NL2031562B1

NL2031562B1 - Curing method for magnesium-based cement concrete products and dedicated system thereof

Info

Publication number: NL2031562B1
Application number: NL2031562A
Authority: NL
Inventors: Luo Fuming; Kou Shicong; Cui Peng
Original assignee: Tianying Shenzhen Ecological Building Materials Tech Co Ltd
Priority date: 2021-05-26
Filing date: 2022-04-12
Publication date: 2023-04-04
Also published as: CN113500687A; CN113500687B; NL2031562A

Abstract

Disclosed are a curing method for magnesium—based cement concrete products and. a dedicated. system. thereof. Temperature—controlled carbonation curing, humidity—controlled carbonation curing, and storage carbonation. curing are provided. for the magnesium—based cement concrete product; the magnesium—based cement concrete product is kept in an appropriate carbon dioxide gas concentration, carbon dioxide gas pressure, ambient temperature, and relative humidity environment in a hydration. process, low— temperature curing and carbonation curing are combined to improve the internal microstructure of the magnesium—based cement, thereby enhancing the compactness, macro—mechanical properties and durability of Inagnesium—based. cement; the curing' method. enables water slag sand and soil dreg to be used directly in the concrete product and enables magnesium—based standard sand to participate in the hydration reaction instead of quartz standard sand, thereby making a contribution to reducing carbon emissions in the construction sector and the whole society and providing very obvious technical advantages and economic and ecological benefits.

Description

CURING METHOD FOR MAGNESIUM-BASED CEMENT CONCRETE PRODUCTS AND

DEDICATED SYSTEM THEREOF

TECHNICAL FIELD

The present invention relates to the curing of concrete prod- ucts, in particular to a curing method for magnesium-based cement concrete products and a dedicated system thereof.

BACKGROUND ART

Magnesium-based cement, including magnesium oxychloride ce- ment, magnesium oxysulfate cement and magnesium phosphate cement, is a kind of low-carbon cement with good development prospects.

Magnesium-based cement generally features a high degree of early hydration and early strength, and the early temperature control and carbon dioxide curing of magnesium-based cement are beneficial to reducing a temperature stress inside the hardened slurry of magnesium-based cement, so that early curing becomes particularly important; the 3D-printed magnesium-based cement products without dies particularly require early temperature control and carbon di- oxide curing to reduce microcracks; however, curing chambers available in the market mainly realize curing by a preset constant temperature or a certain concentration of carbon dioxide gas, and cannot achieve low-temperature and carbon dioxide curing based on the hydration characteristics of the magnesium-based cement, espe- cially for early curing systems (within 3 days) for different kinds of magnesium-based cement; there is a lack of a curing meth- od and a dedicated system for different magnesium-based cement products.

At present, 3D printers in the construction field are mainly designed based on Portland cement-based materials. Magnesium-based cement, because its rate and amount of heat release after adding water are higher than those of the ordinary Portland cement, has a relatively high requirement for 3D printers, and especially for 3D printheads. In particular, the 3D printhead should meet the re- quirements of enhancing carbonation of magnesium-based cement and reducing hydration heat. However, the printhead of the current 3D printers cannot meet such requirements.

Besides, the water slag sand from steel plants cannot be uti- lized generally until it is ground into powder, and there is no effective technical solution for the efficient direct resource utilization of the water slag sand at present. Meanwhile, quartz standard sand can be involved only as an aggregate in 3D printing {additive manufacturing). Failure of quartz standard sand to par- ticipate in the hydration reaction results in a microscopic defect that a bonding interface between quartz standard sand and cement slurry becomes hardened slurry.

Moreover, a large number of construction wastes are produced every year in China, of which more than 70% are soil dreg. As the soil dreg is detrimental impurities in silicate concrete and can- not be added directly to the silicate concrete, it is difficult to solve the direct use problem of soil dreg.

SUMMARY

The present invention provides a curing method for magnesium- based cement concrete products and a dedicated system thereof to at least solve the above-mentioned problems in the prior art, in- cluding lack of a curing method and a dedicated system for differ- ent magnesium-based cement products, failed direct use of water slag sand and soil dreg, and failed participation of quartz stand- ard sand in the hydration reaction.

