Ferrite-aluminate cement-hemihydrate phosphogypsum-based concrete canvas and method for manufacturing the same

Abstract

The present application relates to the technical field of concrete products, and particularly relates to an iron aluminate cement-hemihydrate phosphogypsum-based concrete canvas and a preparation method thereof, so as to alleviate the problems of uneven hydration and poor interface compatibility between polyester fibers and cement matrix of the existing concrete canvas products. The iron aluminate cement-hemihydrate phosphogypsum-based concrete canvas is composed of a three-dimensional spacer fabric and a cement-based matrix filled in the three-dimensional spacer fabric; the three-dimensional spacer fabric has an upper layer, a lower layer and X-direction fibers connecting the upper and lower layers, wherein the lower layer is a dense woven layer and the upper layer is a mesh woven layer; and the cement-based matrix includes a lower water-blocking layer and an upper hydration layer along the thickness direction. The present application effectively solves the structural problems caused by uneven hydration and poor interface compatibility.

Description

Technical Field

[0001] This invention relates to the field of concrete products technology, and in particular to a ferroaluminate cement-hemihydrate phosphogypsum-based concrete canvas and its preparation method. Background Technology

[0002] Concrete canvas, a flexible thin-layer material made by filling cement-based powder materials into a three-dimensional spacer fabric, has been increasingly widely used in slope protection engineering, channel lining, emergency repair and military engineering due to its outstanding advantages of dry storage and transportation, on-site spreading and water hardening.

[0003] Currently, the cement-based matrix of existing concrete canvas mainly adopts the sulfoaluminate cement-natural gypsum system. Although this system has the advantages of fast setting and hardening speed and high early strength, it has many technical defects: First, the production of sulfoaluminate cement depends on high-grade bauxite resources, and the clinker firing temperature is as high as 1350-1450℃, resulting in high carbon emissions and high raw material costs, which does not meet the requirements of green and low-carbon development; Second, the use of natural gypsum as the sulfate source fails to realize the resource utilization of industrial solid waste, while my country's phosphate chemical industry generates approximately 80 tons of phosphate waste annually. The 00,000 tons of phosphogypsum by-products, whose main component is calcium sulfate, have a resource utilization rate of less than 40% due to the presence of small amounts of impurities. Large-scale stockpiling can easily lead to environmental problems such as soil and water pollution. Thirdly, the concrete canvas prepared by this system has the characteristic of thin-layer non-vibration molding, which makes the matrix prone to forming interconnected pores, resulting in poor structural density and insufficient erosion resistance. Its service life is limited in erosion control projects such as ditches and rivers. Fourthly, the hydration products of the sulfoaluminate cement-gypsum system are singular, relying solely on ettringite to provide strength. The strength development in the later stages is slow, and the phenomenon of strength reduction is prone to occur.

[0004] In recent years, to reduce carbon emissions from cement-based materials and utilize industrial solid waste, the preparation of concrete canvas using aluminoferrite cement and hemihydrate phosphogypsum as cementing materials has become an important technological direction. The clinker firing temperature of aluminoferrite cement is 150-250℃ lower than that of sulfoaluminate cement, resulting in a carbon emission reduction of over 30%. However, through extensive engineering verification and microstructure characterization, the inventors of this invention have discovered that the above-mentioned technical solutions still have two deep-seated defects in terms of construction uniformity and long-term durability that have not yet been effectively recognized and overcome.

[0005] The three-dimensional spacer fabric consists of an upper layer, a lower layer, and X-axis fibers vertically connecting the upper and lower layers. In existing technologies, the X-axis fibers are made of conventional polyester multifilaments, which contain a large number of axially continuous micropores. Their capillary water absorption rate is 1-2 orders of magnitude higher than that of the surrounding cement powder accumulation layer. During high-pressure spraying and water addition at the construction site, the sprayed water preferentially seeps rapidly down along the X-axis fiber bundles, resulting in a localized high water-cement ratio zone around each X-axis fiber, while the water-cement ratio is significantly lower in areas far from the X-axis fibers. This uneven water distribution leads to extremely uneven distribution of hydration products within the canvas plane. High water-cement ratio zones form large capillaries and areas rich in ettringite, while low water-cement ratio zones show incomplete hydration, with a large number of unreacted cement particles. This makes it difficult to guarantee the reliability of the project quality; the structural durability is severely degraded, and the service life is significantly shortened under freeze-thaw or wet-dry cycle conditions.

[0006] In addition, the interfacial compatibility between polyester fibers and cement matrix is ​​poor, specifically: Firstly, in the strongly alkaline environment of cement paste, the ester bonds in the polyester molecular chain undergo hydrolysis, generating terephthalate and consuming OH-. - This leads to a local decrease in pH value on the fiber surface. However, the hydration reaction of aluminoferrite cement is highly sensitive to alkalinity. The decrease in alkalinity in the interfacial region severely inhibits the heterogeneous nucleation and growth of ettringite on the fiber surface.

