Phosphate modified self-repairing calcium aluminate cement 3D printing material and preparation method thereof

Abstract

The invention belongs to the field of modified self-repairing calcium aluminate cement 3D printing, and particularly relates to a phosphate modified self-repairing calcium aluminate cement 3D printing material and a preparation method thereof. The phosphate modified self-repairing calcium aluminate cement 3D printing material prepared by the invention is prepared from the following raw materials in parts by mass: 60 to 70 parts of calcium aluminate cement, 3 to 7 parts of silica fume, 2 to 4 parts of metakaolin, 0.5 to 3.5 parts of double-template modified calcium bentonite, 0.8 to 1.5 parts of amino modified sodium polyphosphate and 0.15 to 0.8 part of basalt fiber. The invention relates to a concrete anti-microbial agent, which is prepared from the following raw materials in parts by weight: 20-30 parts of water, 20-30 parts of water, 20-30 parts of water, 20-30 parts of nano calcium carbonate, 20-30 parts of nano calcium carbonate, 20-30 parts of magnesium phosphate cement coated bacteria-loaded porous microspheres, 20-30 parts of a polycarboxylate superplasticizer, 20-30 parts of an organic silicon defoaming agent and 25-35 parts of mixing water. The technical-economic cooperation requirement of building 3D printing under complex working conditions is met, and various indexes of phosphate modified calcium aluminate cement applied to the 3D printing technology are met.

Description

Technical Field

[0001] The present invention belongs to the field of 3D printing of modified self-healing aluminate cement, and particularly relates to a phosphate-modified self-healing calcium aluminate cement 3D printing material and a preparation method thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Building 3D printing technology is a new technology that is significantly different from traditional cement pouring methods. Based on the three-dimensional information of the model, through software design and program control, materials are extruded through a printing nozzle and accumulated layer by layer to generate a 3D entity. It has high operation difficulty and technological content. The commonly used existing 3D printing systems generally use traditional portland cement as their gelling phase. Although traditional portland cement materials have a mature industrial production system, there are still the following problems:

[0004] (1) Hydration kinetics lag: The main hydration products of ordinary portland cement, C3S and C2S, generate amorphous C-S-H gels in the initial stage of hydration, and their nucleation induction period is about 3 hours, resulting in a significant lag in the growth rate of the yield stress of the cement paste compared with the printing requirements. As a result, the extruded cement paste undergoes creep under the action of gravity (slump greater than 30% within 10 minutes), and it is difficult to maintain the original preset geometric shape of the program.

[0005] (2) Low early strength: Due to the slow development of its early strength, the waiting time between layers is forced to exceed 60 minutes or more, resulting in a transition zone at the interface between components with fast hydration rates (such as C3A) and particles that have not yet started to react, leaving a great potential safety hazard for interlayer erosion damage.

[0006] (3) Weak interlayer bonding: Considering its rheological properties, it is difficult for the water-binder ratio and thixotropic index of portland cement paste to simultaneously meet the cutting-edge requirements of 3D printing. For a cement paste with an apparent viscosity < 20 Pa·s, its thixotropic index is reduced to less than 1.2, and it is impossible to maintain the stability between layers. Existing technologies often adjust the rheological properties of the paste by adding additives such as hydroxyethyl methyl cellulose (HEMC) or polyacrylamide (PAM). However, the introduction of such polymer additives will adsorb a large amount of free water, and the large amount of free water introduced will further inhibit the early hydration of cement, exacerbating the problem of lagging strength development.

[0007] (4) Poor erosion resistance: The carbonation sensitivity of portland cement and the anisotropic defects of the printed structure form a negative synergistic effect. Transmission pore channels are formed between the printed layers stacked layer by layer, which provides a natural channel for the diffusion of CO2, accelerating the carbonation rate of the cement. When applied in a high saline-alkali environment, it exacerbates the gypsum crystallization damage under sulfate erosion, significantly reducing its service life in environments such as the ocean and saline-alkali land.

[0008] Based on the significant defects of the above portland cement in the field of 3D printing, the use of a new type of cement, aluminate cement, in 3D printing has gradually started to be studied. Aluminate cement has the characteristics of early strength and rapid hardening. The CA (CaAl2O4) component in it rapidly dissociates into metastable phase CAH10 nanosheets after encountering water, and this structure significantly endows the paste with excellent early hydration kinetics. However, there are still the following problems:

[0009] When aluminate cement is used in a humid and hot environment, CAH10 will undergo a slow crystal form transformation to produce C3AH6, resulting in an irreversible deterioration effect of the material. A series of phenomena such as volume shrinkage, a sharp increase in porosity, and strength reduction of about 30 - 40% occur in the later stage of service, seriously weakening the durability and later bearing capacity of the 3D printed structure. In addition, the early strength and rapid hardening of aluminate cement will inevitably lead to the phenomenon of concentrated heat release during hydration, further exacerbating the deterioration of the fine structure, generating more microcracks inside the material structure, and making the material face the risk of durability. More seriously, the carbonation resistance and sulfate erosion resistance of aluminate cement are significantly weaker than those of portland cement. The C3AH6 formed by its phase transformation undergoes a decalcification reaction under the action of CO2 to generate Al(OH)3 gel and CaCO3, and the volume expansion rate of its product is as high as 10%, accelerating the occurrence of surface spalling. In a sulfate environment, the reaction rate of C3AH6 with gypsum to form ettringite (AFt) is 3 - 4 times faster than that of C3A, causing concentrated expansion stress in the microstructure and severely restricting its engineering practicability.

[0010] Those skilled in the art need to modify aluminate cement to further optimize and improve its early strength, hydration rate, carbonation resistance, rheological durability, and erosion and corrosion resistance, and at the same time achieve the self-healing function of internal cracking and erosion of the 3D printed structure in the later stage. Therefore, there is an urgent need for a calcium aluminate cement system with excellent rheology, durability, self-healing ability, and environmental erosion resistance. Summary of the Invention

[0011] Aiming at the above problems, the purpose of the present invention is to provide a phosphate-modified self-healing calcium aluminate cement 3D printing material and its preparation method. The present invention designs a phosphate-modified self-healing calcium aluminate cement for the field of 3D printing technology. Through the research on the coordinated regulation of multiple contradictions of "rheology-setting-mechanics-durability", the technical-economic coordinated requirements of building 3D printing under complex working conditions are realized, and various indicators for the application of phosphate-modified calcium aluminate cement in 3D printing technology are met.

[0012] The phosphate-modified self-healing calcium aluminate cement prepared by the present invention has good early strength, moderate hydration temperature, excellent rheological properties, durability, erosion resistance and anti-corrosion protection ability. At the same time, it ensures the operability, high efficiency and convenience in the field of 3D printing. It realizes the organic coupling of the trinity of component-structure-property correlation, multi-scale interface structure design and microbial intelligent response, and realizes the leap of 3D printing cement-based materials from passively adapting to the hydration characteristics of the cement system to actively regulating the optimal range ratio of various admixtures and modifiers. It also comprehensively combines the interface enhancement and hydration heat regulation of SBA composite fiber materials, providing a new solution for intelligent construction maintenance and self-healing in engineering fields such as high temperature and high humidity, high salt and strong alkaline environment, and marine erosion environment.

[0013] Specifically, the present invention provides the following technical solutions:

[0014] In the first aspect of the present invention, a phosphate-modified self-healing calcium aluminate cement 3D printing material is provided. Calculated by mass, its raw material composition includes: 60-70 parts of calcium aluminate cement, 3-7 parts of silica fume, 2-4 parts of metakaolin, 0.5-3.5 parts of double-template agent modified calcium-based bentonite, 0.8-1.5 parts of amino-modified sodium polyphosphate, 0.15-0.8 parts of basalt fiber, 0.45-2.0 parts of nano-calcium carbonate hybrid styrene-butyl acrylate copolymer, 4-7 parts of magnesium phosphate cement-coated bacteria-loaded porous microspheres, 0.1-0.25 parts of polycarboxylate water reducer, 0.02-0.04 parts of organosilicon defoamer, and 25-35 parts of mixing water.

[0015] Preferably, the phosphate-modified self-healing calcium aluminate cement 3D printing material, calculated by mass, its raw material composition includes: 65 parts of calcium aluminate cement, 4 parts of silica fume, 2 parts of metakaolin, 1.6 parts of double-template agent modified calcium-based bentonite, 1.15 parts of amino-modified sodium polyphosphate, 0.2 parts of basalt fiber, 0.6 parts of nano-calcium carbonate hybrid styrene-butyl acrylate copolymer, 5 parts of magnesium phosphate cement-coated bacteria-loaded porous microspheres, 0.15 parts of polycarboxylate water reducer, 0.03 parts of organosilicon defoamer, and 33 parts of mixing water.

[0016] Preferably, the double-template agent modified calcium-based bentonite is prepared by the following steps:

[0017] It is obtained by dropping a mixed solution of magnesium nitrate and aluminum nitrate into a sodium-bentonite suspension containing sodium dodecyl sulfate (SDS) and polyethylene glycol (PEG), followed by centrifugation, drying, and grinding.

[0018] Among them, the concentrations of both magnesium nitrate and aluminum nitrate are 0.25 - 0.3 mol / L; the sodium-bentonite is prepared by mixing calcium-based bentonite with a 4 - 6% sodium carbonate solution at a dosage ratio of 1 g:4 - 5 mL; the mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1:1.15 - 1.2. Sodium dodecyl sulfate and polyethylene glycol are used as template agents, and the content of the template agent in the aqueous solution is 5% - 8%. The mass ratio of the template agent to sodium-bentonite is 1:0.45 - 0.47; the volume ratio of the mixed solution of magnesium nitrate and aluminum nitrate to the sodium-bentonite suspension is 1:0.5 - 0.9.

[0019] Preferably, the amino-modified sodium polyphosphate is prepared by the following steps:

[0020] Mix sodium dihydrogen phosphate and disodium hydrogen phosphate in a volume ratio of 4:1, calcine and melt, then cool and grind to less than 200 mesh; react the ground product sodium polyphosphate with a silane coupling agent in a 60 - 80% ethanol solution. The mass ratio of the silane coupling agent to sodium polyphosphate is 0.08 - 0.12:1. The silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, anilinomethyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, and octyltriethoxysilane; further preferably, the silane coupling agent is γ-aminopropyltriethoxysilane.

