Tunnel hole slag concrete for jet 3D printing and construction method

Abstract

The application discloses a kind of spouting 3D printing tunnel hole slag concrete and construction method, according to weight fraction, including component: cement 870-900 parts, fly ash 50-60 parts, silica ash 50-80 parts, fine aggregate 500-600 parts, coarse aggregate 500-600 parts, water 350-355 parts, liquid accelerator 20-50 parts, powder accelerator 10-20 parts, water reducing agent 1-2 parts.The application uses tunnel hole slag to completely replace natural sand, and is modified by two-component accelerator, so that spouting 3D printing concrete meets fast hardening, early strength and good printability requirements.The construction method of the application can intelligently control the accelerator incorporation amount according to the spraying surface angle 0-180°, meet the bonding performance requirements under different spraying surface angles, and effectively control the construction quality.The concrete provided by the application meets the spouting 3D printing requirements in terms of fluidity, printing accuracy and constructability, has excellent mechanical properties, can cope with multi-angle spouting 3D printing, and at the same time improves the utilization rate of tunnel hole slag solid waste resources, has important social and environmental significance.

Description

Technical Field

[0001] This invention relates to the fields of concrete 3D printing and solid waste resource utilization, and in particular to a jet 3D printing method for tunnel muck concrete and its construction method. Background Technology

[0002] Traditional shotcrete construction faces a series of challenges in practice. First, there are unavoidable difficulties in uniformity and quality control; variations in construction techniques and operations can lead to differences in concrete density and strength. Second, surface inhomogeneity can damage the structure's appearance and function. Furthermore, traditional shotcrete construction is slow, requiring specialized equipment and skilled technicians, thus increasing construction time and costs. Safety is also a concern, with potential risks such as splashing and dust generation that can harm workers and the environment. Environmental pollution is also a significant issue, as shotcrete can generate waste and dust that impact the surrounding environment. Finally, challenges in maintenance and repair can lead to further time and cost expenditures.

[0003] Concrete 3D printing offers numerous advantages, including lower labor requirements, the ability to create complex and diverse architectural designs, high design freedom, and formwork-free concrete pouring. Shotcrete 3D printing is a technology that uses a spraying device to spray concrete material layer by layer to build structures. It combines the advantages of 3D printing and traditional shotcrete technology, using a robotic arm to control the movement path and speed of the spraying device to achieve 3D printing of buildings. The advantages of shotcrete 3D printing lie in its high flexibility; by controlling the nozzle position and spraying speed, it can print various shapes and structures, achieving omnidirectional printing. It has a wide range of applications, suitable for buildings of different sizes and dimensions. Due to the working air pressure during spraying, shotcrete 3D printed concrete is denser, has lower porosity, and stronger interlayer bonding, generally exhibiting superior mechanical properties compared to traditionally poured concrete.

[0004] In recent years, railway transportation engineering has rapidly developed, especially in the central and western regions, where tunnel construction has been widely adopted. However, tunnel construction inevitably generates a large amount of excavated soil, and the disposal of this waste has become a thorny issue. It not only occupies a significant amount of permanent land, but the cost of transporting this excavated soil is also substantial. At the same time, the demand for sand in the construction industry has been increasing year by year, especially in areas where natural sand resources are scarce; purchasing and transporting large quantities of sand undoubtedly further increases the cost burden. Currently, however, most of this tunnel excavated soil is simply piled up in nearby landfills or landfilled, resulting in low utilization and significant environmental damage. While excavated soil is currently being used as a raw material for concrete, it cannot be used for jet 3D printing.

[0005] Utilizing tunnel slag through jet 3D printing is a problem that urgently needs to be solved. Summary of the Invention

[0006] To address the problems in existing technologies, this invention provides a spray-painted 3D-printed tunnel muck concrete and its construction method. It utilizes a two-component accelerator to modify the concrete, achieving the requirements of spray-painting 3D printing and improving construction quality. This addresses the issues of low utilization rate of tunnel muck solid waste resources, the impact of tunnel muck on the workability and mechanical properties of concrete, and the low level of intelligence and difficulty in quality control in traditional spray-painted concrete construction. The construction method of this invention can adaptively adjust the amount of liquid accelerator added according to the angle of the sprayed surface to effectively control construction quality.