[0007] Secondly, during the weaving process of polyester fabrics, spinning oils must be added to reduce friction and eliminate static electricity. These oils will be physically adsorbed onto the surface of cement particles, becoming a physical barrier to water penetration and diffusion of hydrated ions, further hindering the overlap and growth of hydration products at the fiber-matrix interface. Summary of the Invention

[0008] This invention provides a ferroaluminate cement-hemihydrate phosphogypsum-based concrete canvas and its preparation method, in order to alleviate the problems of uneven hydration and poor interfacial compatibility between existing concrete canvas products and the cement matrix.

[0009] To alleviate the above-mentioned technical problems, the technical solution provided by the present invention is as follows: A type of aluminoferrite cement-hemihydrate phosphogypsum-based concrete canvas is composed of a three-dimensional spacer fabric and a cement-based matrix filled inside the three-dimensional spacer fabric; the three-dimensional spacer fabric has an upper layer, a lower layer, and X-direction fibers connecting the upper and lower layers, wherein the lower layer is a densely woven layer and the upper layer is a mesh layer; the cement-based matrix includes a lower water-blocking layer and an upper hydration layer along the thickness direction. The lower water-blocking layer comprises the following components by mass: 42-58 parts of aluminoferrite cement, 8-13 parts of hemihydrate phosphogypsum, 6-12 parts of microsilica, 0.8-1.6 parts of nano-CSH seed crystals, 2-5 parts of modified basalt micro powder, 1-3 parts of nano-calcium carbonate, and 3-7 parts of ultrafine slag powder. The upper hydration layer comprises the following components by mass: 72-86 parts of aluminoferrite cement, 14-26 parts of hemihydrate phosphogypsum, 0.1-0.5 parts of nano-CSH seed crystals, 1-3 parts of modified basalt micro powder, 0.6-1.2 parts of interface crystal form regulator, 0.5-1.5 parts of self-curing internal curing agent, and 0.3-0.8 parts of layered bimetallic hydroxide.

[0010] Furthermore, the interface crystal form regulator, by mass parts, includes: 40-60 parts of nano-kaolin, 20-35 parts of modified sodium polyaspartate, and 15-30 parts of nano-alumina sol.

[0011] Furthermore, the preparation method of modified sodium polyaspartate is as follows: maleic anhydride and ammonium carbonate are mixed in a molar ratio of 1:1.2 and thermally condensed at a dehydration temperature of 80 to 100°C and a polymerization temperature of 160 to 200°C to generate polysuccinimide; the polysuccinimide is added to a sodium hydroxide solution with a mass concentration of 20% to 30% and hydrolyzed at 40 to 60°C for 1 to 3 hours to obtain a sodium polyaspartate solution; the solution is then concentrated and dried to obtain the final product.

[0012] Furthermore, the layered bimetallic hydroxide is a magnesium-aluminum type layered bimetallic hydroxide with a Mg / Al molar ratio of 2:1, 3:1, or 4:1 and a particle size of 100-300 nm.

[0013] Furthermore, the self-curing internal curing agent is a composite of superabsorbent resin and porous expanded perlite in a mass ratio of 1:(2-3); wherein the superabsorbent resin is cross-linked polyacrylate; the porous expanded perlite has a particle size of 0.05-0.3 mm; the specific surface area of ​​the microsilica powder is ≥15000 m² / kg, and the SiO2 content is ≥90%; the specific surface area of ​​the ultrafine slag powder is ≥800 m² / kg.

[0014] Furthermore, the preparation method of the modified basalt micro powder is as follows: basalt raw stone is crushed to a particle size of less than or equal to 45 μm, and a 5% silane coupling agent KH-550 ethanol solution is added at a solid-liquid ratio of 1:5. The mixture is stirred and modified in a water bath at 60°C for 30 min, filtered, and then dried at 105°C to constant weight.

[0015] Furthermore, the clinker mineral composition of the aluminoferrite cement is C4AF 45%-55%, C3A 15%-20%, C2S 20%-25%, with the remainder being impurities; the initial setting time is 15-20 minutes, and the final setting time is 30-40 minutes; the hemihydrate phosphogypsum has an SO3 content greater than or equal to 40%, a moisture content less than or equal to 1%, and an impurity content less than or equal to 2%; the nano-CSH seed crystals have a particle size of 50-100 nm and a specific surface area of ​​500-600 m² / g.

