3D-printing-based light building material doped with mixed fibers and preparation method of 3D-printing-based light building material

Abstract

The invention belongs to the technical field of composite materials, and provides a light building material doped with mixed fibers based on 3D printing and a preparation method thereof.The preparation method comprises the steps that polyvinyl alcohol fibers are sequentially subjected to coupling agent modification, polydopamine coating and chitosan-gelatin composite colloid coating treatment, and modified polyvinyl alcohol fibers are obtained; carrying out chemical etching on the basalt fiber to obtain a modified basalt fiber; adding the modified polyvinyl alcohol fiber and the modified basalt fiber into the basic mortar, and uniformly mixing to obtain composite mortar; the composite mortar is injected into 3D printing equipment for layer-by-layer printing, an interface treating agent is sprayed to the surface of a mortar base body layer formed through printing after each layer is printed, and then gradient curing and curing are conducted. According to the invention, a dual synergistic mechanism of a fiber reinforced system and an interlayer sliding interlocking structure is constructed, and the technical problem that the strength and toughness of a traditional cement-based material cannot be considered at the same time is solved from two aspects of microcosmic interface modification and macroscopic structure design.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials and relates to a lightweight building material containing mixed fibers based on 3D printing and a preparation method thereof. Background Art

[0002] In recent years, with the construction industry's growing demand for efficient, sustainable, and multifunctional materials, lightweight building materials have attracted much attention due to their advantages in reducing structural loads, improving construction efficiency, and reducing resource consumption. However, traditional lightweight materials (such as foam concrete and ceramsite concrete) generally suffer from insufficient mechanical properties, poor crack resistance, and limited durability. This makes it difficult to meet the dual requirements of high strength and lightweight, especially in complex building structures. In addition, existing fiber-reinforced materials mostly use a single type of fiber (such as steel fiber, glass fiber, or synthetic fiber). Although this can partially improve the performance of the matrix, the toughening, tensile strength, and impact resistance of a single fiber are limited. In addition, insufficient interfacial bonding between the fiber and the matrix can easily lead to stress concentration, affecting the overall performance of the material.

[0003] At the same time, 3D printing technology provides the construction industry with a new approach to rapid prototyping, customized design, and reduced material waste. However, existing 3D printing building materials face the following bottlenecks: On the one hand, the extrudability, interlayer bonding strength, and hardening speed of traditional printing materials (such as ordinary cement-based materials or polymers) are difficult to balance, making them prone to collapse, interlayer delamination, or shrinkage cracking during printing. On the other hand, in existing fiber-reinforced printing materials, there is a lack of effective means to control the aspect ratio, dispersion uniformity, and orientation of the fibers, resulting in the fiber reinforcement effect not being fully utilized. In addition, research on 3D printing materials for the synergistic optimization of lightness and high strength is still in the exploratory stage. In particular, the synergistic toughening mechanism of hybrid fibers, the regulation of rheological properties, and the adaptability of printing processes have not yet been systematically addressed.

[0004] Therefore, there is an urgent need to develop a new type of building material that is lightweight, high-strength, printable and durable. Through innovations in material design and preparation technology, we can overcome the core problems of existing technologies such as uneven fiber dispersion, weak interface bonding, and difficulty in compatibility between printing performance and mechanical properties, thereby promoting the large-scale application of 3D printing technology in the construction field. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a lightweight building material containing hybrid fibers based on 3D printing and a preparation method thereof, which achieves a breakthrough improvement in the mechanical properties of the material through multi-dimensional synergy. The core invention lies in the construction of a dual synergistic mechanism of fiber reinforcement system and interlayer sliding interlocking structure, breaking through the technical problem of the inability of traditional cement-based materials to achieve both strength and toughness from the two levels of micro-interface modification and macro-structural design.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing, the method comprising:

[0008] (I) Modifying polyvinyl alcohol fibers with a coupling agent, coating them with polydopamine, and coating them with a chitosan-gelatin composite colloid in sequence to obtain modified polyvinyl alcohol fibers; chemically etching basalt fibers to obtain modified basalt fibers; adding the modified polyvinyl alcohol fibers and the modified basalt fibers to a base mortar, and uniformly mixing them to obtain a composite mortar;

[0009] (II) injecting the composite mortar obtained in step (I) into a 3D printing device for layer-by-layer printing, spraying an interface treatment agent on the surface of the printed mortar base layer after each layer is printed to form a flexible interface layer on the surface of the mortar base layer, and continuing to print the next mortar base layer on the surface of the flexible interface layer, and so on, to obtain a composite layered structure consisting of alternating mortar base layers and flexible interface layers, and then performing gradient curing to obtain the lightweight building material doped with mixed fibers.

[0010] The preparation method of lightweight building materials containing mixed fibers provided by the present invention achieves a breakthrough improvement in the mechanical properties of the material through multi-dimensional synergistic effects. The core invention lies in the construction of a dual synergistic mechanism of fiber reinforcement system and interlayer sliding interlocking structure, which breaks through the technical problem of traditional cement-based materials that cannot take into account both strength and toughness from the two levels of microscopic interface modification and macroscopic structural design.

[0011] In terms of fiber reinforcement system construction, the synergistic modification of polyvinyl alcohol fiber and basalt fiber forms a multi-scale reinforcement network. The polyvinyl alcohol fiber is treated with a silane coupling agent, and the hydroxyl groups on its surface chemically bond with the siloxane groups, significantly improving the interfacial bonding strength between the polyvinyl alcohol fiber and the cement matrix. The subsequent polydopamine coating forms a bionic adhesion layer on the fiber surface. Its catechol groups form hydrogen bonds and π-π stacking effects with the amino and carboxyl groups in the chitosan-gelatin composite colloid. This dynamic and reversible interfacial bonding mechanism allows the polyvinyl alcohol fiber and the cement matrix to undergo controllable slip when the material is subjected to stress, which not only ensures stress transfer efficiency but also improves toughness through interfacial friction energy dissipation. After oxalic acid etching, micro-nanoscale pits are formed on the surface of the basalt fiber. Ammonium fluoride treatment further introduces active silanol groups, allowing it to form a dual combination of chemical bonding and mechanical interlocking with the cement hydration products. The length difference between the two types of fibers (6~8mm and 8~12mm) forms a spatially complementary reinforcement network. The short fibers effectively inhibit the propagation of microcracks, while the long fibers take on the principal stress transfer. This multi-scale synergistic effect makes the lightweight building material exhibit progressive failure characteristics when bearing load.

[0012] The synergistic effect between the modified polyvinyl alcohol fiber and the modified basalt fiber used in the present invention is reflected in:

[0013] First, the present invention utilizes basalt fibers and polyvinyl alcohol fibers of varying lengths, leveraging this difference to form a spatial network hierarchical reinforcement structure. Long fibers (basalt fibers) span multiple cement matrix grains, constructing a three-dimensional continuous skeleton that effectively transmits macroscopic stresses. Short fibers (polyvinyl alcohol fibers) fill the gaps in the long fiber network, forming local reinforcement units that inhibit the initiation of microcracks. This multi-scale spatial arrangement requires that crack propagation simultaneously overcome the bridging resistance of the long fibers and the pinning effect of the short fibers, significantly extending the crack path. Simultaneously, the path offset design of adjacent layers in the 3D printing process allows the two fibers to form an interlaced distribution in the Z-axis direction, creating a three-dimensional interlocking system together with the interlayer concave-convex mosaic structure, upgrading the traditional two-dimensional planar reinforcement to a three-dimensional reinforcement network.

[0014] Secondly, the rigid interface of the modified basalt fiber and the flexible response of the modified polyvinyl alcohol fiber form a dynamic synergy, achieving complementary mechanical properties. After the basalt fiber is etched with oxalic acid and ammonium fluoride, the micro-nano grooves and fluorine-silicon active sites generated on the surface enable it to form a high-strength chemical bond with the cement hydration products, assuming the main load transfer function. The polydopamine / chitosan-gelatin composite coating of the polyvinyl alcohol fiber forms a viscoelastic interface through dynamic hydrogen bonding and π-π stacking. When it is subjected to stress exceeding the critical stress, it undergoes controllable slippage, converting the destructive energy into frictional heat dissipation. When the lightweight building material is loaded, the modified basalt fiber network first exerts its high modulus characteristics to suppress deformation, while the modified polyvinyl alcohol fiber initiates slippage energy dissipation in the stress concentration area. The difference in the timing response between the two realizes the adaptive redistribution of the stress field.

[0015] Thirdly, the synergy between modified polyvinyl alcohol fiber and modified basalt fiber creates a modulus transition zone. A dense layer of hydration products forms around the modified basalt fiber, while a low-modulus buffer layer forms at the interface of the modified polyvinyl alcohol fiber due to the presence of the organic coating. This modulus gradient from rigid fiber to flexible interface and then to cement matrix effectively alleviates stress mutations between heterogeneous materials. When the crack propagates to the fiber interface, the rigid interface of the modified basalt fiber forces the crack tip to deflect, while the flexible interface of the modified polyvinyl alcohol fiber absorbs crack energy through large deformation. The synergistic effect of the two requires the crack to repeatedly overcome different resistance mechanisms, and the fracture energy is increased to more than three times that of traditional concrete materials.

[0016] Fourthly, the synergistic effect of modified polyvinyl alcohol fiber and modified basalt fiber is manifested in the simultaneous improvement of the strength and toughness of lightweight building materials. The modified basalt fiber network makes the compressive strength of lightweight building materials exceed 150MPa, reaching the level of ultra-high-strength concrete; while the interface slip and multi-stage crack deflection mechanism of modified polyvinyl alcohol fiber make the fracture energy of lightweight building materials exceed 12kJ / m 2 , yet possessing metal-like deformation capabilities. During impact testing, the lightweight building material exhibited a typical three-stage failure: in the early stages of the test, the modified basalt fiber network maintained structural integrity; in the middle stages, the modified polyvinyl alcohol fibers initiated multi-interface slippage to dissipate energy; and in the late stages, the three-dimensional interlocking structure mechanically engaged to delay overall failure. This multi-stage defense system enables lightweight building materials to maintain residual strength under extreme loads, fundamentally changing the brittle failure nature of cementitious materials.

[0017] In addition to using modified polyvinyl alcohol fiber and modified basalt fiber to synergistically enhance and modify the base mortar, the present invention also constructs an interlayer slip interlocking structure through an innovatively designed 3D printing path. By offsetting the printing path by half the path width layer by layer, a continuous concave-convex mosaic structure is formed between adjacent mortar matrix layers. When this bionic layered structure is subjected to stress, the interlayer interface generates shear resistance through mechanical interlocking, and the presence of the flexible interface layer causes limited slip between the layers. When the lightweight building material is subjected to impact loads, the interlayer slip dissipates energy through friction, while the interlocking structure prevents the layers from completely peeling off. This "rigid and flexible" energy dissipation mechanism significantly improves the fracture toughness of the material. The synergistic effect of styrene acrylic emulsion and nano-silica in the interface treatment agent forms an organic-inorganic hybrid interface layer. The flexible polymer chain segments in the styrene acrylic emulsion absorb deformation energy through entanglement, and the nano-silica increases the interface stiffness through the filling effect. The dynamic balance between the two enables the flexible interface layer to have both stress buffering and load transfer functions.

[0018] After 3D printing is completed, the present invention also optimizes the curing process, adopting a gradient curing process to optimize the material microstructure by regulating various process parameters of the hydration process. In the first stage, high-humidity and normal-pressure curing is carried out in an air atmosphere to accelerate the dissolution and recrystallization of the cement mineral phase, promote the directional growth of hydration products on the fiber surface, and form a dense interface transition zone. In the second stage, high-temperature and high-pressure curing is carried out in a nitrogen atmosphere to promote the polymerization degree of CSH gel by inhibiting the carbonization reaction of calcium hydroxide, and at the same time, thermal densification of the chitosan-gelatin composite coating occurs, thereby enhancing the structural stability of the fiber coating. This staged curing strategy enables the cement matrix and the fiber reinforcement phase to form a gradient interface structure, that is, the high-elasticity area close to the fiber surface can buffer stress concentration, while the outer rigid area ensures load transfer efficiency, thereby achieving a simultaneous improvement in material strength and toughness.

[0019] As a preferred technical solution of the present invention, in step (I), the modified polyvinyl alcohol fiber is prepared by the following method:

[0020] (1) soaking the polyvinyl alcohol fiber in a silane coupling agent solution and heating it, taking out the fiber after soaking, washing and drying it to obtain a silane-modified polyvinyl alcohol fiber; soaking the silane-modified polyvinyl alcohol fiber in a dopamine solution at room temperature and in the dark, taking out the fiber after soaking, washing and drying it to obtain a coated polyvinyl alcohol fiber;

[0021] (2) The chitosan solution and the gelatin solution are uniformly mixed to obtain a precursor solution, and a genipin crosslinking agent is added to the precursor solution, and the mixture is stirred to obtain a composite colloidal solution; the composite colloidal solution is sprayed on the surface of the coated polyvinyl alcohol fiber obtained in step (1), and the sprayed fiber is placed in a sealed box, and a glutaraldehyde solution is placed in the sealed box for in-situ crosslinking, and then the fiber is taken out and immersed in a glycine solution. After the immersion is completed, the fiber is washed and dried to obtain the modified polyvinyl alcohol fiber.

[0022] This invention constructs a fiber-reinforced phase with gradient response characteristics on the surface of polyvinyl alcohol (PVA) fibers through silane coupling agent treatment, polydopamine coating, and chitosan-gelatin coating. The core innovation lies in the synergistic effect of chemical modification and physical coating to achieve dynamic adaptation and energy dissipation at the fiber-matrix interface. Throughout the modification process, the three steps of silane coupling agent surface activation, polydopamine biomimetic adhesion layer construction, and chitosan-gelatin composite colloid coating are organically linked. Each step not only independently improves the performance of the PVA fibers but also forms an intelligent interface structure through molecular-level synergistic effects.

[0023] During the initial silane coupling agent treatment, silanol groups generated by hydrolysis of 3-aminopropyltriethoxysilane (APTES) undergo a condensation reaction with the hydroxyl groups on the surface of the PVA fiber, forming a covalently bonded siloxane network. This process not only improves the surface roughness of the PVA fiber but, more importantly, introduces a large number of amino-active sites, providing ideal chemical anchoring points for the subsequent in situ polymerization of polydopamine. In a pH-controlled acidic environment (pH 4-5), the APTES molecules partially hydrolyze. The directional bonding of its silanol groups to the hydroxyl groups on the PVA fiber surface avoids the brittle interface caused by excessive cross-linking and preserves the necessary molecular mobility for the subsequent step-by-step construction of the interfacial layer. This precise surface activation treatment transforms the PVA fiber from a hydrophobic surface to a reactive, functionalized surface, laying the chemical foundation for subsequent multilayer coating.