[0007] The technical solution of this invention is:

[0008] In a first aspect, the present invention provides a jet-printed 3D-printed tunnel muck concrete, comprising the following components in parts by weight: 870-900 parts cement, 50-60 parts fly ash, 50-80 parts silica fume, 500-600 parts fine aggregate, 500-600 parts coarse aggregate, 350-355 parts water, 20-50 parts liquid accelerator, 10-20 parts powder accelerator, and 1-2 parts water-reducing agent;

[0009] Both the coarse and fine aggregates are made from crushed stone waste during tunnel excavation. The fine aggregate consists of stone powder with a particle size of less than 0.075 mm, tunnel slag with a particle size of not less than 0.075 mm and not greater than 2.36 mm, and tunnel slag with a particle size of greater than 2.36 mm and not greater than 4.75 mm, and is configured in a ratio of (10-15%):(60-70%):(20-30%) to form a fine aggregate with a fineness modulus of 2.95-3.3. The coarse aggregate consists of tunnel slag with a particle size of greater than 4.75 mm and not greater than 8 mm. The crushing value of the coarse aggregate is <10%.

[0010] All dry materials, namely cement, fly ash, silica fume, fine aggregate and coarse aggregate of tunnel muck, and powder accelerator, are added to a mixer in proportion. Then, a mixture of water-reducing agent and water is added to obtain concrete slurry. The concrete slurry is then placed in the feed hopper of a jet 3D printer. The concrete slurry and liquid accelerator are sprayed out together through the nozzle of the jet 3D printer to obtain jet 3D printed tunnel muck concrete.

[0011] Furthermore, the powder accelerator is at least three of the following: alumina clinker, sodium carbonate, quicklime, anhydrous gypsum, and alum mud; commercially available powder accelerators may also be used.

[0012] Preferably, the powdered accelerator is a mixture prepared according to the mass ratio of alumina clinker: sodium carbonate: quicklime: anhydrous gypsum: alum mud = 4:2:1.5:1:1.5, and the dosage of the powdered accelerator is 1-2% of the mass of the cementitious materials (cement, fly ash, and silica fume).

[0013] Preferably, the cement is P·O 42.5 ordinary Portland cement with a specific surface area of ​​300-400 m². 2 / kg. Preferably, the fly ash is Grade I, the silica fume has an SiO2 content ≥91%, and the fly ash specific surface area is 300-430m². 2 / kg, its high fineness can meet the requirements of filling the internal pores of concrete and improving strength. Both can adjust the rheological properties of fresh mortar, improve and enhance the workability and mechanical properties of concrete, and have a significant regulating effect on the sprayable 3D printability of mortar.

[0014] Preferably, the liquid accelerator is an alkali-free liquid accelerator with a 28-day compressive strength ratio greater than 100%.

[0015] Preferably, the water-reducing agent is one or more of methacrylic acid polycarboxylic acid high-performance water-reducing agent and maleic anhydride polycarboxylic acid high-performance water-reducing agent, with a solid content ≥20% and a water reduction rate ≥25%.

[0016] This invention conducts jet 3D printing experiments on sprayed surfaces at 0°, 90°, and 180° to ensure that the bonding performance between 3D printed layers is basically the same, while the quality of 3D printed concrete is relatively good. The results show that when the sprayed surface angle is 0°, 90°, and 180°, the liquid accelerator dosage is 2%, 3.5%, and 5% of the mass of cementitious materials (the sum of cement, fly ash, and silica fume), respectively. Based on these three sets of data, the relationship between the sprayed surface angle and the liquid accelerator dosage is fitted. For other sprayed surface angles, the corresponding liquid accelerator dosage can be determined according to the relationship between the two, which can achieve the ability to control the accelerator dosage to meet the bonding performance requirements under different sprayed surface angles.

[0017] Preferably, the printing window time for the concrete slurry is 30-50 minutes, and the flowability printing window for the sprayed 3D printed tunnel slag concrete material is 180-190 mm. Within this flowability printing window range, accurate and continuous spraying 3D printing is possible.

[0018] The jet 3D printing of tunnel muck concrete has high printing precision, good uniformity of printing surface thickness and high flatness; it has good constructability, and when the sprayed surface angle is 90°, continuous stacking of ≥20 layers does not cause obvious interlayer misalignment, and when the sprayed surface angle is 180°, continuous stacking of ≥15 layers does not cause detachment; all performances meet the requirements of jet 3D printing and can cope with jet 3D printing at multiple angles.

[0019] The high printing accuracy refers to 0≤|K|<0.1 and 0≤RSS<30. In the single-layer strip jet printing test, a single-layer strip with a length of 500mm is jetted vertically onto the jetting surface. Then, three cross-sections of the strip are fitted with cross-sectional contours. The average slope of the contour fitting line on one side of the three printed surfaces is taken as K, and the average of the sum of squared residuals of the contour fitting lines on one side of the three printed surfaces is taken as RSS.

