into a 50 L horizontal mixer, and mix at a mixing speed of 50 rpm for 3 minutes to obtain a uniformly mixed dry material.

[0049] (2) Preparation of precursor slurry: Add water to the dry material obtained in step (1), stir at 50 rpm for 5 min to form a uniform precursor slurry, and let stand for 20 min.

[0050] (3) Precursor slurry and activator are mixed and activated as needed: the precursor slurry and the activator solid sodium silicate powder are respectively pumped to the stirring extrusion device through the pumping system. After the mixing chamber is filled, the stirring blades are started and stirred at 180 rpm for 45s to achieve full mixing and activation.

[0051] (4) Extrusion and printing: The alkali-activated concrete after being mixed evenly is extruded through the print head and stacked layer by layer to form a component. The single-layer printing height is set to 12 mm, the rotation speed of the extrusion blade is 80 rpm, the diameter of the extrusion nozzle is 20 mm, and the printing speed is 80 mm / s.

[0052] (5) Molding and curing: After printing, spray moisturizing measures are taken for components that have not yet set. After the components have set, water curing is carried out for 14 days.

[0053] Example 3

[0054] A type of alkali-activated concrete for 3D printing that improves printability comprises the following components by weight: 600 parts slag, 400 parts fly ash, 50 parts waste glass powder, 1600 parts river sand, 360 parts water, and 60 parts sodium silicate. The waste glass powder undergoes alkali pretreatment by immersing it in a 1wt% sodium hydroxide solution for 1 hour, followed by drying at 80 °C and grinding to a particle size of 10–40 μm.

[0055] The above-mentioned online activation printing method for alkali-activated concrete that improves printability includes the following steps:

[0056] (1) Raw material preparation and dry mixing: Weigh out slag, fly ash, waste glass powder and river sand according to the proportion, put them into a 50 L horizontal mixer, and mix at a mixing speed of 50 rpm for 3 minutes to obtain a uniformly mixed dry material.

[0057] (2) Preparation of precursor slurry: Add water to the dry material obtained in step (1), stir at 50 rpm for 5 min to form a uniform precursor slurry, and let stand for 30 min.

[0058] (3) Precursor slurry and activator are mixed and activated as needed: the precursor slurry and the activator solid sodium silicate powder are respectively pumped to the stirring extrusion device through the pumping system. After the mixing chamber is filled, the stirring blades are started and stirred at 120 rpm for 45s to achieve full mixing and activation.

[0059] (4) Extrusion and printing: The alkali-activated concrete after being mixed evenly is extruded through the print head and stacked layer by layer to form a component. The single-layer printing height is set to 12 mm, the rotation speed of the extrusion blade is 60 rpm, the diameter of the extrusion nozzle is 20 mm, and the printing speed is 60 mm / s.

[0060] (5) Molding and curing: After printing, spray moisturizing measures are taken for components that have not yet set. After the components have set, water curing is carried out for 14 days.

[0061] Example 4

[0062] A type of alkali-activated concrete for 3D printing that improves printability comprises the following components by weight: 900 parts slag, 100 parts fly ash, 50 parts waste glass powder, 1600 parts river sand, 370 parts water, and 60 parts sodium silicate. The waste glass powder undergoes alkali pretreatment by immersing it in a 1wt% sodium hydroxide solution for 1 hour, followed by drying at 80 °C and grinding to a particle size of 10–40 μm.

[0063] The above-mentioned online activation printing method for alkali-activated concrete that improves printability includes the following steps:

[0064] (1) Raw material preparation and dry mixing: Weigh out slag, fly ash, waste glass powder and river sand according to the proportion, put them into a 50 L horizontal mixer, and mix at a mixing speed of 50 rpm for 3 minutes to obtain a uniformly mixed dry material.

[0065] (2) Preparation of precursor slurry: Add water to the dry material obtained in step (1), stir at 50 rpm for 5 min to form a uniform precursor slurry, and let stand for 40 min.