[0024] During the polydopamine coating stage, an interfacial transition layer was constructed through a biomimetic adhesion mechanism. In a weakly alkaline Tris-HCl buffer (pH 8-9), dopamine hydrochloride oxidatively self-polymerized to form a polydopamine layer with a catechol / quinone structure on the surface of the silane-modified polyvinyl alcohol fiber. This process fully utilizes the positive charge of the amino groups on the surface of the silane-modified polyvinyl alcohol fiber, guiding the directional deposition of polydopamine molecules on the surface of the silane-modified polyvinyl alcohol fiber through electrostatic interaction. The function of the formed polydopamine layer is that its quinone group undergoes a Schiff base reaction with the amino group in the chitosan molecular chain to form a chemical bond, while the catechol group produces a physical entanglement with the hydrophobic region of gelatin through hydrogen bonding and π-π stacking. This chemical-physical dual action mechanism not only enhances the bonding strength between the polydopamine layer and the subsequent coated chitosan-gelatin composite coating, but more importantly, forms a viscoelastic interface layer with dynamic reversible properties on the surface of the silane-modified polyvinyl alcohol fiber. When the lightweight building material is under load, this interface layer can achieve energy dissipation through the slippage and bond reconstruction of the molecular chain while maintaining the integrity of the overall structure.

[0025] The chitosan-gelatin composite colloid coating process achieves optimized control of interfacial properties through molecular complementary design. The rigid molecular chains of chitosan and the flexible helical structure of gelatin form an interpenetrating network in an acetic acid medium. The genipin crosslinker selectively acts on the amino groups of chitosan and the carboxyl groups of gelatin, forming a three-dimensional network with a gradient crosslinking density. The introduction of a high-voltage electrostatic spraying process controls the atomization and deposition of the composite colloidal solution through electric field force, forming a nano-scale coating with controllable thickness on the surface of the coated polyvinyl alcohol fiber. The synergistic effect of the substrate platform rotation and heating causes the composite colloidal solution to spread rapidly on the surface of the coated polyvinyl alcohol fiber and undergo pre-crosslinking, forming a uniform and dense primary coating layer. The subsequent glutaraldehyde vapor-phase cross-linking establishes a double cross-linked network inside the coating through penetration and diffusion: the covalent cross-linking points formed by genipin provide structural stability, and the glutaraldehyde-induced gelatin intermolecular cross-linking gives the coating elastic deformation ability. The rigid network maintains the overall structure, while the flexible network dissipates energy through the stretching and rebound of the molecular chain, significantly improving the fatigue resistance of the chitosan-gelatin composite coating.

[0026] During the entire preparation process, first, the chemically active surface formed by silane coupling agent treatment provides an ideal reaction platform for the uniform deposition of the polydopamine layer, avoiding the interfacial defects associated with traditional physical coating. Second, the biomimetic adhesion properties of the polydopamine layer effectively bridge the chemical incompatibility between the silane-modified polyvinyl alcohol fiber surface and the chitosan-gelatin composite coating, achieving stress buffering at the heterogeneous material interface. Finally, the gradient cross-linked structure of the chitosan-gelatin composite colloid, together with the previously formed polydopamine layer, constructs a strain-rate-responsive intelligent interface. Under static load, it exhibits a high-strength bonded state, but under dynamic impact, it transitions to a high-energy dissipation state through molecular chain slippage. This multi-scale synergistic effect enables the modified polyvinyl alcohol fiber to simultaneously achieve two key functions in the cement matrix: at the microscale, chemical bonding and mechanical interlocking enhance the fiber-matrix interface strength, preventing crack initiation; and at the mesoscale, the viscoelastic deformation of the coating absorbs crack propagation energy, delaying material failure.

[0027] As a preferred technical solution of the present invention, in step (1), the length of the polyvinyl alcohol fiber is 6 to 8 mm, for example, it can be 6.0 mm, 6.2 mm, 6.4 mm, 6.6 mm, 6.8 mm, 7.0 mm, 7.2 mm, 7.4 mm, 7.6 mm, 7.8 mm or 8.0 mm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] In some optional examples, the silane coupling agent solution consists of 3-aminopropyltriethoxysilane, anhydrous ethanol and deionized water.

[0029] In some optional examples, the volume ratio of the 3-aminopropyltriethoxysilane, anhydrous ethanol and deionized water is 1:(25~30):(5~6), for example, it can be 1:25:5, 1:25.5:5.1, 1:26:5.2, 1:26.5:5.3, 1:27:5.4, 1:27.5:5.5, 1:28:5.6, 1:28.5:5.7, 1:29:5.8, 1:29.5:5.9 or 1:30:6, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In some optional embodiments, an acetic acid solution is added dropwise to the silane coupling agent solution to adjust its pH value to 4-5, for example, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] In some optional examples, the immersion temperature of the polyvinyl alcohol fiber in the silane coupling agent solution is 40~50°C, for example, it can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C or 50°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In some optional examples, the immersion time of the polyvinyl alcohol fiber in the silane coupling agent solution is 4 to 5 hours, for example, it can be 4.0 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours or 5.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] In some optional examples, the dopamine solution consists of dopamine hydrochloride and Tris-HCl buffer.

[0034] In some optional examples, the pH value of the Tris-HCl buffer is 8-9, for example, it can be 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] In some optional examples, the concentration of dopamine hydrochloride in the dopamine solution is 2-3 mg / mL, for example, 2.0 mg / mL, 2.1 mg / mL, 2.2 mg / mL, 2.3 mg / mL, 2.4 mg / mL, 2.5 mg / mL, 2.6 mg / mL, 2.7 mg / mL, 2.8 mg / mL, 2.9 mg / mL or 3.0 mg / mL, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0036] The present invention specifically limits the concentration of dopamine hydrochloride in the dopamine solution to 2-3 mg / mL. The polydopamine layer formed by the dopamine hydrochloride at a concentration of 2-3 mg / mL plays a key role. The catechol groups in the polydopamine layer on the surface of the modified polyvinyl alcohol fiber and the fluorine-silicon active sites on the surface of the modified basalt fiber form a dynamic hydrogen bond network, and reversible connection nodes are established at the intersection of the two fibers. When the lightweight building material is subjected to a load, these nodes maintain network integrity under low stress to transmit stress, and selectively break under high stress to release energy.

[0037] When the concentration of dopamine hydrochloride is lower than 2 mg / mL, the adsorption rate of dopamine hydrochloride molecules on the surface of silane-modified polyvinyl alcohol fibers falls below the critical nucleation threshold, resulting in discontinuous island-like growth of the polydopamine layer, exposing uncovered areas on the fiber surface. This incomplete coating prevents the subsequent chitosan-gelatin composite colloid from forming a uniform chemical bonding network, leading to a significant decrease in the fiber-matrix interface bonding strength and the tendency to induce stress concentration when subjected to stress. When the concentration of dopamine hydrochloride exceeds 3 mg / mL, the rapid oxidative polymerization rate causes the coating thickness to exceed the critical value, and the internal stress accumulation in the rigid polydopamine layer triggers the initiation of microcracks. At the same time, the excessively thick polydopamine layer hinders the direct bonding of cement hydration products to the polyvinyl alcohol fiber body, causing the interface to degenerate from a chemical-mechanical composite bond to pure physical adsorption, resulting in a decrease in interfacial shear strength and the risk of brittle debonding.

[0038] In some optional examples, the immersion time of the silane-modified polyvinyl alcohol fiber in the dopamine solution is 12 to 24 hours, for example, it can be 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours or 24 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] As a preferred technical solution of the present invention, in step (2), the chitosan solution consists of chitosan and acetic acid solution.

[0040] In some optional examples, the concentration of the acetic acid solution is 0.45~0.55 mol / L, for example, it can be 0.45 mol / L, 0.46 mol / L, 0.47 mol / L, 0.48 mol / L, 0.49 mol / L, 0.5 mol / L, 0.51 mol / L, 0.52 mol / L, 0.53 mol / L, 0.54 mol / L or 0.55 mol / L, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0041] In some optional examples, the mass fraction of chitosan in the chitosan solution is 2~3wt%, for example, it can be 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt% or 3.0wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] In some optional examples, the gelatin solution is prepared by the following method:

[0043] Gelatin is added to deionized water and heated to 55-65°C to dissolve the gelatin to obtain a gelatin solution, and a 0.1 mol / L hydrochloric acid solution is added dropwise to the gelatin solution to adjust its pH value to 4-5, wherein the heating temperature can be 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C or 65°C, and the pH value can be 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] In some optional examples, the mass fraction of gelatin in the gelatin solution is 1.8~2wt%, for example, it can be 1.8wt%, 1.82wt%, 1.84wt%, 1.86wt%, 1.88wt%, 1.9wt%, 1.92wt%, 1.94wt%, 1.96wt%, 1.98wt% or 2.0wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0045] In some optional examples, the volume ratio of the chitosan solution to the gelatin solution is (4~5):1, for example, it can be 4.0:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1, 4.5:1, 4.6:1, 4.7:1, 4.8:1, 4.9:1 or 5.0:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0046] The present invention specifically limits the volume ratio of chitosan solution to gelatin solution to (4-5):1. The rigid β-1,4 glycosidic bond skeleton of chitosan provides structural support, while the flexible helical structure of gelatin imparts elastic deformation ability. The linear molecular chains of chitosan can fully stretch and form multi-point anchoring with the amino groups on the fiber surface. At the same time, the gelatin molecules fill the gaps in the chitosan network through conformational adjustment, forming a dense "rigid-flexible interpenetrating" structure. When the ratio of chitosan solution to gelatin solution is within the range defined by the present invention, the formed chitosan-gelatin composite coating can form a gradient interface with the polydopamine layer and the silane coupling agent layer. The silane coupling agent layer provides a chemical bonding basis, the polydopamine layer achieves stress buffering, and the chitosan-gelatin composite coating dissipates energy through a reversible cross-linked network. The triple synergy improves the shear strength of the fiber-matrix interface.

[0047] When the amount of chitosan solution used is below the lower limit of the range defined by the present invention, the excess gelatin causes the cross-linked network of the composite colloid to become loose, and the chitosan-gelatin composite coating is prone to swelling and dissociation in the alkaline environment of cement, thus losing its protective effect on the polyvinyl alcohol fiber. When the amount of chitosan solution used exceeds the upper limit of the range defined by the present invention, the proportion of chitosan is too high, and its rigid chain segments will compress the viscoelastic layer of the polydopamine layer, weakening the dynamic bonding effect. At the same time, the excessive aggregation of chitosan forms a dense rigid layer, which not only hinders the subsequent cross-linking and penetration of glutaraldehyde, but also causes brittle cracking of the chitosan-gelatin composite coating when the fiber is bent.

[0048] In some optional examples, the amount of the genipin crosslinker added is 0.05~0.07wt% of the mass of the precursor solution, for example, it can be 0.05wt%, 0.052wt%, 0.054wt%, 0.056wt%, 0.058wt%, 0.06wt%, 0.062wt%, 0.064wt%, 0.066wt%, 0.068wt% or 0.07wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0049] In some optional embodiments, the composite colloidal solution is sprayed by high-voltage electrostatic spraying, and the specific operation steps are as follows:

[0050] The conical nozzle and substrate platform are respectively connected to the positive and negative electrodes of a high-voltage power supply. The composite colloid solution is fed into the conical nozzle through a peristaltic pump. The coated polyvinyl alcohol fiber is placed on a rotating substrate platform. The coated polyvinyl alcohol fiber is driven to rotate and heated by the substrate platform. During the rotation of the coated polyvinyl alcohol fiber, the composite colloid solution is sprayed onto the surface of the coated polyvinyl alcohol fiber through the conical nozzle.

[0051] In some optional instances, the voltage of the high-voltage power supply is 15~20kV, for example, it can be 15kV, 15.5kV, 16kV, 16.5kV, 17kV, 17.5kV, 18kV, 18.5kV, 19kV, 19.5kV or 20kV, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0052] In some optional examples, the inner diameter of the conical nozzle is 0.6~0.8mm, for example, it can be 0.6mm, 0.62mm, 0.64mm, 0.66mm, 0.68mm, 0.7mm, 0.72mm, 0.74mm, 0.76mm, 0.78mm or 0.8mm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0053] In some optional examples, the spraying distance between the conical nozzle and the coated polyvinyl alcohol fiber is 130~150mm, for example, it can be 130mm, 132mm, 134mm, 136mm, 138mm, 140mm, 142mm, 144mm, 146mm, 148mm or 150mm, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0054] In some optional examples, the peristaltic pump delivers the composite colloidal solution to the conical nozzle at a liquid supply rate of 1 to 2 mL / min, for example, 1.0 mL / min, 1.1 mL / min, 1.2 mL / min, 1.3 mL / min, 1.4 mL / min, 1.5 mL / min, 1.6 mL / min, 1.7 mL / min, 1.8 mL / min, 1.9 mL / min or 2.0 mL / min, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0055] In some optional examples, the linear speed of the substrate platform during rotation is 0.2~0.4 m / s, for example, it can be 0.2 m / s, 0.22 m / s, 0.24 m / s, 0.26 m / s, 0.28 m / s, 0.3 m / s, 0.32 m / s, 0.34 m / s, 0.36 m / s, 0.38 m / s or 0.4 m / s, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] In some optional examples, the heating temperature of the substrate platform for the coated polyvinyl alcohol fiber is 50~55℃, for example, it can be 50℃, 50.5℃, 51℃, 51.5℃, 52℃, 52.5℃, 53℃, 53.5℃, 54℃, 54.5℃ or 55℃, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0057] In some optional examples, the spraying time of the composite colloidal solution is 5 to 8 minutes, for example, it can be 5.0 minutes, 5.5 minutes, 6.0 minutes, 6.5 minutes, 7.0 minutes, 7.5 minutes or 8.0 minutes, but it is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0058] In some optional examples, the temperature in the sealed box is 45~50℃, for example, it can be 45℃, 45.5℃, 46℃, 46.5℃, 47℃, 47.5℃, 48℃, 48.5℃, 49℃, 49.5℃ or 50℃, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0059] In some optional examples, the humidity in the sealed box is 65~75%, for example, it can be 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74% or 75%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0060] In some optional examples, the mass fraction of the glutaraldehyde solution is 0.4~0.6wt%, for example, it can be 0.4wt%, 0.42wt%, 0.44wt%, 0.46wt%, 0.48wt%, 0.5wt%, 0.52wt%, 0.54wt%, 0.56wt%, 0.58wt% or 0.6wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0061] In some optional examples, the in situ cross-linking time is 2 to 3 hours, for example, it can be 2.0 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] In some optional examples, the mass fraction of the glycine solution is 0.8~1.2wt%, for example, it can be 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt%, 1.0wt%, 1.05wt%, 1.1wt%, 1.15wt% or 1.2wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0063] In some optional examples, the immersion time of the in situ cross-linked fiber in the glycine solution is 25 to 35 minutes, for example, it can be 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes, 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes or 35 minutes, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0064] In some optional embodiments, after soaking, the fiber is removed from the glycine solution, washed, and then vacuum dried at 55-65°C for 10-15 hours, wherein the temperature can be 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C or 65°C, and the time can be 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] As a preferred technical solution of the present invention, in step (I), the modified basalt fiber is prepared by the following method:

[0066] The basalt fiber is soaked in an oxalic acid solution, and after the soaking, the fiber is taken out and repeatedly rinsed with deionized water until it is neutral; then the basalt fiber is soaked in an ammonium fluoride solution, and after the soaking, the fiber is taken out and repeatedly rinsed with deionized water until it is neutral, and then dried to obtain the modified basalt fiber.