[0020] Secondly, the present invention provides a construction method for spraying 3D printed tunnel muck concrete, the construction method comprising the following steps:

[0021] 1) Determine the concrete slurry formula as follows: 870-900 parts cement, 50-60 parts fly ash, 50-80 parts silica fume, 500-600 parts fine aggregate, 500-600 parts coarse aggregate, 350-355 parts water, 10-20 parts powder accelerator, and 1-2 parts water-reducing agent. Add all dry materials, namely cement, fly ash, silica fume, tunnel slag, fine aggregate, coarse aggregate, and powder accelerator, to the mixer and mix until uniform. Mix the water-reducing agent and water in the specified proportions and add them to the mixer, then mix until uniform to obtain the concrete slurry. Both coarse and fine aggregates are made from crushed stone waste during tunnel excavation. The fineness modulus of the fine aggregate is 2.95-3.3, and the coarse aggregate is screened with a particle size greater than 4.75 mm and not greater than 8 mm.

[0022] 2) When the sprayed surface is defined as the ground, the sprayed surface angle is 0°; when the sprayed surface is the top surface, the sprayed surface angle is 180°; when the sprayed surface is a vertical surface, the sprayed surface angle is 90°; other sprayed surface angles are determined according to the above definitions.

[0023] 3) Given the diameter of the concrete slurry supply pipe and the pump flow rate, and the printing parameters of the jet 3D printer, conduct jet 3D printing experiments to obtain the printability and mechanical properties of the sprayed concrete under different liquid accelerator flow rates at a special sprayed surface angle. Select the liquid accelerator flow rate and the corresponding sprayed surface angle when the printability and mechanical properties are optimal to form a set of data pairs. Obtain multiple sets of data pairs and use multiple sets of data pairs to fit the relationship between the sprayed surface angle and the liquid accelerator flow rate.

[0024] 4) During actual construction, the concrete slurry is placed in the supply hopper, and the liquid accelerator is pumped to the liquid interface of the jet 3D printer through the liquid pipe. A sensor is set at the front end of the robotic arm used to control the movement of the spray gun to identify the angle of the sprayed surface in real time during construction. The supply flow rate of the accelerator is then adjusted according to the relationship between the angle of the sprayed surface and the flow rate of the liquid accelerator. The liquid accelerator is fully mixed with the concrete slurry at the nozzle according to the adjusted flow rate and then sprayed out through the nozzle of the jet 3D printer to obtain high-performance jet 3D printed tunnel muck concrete adapted to the current sprayed surface.

[0025] Furthermore, the printing parameters of the jet 3D printer are set as follows: the air compressor pressure is set to ≥70KPa, the nozzle movement speed is ≥200mm / s, the nozzle diameter is ≥15mm, and the spray distance is ≥70mm, so that the thickness of a single-layer printed strip is ≥10mm and the interlayer bonding is tight.

[0026] Furthermore, the jetting 3D printer includes a feed hopper, an air compressor, a material pipe, an air pipe, a liquid pipe, a T-connector, a spray gun, a control system, and a robotic arm for controlling the movement of the spray gun.

[0027] The front end of the robotic arm is equipped with a sensor for detecting the angle of the sprayed surface and a spray gun for spraying.

[0028] A three-way adapter is installed on the spray gun behind the nozzle. The first port of the three-way adapter is connected to the inside of the spray gun, the second port is connected to the air compressor through the air pipe, and the third port is connected to the liquid quick-setting agent through the liquid pipe via the pump. A flow meter and a flow regulating valve are installed on the liquid pipe. A flow meter is also installed at the pump outlet of the feed hopper.

[0029] The control system is electrically connected to the robotic arm, the sensor that detects the angle of the sprayed surface, the flow regulating valve, and the flow meter.

[0030] Furthermore, the angle of the special sprayed surface is an angle value in the range of 0-180°, including at least 0°, 90°, and 180°, and may also include at least one of 30°, 60°, 120°, or 45° and 135°.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. This invention utilizes tunnel slag to completely replace natural sand as fine aggregate, rationally grading the fine aggregate and adding large-diameter tunnel slag as coarse aggregate to concrete. This significantly increases the amount of tunnel slag in concrete, improves the utilization rate of tunnel slag solid waste resources, and provides an efficient and energy-saving method for tunnel slag treatment. It achieves environmental protection and sustainable economic development, aligning with the national policy of tunnel slag resource utilization. Furthermore, the particle sizes of the coarse and fine aggregates meet the diameter requirements of the 3D printing nozzle used, avoiding nozzle clogging. The particle sizes of the coarse and fine aggregates should not be too large to ensure the formation of high-precision printing strips, meeting the performance requirements of jet 3D printing.