[0066] (3) Precursor slurry and activator are mixed and activated as needed: the precursor slurry and the activator solid sodium silicate powder are respectively pumped to the stirring extrusion device through the pumping system. After the mixing chamber is filled, the stirring blades are started and stirred at 180 rpm for 45s to achieve full mixing and activation.

[0067] (4) Extrusion and printing: The alkali-activated concrete after being mixed evenly is extruded through the print head and stacked layer by layer to form a component. The single-layer printing height is set to 12 mm, the rotation speed of the extrusion blade is 60 rpm, the diameter of the extrusion nozzle is 20 mm, and the printing speed is 60 mm / s.

[0068] (5) Molding and curing: After printing, spray moisturizing measures are taken for components that have not yet set. After the components have set, water curing is carried out for 14 days.

[0069] Example 5

[0070] A type of alkali-activated concrete for 3D printing that improves printability comprises the following components by weight: 800 parts slag, 100 parts fly ash, 100 parts waste glass powder, 1600 parts river sand, 360 parts water, and 60 parts sodium silicate. The waste glass powder undergoes alkali pretreatment by immersing it in a 1wt% sodium hydroxide solution for 1 hour, followed by drying at 80 °C and grinding to a particle size of 10–40 μm.

[0071] The above-mentioned online activation printing method for alkali-activated concrete that improves printability includes the following steps:

[0072] (1) Raw material preparation and dry mixing: Weigh out slag, fly ash, waste glass powder and river sand according to the proportion, put them into a 50 L horizontal mixer, and mix at a mixing speed of 50 rpm for 3 minutes to obtain a uniformly mixed dry material.

[0073] (2) Preparation of precursor slurry: Add water to the dry material obtained in step (1), stir at 50 rpm for 5 min to form a uniform precursor slurry, and let stand for 40 min.

[0074] (3) Precursor slurry and activator are mixed and activated as needed: the precursor slurry and the activator solid sodium silicate powder are respectively pumped to the stirring extrusion device through the pumping system. After the mixing chamber is filled, the stirring blades are started and stirred at 180 rpm for 90s to achieve full mixing and activation.

[0075] (4) Extrusion and printing: The alkali-activated concrete after being mixed evenly is extruded through the print head and stacked layer by layer to form a component. The single-layer printing height is set to 12 mm, the rotation speed of the extrusion blade is 60 rpm, the diameter of the extrusion nozzle is 20 mm, and the printing speed is 60 mm / s.

[0076] (5) Molding and curing: After printing, spray moisturizing measures are taken for components that have not yet set. After the components have set, water curing is carried out for 14 days.

[0077] Example 6

[0078] A type of alkali-activated concrete for 3D printing that improves printability comprises the following components by weight: 800 parts slag, 300 parts fly ash, 100 parts waste glass powder, 1800 parts river sand, 400 parts water, and 60 parts sodium silicate. The waste glass powder undergoes mechanical activation treatment: it is ball-milled for 120 minutes to control its particle size to D50 = 10 μm.

[0079] The above-mentioned online activation printing method for alkali-activated concrete that improves printability includes the following steps:

[0080] (1) Raw material preparation and dry mixing: Weigh out slag, fly ash, waste glass powder and river sand according to the proportion, put them into a 50 L horizontal mixer, and mix at a mixing speed of 50 rpm for 3 minutes to obtain a uniformly mixed dry material.

[0081] (2) Preparation of precursor slurry: Add water to the dry material obtained in step (1), continue stirring at 50 rpm for 5 min to form a uniform precursor slurry, and let it stand for 10 min.

[0082] (3) Precursor slurry and activator are mixed and activated as needed: the precursor slurry and the activator solid sodium silicate powder are respectively pumped to the stirring extrusion device through the pumping system. After the mixing chamber is filled, the stirring blades are started and stirred at 180 rpm for 45s to achieve full mixing and activation.

[0083] (4) Extrusion and printing: The alkali-activated concrete after being mixed evenly is extruded through the print head and stacked layer by layer to form a component. The single-layer printing height is set to 20 mm, the rotation speed of the extrusion blade is 120 rpm, the diameter of the extrusion nozzle is 40 mm, and the printing speed is 40 mm / s.

