Recycled aggregate pretreatment method and device for 3D printing full-recycled concrete

Abstract

The invention discloses a recycled aggregate pretreatment method for 3D printing full-recycled concrete, which comprises the following steps: step 1, crushing and sieving treatment, step 2, jet cracking treatment, step 3, centrifugal impact treatment, step 4, interface modification treatment, and step 5, dynamic grading treatment. The device comprises a crushing mechanism, a jet impact mechanism, a centrifugal impact mill and a modification treatment mechanism, according to the invention, the recycled concrete is treated by a three-order treatment method of high-pressure jet flow, centrifugal impact grinding and microwave activation, so that the porosity of the recycled aggregate is effectively reduced, the interlayer bonding strength of the aggregate is improved, and the problems existing in the existing simple crushing treatment of the recycled aggregate are solved; meanwhile, microwave activation and biomimetic mineralization are combined to treat the recycled aggregate, and double breakthrough of the performance and economical efficiency of the aggregate is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of construction solid waste, and in particular to a method and device for pretreating recycled aggregate for 3D printing fully recycled concrete. Background Art

[0002] Concrete is currently an irreplaceable basic building material. 3D printed concrete is a new construction technology that combines 3D printing technology with traditional concrete materials. It uses a printer controlled by a computer software program to quickly print concrete materials layer by layer into complex structures. Traditional 3D printed concrete materials mainly use cement as the gelling component, but cement production not only consumes a lot of energy, but also emits a large amount of carbon dioxide.

[0003] Traditional recycled aggregates are simply crushed and screened, retaining their original defects and resulting in a porosity greater than 25%. 3D printing places higher demands on material fluidity and setting time, and high porosity directly affects the stability of the 3D printed slurry. At the same time, existing water washing methods cause secondary pollution and cannot eliminate weak interfacial bonding areas. Commercial chemical strengtheners (such as epoxy resins) are expensive and affect material sustainability. Therefore, the present invention proposes a recycled aggregate pretreatment method and device for 3D printing fully recycled concrete to address the problems existing in the prior art. Summary of the Invention

[0004] In response to the above problems, the purpose of the present invention is to propose a recycled aggregate pretreatment method and device for 3D printing fully recycled concrete. The recycled aggregate pretreatment method and device for 3D printing fully recycled concrete treat the recycled concrete through a three-stage treatment method of high-pressure jet, centrifugal impact mill and microwave activation, which effectively reduces the porosity of the recycled aggregate, improves the interlayer bonding strength of the aggregate, and solves the problems existing in the simple crushing treatment of existing recycled aggregates; at the same time, microwave activation and bionic mineralization are combined to treat the recycled aggregate, achieving a double breakthrough in aggregate performance and economy.

[0005] To achieve the purpose of the present invention, the present invention is implemented by the following technical solution: a recycled aggregate pretreatment method for 3D printing fully recycled concrete, comprising the following steps:

[0006] Step 1: Crushing and screening: first pour the recycled concrete into the crushing equipment for crushing and screening to obtain small-sized recycled aggregate;

[0007] Step 2: jet pyrolysis treatment, using a high-pressure jet liquid at a pressure of 30-50 MPa to perform directional jet impact on the recycled aggregate, forming a micro-crack network with a depth of 100-500 μm on its surface to obtain pyrolysis aggregate;

[0008] Step 3: Centrifugal impact treatment: inject the cracked aggregate into a centrifugal impact mill and grind it at a speed of 8000-12000 rpm for 1-3 minutes to cause a phase change in the surface crystal structure to obtain surface reconstructed aggregate;

[0009] Step 4: Interface modification treatment: In a 2450 MHz microwave field, the pH value is stepwise controlled, and an aluminosilicate mineralizer and nanocellulose solution are simultaneously sprayed to form an interface transition layer;

[0010] Step 5: Dynamic grading treatment: Use a laser particle size sensor to monitor the aggregate particle size distribution in real time, and use a cyclone separator to optimize the grading process to obtain recycled aggregate.