[0067] The present invention constructs a micro-nano structure on the surface of basalt fiber through phased chemical etching and surface activation treatment, forming a spatially complementary reinforcement network with modified polyvinyl alcohol fiber, thereby achieving a synergistic improvement in the strength and toughness of lightweight building materials.

[0068] On the one hand, the step-by-step treatment with oxalic acid and ammonium fluoride creates a gradient surface reconstruction process. Oxalic acid, as a weak organic acid, preferentially reacts with metal oxides such as iron and magnesium on the basalt fiber surface, selectively dissolving the amorphous phase and forming micron-scale groove structures on the basalt fiber surface. This directional etching not only increases the specific surface area of ​​the basalt fiber but, more importantly, exposes active sites within the internal silicon-oxygen network, creating a reaction interface for subsequent ammonium fluoride treatment.

[0069] On the other hand, the fluoride ions in the ammonium fluoride solution undergo a coordination substitution reaction with the exposed silicate, converting some Si-O-Si bonds into Si-F bonds, while generating nano-scale fluorosilicate protrusions on the surface. This multi-scale surface morphology reconstruction forms a unique "groove-protrusion" composite structure. The micron-scale grooves can enhance the mechanical interlocking of the modified basalt fiber and the cement matrix, while the nano-protrusions promote the heterogeneous nucleation of hydration products by increasing the surface energy of the modified basalt fiber. In addition, the acidic environment formed by the oxalic acid treatment provides an ideal pH condition for the ammonium fluoride reaction. The synergistic effect of the two enables the surface modification depth of the modified basalt fiber to be controlled within the range of 5-8μm, ensuring the interface strengthening effect while avoiding the loss of fiber strength caused by excessive etching.

[0070] Different modification methods were used to modify the surface of polyvinyl alcohol fiber and basalt fiber, which enhanced the synergistic effect between the two:

[0071] On the one hand, the silicon-fluorinated surface of the modified basalt fiber forms chemical bonds with cement hydration products, providing rigid interfacial support. The polydopamine layer and chitosan-gelatin composite coating on the surface of the modified polyvinyl alcohol fiber dissipate energy through viscoelastic deformation, forming a flexible, buffering interface. When the lightweight building material is subjected to load, the rigid modified basalt fiber is the first to bear the stress transfer, and its high modulus effectively inhibits deformation of the cement matrix. As stress increases, the flexible interface of the modified polyvinyl alcohol fiber initiates a slip mechanism, slowing crack propagation through frictional energy dissipation. The spatial interweaving of the two fiber networks forces the crack path to undergo multiple deflections, significantly extending the crack propagation path.

[0072] On the other hand, the synergistic modification of PVA fibers and basalt fibers creates a stress transfer gradient. The high surface energy of the modified basalt fibers creates a dense layer of hydration products around them, and the high elastic modulus of this region effectively transmits compressive stress. The organic coating region on the surface of the modified PVA fibers forms a low-modulus transition zone, which can buffer tensile stress concentrations. This modulus gradient design enables a microscale redistribution of stress fields in lightweight building materials: compressive stress is efficiently transmitted through the modified basalt fiber network, while tensile stress is softened and absorbed by the modified PVA fiber interface layer. Furthermore, the fluorosilicon active sites introduced by oxalic acid-ammonium fluoride modification on the surface of the modified basalt fibers can form weak bonds with the amino groups in the chitosan-gelatin composite coating on the surface of the modified PVA fibers, forming dynamic connection nodes at the intersections of the two fibers. These nodes remain connected under low stress to transmit stress and reversibly break under high stress to dissipate energy, achieving adaptive regulation of the enhanced network.

[0073] In some optional examples, the length of the basalt fiber is 8~12mm, for example, it can be 8.0mm, 8.5mm, 9.0mm, 9.5mm, 10.0mm, 10.5mm, 11.0mm, 11.5mm or 12.0mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0074] In some optional examples, the mass fraction of the oxalic acid solution is 5~8wt%, for example, it can be 5.0wt%, 5.5wt%, 6.0wt%, 6.5wt%, 7.0wt%, 7.5wt% or 8.0wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0075] The present invention specifically limits the mass fraction of the oxalic acid solution to 5-8wt%. Oxalic acid, as an organic weak acid, preferentially reacts with metal oxides such as Fe and Mg on the surface of the basalt fiber, selectively dissolving the amorphous phase region while retaining the integrity of the silicon-oxygen network skeleton. After oxalic acid etching, directional grooves with a depth of 0.5-2μm are formed on the surface of the basalt fiber, and nano-scale protrusion structures are simultaneously generated, thereby increasing the specific surface area of ​​the basalt fiber by more than 3 times, while ensuring that the tensile strength of the basalt fiber is not significantly affected.

[0076] When the mass fraction of the oxalic acid solution is less than 5wt%, the H⁺ concentration in the oxalic acid solution is insufficient to break through the passivation layer on the surface of the basalt fiber. Etching only stops at the nanoscale roughness and fails to form an effective micron-scale groove structure. This leads to insufficient exposure of active sites during subsequent ammonium fluoride treatment and a decrease in the chemical bonding density at the fiber-matrix interface. When the mass fraction of the oxalic acid solution exceeds 8%, the excessive acid hydrolysis not only erodes the amorphous phase but also destroys the silicon-oxygen tetrahedral structure, causing a significant decrease in the strength of the basalt fiber itself. Deep etch pits form on the surface, triggering stress concentration, causing the lightweight building material to break preferentially at the defects of the modified basalt fiber when subjected to stress.

[0077] In some optional examples, the immersion temperature of the basalt fiber in the oxalic acid solution is 40~50℃, for example, it can be 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃ or 50℃, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0078] In some optional examples, the immersion time of the basalt fiber in the oxalic acid solution is 20 to 30 minutes, for example, it can be 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes or 30 minutes, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0079] In some optional examples, the mass fraction of the ammonium fluoride solution is 1-2 wt%, for example, it can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0080] The present invention specifically limits the mass fraction of ammonium fluoride solution to 1-2wt%. The fluoride ions generated by the dissociation of ammonium fluoride in the solution undergo a coordination substitution reaction with the silicon-oxygen tetrahedron on the surface of the basalt fiber, converting some Si-O bonds into Si-F bonds. The high bond energy of the Si-F bond provides a strong chemical anchor point for the cement hydration product. At the same time, it can also form a molecular coupling mechanism with the chitosan-gelatin composite coating of the modified polyvinyl alcohol fiber. The Si-F bonds on the surface of the modified basalt fiber and the amino groups in the chitosan-gelatin composite coating form a dynamic connection network through NH···F hydrogen bonds, establishing reversible stress transfer points at the intersection of the two fibers. When the lightweight building material is subjected to load, these nodes maintain network integrity under low stress to evenly distribute stress, and selectively break under high stress and dissipate energy through friction. At the same time, after being treated with ammonium fluoride, nano-scale fluorosilicate protrusions can be generated on the surface of the basalt fiber. These nano-scale fluorosilicate protrusions can enhance the mechanical interlocking effect by increasing the specific surface area of ​​the modified basalt fiber.

[0081] When the mass fraction of ammonium fluoride solution is less than 1wt%, the fluoride ion concentration is insufficient to break through the diffusion resistance of the hydration layer on the surface of the basalt fiber, and only sporadic active sites are formed locally on the basalt fiber, resulting in insufficient heterogeneous nucleation density of subsequent cement hydration products and low interfacial chemical bonding strength. When the mass fraction of ammonium fluoride solution exceeds 2wt%, the excessive fluoride ions trigger excessive depolymerization of the silicon-oxygen network, resulting in the formation of pits with a depth of more than 50nm on the surface of the basalt fiber, causing a significant decrease in the tensile strength of the modified basalt fiber. In addition, the generated fluorosilicate layer produces microcracks due to internal stress accumulation, becoming the preferred path for interfacial failure.

[0082] In some optional examples, the immersion time of the basalt fiber in the ammonium fluoride solution is 10 to 15 minutes, for example, it can be 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes, 12 minutes, 12.5 minutes, 13 minutes, 13.5 minutes, 14 minutes, 14.5 minutes or 15 minutes, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0083] As a preferred technical solution of the present invention, in step (I), the base mortar includes silicate cement, quartz sand, fly ash, metakaolin, a water reducer and water.

[0084] In some optional examples, the weight proportions of the components in the base mortar are as follows:

[0085] 45-55 parts of Portland cement;

[0086] 40-50 parts of quartz sand;

[0087] 15-25 parts fly ash;

[0088] 5-8 parts of metakaolin;

[0089] 0.3~0.8 parts of water reducer;

[0090] 35~40 parts water.

[0091] wherein the weight portion of silicate cement may be 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts or 55 parts, the weight portion of quartz sand may be 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts or 50 parts, the weight portion of fly ash may be 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts or 25 parts, and the weight portion of metakaolin may be 5.0 parts, 5.5 parts, The weight parts of the water reducing agent can be 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, 0.5 parts, 0.55 parts, 0.6 parts, 0.65 parts, 0.7 parts, 0.75 parts or 0.8 parts, and the weight parts of water can be 35 parts, 35.5 parts, 36 parts, 36.5 parts, 37 parts, 37.5 parts, 38 parts, 38.5 parts, 39 parts, 39.5 parts or 40 parts, but are not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0092] In some optional examples, the mass fraction of the modified polyvinyl alcohol fiber in the composite mortar is 1.5~2wt%, for example, it can be 1.5wt%, 1.55wt%, 1.6wt%, 1.65wt%, 1.7wt%, 1.75wt%, 1.8wt%, 1.85wt%, 1.9wt%, 1.95wt% or 2.0wt%, but it is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0093] In some optional examples, the mass fraction of the modified basalt fiber in the composite mortar is 0.8~1wt%, for example, it can be 0.8wt%, 0.82wt%, 0.84wt%, 0.86wt%, 0.88wt%, 0.9wt%, 0.92wt%, 0.94wt%, 0.96wt%, 0.98wt% or 1wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0094] As a preferred technical solution of the present invention, in step (II), the specific operation steps of the layer-by-layer printing include:

[0095] After the composite mortar is injected into the 3D printing equipment, the cement mortar strips are extruded through the extruder head. The diameter of the extruder head is 40-50 mm, for example, 40 mm, 41 mm, 42 mm, 43 mm, 44 mm, 45 mm, 46 mm, 47 mm, 48 mm, 49 mm or 50 mm. The extrusion pressure of the extruder head is 2-3 MPa, for example, 2.0 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa. , 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa or 3.0 MPa, the extrusion head moves back and forth in a broken line along the X-axis direction and advances line by line in the Y-axis direction with a path width of 35 to 45 mm, for example, it can be 35 mm, 36 mm, 37 mm, 38 mm, 39 mm, 40 mm, 41 mm, 42 mm, 43 mm, 44 mm or 45 mm, so that the extruded cement mortar strips are tightly laid in a continuous S-shape to obtain a first mortar matrix layer;

[0096] After the first mortar base layer is printed, an interface treatment agent is sprayed on the surface of the first mortar base layer, and the surface is left to stand for 2 to 3 minutes, for example, 2.0 minutes, 2.1 minutes, 2.2 minutes, 2.3 minutes, 2.4 minutes, 2.5 minutes, 2.6 minutes, 2.7 minutes, 2.8 minutes, 2.9 minutes or 3.0 minutes, to form a first flexible interface layer on the surface of the first mortar base layer;

[0097] Subsequently, the second mortar matrix layer is extruded, and the extrusion head is vertically raised in the Z-axis direction by 20 to 30 mm, for example, 20 mm, 21 mm, 22 mm, 23 mm, 24 mm, 25 mm, 26 mm, 27 mm, 28 mm, 29 mm or 30 mm. In the XY plane, the extrusion head is offset by half the path width in the positive direction of the Y-axis with the starting point of the first mortar matrix layer as the reference, as the extrusion starting point of the second mortar matrix layer; the extruded cement mortar strips are embedded in the gaps between adjacent cement mortar strips in the first mortar matrix layer. After the second mortar matrix layer is printed, a continuous concave-convex mosaic structure is formed between the first mortar matrix layer and the second mortar matrix layer;

[0098] After the second mortar base layer is printed, an interface treatment agent is sprayed on the surface of the second mortar base layer, and the surface is left to stand for 2 to 3 minutes, for example, 2.0 minutes, 2.1 minutes, 2.2 minutes, 2.3 minutes, 2.4 minutes, 2.5 minutes, 2.6 minutes, 2.7 minutes, 2.8 minutes, 2.9 minutes or 3.0 minutes, to form a second flexible interface layer on the surface of the second mortar base layer;

[0099] Subsequently, the third mortar matrix layer is extruded. The extrusion head is vertically lifted 20-30 mm in the Z-axis direction. In the XY plane, the extrusion head is offset by half the path width in the negative direction of the Y-axis with the starting point of the second mortar matrix layer as the reference, and the extrusion head is used as the extrusion starting point of the third mortar matrix layer. At this time, the position of the extrusion head returns to the extrusion starting point of the first mortar matrix layer in the XY plane. The extruded cement mortar strips are embedded in the gaps between adjacent cement mortar strips in the second mortar matrix layer. After the second mortar matrix layer is printed, a continuous concave-convex mosaic structure is formed between the second and third mortar matrix layers.

[0100] After the third mortar base layer is printed, an interface treatment agent is sprayed on the surface of the third mortar base layer. The surface of the third mortar base layer is left to stand for 2 to 3 minutes to form a third flexible interface layer on the surface of the third mortar base layer.

[0101] Printing is carried out layer by layer in this way. When printing a single mortar base layer, the extruder moves back and forth in the X-axis direction, advances line by line with a path width of 35 to 45 mm in the Y-axis direction, remains unchanged in the Z-axis direction, and adopts a zigzag movement path for single-layer filling; after the single-layer printing is completed, the interface treatment agent is sprayed on the surface of the single-layer mortar base layer and dried naturally. Then, the extruder head is lifted vertically along the Z-axis direction. In the XY plane, the extruder head moves to the extrusion starting point of the newly printed mortar base layer, and based on this, the position of half the path width is alternately offset in the positive or negative direction of the Y-axis as the extrusion starting point of the new layer, and finally the lightweight building material is obtained.

[0102] The layer-by-layer printing process designed in the present invention constructs a three-dimensional continuous interlocking layered structure through precise control of the spatial path. During the printing process, each layer is offset by half the path width, so that a bionic scaly concave-convex mosaic structure is formed between adjacent mortar matrix layers. This structural design forms a unique slip-interlocking coupling effect, fundamentally changing the failure mode and energy dissipation mechanism of lightweight building materials.