[0021] Preferably, the bacteria in the magnesium phosphate cement-coated porous microspheres are selected from one or more of Bacillus pasteurii, Bacillus thuringiensis, Bacillus licheniformis, and Sarcina pasteurii, preferably Bacillus pasteurii. The spore concentration of Bacillus pasteurii is (2 - 5)×108 CFU / mL, and the microsphere shell is a dense MgKPO4·6H2O structure formed by magnesium phosphate cement.

[0022] Preferably, the nano-calcium carbonate hybridized styrene-butyl acrylate copolymer is prepared by the following steps:

[0023] Carbonize the calcium hydroxide suspension with CO2. The obtained precipitate nano-calcium carbonate is modified with stearic acid and then mixed with the styrene-butyl acrylate copolymer emulsion; among them, the concentration of the calcium hydroxide suspension is 8 - 10%, the concentration of the stearic acid solution is 1.5 - 2%, and the mass ratio of the stearic acid-modified nano-calcium carbonate to the styrene-butyl acrylate copolymer emulsion is 1:19 - 21.

[0024] Preferably, the basalt fiber has a length of 3-6 mm, a fiber diameter of 10-18 μm, and is randomly distributed in three dimensions in the slurry.

[0025] In a second aspect of the present invention, a method for preparing the above phosphate-modified self-healing calcium aluminate cement 3D printing material is provided, including the following steps:

[0026] S1. Mix sodium dihydrogen phosphate and disodium hydrogen phosphate, calcine and melt them, cool, grind, disperse in an ethanol solution for reaction, and then add a silane coupling agent. After reaction, amino-modified sodium polyphosphate is obtained;

[0027] S2. Mix magnesium nitrate and aluminum nitrate to form a mixed solution A, mix calcium-based bentonite and sodium carbonate solution to form a mixed solution B, dissolve sodium dodecyl sulfate in a polyethylene glycol solution to form a mixed solution C. First, mix solution B and solution C and stir to obtain a mixed solution BC. Subsequently, drop solution A into the mixed solution BC and carry out a heating reaction to obtain calcium-based bentonite co-modified by a double template agent;

[0028] S3. React a calcium hydroxide suspension with CO2 gas, take the suspended precipitate, modify it with a stearic acid solution, and mix it with a styrene-butyl acrylate copolymer emulsion to form a styrene-butyl acrylate copolymer hybridized with nano-calcium carbonate;

[0029] S4. Mix bacterial spores with a dihydrogen phosphate solution and a culture solution, spray on over-burned magnesium oxide powder, and dry to form bacteria-loaded porous microspheres coated with magnesium phosphate cement;

[0030] S5. Dry-mix calcium aluminate cement, silica fume, metakaolin, calcium-based bentonite co-modified by a double template agent, amino-modified sodium polyphosphate, and basalt fiber to obtain a dry-mixed mixture;

[0031] S6. Uniformly stir a polycarboxylate-based water reducer, an organosilicon defoamer, and mixing water, then add the dry-mixed mixture described in step S5 and continue stirring. After standing, a phosphate-modified calcium aluminate cement slurry is obtained;

[0032] S7. Mix the styrene-butyl acrylate copolymer hybridized with nano-calcium carbonate with the mixture, then add the phosphate-modified calcium aluminate cement slurry described in step S6 and stir to obtain a mixed slurry;

[0033] S8. Take the bacteria-loaded porous microspheres coated with magnesium phosphate cement described in step S4 and add them to the mixed slurry in step S7, and stir to obtain the phosphate-modified self-healing calcium aluminate cement 3D printing material.

[0034] Preferably, in step S1, the solution concentrations of sodium dihydrogen phosphate and disodium hydrogen phosphate are both 2 mol / L. The calcination is carried out by heating to 700 - 850 °C in an N2 environment until melting, and then quickly pouring it into liquid nitrogen to cool to below -20 °C to obtain a vitreous product of sodium polyphosphate, followed by grinding. The ratio of the ground sodium polyphosphate to the ethanol solution is 1:7 - 9. The reaction temperature is 60 - 75 °C and the time is 2 - 3 hours.

[0035] Preferably, in step S2, the reaction temperature when the calcium-based bentonite is mixed with the sodium carbonate solution is 55 - 65 °C and the time is 10 - 15 minutes. The reaction temperature for mixing and stirring solution B and solution C is 55 - 65 °C, and then it is allowed to stand and react for 8 - 12 minutes. The calcium-based bentonite modified by the double template agent needs to be dried at 50 - 70 °C and then ground to 200 meshes for standby.

[0036] Preferably, in step S3, the pH of the reaction environment is 9 - 10.

[0037] Preferably, in step S4, the concentration of the dihydrogen phosphate is 0.1 - 0.3 mol / L. The dihydrogen phosphate is selected from one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, and sodium dihydrogen phosphate.

[0038] Preferably, in step S7, the stirring time does not exceed 1 min.

[0039] Preferably, in step S8, the stirring is manual, and slow stirring is carried out for 25 - 35 s to prevent the fragmentation of the bacteria-coated microspheres.

[0040] In the third aspect of the present invention, there is provided an application method of the phosphate-modified self-healing calcium aluminate cement 3D printing material described in the first aspect, including the following steps:

[0041] (1) Using a twin-screw extrusion 3D printer, configuring a constant-temperature cold water system and a vacuum degassing module, and adjusting the key printing parameters;

[0042] (2) Controlling the material adaptability, and dynamically adjusting the screw speed by the in-embedded ultrasonic viscometer to real-time feedback the thixotropy index of the cement paste;

[0043] (3) Immediately covering with a moisture-retaining film for curing after 3D printing, and then carrying out treatment with saturated steam, and performing self-healing environment treatment for the 3D printing application environment.

[0044] Preferably, in step (1), the printer screw diameter of the 3D printer is 45 mm, the length-diameter ratio L / D = 12:1, the printing speed is 80 - 120 mm / min in the horizontal direction and 30 - 50 mm / min in the vertical direction, the printing layer thickness is 5 - 15 mm, and the interlayer interval time is less than 60 s.

[0045] Preferably, in step (1), the key parameter setting includes an environmental temperature of 10 to 35 °C and a relative air humidity of ≥50%.

[0046] Preferably, in step (2), the frequency of the ultrasonic viscometer is 2 MHz, and the adjustment range of the screw speed is 20 - 40 rpm; by adjusting the speed, the thixotropic index (TI) of the slurry is ensured to be between 1.8 and 2.1.

[0047] Preferably, in step (3), after covering with the moisture - retaining film, it needs to be cured at a temperature of 23 - 28 °C for 20 - 30 h.

[0048] Preferably, in step (3), the saturated steam is saturated steam at 60 °C, and the pressure is 0.15 Mpa. Preferably, the saturated steam treatment time is 1 - 5 h.

[0049] Preferably, in step (3), the self - repair environment treatment for the 3D printing application environment includes: for the high - salinity and high - alkalinity environment, spraying 0.1 mol / L urea - calcium chloride solution to adjust the pH value to 8 - 9; for the acidic soil environment, spraying 0.2 mol / L sodium lactate - calcium hydroxide solution for regulation.

[0050] One or more embodiments of the present invention have at least the following beneficial effects:

[0051] (1) By introducing the sodium polyphosphate (NaPO3) n system, a phosphoric acid system modification is introduced into the calcium aluminate cement, which will react with the hydration product CaAl2O4 of CAC to generate calcium - aluminum - phosphate colloid (CaAlPO4·nH2O). Such colloid can not only serve as nucleation sites in the later stage to promote the improvement of the system's later strength, but also cover the surface of calcium aluminate cement particles to delay its hydration process and reduce its early heat release rate. As shown by the DSC test of the 3D - printed cement material added with the sodium polyphosphate system in the embodiment, the peak temperature of cement hydration decreases by 15 - 30 °C from 82 °C.

[0052] It can also react with the bacteria - loaded porous microspheres coated with magnesium phosphate cement added later to form struvite K as a strength structure, promoting the development of the early strength of the material. The magnesium phosphate cement system has less porosity, a dense structure, strong resistance to acid and alkali erosion, and struvite is distributed in the hydration structure system, improving the anti - penetration ability of the cement paste forming.

[0053] In addition, long-chain polyphosphates can play a certain "lubricating" role in the system, generating disentanglement-arrangement behavior during the shear process of stirring, which will endow the neat cement paste with shear-thinning characteristics and have great advantages for the initial rheological properties and pumping properties. The end of the sodium polyphosphate group modified by a silane coupling agent will introduce amino groups, forming an electrostatic adsorption effect with the surface of cement particles, reducing the yield stress of the paste, and at the same time increasing the thixotropic recovery rate, ensuring the extrusion fluidity and interlayer bonding strength during the 3D printing process. The ethoxy group (-OCH2CH3) of the silane hydrolyzes to form silanol (-Si-OH), which combines with the -PO3 - group through hydrogen bonds and ionic bonds to form a stable Si-O-P covalent bond,

[0054] The introduction of the organic segment improves the compatibility between sodium polyphosphate and the subsequently introduced styrene-acrylate copolymer, reducing the defects at the organic-inorganic phase interface between layers during the 3D printing process. The introduction of amino groups endows the sodium polyphosphate molecule with hydrophobicity, reducing the premature dissolution of polyphosphate molecules in the cement paste, ensuring the slow release of ions, and contributing to the improvement of long-term strength and uniform hydration.

[0055] (2) The calcium-based bentonite is synergistically modified by magnesium nitrate, aluminum nitrate and dual template agents (SDS and PEG), enabling the modified bentonite to possess the interlayer structure and adsorption characteristics of layered double hydroxides. At the same time, the price of the modified bentonite is much lower than that of layered double hydroxides, greatly reducing the engineering application cost of 3D printing of modified calcium aluminate cement.

[0056] First, the calcium-based bentonite is modified with a sodium carbonate solution, using Na + to displace Ca 2+ so that the interlayer cation spacing of the bentonite expands from 1.2 nm to about 1.5 nm, enhancing the water molecule and ion accommodation capacity between bentonite layers, and can efficiently capture Cl - , SO4 2- and other erosive ions in the environment, and fix the ions in the interlayer through ion exchange, which is suitable for the repair and construction of infrastructure in coastal areas or the interior of the ocean.