The present invention provides a curing method for magnesium- based cement concrete products, including the following steps:

S101, reference samples and test samples are arranged for a concrete product;

S102, temperature-controlled carbonation curing is performed, and a temperature of the test samples is adjusted according to that of the reference samples, wherein a carbon dioxide concentra- tion of the temperature-controlled carbonation curing is 75-95%, a carbon dioxide gas pressure is 80-90kPa, and a temperature is be- low -60°C; 8103, humidity-controlled carbonation curing is performed for the concrete product cured by S102, wherein a relative humidity of the humidity-controlled carbonation curing is 80-95%; and 3104, storage carbonation curing is performed for the con- crete product cured by S103, wherein a carbon dioxide concentra- tion of the storage carbonation curing is 80-95%, a temperature is 20-35°C, and a relative humidity is 80-96%.

Further, the humidity-controlled carbonation curing is curing by dry ice, and the temperature-controlled carbonation curing and the storage carbonation curing are curing by carbon dioxide gas; the preparation of the reference samples includes the follow- ing steps: temperature sensors are pre-embedded in the concrete product prior to final setting; and then the concrete product is cut, pieces with the temperature sensors are taken as reference samples, and pieces without the temperature sensors are taken as test samples; the temperature-controlled carbonation curing includes the following steps: the temperature sensors of the reference samples are connected with temperature controllers, and the temperature controllers adjust a temperature of the test samples according to that of the reference samples for the temperature-controlled car- bonation curing; and when a surface temperature of the reference samples and the test samples falls to a room temperature again, humidity- controlled carbonation curing is performed for the reference sam- ples and the test samples.

The present invention provides a dedicated curing system for magnesium-based cement concrete products, wherein the dedicated system includes temperature-controlled carbonation chambers, hu- midity-controlled carbonation chambers, and storage curing cham- bers; and a carbon dioxide device is arranged in each of the tempera- ture-controlled carbonation chambers and each of the storage cur- ing chambers, and a dry ice device is arranged in each of the hu- midity-controlled carbonation chambers.

Further, each of the temperature-controlled carbonation cham- bers includes a temperature controller, a cooling device, and a heating device.

A reference sample platform and a test sample platform are arranged in each of the temperature-controlled carbonation cham- bers; the cooling device and the heating device are arranged in the periphery of each test sample platform, the temperature con- troller is connected to the test sample platform by the tempera- ture sensor, and the cooling device and the heating device are electrically connected with the temperature controller; dry ice is arranged around the concrete product, and a carbon dioxide concen- tration and a temperature in each of the temperature-controlled carbonation chambers are adjusted by controlling an addition amount of dry ice.

Each of the humidity-controlled carbonation chambers includes a test sample chamber, a dry ice storage chamber, a dry ice regu- lator, and a relative humidity regulator; the test sample chamber is connected with the dry ice storage chambers by the temperature sensor and the dry ice regulator; and the test sample chamber is connected with the relative humidity regulator by a relative hu- midity sensor.

A temperature and humidity regulator is arranged in each of the storage curing chambers.

Each of the carbon dioxide devices includes a carbon dioxide gas regulator, a carbon dioxide gas cylinder, and a carbon dioxide gas concentration sensor, and the carbon dioxide gas regulator is connected with the carbon dioxide gas cylinder and the carbon di- oxide gas concentration sensor.

Further, the curing system includes a recognition system, and the recognition system includes a recognition device, an infrared volume measuring device, a weight measuring device, and a sorting screening machine.

Further, the curing system includes a 3D printer.

A dedicated printhead for magnesium-based cement is arranged in the 3D printer, and the printhead includes a hopper and a dry ice hopper, wherein the dry ice hopper is connected to the hopper, a stirrer is arranged in the hopper, and a nozzle is connected at a bottom of the hopper.

A dry ice controller is arranged between the dry ice hopper and the hopper.

Further, the stirrer includes a supporting rod and a spiral piece, wherein the supporting rod is fixed at a bottom of the hop- per, and the spiral piece is spirally fixed at the supporting rod.