[0033] 2. In this invention, a two-component accelerator is used to modify the raw materials, so that the sprayed 3D printed concrete meets the performance requirements of rapid hardening and early strength. The powder accelerator component of the two-component accelerator is directly added to the mixture and mixed, while the liquid accelerator component is not directly added and is sprayed together with the concrete slurry, which ensures that the concrete printing window time is 30-50 minutes.

[0034] 3. Due to the working air pressure during spraying, sprayed 3D printed concrete is denser, has lower porosity, and exhibits stronger interlayer bonding, resulting in mechanical properties generally superior to traditional cast concrete. Compared to traditional concrete construction methods, sprayed 3D printed concrete can also reduce labor costs and material waste. Because sprayed 3D printing technology allows for on-demand adjustment of printing speed and path, the amount of material transported can be flexibly controlled according to actual needs, reducing waste generation. The formulated sprayed 3D printed tunnel muck concrete boasts high printing precision, is more economical in material usage, and avoids waste and resource depletion.

[0035] 4. This invention utilizes jet 3D printing technology and a two-component accelerator (powder and liquid components) to modify concrete, accelerating the curing speed and strength development of tunnel muck concrete. This meets the requirements for rapid hardening and early strength, overcoming the inherent long curing time of tunnel muck concrete, thereby improving construction quality and efficiency. The synergistic effect of the two-component accelerator optimizes the fluidity of the concrete, making it easier to jet mold, reducing collapse, misalignment, and falling off, and enhancing interlayer bond strength, thus improving the overall strength and stability of the printed parts.

[0036] 5. Based on the 3D printed digital model, sensors automatically identify the angle of the sprayed surface and intelligently adjust the amount of liquid accelerator added to cope with spraying 3D printing at multiple angles. This solves the problems of low intelligence and difficult quality control in traditional shotcrete construction.

[0037] 6. The concrete formula of this invention effectively improves the poor workability of tunnel muck concrete, while also possessing good 3D printability and mechanical properties, producing high-quality, high-strength tunnel muck concrete. This provides a new material combination for jet 3D printed concrete and has a certain promoting effect on the development of 3D printing. Detailed Implementation

[0038] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0039] This invention relates to a spray-printed 3D-printed tunnel muck concrete, comprising the following components in parts by weight: 870-900 parts cement, 50-60 parts fly ash, 50-80 parts silica fume, 500-600 parts fine aggregate, 500-600 parts coarse aggregate, 350-355 parts water, 20-50 parts liquid accelerator, 10-20 parts powder accelerator, and 1-2 parts water-reducing agent;

[0040] Both the coarse and fine aggregates are made from crushed stone waste during tunnel excavation. The fine aggregate consists of stone powder with a particle size of less than 0.075 mm, tunnel slag with a particle size of not less than 0.075 mm and not greater than 2.36 mm, and tunnel slag with a particle size of greater than 2.36 mm and not greater than 4.75 mm, and is configured in a ratio of (10-15%):(60-70%):(20-30%) to form a fine aggregate with a fineness modulus of 2.95-3.3. The coarse aggregate consists of tunnel slag with a particle size of greater than 4.75 mm and not greater than 8 mm. The crushing value of the coarse aggregate is <10%.

[0041] All dry materials, namely cement, fly ash, silica fume, fine aggregate, coarse aggregate, and powder accelerator, are added to a mixer in proportion. Then, a mixture of water-reducing agent and water is added to obtain concrete slurry. The concrete slurry is then placed in the feed hopper of a jet 3D printer. The concrete slurry and liquid accelerator are sprayed out together through the nozzle of the jet 3D printer to obtain jet 3D printed tunnel muck concrete.