[0011] A further improvement is that: in step 1, after crushing, the aggregate is screened through a 6-mesh sieve, and the aggregate with a particle size of less than 4 mm after screening is recovered as fine aggregate, and the aggregate with a particle size greater than 4 mm is treated as small-size recycled aggregate and enters the next step of processing.

[0012] A further improvement is that in step 2, a jet nozzle with a spiral oscillating structure having an oscillation frequency of 5-15 Hz is used for jet treatment, and the jet liquid is a water-based jet liquid containing 0.1-0.3 wt% of a surfactant.

[0013] A further improvement is that the grinding medium of the centrifugal impact mill in step 3 is corundum balls with a diameter of 3-8 mm, and the loading amount accounts for 60-70% of the volume of the grinding chamber.

[0014] Further improvements are: in step 4, the microwave power density is 80-150W / g, and the ratio of irradiation time t to aggregate mass m satisfies t=2.5×m -1 , the unit of m is kg; the aluminosilicate mineralizer is prepared by mixing sodium silicate and metakaolin sol in a mass ratio of 3:1, and the injection pressure of the aluminosilicate mineralizer is 0.5-1.2 MPa.

[0015] Further improvements are: in step 4, the pH value is adjusted to a stepwise change of 11→4→9; the thickness of the interface transition layer finally formed is 50-200 nm; and in step 5, the rotation speed of the cyclone separator is 1500-3000 rpm.

[0016] A recycled aggregate pretreatment device for 3D printing fully recycled concrete comprises a crushing mechanism, a jet impact mechanism, a centrifugal impact mill and a modification treatment mechanism, wherein the jet impact mechanism comprises a treatment box, an articulated mesh plate, an articulated rod, a high-pressure jet nozzle and a feeding mesh plate, wherein one side of the crushing mechanism is connected to the treatment box via a lifting spiral drum, and the lifting spiral drum drives the screw lifting rod through a motor to send the crushed and screened concrete aggregate into the jet impact mechanism, the treatment box is symmetrically provided with articulated mesh plates, the articulated mesh plates are symmetrical in structure, an articulated rod is provided between the bottom of the articulated mesh plates and the side wall of the treatment box, a high-pressure jet nozzle is symmetrically provided at the top of the treatment box, the high-pressure jet nozzle is connected to an external high-pressure infusion pipe to spray jet liquid, and the high-pressure jet nozzle is driven by a servo motor to swing and adjust, a feeding mesh plate is tiltedly provided in the treatment box below the articulated mesh plate, a centrifugal impact mill is provided below the treatment box to grind the aggregate, and one side of the centrifugal impact mill is connected to the modification treatment mechanism.

[0017] Further improvements are as follows: the crushing mechanism includes a crushing box, a crushing roller, a screening net, a connecting port and a discharge port; the crushing rollers are symmetrically arranged in the crushing box; the crushing rollers are symmetrically arranged in two groups and are vertically staggered into an upper and lower layer for crushing the recycled concrete; a screening net is arranged below the crushing rollers; the screening net is detachable and inclined toward the side of the lifting spiral drum, so that it is easy to replace according to the aggregate particle size requirements; the inclined end of the screening net is connected to the lower end of one side of the lifting spiral drum through the connecting port; a discharge port is provided on the other side below the crushing box for centralized recovery of the screened fine aggregate.

[0018] Further improvements are: the pipe on the other side of the upper end of the lifting spiral cylinder is connected to the top of the processing box, and a drain pipe is provided under the processing box to discharge the sprayed jet liquid and filter and recycle it through a recovery device, and the inclined end of the discharge screen is connected to the centrifugal impact mill through a pipe.

[0019] Further improvements are as follows: the modification treatment mechanism includes a microwave box, a microwave generator, a spray pipe, a vibration motor and a vibration loading platform; the pipeline on one side of the centrifugal impact mill is connected to the microwave box; the microwave generators are symmetrically arranged at the top and both sides of the microwave box; the spray pipes are symmetrically arranged in the middle section of the microwave box; the spray pipes are connected to the external aluminosilicate mineralizer and nanocellulose mixed solution box; a vibration loading platform is arranged at the bottom of the microwave box through a vibration motor; the vibration loading platform can vibrate and roll the aggregate so that it is evenly irradiated and sprayed.