At least one stirring blade is arranged on the spiral piece.

When there are several stirring blades, an end of the stir- 5 ring blades arranged close to the motor are inclines upwards, and an end of the stirring blades arranged close to the nozzle are in- clines downwards.

Further, the stirring blade is in a shape of folding sheet protruding outwards.

Further, an exhaust device arranged in a lower middle part of the hopper includes a exhaust hole and a exhaust slot, and the ex- haust slot is arranged at a lower part of the exhaust hole.

The exhaust hole is a filter screen, and the exhaust slot is arranged around the hopper.

Further, components of the dedicated curing system are con- nected by conveyors.

Compared to the prior art, according to the method, tempera- ture-controlled carbonation curing, humidity-controlled carbona- tion curing, and storage carbonation curing are provided for the magnesium-based cement concrete product; the magnesium based ce- ment concrete product is kept in an appropriate carbon dioxide gas concentration, carbon dioxide gas pressure, ambient temperature, and relative humidity environment in a hydration process, low- temperature curing and carbonation curing are combined to improve the internal microstructure of the magnesium-based cement, thereby enhancing the compactness, macro-mechanical properties and dura- bility of magnesium-based cement; the curing method enables water slag sand and soil dreg to be used directly in the concrete prod- uct and enables magnesium-based standard sand to participate in the hydration reaction instead of quartz standard sand, thereby making a contribution to reducing carbon emissions in the con- struction sector and the whole society and providing very obvious technical advantages and economic and ecological benefits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a dedicated system for magnesium- based cement concrete products.

FIG. 2 is a schematic diagram of a dedicated system for mag- nesium-based cement concrete products.

FIG. 3 is a schematic diagram of a 3D printer for magnesium- based cement.

FIG. 4 is a schematic diagram of a dedicated 3D printhead for magnesium-based cement.

FIG. 5 is a schematic diagram of a recognizer for magnesium- based cement concrete products.

FIG. 6 is a schematic diagram of temperature-controlled car- bonation chambers for magnesium-based cement concrete products.

FIG. 7 is a schematic diagram of humidity-controlled carbona- tion chambers for magnesium-based cement concrete products.

FIG. 8 is a schematic diagram of storage curing chambers for magnesium-based cement concrete products. 1. printhead; 2. 3D printer support; 3. motor; 4. motor con- trol line; 5. stirrer; 6. hopper; 7. nozzle; 8. dry ice hopper; 9. dry ice controller; 10. drive control system for 3D printing; 11. supporting rod; 12. spiral piece; 13. stirring blade; 14. filter screen; 15. exhaust slot; 16. dry ice; 17. conveyor; 18. recogniz- er; 19. temperature-controlled carbonation chamber; 20. humidity- controlled carbonation chamber; 21. storage curing chamber; 22. printing conveyor; 23. curing conveyor; 24. reference sample con- veyor; 25. conveyor; 26. image recognition device; 27. infrared volume measuring device; 28. weight measuring device; 29. sorting screening machine; 30. control display; 31. reference sample stor- age platform; 32. test sample platform; 33. temperature control- ler; 34. cooling device; 35. heating device; 36. carbon dioxide gas cylinder; 37. carbon dioxide gas regulator; 38. temperature- controlled carbonation display; 39. temperature sensor; 40. dry ice storage chamber; 41. dry ice regulator; 42. test sample cham- ber; 43. carbon dioxide gas pressure sensor; 44. pressure relief valve; 45. carbon dioxide gas concentration sensor; 46. relative humidity sensor; 47. relative humidity regulator; 48. humidity- controlled carbonation display; 49. test sample storage rack; 50. temperature and humidity regulator; 51. storage curing display.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to achieve the purpose that those skilled in the art can better understand the technical solution of the present inven- tion, the technical solution in the embodiments of the present in- vention will be clearly and completely described below. It is ob- vious that the described embodiments are only part of, rather than all of, the embodiments of the present invention.