[0084] (5) Molding and curing: After printing, spray moisturizing measures are taken for components that have not yet set. After the components have set, water is sprayed for curing for 10 days.

[0085] Example 7

[0086] A type of alkali-activated concrete for 3D printing that improves printability comprises the following components by weight: 800 parts slag, 500 parts fly ash, 100 parts waste glass powder, 1600 parts river sand, 360 parts water, and 30 parts sodium silicate. The waste glass powder undergoes surface treatment with a silane coupling agent. The glass powder is added to an ethanol solution containing 1 wt% KH-550 silane coupling agent and mixed for 60 minutes, followed by drying and grinding.

[0087] The above-mentioned online activation printing method for alkali-activated concrete that improves printability includes the following steps:

[0088] (1) Raw material preparation and dry mixing: Weigh out slag, fly ash, waste glass powder and river sand according to the proportion, put them into a 50 L horizontal mixer, and mix at a mixing speed of 50 rpm for 3 minutes to obtain a uniformly mixed dry material.

[0089] (2) Preparation of precursor slurry: Add water to the dry material obtained in step (1), continue stirring at 50 rpm for 5 min to form a uniform precursor slurry, and let it stand for 10 min.

[0090] (3) Precursor slurry and activator are mixed and activated as needed: the precursor slurry and the activator solid sodium silicate powder are respectively pumped to the stirring extrusion device through the pumping system. After the mixing chamber is filled, the stirring blades are started and stirred at 240 rpm for 45s to achieve full mixing and activation.

[0091] (4) Extrusion and printing: The alkali-activated concrete after being mixed evenly is extruded through the print head and stacked layer by layer to form a component. The single-layer printing height is set to 16 mm, the rotation speed of the extrusion blade is 90 rpm, the diameter of the extrusion nozzle is 30 mm, and the printing speed is 120 mm / s.

[0092] (5) Molding and curing: After printing, spray moisturizing measures are taken for components that have not yet set. After the components have set, water is sprayed for curing for 14 days.

[0093] Comparative Example 1

[0094] This comparative example is identical to Example 5 in terms of steps and procedures, except that 60 parts of sodium silicate are replaced with 10 parts of sodium silicate.

[0095] Comparative Example 2

[0096] This comparative example is the same as the steps in Example 5, except that 100 parts of waste glass powder are replaced with 10 parts of waste glass powder.

[0097] Comparative Example 3

[0098] This comparative example is identical to Example 5 in terms of steps and procedures, except that solid sodium silicate is replaced with liquid sodium silicate.

[0099] Comparative Example 4

[0100] This comparative example is identical to Example 5 in terms of steps and procedures, except that the waste glass powder is not treated in any way.

[0101] Comparative Example 5

[0102] This comparative example is identical to Example 5 in terms of steps, except that in step three, stirring at 20 rpm for 45 seconds is replaced with stirring at 240 rpm for 44 seconds.

[0103] Table 1. Rheological properties and compressive strength test results of alkali-activated concrete obtained in Examples 1-7 and Comparative Examples 1-5

[0104]

[0105] As can be seen from Examples 1-7, the 3D-printed alkali-activated concrete prepared by this invention exhibits a small change in static yield stress during the static settling process of the precursor slurry, thus maintaining good pumpability over a relatively long period. According to relevant literature, the rheological parameters of all examples demonstrate that the printing material possesses excellent extrudability and constructability, while the hardened compressive strength reaches levels above C60, exhibiting good mechanical properties.

[0106] Compared to Comparative Example 1, when the activator dosage was too low, the yield strength was insufficient, leading to reduced constructability of the printed component and a significant decrease in the mechanical strength after hardening. This indicates that the activator dosage should not be too low. Compared to Comparative Examples 2 and 4, low waste glass powder content or no treatment of waste glass powder reduced the yield strength and mechanical strength after hardening of the printed material to a certain extent, indicating that waste glass powder has a certain degree of activity, which is further enhanced after treatment. Compared to Comparative Example 3, the use of liquid activators resulted in a general decrease in rheological parameters, rendering the material unprintable. Therefore, solid activators were required to minimize the change in rheological parameters when the precursor slurry was converted into alkali-activated concrete. Further comparison with Comparative Example 5 revealed that increasing the mixing speed improved the uniformity of alkali-activated concrete, significantly improving extrudability, constructability, and mechanical strength after hardening. This underscores the importance of online mixing and activation.