[0057] In addition, when the structure is in an alkaline environment, the modified bentonite will slowly release Mg 2+ and Al 3+ to react with the amino-modified sodium polyphosphate to form Mg3(PO4)2 and AlPO4 precipitates, filling the pores of the cement system and blocking the erosion path of ions.

[0058] Sodium dodecyl sulfate is a typical anionic surfactant, which forms an adsorption effect with the Si-O surface layer of bentonite through the hydrophobic chain C12 alkyl group, and the hydrophilic group SO4 2-Facing outward, it is easy to combine to form ettringite; while polyethylene glycol is a typical non-ionic polymer, which combines with the hydroxyl hydrogen bond of bentonite through the ether bond -O-, inserts into the interlayer to form a helical structure. The synergistic effect of the two forms a hydrophobic-hydrophilic composite structure intercalation, for subsequent metal ions such as Mg 2+ , Ca 2+ and heavy metal ions Pb that may exist in the soil 2+ etc. provide adsorption space, and at the same time construct a multi-level pore channel (micropore-mesopore), further enhancing the ion exchange ability.

[0059] (3) When microcracks occur in the 3D printing material during engineering practice, moisture in the air or soil invades the material matrix along the cracks. The unhydrated sodium polyphosphate quickly releases phosphate radicals when encountering water. At this time, it can react with Ca 2+ in the hydration product CAH10 of calcium silicate cement to generate hydroxyapatite (Ca5(PO4)3OH) to fill the microcracks. In addition, the released PO4 3- cooperates with the metabolites (CO3 2- ) of Bacillus pasteurii in the magnesium phosphate cement microcapsule to promote the release of calcite-type CaCO3 precipitation, realizing microbial metabolism-chemical dual repair. At the same time, the modified bentonite at the crack will absorb water and slowly expand, driving the unhydrated cement particles to contact the crack section to continue the hydration reaction, realizing the dynamic repair of the crack.

[0060] The modified bentonite can also increase the interlayer moisture content from 12% to about 4-6%, endowing the cement paste with excellent rheological properties. The thixotropic loop area can be reduced from 850 Pa / s to about 300-500. The organic chain segments remaining in the system of SDS-PEG can also adsorb on the surface of calcium aluminate cement to produce a steric hindrance effect, reducing the yield stress of the paste and at the same time improving the thermal stability of the system.

[0061] (4) Stearic acid (C 17 H 35 COOH) dissociates into stearate (C 17 H 35 COO - ) in an alkaline solution, combines with Ca 2+ on the surface of CaCO3 through a coordination bond to form a monolayer coating, realizing the steric hindrance effect of the stearic acid chain to inhibit the agglomeration of nano-CaCO3, so that the nano-calcium carbonate particles are distributed in the cement collective system to provide nucleation sites for subsequent reactions.

[0062] The hydrophobic chain segment of stearate (C 17 H 35 -) It forms π-alkyl interactions with the benzene ring structure of the styrene-butyl acrylate copolymer, enhancing the interfacial binding energy between the inorganic and organic phases, resulting in stronger interlayer adhesion during 3D printing, overcoming the key problem of insufficient interlayer adhesion in 3D printing and prone to erosion damage. In addition, nano-calcium carbonate forms a continuous hydrophobic film structure in the copolymer in the cement matrix, which can effectively block the migration of erosion ions in the system. At the same time, nano-calcium carbonate can provide nucleation sites for the suspended calcium aluminate cement particles in the system, and the hydration products such as ettringite show a nano-flower-like microstructure based on the fine nucleation sites and continuously extend around, forming a cementitious skeleton with higher strength and greater density. Finally, in the saturated steam treatment stage after 3D printing, the styrene segments of the copolymer form an interpenetrating network with the unhydrated cement paste at 60 °C, increasing the interlayer bonding strength of the cement to greater than 1.5 MPa.

[0063] (5) In the early stage of the modified calcium aluminate cement, due to the retardation effect of the organic matter, the hydration temperature is about 60 °C, while the spores of Bacillus pasteurii have good heat resistance and can resist high temperatures greater than or equal to 80 °C. After the bacterial spores are mixed evenly with the ammonium dihydrogen phosphate solution and the bacterial culture solution, porous microspheres are formed by spray drying into the overburned magnesium oxide. The high reactivity of magnesium phosphate cement will promote the rapid formation of a dense MgKPO4·6H2O shell around the spores, blocking oxygen and moisture and maintaining the dormant state of the spores. When cracks appear in the 3D printed structure, the microsphere shell is broken by stress, and the spores inside are released. After contacting the external moisture, they are activated and initiate the urease-driven biomineralization reaction:

[0064]

[0065] The generated CO3 2- Combines with the released Mg released from the dissolution of microsphere magnesium oxide in water 2+ And Ca in the environment 2+ Combines with CO2 in the air to form calcite-bioapatite double repair products, realizing rapid and high-strength filling of cracks and hardening and plugging of pores. In addition, the honeycomb-like pores inside the microspheres can also adsorb some ions and organic impurities in the environment, and inhibit the corrosion of steel bars through the ion exchange of Mg 2+ / Ca 2+ .

[0066] (6) The introduced basalt fibers are randomly distributed in three dimensions in the cement paste, enhancing the material anisotropy and forming a mechanical interlocking effect with the C-S-H gel generated by cement hydration, realizing the fiber bridging of the three-dimensional cement matrix-hydration products. In addition, when the fibers are pulled out from the matrix, the interface slip and the fiber cross-section cooperate to dissipate energy, significantly improving the crack resistance and toughness of the 3D printed structure.

[0067] Basalt fiber can form a modulus gradient with a nanometer calcium carbonate hybridized styrene-butyl acrylate copolymer, promoting the dispersion of the tip stress when cracks occur and enhancing the fracture resistance of the material.

[0068] Finally, adding basalt fiber will increase the plasticizing ability of the cement paste, making the viscosity higher in the early stage of 3D printing, the shape relatively stable, and not prone to slump and deformation.

[0069] (7) The phosphate-modified self-healing calcium aluminate cement 3D printing material prepared by the present invention can be applied in marine structures, highly corrosive environments such as saline-alkali soil, reinforcement support for underground high-temperature coal mine roadways, reinforcement of deep soft soil, and large-span and spiral new structures with high design requirements, and has broad application prospects. Specific Embodiments

[0070] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0071] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are interpretations rather than limitations of the present invention.

[0072] In the following embodiments, the preparation steps of the culture solution are as follows: Take 100 mL of peptone (10 g / L), 100 mL of beef extract (5 g / L), and 100 mL of NaCl (5 g / L), mix them evenly, add 0.5 g of urea and 0.25 g of CaCl2, first perform high-temperature sterilization at 121 °C for 20 minutes, and then let it stand to 15 °C to obtain it.

[0073] Example 1 : This embodiment provides a phosphate-modified self-healing calcium aluminate cement 3D printing material and its preparation method

[0074] The phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this embodiment, by mass, its raw material composition includes: 65 parts of calcium aluminate cement, 4 parts of silica fume, 2 parts of metakaolin, 1.6 parts of double-template agent-modified calcium-based bentonite, 1.15 parts of amino-modified sodium polyphosphate, 0.2 parts of basalt fiber, 0.6 parts of nanometer calcium carbonate hybridized styrene-butyl acrylate copolymer, 5 parts of magnesium phosphate cement-coated bacteria-loaded porous microspheres, 0.15 parts of polycarboxylate water reducer, 0.03 parts of silicone defoamer, and 33 parts of mixing water.

[0075] The specific preparation method includes the following steps:

[0076] (1) Mix 2 mol / L sodium dihydrogen phosphate (400 mL) and 2 mol / L disodium hydrogen phosphate (100 mL) in a volume ratio of 4:1. Then calcine the mixture in a muffle furnace at 750 °C until it melts. Pour the molten material into liquid nitrogen and quickly cool it to -20 °C. After grinding, disperse it in a 60% ethanol solution at a solid-liquid ratio of 1:8 (102 g of sodium polyphosphate is dispersed in 816 mL of ethanol solution), and add 10.2 g of silane coupling agent. Heat it with sodium polyphosphate in an oven at 60 °C for 2 h to obtain amino-modified sodium polyphosphate.

[0077] (2) Mix 0.25 mol / L magnesium nitrate (100 mL) and 0.25 mol / L aluminum nitrate (100 mL) in a volume ratio of 1:1 to form mixture A. Mix 100 g of calcium-based bentonite with 400 mL of 5% sodium carbonate solution to form mixture B. At the same time, mix 18 g of sodium dodecyl sulfate and 20.7 g of polyethylene glycol, and add 500 mL of pure water to form mixture C. First, mix solution B (400 mL) and solution C (200 mL) at 60 °C with stirring for 5 min. Then, slowly add solution A (320 mL) dropwise to the above mixture and stir evenly during heating to obtain calcium-based bentonite co-modified by a double template agent.

[0078] (3) React 50 g of 10% calcium hydroxide suspension with 500 mL of CO2 gas under the condition of pH = 9 to obtain a suspension. Dissolve 2.5 g of sodium stearate in 125 mL of distilled water to obtain a 2% sodium stearate solution. Take 6.08 g of the suspended precipitate, 12 mL of the sodium stearate solution, and mix them with 950 g of styrene-butyl acrylate copolymer emulsion to form a styrene-butyl acrylate copolymer hybridized with nano calcium carbonate.

[0079] (4) Take 14.3 mL of Bacillus pasteurii spore solution with a spore concentration of 3.5×10 8 CFU / mL, 760 mL of 0.2 mol / L ammonium dihydrogen phosphate solution, and 28.6 mL of culture medium. Load them into a spray dryer and spray them onto 1000 g of overburned magnesium oxide powder. After drying, form bacteria-loaded porous microspheres coated with magnesium phosphate cement.

[0080] (5) Dry-mix 65 parts by mass of calcium aluminate cement, 4 parts by mass of silica fume, 2 parts by mass of metakaolin, 1.6 parts by mass of calcium-based bentonite co-modified by a double template agent, 1.15 parts by mass of amino-modified sodium polyphosphate, and 0.2 parts by mass of basalt fiber to obtain a dry-mixed mixture.