[0103] The extruder head's printing path, with alternating positive and negative offsets along the Y-axis, creates a spatially staggered arrangement of cement mortar strips in adjacent layers. When the cement mortar strips of the previous layer are embedded in the gaps between the adjacent cement mortar strips in the next layer, the unsolidified cement mortar strips flow and fill locally under the action of gravity and extrusion, forming a mechanical interlocking structure similar to a "mortise and tenon joint." The function of this interlocking interface is to combine the dual characteristics of geometric interlocking and controlled slip. The mechanical interlocking of the concave and convex structure provides initial shear strength, while the flexible interface layer formed by the interface treatment agent between adjacent mortar matrix layers allows limited displacement. When lightweight building materials are subjected to shear stress, the interlocking structure prevents complete interlayer slip through mechanical resistance, while the preset interface slip converts part of the mechanical energy into heat energy dissipation through friction.

[0104] Under low stress loads, the interlayer interlocking structure absorbs energy through elastic deformation, maintaining overall stiffness. When stress exceeds a critical value, interfacial slip initiates, accompanied by frictional energy dissipation. At this point, the interlocking structure maintains its load transfer function, preventing brittle fracture caused by stress concentration. Under extreme conditions, the mechanical engagement of the concave and convex interlocking areas forces a three-dimensional deflection in the crack propagation path, significantly extending it and increasing surface energy consumption. Compared to the single crack propagation mode of traditional homogeneous cement materials, this structure requires the failure process to continuously overcome mechanical interlocking resistance and interfacial slip friction, dissipating the energy originally concentrated on a single crack surface into multiple layers of dissipation channels.

[0105] In practical applications, this structural design enables lightweight building materials to exhibit a unique adaptive response to impact loads. When subjected to instantaneous impact, rapid interface sliding consumes a large amount of kinetic energy; and under continuous static loads, the interlocking structure can provide stable bearing capacity. This intelligent mechanical property gives it important application value in earthquake-resistant structures, protective engineering and other fields.

[0106] As a preferred technical solution of the present invention, in step (II), based on the total mass fraction of the interface treatment agent being 100 wt%, the interface treatment agent comprises the following components in mass fractions:

[0107] Styrene acrylic emulsion 70~75wt%;

[0108] Nano-silicon dioxide 10~12wt%;

[0109] Nanocellulose 1~2wt%;

[0110] Acetyl tributyl citrate plasticizer 4~5wt%;

[0111] Microsilica fume 5~8wt%;

[0112] Silane coupling agent 0.5~1.5wt%;

[0113] Silicone leveling agent 2~2.5wt%;

[0114] Among them, the mass fraction of styrene acrylic emulsion can be 70wt%, 70.5wt%, 71wt%, 71.5wt%, 72wt%, 72.5wt%, 73wt%, 73.5wt%, 74wt%, 74.5wt% or 75wt%, and the mass fraction of nano silicon dioxide can be 10wt%, 10.2wt%, 10.4wt%, 10.6wt%, 10.8wt%, 11wt%, 11.2wt%, 11.4wt%, 11.6wt%, 11.8wt% t% or 12wt%, the mass fraction of nanocellulose can be 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt% or 2.0wt%, and the mass fraction of acetyl tributyl citrate plasticizer can be 4.0wt%, 4.1wt%, 4.2wt%, 4.3wt%, 4.4wt%, 4.5wt%, 4.6wt%, 4.7wt%, 4.8wt%. %, 4.9wt% or 5.0wt%, the mass fraction of microsilica fume can be 5.0wt%, 5.2wt%, 5.4wt%, 5.6wt%, 5.8wt%, 6.0wt%, 6.2wt%, 6.4wt%, 6.6wt%, 6.8wt%, 7.0wt%, 7.2wt%, 7.4wt%, 7.6wt%, 7.8wt% or 8.0wt%, and the mass fraction of silane coupling agent can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%. %, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt% or 1.5wt%; the mass fraction of the silicone leveling agent can be 2.0wt%, 2.05wt%, 2.1wt%, 2.15wt%, 2.2wt%, 2.25wt%, 2.3wt%, 2.35wt%, 2.4wt%, 2.45wt% or 2.5wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0115] In the present invention, the performance of the flexible interface layer is greatly improved through the synergistic mechanism between the components in the interface treatment agent. Among them, the nanocellulose and styrene acrylic network dissipate impact energy through molecular chain slippage and dynamic bond breakage, the dual-scale reinforcement system of microsilica and nanosilica maintains structural stability, and the silane cross-linking network ensures the interlayer interface bonding strength.

[0116] Styrene-acrylic emulsion serves as the continuous phase, forming a flexible polymer network backbone. The carboxyl groups in its molecular chains form physical crosslinks with the silanol groups on the surface of the nanosilica through hydrogen bonding. Simultaneously, during film formation, the styrene-acrylic emulsion particles encapsulate the microsilica fume, forming a "core-shell" structure. The rigid core of the microsilica fume resists compressive stress, while the styrene-acrylic polymer shell absorbs shear energy through elastic deformation. The fibrillated structure of nanocellulose intersperses the gaps between the styrene-acrylic network, forming a bridge network that spans the organic-inorganic phase. When the flexible interface layer is loaded, energy is dissipated through the slip and bond reconstruction of the cellulose fibrils. Acetyl tributyl citrate plasticizer selectively softens the glassy region of the styrene-acrylic emulsion and, in conjunction with the silicone leveling agent, modulates the modulus gradient distribution of the flexible interface layer. The high packing density of the microsilica fume forms a rigid transition layer near the mortar base layer, ensuring efficient stress transfer. The central region of the flexible interface layer retains a moderate degree of flexibility to buffer interlayer deformation differences. During the curing process, the silane coupling agent simultaneously anchors the surface of nano-silica and penetrates into the pores of cement hydration products. Its silanol groups form coordination bonds with calcium ions in the CSH gel, thereby improving the interfacial bonding strength between the flexible interface layer and the mortar matrix layer.

[0117] During the 3D printing process, the interface treatment agent optimizes and improves the performance of lightweight building materials through a three-stage mechanism. In the initial penetration stage, the low-viscosity styrene-acrylic emulsion carries nano-silica to a depth of 50-100μm on the surface of the mortar matrix layer, forming a root-like anchoring structure in the pores of the mortar matrix layer; in the curing reaction stage, the microsilica powder and cement continue to hydrate to produce volume expansion, so that a prestressed bond is generated between the flexible interface layer and the mortar matrix layer; in the material service stage, the nanocellulose network and modified basalt fiber form cross-interface reinforcement, and the single main crack is dispersed into multiple microcracks through the crack tip bridging effect.

[0118] In some optional examples, the solid content of the styrene acrylic emulsion is 40-50%, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0119] In some optional embodiments, the spraying amount of the interface treatment agent is 20-30 g / m 2 , for example, it can be 20g / m 2 , 21g / m 2 , 22g / m 2 , 23g / m 2 , 24g / m 2 , 25g / m 2 , 26g / m 2 , 27g / m 2 , 28g / m2 , 29g / m 2 or 30g / m 2 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0120] The present invention specifically limits the spraying amount of the interface treatment agent to 20~30g / m 2 Within this spraying amount range, the nano-silica and micro-silica powder in the interface treatment agent form a gradient penetration on the surface of the mortar matrix layer. The area within 20μm depth of the surface of the mortar matrix layer is mainly composed of styrene-acrylic emulsion-nano-silica composite film, the area with a depth of 30~50μm on the surface of the mortar matrix layer is the transition zone between the interface treatment agent and the cement hydration product, and the area with a depth of 50~100μm on the surface of the mortar matrix layer is the reinforced bonding zone formed by the penetration of the interface treatment agent. This "soft-medium-hard" gradient structure guides the progressive attenuation of stress waves through modulus differences when subjected to stress, thereby greatly improving the interface fracture energy.

[0121] When the spraying amount of the interface treatment agent is less than 20g / m 2 When the interface treatment agent is sprayed in an amount exceeding 30 g / m2, it cannot form a continuous and complete flexible interface layer on the surface of the mortar matrix layer. The filling density of nano-silica in the flexible interface layer is insufficient, resulting in a high interface porosity between the flexible interface layer and the mortar matrix layer. In addition, the styrene-acrylic emulsion is difficult to penetrate into the capillary pores below 50 μm on the surface of the mortar matrix layer, resulting in the loss of the "tree root-like" anchoring effect and a significant reduction in the interlayer shear strength. When the spraying amount of the interface treatment agent exceeds 30 g / m2, the interface treatment agent cannot form a continuous and complete flexible interface layer on the surface of the mortar matrix layer. The filling density of nano-silica in the flexible interface layer is insufficient, resulting in a high interface porosity between the flexible interface layer and the mortar matrix layer. In addition, the styrene-acrylic emulsion is difficult to penetrate into the capillary pores below 50 μm on the surface of the mortar matrix layer, resulting in a loss of the "tree root-like" anchoring effect and a significant reduction in the interlayer shear strength. 2 When the thickness of the flexible interface layer is too thick (>80μm), it is formed. During the curing process, the flexible interface layer generates internal stress due to volume shrinkage, which triggers a micro-crack network in the interface layer between the flexible interface layer and the mortar matrix layer, and at the same time hinders the formation of the mechanical interlocking structure between adjacent mortar matrix layers, causing the concave-convex mosaic effect constructed by 3D printing to fail.

[0122] As a preferred technical solution of the present invention, the gradient curing and solidification includes a first curing stage and a second curing stage performed sequentially.

[0123] In some optional examples, the curing temperature of the first curing stage is 35~45°C, for example, it can be 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C or 45°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0124] In some optional examples, the relative humidity in the first curing stage is 90-95%, for example, it can be 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5% or 95%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0125] In some optional examples, the curing time of the first curing stage is 24 to 36 hours, for example, it can be 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32 hours, 33 hours, 34 hours, 35 hours or 36 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0126] In some optional examples, the curing pressure in the first curing stage is 0.1 MPa.

[0127] In some optional examples, the curing atmosphere in the first curing stage is air.

[0128] In some optional examples, the curing temperature of the second curing stage is 55~65°C, for example, it can be 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C or 65°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0129] In some optional examples, the relative humidity in the second curing stage is 60-70%, for example, it can be 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69% or 70%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0130] In some optional examples, the curing time of the second curing stage is 24 to 36 hours, for example, it can be 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32 hours, 33 hours, 34 hours, 35 hours or 36 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0131] In some optional examples, the curing pressure of the second curing stage is 0.2~0.3MPa, for example, it can be 0.2MPa, 0.21MPa, 0.22MPa, 0.23MPa, 0.24MPa, 0.25MPa, 0.26MPa, 0.27MPa, 0.28MPa, 0.29MPa or 0.3MPa, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0132] The present invention specifically limits the curing pressure of the second curing stage to 0.2~0.3MPa. Applying appropriate pressure in the middle and late stages of cement hydration can effectively improve the comprehensive mechanical properties of lightweight building materials. First, appropriate pressure can drive the nano-scale hydration products to migrate directionally to the fiber-matrix interface area, forming a dense transition layer on the surface of modified polyvinyl alcohol fiber and modified basalt fiber; second, appropriate pressure can promote the active components such as microsilica in the flexible interface layer to fully react with Ca(OH)2 to generate secondary CSH gel, filling the 10~100nm pores; third, appropriate pressure can promote the prestressed bonding of the fluorosilicate layer on the surface of the modified basalt fiber with the cement matrix, thereby greatly improving the shear strength of the fiber-matrix interface.

[0133] When the curing pressure in the second curing stage is lower than 0.2 MPa, the pressure is insufficient to overcome the frictional resistance between the nano-silica particles, resulting in low efficiency in the reconstruction of the pore structure of the interface layer between the flexible interface layer and the mortar matrix layer, forming a continuous weakened channel; when the curing pressure in the second curing stage exceeds 0.3 MPa, the excessive compressive stress will destroy the primary CSH gel network, resulting in disordered orientation of the hydration products, and at the same time causing plastic deformation of the chitosan-gelatin composite coating on the surface of the modified polyvinyl alcohol fiber, the interface slip energy dissipation mechanism to fail, and the loss of the ability to buffer impact energy.

[0134] In some optional examples, the curing atmosphere in the second curing stage is nitrogen.

[0135] In a second aspect, the present invention provides a 3D printing-based lightweight building material containing mixed fibers, prepared by the preparation method described in the first aspect. The lightweight building material containing mixed fibers comprises a mortar base layer and a flexible interface layer stacked in sequence.

[0136] Compared with the prior art, the present invention has the following beneficial effects:

[0137] The preparation method of lightweight building materials provided by the present invention achieves a breakthrough improvement in the mechanical properties of materials through multi-dimensional synergistic effects. The core invention lies in the construction of a dual synergistic mechanism of fiber reinforcement system and interlayer sliding interlocking structure, which breaks through the technical problem of traditional cement-based materials that cannot take into account both strength and toughness from the two levels of micro-interface modification and macro-structure design. BRIEF DESCRIPTION OF THE DRAWINGS

[0138] Figure 1 This is a schematic diagram of the cross-sectional structure of the lightweight building material mixed with mixed fibers prepared in Example 1 of the present invention;

[0139] Figure 2 This is a scanning electron microscope image of the polyvinyl alcohol fiber used in Example 1 of the present invention;

[0140] Figure 3 This is a scanning electron microscope image of the silane-modified polyvinyl alcohol fiber prepared in Example 1 of the present invention;

[0141] Figure 4 This is a scanning electron microscope image of the coated polyvinyl alcohol fiber prepared in Example 1 of the present invention;

[0142] Figure 5 This is a scanning electron microscope image of the modified polyvinyl alcohol fiber prepared in Example 1 of the present invention;

[0143] Figure 6 This is a surface AFM image of the silane-modified polyvinyl alcohol fiber prepared in Example 1 of the present invention;

[0144] Figure 7 This is a surface AFM image of the modified polyvinyl alcohol fiber prepared in Example 1 of the present invention;

[0145] Figure 8 This is an infrared spectrum of the coated polyvinyl alcohol fiber prepared in Example 1 of the present invention;

[0146] Figure 9 The infrared spectra of gelatin, chitosan and the modified polyvinyl alcohol fiber prepared in Example 1 of the present invention are shown;

[0147] Figure 10 This is a scanning electron microscope image of the basalt fiber modified with oxalic acid in Example 1 of the present invention;

[0148] Figure 11 This is a scanning electron microscope image of the modified basalt fiber prepared in Example 1 of the present invention;

[0149] Figure 12 This is a scanning electron microscope image of the cross-sectional structure of the lightweight building material prepared in Comparative Example 1 of the present invention;

[0150] Figure 13 This is a scanning electron microscope image of the fiber pullout of the lightweight building material prepared in Comparative Example 1 of the present invention;

[0151] Figure 14 This is a scanning electron microscope image of the cross-sectional structure of the lightweight building material prepared in Example 1 of the present invention;

[0152] Figure 15 This is a scanning electron microscope image of the fiber pullout of the lightweight building material prepared in Example 1 of the present invention;

[0153] Figure 16 This is a physical picture of the printed composite layered structure prepared in Example 1 of the present invention.