[0016] A method for preparing a ferroaluminate cement-hemihydrate phosphogypsum-based concrete canvas includes the following steps: S1. Weigh out each component of the lower water-blocking layer and each component of the upper hydration layer, and add them to the mixer and dry mix them evenly. S2. Lay the three-dimensional spacer fabric flat on the vibrating worktable with the densely woven layer facing down and the mesh layer facing up. Add the lower water-blocking layer mixing powder evenly from one side of the mesh layer, turn on the vibrating table, and let the powder pass through the mesh layer into the fabric and be preferentially deposited on the densely woven layer side. Use pressure rollers to perform light pre-compaction to form a lower water-blocking layer blank with uniform thickness, and the filling thickness is one-quarter to one-third of the total fabric thickness. S3. Above the already formed lower water-blocking layer blank, continue to uniformly add the upper hydration layer mixed powder from the side of the mesh layer; through secondary vibration, the hydration layer powder fills the remaining space of the fabric, and the pressure roller is used to compact the whole to obtain a dry double-layer functional filling concrete canvas blank; wherein: the lower water-blocking layer is located on the densely woven layer side, and the upper hydration layer is located on the mesh layer side. S4. Turn the dry green body over so that the densely woven layer is facing up and the mesh layer is facing down. Then spray water evenly onto the surface of the densely woven layer facing up so that the green body is saturated with water. After spraying, cover and cure to harden and shape.

[0017] Furthermore, the spray water in step S4 contains 0.05%-0.1% of a nano-calcium carbonate suspension, wherein the nano-calcium carbonate particles have a diameter of 20-50 nm.

[0018] Furthermore, the amount of spray water used is 35%-50% of the total mass of the cementitious materials in the lower water-blocking layer and the upper hydration layer.

[0019] The technical effects are analyzed as follows: To address the uneven hydration problem caused by the preferential downward penetration of moisture along the X-axis fibers, this invention employs an ultrafine powder compound system in the lower water-blocking layer, which rapidly forms a tight-sealing layer upon contact with water. Simultaneously, the dry preform is inverted and sprayed once, allowing water to preferentially contact and activate the water-blocking layer on the densely woven layer side, quickly sealing the preferential water-conducting channel of the X-axis fibers. Subsequently, the moisture gradually penetrates into the hydration layer on the mesh layer side, effectively avoiding localized high water-to-binder ratio areas caused by concentrated downward penetration of moisture along the fiber bundles. At the same time, CSH seed crystals provide uniform nucleation sites for hydration products, and the upper self-curing internal curing agent continuously releases moisture and diffuses downward during the curing period, alleviating the self-drying shrinkage of the lower layer due to low water consumption. Ultimately, this achieves a balanced distribution and stable hydration of moisture in the thickness direction.

[0020] To address the poor interfacial compatibility between polyester fibers and cementitious matrices, this invention utilizes nano-kaolin adsorbed onto the surface of polyester fibers to provide a nucleation substrate. Layered bimetallic hydroxides adsorb terephthalate ions generated from the alkaline hydrolysis of fibers via anion exchange, maintaining a high-alkalinity environment at the interface to ensure ettringite nucleation. Modified sodium polyaspartate selectively adsorbs onto specific crystal faces of ettringite, inhibiting its axial growth and promoting its transformation from needle-like to short columnar shapes to increase the contact area and anchoring force with the fibers. Nano-alumina sol gels at the interface to form a continuous adhesive film. Modified basalt micropowder, after modification with a coupling agent, is grafted with amino active groups, electrostatically adsorbing with carboxylate ions generated from fiber hydrolysis. Simultaneously, its silanol groups condense with hydration products to form covalent bonds, building molecular bridges between the fibers and the matrix. A self-curing internal curing agent continuously releases moisture, maintaining relative humidity at the interface and eliminating microcracks caused by self-drying shrinkage, thereby synergistically improving the interfacial bonding quality between the fiber and the matrix. Detailed Implementation

[0021] The total thickness of the three-dimensional spacer fabric is 10mm. The upper layer (mesh layer) has a mesh size of 4mm × 3mm (radial × weft), and the lower layer (dense weave layer) has a fiber spacing of 3mm in the X direction. Tested after 28 days of curing.

[0022] The concrete canvases prepared in each embodiment and comparative example were tested according to the following test methods: Bending strength: The three-point bending method was used for testing. The sample size was 160mm×40mm×10mm, the span was 100mm, and the loading rate was 50mm / min.

[0023] Tensile strength: Measured using a material tensile testing machine in displacement control mode. The tensile specimen dimensions were 200mm × 100mm × 10mm, with a gauge length of 100mm; the fixture directly clamped the rectangular clamping areas at both ends of the specimen. The tensile loading rate was set to 10mm / min.

