Potassium magnesium phosphate cement-based material with high compactness and high salt corrosion resistance and application of potassium magnesium phosphate cement-based material

Abstract

The invention relates to the technical field of magnesium phosphate cement materials, and particularly discloses a magnesium potassium phosphate cement-based material with high compactness and high salt corrosion resistance and application of the magnesium potassium phosphate cement-based material. The magnesium potassium phosphate cement-based material is prepared from the following components in parts by weight: 30 to 40 parts of dead burned magnesium oxide, 15 to 20 parts of monopotassium phosphate, 3 to 5 parts of retarder, 0.01 to 0.03 part of crystalline phosphate, 30 to 40 parts of fine aggregate and 8 to 13 parts of mixing water. Wherein the molecular formula of the crystalline phosphate is KNaMg2 (PO4) 2.14 H2O. By introducing the crystalline phosphate in a special structural form, the hydration evolution path and the microstructure of the magnesium potassium phosphate cement-based material in a salt erosion environment are effectively improved, and the salt erosion resistance is remarkably improved.

Description

A potassium magnesium phosphate cement-based material with high density and high resistance to salt erosion and its application. Technical Field

[0001] This invention relates to the field of magnesium phosphate cement materials technology, specifically to a potassium magnesium phosphate cement-based material with high density and high resistance to salt erosion, and its applications. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In salt lake areas, coastal regions, and cold climates where de-icing salt environments exist, concrete structures are constantly exposed to high concentrations of corrosive ions such as chlorides. Especially under complex climatic conditions including wet-dry cycles and freeze-thaw cycles, they are highly susceptible to durability degradation issues such as cracking, erosion, and steel reinforcement corrosion, severely impacting the service life and safety of the project. Although high-performance repair materials such as sulfoaluminate cement and supersulfate cement have improved the salt erosion resistance of concrete structures to some extent, problems such as unstable durability, insufficient interfacial bonding, and poor adaptability to construction environments still exist.

[0004] Magnesium potassium phosphate cement (MKPC) is a novel inorganic cementitious material that rapidly hardens through an acid-base reaction, primarily composed of recalcined magnesium oxide and potassium dihydrogen phosphate. This material boasts advantages such as early strength and rapid hardening, low shrinkage, and good adhesion to various substrates, making it widely applicable in the rapid repair and emergency maintenance of roads, bridges, and water conservancy projects. It is particularly suitable for scenarios requiring rapid reopening of traffic. Furthermore, MKPC exhibits good water resistance and freeze-thaw resistance to a certain extent. However, under complex chloride-salt corrosion environments, MKPC still faces challenges such as the dissolution of hydration products and a decrease in structural density, limiting its long-term use in high-salt areas. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a potassium magnesium phosphate cement-based material with high density and high resistance to salt corrosion, and its application, which can significantly improve the stability and durability of MKPC in salt corrosion environments. Specifically, the technical solution of this invention is as follows.

[0006] First, this invention discloses a potassium magnesium phosphate cement-based material with high density and high resistance to salt erosion, comprising the following components in the following proportions: 30-40 parts by weight of reburned magnesium oxide, 15-20 parts by weight of potassium dihydrogen phosphate, 3-5 parts by weight of retarder, 0.01-0.03 parts by weight of crystalline phosphate, 30-40 parts by weight of fine aggregate, and 8-13 parts by weight of mixing water. The crystalline phosphate has the molecular formula KNaMg2(PO4)2·14H2O.

[0007] Furthermore, the retarder includes at least one of borax, sodium citrate, sodium hexametaphosphate, sodium tripolyphosphate, etc.

[0008] Furthermore, the crystalline phosphate is prepared using the following method: according to K + Na + Mg 2+ :PO4 3- A molar ratio of 1:1:2:2 will K + Source, Na + Source, Mg 2+ Source, PO4 3- The source is added to water and mixed thoroughly. The resulting mixture is then adjusted to alkaline conditions and heated under stirring. After completion, the solid product is separated, washed, and dried to obtain the crystalline phosphate.

[0009] Furthermore, the K + The sources include at least one of potassium chloride, potassium sulfate, and potassium nitrate.

[0010] Furthermore, the Na + The source includes at least one of sodium chloride, sodium sulfate, sodium nitrate, etc.

[0011] Furthermore, the Mg 2+ The sources include at least one of magnesium chloride, magnesium sulfate, and magnesium nitrate.

[0012] Furthermore, the PO4 3- The source includes at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, etc.

[0013] Further, the pH of the mixture is adjusted to 9-11. Optionally, at least one of sodium hydroxide, potassium hydroxide, ammonia, etc., is used for pH adjustment.

[0014] Furthermore, the heating reaction is carried out at a temperature of 40-60°C for 5-6 hours.

[0015] Furthermore, the drying temperature is 40~45℃, and the time is 40~48 hours.

[0016] Furthermore, the particle size of the crystalline phosphate is 5~100μm.

[0017] Furthermore, the potassium magnesium phosphate cement-based material also includes 0.5 to 2 parts by weight of modified hydrotalcite, which is formed by the intercalation of borate ions and phosphate ions between the hydrotalcite layers.