[0154] Explanation of the accompanying drawings: 1. Mortar base layer; 2. Flexible interface layer. DETAILED DESCRIPTION

[0155] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments described herein.

[0156] Example 1

[0157] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing, the method comprising:

[0158] (1) 3-aminopropyltriethoxysilane, anhydrous ethanol and deionized water were mixed uniformly in a volume ratio of 1:25:5 to obtain a silane coupling agent solution, and an acetic acid solution was added dropwise to the silane coupling agent solution to adjust its pH value to 4; polyvinyl alcohol fiber with a length of 6 mm was immersed in the silane coupling agent solution at 40°C for 5 h. After the immersion, the fiber was taken out, washed and dried to obtain silane-modified polyvinyl alcohol fiber;

[0159] (2) adding dopamine hydrochloride to a Tris-HCl buffer solution with a pH value of 8 to obtain a dopamine solution, wherein the concentration of dopamine hydrochloride in the dopamine solution is 2 mg / mL, and immersing the silane-modified polyvinyl alcohol fiber in the dopamine solution at room temperature and in the dark for 24 hours. The fiber is then taken out, washed, and dried to obtain a coated polyvinyl alcohol fiber;

[0160] (3) Chitosan was dissolved in 0.45 mol / L acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution was 2 wt %. Gelatin was added to deionized water and heated to 55°C to dissolve the gelatin to obtain a gelatin solution, wherein the mass fraction of gelatin in the gelatin solution was 1.8 wt %. 0.1 mol / L hydrochloric acid solution was added dropwise to the gelatin solution to adjust its pH value to 4. The chitosan solution and the gelatin solution were mixed uniformly in a volume ratio of 4:1 to obtain a precursor solution, and a genipin crosslinker was added to the precursor solution in an amount of 0.05 wt % of the mass of the precursor solution. The mixture was mixed and stirred to obtain a composite colloidal solution.

[0161] (4) The composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber using a high-voltage electrostatic spraying process. The conical nozzle and the substrate platform were connected to the positive and negative electrodes of a high-voltage power supply with a voltage of 15 kV, respectively. The composite colloidal solution was fed into the conical nozzle at a liquid supply rate of 1 mL / min by a peristaltic pump. The inner diameter of the conical nozzle was 0.8 mm. The coated polyvinyl alcohol fiber was placed on a rotating substrate platform. The substrate platform drove the coated polyvinyl alcohol fiber to rotate at a linear speed of 0.4 m / s and heated it to 50 °C. During the rotation of the coated polyvinyl alcohol fiber, a composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber through a conical nozzle for a total of 5 minutes. The sprayed fiber was placed in a closed box at a temperature of 45°C and a humidity of 65%. A 0.4wt% glutaraldehyde solution was placed in the closed box for in-situ crosslinking for 3 hours. The fiber was then removed and immersed in a 0.8wt% glycine solution for 35 minutes. After soaking, it was removed, washed, and vacuum dried at 55°C for 15 hours to obtain a modified polyvinyl alcohol fiber.

[0162] (5) Soak 8 mm long basalt fiber in 5 wt% oxalic acid solution at 40 °C for 30 min. After soaking, take out the fiber and rinse it repeatedly with deionized water until it is neutral. Then soak the basalt fiber in 1 wt% ammonium fluoride solution for 15 min. After soaking, take out the fiber and rinse it repeatedly with deionized water until it is neutral. After drying, the modified basalt fiber is obtained.

[0163] (6) Adding modified polyvinyl alcohol fiber and modified basalt fiber to the base mortar and mixing them evenly to obtain a composite mortar; wherein the base mortar includes 45 parts of Portland cement, 40 parts of quartz sand, 15 parts of fly ash, 5 parts of metakaolin, 0.3 parts of water reducer and 35 parts of water; the mass fraction of the modified polyvinyl alcohol fiber in the composite mortar is 1.5wt%, and the mass fraction of the modified basalt fiber is 0.8wt%;

[0164] (7) The composite mortar is injected into the 3D printing equipment for layer-by-layer printing. The diameter of the extruder head is 40 mm, and the extrusion pressure of the extruder head is 2 MPa. When printing a single-layer mortar base layer 1, the extruder head moves back and forth in the X-axis direction, advances line by line with a path width of 35 mm in the Y-axis direction, and remains unchanged in the Z-axis direction. A zigzag moving path is used for single-layer filling. After the single-layer printing is completed, an interface treatment agent is sprayed on the surface of the single-layer mortar base layer 1. The interface treatment agent includes 70 wt% styrene acrylic emulsion (solid content of 40%), 12 wt% nano-silica (particle size of 30 nm), 2 wt% nano-cellulose, 5 wt% acetyl tributyl citrate plasticizer, 8 wt% microsilica powder, 2 wt% BYK-306 silicone leveling agent and 1 wt% silane coupling agent KH550. The spraying amount of the interface treatment agent is 20 g / m 2After spraying, it was left to stand for 3 minutes to form a flexible interface layer 2 on the surface of the mortar matrix layer 1; then, the extruder head was vertically lifted 20 mm along the Z axis direction, and in the XY plane, the extruder head was moved to the extrusion starting point of the mortar matrix layer 1 that had just been printed. Based on this, the position of half the path width was alternately offset in the positive or negative direction of the Y axis as the extrusion starting point of the new layer, so that a continuous concave-convex mosaic structure was formed between the two adjacent mortar matrix layers 1. This process was repeated layer by layer until the printing was completed, and a composite layered structure (such as Figure 1 and Figure 16 shown);

[0165] (8) The composite layered structure is subjected to a first curing in an air atmosphere, wherein the curing temperature of the first curing is 40° C., the relative humidity is 90%, the curing time is 30 h, and the curing pressure is 0.1 MPa. Subsequently, the temperature, humidity, and pressure of the curing environment are adjusted, and the composite layered structure is subjected to a second curing in a nitrogen atmosphere, wherein the curing temperature of the second curing is 60° C., the relative humidity is 70%, the curing time is 30 h, and the curing pressure is 0.3 MPa. After gradient curing and curing, the lightweight building material containing the mixed fiber is obtained.

[0166] Figure 1 This is a schematic diagram of the cross-sectional structure of the lightweight building material mixed with mixed fibers prepared in this embodiment. Figure 16 This is a physical picture of the printed composite layered structure prepared in this embodiment. It can be seen from the figure that the lightweight building material mixed with mixed fibers prepared in this embodiment of the present invention is composed of a multi-layer structure, including a mortar base layer 1 and a flexible interface layer 2 stacked in sequence, and a continuous concave-convex mosaic structure is formed between the interfaces of adjacent mortar base layers 1.

[0167] Figure 2 、 Figure 3 、 Figure 4 and Figure 5 The scanning electron microscope images of the polyvinyl alcohol fiber used in this embodiment, the silane-modified polyvinyl alcohol fiber prepared in this embodiment, the coated polyvinyl alcohol fiber and the modified polyvinyl alcohol fiber are shown in FIG. Figure 2 It can be seen that the surface of polyvinyl alcohol fiber is smooth and flat, and the hydroxyl groups are evenly distributed, but the reaction activity is low, and it is difficult to form an effective bond with the cement matrix. Figure 3 It can be seen that nanoscale protrusions (siloxane network) appear on the surface of silane-modified polyvinyl alcohol fibers, providing sufficient anchoring points for subsequent polydopamine coating. Figure 4 It can be seen that a continuous polydopamine biomimetic adhesion layer is formed on the surface of the coated polyvinyl alcohol fiber, which is beneficial to the penetration of the chitosan-gelatin composite gel. Figure 5 It can be seen that the surface of the modified polyvinyl alcohol fiber presents a "groove-protrusion" hierarchical structure, and the thickness of the chitosan-gelatin composite layer reaches 1.2 μm.

[0168] Figure 6 and Figure 7 The surface AFM images of the silane-modified polyvinyl alcohol fiber and the modified polyvinyl alcohol fiber prepared in this embodiment are shown in FIG. Figure 6 It can be seen that nano-scale protrusions appear on the surface of the silane-modified polyvinyl alcohol fiber, and the surface roughness is slightly improved. Figure 7 It can be seen that the surface of the modified polyvinyl alcohol fiber presents a "groove-protrusion" hierarchical structure, and the surface roughness is significantly improved.

[0169] Figure 8 This is the infrared spectrum of the coated polyvinyl alcohol fiber prepared in this example. It can be seen from the figure that 3421cm -1 The stretching vibration absorption peak corresponding to the phenolic hydroxyl group of polyvinyl alcohol fiber and polydopamine is 2920 cm -1 and 2851cm -1 The corresponding stretching vibration absorption peak of -CH2 in the 3-aminopropyltriethoxysilane molecular chain is 1637 cm -1 The C=O stretching vibration absorption peak in the quinone structure of polydopamine is 1507 cm -1 The corresponding absorption peak of NH bending vibration in polydopamine is 1301 cm -1 The CN stretching vibration absorption peak corresponding to the aromatic amine in polydopamine is 1184 cm -1 The CO stretching vibration absorption peak corresponding to the phenolic hydroxyl group of polydopamine is 1117 cm -1 The stretching vibration absorption peak of Si-O-Si in the siloxane network is 905 cm -1 The corresponding stretching vibration absorption peak of Si-OC formed by the bonding of polyvinyl alcohol fiber and silane indicates that the surface of polyvinyl alcohol fiber is successfully loaded with 3-aminopropyltriethoxysilane and coated with a polydopamine layer.

[0170] Figure 9 The infrared spectra of gelatin, chitosan and the modified polyvinyl alcohol fiber prepared in this example are shown in Figure 2. In the infrared spectrum curve of gelatin, 1621 cm -1 、1519cm -1 and 1444cm -1 They correspond to the amide I group (characteristic stretching absorption peak of C=O), amide II group (characteristic absorption peak of CH and NH), and amide III group (characteristic absorption peak of NH) of gelatin. In the infrared spectrum curve of chitosan, 1577cm -1 The bending vibration absorption peak corresponding to NH is 1403 cm -1 The corresponding CH bending vibration absorption peak is at 3245cm-1 The stretching vibration absorption peak corresponding to OH is 1541 cm -1 The bending vibration absorption peak corresponding to NH is 1411 cm -1 The CH bending vibration absorption peak corresponding to the methylene group is 1081 cm -1 The stretching vibration absorption peak of COC corresponding to the ether bond is shown above, which indicates that the chitosan-gelatin composite layer has been successfully coated on the surface of the polyvinyl alcohol fiber.

[0171] Figure 10 and Figure 11 The scanning electron microscope images of the basalt fiber and the modified basalt fiber after oxalic acid modification in this embodiment are shown in FIG. Figure 10 It can be seen that after being treated with oxalic acid solution, the surface of the basalt fiber is etched to form a small amount of groove structure, exposing the silicon-oxygen network active sites. Figure 11 It can be seen that the groove structure on the surface of the modified basalt fiber obtained after the combined modification treatment of oxalic acid solution and ammonium fluoride solution is deepened and increased in number, and 50~200nm fluorosilicate protrusions are generated on the surface of the modified basalt fiber.

[0172] Example 2

[0173] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing, the method comprising:

[0174] (1) 3-Aminopropyltriethoxysilane, anhydrous ethanol and deionized water were mixed uniformly in a volume ratio of 1:30:6 to obtain a silane coupling agent solution, and an acetic acid solution was added dropwise to the silane coupling agent solution to adjust its pH value to 5; polyvinyl alcohol fiber with a length of 8 mm was immersed in the silane coupling agent solution at 50°C for 4 h. After the immersion, the fiber was taken out, washed and dried to obtain silane-modified polyvinyl alcohol fiber;

[0175] (2) Dopamine hydrochloride was added to a Tris-HCl buffer solution with a pH value of 9 to obtain a dopamine solution, wherein the concentration of dopamine hydrochloride in the dopamine solution was 3 mg / mL. Silane-modified polyvinyl alcohol fibers were immersed in the dopamine solution at room temperature and in the dark for 12 h. The fibers were then taken out, washed, and dried to obtain coated polyvinyl alcohol fibers.

[0176] (3) Chitosan was dissolved in 0.55 mol / L acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution was 3 wt %. Gelatin was added to deionized water and heated to 65°C to dissolve the gelatin to obtain a gelatin solution, wherein the mass fraction of gelatin in the gelatin solution was 2 wt %. 0.1 mol / L hydrochloric acid solution was added dropwise to the gelatin solution to adjust its pH value to 5. The chitosan solution and the gelatin solution were mixed uniformly in a volume ratio of 5:1 to obtain a precursor solution, and a genipin crosslinker was added to the precursor solution in an amount of 0.07 wt % of the mass of the precursor solution. The mixture was mixed and stirred to obtain a composite colloidal solution.

[0177] (4) The composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber using a high-voltage electrostatic spraying process. The conical nozzle and the substrate platform were connected to the positive and negative electrodes of a high-voltage power supply with a voltage of 20 kV, respectively. The composite colloidal solution was fed into the conical nozzle at a liquid supply rate of 2 mL / min by a peristaltic pump. The inner diameter of the conical nozzle was 0.6 mm. The coated polyvinyl alcohol fiber was placed on a rotating substrate platform. The substrate platform drove the coated polyvinyl alcohol fiber to rotate at a linear speed of 0.2 m / s and heated it to 55 °C. During the rotation of the coated polyvinyl alcohol fiber, a composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber through a conical nozzle for a total of 8 minutes. The sprayed fiber was placed in a closed box at a temperature of 50°C and a humidity of 75%. A 0.6wt% glutaraldehyde solution was placed in the closed box for in-situ crosslinking for 2 hours. The fiber was then removed and immersed in a 1.2wt% glycine solution for 25 minutes. After being removed, washed, and vacuum-dried at 65°C for 10 hours to obtain a modified polyvinyl alcohol fiber.

[0178] (5) Soak basalt fibers with a length of 12 mm in an 8 wt% oxalic acid solution at 50 °C for 20 min. After soaking, take out the fibers and rinse them repeatedly with deionized water until they are neutral. Then, soak the basalt fibers in a 2 wt% ammonium fluoride solution for 10 min. After soaking, take out the fibers and rinse them repeatedly with deionized water until they are neutral. After drying, the modified basalt fibers are obtained.