[0024] Freeze-thaw cycle count: According to GB / T 50082 rapid freezing method, the center temperature of the sample is controlled between -18℃ and 5℃ for cycling. Mass loss is tested once every 25 cycles. The number of cycles when the mass loss rate reaches 5% is taken as the number of freeze-thaw cycles.

[0025] Drying shrinkage rate: The sample size is 160mm×40mm×10mm. After measuring the initial length under standard test conditions (temperature 20℃±2℃, relative humidity 50%±5%), it is dried in a drying oven at 105℃±5℃ until constant weight. After cooling, the length is measured again. The drying shrinkage rate is calculated according to the following formula:

[0026] Where: S is the drying shrinkage rate (%), L0 is the sample length before drying (mm), and L1 is the sample length after drying (mm). Each test group shall have no less than 3 samples, and the arithmetic mean shall be taken.

[0027] Unless otherwise specified, all components used in this invention are prepared according to the following methods: (1) Preparation of modified polyaspartic acid sodium: Maleic anhydride and ammonium carbonate were mixed in a molar ratio of 1:1.2. The mixture was dehydrated at 85°C for 2 hours and polymerized at 180°C for 3 hours. The resulting polysuccinimide was then thermally condensed to produce polysuccinimide. The polysuccinimide was added to a 25% sodium hydroxide solution and hydrolyzed at 50°C for 2 hours to obtain a polyaspartic acid sodium solution. The obtained solution was concentrated under reduced pressure at 60°C to a solid content of 40%, and then dried in a vacuum drying oven at 55°C to a constant weight to obtain modified polyaspartic acid sodium.

[0028] (2) Formulation of interfacial crystal form regulator: The interfacial crystal form regulator is composed of nano-kaolin, modified sodium polyaspartate, and nano alumina sol in a mass ratio of (40~60):(20~35):(15~30). Nano-kaolin, modified sodium polyaspartate, and nano alumina sol are added to a high-speed mixer in proportion and stirred at 800 r / min for 15 min until they are uniformly mixed.

[0029] (3) Preparation of layered bimetallic hydroxides: Magnesium-aluminum type layered bimetallic hydroxides were prepared by co-precipitation method with a Mg / Al molar ratio of 3:1 and a particle size of 200 nm. Mg(NO3)2·6H2O and Al(NO3)3·9H2O were weighed according to the ratio and dissolved in deionized water to prepare a mixed salt solution with a total metal ion concentration of 0.8 mol / L. A 1.5 mol / L NaOH solution was prepared as a precipitant. The mixed salt solution and precipitant were added dropwise at a rate of 2 mL / min under vigorous stirring at 70 °C, maintaining pH=10. After the addition was completed, the product was crystallized at 70 °C for 18 h. The product was washed by centrifugation with deionized water until neutral, dried at 105 °C to constant weight, and ground through a 200-mesh sieve to obtain the final product.

[0030] (4) Preparation of self-curing internal curing agent: The self-curing internal curing agent is a composite of cross-linked polyacrylate superabsorbent resin and porous expanded perlite at a mass ratio of 1:2.5; the expanded perlite has a particle size of 0.05~0.3mm. The superabsorbent resin and porous expanded perlite are added to a mixer in proportion and stirred at 300r / min for 20min to ensure that the two are fully mixed and homogeneous.

[0031] (5) Preparation of modified basalt micro powder: The raw basalt stone was crushed and ball-milled to a particle size ≤45μm; 5% KH-550 anhydrous ethanol solution of silane coupling agent was added at a solid-liquid ratio of 1:5; the mixture was stirred and modified in a water bath at 60℃ for 30min; vacuum filtered; and dried at 105℃ for 4h to constant weight to obtain modified basalt micro powder.

[0032] (6) Preparation of nano calcium carbonate suspension: Add nano calcium carbonate powder with a particle size of 20~50nm to water and disperse it by ultrasonication for 8min to form a uniform and stable suspension with a concentration of 0.05%~0.1%.

[0033] (7) Preparation of nano CSH seeds: Calcium nitrate and sodium silicate are mixed at a calcium-silicon molar ratio (Ca / Si) of 1.5-2.0 and co-precipitated under alkaline conditions (pH=11.5-12.5) to generate amorphous CSH precursors; the reaction system is then transferred to a reaction vessel and hydrothermally crystallized at 80-95℃ for 6-24 hours to promote the ordered growth of seed structures; after the reaction is completed, the seeds are centrifuged, washed and dried to obtain nano CSH seeds with a particle size of 50-100 nm and a specific surface area of ​​500-600 m² / g.