[0081] (6) Mix 0.15 parts by mass of polycarboxylate superplasticizer, 0.03 parts by mass of silicone defoamer, and 28 parts by mass of mixing water uniformly, then add the dry-mixed mixture described in step (5) and continue stirring. Let it stand for 1 min to release bubbles to obtain a phosphate-modified calcium aluminate cement paste.

[0082] (7) Mix 0.6 parts by mass of a nano-calcium carbonate hybridized styrene-butyl acrylate copolymer with 5 parts by mass of mixing water, and then add the calcium aluminate cement paste described in step (6) and stir.

[0083] (8) Take 5 parts by mass of the above-mentioned magnesium phosphate cement-coated bacteria-carrying porous microspheres described in step (4) and add them to the mixed paste after step (7) is completed, and stir. Thus, the phosphate-modified self-healing calcium aluminate cement 3D printing material is obtained.

[0084] Example 2 : This example provides a phosphate-modified self-healing calcium aluminate cement 3D printing material and its preparation method

[0085] For the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this example, calculated by parts by mass, its raw material composition includes: 70 parts of calcium aluminate cement, 3 parts of silica fume, 2.5 parts of metakaolin, 0.9 part of double-template agent-modified calcium-based bentonite, 1.35 parts of amino-modified sodium polyphosphate, 0.15 part of basalt fiber, 0.5 part of nano-calcium carbonate hybridized styrene-butyl acrylate copolymer, 4.5 parts of magnesium phosphate cement-coated bacteria-carrying porous microspheres, 0.2 part of polycarboxylate superplasticizer, 0.02 part of silicone defoamer, and 34 parts of mixing water. The preparation steps are the same as those in Example 1.

[0086] Example 3 : This example provides a phosphate-modified self-healing calcium aluminate cement 3D printing material and its preparation method

[0087] For the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this example, calculated by parts by mass, its raw material composition includes: 68 parts of calcium aluminate cement, 3.4 parts of silica fume, 2.3 parts of metakaolin, 2.2 parts of double-template agent-modified calcium-based bentonite, 1.12 parts of amino-modified sodium polyphosphate, 0.25 part of basalt fiber, 0.7 part of nano-calcium carbonate hybridized styrene-butyl acrylate copolymer, 5 parts of magnesium phosphate cement-coated bacteria-carrying porous microspheres, 0.2 part of polycarboxylate superplasticizer, 0.04 part of silicone defoamer, and 34 parts of mixing water. The preparation steps are the same as those in Example 1.

[0088] Example 4 : This example provides a phosphate-modified self-healing calcium aluminate cement 3D printing material and its preparation method

[0089] The phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this example, by mass, its raw material composition includes: 65 parts of calcium aluminate cement, 4 parts of silica fume, 2 parts of metakaolin, 1.6 parts of double-template agent modified calcium-based bentonite, 1.15 parts of amino-modified sodium polyphosphate, 0.2 parts of basalt fiber, 1.2 parts of nano-calcium carbonate hybrid styrene-butyl acrylate copolymer, 5 parts of magnesium phosphate cement-coated bacteria-carrying porous microspheres, 0.15 parts of polycarboxylate water reducer, 0.03 parts of silicone defoamer, and 35 parts of mixing water. The preparation steps are the same as those in Example 1.

[0090] Example 5 This example provides a phosphate-modified self-healing calcium aluminate cement 3D printing material and its preparation method

[0091] The phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this example, by mass, its raw material composition includes: 70 parts of calcium aluminate cement, 3.5 parts of silica fume, 2.5 parts of metakaolin, 1.8 parts of double-template agent modified calcium-based bentonite, 1.3 parts of amino-modified sodium polyphosphate, 0.4 parts of basalt fiber, 0.7 parts of nano-calcium carbonate hybrid styrene-butyl acrylate copolymer, 7 parts of magnesium phosphate cement-coated bacteria-carrying porous microspheres, 0.15 parts of polycarboxylate water reducer, 0.03 parts of silicone defoamer, and 34 parts of mixing water. The preparation steps are the same as those in Example 1.

[0092] Example 6 This example provides a phosphate-modified self-healing calcium aluminate cement 3D printing material and its preparation method

[0093] The phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this example, by mass, its raw material composition includes: 65 parts of calcium aluminate cement, 4 parts of silica fume, 2 parts of metakaolin, 1.6 parts of double-template agent modified calcium-based bentonite, 1.15 parts of amino-modified sodium polyphosphate, 0.5 parts of basalt fiber, 0.6 parts of nano-calcium carbonate hybrid styrene-butyl acrylate copolymer, 5 parts of magnesium phosphate cement-coated bacteria-carrying porous microspheres, 0.15 parts of polycarboxylate water reducer, 0.03 parts of silicone defoamer, and 35 parts of mixing water. The preparation steps are the same as those in Example 1.

[0094] Comparative Example 1 This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0095] Different from the components in Example 1, the material prepared in this comparative example is only undisturbed soil. Specifically, for the prepared calcium aluminate cement 3D printing material, by mass, the raw material composition includes: 65 parts of calcium aluminate cement, 4 parts of silica fume, 2 parts of metakaolin, 0.2 parts of basalt fiber, 0.15 parts of polycarboxylate water reducer, 0.03 parts of silicone defoamer, and 30 parts of mixing water.

[0096] Specific preparation method, including the following steps:

[0097] (1) Dry-mix 65 parts by mass of calcium aluminate cement, 4 parts by mass of silica fume, 2 parts by mass of metakaolin, and 0.2 parts by mass of basalt fiber to obtain a dry-mixed mixture.

[0098] (2) Uniformly stir 0.15 parts by mass of polycarboxylate-based water reducer, 0.03 parts by mass of silicone defoamer, and 30 parts by mass of mixing water, and let it stand for 1 min to release bubbles to obtain a calcium aluminate cement paste.

[0099] Comparative Example 2 This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0100] Different from the components in Example 1, the raw material composition of the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this comparative example does not include amino-modified sodium polyphosphate, and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0101] Comparative Example 3 This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0102] Different from the components in Example 1, the raw material composition of the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this comparative example does not include double-template agent-modified calcium-based bentonite, and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0103] Comparative Example 4 This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0104] Different from the components in Example 1, the raw material composition of the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this comparative example does not include nano-calcium carbonate hybridized styrene-butyl acrylate copolymer, and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0105] Comparative Example 5 This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0106] Different from the components in Example 1, the raw material composition of the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this comparative example does not include magnesium phosphate cement-coated bacteria-loaded porous microspheres, and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0107] Comparative Example 6 This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0108] Different from the components in Example 1, the raw material composition of the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this comparative example does not include basalt fibers, and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0109] Comparative Example 7 This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0110] Different from the components in Example 1, in the raw material composition of the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this comparative example, the sodium polyphosphate modified with amino groups is replaced by single sodium polyphosphate, but the added mass remains unchanged (1.15 parts), and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0111] The preparation method of single sodium polyphosphate is as follows (replacing step (1) in Example 1):

[0112] After mixing 2 mol / L sodium dihydrogen phosphate (400 mL) and 2 mol / L disodium hydrogen phosphate (100 mL), it is calcined in a muffle furnace to 750 °C, melted and then poured into liquid nitrogen and rapidly cooled to -20 °C, and after grinding, 102 g of sodium polyphosphate is obtained.

[0113] Comparative Example 8 This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0114] Different from the components in Example 1, in the raw material composition of the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this comparative example, the double-template agent modified calcium-based bentonite is replaced by single-template agent modified calcium-based bentonite, but the added mass remains unchanged (1.6 parts), and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0115] The preparation method of single-template agent modified calcium-based bentonite is as follows (replacing step (2) in Example 1):

[0116] After mixing 0.25 mol / L magnesium nitrate (200 mL) and 0.25 mol / L aluminum nitrate (200 mL), a mixed solution A is formed; calcium-based bentonite (100 g) is uniformly mixed with 5% concentration sodium carbonate solution (400 mL) to form a mixed solution B; 18 g of sodium dodecyl sulfate is dissolved in pure water (500 mL) and stirred evenly to form a mixed solution C; first, solution B (400 mL) and solution C (200 mL) are stirred and mixed at 60 °C for 5 min, then solution A (320 mL) is added dropwise to the above mixed solution and stirred evenly during heating, and then placed in an oven and dried at a temperature of 60 °C to obtain single-template agent synergistically modified calcium-based bentonite.

[0117] Comparative Example 9 : This comparative example provides a calcium aluminate cement 3D printing material and its preparation method.

[0118] Different from the components in Example 1, in the raw material composition of the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in this comparative example, the double-template agent-modified calcium-based bentonite is replaced by template-free agent-modified calcium-based bentonite, but the added mass remains unchanged (1.6 parts), and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0119] The preparation method of the template-free agent-modified calcium-based bentonite is as follows (replacing step (2) in Example 1):

[0120] Mix 0.25 mol / L magnesium nitrate (200 mL) with 0.25 mol / L aluminum nitrate (200 mL) to form a mixed solution A, and uniformly mix calcium-based bentonite (100 g) with 5% sodium carbonate solution (400 mL) to form a mixed solution B; first, mix solution B (400 mL) and 200 mL of pure water at 60 °C with stirring for 5 min, then dropwise add solution A (320 mL) to the above-mentioned mixed solution and stir evenly during the heating process, and then place it in an oven and dry at a temperature of 60 °C to obtain double-template agent synergistically modified calcium-based bentonite.

[0121] Comparative Example 10 : This comparative example provides a calcium aluminate cement 3D printing material and its preparation method.

[0122] Different from the components in Example 1, in step (2), do not add sodium carbonate solution (do not perform ion exchange), but the added mass remains unchanged (1.6 parts), and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0123] The specific preparation method is as follows (replacing step (2) in Example 1):

[0124] Mix 0.25 mol / L magnesium nitrate (200 mL) with 0.25 mol / L aluminum nitrate (200 mL) to form a mixed solution A; uniformly mix calcium-based bentonite (100 g) with pure water (400 mL) to form a mixed solution B; mix 18 g of sodium dodecyl sulfate and 20.7 g of polyethylene glycol, add pure water (500 mL) and stir evenly to form a mixed solution C; first, mix solution B (400 mL) and solution C (200 mL) at 60 °C with stirring for 5 min, then dropwise add solution A (320 mL) to the above-mentioned mixed solution and stir evenly during the heating process, and then place it in an oven and dry at a temperature of 60 °C to obtain double-template agent synergistically modified calcium-based bentonite.