[0179] (6) Adding modified polyvinyl alcohol fiber and modified basalt fiber to the base mortar and mixing them evenly to obtain a composite mortar; wherein the base mortar includes 55 parts of silicate cement, 50 parts of quartz sand, 25 parts of fly ash, 8 parts of metakaolin, 0.8 parts of water reducer and 40 parts of water; the mass fraction of the modified polyvinyl alcohol fiber in the composite mortar is 2wt%, and the mass fraction of the modified basalt fiber is 1wt%;

[0180] (7) The composite mortar is injected into the 3D printing equipment for layer-by-layer printing. The diameter of the extruder head is 50 mm, and the extrusion pressure of the extruder head is 3 MPa. When printing a single-layer mortar base layer 1, the extruder head moves back and forth in the X-axis direction, advances line by line with a path width of 45 mm in the Y-axis direction, and remains unchanged in the Z-axis direction. A zigzag moving path is used for single-layer filling. After the single-layer printing is completed, an interface treatment agent is sprayed on the surface of the single-layer mortar base layer 1. The interface treatment agent includes 72 wt% styrene acrylic emulsion (solid content of 50%), 11 wt% nano-silica (particle size of 30 nm), 2 wt% nano-cellulose, 5 wt% acetyl tributyl citrate plasticizer, 7 wt% microsilica powder, 2 wt% BYK-306 silicone leveling agent and 1 wt% silane coupling agent KH550. The spraying amount of the interface treatment agent is 30 g / m 2 After spraying, it was left to stand for 2 minutes to form a flexible interface layer 2 on the surface of the mortar matrix layer 1; then, the extruder head was vertically lifted 30 mm along the Z axis direction, and in the XY plane, the extruder head was moved to the extrusion starting point of the mortar matrix layer 1 that had just been printed. Based on this, the position of half the path width was alternately offset in the positive or negative direction of the Y axis as the extrusion starting point of the new layer, so that a continuous concave-convex mosaic structure was formed between the two adjacent mortar matrix layers 1. This process was repeated layer by layer until the printing was completed, and a composite layered structure (such as Figure 1 and Figure 16 shown);

[0181] (8) The composite layered structure is subjected to a first curing in an air atmosphere, wherein the curing temperature of the first curing is 45° C., the relative humidity is 95%, the curing time is 24 h, and the curing pressure is 0.1 MPa. Subsequently, the temperature, humidity, and pressure of the curing environment are adjusted, and the composite layered structure is subjected to a second curing in a nitrogen atmosphere, wherein the curing temperature of the second curing is 65° C., the relative humidity is 65%, the curing time is 36 h, and the curing pressure is 0.25 MPa. After gradient curing and curing, the lightweight building material containing the mixed fiber is obtained.

[0182] Example 3

[0183] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing, the method comprising:

[0184] (1) 3-Aminopropyltriethoxysilane, anhydrous ethanol and deionized water were mixed uniformly in a volume ratio of 1:27.5:5.5 to obtain a silane coupling agent solution, and an acetic acid solution was added dropwise to the silane coupling agent solution to adjust its pH value to 4.5; polyvinyl alcohol fiber with a length of 7 mm was immersed in the silane coupling agent solution at 45°C for 4.5 hours. After the immersion, the fiber was taken out, washed and dried to obtain silane-modified polyvinyl alcohol fiber;

[0185] (2) adding dopamine hydrochloride to a Tris-HCl buffer solution having a pH value of 8.5 to obtain a dopamine solution, wherein the concentration of dopamine hydrochloride in the dopamine solution is 2.5 mg / mL, and immersing the silane-modified polyvinyl alcohol fiber in the dopamine solution at room temperature and in the dark for 18 h. The fiber is then taken out, washed, and dried to obtain a coated polyvinyl alcohol fiber;

[0186] (3) Chitosan was dissolved in 0.5 mol / L acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution was 2.5 wt %. Gelatin was added to deionized water and heated to 60°C to dissolve the gelatin to obtain a gelatin solution, wherein the mass fraction of gelatin in the gelatin solution was 1.9 wt %. 0.1 mol / L hydrochloric acid solution was added dropwise to the gelatin solution to adjust its pH value to 4.5. The chitosan solution and the gelatin solution were mixed uniformly in a volume ratio of 4.5:1 to obtain a precursor solution, and a genipin crosslinker was added to the precursor solution in an amount of 0.06 wt % of the mass of the precursor solution. The mixture was mixed and stirred to obtain a composite colloidal solution.

[0187] (4) The composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber using a high-voltage electrostatic spraying process. The conical nozzle and the substrate platform were connected to the positive and negative electrodes of a high-voltage power supply with a voltage of 17 kV, respectively. The composite colloidal solution was fed into the conical nozzle at a liquid supply rate of 1.5 mL / min through a peristaltic pump. The inner diameter of the conical nozzle was 0.7 mm. The coated polyvinyl alcohol fiber was placed on a rotating substrate platform. The substrate platform drove the coated polyvinyl alcohol fiber to rotate at a linear speed of 0.3 m / s and heated it to 52 °C. During the rotation of the coated polyvinyl alcohol fiber, a composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber through a conical nozzle for a total of 7 minutes. The sprayed fiber was placed in a closed box at a temperature of 47°C and a humidity of 70%. A 0.5wt% glutaraldehyde solution was placed in the closed box for in-situ crosslinking for 2.5 hours. The fiber was then removed and immersed in a 1.0wt% glycine solution for 30 minutes. After being removed, washed, and vacuum dried at 60°C for 12 hours to obtain a modified polyvinyl alcohol fiber.

[0188] (5) Basalt fibers with a length of 10 mm were immersed in a 6.5 wt% oxalic acid solution at 45 °C for 25 min. After the immersion, the fibers were taken out and repeatedly rinsed with deionized water until neutral. Subsequently, the basalt fibers were immersed in a 1.5 wt% ammonium fluoride solution for 12 min. After the immersion, the fibers were taken out and repeatedly rinsed with deionized water until neutral. After drying, the modified basalt fibers were obtained.

[0189] (6) Adding modified polyvinyl alcohol fiber and modified basalt fiber to the base mortar and mixing them evenly to obtain a composite mortar; wherein the base mortar includes 50 parts of Portland cement, 45 parts of quartz sand, 20 parts of fly ash, 6.5 parts of metakaolin, 0.55 parts of water reducer and 37.5 parts of water; the mass fraction of the modified polyvinyl alcohol fiber in the composite mortar is 1.7wt%, and the mass fraction of the modified basalt fiber is 0.9wt%;

[0190] (7) The composite mortar is injected into the 3D printing equipment for layer-by-layer printing. The diameter of the extruder head is 45 mm, and the extrusion pressure of the extruder head is 2.5 MPa. When printing a single-layer mortar base layer 1, the extruder head moves back and forth in the X-axis direction, advances line by line with a path width of 40 mm in the Y-axis direction, and remains unchanged in the Z-axis direction. A zigzag moving path is used for single-layer filling. After the single-layer printing is completed, an interface treatment agent is sprayed on the surface of the single-layer mortar base layer 1. The interface treatment agent includes 73 wt% styrene acrylic emulsion (solid content of 45%), 11 wt% nano-silica (particle size of 30 nm), 1.5 wt% nano-cellulose, 4.5 wt% acetyl tributyl citrate plasticizer, 6.5 wt% microsilica powder, 2.5 wt% BYK-306 silicone leveling agent and 1 wt% silane coupling agent KH550. The spraying amount of the interface treatment agent is 25 g / m 2 After spraying, it was left to stand for 2.5 minutes to form a flexible interface layer 2 on the surface of the mortar matrix layer 1; then, the extruder head was vertically lifted 25 mm along the Z axis direction, and in the XY plane, the extruder head was moved to the extrusion starting point of the mortar matrix layer 1 that had just been printed. Based on this, the position of half the path width was alternately offset in the positive or negative direction of the Y axis as the extrusion starting point of the new layer, so that a continuous concave-convex mosaic structure was formed between the two adjacent mortar matrix layers 1. This process was repeated layer by layer until the printing was completed, and a composite layered structure (such as Figure 1 and Figure 16 shown);

[0191] (8) The composite layered structure is subjected to a first curing in an air atmosphere, wherein the curing temperature of the first curing is 35° C., the relative humidity is 92%, the curing time is 28 h, and the curing pressure is 0.1 MPa. Subsequently, the temperature, humidity, and pressure of the curing environment are adjusted, and the composite layered structure is subjected to a second curing in a nitrogen atmosphere, wherein the curing temperature of the second curing is 55° C., the relative humidity is 68%, the curing time is 24 h, and the curing pressure is 0.2 MPa. After gradient curing and curing, the lightweight building material containing the mixed fiber is obtained.

[0192] Example 4

[0193] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing, the method comprising:

[0194] (1) 3-Aminopropyltriethoxysilane, anhydrous ethanol and deionized water were mixed uniformly in a volume ratio of 1:26:5.2 to obtain a silane coupling agent solution, and acetic acid solution was added dropwise to the silane coupling agent solution to adjust its pH value to 4.3; polyvinyl alcohol fiber with a length of 6.5 mm was immersed in the silane coupling agent solution at 42°C for 4.8 h. After the soaking, the fiber was taken out, washed and dried to obtain silane-modified polyvinyl alcohol fiber;

[0195] (2) Dopamine hydrochloride was added to a Tris-HCl buffer solution with a pH value of 8.2 to obtain a dopamine solution, wherein the concentration of dopamine hydrochloride in the dopamine solution was 2.2 mg / mL. Silane-modified polyvinyl alcohol fibers were immersed in the dopamine solution at room temperature and in the dark for 20 h. The fibers were then taken out, washed, and dried to obtain coated polyvinyl alcohol fibers.

[0196] (3) Chitosan was dissolved in 0.48 mol / L acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution was 2.2 wt %. Gelatin was added to deionized water and heated to 58°C to dissolve the gelatin to obtain a gelatin solution, wherein the mass fraction of gelatin in the gelatin solution was 1.85 wt %. 0.1 mol / L hydrochloric acid solution was added dropwise to the gelatin solution to adjust its pH value to 4.3. The chitosan solution and the gelatin solution were mixed uniformly in a volume ratio of 4.2:1 to obtain a precursor solution, and a genipin crosslinker was added to the precursor solution in an amount of 0.055 wt % of the mass of the precursor solution. The mixture was mixed and stirred to obtain a composite colloidal solution.

[0197] (4) The composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber using a high-voltage electrostatic spraying process. The conical nozzle and the substrate platform were connected to the positive and negative electrodes of a high-voltage power supply with a voltage of 16 kV, respectively. The composite colloidal solution was fed into the conical nozzle at a liquid supply rate of 1.2 mL / min by a peristaltic pump. The inner diameter of the conical nozzle was 0.75 mm. The coated polyvinyl alcohol fiber was placed on a rotating substrate platform. The substrate platform drove the coated polyvinyl alcohol fiber to rotate at a linear speed of 0.35 m / s and heated it to 51 °C. During the rotation of the coated polyvinyl alcohol fiber, a composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber through a conical nozzle for a total of 6 minutes. The sprayed fiber was placed in a closed box at a temperature of 48°C and a humidity of 68%. A 0.45wt% glutaraldehyde solution was placed in the closed box for in-situ crosslinking for 2.8 hours. The fiber was then removed and immersed in a 0.9wt% glycine solution for 33 minutes. After being removed, washed, and vacuum dried at 58°C for 14 hours to obtain a modified polyvinyl alcohol fiber.

[0198] (5) A 9 mm long basalt fiber was soaked in a 7 wt% oxalic acid solution at 48 °C for 22 min. After soaking, the fiber was taken out and repeatedly rinsed with deionized water until it was neutral. The basalt fiber was then soaked in a 1.8 wt% ammonium fluoride solution for 11 min. After soaking, the fiber was taken out and repeatedly rinsed with deionized water until it was neutral. After drying, the modified basalt fiber was obtained.

[0199] (6) Adding modified polyvinyl alcohol fiber and modified basalt fiber to the base mortar and mixing them evenly to obtain a composite mortar; wherein the base mortar includes 48 parts of Portland cement, 43 parts of quartz sand, 18 parts of fly ash, 7 parts of metakaolin, 0.6 parts of water reducer and 36 parts of water; the mass fraction of the modified polyvinyl alcohol fiber in the composite mortar is 1.6wt%, and the mass fraction of the modified basalt fiber is 0.85wt%;

[0200] (7) The composite mortar is injected into the 3D printing equipment for layer-by-layer printing. The diameter of the extruder head is 42 mm, and the extrusion pressure of the extruder head is 2.2 MPa. When printing a single-layer mortar base layer 1, the extruder head moves back and forth in the X-axis direction, advances line by line with a path width of 38 mm in the Y-axis direction, and remains unchanged in the Z-axis direction. A zigzag moving path is used for single-layer filling. After the single-layer printing is completed, an interface treatment agent is sprayed on the surface of the single-layer mortar base layer 1. The interface treatment agent includes 74 wt% styrene acrylic emulsion (solid content of 42%), 11 wt% nano-silica (particle size of 30 nm), 2 wt% nano-cellulose, 4 wt% acetyl tributyl citrate plasticizer, 6 wt% microsilica powder, 2.5 wt% BYK-306 silicone leveling agent and 0.5 wt% silane coupling agent KH550. The spraying amount of the interface treatment agent is 22 g / m 2 After spraying, it was left to stand for 2.8 minutes to form a flexible interface layer 2 on the surface of the mortar matrix layer 1; then, the extruder head was vertically lifted 22 mm along the Z axis direction, and in the XY plane, the extruder head moved to the extrusion starting point of the mortar matrix layer 1 that had just been printed, and based on this, the position of half the path width was alternately offset in the positive or negative direction of the Y axis as the extrusion starting point of the new layer, so that a continuous concave-convex mosaic structure was formed between the two adjacent mortar matrix layers 1, and so on. Printing layer by layer until printing is completed, and a composite layered structure (such as Figure 1 and Figure 16 shown);

[0201] (8) The composite layered structure is subjected to a first curing in an air atmosphere, wherein the curing temperature of the first curing is 38° C., the relative humidity is 93%, the curing time is 32 h, and the curing pressure is 0.1 MPa. Subsequently, the temperature, humidity, and pressure of the curing environment are adjusted, and the composite layered structure is subjected to a second curing in a nitrogen atmosphere, wherein the curing temperature of the second curing is 62° C., the relative humidity is 70%, the curing time is 30 h, and the curing pressure is 0.28 MPa. After gradient curing and curing, the lightweight building material containing the mixed fiber is obtained.

[0202] Example 5

[0203] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing, the method comprising:

[0204] (1) 3-Aminopropyltriethoxysilane, anhydrous ethanol and deionized water were mixed uniformly in a volume ratio of 1:28:5.8 to obtain a silane coupling agent solution, and acetic acid solution was added dropwise to the silane coupling agent solution to adjust its pH value to 4.8; polyvinyl alcohol fiber with a length of 7.5 mm was immersed in the silane coupling agent solution at 47°C for 4.2 h. After the soaking, the fiber was taken out, washed and dried to obtain silane-modified polyvinyl alcohol fiber;

[0205] (2) Dopamine hydrochloride was added to a Tris-HCl buffer solution with a pH value of 8.8 to obtain a dopamine solution, wherein the concentration of dopamine hydrochloride in the dopamine solution was 2.8 mg / mL. Silane-modified polyvinyl alcohol fibers were immersed in the dopamine solution at room temperature and in the dark for 15 h. The fibers were then taken out, washed, and dried to obtain coated polyvinyl alcohol fibers.