[0034] In this invention, "cementing material" refers to the main powder material that provides bonding strength after hydration, specifically including: aluminoferrite cement and hemihydrate phosphogypsum. Other components, such as: silica fume, ultrafine slag powder, nano-CSH seed crystals, modified basalt powder, nano-calcium carbonate, interface crystal form regulator, self-curing internal curing agent, layered bimetallic hydroxide, etc., are all functional admixtures or additives and are not included in the mass calculation of "cementing material".

[0035] Example 1 Lower water-blocking layer: by mass parts, 50 parts of aluminoferrite cement, 10 parts of hemihydrate phosphogypsum, 8 parts of microsilica, 1.2 parts of nano CSH seed crystals, 3 parts of modified basalt micro powder, 2 parts of nano calcium carbonate, and 5 parts of ultrafine slag powder.

[0036] Upper hydration layer: by mass parts, 78 parts of aluminoferrite cement, 20 parts of hemihydrate phosphogypsum, 0.3 parts of nano-CSH seed crystals, 2 parts of modified basalt micro powder, 0.9 parts of interface crystal form regulator, 1.0 part of self-curing internal curing agent, and 0.5 parts of layered bimetallic hydroxide.

[0037] The interface crystal form regulator is composed of nano-kaolin, modified sodium polyaspartate, and nano-alumina sol in a mass ratio of 50:28:22. The layered bimetallic hydroxide is magnesium-aluminum type, with a Mg / Al molar ratio of 3:1 and a particle size of 200 nm. The self-curing internal curing agent is a composite of superabsorbent resin and porous expanded perlite in a mass ratio of 1:2.5. The modified basalt micro powder is surface-modified with silane coupling agent KH-550. The mineral composition of the aluminoferrite cement clinker is C4AF 50%, C3A 18%, and C2S 22%. The hemihydrate phosphogypsum has an SO3 content of 42%, a moisture content of 1%, and an impurity content of 1.5%. The specific surface area of ​​the microsilica powder is ≥15000 m² / kg, and the SiO2 content is ≥90%; the specific surface area of ​​the ultrafine slag powder is ≥800 m² / kg.

[0038] The preparation method is as follows: S1. Preparation of layered powder: Weigh each component of the lower water-blocking layer and each component of the upper hydration layer, and add them to a mixer and dry mix for 5 minutes until they are evenly mixed.

[0039] S2. Laying and pre-compacting the lower water-blocking layer: Lay the three-dimensional spacer fabric flat on the vibrating worktable with the densely woven layer facing down and the mesh layer facing up. Evenly add the lower water-blocking layer mixing powder from the mesh layer side. Turn on the vibrating table with an amplitude of 0.3 mm and a frequency of 50 Hz for 2 minutes to allow the powder to pass through the mesh layer and enter the interior of the three-dimensional spacer fabric, preferentially settling to the side closer to the densely woven layer. Use a pressure roller to perform light pre-compacting with a pressure of 0.1 MPa to form the lower water-blocking layer blank, with a filling thickness of about 3 mm, which is about one-third of the total fabric thickness.

[0040] S3. Laying and compacting the upper hydration layer: Above the already formed lower water-blocking layer blank, continue to uniformly add the upper hydration layer mixed powder from the side of the woven layer. Through secondary vibration, with an amplitude of 0.3 mm and a frequency of 50 Hz, vibrate for 3 minutes to fill the remaining space inside the fabric. Then, use a pressure roller to compact the entire blank with a pressure of 0.2 MPa to obtain a dry double-layer functional filled concrete canvas blank, in which the lower water-blocking layer is located on the dense woven layer side and the upper hydration layer is located on the woven layer side.

[0041] S4. On-site hydration and hardening: Turn the dry blank over so that the densely woven layer faces up and the mesh layer faces down. Then spray water evenly onto the surface of the densely woven layer facing up. The total amount of water used for spraying should be controlled at 45% of the total mass of the cementitious material in the lower water-blocking layer and the upper hydration layer.

[0042] The water contained 0.08% nano-calcium carbonate suspension with a particle size of 30nm. After spraying, the solution was covered with a plastic film for 7 days and then allowed to cure naturally for 28 days.

[0043] Test results of Example 1: Flexural strength 12.8 MPa, tensile strength 4.25 MPa, drying shrinkage 0.032%, and freeze-thaw cycle resistance 275 times.

[0044] Example 2 The lower water-blocking layer, by mass parts, consists of: 55 parts of aluminoferrite cement, 12 parts of hemihydrate phosphogypsum, 10 parts of microsilica, 1.5 parts of nano-CSH seed crystals, 4 parts of modified basalt micro powder, 2.5 parts of nano-calcium carbonate, and 6 parts of ultrafine slag powder.

