Nanometer modified fiber reinforced 3D printing magnesium phosphate cement-based material as well as preparation method and application thereof

Abstract

The invention discloses a nano-modified fiber reinforced 3D printing magnesium phosphate cement-based material as well as a preparation method and application thereof. The material is prepared from the following components in parts by weight: 40 to 70 parts of dead burned magnesium oxide, 10 to 25 parts of basic hydrogen phosphate, 5 to 25 parts of silica fume, 30 to 60 parts of fine aggregate, 10 to 30 parts of water, 0.1 to 1 part of fiber dispersing agent and 0.5 to 5 parts of nano modified fiber, the surface activity of the fiber is remarkably improved through a nano modification process, active SiO2 sites attached to the surface of the fiber are activated by using an alkali solution, and a hydration product is generated in situ, so that the interface bonding strength between the fiber and a cement matrix is enhanced, and the surface strength of the fiber is improved by relying on the high-rigidity characteristic of the fiber. The yield stress, thixotropic property and constructability of the material are effectively improved, structural deformation in the printing process is remarkably inhibited, and the 3D printing material has excellent rheological property, strengthened mechanical property and tough fiber-matrix interface bonding property.

Description

Technical Field

[0001] This invention relates to a magnesium phosphate cement-based material, particularly to a nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material, and also to a method for preparing the above-mentioned cement-based material and its application. Background Technology

[0002] 3D printing technology in construction is driving the transformation of industrialized building towards intelligent construction due to its capabilities in digital modeling, moldless construction, and the creation of complex geometric shapes. Magnesium phosphate cement (MPC), as a special cementitious material, has proven its effectiveness in rapid repair and military engineering due to its rapid setting, early strength, low-temperature workability, and high bond strength with existing concrete. In recent years, it has also been introduced into the 3D printing field. However, MPC's inherent brittleness, insufficient toughness, and significant setting shrinkage lead to problems such as weakened interlayer bonding and stress concentration cracking in printed components, severely limiting its reliability in printing load-bearing structures.

[0003] To improve the fracture toughness of magnesium phosphate cement (MPC), traditional methods often incorporate reinforcing phases such as steel fibers, polypropylene fibers, or basalt fibers. Invention patent CN119874324A proposes an early-strength magnesium phosphate slag cement mortar and its preparation method, incorporating polypropylene fibers to improve the flexural strength of the mortar. Invention patent CN118666561A proposes using basalt fibers and a unique preparation technique in magnesium phosphate cement to improve the quality of concrete preparation and solve the problem of uneven concrete mixing. Invention patent CN118145953A discloses a high-strength, crack-resistant magnesium phosphate cement mortar and its preparation method, incorporating an appropriate amount of modified polyvinyl alcohol fibers to prepare a mortar with high mechanical properties, good crack resistance, and cost-effectiveness. The materials mentioned in the patents are mostly designed to address engineering mechanical performance requirements. However, these fibers have poor interfacial compatibility with the MPC matrix, often leading to multiple problems during 3D printing: on the one hand, uneven fiber dispersion in the slurry can easily cause nozzle clogging, disrupting extrusion continuity; on the other hand, weak interfacial adhesion results in low stress transfer efficiency in the stacked layers, limiting the toughening effect of the fibers. More importantly, when increasing the fiber content to achieve significant toughening, the rheological properties of the slurry deteriorate drastically, and the imbalance between extrudability, pumpability, and constructability makes it difficult to guarantee printing accuracy.

[0004] Nanomaterial modification is considered a new approach to overcome the performance bottlenecks of cement-based materials. For example, nano-SiO2 can improve matrix density through the pozzolanic effect and filling effect. However, directly incorporating nanoparticles into MPC systems faces severe challenges. On the one hand, nanoparticles are prone to agglomeration due to their high surface energy, making it difficult to disperse uniformly during stirring and easily affecting the pore structure distribution of the slurry, resulting in limited mechanical property enhancement. On the other hand, excessive addition can drastically increase the plastic viscosity of the slurry, hindering printing smoothness and even posing a risk of extrusion collapse. In addition, the multi-scale interface synergistic mechanism among nanoparticles, fibers, and the matrix is ​​not yet clear, and it is difficult to achieve directional performance regulation in randomly mixed composite systems. Current research focuses on single-scale enhancement strategies, lacking systematic exploration of fiber-nano synergistic enhancement mechanisms and printability optimization. Especially in the field of 3D printed MPCs, there is a lack of directional loading technology for nanofunctional modification of fiber surfaces, and few material design methods that balance high toughness and high printability. There is an urgent need to develop materials with stronger mechanical strength and plastic viscosity suitable for 3D printed MPCs. Summary of the Invention