[0042] The process of preparing 3D-printed tunnel muck concrete according to the present invention is as follows:

[0043] 1) Add all dry materials, namely cement, fly ash, silica fume, tunnel slag fine aggregate, coarse aggregate, and powder quick-setting agent, to the mixer in proportion and mix at a mixing speed of 100-140 rad / min for no less than 3 minutes; add the water-reducing agent and water in proportion to the mixer, mix at a mixing speed of 100-140 rad / min for 1.5-3 minutes, then mix rapidly at 360-400 rad / min for no less than 2.5 minutes to obtain concrete slurry;

[0044] 2) Place the concrete slurry into the feed hopper of the jet 3D printer, turn on the air compressor and feed hopper shaft of the jet 3D printer, and pump the liquid accelerator through the liquid pipe to the liquid interface. The liquid interface and the gas interface are connected to the side of the spray gun (located behind the nozzle). Print under the relevant printing parameters and 3D printing digital model. The concrete slurry and the liquid accelerator are sprayed out through the nozzle of the jet 3D printer to obtain a jet 3D printed concrete made from tunnel muck.

[0045] This invention features a sensor at the front end of the robotic arm that controls the movement of the spray gun. This sensor can automatically identify the angle of the surface to be sprayed. The flow rate of the liquid accelerator is controlled by a flow meter and regulating valve on the liquid pipe. The amount of liquid accelerator added is intelligently adjusted. During printing, the liquid accelerator and concrete slurry are fully mixed at the nozzle and then sprayed out.

[0046] In the following examples, the powder accelerator is a mixture prepared by mass ratio of alumina clinker: sodium carbonate: quicklime: anhydrous gypsum: alum mud = 4:2:1.5:1:1.5, and the fineness modulus of the fine aggregate is 2.95.

[0047] Example 1

[0048] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate and 500 parts coarse aggregate of limestone slag from the Xinxiang Tunnel Project in Henan Province, 350 parts water, 20 parts liquid accelerator, 10 parts powder accelerator, and 2 parts polycarboxylate superplasticizer. The method of implementation is jet 3D printing with a 0° angle on the sprayed surface.

[0049] The preparation steps are as follows:

[0050] 1) Add all dry materials, namely cement, fly ash, silica fume, tunnel slag fine aggregate, coarse aggregate, and powder quick-setting agent, to the mixer in proportion and mix at 120 rad / min for 3 minutes; mix the water-reducing agent and water in proportion, add the mixture to the mixer, mix at 120 rad / min for 1.5 minutes, and then mix at 380 rad / min for 3 minutes to obtain concrete slurry;

[0051] 2) Place the prepared concrete slurry into the feed hopper of the jet 3D printer, turn on the air compressor and feed hopper shaft of the jet 3D printer, and print under the relevant printing parameters and 3D printing digital model. The concrete slurry and liquid quick-setting agent are sprayed out through the nozzle of the jet 3D printer to obtain jet 3D printed tunnel muck concrete.

[0052] Example 2

[0053] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, 35 parts liquid accelerator, 10 parts powder accelerator, and 2 parts water-reducing agent. The method of implementation is jet 3D printing, with the sprayed surface angle at 90°. The preparation steps are the same as in Example 1.

[0054] Example 3

[0055] Weigh the following components by weight: 880 parts cement, 60 parts fly ash, 60 parts silica fume, 500 parts fine aggregate, 600 parts coarse aggregate, 355 parts water, 35 parts liquid accelerator, 20 parts powder accelerator, and 1 part water-reducing agent. The method of implementation is jet 3D printing, with the sprayed surface angle at 90°. The preparation steps are the same as in Example 1.

[0056] Example 4

[0057] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, 50 parts liquid accelerator, 10 parts powder accelerator, and 2 parts water-reducing agent. The method of implementation is jet 3D printing with a jetting angle of 180°. The preparation steps are the same as in Example 1.

[0058] Example 5

[0059] Weigh the following components by weight: 870 parts cement, 50 parts fly ash, 80 parts silica fume, 500 parts fine aggregate, 600 parts coarse aggregate, 355 parts water, 50 parts liquid accelerator, 20 parts powder accelerator, and 1 part water-reducing agent. The method of implementation is jet 3D printing with a jetting angle of 180°. The preparation steps are the same as in Example 1.

[0060] Compare with Example 1

[0061] Weigh the following components by weight: 1000 parts cement, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, 35 parts liquid accelerator, 10 parts powder accelerator, and 2 parts water-reducing agent. Do not add fly ash or silica fume. The method of implementation is jet 3D printing with a jetting angle of 90°. The preparation steps are the same as in Example 1.

[0062] Compare with Example 2

[0063] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, 20 parts liquid accelerator, 10 parts powder accelerator, and 2 parts water-reducing agent. The method of implementation is jet 3D printing, with the sprayed surface angle at 180°. The preparation steps are the same as in Example 1.