[0045] The upper hydration layer, by mass parts, consists of: 82 parts of aluminoferrite cement, 24 parts of hemihydrate phosphogypsum, 0.15 parts of nano-CSH seed crystals, 2.5 parts of modified basalt micro powder, 1.0 part of interface crystal form regulator, 1.2 parts of self-curing internal curing agent, and 0.7 parts of layered bimetallic hydroxide.

[0046] In this example, the mass ratio of nano-kaolin, modified sodium polyaspartate, and nano-alumina sol in the interface crystal form regulator is 55:25:20. The total amount of water used for spraying is controlled at 44% of the total mass of the cementitious materials in the lower water-blocking layer and the upper hydration layer. The sources and specifications of the remaining components are the same as in Example 1.

[0047] The preparation method is the same as in Example 1, except that the thickness of the lower water-blocking layer is controlled to be 2.5 mm, which is about one-quarter of the total thickness of the fabric, and the concentration of nano-calcium carbonate suspension in the spray water is 0.06%.

[0048] Test results of Example 2: flexural strength 13.1 MPa, tensile strength 4.32 MPa, drying shrinkage 0.030%, and freeze-thaw cycle resistance 288 times.

[0049] Comparative Example 1 This comparative example does not distinguish between upper and lower layers. The entire layer uses the following proportions: 78 parts of aluminoferrite cement, 20 parts of hemihydrate phosphogypsum, 0.3 parts of nano-CSH seed crystals, 2 parts of modified basalt micro powder, 0.9 parts of interface crystal form regulator, 1.0 part of self-curing internal curing agent, and 0.5 parts of layered bimetallic hydroxide.

[0050] The preparation method is as follows: S1. Powder preparation: Weigh the above components and add them to a mixer and dry mix for 5 minutes until uniformly mixed.

[0051] S2. Single-layer filling: The three-dimensional spacer fabric is laid flat on a vibrating worktable with the densely woven layer facing down and the mesh layer facing up. The mixed powder is evenly added from one side of the mesh layer. The vibrating table is turned on with an amplitude of 0.3 mm and a frequency of 50 Hz for 5 minutes to fill all the pores of the fabric with powder. Then, a pressure roller is used to compact it with a pressure of 0.2 MPa to obtain a dry concrete canvas blank. A PVC film is pasted onto the densely woven layer on the lower surface of the dry blank.

[0052] S3. Spray hardening: Turn the dry blank over so that the densely woven layer is facing up and the mesh layer is facing down. Then spray water onto the surface of the densely woven layer facing up. The total amount of water sprayed should be controlled at 40% of the total mass of the cementitious material. After spraying, cover with plastic film for 7 days and then let it cure naturally for 28 days.

[0053] Comparative Example 1 test results: flexural strength 7.6 MPa, tensile strength 3.23 MPa, drying shrinkage rate 0.058%, freeze-thaw cycle resistance 89 times.

[0054] Comparative Example 2 The ratio of the lower water-blocking layer and the upper hydration layer in this comparative example is exactly the same as that in Example 1.

[0055] The preparation method, steps S1 to S3, is exactly the same as in Example 1 (layer-by-layer laying), except that step S4 uses a traditional one-time spraying process, as detailed below: S4. Spray hardening: Turn the dry blank over so that the densely woven layer is facing up and the mesh layer is facing down. Then spray water onto the surface of the densely woven layer facing up. The total amount of water sprayed should be controlled at 50% of the total mass of the cementitious material in the lower water-blocking layer and the upper hydration layer. After spraying, cover with plastic film for 7 days of curing, and then allow to cure naturally for 28 days.

[0056] Comparative Example 2 test results: flexural strength 9.3 MPa, tensile strength 3.55 MPa, drying shrinkage 0.045%, and freeze-thaw cycle resistance 142 times.

[0057] Comparative Example 3 The composition of the lower water-blocking layer in this comparative example is exactly the same as that in Example 1.

[0058] The upper hydration layer removes four components: nano-kaolin, modified sodium polyaspartate, nano-alumina sol, and layered bimetallic hydroxide, while retaining modified basalt micropowder. The specific proportions are: 78 parts aluminoferrite cement, 20 parts hemihydrate phosphogypsum, 0.3 parts nano-CSH seed crystals, 2 parts modified basalt micropowder, and 1.0 part self-curing internal curing agent.

[0059] The preparation method is the same as in Example 1.

[0060] Comparative Example 3 test results: flexural strength 9.8 MPa, tensile strength 3.68 MPa, drying shrinkage rate 0.041%, and freeze-thaw cycle resistance 156 times.