Examples

The example provides a curing method for magnesium-based ce- ment concrete products, as shown in FIG. 1 and FIG. 2, including the following steps: 3101, reference samples and test samples were arranged for a concrete product; 8102, temperature-controlled carbonation curing was per- formed, a temperature of the test samples was adjusted according to that of the reference samples, wherein a carbon dioxide concen- tration of the temperature-controlled carbonation curing was 75- 95%, a carbon dioxide gas pressure was 80-90 kPa; and a tempera- ture was below -60°C;

S103, humidity-controlled carbonation curing was performed for the concrete product cured by S102, wherein a relative humidi- ty of the humidity-controlled carbonation curing was 80-953; and

S104, storage carbonation curing was performed for the con- crete product cured by S103, wherein a carbon dioxide concentra- tion of the storage carbonation curing was 80-95%, a temperature was 20-35°C, and a relative humidity was 80-96%.

Wherein the humidity-controlled carbonation curing was curing by dry ice, and the temperature-controlled carbonation curing and the storage carbonation curing were curing by carbon dioxide gas.

Wherein the preparation of the reference samples in S101 in- cluded the following steps: temperature sensors were pre-embedded in the concrete product prior to final setting; and then the con- crete product was cut, pieces with the temperature sensors were taken as reference samples, and pieces without the temperature sensors were taken as test samples;

Wherein the temperature-controlled carbonation curing in S102 included the following steps: the temperature sensors of the ref-

erence samples were connected with temperature controllers, and the temperature controllers adjusted a temperature of the test samples according to that of the reference samples for the temper- ature-controlled carbonation curing; and when a surface tempera- ture of the reference samples and the test samples fell to a room temperature again, humidity-controlled carbonation curing was per- formed for the reference samples and the test samples.

In a carbon dioxide gas environment, the gas carbon dioxide of the magnesium-based cement of the present example would undergo the following chemical reactions:

CO, «> CO, +H,0«< H,CO, > H'+HCO, <>H'+CO,"” (1)

Mg (OH), + CO:-MgCO3 + HO (2)

MgO + CO. + H.0-MgCQ; + H,0 (3) 2Mg°% + CO3% + OH + Cl + 3H:0>Mg; (CO) C1 (OH) :3 (H:0) (4)

Because magnesium-based cement concrete product contains a large amount of unreacted magnesium oxide and magnesium hydroxide generated by the reaction, a carbon dioxide gas environment with a certain temperature and humidity, concentration and pressure is conducive to the further carbonation of the magnesium-based cement concrete product, which can improve the mechanical properties and water resistance of the magnesium-based cement and increase the fixed carbon content of the magnesium-based cement concrete prod- uct, thereby effectively reducing greenhouse gases. In particular, a dedicated 3D printhead for magnesium-based cement and a dedicat- ed system for 3D-printed magnesium-based cement products can make 1 ton of 3D-printed magnesium-based cement products absorb 11.76 kg of carbon dioxide per year.

Example 2: The example provides a dedicated curing system for magnesium-based cement concrete products, as shown in FIG. 2, in- cluding temperature-controlled carbonation chambers, humidity- controlled carbonation chambers, and storage curing chambers.

Wherein a carbon dioxide device is arranged in each of the temperature-controlled carbonation chambers and each of the stor- age curing chambers, and a dry ice device is arranged in each of the humidity-controlled carbonation chambers.

As shown in FIG. 5-FIG. 8, the dedicated system for magnesi-

um-based cement concrete products includes a conveyor 17, a recog- nizer 18, temperature-controlled carbonation chambers 19, humidi- ty-controlled carbonation chambers 20 and storage curing chambers 21.

The conveyor 17 includes a printing conveyor 22 and a curing conveyor 23; the curing conveyor 23 includes a reference sample conveyor 24 and a conveyor 25; the printing conveyor 22, a 3D printer and the recognizer 18 were connected by rails; and the curing conveyor 23 is connected with the temperature-controlled carbonation chambers 19, the humidity-controlled carbonation cham- bers 20 and the storage curing chambers 21 by rails.

The recognizer 18 includes an image recognition device 26, an infrared volume measuring device 27, a weight measuring device 28, a sorting screening machine 29 and a control display 30.