[0064] Compare with Example 3

[0065] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, 10 parts powder accelerator, and 2 parts water-reducing agent. No liquid accelerator is added. The method of implementation is jet 3D printing, with the sprayed surface angle at 90°. The preparation steps are the same as in Example 1.

[0066] Compare with Example 4

[0067] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, 35 parts liquid accelerator, and 2 parts water-reducing agent. No powder accelerator is added. The method of implementation is jet 3D printing, with the sprayed surface angle at 90°. The preparation steps are the same as in Example 1.

[0068] Compare with Example 5

[0069] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, and 2 parts water-reducing agent. No liquid or powder accelerators are added. The method of implementation is jet 3D printing with a jetting angle of 90°. The preparation steps are the same as in Example 1.

[0070] Compare with Example 6

[0071] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, 20 parts liquid accelerator, and 10 parts powder accelerator. No water-reducing agent is added. The method of implementation is jet 3D printing with a jetting angle of 180°. The preparation steps are the same as in Example 1.

[0072] Compare with Example 7

[0073] Weigh the following components by weight: 900 parts cement, 50 parts fly ash, 50 parts silica fume, 600 parts fine aggregate, 500 parts coarse aggregate, 350 parts water, 2 parts water-reducing agent, 20 parts liquid accelerator, and 10 parts powder accelerator. The method of implementation is pouring.

[0074] The preparation steps are as follows:

[0075] 1) Add all dry materials, namely cement, fly ash, silica fume, fine aggregate of tunnel slag, coarse aggregate of tunnel slag, and powder accelerator, to the mixer in proportion and mix at low speed for 3 minutes; mix the water-reducing agent and water in proportion, add the mixture to the mixer, mix at low speed for 1.5 minutes, then add the liquid accelerator and mix at high speed for 3 minutes to obtain concrete slurry;

[0076] 2) Place the prepared concrete slurry into a mold and vibrate it to obtain the poured concrete material.

[0077] The mortars prepared in Examples 1-5 and Comparative Examples 1-7 were printed layer by layer using a jet 3D printer or poured to obtain samples of each example and comparative example. The samples were then cured using standard curing methods, with a curing temperature of 18-22℃, a humidity of 90%-95%, and a curing age of 28 days.

[0078] Table 1. Dosage (parts) of each component in the tunnel muck concrete prepared in Examples 1-5 and Comparative Examples 1-7

[0079]

[0080] The printability and mechanical properties of the spray-printed 3D-printed tunnel muck concrete of this invention were tested as follows:

[0081] (1) Flowability: The flowability of the material was determined according to the national standard GB / T2419-2005 "Test for Flowability of Cementitious Mortar".

[0082] (2) Printing Accuracy: Single-layer strip printing experiment using jet printing. A 500mm long strip was jetted onto the surface to be printed, and the cross-sectional morphology of the single-layer strip was observed. Then, the contour of one side of the printed surface of the strip cross-section was fitted to quantitatively analyze the printing accuracy. The slope (K) and the sum of squared residuals (RSS) were used to evaluate the uniformity of strip thickness and flatness. High printing accuracy was defined as: 0 ≤ |K| < 0.1 and 0 ≤ RSS < 30; Low printing accuracy was defined as: |K| ≥ 0.1 or RSS ≥ 30.

[0083] More specifically, a 500mm long strip of 3D printing is sprayed vertically onto the sprayed surface. Then, three sections of the strip are randomly selected along the width direction and their profiles are fitted. The slope of the profile fitting line on one side of the printed surface and the sum of squared residuals are used as evaluation indicators. The average slope of the profile fitting line on one side of the printed surface is taken as K; the average sum of squared residuals of the profile fitting line on one side of the printed surface is taken as RSS.

[0084] (3) Constructability: Spray 3D printing continuous stacking test. A 500mm long strip was continuously printed onto the sprayed surface without time interval, and the cumulative number of printed layers for different groups was recorded. The more cumulative layers, the better the constructability of the spray 3D printed concrete material.

[0085] (4) Mechanical properties: For cast-in-place specimens, the compressive strength test of concrete was conducted in accordance with the national standard GB / T17671-2020 "Mechanical Strength Test of Cementitious Mortar". For 3D-printed specimens, test blocks were cut from the jet-printed 3D specimens to test the compressive and flexural strengths. Due to the mechanical anisotropy of jet-printed concrete, the mechanical properties of jet-printed 3D concrete in different directions were tested.