[0020] The beneficial effects of the present invention are as follows: the present invention processes recycled concrete through a three-stage treatment method of high-pressure jet, centrifugal impact mill and microwave activation, effectively reducing the porosity of recycled aggregate, improving the interlayer bonding strength of aggregate, and solving the problems existing in the simple crushing treatment of existing recycled aggregate;

[0021] At the same time, this invention combines microwave activation with bionic mineralization for the first time to process recycled aggregate, achieving a double breakthrough in aggregate performance and economy. The prepared recycled aggregate is adapted to the characteristics of 3D printing process, solving the problems of interlayer bonding strength and volume stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of the method of Example 1 of the present invention.

[0023] Figure 2 This is a main cross-sectional structural diagram of embodiment 2 of the present invention.

[0024] Figure 3 This is a main cross-sectional structural diagram of the microwave box according to embodiment 2 of the present invention.

[0025] Among them: 1. Centrifugal impact mill; 2. Processing box; 3. Articulated mesh plate; 4. Articulated rod; 5. High-pressure jet nozzle; 6. Discharge mesh plate; 7. Lifting screw; 8. Crushing box; 9. Crushing roller; 10. Screening net; 11. Connection port; 12. Discharge port; 13. Drain pipe; 14. Microwave box; 15. Microwave generator; 16. Jet pipe; 17. Vibration motor; 18. Vibration loading platform. DETAILED DESCRIPTION

[0026] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the examples. The examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0027] Traditional recycled aggregate processing has the following defects:

[0028] As for physical treatment methods, traditional methods only use jaw crushers for processing, with a crushing ratio of ≤5 and an aggregate angular coefficient of >1.8, which leads to a decrease in the fluidity of the 3D printing slurry and a loss of slurry expansion of >30%. At the same time, there are also methods using high-pressure jet technology. For example, the announcement number CN110563218A discloses a method using high-pressure jet treatment. The crack depth produced by the method is only 200-300μm, the cracks are relatively shallow, and the weak interface bonding area cannot be eliminated. SEM shows that the interface porosity is >18%.

[0029] As for chemical modification treatment methods, traditional methods also use epoxy resin to replace the interface bonding strength, but there is a mismatch in thermal expansion coefficients and the cost is relatively high; the use of silane coupling agent treatment requires an acidic environment with a pH value of 4, which will lead to an increase in the dissolution of Ca(OH)2 on the aggregate surface, accelerate the carbonization of the aggregate, and affect the quality of the aggregate.

[0030] The recycled aggregates processed by traditional methods have defects such as high porosity (average 25-35%) and high water absorption (water absorption > 12%), which leads to a 40% drop in peel strength and a shrinkage rate > 600×10 -6 , problems such as interlayer delamination and poor dimensional stability occur.

[0031] For 3D printed concrete, the paste must meet both thixotropy and long-term stability. The thixotropic index must be greater than 1.8 and the water bleeding rate must be less than 3%. However, the recycled aggregate processed by traditional methods has high water absorption, with a 24-hour water absorption of more than 15%, which can cause paste segregation and a stratification degree of more than 5%, seriously affecting the quality of 3D printed concrete.

[0032] At the same time, the interval between printing layers is usually greater than 30 minutes, while the thickness of the interface transition zone (ITZ) of existing recycled aggregates is greater than 150μm. The ITZ of traditional concrete is ≈50μm, which becomes a weak point in mechanical properties, resulting in a 50% decrease in fracture energy. The current cost of commercial 3D printing concrete needs to be controlled at 600 yuan / m 3 The current recycled aggregate processing cost is more than 450 yuan / m 3 .

[0033] This invention uses multi-physical field collaboration to achieve aggregate performance improvement and energy consumption control, proposes a biomimetic mineralization modification strategy, replaces epoxy resin with aluminosilicate mineralizer, greatly reduces costs, and reduces the ITZ thickness to 75μm. The treated aggregate is applied to 3D printed concrete and achieves good results.