[0005] Purpose of the Invention: The purpose of this invention is to provide a nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material with excellent rheological properties, good durability, and strong fiber-matrix interfacial bonding. It also provides a method for preparing the aforementioned 3D-printed magnesium phosphate cement-based material. This material, through nano-modified fibers, achieves interfacial reinforcement in 3D-printed MPC materials, not only maintaining the plastic viscosity of the slurry at around 15 Pa·s but also significantly improving the mechanical strength of the material. This is of great significance for promoting the development of high-performance building printing technology.

[0006] Technical solution: The nano-modified fiber reinforced 3D printing magnesium phosphate cement-based material of the present invention comprises the following components by weight: 40-70 parts of calcined magnesium oxide, 10-25 parts of basic hydrogen phosphate, 5-25 parts of silica fume, 30-60 parts of fine aggregate, 10-30 parts of water, 0.1-1 parts of fiber dispersant, and 0.5-5 parts of nano-modified fiber.

[0007] The nano-modified fibers include one or more combinations of nano-modified basalt fibers, nano-modified steel fibers, nano-modified polyethylene fibers, and nano-modified polypropylene fibers. The nano-modified fibers have γ-aminopropyltriethoxysilane bridged on the fiber surface to construct a chemically active amino transition layer, and the amino functional group is used to chemically react with nano-silica to anchor nano-silica on the fiber surface, forming a stronger and more stable chemical connection than simple physical adsorption or hydrogen bonding.

[0008] The method for preparing the nano-modified fiber is as follows: First, the fiber is pretreated with hydrogen peroxide solution to introduce active hydroxyl groups on the fiber surface to enhance its reactivity; then, γ-aminopropyltriethoxysilane is pre-hydrolyzed in a deionized water-ethanol system to generate active silanol, which forms a silanized transition layer covalently bonded with the hydroxyl groups on the fiber surface through a condensation reaction; the amino functional groups at the end of the transition layer are further anchored to the fiber surface through hydrogen bonding and heating dehydration condensation.

[0009] The method for preparing the nano-modified fibers specifically includes the following steps:

[0010] (1) The fiber was soaked in hydrogen peroxide solution as a pretreatment agent, then washed and dried to obtain a neutral fiber substrate.

[0011] (2) Deionized water, anhydrous ethanol and γ-aminopropyltriethoxysilane were mixed to form a silane solution, and pre-hydrolyzed under constant temperature conditions.

[0012] (3) The neutral fiber substrate is immersed in a pre-hydrolyzed silane solution and surface modification is carried out by constant temperature stirring;

[0013] (4) Add nano-silica, heat and stir to load nanoparticles onto the fiber surface;

[0014] (5) The nano-modified fiber is obtained after washing and drying with anhydrous ethanol.

[0015] In step (1), the fiber is one or more of basalt fiber, steel fiber, polyethylene fiber, and polypropylene fiber, with a fiber length of 6-10 mm, a hydrogen peroxide solution concentration of 5-10%, an immersion temperature of 50-60℃, an immersion time of 30-40 min, and a drying temperature of 85-100℃; in step (2), the ratio of deionized water, anhydrous ethanol, and γ-aminopropyltriethoxysilane is 90-100:2-4:1-3. The hydrolysis temperature is 60-80℃, and the pre-hydrolysis time is 1-1.5h; the amount of neutral fiber substrate in step (3) is 5-10% of the weight of the pre-hydrolyzed silane solution, the stirring temperature is 40-60℃, and the stirring time is 1-1.5h; the amount of nano silica in step (4) is 0.7-1.6% of the weight of the pre-hydrolyzed silane solution, the stirring temperature is 50-70℃, and the stirring time is 1-2h; the drying temperature in step (5) is 85-100℃.