[0086] Table 2 shows the flowability, printing accuracy, constructability, compressive strength, and flexural strength of the tunnel muck concrete prepared in Examples 1-5 and Comparative Examples 1-7.

[0087]

[0088] Because the mechanical properties of jet-printed 3D-printed concrete are anisotropic, the compressive strength and flexural strength of the concrete in this invention are both based on the strength values ​​in the direction of minimum strength.

[0089] Based on Examples 1-5, Comparative Examples 1-7, and Table 2, it can be seen that the strength of jet-printed 3D specimens is affected by the printing accuracy and constructability of the concrete; concrete with poor printing accuracy and constructability also has low strength. Adding fly ash and silica fume improves the fluidity, printing accuracy, and constructability of tunnel muck concrete, thus increasing its mechanical properties. The dosage of liquid accelerator at different spray angles affects the printing accuracy and constructability of the concrete; insufficient accelerator dosage leads to excessive concrete fluidity, reduced printing accuracy and constructability, and worsened mechanical properties. The synergistic effect of the two-component accelerator optimizes the fluidity of the concrete and enhances the interlayer bond strength, enabling the concrete to meet the bond performance requirements at large spray angles, thereby improving the printing accuracy and constructability of the concrete and increasing its mechanical properties. The mechanical properties of jet-printed 3D concrete are superior to those of cast concrete. The compressive and flexural strengths of the spray-printed 3D-printed concrete of this invention can reach above 45 MPa and 8 MPa, respectively, with preferred strengths reaching 49.8 MPa and 8.9 MPa. This facilitates the practical engineering application of spray-printed 3D-printed tunnel muck concrete. Simultaneously, this invention improves the utilization rate of tunnel muck solid waste resources, which has positive significance for sustainable environmental development.

[0090] The above description is merely a technical solution of the present invention and is not intended to limit it. It should be noted that those skilled in the art can still modify or make equivalent substitutions to the above embodiments without departing from the principle of the present invention, and such modifications or equivalent substitutions should also be considered within the scope of protection of the present invention.

[0091] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A spray-printed 3D-printed tunnel muck concrete, characterized in that: The following components are included in parts by weight: 870-900 parts cement, 50-60 parts fly ash, 50-80 parts silica fume, 500-600 parts fine aggregate, 500-600 parts coarse aggregate, 350-355 parts water, 20-50 parts liquid accelerator, 10-20 parts powder accelerator, and 1-2 parts water-reducing agent. Both coarse and fine aggregates are made from crushed stone waste during tunnel excavation. Stone powder with a particle size of less than 0.075 mm, tunnel slag with a particle size of not less than 0.075 mm and not greater than 2.36 mm, and tunnel slag with a particle size of greater than 2.36 mm and not greater than 4.75 mm are screened and configured in a ratio of (10-15%):(60-70%):(20-30%) to form fine aggregate with a fineness modulus of 2.95-3.

3. Tunnel slag with a particle size of greater than 4.75 mm and not greater than 8 mm is used as coarse aggregate. The crushing value of coarse aggregate is <10%. All dry materials, namely cement, fly ash, silica fume, fine aggregate, coarse aggregate, and powder accelerator, are added to a mixer in proportion, and then a mixture of water-reducing agent and water is added to obtain concrete slurry. The concrete slurry is then placed in the feed hopper of the jet 3D printer, and the concrete slurry and liquid accelerator are sprayed out together through the nozzle of the jet 3D printer to obtain jet 3D printed tunnel muck concrete. When the sprayed surface angle is 0°, 90° and 180°, the dosage of liquid accelerator is 2%, 3.5% and 5% of the mass of cementitious material, respectively. The relationship between the sprayed surface angle and the dosage of liquid accelerator is fitted based on these three sets of data. For other sprayed surface angles, the corresponding dosage of liquid accelerator is determined according to the relationship between the two. The jet 3D printed tunnel muck concrete exhibits high printing precision, excellent uniformity in printing surface thickness, and high flatness; it also demonstrates good constructability, with no significant interlayer misalignment occurring when continuously stacking ≥20 layers at a 90° spray angle and no detachment when continuously stacking ≥15 layers at a 180° spray angle; its 28-day compressive strength exceeds 45 MPa; all properties meet the requirements of jet 3D printing and it can handle jet 3D printing at multiple angles; The high printing accuracy refers to 0≤|K|<0.1 and 0≤RSS<30. In the single-layer strip jet printing test, a single-layer strip with a length of 500mm is jetted vertically onto the jetting surface. Then, three cross-sections of the strip are fitted with cross-sectional contours. The average slope of the contour fitting line on one side of the three printed surfaces is taken as K, and the average of the sum of squared residuals of the contour fitting lines on one side of the three printed surfaces is taken as RSS.