[0125] Comparative Example 11:This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0126] Different from the components in Example 1, in step (3), sodium stearate is not added, but the mass fraction remains unchanged (0.6 parts), and other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0127] The specific preparation method is as follows (replacing step (3) in Example 1):

[0128] React 50 g of 10% calcium hydroxide suspension with 500 mL of CO2 gas under the condition of pH = 9 to obtain a suspension. Take the suspended precipitate (6.08 g) and pure water (12 mL), and mix them with 950 g of styrene-butyl acrylate copolymer emulsion to form a styrene-butyl acrylate copolymer hybridized with nano calcium carbonate.

[0129] Comparative Example 12 :This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0130] Different from the components in Example 1, in step (3), styrene-butyl acrylate copolymer is not added, but the mass fraction remains unchanged (0.6 parts), and other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0131] The specific preparation method is as follows (replacing step (3) in Example 1):

[0132] React 50 g of 10% calcium hydroxide suspension with 500 mL of CO2 gas under the condition of pH = 9 to obtain a suspension. Dissolve 2.5 g of sodium stearate in 125 mL of distilled water to form a 2% sodium stearate solution. Take the suspended precipitate (6.08 g) and modify it with the sodium stearate solution (12 mL) to form a mixed solution of nano carbonic acid and sodium stearate.

[0133] Comparative Example 13 :This comparative example provides a calcium aluminate cement 3D printing material and its preparation method

[0134] Different from the components in Example 1, in step (3), only sodium stearate is added, but the mass fraction remains unchanged (0.6 parts), and other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0135] The specific preparation method is as follows (replacing step (3) in Example 1): Dissolve 2.5 g of sodium stearate in 125 mL of distilled water to obtain a 2% sodium stearate solution. Take the sodium stearate solution (12 mL) to form a sodium stearate solution.

[0136] Comparative Example 14: This comparative example provides a calcium aluminate cement 3D printing material and its preparation method.

[0137] Different from the components in Example 1, in step (3), only styrene-butyl acrylate copolymer is added, but the added mass remains unchanged (0.6 parts), and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0138] Comparative Example 15 : This comparative example provides a calcium aluminate cement 3D printing material and its preparation method.

[0139] Different from the components in Example 1, in step (3), only the carbonization operation of calcium hydroxide is carried out, but the added mass remains unchanged (0.6 parts), and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0140] The specific preparation method is as follows (replacing step (3) in Example 1): React 50 g of a 10% concentration calcium hydroxide suspension with 500 mL of CO2 gas under the condition of pH = 9 to obtain a suspension, take the suspended precipitate (6.08 g) and mix it with pure water (12 mL) to form a nano-calcium carbonate suspension.

[0141] Comparative Example 16 : This comparative example provides a calcium aluminate cement 3D printing material and its preparation method.

[0142] Different from the components in Example 1, in step (4), ammonium dihydrogen phosphate solution is not added, but the added mass remains unchanged (5 parts), and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0143] The specific preparation method is as follows (replacing step (4) in Example 1): Take 14.3 mL of a Bacillus pasteurii spore solution with a spore concentration of 3.5×10 8 CFU / mL, mix it with 788.6 mL of a culture solution, load it into a spray dryer, and spray it onto 1000 g of overburned magnesium oxide powder, and obtain it after drying.

[0144] Comparative Example 17 : This comparative example provides a calcium aluminate cement 3D printing material and its preparation method.

[0145] Different from the components in Example 1, in step (4), overburned magnesium oxide is not added, but the added mass remains unchanged (5 parts), and the other components and their contents are the same as those in Example 1; the preparation steps are the same as those in Example 1.

[0146] The specific preparation method is as follows (replacing step (4) in Example 1): Take 14.3 mL of a Bacillus pasteurii spore solution with a spore concentration of 3.5×10 8It is obtained by mixing a solution of Bacillus pasteurii spores at CFU / mL with 760 mL of 0.2 mol / L ammonium dihydrogen phosphate solution and 28.6 mL of culture solution.

[0147] Test Example 1 :

[0148] Take a part of the materials prepared in Examples 1-6 and Comparative Examples 1-17 and pour them into a specific mold. After curing for 1 day, demold, and then continue to cure the specimen naturally. Cover it with plastic wrap during the curing period. After reaching the specified age, test the unconfined compressive strength, chloride ion diffusion coefficient, and compressive strength loss rate after 150 wet-dry cycles under sulfate environment of the obtained cement paste at 7 days and 56 days. At the same time, take another part to test a series of indexes such as thixotropy index TI, interlayer bond strength, and peak hydration heat. The test data are shown in Tables 1-2.

[0149] According to "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021) and "Standard Test Method for Basic Properties of Building Mortar" (JGJ / T 70-2009), use standard cube specimens of 40×40×40 mm and prism specimens of 40×40×160 mm to load at a rate of 1 kN / s on an electronic universal testing machine to measure their 7-day strength (early stage) and 56-day strength (long term).

[0150] According to the rapid chloride migration coefficient method in "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082-2009), measure the chloride ion diffusion coefficient at 56 days.

[0151] According to "Test Method for Resistance of Cement to Sulfate Attack" (GB / T 749-2008), immerse the specimens in 5% Na2SO4 solution and test the compressive strength loss rate after 150 wet-dry cycles.

[0152] According to "Standard Test Methods for Geotechnical Engineering" (GB / T 50123-2019), use a HAKKE MARS60 rotational rheometer to test the shear stress-rate curve and calculate the thixotropy index TI of the paste.

[0153] According to "3D Printing Cementitious Materials for Construction" (T / CECS 786-2020), use Z-shaped specimens to conduct a direct tensile test to measure the interlayer bond strength.

[0154] According to "Test Method for Heat of Hydration of Cement" (GB / T 12959-2023), use an isothermal calorimeter to measure the peak heat release of cement hydration.

[0155] Table 1

[0156]

[0157]

[0158] Table 2

[0159]

[0160]

[0161] It can be obtained from the data analysis in Table 2 that:

[0162] (1) Compared with Example 1, although Examples 2-6 meet the relevant requirements of the compressive strength, flexural strength, chloride ion diffusion coefficient, compressive strength loss rate, thixotropic index, bond strength, and exothermic peak value of the 3D printing material in the engineering application scenario, there are still deficiencies in the specific performance: Compared with Example 1, the early compressive and flexural strengths of Examples 2-3 are slightly reduced, while the chloride ion diffusion coefficient increases significantly, indicating that the erosion resistance ability is relatively poor compared with Example 1. In addition, the compressive strength loss rate also increases, indicating that its durability performance is significantly reduced compared with Example 1. The bond strength is relatively low, indicating that the 3D printing effect becomes worse and it is easy to cause peeling and separation between layers. The exothermic peak values of the hydration heat of Examples 2-3 are also relatively high, which is easy to cause heat accumulation. The thixotropic indexes of Examples 2-3 are all between 2.0 and 2.3, which are relatively suitable for 3D printing.

[0163] Compared with Example 1, the early compressive strength and long-term compressive strength of Example 4 are slightly reduced, the chloride ion diffusion coefficient increases, the bond strength decreases, the exothermic peak value of the hydration heat becomes higher, and the thixotropic index is lower than 2.0. This is because the addition of 1.2 parts of nano calcium carbonate hybrid copolymer is relatively high compared with the optimal addition amount (0.6 parts) of Example 1, and the nano calcium carbonate is relatively excessively distributed in the calcium aluminate cementitious system, resulting in a decrease in the thixotropic index. At the same time, since the styrene-acrylate copolymer hybridized with nano calcium carbonate helps to enhance the binding energy of the organic-inorganic interface, excessive addition will cause the 7-day flexural strength to be greater than that of Example 1. As time goes by, the overall hydration effect of Example 1 is better than that of Example 4, so the 56-day flexural strengths are similar.

[0164] Compared with Example 1, Example 5 is characterized by a decrease in early and long-term compressive strength, thixotropy index, and bond strength, as well as an increase in chloride ion diffusion coefficient, compressive strength loss rate, and peak heat release of hydration. The increase in flexural strength at 7 days and 56 days in Example 5 is due to the addition of more metakaolin, amino-modified sodium polyphosphate, nano-calcium carbonate hybridized styrene-butyl acrylate copolymer, and basalt fiber, which significantly enhances the flexural strength of the system. However, significantly, the addition of excessive basalt fiber significantly reduces its ability to resist chloride ion penetration and diffusion and its durability, specifically manifested as a significant increase in chloride ion diffusion coefficient and compressive strength loss rate. For 3D printing materials applicable to extreme environments and special structures, the increase in flexural strength cannot come at the cost of a large loss in durability, thixotropy, and erosion resistance. Therefore, through comprehensive comparison of various properties, it can be concluded that the proportion of Example 1 is the optimal range described above.

[0165] (2) Compared with Example 1, the material prepared in Comparative Example 1 is only raw soil, calcium aluminate cement, silica fume, metakaolin, basalt fiber, polycarboxylate superplasticizer, silicone defoamer, and mixing water. No modification was made to the cement system, so it is inferior to the modified cement system in all performance indicators described in the present invention.