[0016] The median particle size of the recalcined magnesium oxide is 35.00–64.25 μm, and the magnesium oxide content is ≥90%; the basic hydrogen phosphate is one or a combination of dipotassium hydrogen phosphate or disodium hydrogen phosphate; the silica fume has a particle size range of 0.2–100 μm and a SiO2 content of ≥90%.

[0017] The fine aggregate is one or more of the following: quartz sand, sea sand, calcareous sand, and recycled fine aggregate; the average particle size of the quartz sand is 110-115 mesh; the sea sand is desalinated sea sand with a chloride ion content of less than 0.3% and an average particle size of 0.47-0.57 mm; the calcareous sand has a calcium carbonate content of ≥80% and an average particle size of 0.5-0.7 mm; the recycled aggregate is derived from construction waste concrete or mortar, with a crushing index ≤20%, a water absorption rate ≤10%, and an average particle size of 0.65-1.20 mm.

[0018] The fiber dispersant is one or more combinations of unsaturated polyester polyurethane epoxy UV system dispersant, acrylic alkyd phenolic modified rosin resin system dispersant, and sodium carboxymethyl cellulose; the density of the unsaturated polyester polyurethane epoxy UV system dispersant is 1.01–1.57 g / cm³. 3 The density of the dispersant in the acrylic alkyd phenolic modified rosin resin system is 1.49–1.32 g / cm³. 3 The density of sodium carboxymethyl cellulose is 1.71–1.90 g / cm³. 3 .

[0019] The preparation method of the above-mentioned nano-modified fiber reinforced 3D printed magnesium phosphate cement-based material is as follows: calcined magnesium oxide, basic hydrogen phosphate, silica fume, fine aggregate, water, fiber dispersant, and nano-modified fibers are mixed to obtain the nano-modified fiber reinforced 3D printed magnesium phosphate cement-based material.

[0020] The preparation method specifically includes the following steps:

[0021] (1) Magnesium oxide, basic hydrogen phosphate, silica fume, and water are stirred at low speed to obtain a mixture;

[0022] (2) Add nano-modified fibers to the mixture obtained in step (1) and stir at low speed to obtain a fiber mixture;

[0023] (3) Add fiber dispersant to the fiber mixture obtained in step (2) and stir at high speed to obtain the nano-modified fiber reinforced 3D printed magnesium phosphate cement-based material.

[0024] In step (1), the speed of low-speed stirring is 20-60 r / min and the stirring time is 30-60 s; in step (2), the speed of low-speed stirring is 30-70 r / min and the stirring time is 20-40 s; in step (3), the speed of high-speed stirring is 55-90 r / min and the stirring time is 300-400 s.

[0025] The aforementioned nano-modified fiber-reinforced 3D printed magnesium phosphate cement-based material can also be applied in the field of 3D printed building materials.

[0026] Invention Principle: The nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material of this invention constructs an ordered nanocomposite interface on the fiber surface through chemical bonding, achieving synergistic optimization of toughening and 3D printing suitability of magnesium phosphate cement (MPC) material. Its principle begins with the multi-level functionalization design of the fiber surface: First, the fiber is pre-treated with hydrogen peroxide solution to introduce active hydroxyl groups on the fiber surface to enhance its reactivity; then, γ-aminopropyltriethoxysilane is pre-hydrolyzed in a deionized water-ethanol system to generate active silanol, which forms a covalently bonded silanized transition layer with the hydroxyl groups on the fiber surface through a condensation reaction; the amino functional groups at the end of this transition layer further anchor nano-silica to the fiber surface through hydrogen bonding and thermal dehydration condensation, ultimately forming a composite reinforcing unit of "fiber-nano-silica".

[0027] The nano-modified fibers exhibit a multi-scale synergistic toughening mechanism. On one hand, the fibers can act as deflection nodes for microcracks, causing the crack propagation path to become tortuous to dissipate fracture energy, while simultaneously filling the pores of the matrix. On the other hand, the prepared magnesium phosphate cement-based material is alkaline, and the active nano-silica loaded on the fiber surface reacts with OH radicals in the alkaline environment. - The ions nucleophilically attack the positively charged Si atoms, causing dissociation to form many silanol groups (Si-OH), which then further dissociate to form HSiO4. 3- H2SiO4 2- H3SiO4 3- , with alkali metal ions Mg 2+ In combination, the hydrated magnesium silicate gel (MSH) on the surface of the product layer significantly enhances the density, chemical bonding strength, and adhesion strength of the upper and lower printed layers in the fiber-matrix interface transition zone. The nano-modified fibers achieve efficient stress transfer through strong interfacial adhesion, allowing the high modulus tensile properties of the fibers to be fully utilized, fundamentally overcoming the brittleness of MPC materials.