[0061] Comparative Example 4 In this comparative example, the ratio of the lower water-blocking layer to the upper hydration layer is adjusted based on Example 1, with the amount of nano-CSH seed crystals added to make the ratio identical in both layers. Specifically: Lower water-blocking layer: 50 parts of aluminoferrite cement, 10 parts of hemihydrate phosphogypsum, 8 parts of silica fume, 0.3 parts of nano-CSH seed crystals, 3 parts of modified basalt micro powder, 2 parts of nano-calcium carbonate, and 5 parts of ultrafine slag powder.

[0062] Upper hydration layer: 78 parts of aluminoferrite cement, 20 parts of hemihydrate phosphogypsum, 0.3 parts of nano-CSH seed crystals, 2 parts of modified basalt micro powder, 0.9 parts of interface crystal form regulator, 1.0 part of self-curing internal curing agent, and 0.5 parts of layered bimetallic hydroxide.

[0063] The sources and specifications of the remaining components are the same as in Example 1.

[0064] The preparation method is the same as in Example 1.

[0065] Comparative Example 4 test results: flexural strength 10.5 MPa, tensile strength 3.86 MPa, drying shrinkage rate 0.038%, and freeze-thaw cycle resistance 198 times.

[0066] Comparative Example 5 This comparative example uses sulfoaluminate cement instead of ferroaluminate cement and natural gypsum (calcium sulfate dihydrate, purity ≥95%) instead of hemihydrate phosphogypsum. The mass ratio of the upper and lower layers is the same as in Example 1, only the type of cementitious material is changed. Specifically: Lower water-blocking layer: 50 parts sulfoaluminate cement, 10 parts natural gypsum, 8 parts microsilica, 1.2 parts nano CSH seed crystals, 3 parts modified basalt micro powder, 2 parts nano calcium carbonate, and 5 parts ultrafine slag powder.

[0067] Upper hydration layer: 78 parts sulfoaluminate cement, 20 parts natural gypsum, 0.3 parts nano CSH seed crystals, 2 parts modified basalt micro powder, 0.9 parts interface crystal form regulator, 1.0 part self-curing internal curing agent, and 0.5 parts layered bimetallic hydroxide.

[0068] The preparation method is the same as in Example 1.

[0069] Comparative Example 5 test results: flexural strength 11.2 MPa, tensile strength 3.96 MPa, drying shrinkage rate 0.048%, and freeze-thaw cycle resistance 167 times.

[0070] Comparative Example 6 In this comparative example, the modified basalt micro powder component was removed from the lower water-blocking layer. The specific proportions are as follows: 50 parts of aluminoferrite cement, 10 parts of hemihydrate phosphogypsum, 8 parts of microsilica, 1.2 parts of nano-CSH seed crystals, 2 parts of nano-calcium carbonate, and 5 parts of ultrafine slag powder.

[0071] The modified basalt micro powder component was removed from the upper hydration layer. The specific proportions are as follows: 78 parts of aluminoferrite cement, 20 parts of hemihydrate phosphogypsum, 0.3 parts of nano CSH seed crystals, 0.9 parts of interface crystal form regulator, 1.0 part of self-curing internal curing agent, and 0.5 parts of layered bimetallic hydroxide.

[0072] The sources and specifications of the remaining components are the same as in Example 1.

[0073] The preparation method is the same as in Example 1.

[0074] Comparative Example 6 test results: flexural strength 11.0 MPa, tensile strength 3.89 MPa, drying shrinkage 0.035%, and freeze-thaw cycle resistance 212 times.

[0075] Table 1 lists the test results for each embodiment and comparative example.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A type of ferroaluminate cement-hemihydrate phosphogypsum-based concrete canvas, characterized in that, It is composed of a three-dimensional spacer fabric and a cement-based matrix filled inside the three-dimensional spacer fabric; the three-dimensional spacer fabric has an upper layer, a lower layer and X-direction fibers connecting the upper and lower layers, wherein the lower layer is a densely woven layer and the upper layer is a mesh layer; the cement-based matrix includes a lower water-blocking layer and an upper hydration layer along the thickness direction. The lower water-blocking layer comprises the following components by mass: 42-58 parts of aluminoferrite cement, 8-13 parts of hemihydrate phosphogypsum, 6-12 parts of microsilica, 0.8-1.6 parts of nano-CSH seed crystals, 2-5 parts of modified basalt micro powder, 1-3 parts of nano-calcium carbonate, and 3-7 parts of ultrafine slag powder. The upper hydration layer comprises the following components by mass: 72-86 parts of aluminoferrite cement, 14-26 parts of hemihydrate phosphogypsum, 0.1-0.5 parts of nano-CSH seed crystals, 1-3 parts of modified basalt micro powder, 0.6-1.2 parts of interface crystal form regulator, 0.5-1.5 parts of self-curing internal curing agent, and 0.3-0.8 parts of layered bimetallic hydroxide.