Each of the temperature-controlled carbonation chambers 19 includes a reference sample platform 31, a test sample platform 32, a temperature controller 33, a cooling device 34, a heating device 35, a carbon dioxide gas cylinder 36, a carbon dioxide gas regulator 37 and a temperature-controlled carbonation display 38, wherein the cooling devices 34 and the heating devices 35 are ar- ranged in the periphery of each test sample platform; the tempera- ture controller 33 is connected with the test sample platforms 32 by the temperature sensor 39, the temperature sensor 39 is embed- ded in the reference sample, the temperature controller 33 is con- nected with the reference sample by the temperature sensor 39, and the cooling device 34 and the heating device 35 are connected with the temperature controller 33.

Each of the humidity-controlled carbonation chambers 20 in- cludes a dry ice storage chamber 40, a dry ice regulator 41, a test sample chamber 42, a carbon dioxide gas pressure sensor 43, a pressure relief valve 44, a carbon dioxide gas concentration sen- sor 45, a temperature sensor 39, a relative humidity sensor 46, a relative humidity regulator 47 and a humidity-controlled carbona- tion display 48, wherein the test sample chamber 42 is connected with the dry ice storage chamber 40 through a pipeline with a valve; the test sample chamber 42 is connected with the dry ice regulator 41 by the carbon dioxide gas concentration sensor 45,

carbon dioxide gas pressure sensor 43, pressure relief valve 44 and temperature sensor 39; and the test sample chamber 42 is con- nected with the relative humidity regulator 47 through the rela- tive humidity sensor 46.

Each of the storage curing chamber 21 includes a test sample storage rack 49, a carbon dioxide gas regulator 37, a temperature and humidity regulator 50 and a storage curing display 51, wherein the carbon dioxide gas regulator 37 is connected with the carbon dioxide gas cylinder 36 and the carbon dioxide gas concentration sensors 45.

Wherein, the specific curing included the following steps: the temperature sensors 39 were pre-embedded in the magnesium- based cement concrete product prior to final setting, the magnesi- um-based cement concrete product was cut into test cubes of 40mmx40mmx40mm, the test cubes with the temperature sensors 39 were taken as reference samples, and the remaining were taken as test samples; and the test cubes were conveyed to the recognizer 18 through the printing conveyor 22.

The image recognition device 26 includes a camera with a pho- tographing function and an image comparison and recognition sys- tem, wherein the camera takes a picture of the magnesium-based ce- ment concrete product and sends the picture to the image compari- son and recognition system. The image comparison and recognition system compares the picture photographed by the camera with stand- ard images and reference sample images pre-saved in the image com- parison and recognition system, determines the reference samples and the test samples of the magnesium-based cement concrete prod- uct according to color and appearance, and then sends the recogni- tion results to the control display 30.

The infrared volume measuring device 27 measures an external volume of the magnesium-based cement concrete product and sends the measurement results to the control display 30; the weight measuring device 28 measures a mass of the magnesium-based cement concrete product and sends the weighing results to the control display 30; the control display 30 automatically calculates a den- sity of the magnesium-based cement concrete products according to the measurement results of the infrared volume measuring device 27 and the weight measuring device 28, and judges the uniformity in combination with the test samples and the reference samples of the magnesium-based cement concrete product recognized by the image recognition device. If the results are inconsistent, a prompt will be sent out to request manual identification.

If the results are consistent, the curing conveyor conveys the reference samples and the test samples recognized to the tem- perature-controlled carbonation chambers; after a surface tempera- ture of the magnesium-based cement concrete product falls to a room temperature, the product is conveyed from the temperature- controlled carbonation chambers to the humidity-controlled carbon- ation chambers, and then conveyed to the storage curing chambers by the curing conveyor for storage carbonation curing after being cured for a certain age.