[0206] (3) Chitosan was dissolved in 0.52 mol / L acetic acid solution to obtain a chitosan solution, wherein the mass fraction of chitosan in the chitosan solution was 2.8 wt %. Gelatin was added to deionized water and heated to 62°C to dissolve the gelatin to obtain a gelatin solution, wherein the mass fraction of gelatin in the gelatin solution was 1.95 wt %. 0.1 mol / L hydrochloric acid solution was added dropwise to the gelatin solution to adjust its pH value to 4.8. The chitosan solution and the gelatin solution were mixed uniformly in a volume ratio of 4.8:1 to obtain a precursor solution, and a genipin crosslinker was added to the precursor solution in an amount of 0.065 wt % of the mass of the precursor solution. The mixture was mixed and stirred to obtain a composite colloidal solution.

[0207] (4) The composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber using a high-voltage electrostatic spraying process. The conical nozzle and the substrate platform were connected to the positive and negative electrodes of a high-voltage power supply with a voltage of 19 kV, respectively. The composite colloidal solution was fed into the conical nozzle at a liquid supply rate of 1.8 mL / min through a peristaltic pump. The inner diameter of the conical nozzle was 0.65 mm. The coated polyvinyl alcohol fiber was placed on a rotating substrate platform. The substrate platform drove the coated polyvinyl alcohol fiber to rotate at a linear speed of 0.25 m / s and heated it to 54 °C. During the rotation of the polyvinyl alcohol-coated fiber, a composite colloidal solution was sprayed onto the surface of the coated polyvinyl alcohol fiber through a conical nozzle for a total of 7.5 minutes. The sprayed fiber was placed in a closed box at a temperature of 49°C and a humidity of 73%. A 0.55wt% glutaraldehyde solution was placed in the closed box for in-situ crosslinking for 2.2 hours. The fiber was then removed and immersed in a 1.1wt% glycine solution for 28 minutes. After soaking, it was removed, washed, and vacuum-dried at 62°C for 13 hours to obtain a modified polyvinyl alcohol fiber.

[0208] (5) Basalt fibers with a length of 11 mm were immersed in a 7.5 wt% oxalic acid solution at 47 °C for 27 min. After the immersion, the fibers were taken out and repeatedly rinsed with deionized water until neutral. Subsequently, the basalt fibers were immersed in a 1.2 wt% ammonium fluoride solution for 13 min. After the immersion, the fibers were taken out and repeatedly rinsed with deionized water until neutral. After drying, the modified basalt fibers were obtained.

[0209] (6) Adding modified polyvinyl alcohol fiber and modified basalt fiber to the base mortar and mixing them evenly to obtain a composite mortar; wherein the base mortar includes 53 parts of Portland cement, 47 parts of quartz sand, 22 parts of fly ash, 7.5 parts of metakaolin, 0.7 parts of water reducer and 38 parts of water; the mass fraction of the modified polyvinyl alcohol fiber in the composite mortar is 1.9wt%, and the mass fraction of the modified basalt fiber is 0.95wt%;

[0210] (7) The composite mortar is injected into the 3D printing equipment for layer-by-layer printing. The diameter of the extruder head is 48 mm, and the extrusion pressure of the extruder head is 2.8 MPa. When printing a single-layer mortar base layer 1, the extruder head moves back and forth in the X-axis direction, advances line by line with a path width of 42 mm in the Y-axis direction, and remains unchanged in the Z-axis direction. A zigzag moving path is used for single-layer filling. After the single-layer printing is completed, an interface treatment agent is sprayed on the surface of the single-layer mortar base layer 1. The interface treatment agent includes 75 wt% styrene acrylic emulsion (solid content of 48%), 10 wt% nano-silica (particle size of 30 nm), 1 wt% nano-cellulose, 5 wt% acetyl tributyl citrate plasticizer, 5 wt% microsilica powder, 2.5 wt% BYK-306 silicone leveling agent and 1.5 wt% silane coupling agent KH550. The spraying amount of the interface treatment agent is 28 g / m2 After spraying, it was left to stand for 2.2 minutes to form a flexible interface layer 2 on the surface of the mortar matrix layer 1; then, the extruder head was vertically lifted 28 mm along the Z axis direction, and in the XY plane, the extruder head moved to the extrusion starting point of the mortar matrix layer 1 that had just been printed, and based on this, the position of half the path width was alternately offset in the positive or negative direction of the Y axis as the extrusion starting point of the new layer, so that a continuous concave-convex mosaic structure was formed between the two adjacent mortar matrix layers 1, and so on. Printing layer by layer until the printing is completed, and a composite layered structure (such as Figure 1 and Figure 16 shown);

[0211] (8) The composite layered structure is subjected to a first curing in an air atmosphere, wherein the curing temperature of the first curing is 42° C., the relative humidity is 90%, the curing time is 36 h, and the curing pressure is 0.1 MPa. Subsequently, the temperature, humidity, and pressure of the curing environment are adjusted, and the composite layered structure is subjected to a second curing in a nitrogen atmosphere, wherein the curing temperature of the second curing is 58° C., the relative humidity is 60%, the curing time is 28 h, and the curing pressure is 0.3 MPa. After gradient curing and curing, the lightweight building material containing the mixed fiber is obtained.

[0212] Example 6

[0213] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (2), the concentration of dopamine hydrochloride in the dopamine solution is adjusted to 1.5 mg / mL, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0214] Example 7

[0215] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (2), the concentration of dopamine hydrochloride in the dopamine solution is adjusted to 3.5 mg / mL, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0216] Example 8

[0217] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (3), the volume ratio of the chitosan solution to the gelatin solution is adjusted to 3:1, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0218] Example 9

[0219] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (3), the volume ratio of the chitosan solution to the gelatin solution is adjusted to 6:1, and the other process parameters and operation steps are exactly the same as those in Example 1.

[0220] Example 10

[0221] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (5), the mass fraction of the oxalic acid solution is adjusted to 3 wt %, and the other process parameters and operation steps are exactly the same as those in Example 1.

[0222] Example 11

[0223] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (5), the mass fraction of the oxalic acid solution is adjusted to 10 wt %, and the other process parameters and operation steps are exactly the same as those in Example 1.

[0224] Example 12

[0225] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (5), the mass fraction of the ammonium fluoride solution is adjusted to 0.5 wt %. The other process parameters and operation steps are exactly the same as those in Example 1.

[0226] Example 13

[0227] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (5), the mass fraction of the ammonium fluoride solution is adjusted to 3 wt %. The other process parameters and operation steps are exactly the same as those in Example 1.

[0228] Example 14

[0229] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (7), the spraying amount of the interface treatment agent is adjusted to 15 g / m 2 , other process parameters and operating steps are exactly the same as those in Example 1.

[0230] Example 15

[0231] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (7), the spraying amount of the interface treatment agent is adjusted to 35 g / m 2, other process parameters and operating steps are exactly the same as those in Example 1.

[0232] Example 16

[0233] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (8), the curing pressure of the second curing stage is adjusted to 0.15 MPa, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0234] Example 17

[0235] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (8), the curing pressure of the second curing stage is adjusted to 0.35 MPa, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0236] Comparative Example 1

[0237] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that steps (1) to (5) are omitted, the polyvinyl alcohol fiber and the basalt fiber are not modified, and the unmodified polyvinyl alcohol fiber and the basalt fiber are added to the base mortar and mixed evenly to obtain a composite mortar. The other process parameters and operating steps are exactly the same as those in Example 1.

[0238] Figure 12 and Figure 13 The cross-sectional structure of the lightweight building material prepared in Comparative Example 1 and the scanning electron microscope images of the fiber pull-out are shown. Figure 12 ) It can be seen that there are obvious pores and voids at the interface between the fiber and the cement matrix, which indicates that the interface compatibility between the fiber and the matrix is ​​poor and the load stress cannot be smoothly transferred to the fiber through the cement matrix. Figure 13 ) It can be seen that the surface of the pulled-out fiber is smooth and free of attachments, which indicates that the fiber does not play an effective mechanical reinforcement role and the load stress is not effectively transmitted.

[0239] Figure 14 and Figure 15 The cross-sectional structure of the lightweight building material prepared in Example 1 and the scanning electron microscope images of the fiber extraction are shown in FIG. Figure 14 ) It can be seen that the fiber and the cement matrix are closely fitted, and the interface is dense and defect-free, which indicates that the interface compatibility between the fiber and the matrix is ​​good, and the load stress can be smoothly transferred to the fiber through the cement matrix. Figure 15) It can be seen that a 2~3 μm thick hydration product layer is attached to the surface of the pulled out fiber, which indicates that the fiber effectively plays a mechanical reinforcement role and the load stress is effectively transferred.

[0240] Comparative Example 2

[0241] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that steps (1) to (4) are omitted, and in step (6), modified polyvinyl alcohol fiber is not added to the base mortar. The other process parameters and operating steps are exactly the same as those in Example 1.

[0242] Comparative Example 3

[0243] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that step (5) is omitted, and in step (6), modified basalt fiber is not added to the base mortar. The other process parameters and operating steps are exactly the same as those in Example 1.

[0244] Comparative Example 4

[0245] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that steps (1) to (5) are omitted, modified polyvinyl alcohol fiber and modified basalt fiber are not added to the base mortar, and the base mortar is directly printed layer by layer. The other process parameters and operating steps are exactly the same as those in Example 1.

[0246] Comparative Example 5

[0247] This embodiment provides a method for preparing a lightweight building material containing mixed fibers based on 3D printing. The difference from Example 1 is that in step (7), after each mortar base layer 1 is printed, an interface treatment agent is not sprayed on its surface. The obtained lightweight building material only includes multiple layers of stacked mortar base layers 1. The other process parameters and operation steps are exactly the same as those in Example 1.

[0248] The compressive strength, flexural strength, splitting tensile strength and static compressive elastic modulus of the lightweight building materials containing mixed fibers prepared in Examples 1-17 and Comparative Examples 1-5 were tested. The specific testing steps are as follows:

[0249] (1) Compressive strength

[0250] The compressive strength of lightweight building materials was tested using GB / T 50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete". The specimen size was a cube with a side length of 150 mm, and the load loading speed was 1 MPa / s.

[0251] (2) Flexural strength

[0252] The flexural strength of lightweight building materials was tested using GB / T 50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete". The specimen size was 150mm×150mm×600mm, and the loading speed was 0.1MPa / s.

[0253] (3) Splitting tensile strength

[0254] The splitting tensile strength of lightweight building materials was tested using GB / T 50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete". The specimen size was a cube with a side length of 150 mm, and the load loading speed was 0.1 MPa / s.

[0255] (4) Static compressive elastic modulus

[0256] The static compressive elastic modulus of lightweight building materials was tested using GB / T 50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete". The specimen size was 150mm×150mm×300mm.

[0257] The test results are shown in Table 1.

[0258] Table 1

[0259]

[0260] The test data provided in Table 1 demonstrates that the lightweight building materials prepared in Examples 1-5 of the present invention achieve compressive strength (148-152 MPa), flexural strength (25.3-26.5 MPa), and static compressive elastic modulus (43.7-44.8 GPa), all reaching top-tier levels for ultra-high-performance concrete (UHPC). Modified polyvinyl alcohol (PVA) fibers and modified basalt fibers synergistically enhance the strength and toughness of the lightweight building materials. The modified PVA fibers dissipate energy through the dynamic slip interface of the polydopamine / chitosan-gelatin composite coating, while the modified basalt fibers, with enhanced surface roughness, absorb the principal stress through mechanical interlocking and chemical bonding. Subsequently, interlayer interlocking is achieved through 3D printing, with adjacent layers offset by half the path width to form a concave-convex interlocking structure. During the gradient curing stage, the first stage of atmospheric pressure air curing (35-45°C / 90-95% RH) promotes the directional growth of CSH gel on the fiber surface; the second stage of nitrogen high-pressure curing (0.2-0.3 MPa) inhibits the carbonization of Ca(OH)2, and the porosity of the mortar matrix layer 1 is reduced to 2.3%. The preparation method of the lightweight building material provided by the present invention achieves a synergistic improvement in the strength and toughness of the material.

[0261] It can be seen from the test data of Example 1, Example 6 and Example 7 that the concentration of dopamine hydrochloride in the dopamine solution in Example 6 is too low, resulting in the compressive strength of the resulting lightweight building material being reduced to 138 MPa and the flexural strength being reduced to 21.4 MPa. This is because the low dosage of dopamine hydrochloride causes the polydopamine coating to be discontinuous, resulting in a reduction in the effective fiber-matrix bonding area and a reduction in the interfacial shear strength. The concentration of dopamine hydrochloride in the dopamine solution in Example 7 is too high, resulting in the compressive strength of the resulting lightweight building material being reduced to 136 MPa and the static compressive elastic modulus being reduced to 37.2 GPa. This is because the high dosage of dopamine hydrochloride forms an excessively thick polydopamine layer, which induces internal stress microcracks, increases the brittleness index of the coating, and loses dynamic slip ability.

[0262] From the test data of Examples 1, 8, and 9, it can be seen that the proportion of chitosan solution in Example 8 is too low, resulting in the compressive strength of the resulting lightweight building material being reduced to 141 MPa. This is because the excessive amount of gelatin leads to a decrease in crosslinking density, an increase in the swelling rate of the chitosan-gelatin composite coating, and a decrease in interfacial slip resistance. In Example 9, the proportion of chitosan solution is too high, resulting in the static compressive elastic modulus of the resulting lightweight building material being reduced to 38.6 GPa. This is because the excessive amount of chitosan forms a rigid network, restricting the movement of gelatin molecular chains, and significantly reducing the elongation at break of the chitosan-gelatin composite coating.

[0263] The test data from Examples 1, 10, and 11 show that the mass fraction of the oxalic acid solution in Example 10 was too low, resulting in a reduction in the compressive strength of the resulting lightweight building material to 143 MPa. This is because the low mass fraction of the oxalic acid solution resulted in insufficient etching, resulting in a low surface roughness Ra of the basalt fiber and reduced mechanical interlocking efficiency. The high mass fraction of the oxalic acid solution in Example 11 resulted in a reduction in the flexural strength of the resulting lightweight building material to 19.6 MPa. This is because excessive etching significantly reduced the single-filament strength of the basalt fiber and increased the density of surface microcracks.

[0264] The test data from Examples 1, 12, and 13 show that the mass fraction of the ammonium fluoride solution in Example 12 was too low, resulting in a decrease in the splitting tensile strength of the resulting lightweight building material to 7.2 MPa. This is due to insufficient activation of the silanol groups and a reduced chemical bonding ratio caused by the low mass fraction of the ammonium fluoride solution. In Example 13, the mass fraction of the ammonium fluoride solution was too high, resulting in a decrease in the static compressive elastic modulus of the resulting lightweight building material to 37.0 GPa. This is due to excessive fluoride ions attacking the fiber surface, forming pits with a depth of >500 nm and a significant increase in the stress concentration factor.