[0107] Based on the results of the above embodiments, this invention, through optimization of key parameters such as activator dosage, precursor ratio, and stirring speed, achieves good pumpability of the precursor slurry over a longer period, while significantly improving the extrudability and constructability of alkali-activated concrete. The hardened printed structure exhibits excellent mechanical properties and structural stability, thereby effectively improving the overall printability and mechanical strength of 3D-printed alkali-activated concrete and meeting engineering application requirements. The optimal embodiment is Example 5.

Claims

1. A highly printable 3D-printable alkali-activated concrete, characterized in that, It comprises the following components in parts by weight: 600-900 parts slag, 100-400 parts fly ash, 50-100 parts waste glass powder, 1000-1800 parts river sand, 340-400 parts water, and 30-60 parts activator; wherein the waste glass powder contains more than 80% silicon by mass.

2. The highly printable 3D-printable alkali-activated concrete according to claim 1, characterized in that: The slag is granulated blast furnace slag powder with a specific surface area greater than 400 m². 2 / kg.

3. The highly printable 3D-printable alkali-activated concrete according to claim 1, characterized in that: The fly ash is collected during the combustion of coal in thermal power plants and has an activity index of 70% or higher.

4. The highly printable 3D-printable alkali-activated concrete according to claim 1, characterized in that: The waste glass powder is subjected to alkali pretreatment, mechanical activation treatment, or silane coupling agent surface treatment.

5. The highly printable 3D-printable alkali-activated concrete according to claim 4, characterized in that: The alkaline pretreatment is as follows: glass powder is soaked in a 0.5-2 wt% sodium hydroxide solution for 0.5-2 hours, dried at 60-80 ℃, and ground to a D50 of 10-40 μm.

6. The highly printable 3D-printable alkali-activated concrete according to claim 4, characterized in that: The mechanical activation treatment is as follows: the glass powder is ball-milled for 30~120 min to control its particle size to D50 of 5~20 μm.

7. The highly printable 3D-printable alkali-activated concrete according to claim 4, characterized in that: The surface treatment of the silane coupling agent is as follows: glass powder is added to an ethanol solution containing 0.5~1 wt% KH-550 type silane coupling agent and mixed for 15~60 min, then dried and ground.

8. The highly printable 3D-printable alkali-activated concrete according to claim 1, characterized in that: The activator is solid sodium silicate.

9. A method for printing highly printable alkali-activated concrete using 3D printing according to any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Mix the slag, fly ash, waste glass powder and river sand in the specified proportions. Step 2: Add water to the dry material obtained in Step 1 and stir to form a precursor slurry; Step 3: Pump the precursor slurry obtained in Step 2 and the activator into a mixing and extrusion device, and mix them evenly at a speed of 60~240 rpm to obtain alkali-activated concrete; Step 4: Alkali-activated concrete is extruded through a mixing and extrusion device and stacked layer by layer to form components. The height of a single layer of the component is 12~20 mm, the rotation speed of the extrusion screw is 60~120 rpm, the diameter of the extrusion nozzle is 20~40 mm, and the printing speed is 40~120 mm / s. Step 5: After printing, spray or sprinkle water for curing, and the curing time should be greater than or equal to 7 days.

10. The printing method for alkali-activated concrete with high printability in 3D printing according to claim 9, characterized in that: The stirring extrusion device includes a stirring chamber (1) and an extrusion chamber (2) arranged perpendicularly to each other. The stirring chamber (1) includes a stirring motor (11) and stirring blades (12). The extrusion chamber (2) includes an extrusion motor (21) and extrusion blades (22). The stirring chamber (1) is provided with an inlet one (13) for pumping in the precursor slurry and an inlet two (14) for pumping in the activator.

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