2. The spray-printed 3D-printed tunnel muck concrete according to claim 1, characterized in that: The powder accelerator is at least three of the following: alumina clinker, sodium carbonate, quicklime, anhydrous gypsum, and alum mud; the printing window time for the concrete slurry is 30-50 minutes, and the flowability printing window for the sprayed 3D printed concrete material is 180-190 mm.

3. The spray-printed 3D-printed tunnel muck concrete according to claim 2, characterized in that: The powder accelerator is a mixture prepared according to the mass ratio of alumina clinker: sodium carbonate: quicklime: anhydrous gypsum: alum mud = 4:2:1.5:1:1.

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4. The construction method for spraying 3D printed tunnel muck concrete according to any one of claims 1-3, characterized in that: The construction method includes the following steps: 1) The concrete slurry consists of: 870-900 parts cement, 50-60 parts fly ash, 50-80 parts silica fume, 500-600 parts fine aggregate, 500-600 parts coarse aggregate, 350-355 parts water, 10-20 parts powder accelerator, and 1-2 parts water-reducing agent. All dry materials, namely cement, fly ash, silica fume, fine aggregate, coarse aggregate, and powder accelerator, are added to a mixer and mixed until homogeneous. The water-reducing agent is then mixed with water in the specified proportions and added to the mixer, and mixed until homogeneous to obtain the concrete slurry. Both the coarse and fine aggregates are made from crushed stone waste from tunnel excavation. The fineness modulus of the fine aggregate is 2.95-3.3, and the coarse aggregate has a screened particle size greater than 4.75 mm and not greater than 8 mm. 2) When the sprayed surface is defined as the ground, the sprayed surface angle is 0°; when the sprayed surface is the top surface, the sprayed surface angle is 180°; when the sprayed surface is a vertical surface, the sprayed surface angle is 90°; other sprayed surface angles are determined according to the definition. 3) Given the diameter of the concrete slurry supply pipe and the pump flow rate, and the printing parameters of the jet 3D printer, conduct jet 3D printing experiments to obtain the printability and mechanical properties of the sprayed concrete under different liquid accelerator flow rates at a special sprayed surface angle. Select the liquid accelerator flow rate and the corresponding sprayed surface angle when the printability and mechanical properties are optimal to form a set of data pairs. Obtain multiple sets of data pairs and use multiple sets of data pairs to fit the relationship between the sprayed surface angle and the liquid accelerator flow rate. 4) During actual construction, the concrete slurry is placed in the feed hopper of the jet 3D printer. The liquid accelerator is pumped to the liquid interface of the jet 3D printer through the liquid pipe. A sensor is set at the front end of the robotic arm used to control the movement of the spray gun to identify the angle of the sprayed surface in real time during construction. The supply flow rate of the accelerator is adjusted according to the relationship between the angle of the sprayed surface and the flow rate of the liquid accelerator. The liquid accelerator is fully mixed with the concrete slurry at the nozzle according to the adjusted flow rate and sprayed out through the nozzle of the jet 3D printer to obtain high-performance jet 3D printed tunnel muck concrete adapted to the current sprayed surface.

5. The construction method according to claim 4, characterized in that, The printing parameters for the jet 3D printer are set as follows: air compressor pressure ≥70 kPa, nozzle movement speed ≥200mm / s, nozzle diameter ≥15mm, and spray distance ≥70mm, so that the thickness of a single-layer printed strip is ≥10mm and the interlayer bonding is tight.

6. The construction method according to claim 5, characterized in that, The jetting 3D printer includes a feed hopper, an air compressor, a feed pipe, an air pipe, a liquid pipe, a T-connector, a spray gun, a control system, and a robotic arm for controlling the movement of the spray gun. The front end of the robotic arm is equipped with a sensor for detecting the angle of the sprayed surface and a spray gun for spraying. A three-way adapter is installed on the spray gun behind the nozzle. The first port of the three-way adapter is connected to the inside of the spray gun, the second port is connected to the air compressor through the air pipe, and the third port is connected to the liquid quick-setting agent through the liquid pipe via the pump. A flow meter and a flow regulating valve are installed on the liquid pipe. A flow meter is also installed at the pump outlet of the feed hopper. The control system is electrically connected to the robotic arm, the sensor that detects the angle of the sprayed surface, the flow regulating valve, and the flow meter.

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