Wherein for the temperature-controlled carbonation curing, dry ice was arranged around the magnesium-based cement concrete product in each of the temperature-controlled carbonation cham- bers, and the dry ice was in a shape of rich grains or rods with a length of 10 mm-40 mm. The test sample chamber for the magnesium- based cement concrete was kept with the required carbon dioxide concentration, carbon dioxide pressure and temperature, so that the carbonation of the magnesium-based cement concrete could be more sufficient. An optimal carbon dioxide concentration for the temperature-controlled carbonation curing of magnesium oxysulfate cement, magnesium chloride cement, and magnesium phosphate cement was 70%, 80% and 90% respectively; an optimal carbon dioxide gas pressure was 70 kPa, 80 kPa and 90 kPa respectively; and an opti- mal temperature was -40°C, -50°C and -60°C respectively.

An amount of the dry ice added into the test sample chamber was controlled by the dry ice regulator in each of the humidity- controlled carbonation chambers through the carbon dioxide gas concentration sensor, the carbon dioxide gas pressure sensor and temperature sensor; a relative humidity in the test sample chamber was controlled by the relative humidity sensor and the relative humidity regulator to keep the test sample chamber for magnesium- based cement concrete reaching an appropriate relative humidity, and an optimal relative humidity in the test sample chambers for magnesium oxysulfate cement, magnesium oxychloride cement, and magnesium phosphate cement was 92%, 94% and 96% respectively.

A carbon dioxide concentration, temperature, and relative hu- midity of the storage curing chamber were regulated in the storage curing chamber through the carbon dioxide gas regulator and the temperature and humidity regulator. An optimal carbon dioxide con- centration in the storage curing chamber for magnesium oxysulfate cement products, storage curing chamber for magnesium chloride ce- ment products, and storage curing chamber for magnesium phosphate cement products was 75%, 85% and 95%, respectively, a temperature was 10°C, 20°C and 30°C, respectively, and a relative humidity was 91%, 93% and 95%.

After the magnesium-based cement concrete of the present ex- ample was cured, the storage curing chambers provided a specific carbon dioxide concentration, temperature and relative humidity, enabling the continuous carbonation of the magnesium-based cement concrete.

A dedicated 3D printhead for magnesium-based cement is ar- ranged in the dedicated system in the example of the present in- vention. As shown in FIG. 3 and FIG. 4, the dedicated 3D printhead 1 for green magnesium-based cement is arranged at a 3D printer support 2. The dedicated 3D printhead for green magnesium-based cement concrete includes a motor 3, a motor control line 4, a stirrer 5, a hopper 6, a nozzle 7, a dry ice hopper 8 and a dry ice controller 9, wherein the motor 3 is connected with the drive control system for 3D printing 10 through the motor control line 4, the stirrer 5 is located in a middle of the hopper 6, the hop- per 6 is connected with the nozzle 7 through threads, the dry ice hopper 8 is connected with the dry ice controller 9, the dry ice controller 9 is connected with the hopper 6, and the dry ice con- troller 9 is connected with the motor control line 4; the motor 3 is fixed to the 3D printer support 2, a removable buckle connec- tion is arranged between the stirrer 5 and the motor 3, and a re- movable buckle connection is arranged between the hopper 6 and the 3D printing bracket 2.

The stirrer 5 includes a supporting rod 11, a spiral piece 12 and a stirring blade 13, wherein the supporting rod 11 is connect-

ed with the motor 3, the spiral piece 12 is enwinded on the sup- porting rod 11 downwards, the stirring blade 13 is connected with the spiral piece 12, the stirring blade 13 is in a shape of fold- ing sheet protruding outwards, a protruding side of the stirring blade 13 is 10 mm from an inner wall of the hopper, one end of the stirring blade 13 arranged close to the motor inclines upwards, and one end of the stirring blade 13 arranged close to the nozzle inclines downwards.

An exhaust slot 15 with a filter screen 14 is arranged in a middle of the hopper 6, a mesh diameter of the filter screen 14 is 35 um-74 um, and the exhaust slot 15 is 10 mm wide and 20 mm high.

The exhaust slot is arranged at the nozzle, which ensures that the bubbles produced by the stirrer in the slurry in the mix- ing process and the large carbon dioxide bubbles produced from vo- latilization of the dry ice are discharged from the slurry prior to slurry printing. Therefore, the 3D-printed magnesium-based ce- ment concrete product contains a certain amount of carbon dioxide gas required for later carbonation, and additionally the influence of large bubbles on the printing performance, strength and dura- bility of the magnesium-based cement 3D-printed product can be controlled.