[0166] (3) Compared with Example 1, Comparative Example 2 and Comparative Example 7 mainly explored the effects of amino-modified sodium polyphosphate on the 3D printing material system of modified calcium aluminate cement. Comparative Example 2 did not add amino-modified sodium polyphosphate, and Comparative Example 7 used sodium polyphosphate for modification without amino modification. It can be seen that both Comparative Example 2 and Comparative Example 7 are significantly lower than Example 1 in terms of compressive strength, flexural strength, bond strength, etc. The overall performance of Comparative Example 7 is better than that of Comparative Example 2. It can be first concluded that the beneficial effects of sodium polyphosphate on the modification of calcium aluminate cement are reflected in compressive strength, durability, thixotropic properties, bond properties, and peak heat release of hydration. In addition, the amino-modified sodium polyphosphate endows the sodium polyphosphate molecule with hydrophobicity due to the introduction of amino groups, reducing the premature dissolution of polyphosphate molecules in the cement paste and ensuring the slow release of ions, which helps to improve the long-term strength and uniform hydration. Therefore, compared with the single sodium polyphosphate system, there is a significant improvement in compressive strength and other aspects. It should be particularly noted that compared with the system without the introduction of sodium polyphosphate, the introduction of a single sodium polyphosphate will slightly increase the chloride ion diffusion coefficient because when only a single sodium polyphosphate long chain is introduced, due to its lubricating effect, it endows the cement paste with shear thinning characteristics and is likely to introduce a certain amount of microbubbles, which play an adverse role in the chloride ion diffusion experiment.

[0167] (4) Compared with Example 1, Comparative Examples 3 / 8 / 9 / 10 mainly explored the role of double-template modified calcium-based bentonite. In Comparative Example 3, double-template modified calcium-based bentonite was not added; in Comparative Example 8, only single-template modification of calcium-based bentonite was carried out; in Example 9, only calcium-based bentonite was added without modification; in Comparative Example 10, sodium carbonate solution was not added to the double-template modified calcium-based bentonite (ion exchange was not carried out); the analysis of the reasons for each performance parameter is as follows:

[0168] a) Compared with Example 1, Comparative Example 3 showed a significant decline in all performances, which proved the significant advantages of double-template modified calcium-based bentonite in improving early compressive and flexural strengths and interlayer bonding properties. At the same time, due to its good adsorption performance, it also had significant advantages in properties such as compressive strength loss rate and resistance to chloride ion erosion. The specific reason analysis is as described in the advantageous effects (2) of the present invention above.

[0169] b) By comparing Comparative Example 8 with Comparative Example 3 and Example 1, it can be seen that when single-template modified calcium-based bentonite was added, there was an obvious improvement in compressive and flexural strengths, thixotropic properties, and bonding strength, but the effect was worse than that of double-template modification. In addition, the compressive strength loss rate decreased significantly because after modification with the template agent, although the complexity of the spatial structure and adsorption performance were lower than those of double-template modification, the interlayer spacing of calcium-based bentonite was expanded, and at the same time, it had a partial interlayer structure and adsorption characteristics of layered double hydroxides, showing obvious advantages in durability. It should be noted that the chloride ion diffusion coefficient of Comparative Example 8 was greater than that of Comparative Example 3 because the addition of the single-template modifier caused tiny gaps to appear between the organic matter-calcium aluminate cement aggregate particles, and some of the template modifiers could not be in close contact with the hydration products of calcium-based bentonite and calcium aluminate cement, resulting in an increase in the chloride ion diffusion coefficient.

[0170] c) The unmodified calcium-based bentonite in Comparative Example 9 showed an obvious decrease in compressive and flexural strengths, bonding strength, and thixotropic properties because the unmodified calcium-based bentonite only acted as a pore filler and could not play a long-term role in strong adsorption and slow release of examples, contributing less to strength and durability. At the same time, due to the absence of template agent addition, compared with Example 1, there was no ether bond -O- hydrogen bonding with the hydroxyl groups of bentonite, and neither the helical structure nor the hydrophobic-hydrophilic composite structure intercalation was formed. Therefore, Comparative Example 9 also had significant disadvantages in terms of erosion resistance and thixotropic properties.

[0171] d) In Comparative Example 10, the replacement of sodium ions and calcium ions was not carried out. Due to the change in interlayer spacing, Mg 2+ and Al 3+, its ability to react with amino-modified sodium polyphosphate to form Mg3(PO4)2 and AlPO4 precipitates is slightly weakened. At the same time, the thixotropic performance is not conducive to the thixotropic performance due to the decrease in its layer spacing, resulting in an increase in the interlayer attraction.

[0172] (5) Compared with Example 1, Comparative Examples 4 / 11 / 12 / 13 / 14 / 15 studied and explored the 3D printing performance of nano-calcium carbonate hybrid styrene-butyl acrylate copolymer on modified calcium aluminate cement. Comparative Example 4 did not add nano-calcium carbonate hybrid styrene-butyl acrylate copolymer; Comparative Example 11 did not add sodium stearate solution; Comparative Example 12 did not add styrene-butyl acrylate copolymer; Comparative Example 13 only added sodium stearate, and neither nano-calcium carbonate nor styrene-butyl acrylate was added; Comparative Example 14 only added styrene-butyl acrylate, and neither sodium stearate nor nano-calcium carbonate was added; Comparative Example 15 added nano-calcium carbonate after the carbonation operation of calcium hydroxide, and neither sodium stearate nor styrene-butyl acrylate copolymer was added; The data analysis of the experiments is as follows:

[0173] a) Compared with Example 1, the performance of Comparative Example 4 deteriorated in all aspects, especially in key indexes such as compressive and flexural strength, bond strength, chloride ion diffusion coefficient, and compressive strength loss rate, showing a very serious decline. It fully reflects that the hydrophobic chain segment (C 17 H 35 -) of the stearate root forms a π-alkyl interaction with the benzene ring structure of the styrene-butyl acrylate copolymer, enhancing the interfacial binding energy of the inorganic-organic phase; at the same time, the filling and nucleation site-providing effects of nano-calcium carbonate, which further enhance the system strength, are also fully demonstrated by this comparison. The specific principle has been described in the above beneficial effect (4) and will not be elaborated here.

[0174] b) Comparing Comparative Example 12 with Example 1, it can be seen that all parameters of Comparative Example 12 have significantly deteriorated, but the hydration temperature has increased significantly. This is because styrene-butyl acrylate has a certain retarding effect and can reduce the peak value of the hydration heat temperature. At the same time, comparing with Comparative Examples 4 and 13, it can be seen that the compressive and flexural strengths of Comparative Example 12 are also significantly better than those of Comparative Examples 4 and 13. It is analyzed that this is the result of adding nano-calcium carbonate in Comparative Example 12.

[0175] c) By comparing Comparative Example 13 with Comparative Example 4 and Example 1, it can be seen that Comparative Example 13 is lower than Example 1 in terms of compressive and flexural strength, etc. Compared with Comparative Example 4, there are no obvious changes in other aspects except for the thixotropic index. This is because only adding sodium stearate solution and not adding styrene-butyl acrylate copolymer and nano calcium carbonate simultaneously cannot play an obvious role in increasing strength; however, since sodium stearate molecules are dispersed in water, the hydrophilic and hydrophobic ends of the molecules are arranged directionally, which improves the fluidity of the slurry and significantly improves the thixotropic performance of the coordinated system. At the same time, the introduction of organic matter also reduces the peak value of the heat of hydration. However, the bond strength and the loss rate of compressive strength are slightly lower compared with Comparative Example 4. This is because the single addition of sodium stearate does not produce a synergistic effect with styrene-butyl acrylate copolymer and nano calcium carbonate. Sodium stearate molecules can neither participate in the bonding and bridging of the inorganic system nor form a complex spatial structure alone to enhance the interfacial performance. Therefore, the finally hydrated structural system is relatively loose, and the flexural strength and long-term stability performance are poor. The loose system can also explain why the chloride ion diffusion coefficient of Comparative Example 13 is greater than that of Comparative Example 4.

[0176] d) By comparing Comparative Example 14 with Comparative Example 4 and Example 1, it can be seen that the compressive and flexural strengths of Comparative Example 14 are higher than those of Comparative Example 4. In addition, its chloride ion diffusion performance, thixotropic performance, and bonding performance are also better than those of Comparative Example 4. Its heat of hydration peak value is lower, indicating that styrene-butyl acrylate copolymer has a certain effect on improving the structural strength and interlayer bonding force, and at the same time plays a certain retarding role, making the initial hydration time relatively prolonged and the heat of hydration peak value not obvious. However, according to the compressive strength loss rate of 14.4% which is much higher than that of Comparative Example 4 and Example 1, it is because styrene-butyl acrylate copolymer, as an admixture that cannot be compatible with the calcium aluminate cement system, will leave certain gaps between the key hydration products and particles. With the continuous progress of the wet-dry cycle, these fine gaps are the key occurrence sites of strength loss and interfacial damage, resulting in an increase in the compressive strength loss rate.

[0177] e) By comparing Comparative Example 15 with Comparative Example 4, Comparative Example 14, and Example 1, it can be seen that the early (7d) compressive and flexural strengths of Comparative Example 15 are significantly better than those of Comparative Example 4 and Comparative Example 14. However, the compressive and flexural strengths at 56d have no significant difference from those of Comparative Example 14, but are still significantly better than those of Comparative Example 4. This is because when only nano-calcium carbonate is added, it can provide more nucleation sites for the calcium aluminate system in the early stage, facilitating the acceleration of the hydration rate and resulting in an increase in early strength. However, when hydration is complete in the later stage, there will be no significant difference in the final strength. The acceleration of the early hydration rate exactly explains why the exothermic peak of the hydration heat of Comparative Example 15 is 75.6, which is significantly higher than that of other comparative examples. The chloride ion erosion resistance of Comparative Example 15 is significantly better than that of Comparative Example 4 and Comparative Example 14 because the addition of nano-calcium carbonate reduces the porosity in the cement hydration system, and the denser pore structure further enhances the ability to resist the diffusion of chloride ion erosion and the bond strength. However, the addition of nano-calcium carbonate slightly reduces the fluidity and thixotropic properties of calcium aluminate cement.