[0034] Example 1

[0035] according to Figure 1 As shown, this embodiment provides a method for pretreating recycled aggregate for 3D printing fully recycled concrete, comprising the following steps:

[0036] Step 1: crushing and screening. First, pour the recycled concrete into the crushing equipment for crushing and screening through a 6-mesh screen to obtain small-sized recycled aggregate;

[0037] After screening, aggregates with a particle size of less than 4 mm are recycled as fine aggregate, and aggregates larger than 4 mm are treated as small-sized recycled aggregate in the next step.

[0038] Step 2: jet pyrolysis treatment, using a high-pressure jet liquid at a pressure of 50 MPa to perform directional jet impact on the recycled aggregate, forming a micro-crack network with a depth of 100-500 μm on its surface to obtain pyrolysis aggregate;

[0039] A jet nozzle with a spiral oscillating structure and an oscillation frequency of 10 Hz is used for jet treatment to make the micro cracks evenly distributed along the circumference of the aggregate. The jet fluid uses a water-based jet fluid containing 0.3 wt% surfactant to reduce surface tension and promote crack propagation.

[0040] Step 3: Centrifugal impact treatment: inject the cracked aggregate into the centrifugal impact mill 1 and grind it at a speed of 12000 rpm for 1.5 minutes to cause a phase change in the surface crystal structure to obtain surface reconstructed aggregate;

[0041] The grinding media of the centrifugal impact mill 1 is corundum balls with a diameter of 3-8 mm, and the loading capacity accounts for 70% of the grinding chamber volume. The speed difference of the centrifugal impact mill classifying wheel is set (main rotor 12000 rpm vs. classifying wheel 8000 rpm) to achieve particle size classification control.

[0042] Step 4: Interface modification treatment: In a 2450 MHz microwave field, the pH value is adjusted to a stepwise change from 11 to 4 to 9, and a 50-200 nm interface transition layer is formed by simultaneously spraying an aluminosilicate mineralizer and a nanocellulose solution;

[0043] The microwave power density is 150W / g, and the ratio of irradiation time t to aggregate mass m satisfies t=2.5×m -1 , the unit of m is kg;

[0044] The aluminosilicate mineralizer is prepared by mixing sodium silicate and metakaolin sol in a mass ratio of 3:1, and the injection pressure of the aluminosilicate mineralizer is 1.2 MPa.

[0045] Step 5: Dynamic grading treatment: The aggregate particle size distribution is monitored in real time by a laser particle size sensor, and a cyclone separator with a rotation speed of 3000 rpm is connected to perform grading optimization treatment to obtain recycled aggregate.

[0046] The crushing value of the recycled aggregate pretreated according to the above method is ≤12%, the water absorption rate is ≤4.5%, and the 24h water absorption rate is ≤0.05g / min·cm 2 When used in 3D printing slurry, the slurry expansion is ≥240mm and the delamination is ≤1.5%.

[0047] Example 2

[0048] according to Figure 2 and Figure 3As shown, this embodiment provides a recycled aggregate pretreatment device for 3D printing fully recycled concrete, including a crushing mechanism, a jet impact mechanism, a centrifugal impact mill 1 and a modification treatment mechanism. The jet impact mechanism includes a treatment box 2, a hinged mesh plate 3, a hinged rod 4, a high-pressure jet nozzle 5 and a feeding mesh plate 6. One side of the crushing mechanism is connected to the treatment box 2 through a lifting spiral cylinder 7. The lifting spiral cylinder drives the spiral lifting rod through a motor to send the crushed and screened concrete aggregate into the jet impact mechanism. The treatment box 2 is symmetrically provided with hinged mesh plates 3, and the hinged mesh plates It is a symmetrical structure. A hinged rod 4 is provided between the bottom of the hinged mesh plate 3 and the side wall of the processing box 2. The opening and closing of the two hinged mesh plates are controlled by the hinged rod. A high-pressure jet nozzle 5 is symmetrically rotated on the upper part of the processing box 2. The high-pressure jet nozzle is connected to an external high-pressure infusion tube to spray jet liquid. At the same time, the high-pressure jet nozzle is driven by a servo motor for swing adjustment. A discharge mesh plate 6 is tilted in the processing box 2 below the hinged mesh plate 3. A centrifugal impact mill 1 is provided below the processing box 2 to grind the aggregate. A modification processing mechanism is connected to one side of the centrifugal impact mill 1.