A dry ice hopper and a dry ice controller are arranged at a 3D printhead of the present example, and the carbon dioxide re- quired for magnesium-based cement carbonation is provided by add- ing dry ice in the printing process. The temperature of dry ice is below -60°C and absorbs heat during volatilization, so that the requirements for carbonation and reduced hydration heat of magne- sium-based cement in the 3D printing process can be met, thereby avoiding the temperature stress caused by excessive temperature difference inside and outside of the samples, reducing the mi- crocracks inside the samples caused by the temperature stress, and increasing the early fixed carbon content of magnesium-based ce- ment. Meanwhile, because the low-temperature environment in the slurry hopper prolongs the setting time of magnesium-based cement, it is more beneficial to the 3D printing of magnesium-based ce- ment; moreover, the dry ice added in the printing process intro- duces carbon dioxide into the 3D-printed product, which is condu-

cive to the long-term carbonation inside the 3D-printed product and ensures that the 3D-printed magnesium-based cement has a rela- tively high compactness, macro-mechanical properties and durabil- ity.

The dedicated 3D printhead for magnesium-based cement not on- ly contributes to the realization of magnesium-based cement 3D printing, but also significantly improves the carbon fixation ca- pacity in the magnesium-based cement in the 3D printing process.

The modern production process of the magnesium-based cement prod- uct is improved, making a contribution to reducing carbon emis- sions in the construction sector and the whole society and provid- ing very obvious technical advantages and economic and ecological benefits.

The present invention provides temperature-controlled carbon- ation curing, humidity-controlled carbonation curing, and storage carbonation curing for magnesium-based cement concrete products to effectively ensure that different 3D-printed magnesium based ce- ment products is kept in an environment with different carbon di- oxide gas concentrations, carbon dioxide gas pressures, ambient temperatures, and relative humidities in the hydration process.

The low-temperature curing and carbonation curing are combined ef- fectively to further improve the internal microstructure of the magnesium-based cement, thereby providing a guarantee for the com- pactness, macro-mechanical properties and durability of magnesium- based cement. This is very conducive to the intelligent tempera- ture and carbonation curing of 3D-printed magnesium-based cement products. Enhanced carbonation in the whole process of magnesium- based cement 3D printing and curing can be realized through the dedicated 3D printhead for magnesium-based cement and the curing system for magnesium-based cement concrete products.

Finally, it should be noted that the above-mentioned embodi- ments are only used for explaining, rather than limiting, the technical solutions of the prevent invention. Although the present invention is explained in detail by reference to the above- mentioned embodiments, it should be understood that those of ordi- nary skill in the art, after reading the specification, may still make modifications or equivalent substitutions to the particular embodiments of the present invention, but such modifications or equivalent substitutions do not depart from the protection scope of the pending claims of the present invention.

Claims

CONCLUSIONS

A method for curing magnesium-based cement concrete products, the method comprising the steps of: S101, reference samples and test samples are set up for a concrete product; S102, temperature-controlled carbonation hardening is performed, and a temperature of the test samples is adjusted in accordance with that of the reference samples, wherein a carbon dioxide concentration of the temperature-controlled carbonation hardening is 75 to 95%, a carbon dioxide gas pressure is 80 to 90 kPa , and a temperature lower than -60 °C; S103, humidity-controlled carbonation hardening is performed for the concrete product cured by S102, where a relative humidity of the humidity-controlled carbonation hardening is 80 to 95%; and S104, storage carbonation hardening is performed for the concrete product hardened by S103, wherein a carbon dioxide concentration of the storage carbonation is 80 to 95%, a temperature is 20 to 35 °C, and a relative humidity is 80 up to 96%

is.