[0028] To address the specific process requirements of 3D printing, this invention simultaneously solves the challenge of rheological property adaptation: by fixing nano-SiO2, which has potential chemical compatibility with MPC hydration products, onto a fiber carrier, it avoids the agglomerative viscosity surge caused by direct incorporation into the matrix, making it easier for the fibers to orient themselves in the extrusion shear field, strongly inducing dynamic shear thinning, and ensuring smooth extrusion of high-solids-content slurry. Simultaneously, the modified fibers synergistically and significantly increase the static yield stress of the slurry, effectively suppressing printed structure deformation and significantly increasing the number of printable layers. Furthermore, the addition of a fiber dispersant ensures uniform fiber dispersion in the slurry, guaranteeing the continuity of pumping and extrusion. At a specific nano-SiO2 dosage, maximum interfacial modification is achieved, and an appropriate amount of nano-modified fibers fully react with the matrix to produce a hydration reaction, anchoring the interlayer interface and increasing mechanical properties.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention uses nano-modified fibers to construct a multi-level reinforcing interface of "fiber-nanoparticle-matrix" in the MPC matrix, which significantly improves the comprehensive mechanical properties of the composite material by about 30%, and effectively suppresses interlayer delamination and shrinkage cracks in the printed components; (2) By anchoring nanoparticles to the fiber carrier, the problem of rheological performance deterioration caused by traditional nanoparticle mixing is solved, the plastic viscosity of the slurry is maintained at about 15 Pa·s, and the static yield stress is increased by about 120%, achieving better matching with the 3D printing system and suitable for large-scale production; (3) The amount of nanomaterials is reduced by 50%, but the crack resistance and toughness are significantly improved. High performance is achieved with low dosage, avoiding the excessive use of high-cost nanomaterials. Attached Figure Description

[0030] Figure 1 The images show the SEM images of the nano-modified basalt fiber material and the corresponding EDS energy dispersive spectra of the marked sites. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the embodiments. The test materials used in the embodiments can all be purchased through conventional means.

[0032] Example 1

[0033] The nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material of the present invention comprises the following components in parts by weight:

[0034] The composition includes 45 parts recalcined magnesium oxide, 17 parts basic hydrogen phosphate, 10 parts silica fume, 40 parts fine aggregate, 15 parts water, 0.2 parts fiber dispersant, and 0.7 parts nano-modified fiber. The basic hydrogen phosphate is dipotassium hydrogen phosphate. The fine aggregate is quartz sand. The fiber dispersant is an unsaturated polyester polyurethane epoxy UV system dispersant. The nano-modified fiber is nano-modified basalt fiber.

[0035] The preparation method of the nano-modified basalt fiber is as follows: A 5% hydrogen peroxide solution is used as a pretreatment agent, and the temperature is raised to 50°C to soak the fiber for 30 minutes. The fiber is then washed with water and dried at 85°C to obtain a neutral fiber substrate. Deionized water, anhydrous ethanol, and γ-aminopropyltriethoxysilane are mixed in a 90:2:1 ratio to form a silane solution, which is then pre-hydrolyzed at a constant temperature of 60°C for 1 hour. 5% of the weight of the pre-hydrolyzed silane solution of the neutral fiber substrate is immersed in the pre-hydrolyzed silane solution and stirred at a constant temperature of 40°C for 1 hour to perform surface modification. 0.7% of the weight of the pre-hydrolyzed silane solution of nano-silica is added, and the mixture is heated to 50°C and stirred for 1 hour to load nanoparticles onto the fiber surface. After washing with anhydrous ethanol and drying at 85°C, the nano-modified fiber is obtained.