[0049] The crushing mechanism includes a crushing box 8, a crushing roller 9, a screening net 10, a connecting port 11 and a discharge port 12. The crushing rollers 9 are symmetrically arranged in the crushing box 8. There are two groups of crushing rollers symmetrically arranged and vertically staggered into upper and lower layers for crushing the recycled concrete. A screening net 10 is arranged below the crushing rollers 9. The screening net 10 is detachable and tilted toward the side of the lifting spiral drum 7, which is convenient for replacement according to the aggregate particle size requirements. The inclined end of the screening net 10 is connected to the lower end of one side of the lifting spiral drum 7 through the connecting port 11. A discharge port 12 is provided on the other side below the crushing box 8 to centrally recover the fine aggregate screened.

[0050] The pipe on the other side of the upper end of the lifting spiral drum 7 is connected to the top of the processing box 2. A drain pipe 13 is provided under the processing box 2 to discharge the ejected jet liquid and filter and recycle it through a recovery device. The inclined end of the discharge screen plate 6 is connected to the centrifugal impact mill 1 through a pipe.

[0051] The modification treatment mechanism includes a microwave box 14, a microwave generator 15, a spray pipe 16, a vibration motor 17 and a vibration loading platform 18. The microwave box 14 is connected to the pipeline on one side of the centrifugal impact mill 1. The microwave generator 15 is symmetrically arranged at the top and both sides of the microwave box 14. The spray pipe 16 is symmetrically arranged in the middle section of the microwave box 14. The spray pipe is connected to the external aluminosilicate mineralizer and nanocellulose mixed solution tank, which is used to spray the aluminosilicate mineralizer and nanocellulose on the surface of the aggregate to form an interface transition layer. A vibration loading platform 18 is arranged at the bottom of the microwave box 14 through the vibration motor 17. The vibration loading platform can vibrate and tumble the aggregate so that it is evenly irradiated and sprayed. The sprayed aggregate enters the subsequent dynamic grading process to complete the pretreatment of the recycled aggregate.

[0052] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for pretreating recycled aggregate for 3D printing fully recycled concrete, characterized in that: The following steps are involved: Step 1: Crushing and screening: first pour the recycled concrete into the crushing equipment for crushing and screening to obtain small-sized recycled aggregate; Step 2: jet pyrolysis treatment, using a high-pressure jet liquid at a pressure of 30-50 MPa to perform directional jet impact on the recycled aggregate, forming a micro-crack network with a depth of 100-500 μm on its surface to obtain pyrolysis aggregate; Step 3: Centrifugal impact treatment: inject the cracked aggregate into a centrifugal impact mill (1) and grind it at a speed of 8000-12000 rpm for 1-3 minutes to cause a phase change in the surface crystal structure to obtain a surface reconstructed aggregate; Step 4: Interface modification treatment: In a 2450 MHz microwave field, the pH value is stepwise controlled, and an aluminosilicate mineralizer and nanocellulose solution are simultaneously sprayed to form an interface transition layer; Step 5: Dynamic grading treatment: Use a laser particle size sensor to monitor the aggregate particle size distribution in real time, and use a cyclone separator to optimize the grading process to obtain recycled aggregate.

2. A method for pretreating recycled aggregate for 3D printing of fully recycled concrete according to claim 1, characterized in that: After crushing in step 1, the aggregate is sieved through a 6-mesh sieve. Aggregates with a particle size of less than 4 mm after screening are recovered as fine aggregates, and aggregates with a particle size greater than 4 mm are treated as small-sized recycled aggregates and enter the next step of processing.