[0178] (6) Comparative Examples 5 / 16 / 17 mainly studied the effects of bacterium-loaded porous microspheres coated with magnesium phosphate cement on various parameters of 3D printing of modified calcium aluminate cement. Comparative Example 5 did not add bacterium-loaded porous microspheres coated with magnesium phosphate cement; Comparative Example 16 did not add ammonium dihydrogen phosphate solution, and Comparative Example 17 did not add magnesium peroxide. The following is the analysis of the test data of Comparative Example 5:

[0179] a) By comparing Comparative Example 5 with Comparative Example 1 and Example 1, it can be found that the decrease in the early compressive and flexural strengths of Comparative Example 5 is not significant compared with that of Example 1, and the effect is significantly better than that of Comparative Example 1. However, the compressive and flexural strengths at 56d are significantly lower than those of Example 1 because without bacterium-loaded porous microspheres coated with magnesium phosphate cement, when the structure is eroded and deteriorated, bacteria in the microspheres cannot be released through the rupture of the bacterium-loaded microspheres for self-repair, resulting in subsequent strength reduction and poor durability. And since no magnesium phosphate cement bacterium-loaded microspheres are added, its compactness and the basic process of calcium aluminate cement hydration are not affected. At the same time, not adding magnesium phosphate cement bacterium-loaded porous microspheres has a certain adverse effect on the thixotropy index and interlayer bond strength, but the effect is not significant (<10%). The exothermic peak of the hydration heat is slightly higher than that of Example 1 because the microspheres distributed in the calcium aluminate cement system play a role in lubrication and uniform water distribution, promoting hydration to a certain extent and making the exothermic peak of the hydration heat slightly higher than that of Example 1. Although the addition or not of magnesium phosphate cement bacterium-loaded porous microspheres has no obvious effect on the performance in terms of early strength, thixotropy, and hydration heat peak, its durability and continuous self-repair level are far lower than those of Example 1. Therefore, it can be predicted that when facing 3D printing projects for more complex structures and adverse environments, adding magnesium phosphate cement bacterium-loaded porous microspheres to enable the system to perform self-repair is of great significance.

[0180] b) The relevant data of Comparative Examples 16 / 17 were not detected because the magnesium phosphate cement hard shell of the magnesium phosphate cement bacteria-loaded porous microspheres is mainly composed of struvite, a hydration product formed by the components of ammonium dihydrogen phosphate + magnesium oxide. Without either ammonium dihydrogen phosphate or magnesium oxide, it is impossible to properly coat the bacteria carried, and it is impossible to form a microsphere system with bacterial strains inside and a hard shell coating outside. At this time, it is impossible to prepare suitable magnesium phosphate cement bacteria-loaded porous microspheres, so the performance of Comparative Examples 16 / 17 is not tested. Test Example 2 : In this test example, the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in Example 1 was applied to 3D printing.

[0181] (1) A twin-screw extrusion 3D printer with a diameter of 45 mm and a length-to-diameter ratio L / D = 12:1 was used, equipped with a constant-temperature cold water system and a vacuum degassing module. The basic parameters of the printing speed were: 90 mm / min in the horizontal direction and 30 mm / min in the vertical direction. A standard structure of 300×300×300 mm 3 , a hollow cylinder with a honeycomb-shaped inner cavity structure with a wall thickness of 40 mm and a pore diameter of 50 mm was printed. The printing layer thickness was set to 5 mm according to the printing structure requirements, and the interlayer interval time was less than 60 s.

[0182] (2) The material adaptability was regulated. Through an embedded ultrasonic viscometer with a frequency of 2 MHz and a screw rotation speed of 30 rpm. The thixotropic index of the cement paste was feedback in real time, and the screw rotation speed was dynamically regulated to ensure that the thixotropic index was 1.9.

[0183] (3) Immediately after 3D printing, a moisture-proof film was covered and cured at a temperature near 25°C for 24 h, and then treated with saturated steam at a pressure of 0.15 Mpa and 60°C for more than 1 h.

[0184] An embedded temperature-resistivity dual-parameter sensor (accuracy ±0.5°C) was used to monitor the performance evolution of the printed body in real time:

[0185] Stage I (0 - 60 minutes): The resistivity increased from 2.5 Ω·m to 8.3 Ω·m, corresponding to the rapid generation of CAH10;

[0186] Stage II (60 - 240 minutes): The peak temperature was 58°C (24°C lower than that of pure CAC), inhibiting thermal stress cracking;

[0187] Stage III (after 24 hours): The resistivity stabilized at 15.6 Ω·m, indicating that the microstructural densification was completed.

[0188] According to long-term monitoring, the initial setting time, 1h compressive strength, interlayer bonding strength, self-healing efficiency, and 28d drying shrinkage value of the 3D printed material after printing are shown in Table 3 below:

[0189] Table 3

[0190]

[0191] From the data in Table 3, it can be seen that compared with the 3D printing of the printing material prepared in Example 1 and ordinary Portland cement, the initial setting time is shortened from 60 min to 35 min. The phosphate accelerates the hydration of CAC, shortens the initial setting time, and avoids the occurrence of interlayer cold joints. The 1d compressive strength is increased from 4.5 MPa to 8.1 MPa compared with ordinary Portland cement, indicating its ultra-early strength characteristics. Calcium aluminate cement (CAC) rapidly generates the CAH10 phase, and the interface of magnesium phosphate microspheres is strengthened. The 1d strength can support the subsequent printing layer, and the 1d strength has significant engineering application significance. The interlayer bonding strength is increased from 1.05 MPa of ordinary Portland cement to 1.45 MPa. The bridging effect between fibers, vacuum degassing and steam curing promote the interweaving of interlayer hydration products, resulting in a more than 30% increase in the bonding strength. Magnesium phosphate-coated bacteria-loaded microspheres release the repair agent at the crack, react with the residual Ca 2+ to generate CaCO3 to fill the microcracks, and the self-healing efficiency is significantly improved compared with ordinary Portland cement (60%). Due to the large dry shrinkage of the structure of ordinary Portland cement, the drying shrinkage value is reduced from about 0.05% to 0.025%. Nano-calcium carbonate hybrid copolymer inhibits shrinkage, and the expansion component (metakaolin) compensates for deformation, reducing the risk of structural cracking.

[0192] Test Example 3 : In this test example, a large-span curved surface structure printing application test was carried out on the phosphate-modified self-healing calcium aluminate cement 3D printing material prepared in Example 1

[0193] including the following steps:

[0194] (1) Use a twin-screw extrusion 3D printer with a screw diameter of 55 mm and a length-diameter ratio L / D = 135:1, equipped with a constant-temperature cold water circulation system and a vacuum degassing module. At the same time, the print head is equipped with a high-frequency vibration device with a vibration frequency of 50 Hz and an amplitude of 0.3 mm.

[0195] (2) Configure the extrusion pressure parameter to be 1.2 MPa, and control the extrusion flow rate at about 1.8 L / min. Print horizontally at a speed of 120 mm / s in the area where the radius of curvature is less than or equal to 5 m. Print at a speed of 80 mm / s in the area where the radius of curvature is greater than 5 m. The vertical layer thickness is 5 mm, and the interlayer interval time is less than 30 s.

[0196] (3) A 2.5MHz ultrasonic viscometer is embedded in the front section of the print head to monitor the rheological parameters of the slurry in real time. The screw speed is dynamically adjusted within the speed range of 25-35rpm to maintain the thixotropic index around 2.0. At the same time, the vacuum degassing module controls the gas content of the slurry to be less than or equal to 1.5%. The constant temperature system maintains the slurry temperature at 20±2℃, and the interlayer contact surface is preheated to 35℃ using an infrared heating plate.

[0197] (4) During the printing process, key nodes are reinforced. A 10×10mm carbon fiber grid with a fiber diameter of 7um is pre-embedded in the vault area of the large-span arch structure with an embedding depth of 2mm. After every 5 layers of printing, nano-SiO2 with a concentration of 4% is sprayed on the interface to enhance the interface performance.

[0198] (5) After printing is completed, the double-layer PVF moisturizing film is covered within 30 minutes, and 0.18MPa saturated steam is used for curing at 60℃ for 12 hours. After steam curing, it is moved to room temperature for natural curing. A 0.3% CaCl2 solution is sprayed daily at a spraying rate of 50mL / m 2 .

[0199] (6) After the curing was completed, the 28d compressive strength, interlayer bonding strength, ultimate bearing capacity, 56d drying shrinkage and thermal deformation temperature were tested as shown in Table 4:

[0200] Table 4

[0201]

[0202]

[0203] As can be seen from the data in Table 4, the test results of the printing application of large-span curved surface structures using phosphate-modified self-healing calcium aluminate cement 3D printing materials in the above embodiment are compared with the printing application test of large-span curved surface structures using ordinary Portland cement 3D printing materials. The inter-layer interval time is less than 30 seconds (ordinary cement requires about 2 minutes), and the 5mm layer thickness in the vertical direction achieves high-precision and rapid stacking, shortening the construction period by 40%;

[0204] In addition, the 28-day compressive strength increased from 43 MPa to 59.4 MPa, which is due to the high density of the phosphate-modified CAC hydration product. In addition, the self-healing effect of basalt fiber and magnesium phosphate cement microspheres increased the 28-day compressive strength by about 30%.

[0205] Its ultra-low drying shrinkage rate is 0.25‰ (compared with 0.5‰ of portland cement). Ultra-low shrinkage rate: due to nano-calcium carbonate hybrid copolymer + steam curing to inhibit shrinkage deformation and avoid the cracking risk of long-span structures; the thermal deformation temperature of ordinary portland cement structure is about 220°C, while the calcium aluminate system has remarkable high-temperature resistance characteristics. In addition, the styrene-butyl acrylate copolymer hybridized with nano-calcium carbonate can further optimize the heat resistance performance of the material and is applicable to high-temperature industrial buildings (such as the vault of a smelter);

[0206] The ultimate bearing capacity of ordinary portland cement is about 10 N / m 2 or so, and the interlayer bonding strength is about 1.45 MPa or so. The experimental example method described in the present invention is significantly superior to ordinary portland cement in terms of interlayer bonding strength and ultimate bearing capacity. The improvement of the above properties is due to sodium polyphosphate (NaPO3) n generating calcium-aluminum-phosphate colloid (CaAlPO4·nH2O), delaying the heat release of hydration and serving as a nucleation site to enhance the later strength; sodium polyphosphate modified by silane coupling agent enhances the organic-inorganic interface combination, reduces the yield stress and increases the thixotropic recovery rate, and strengthens the interlayer bonding. Modified bentonite adsorbs Cl - / SO4 2- through ion exchange and releases Mg 2+ / Al 3+ to generate Mg3(PO4)2 / AlPO4 to fill the pores, and cooperate with magnesium phosphate microspheres for crack repair to form a dense structure. Stearic acid-coated nano-CaCO3 inhibits agglomeration, forms a hydrophobic film and an interpenetrating network with the copolymer, and combines with the three-dimensional bridging of basalt fibers to significantly improve the compressive strength, bonding strength, crack resistance and bearing capacity.