[0036] The preparation method of the above-mentioned nano-modified fiber-reinforced 3D printed magnesium phosphate cement-based material is as follows:

[0037] (1) Mix magnesium oxide, basic hydrogen phosphate, silica fume, and water at a low speed of 30 r / min for 30 s to obtain a mixture;

[0038] (2) Add nano-modified fibers to the mixture obtained in step (1) and stir at low speed of 45 r / min for 60 s to obtain a fiber mixture;

[0039] (3) Add fiber dispersant to the fiber mixture obtained in step (3) and stir at high speed of 90 r / min for 350 min to obtain the nano-modified fiber reinforced 3D printed magnesium phosphate cement-based material.

[0040] Example 2

[0041] The nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material of the present invention comprises the following components in parts by weight:

[0042] The composition includes 60 parts recalcined magnesium oxide, 11 parts basic hydrogen phosphate, 24 parts silica fume, 35 parts fine aggregate, 25 parts water, 0.4 parts fiber dispersant, and 3 parts nano-modified fibers. The basic hydrogen phosphate is disodium hydrogen phosphate. The fine aggregate is calcareous sand. The fiber dispersant is an acrylic alkyd phenolic modified rosin resin system dispersant. The nano-modified fibers are nano-modified steel fibers.

[0043] The preparation method is the same as in Example 1, and a nano-modified fiber-reinforced 3D printed magnesium phosphate cement-based material is obtained.

[0044] Example 3

[0045] The nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material of the present invention comprises the following components in parts by weight:

[0046] The composition includes 53 parts recalcined magnesium oxide, 21 parts basic hydrogen phosphate, 15 parts silica fume, 55 parts fine aggregate, 12 parts water, 0.8 parts fiber dispersant, and 2 parts nano-modified fibers. The basic hydrogen phosphate is a mixture of dipotassium hydrogen phosphate and disodium hydrogen phosphate in a mass ratio of 3:1. The fine aggregate is sea sand. The fiber dispersant is a mixture of unsaturated polyester polyurethane epoxy UV system dispersant and sodium carboxymethyl cellulose in a mass ratio of 2:1. The nano-modified fibers are nano-modified polyethylene fibers.

[0047] The preparation method is the same as in Example 1, and a nano-modified fiber-reinforced 3D printed magnesium phosphate cement-based material is obtained.

[0048] Example 4

[0049] The nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material of the present invention comprises the following components in parts by weight:

[0050] The composition includes 67 parts recalcined magnesium oxide, 10 parts basic hydrogen phosphate, 21 parts silica fume, 47 parts fine aggregate, 19 parts water, 0.5 parts fiber dispersant, and 5 parts nano-modified fibers. The basic hydrogen phosphate is disodium hydrogen phosphate. The fine aggregate is a mixture of sea sand and calcareous sand in a mass ratio of 4:1. The fiber dispersant is sodium carboxymethyl cellulose. The nano-modified fibers are a mixture of nano-modified basalt fibers and nano-modified steel fibers in a mass ratio of 1:1.

[0051] The preparation method is the same as in Example 1, and a nano-modified fiber-reinforced 3D printed magnesium phosphate cement-based material is obtained.

[0052] Example 5

[0053] The nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material of the present invention comprises the following components in parts by weight:

[0054] The composition includes 40 parts of recalcined magnesium oxide, 23 parts of basic hydrogen phosphate, 7 parts of silica fume, 30 parts of fine aggregate, 29 parts of water, 0.1 parts of fiber dispersant, and 1.5 parts of nano-modified fiber. The basic hydrogen phosphate is dipotassium hydrogen phosphate. The fine aggregate is a mixture of quartz sand and calcareous sand in a mass ratio of 1:3. The fiber dispersant is an acrylic alkyd phenolic modified rosin resin system dispersant. The nano-modified fiber is a mixture of nano-modified steel fiber, nano-modified polyethylene fiber, and nano-modified polypropylene fiber in a mass ratio of 1:3:2.

[0055] The preparation method is the same as in Example 1, and a nano-modified fiber-reinforced 3D printed magnesium phosphate cement-based material is obtained.

[0056] Example 6

[0057] The nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material of the present invention comprises the following components in parts by weight:

[0058] The composition includes 59 parts recalcined magnesium oxide, 14 parts basic hydrogen phosphate, 18 parts silica fume, 57 parts fine aggregate, 25 parts water, 0.3 parts fiber dispersant, and 2.7 parts nano-modified fibers. The basic hydrogen phosphate is dipotassium hydrogen phosphate. The fine aggregate is a mixture of quartz sand, sea sand, and calcareous sand in a mass ratio of 1:1:1. The fiber dispersant is a mixture of an unsaturated polyester polyurethane epoxy UV system dispersant and an acrylic alkyd phenolic modified rosin resin system dispersant in a mass ratio of 1:3. The nano-modified fibers are nano-modified polypropylene fibers.