3. The method for pretreating recycled aggregate for 3D printing of fully recycled concrete according to claim 1, characterized in that: In the step 2, a jet nozzle with a spiral oscillating structure and an oscillation frequency of 5-15 Hz is used for jet treatment, and the jet liquid is a water-based jet liquid containing 0.1-0.3 wt% of a surfactant.

4. The method for pretreating recycled aggregate for 3D printing of fully recycled concrete according to claim 1, characterized in that: The grinding medium of the centrifugal impact mill (1) in step 3 is a corundum ball with a diameter of 3-8 mm, and the loading amount accounts for 60-70% of the volume of the grinding chamber.

5. The method for pretreating recycled aggregate for 3D printing of fully recycled concrete according to claim 1, characterized in that: In the fourth step, the microwave power density is 80-150 W / g, and the ratio of the irradiation time t to the aggregate mass m satisfies t=2.5×m -1 , the unit of m is kg; the aluminosilicate mineralizer is prepared by mixing sodium silicate and metakaolin sol in a mass ratio of 3:1, and the injection pressure of the aluminosilicate mineralizer is 0.5-1.2 MPa.

6. The method for pretreating recycled aggregate for 3D printing of fully recycled concrete according to claim 1, characterized in that: In the step 4, the pH value is adjusted to a stepwise change of 11→4→9; the thickness of the finally formed interface transition layer is 50-200 nm; and in the step 5, the rotation speed of the cyclone separator is 1500-3000 rpm.

7. A recycled aggregate pretreatment device for 3D printing fully recycled concrete, characterized by: The invention comprises a crushing mechanism, a jet impact mechanism, a centrifugal impact mill (1) and a modification treatment mechanism, wherein the jet impact mechanism comprises a treatment box (2), a hinged mesh plate (3), a hinged rod (4), a high-pressure jet nozzle (5) and a discharge mesh plate (6); one side of the crushing mechanism is connected to the treatment box (2) via a lifting spiral drum (7); the treatment box (2) is symmetrically provided with hinged mesh plates (3); a hinged rod (4) is provided between the lower side of the hinged mesh plates (3) and the side wall of the treatment box (2); a high-pressure jet nozzle (5) is symmetrically rotated in the upper part of the treatment box (2); a discharge mesh plate (6) is tilted in the treatment box (2) below the hinged mesh plate (3); a centrifugal impact mill (1) is provided below the treatment box (2); and one side of the centrifugal impact mill (1) is connected to the modification treatment mechanism.

8. The recycled aggregate pretreatment device for 3D printing fully recycled concrete according to claim 7, characterized in that: The crushing mechanism comprises a crushing box (8), a crushing roller (9), a screening net (10), a connecting port (11) and a discharge port (12). The crushing roller (9) is symmetrically arranged in the crushing box (8), and a screening net (10) is arranged below the crushing roller (9). The screening net (10) is detachable and inclined toward the side of the lifting spiral drum (7). The inclined end of the screening net (10) is connected to the lower end of one side of the lifting spiral drum (7) through the connecting port (11). The discharge port (12) is arranged on the other side below the crushing box (8).

9. The recycled aggregate pretreatment device for 3D printing fully recycled concrete according to claim 7, characterized in that: The other side of the upper end of the lifting spiral drum (7) is connected to the top of the processing box (2) through a pipe. A drainage pipe (13) is provided below the processing box (2). The inclined end of the discharge screen (6) is connected to the centrifugal impact mill (1) through a pipe.

10. The recycled aggregate pretreatment device for 3D printing fully recycled concrete according to claim 7, characterized in that: The modification treatment mechanism comprises a microwave box (14), a microwave generator (15), an injection pipe (16), a vibration motor (17) and a vibration loading platform (18); a pipeline on one side of the centrifugal impact mill (1) is connected to the microwave box (14); the microwave generator (15) is symmetrically arranged at the top and both sides of the microwave box (14); the injection pipe (16) is symmetrically arranged in the middle section of the microwave box (14); and the vibration loading platform (18) is provided at the bottom of the microwave box (14) via the vibration motor (17).

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