[0265] The test data from Examples 1, 14, and 15 show that the spraying amount of the interface treatment agent in Example 14 was too low, resulting in the static compressive elastic modulus of the resulting lightweight building material being reduced to 41.5 GPa. This is because the low spraying amount of the interface treatment agent reduced the interlayer bonding area between the mortar base layer 1 and the flexible interface layer 2, thereby decreasing the shear strength. The excessive spraying amount of the interface treatment agent in Example 15 resulted in the compressive strength of the resulting lightweight building material being reduced to 134 MPa. This is because the excessive spraying amount of the interface treatment agent enriched the styrene-acrylic emulsion to form a weak interface layer, increasing the volume proportion of the organic phase and inducing interlayer delamination.

[0266] The test data from Examples 1, 16, and 17 show that the curing pressure in the second curing stage of Example 16 was too low, resulting in a decrease in the compressive strength of the resulting lightweight building material to 140 MPa. This is because the low curing pressure increased the porosity of the mortar matrix layer 1 and reduced the polymerization degree of the CSH gel. The curing pressure in the second curing stage of Example 17 was too high, resulting in a decrease in the flexural strength of the resulting lightweight building material to 20.5 MPa. This is because the high pressure disrupted the orientation of the three-dimensional fiber arrangement and caused the interlocking structure to become unstable.

[0267] It can be seen from the test data of Example 1 and Comparative Example 1 that the polyvinyl alcohol fiber and basalt fiber were not modified in Comparative Example 1, resulting in the compressive strength of the final lightweight building material being reduced to 98 MPa and the flexural strength being reduced to 12.3 MPa. This is because the polyvinyl alcohol fiber and basalt fiber were not modified, resulting in a purely physical bond forming at the fiber-matrix interface, which easily causes cracks to expand rapidly along the interface.

[0268] It can be seen from the test data of Example 1 and Comparative Example 2 that no modified polyvinyl alcohol fiber was added in Comparative Example 2, resulting in the splitting tensile strength of the final lightweight building material being reduced to 5.4 MPa. This is because the lack of modified polyvinyl alcohol fiber causes the crack to propagate in a straight line, significantly reduces the fracture energy, and loses the flexible energy dissipation mechanism.

[0269] It can be seen from the test data of Example 1 and Comparative Example 3 that no modified basalt fiber was added in Comparative Example 3, resulting in the static compressive elastic modulus of the final lightweight building material being reduced to 35.8 GPa. This is because the lack of modified basalt fiber resulted in the lack of a rigid reinforcement network and the failure mode was converted to brittle fracture.

[0270] It can be seen from the test data of Example 1 and Comparative Example 4 that modified polyvinyl alcohol fiber and modified basalt fiber were not added in Comparative Example 4, resulting in the compressive strength of the final lightweight building material being reduced to 85 MPa, and the flexural strength being reduced to 10.5 MPa. The various performance properties of the lightweight building material return to the level of ordinary concrete, the porosity of the mortar base layer 1 is increased, and there is no fiber bridging effect.

[0271] It can be seen from the test data of Example 1 and Comparative Example 5 that the interface treatment agent was not sprayed in Comparative Example 5, resulting in the flexural strength of the lightweight building material finally obtained being reduced to 14.8 MPa. This is because the failure to spray the interface treatment agent leads to interlayer slip interlocking failure, and the cracks extend along the straight line between the layers.

[0272] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a lightweight building material containing mixed fibers based on 3D printing, characterized in that: The preparation method comprises: (I) sequentially subjecting polyvinyl alcohol fibers to coupling agent modification, polydopamine coating, and chitosan-gelatin composite colloid coating to obtain modified polyvinyl alcohol fibers; chemically etching basalt fibers to obtain modified basalt fibers; and adding the modified polyvinyl alcohol fibers and the modified basalt fibers to a base mortar and uniformly mixing them to obtain a composite mortar; (II) injecting the composite mortar obtained in step (I) into a 3D printing device for layer-by-layer printing, spraying an interface treatment agent on the surface of the printed mortar matrix layer after each layer is printed to form a flexible interface layer on the surface of the mortar matrix layer, and continuing to print the next mortar matrix layer on the surface of the flexible interface layer, and so on, to obtain a composite layered structure consisting of alternating mortar matrix layers and flexible interface layers, followed by gradient curing and solidification to obtain the lightweight building material doped with mixed fibers.

2. The method for preparing a lightweight building material containing mixed fibers based on 3D printing according to claim 1, characterized in that: In step (I), the modified polyvinyl alcohol fiber is prepared by the following method: (1) soaking the polyvinyl alcohol fiber in a silane coupling agent solution and heating it, taking out the fiber after soaking, washing and drying it to obtain a silane-modified polyvinyl alcohol fiber; soaking the silane-modified polyvinyl alcohol fiber in a dopamine solution at room temperature and in the dark, taking out the fiber after soaking, washing and drying it to obtain a coated polyvinyl alcohol fiber; (2) mixing the chitosan solution and the gelatin solution to obtain a precursor solution, adding a genipin crosslinking agent to the precursor solution, mixing and stirring to obtain a composite colloidal solution; spraying the composite colloidal solution on the surface of the coated polyvinyl alcohol fiber obtained in step (1), placing the sprayed fiber in a closed box, placing a glutaraldehyde solution in the closed box for in-situ crosslinking, then taking out the fiber and immersing it in a glycine solution, washing and drying the fiber after immersion to obtain the modified polyvinyl alcohol fiber.

3. The method for preparing a lightweight building material containing mixed fibers based on 3D printing according to claim 2, characterized in that: In step (1), the length of the polyvinyl alcohol fiber is 6 to 8 mm; The silane coupling agent solution is composed of 3-aminopropyltriethoxysilane, anhydrous ethanol and deionized water; The volume ratio of the 3-aminopropyltriethoxysilane, anhydrous ethanol and deionized water is 1:(25-30):(5-6); adding acetic acid solution dropwise to the silane coupling agent solution to adjust the pH value thereof to 4-5; The immersion temperature of the polyvinyl alcohol fiber in the silane coupling agent solution is 40-50°C; The polyvinyl alcohol fiber is immersed in the silane coupling agent solution for 4 to 5 hours; The dopamine solution consists of dopamine hydrochloride and Tris-HCl buffer; The pH value of the Tris-HCl buffer is 8 to 9; The concentration of dopamine hydrochloride in the dopamine solution is 2-3 mg / mL; The silane-modified polyvinyl alcohol fiber is immersed in the dopamine solution for 12 to 24 hours.

4. The method for preparing a lightweight building material containing mixed fibers based on 3D printing according to claim 2, characterized in that: In step (2), the chitosan solution consists of chitosan and acetic acid solution; The concentration of the acetic acid solution is 0.45 to 0.55 mol / L; The mass fraction of chitosan in the chitosan solution is 2 to 3 wt%; The gelatin solution is prepared by the following method: Adding gelatin to deionized water and heating it to 55-65° C. to dissolve the gelatin to obtain a gelatin solution, and adding 0.1 mol / L hydrochloric acid solution dropwise to the gelatin solution to adjust its pH value to 4-5; The mass fraction of gelatin in the gelatin solution is 1.8-2 wt%; The volume ratio of the chitosan solution to the gelatin solution is (4-5):1; The amount of the genipin cross-linking agent added is 0.05-0.07 wt% of the precursor solution mass; The spraying method of the composite colloidal solution is high-voltage electrostatic spraying, and the specific operation steps are as follows: The conical nozzle and substrate platform are connected to the positive and negative electrodes of a high-voltage power supply, respectively. A composite colloidal solution is fed into the conical nozzle via a peristaltic pump. The coated polyvinyl alcohol fiber is placed on a rotating substrate platform, which drives the coated polyvinyl alcohol fiber to rotate and heat it. During the rotation of the coated polyvinyl alcohol fiber, the composite colloidal solution is sprayed onto the surface of the coated polyvinyl alcohol fiber through the conical nozzle. The voltage of the high-voltage power supply is 15-20 kV; The inner diameter of the conical nozzle is 0.6 to 0.8 mm; The spraying distance between the conical nozzle and the coated polyvinyl alcohol fiber is 130 to 150 mm; The peristaltic pump delivers the composite colloid solution to the conical nozzle at a rate of 1 to 2 mL / min; The linear speed of the substrate platform during rotation is 0.2 to 0.4 m / s; The heating temperature of the substrate platform for the coated polyvinyl alcohol fiber is 50-55°C; The spraying time of the composite colloid solution is 5 to 8 minutes; The temperature in the sealed box is 45-50°C; The humidity in the sealed box is 65-75%; The mass fraction of the glutaraldehyde solution is 0.4-0.6wt%; The in situ cross-linking time is 2 to 3 hours; The mass fraction of the glycine solution is 0.8-1.2 wt %; The in-situ cross-linked fibers are immersed in the glycine solution for 25 to 35 minutes; After soaking, the fiber is taken out from the glycine solution, washed, and then vacuum-dried at 55-65° C. for 10-15 hours.

5. The method for preparing a lightweight building material containing mixed fibers based on 3D printing according to claim 1, characterized in that: In step (I), the modified basalt fiber is prepared by the following method: The basalt fiber is immersed in an oxalic acid solution, and after the immersion is completed, the fiber is taken out and repeatedly rinsed with deionized water until it is neutral; then the basalt fiber is immersed in an ammonium fluoride solution, and after the immersion is completed, the fiber is taken out and repeatedly rinsed with deionized water until it is neutral, and then dried to obtain the modified basalt fiber; The length of the basalt fiber is 8 to 12 mm; The mass fraction of the oxalic acid solution is 5 to 8 wt%; The basalt fiber is immersed in the oxalic acid solution at a temperature of 40 to 50°C; The basalt fiber is immersed in the oxalic acid solution for 20 to 30 minutes; The mass fraction of the ammonium fluoride solution is 1 to 2 wt%; The basalt fiber is immersed in the ammonium fluoride solution for 10 to 15 minutes.

6. The method for preparing a lightweight building material containing mixed fibers based on 3D printing according to claim 1, characterized in that: In step (I), the base mortar comprises Portland cement, quartz sand, fly ash, metakaolin, a water reducing agent and water; The weight parts of each component in the basic mortar are as follows: The mass fraction of the modified polyvinyl alcohol fiber in the composite mortar is 1.5 to 2 wt%; The mass fraction of the modified basalt fiber in the composite mortar is 0.8-1 wt %.

7. The method for preparing a lightweight building material containing mixed fibers based on 3D printing according to claim 1, characterized in that: In step (II), the specific operation steps of the layer-by-layer printing include: After the composite mortar is injected into the 3D printing device, cement mortar strips are extruded through an extruder. The diameter of the extruder is 40 to 50 mm, and the extrusion pressure is 2 to 3 MPa. The extruder moves back and forth along the X-axis and advances line by line along the Y-axis with a path width of 35 to 45 mm. The extruded cement mortar strips are tightly laid in a continuous S-shape to obtain the first mortar matrix layer. After the first mortar base layer is printed, an interface treatment agent is sprayed on the surface of the first mortar base layer, and the surface is left to stand for 2 to 3 minutes to form a first flexible interface layer on the surface of the first mortar base layer; Subsequently, the second mortar matrix layer is extruded. The extrusion head is vertically raised 20 to 30 mm in the Z-axis direction. In the XY plane, the extrusion head is offset by half the path width in the positive direction of the Y-axis with the starting point of the first mortar matrix layer as the reference, and serves as the extrusion starting point of the second mortar matrix layer. The extruded cement mortar strips are embedded in the gaps between adjacent cement mortar strips in the first mortar matrix layer. After the second mortar matrix layer is printed, a continuous concave-convex mosaic structure is formed between the first and second mortar matrix layers. After the second mortar base layer is printed, an interface treatment agent is sprayed on the surface of the second mortar base layer, and the surface is left to stand for 2 to 3 minutes to form a second flexible interface layer on the surface of the second mortar base layer; Subsequently, the third mortar matrix layer is extruded. The extrusion head is vertically lifted 20 to 30 mm in the Z-axis direction. In the XY plane, the extrusion head is offset by half the path width in the negative direction of the Y-axis with the starting point of the second mortar matrix layer as the reference, as the extrusion starting point of the third mortar matrix layer. At this time, the position of the extrusion head returns to the extrusion starting point of the first mortar matrix layer in the XY plane. The extruded cement mortar strips are embedded in the gaps between adjacent cement mortar strips in the second mortar matrix layer. After the second mortar matrix layer is printed, a continuous concave-convex mosaic structure is formed between the second and third mortar matrix layers. After the third mortar base layer is printed, an interface treatment agent is sprayed on the surface of the third mortar base layer and allowed to stand for 2 to 3 minutes to form a third flexible interface layer on the surface of the third mortar base layer; Printing is carried out layer by layer in this way. When printing a single mortar base layer, the extruder moves back and forth in the X-axis direction, advances line by line with a path width of 35 to 45 mm in the Y-axis direction, remains unchanged in the Z-axis direction, and adopts a zigzag movement path for single-layer filling; after the single-layer printing is completed, the interface treatment agent is sprayed on the surface of the single-layer mortar base layer and dried naturally. Then, the extruder head is lifted vertically along the Z-axis direction. In the XY plane, the extruder head moves to the extrusion starting point of the newly printed mortar base layer, and based on this, the position of half the path width is alternately offset in the positive or negative direction of the Y-axis as the extrusion starting point of the new layer, and finally the lightweight building material is obtained.

8. The method for preparing a lightweight building material containing mixed fibers based on 3D printing according to claim 1, characterized in that: In step (II), based on the total mass fraction of the interface treatment agent being 100 wt%, the interface treatment agent comprises the following components in mass fractions: The solid content of the styrene acrylic emulsion is 40-50%; The spraying amount of the interface treatment agent is 20 to 30 g / m 2 .

9. The method for preparing a lightweight building material containing mixed fibers based on 3D printing according to claim 1, characterized in that: The gradient curing and solidification comprises a first curing stage and a second curing stage carried out in sequence; The curing temperature in the first curing stage is 35-45°C; The relative humidity in the first curing stage is 90-95%; The curing time of the first curing stage is 24 to 36 hours; The curing pressure in the first curing stage is 0.1 MPa; The curing atmosphere in the first curing stage is air; The curing temperature of the second curing stage is 55-65°C; The relative humidity in the second curing stage is 60-70%; The curing time of the second curing stage is 24 to 36 hours; The curing pressure in the second curing stage is 0.2-0.3 MPa; The curing atmosphere in the second curing stage is nitrogen.

10. A lightweight building material containing mixed fibers and prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The lightweight building material mixed with mixed fibers comprises a mortar matrix layer and a flexible interface layer stacked in sequence.

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