[0059] The preparation method is the same as in Example 1, and a nano-modified fiber-reinforced 3D printed magnesium phosphate cement-based material is obtained.

[0060] Comparative Example 1

[0061] A 3D-printable magnesium phosphate cement-based material, compared to the examples, does not contain fiber dispersants and modified fibers, and the magnesium phosphate cement-based material comprises the following components by weight:

[0062] The mixture consists of 60 parts recalcined magnesium oxide, 11 parts basic hydrogen phosphate, 24 parts silica fume, 35 parts fine aggregate, and 25 parts water. The basic hydrogen phosphate is disodium hydrogen phosphate. The fine aggregate is calcareous sand.

[0063] The preparation method is the same as in Example 1, and 3D printing magnesium phosphate cement-based material is obtained.

[0064] Comparative Example 2

[0065] A 3D-printable magnesium phosphate cement-based material, which, compared to the examples, has not undergone fiber modification, comprises the following components by weight:

[0066] The composition includes 67 parts recalcined magnesium oxide, 10 parts basic hydrogen phosphate, 21 parts silica fume, 47 parts fine aggregate, 19 parts water, 0.5 parts fiber dispersant, and 5 parts fiber. The basic hydrogen phosphate is disodium hydrogen phosphate. The fine aggregate is a mixture of sea sand and calcareous sand in a mass ratio of 4:1. The fiber dispersant is sodium carboxymethyl cellulose. The fiber is a mixture of basalt fiber and steel fiber in a mass ratio of 1:1.

[0067] The preparation method is the same as in Example 1, and 3D printing magnesium phosphate cement-based material is obtained.

[0068] Comparative Example 3

[0069] A 3D-printable magnesium phosphate cement-based material, compared to the examples, does not contain fiber dispersants, and the magnesium phosphate cement-based material comprises the following components by weight:

[0070] The composition includes 45 parts recalcined magnesium oxide, 17 parts basic hydrogen phosphate, 10 parts silica fume, 40 parts fine aggregate, 15 parts water, and 0.7 parts nano-modified fiber. The basic hydrogen phosphate is dipotassium hydrogen phosphate. The fine aggregate is silica sand. The nano-modified fiber is nano-modified basalt fiber.

[0071] The preparation method is the same as in Example 1, and 3D printing magnesium phosphate cement-based material is obtained.

[0072] Table 1. Performance comparison of 3D-printed magnesium phosphate cement-based materials prepared in the examples and comparative examples.

[0073]

[0074] The performance of the 3D-printed magnesium phosphate cement-based materials prepared in the embodiments and comparative examples was tested. The test results are shown in Table 1. It can be seen that the 3D-printed magnesium phosphate cement-based material of the embodiments of the present invention can control the plastic viscosity, static yield stress, and thixotropic ring area of ​​the 3D printing slurry to 12.08~21.54 Pa·s, 539.55~982.36 Pa, and 3.203×10⁻⁶ Pa, respectively. 4 ~6.631×10 4 Within the Pa / s range, the low plastic viscosity allows for smooth pumping and extrusion of the slurry, avoiding the risks of pipe blockage and "tailing." The high static yield stress affects the stability of the printed structure, preventing the collapse of stacked layers and increasing the number of printed layers. The high thixotropy balances the contradictions between pumpability, extrudability, and buildability, making this material extremely suitable for 3D printing. Meanwhile, Comparative Example 1, lacking fiber network support and interface reinforcement, exhibits a significant decrease in static yield stress, and the bottom layer cannot effectively resist the slurry's own gravity, easily leading to instability of the printed structure. Comparative Example 2, although fibers provide basic reinforcement, the unmodified fibers are only physically interlocked with the matrix, lacking the linkage of hydration products, resulting in a minimal improvement in thixotropy. The key defect of Comparative Example 3 lies in the uneven fiber dispersion; localized fiber bundles increase rheological resistance, while the static yield stress drops sharply in areas of insufficient dispersion.