2. The aluminoferrite cement-hemihydrate phosphogypsum-based concrete canvas according to claim 1, characterized in that, The interface crystal form regulator, by mass parts, includes: 40-60 parts of nano-kaolin, 20-35 parts of modified sodium polyaspartate, and 15-30 parts of nano-alumina sol.

3. The aluminoferrite cement-hemihydrate phosphogypsum-based concrete canvas according to claim 2, characterized in that, The modified sodium polyaspartate is prepared as follows: maleic anhydride and ammonium carbonate are mixed in a molar ratio of 1:1.2 and thermally condensed at a dehydration temperature of 80 to 100°C and a polymerization temperature of 160 to 200°C to generate polysuccinimide; the polysuccinimide is added to a sodium hydroxide solution with a mass concentration of 20% to 30% and hydrolyzed at 40 to 60°C for 1 to 3 hours to obtain a sodium polyaspartate solution; the solution is then concentrated and dried to obtain the final product.

4. The aluminoferrite cement-hemihydrate phosphogypsum-based concrete canvas according to claim 3, characterized in that, The layered bimetallic hydroxide is a magnesium-aluminum type layered bimetallic hydroxide with a Mg / Al molar ratio of 2:1, 3:1, or 4:1 and a particle size of 100-300 nm.

5. The aluminoferrite cement-hemihydrate phosphogypsum-based concrete canvas according to claim 4, characterized in that, The self-curing internal curing agent is a composite of superabsorbent resin and porous expanded perlite in a mass ratio of 1:(2-3); wherein the superabsorbent resin is cross-linked polyacrylate; and the porous expanded perlite has a particle size of 0.05-0.3 mm. The specific surface area of ​​the microsilica powder is ≥15000m² / kg, and the SiO2 content is ≥90%. The specific surface area of ​​the ultrafine slag powder is ≥800m² / kg.

6. The aluminoferrite cement-hemihydrate phosphogypsum-based concrete canvas according to claim 5, characterized in that, The modified basalt micro powder is prepared by crushing the raw basalt stone to a particle size of less than or equal to 45 μm, adding a 5% silane coupling agent KH-550 ethanol solution at a solid-liquid ratio of 1:5, stirring and modifying in a 60℃ water bath for 30 min, filtering, and drying at 105℃ to constant weight.

7. The aluminoferrite cement-hemihydrate phosphogypsum-based concrete canvas according to claim 6, characterized in that, The clinker mineral composition of the aluminoferrite cement is C4AF 45%-55%, C3A 15%-20%, C2S 20%-25%, with the remainder being impurities. The initial setting time is 15-20 minutes, and the final setting time is 30-40 minutes. The hemihydrate phosphogypsum has an SO3 content of ≥40%, a moisture content of ≤1%, and an impurity content of ≤2%. The nano-CSH seed crystals have a particle size of 50-100 nm and a specific surface area of ​​500-600 m² / g.

8. A method for preparing a ferroaluminate cement-hemihydrate phosphogypsum-based concrete canvas as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Weigh out each component of the lower water-blocking layer and each component of the upper hydration layer, and add them to the mixer and dry mix them evenly. S2. Lay the three-dimensional spacer fabric flat on the vibrating worktable with the densely woven layer facing down and the mesh layer facing up. Add the lower water-blocking layer mixing powder evenly from one side of the mesh layer, turn on the vibrating table, and let the powder pass through the mesh layer into the fabric and be preferentially deposited on the densely woven layer side. Use pressure rollers to perform light pre-compaction to form a lower water-blocking layer blank with uniform thickness, and the filling thickness is one-quarter to one-third of the total fabric thickness. S3. Above the already formed lower water-blocking layer blank, continue to uniformly add the upper hydration layer mixed powder from the side of the mesh layer; through secondary vibration, the hydration layer powder fills the remaining space of the fabric, and the pressure roller is used to compact the whole to obtain a dry double-layer functional filling concrete canvas blank; wherein: the lower water-blocking layer is located on the densely woven layer side, and the upper hydration layer is located on the mesh layer side. S4. Turn the dry green body over so that the densely woven layer is facing up and the mesh layer is facing down. Then spray water evenly onto the surface of the densely woven layer facing up so that the green body is saturated with water. After spraying, cover and cure to harden and shape.

9. The preparation method according to claim 8, characterized in that, The spray water in step S4 contains 0.05%-0.1% of nano-calcium carbonate suspension, wherein the nano-calcium carbonate particles have a diameter of 20-50 nm.

10. The preparation method according to claim 9, characterized in that, The amount of spray water used is 35%-50% of the total mass of the cementitious materials in the lower water-blocking layer and the upper hydration layer.

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