The method for hardening magnesium-based cement concrete products according to claim 1, wherein the moisture-controlled carbonation hardening is hardened by dry ice, and the temperature-controlled carbonation hardening and the storage carbonation hardening are hardened by carbon dioxide gas; where the preparation of the reference samples includes the following steps: temperature sensors are pre-embedded in the concrete product before final curing; and the concrete product is then cut, pieces with the temperature sensors are taken as reference samples, and pieces without the temperature sensors are taken as test samples; the temperature-controlled carbonation hardening includes the following steps: the temperature sensors of the reference samples are

connected to temperature controllers, and the temperature controllers adjust a temperature of the test samples in accordance with that of the reference samples for the temperature-controlled carbonation hardening; and when a surface temperature of the reference samples and the test samples falls back to room temperature, a humidity-controlled carbonation hardening is performed for the reference samples and the test samples.

A specific system for the method of hardening magnesium-based cement concrete products according to claims 1-2, wherein the special system comprises temperature-controlled carbonation chambers, humidity-controlled carbonation chambers and storage curing chambers; and a carbon dioxide device is disposed in each of the temperature-controlled carbonation chambers and each of the storage curing chambers, and a dry ice device is disposed in each of the humidity-controlled carbonation chambers.

The specific system for curing magnesium-based cement concrete products according to claim 3, wherein each of the temperature-controlled carbonation chambers comprises a temperature controller, a cooling device and a heating device; wherein a reference sample platform and a test sample platform are disposed in each of the temperature-controlled carbonation chambers; the cooling device and the heating device are arranged in the periphery of each test sample platform, the temperature controller is connected to the test sample platform through the temperature sensor, and the cooling device and the heating device are electrically connected to the temperature controller; wherein dry ice is applied around the concrete product and a carbon dioxide concentration and a temperature in each of the temperature-controlled carbonation chambers are adjusted by controlling an amount of dry ice supplied; wherein each of the humidity-controlled carbonation chambers includes a test sample chamber, a dry ice storage chamber, a dry ice controller, and a relative humidity controller; the test sample

star chamber is connected with the dry ice storage chamber by the temperature sensor and the dry ice controller; and wherein the test sample chamber is connected to the relative humidity controller by a relative humidity sensor; wherein a temperature and humidity controller is provided in each of the chambers for curing during storage; and wherein each of the carbon dioxide devices comprises a carbon dioxide gas regulator, a carbon dioxide gas cylinder and a sensor for measuring the concentration of the carbon dioxide gas, and wherein the carbon dioxide gas regulator is connected to the carbon dioxide gas cylinder and the sensor for measuring the concentration of the carbon dioxide gas the carbon dioxide gas.

A specific system for curing magnesium-based cement concrete products according to claim 3, wherein the curing system comprises a recognition system, and the recognition system comprises a recognition device, an infrared volume measuring device, a weight measuring device and a sorting screen machine to

barrel.

A specific system for curing magnesium-based cement concrete products according to claim 3, wherein the curing system comprises a 3D printer; a special print head for magnesium-based cement is provided in the 3D printer, and the print head includes a hopper and a dry ice hopper, the dry ice hopper is connected to the hopper, an agitator is provided in the hopper, and a nozzle is connected to a bottom of the hopper; and a dry ice controller is arranged between the dry ice hopper and the hopper.

A specific system for curing magnesium-based cement concrete products according to claim 6, wherein the agitator comprises a support bar and a spiral piece, the support bar being attached to the bottom of the hopper, and the spiral piece being spirally is fixed on the support bar; and wherein at least one rudder blade is mounted on the spiral piece;

wherein when there are multiple rudder blades, one end of the rudder blades mounted close to the motor is inclined upwards and one end of the rudder blades mounted close to the nozzle is inclined downward.

A specific system for curing magnesium-based cement concrete products according to claim 7, wherein the agitator blade is in the form of a folding blade protruding outwardly.

A specific system for hardening magnesium-based cement concrete products according to claim 6, wherein an outlet device provided in a lower middle part of the hopper comprises an outlet hole and an outlet slot, the outlet slot being provided in a lower part of the hopper. the exhaust hole; and wherein the outlet hole is a filter screen and the outlet slot is arranged around the funnel.

A specific system for curing magnesium-based cement concrete products according to claim 3, wherein components of the specific curing system are connected by conveyor belts.