[0075] Table 1 also shows the compressive and flexural strength of the materials. The order of the 28-day compressive and flexural strength results is: Example 3 > Example 5 > Example 2 > Example 1 > Example 6 > Example 4 > Comparative Example 1. This indicates that Comparative Example 1 suffers from multiple mechanical property degradations due to the lack of fiber network support and interface reinforcement. Although Comparative Example 2 provides basic physical reinforcement through fibers, the lack of chemical bonding induced by nano-SiO2 and MSH gel reinforcement leads to significant weakening of the interface transition zone, resulting in low stress transfer efficiency and rapid crack propagation along the interface. While Comparative Example 3 optimizes the interface of individual fibers through nano-modification, uneven dispersion causes fatal defects. Local fiber agglomeration areas form stress voids, while insufficiently dispersed areas lose some toughening effect, ultimately resulting in a significantly lower flexural strength than the same fiber content. Simultaneously, excessive fiber can also locally agglomerate, weakening the matrix density. The optimal compressive and flexural strength was obtained at the addition amount specified in the embodiments of this invention.

[0076] The results of fiber-matrix bond strength and interlayer bond strength show that, compared with Example 4, the unmodified fiber in Comparative Example 2 has lower matrix bond strength and interlayer bond strength than the nano-modified fiber. This is attributed to the lack of MSH bonding between the fiber surface and the matrix, resulting in microcracks at the fiber-matrix interface. Comparing Comparative Example 3 with Example 6, the proportion of effective toughening fiber in cement without fiber dispersant is reduced, resulting in a slight decrease in mechanical properties. This indicates that the dispersant, through steric hindrance effect, destroys fiber aggregates and is a necessary auxiliary means to ensure uniform distribution of nano-modified fiber and achieve synergistic effects of strong interface and high toughness.

[0077] Therefore, this invention significantly enhances the activity of the fiber surface through nano-modification, activates the active SiO2 sites attached to the fiber surface using alkaline solution, and generates hydration products in situ, thereby strengthening the interfacial bonding strength between the fiber and the cement matrix. Furthermore, relying on the high stiffness of the fiber itself, it effectively improves the yield stress, thixotropic properties, and buildability of the material, significantly suppressing structural deformation during the printing process. This results in 3D printing materials with excellent rheological properties, enhanced mechanical properties, and strong fiber-matrix interfacial bonding. By controlling the rheological properties of the nano-modified fiber-reinforced 3D printed magnesium phosphate cement-based material within a reasonable range, the printability of the material is guaranteed. Simultaneously, the significant enhancement of mechanical properties, fiber-matrix interfacial bonding, and interlayer bonding properties by the nano-modified fiber demonstrates great application potential.

Claims

1. A nanomodified fiber-reinforced 3D-printed magnesium phosphate cement-based material, characterized in that, The magnesium phosphate cement-based material comprises the following components by weight: 40-70 of dead burned magnesium oxide, 10-25 of alkaline hydrogen phosphate, 5-25 of silica fume, 30-60 of fine aggregate, 10-30 of water, 0.1-1 of fiber dispersant, and 0.5-5 of nano-modified fiber.

2. The magnesium oxyphosphate cement-based material according to claim 1, characterized in that, The nano-modified fiber comprises one or more of nano-modified basalt fiber, nano-modified steel fiber, nano-modified polyethylene fiber, and nano-modified polypropylene fiber; the nano-modified fiber has a transition layer of amino groups on the surface of the fiber by bridging γ-aminopropyl triethoxysilane, and has nano-silica anchored on the surface of the fiber.

3. The magnesium oxyphosphate cement-based material according to claim 1, characterized in that, The method for preparing the nano-modified fiber comprises the following steps: (1) soaking the fiber in a hydrogen peroxide solution as a pretreatment agent at an elevated temperature, washing with water, and drying to obtain a neutral fiber base material; (2) mixing deionized water, anhydrous ethanol, and γ-aminopropyl triethoxysilane to form a silane solution, and pre-hydrolyzing under constant temperature conditions; (3) immersing the neutral fiber base material in the pre-hydrolyzed silane solution, and stirring under constant temperature conditions to perform surface modification; (4) adding nano-silica, and stirring under heating to load nano-particles on the surface of the fiber; (5) washing with anhydrous ethanol and drying to obtain the nano-modified fiber.