[0207] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A phosphate-modified self-healing calcium aluminate cement 3D printing material, characterized in that, By mass, its raw material composition includes: 60-70 parts of calcium aluminate cement, 3-7 parts of silica fume, 2-4 parts of metakaolin, 0.5-3.5 parts of double-template agent modified calcium-based bentonite, 0.8-1.5 parts of amino-modified sodium polyphosphate, 0.15-0.8 parts of basalt fiber, 0.45-2.0 parts of nano-calcium carbonate hybrid styrene-butyl acrylate copolymer, 4-7 parts of bacterium-loaded porous microspheres coated with magnesium phosphate cement, 0.1-0.25 parts of polycarboxylate water reducer, 0.02-0.04 parts of silicone defoamer, and 25-35 parts of mixing water.

2. The phosphate-modified self-healing calcium aluminate cement 3D printing material according to claim 1, characterized in that, For the phosphate-modified self-healing calcium aluminate cement 3D printing material, by mass, its raw material composition includes: 65 parts of calcium aluminate cement, 4 parts of silica fume, 2 parts of metakaolin, 1.6 parts of double-template agent modified calcium-based bentonite, 1.15 parts of amino-modified sodium polyphosphate, 0.2 parts of basalt fiber, 0.6 parts of nano-calcium carbonate hybrid styrene-butyl acrylate copolymer, 5 parts of bacterium-loaded porous microspheres coated with magnesium phosphate cement, 0.15 parts of polycarboxylate water reducer, 0.03 parts of silicone defoamer, and 33 parts of mixing water.

3. The phosphate-modified self-healing calcium aluminate cement 3D printing material according to claim 1, characterized in that, The double-template agent modified calcium-based bentonite is prepared by the following steps: Drop the mixed solution of magnesium nitrate and aluminum nitrate into the sodium-bentonite suspension containing sodium dodecyl sulfate and polyethylene glycol, and obtain it through centrifugation, drying, and grinding. Among them, the concentrations of both magnesium nitrate and aluminum nitrate are 0.25-0.3 mol / L; the sodium-bentonite is prepared by mixing calcium-based bentonite and a sodium carbonate solution with a concentration of 4-6% according to a dosage ratio of 1 g:4-5 mL; the mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1:1.15-1.

2. Sodium dodecyl sulfate and polyethylene glycol are used as template agents, and the content of the template agent in the aqueous solution is 5%-8%. The mass ratio of the template agent to sodium-bentonite is 1:0.45-0.47; the volume ratio of the mixed solution of magnesium nitrate and aluminum nitrate to the sodium-bentonite suspension is 1:0.5-0.

9.

4. The phosphate-modified self-healing calcium aluminate cement 3D printing material according to claim 1, characterized in that, The amino-modified sodium polyphosphate is prepared by the following steps: Mix sodium dihydrogen phosphate and sodium hydrogen phosphate according to a volume ratio of 4:1, calcine and melt, and then cool and grind to less than 200 meshes; react the ground product sodium polyphosphate with a silane coupling agent in a 60-80% ethanol solution. The mass ratio of the silane coupling agent to sodium polyphosphate is 0.08-0.12:

1. The silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, anilinomethyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, and octyltriethoxysilane, preferably γ-aminopropyltriethoxysilane.

5. The phosphate-modified self-healing calcium aluminate cement 3D printing material according to claim 4, characterized in that, The bacteria in the bacterium-loaded porous microspheres coated with magnesium phosphate cement are selected from one or more of Bacillus pasteurii, Bacillus thuringiensis, Bacillus licheniformis, and Sarcina pasteurii, preferably Bacillus pasteurii. The spore concentration of Bacillus pasteurii is (2-5)×108 CFU / mL, and the outer shell of the microspheres is a dense MgKPO4·6H2O structure formed by magnesium phosphate cement. Preferably, the basalt fiber has a length of 3-6 mm, a fiber diameter of 10-18 μm, and is randomly distributed in three dimensions in the paste.

6. The phosphate-modified self-healing calcium aluminate cement 3D printing material according to claim 4, wherein The nano-calcium carbonate hybridized styrene-butyl acrylate copolymer is prepared by the following steps: Carbonize the calcium hydroxide suspension with CO2. The obtained precipitate, nano-calcium carbonate, is modified with stearic acid and then mixed with the styrene-butyl acrylate copolymer emulsion; wherein, the concentration of the calcium hydroxide suspension is 8-10%, the solubility of the stearic acid solution is 1.5-2%, and the mass ratio of the stearic acid-modified nano-calcium carbonate to the styrene-butyl acrylate copolymer emulsion is 1:19-21.

7. The preparation method of the phosphate-modified self-healing calcium aluminate cement 3D printing material according to any one of claims 1 to 6, characterized in that, It includes the following steps: S1. Mix sodium dihydrogen phosphate and disodium hydrogen phosphate, calcine and melt them, then cool, grind, disperse in an ethanol solution for reaction, and then add a silane coupling agent. After reaction, amino-modified sodium polyphosphate is obtained; S2. Mix magnesium nitrate and aluminum nitrate to form a mixed solution A, mix calcium-based bentonite and sodium carbonate solution to form a mixed solution B, dissolve sodium dodecyl sulfate in a polyethylene glycol solution to form a mixed solution C. First, mix solution B and solution C and stir to obtain a mixed solution BC, and then drop solution A into the mixed solution BC, heat and react to obtain calcium-based bentonite modified by a double template agent; S3. React the calcium hydroxide suspension with CO2 gas, take the suspended precipitate, modify it with a stearic acid solution, and then mix it with the styrene-butyl acrylate copolymer emulsion to form a nano-calcium carbonate hybridized styrene-butyl acrylate copolymer; S4. Mix the bacterial spores with a dihydrogen phosphate solution and a culture solution, spray them on the over-burned magnesium oxide powder, and dry to form a bacteria-loaded porous microsphere coated with magnesium phosphate cement; S5. Dry-mix calcium aluminate cement, silica fume, metakaolin, calcium-based bentonite modified by a double template agent, amino-modified sodium polyphosphate, and basalt fiber to obtain a dry-mixed mixture; S6. Uniformly stir a polycarboxylate-based water reducer, an organosilicon defoamer, and mixing water, then add the dry-mixed mixture described in step S5 and continue to stir. After standing, a phosphate-modified calcium aluminate cement paste is obtained; S7. Mix the nano-calcium carbonate hybridized styrene-butyl acrylate copolymer with the mixture, and then add the phosphate-modified calcium aluminate cement paste described in step S6 and stir to obtain a mixed paste; S8. Take the bacteria-loaded porous microsphere coated with magnesium phosphate cement described in step S4 and add it to the mixed paste in step S7, and stir to obtain the phosphate-modified self-healing calcium aluminate cement 3D printing material.

8. The preparation method according to claim 7, characterized in that, In step S1, the solution concentrations of sodium dihydrogen phosphate and disodium hydrogen phosphate are both 2 mol / L. The calcination is to heat to 700-850 °C in an N2 environment for melting, and then quickly pour it into liquid nitrogen to cool to below -20 °C to obtain a glassy product, sodium polyphosphate, and then grind it; the material-liquid ratio of the ground sodium polyphosphate to the ethanol solution is 1:7-9; the reaction temperature is 60-75 °C, and the time is 2-3 hours; Preferably, in step S2, the reaction temperature when the calcium-based bentonite is mixed with the sodium carbonate solution is 55-65°C, and the time is 10-15 minutes; the reaction temperature for mixing and stirring the solution B and the solution C is 55-65°C, and then it is left to react for 8-12 minutes; the calcium-based bentonite modified by the double template agent needs to be dried at 50-70°C and then ground to 200 meshes for standby; Preferably, in step S3, the pH of the reaction environment is 9-10; Preferably, in step S4, the concentration of the dihydrogen phosphate is 0.1-0.3 mol / L; the dihydrogen phosphate is selected from one or more of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, and sodium dihydrogen phosphate; Preferably, in step S7, the stirring time does not exceed 1 min; Preferably, in step S8, the stirring is manual, and slow stirring is carried out for 25-35 s to prevent the fragmentation of the bacteria-coated microspheres.

9. The application method of the phosphate-modified self-healing calcium aluminate cement 3D printing material according to any one of claims 1 to 6, characterized in that, It includes the following steps: (1) Use a twin-screw extrusion 3D printer, configure a constant-temperature cold water system and a vacuum degassing module, and adjust the key printing parameters; (2) Regulate the material adaptability, and dynamically regulate the screw speed by the in-embedded ultrasonic viscometer to real-time feedback the thixotropic index of the cement paste; (3) Immediately cover with a moisture-keeping film for curing after 3D printing, and then pass in saturated steam for treatment, and perform self-repair environment treatment for the 3D printing application environment.

10. The application method according to claim 9, characterized in that, In step (1), the printer screw diameter of the 3D printer is 45 mm, the length-diameter ratio L / D = 12:1, the printing speed is 80-120 mm / min in the horizontal direction and 30-50 mm / min in the vertical direction, the printing layer thickness is 5-15 mm, and the interlayer interval time is less than 60 s; the setting of the key parameters includes the environmental temperature of 10-35°C and the relative air humidity ≥ 50%; Preferably, in step (2), the frequency of the ultrasonic viscometer is 2 MHz, and the adjustment range of the screw speed is 20-40 rpm; the thixotropic index of the paste is ensured to be in the range of 1.8-2.1 by adjusting the speed; Preferably, in step (3), after covering with the moisture-keeping film, it needs to be cured at a temperature of 23-28°C for 20-30 h; the saturated steam is 60°C saturated steam, the pressure is 0.15 Mpa, and the saturated steam treatment time is 1-5 h; the self-repair environment treatment for the 3D printing application environment includes: for the high-salt and high-alkali environment, the pH value is adjusted to 8-9 by spraying 0.1 mol / L urea-calcium chloride solution; for the acidic soil environment, it is regulated by spraying 0.2 mol / L sodium lactate-calcium hydroxide solution.

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