4. The magnesium oxyphosphate cement-based material according to claim 3, characterized in that, In step (1), the fiber is one or more of basalt fiber, steel fiber, polyethylene fiber, and polypropylene fiber, the length of the fiber is 6-10 mm, the concentration of the hydrogen peroxide solution is 5-10%, the soaking temperature is 50-60°C, the soaking time is 30-40 min, and the drying temperature is 85-100°C; in step (2), the ratio of deionized water, anhydrous ethanol, and γ-aminopropyl triethoxysilane is 90-100:2-4:1-3, the pre-hydrolysis temperature is 60-80°C, and the pre-hydrolysis time is 1-1.5 h; in step (3), the dosage of the neutral fiber base material is 5-10% of the weight of the pre-hydrolyzed silane solution, the stirring temperature is 40-60°C, and the stirring time is 1-1.5 h; in step (4), the dosage of the nano-silica is 0.7-1.6% of the weight of the pre-hydrolyzed silane solution, the stirring temperature is 50-70°C, and the stirring time is 1-2 h; and in step (5), the drying temperature is 85-100°C.

5. The magnesium oxyphosphate cement-based material according to claim 1, wherein The dead burned magnesium oxide has a median particle size of 35.00-64.25 μm, and the content of magnesium oxide is ≥90%; the alkaline hydrogen phosphate is one or a combination of dipotassium hydrogen phosphate or disodium hydrogen phosphate; and the silica fume has a particle size range of 0.2-100 μm, and a SiO2 content of ≥90%.

6. The magnesium oxyphosphate cement-based material according to claim 1, characterized in that, The fine aggregate is one or a combination of quartz sand, sea sand, calcareous sand, and recycled fine aggregate; the average particle size of the quartz sand is 110-115 mesh; the sea sand is desalinated sea sand, has a chlorine ion content of less than 0.3%, and an average particle size of 0.47-0.57 mm; the calcareous sand has a calcium carbonate content of ≥80%, and an average particle size of 0.5-0.7 mm; and the recycled aggregate is derived from construction waste concrete or mortar, has a crushing index of ≤20%, a water absorption rate of ≤10%, and an average particle size of 0.65-1.20 mm. The fiber dispersant is one or more combinations of unsaturated polyester polyurethane epoxy UV system dispersant, acrylic alcohol acid phenolic modified rosin resin system dispersant, sodium carboxymethyl cellulose; the density of the unsaturated polyester polyurethane epoxy UV system dispersant is 1.01-1.57 g / cm 3 , the density of the acrylic alcohol acid phenolic modified rosin resin system dispersant is 1.49-1.32 g / cm 3 , and the density of the sodium carboxymethyl cellulose is 1.71-1.90 g / cm 3 .

7. A method for preparing the nanomodified fiber-reinforced 3D-printed magnesium phosphate cement-based material according to claim 1, characterized in that, The preparation method involves mixing calcined magnesium oxide, basic hydrogen phosphate, silica fume, fine aggregate, water, fiber dispersant, and nano-modified fibers to obtain a nano-modified fiber-reinforced 3D printing magnesium phosphate cement-based material.

8. The method for preparing nano-modified fiber reinforced 3D printed magnesium phosphate cement-based material according to claim 7, characterized in that, Specifically, the following steps are included: (1) Magnesium oxide, basic hydrogen phosphate, silica fume, and water are stirred at low speed to obtain a mixture; (2) Add nano-modified fibers to the mixture obtained in step (1) and stir at low speed to obtain a fiber mixture; (3) Add fiber dispersant to the fiber mixture obtained in step (2) and stir at high speed to obtain the nano-modified fiber reinforced 3D printed magnesium phosphate cement-based material.

9. The preparation method according to claim 8, characterized in that, In step (1), the speed of low-speed stirring is 20-60 r / min and the stirring time is 30-60 s; in step (2), the speed of low-speed stirring is 30-70 r / min and the stirring time is 20-40 s; in step (3), the speed of high-speed stirring is 55-90 r / min and the stirring time is 300-400 s.

10. The application of the nano-modified fiber-reinforced 3D-printed magnesium phosphate cement-based material as described in claim 1 in the field of 3D-printed building materials.

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