[0018] Furthermore, the modified hydrotalcite is prepared by the following method: carbonate-type Mg-Al hydrotalcite is calcined to remove its interlayer anions, and then the obtained calcined product is added to a mixed solution containing boric acid and phosphate and stirred to react. After the reaction is completed, the solid product is separated and dried to obtain the modified hydrotalcite.

[0019] Furthermore, the calcination temperature is 350~450℃, and the time is 0.5~3 hours.

[0020] Furthermore, the ratio of the carbonate-type Mg-Al hydrotalcite to the mixed solution is 1g:20~30mL, and the concentration of boric acid in the mixed solution is 0.02~0.2mol / L, and the concentration of phosphate is 0.05~0.3mol / L.

[0021] Furthermore, the boric acid substance includes at least one of borax, boric acid, etc.; further, the phosphate includes at least one of dipotassium hydrogen phosphate, sodium hexametaphosphate, sodium tripolyphosphate, etc.

[0022] Furthermore, the temperature of the stirring reaction is 25~60℃, and the time is 0.5~8 hours.

[0023] Furthermore, the drying temperature is 40~60℃, and the drying time is 12~48 hours.

[0024] Secondly, this invention discloses the application of the potassium magnesium phosphate cement-based material with high density and high salt erosion resistance in the fields of roads, bridges, water conservancy, and marine engineering.

[0025] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects: (1) The potassium magnesium phosphate cement-based material of the present invention adds the synthesized crystalline phosphate KNaMg2(PO4)2·14H2O, which achieves the effect of "reduced porosity-densified structure-simultaneous improvement of mechanical and salt corrosion resistance". The reason is that: on the one hand, the crystalline phosphate can be used as the crystal nucleus of the hydration products of calcined magnesium oxide and potassium dihydrogen phosphate, such as struvite-K, to induce heterogeneous nucleation and epitaxial growth on the surface of the crystalline phosphate. At the same time, the dense crystal structure of the crystalline phosphate itself can act as a "rigid skeleton" to fill the capillary channels in the hydration products, forming a continuous and dense phosphate crystal network, thereby inhibiting the dissolution and shedding of the hydration products, thereby improving the stability and durability of the potassium magnesium phosphate cement-based material in the salt corrosion environment. On the other hand, the total porosity of the hydration products containing the crystalline phosphate significantly decreases after immersion in salt solution, with the pores shifting towards micropores and gel pores, microcrack propagation being suppressed, and ion channels being effectively sealed. This improves the material's impermeability and salt erosion resistance at the microstructural level, significantly extending the service life of the potassium magnesium phosphate cement-based material in high-salt areas. Furthermore, the introduction of the crystalline phosphate does not significantly shorten the setting time or reduce early strength; on the contrary, it promotes the early strength of the potassium magnesium phosphate cement-based material of the present invention. This is because the crystalline phosphate acts as a seed nucleator and microfiller while dissolving slowly, without significantly increasing the phosphate ion concentration in the system and thus preventing instantaneous setting. Simultaneously, it promotes faster and more uniform precipitation of early hydration products, forming a dense skeleton, thereby increasing early strength. Therefore, the potassium magnesium phosphate cement-based material prepared by the present invention can simultaneously meet the comprehensive requirements of rapid repair, early strength and rapid hardening, and long-term durability.

[0026] (2) The potassium magnesium phosphate cement-based material of the present invention incorporates a modified hydrotalcite-like material formed by the synergistic intercalation of borate and phosphate ions, which simultaneously maintains the stability of the layered structure, the interlayer anion exchange activity, and the chemical compatibility with the potassium magnesium phosphate cement system. Specifically, phosphate ions exhibit good homology compatibility with the potassium magnesium phosphate cement system, which is beneficial for improving the structural stability of the hydrotalcite-like material in a phosphate environment and promoting interfacial bonding between it and the phosphate salt products in the matrix; borate ions, on the other hand, are beneficial for regulating the interlayer microenvironment, increasing the interlayer spacing, and improving the openness of the anion exchange channels, thereby enhancing the adsorption / exchange / fixation capacity of Cl- from the external environment. The synergistic effect of these two components results in a modified hydrotalcite-like material that possesses both good chloride fixation efficiency and structural stability. Meanwhile, the crystalline phosphate KNaMg2(PO4)2·14H2O introduced in this invention can serve as a heterogeneous nucleation site for hydration products such as struvite-K in the MKPC system, inducing preferential precipitation and uniform growth of hydration products on its surface, reducing the tendency for disordered deposition. As the hydration reaction proceeds, the crystalline phosphate and its induced hydration products further fill the capillaries and microcracks in the matrix, promoting pore structure refinement, channel tortuosity, and the formation of a more continuous and dense inorganic phase framework, i.e., "nucleation-densification". Based on this effect, on the one hand, the dense microstructure induced by the crystalline phosphate can block the salt transport path from a physical level; on the other hand, in conjunction with the modified hydrotalcite-like material, it can adsorb, exchange, and fix the invading Cl-, reducing the content of free chloride ions. Together, they achieve a dual salt-resistant channel closure of "physical dense barrier + chemical adsorption solidification", thereby significantly improving the material's density, impermeability, and salt erosion resistance. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention and do not constitute an undue limitation of the invention.

[0028] Figure 1 shows a sample of crystalline phosphate prepared in Example 1 below.

[0029] Figure 2 shows the XRD pattern of the crystalline phosphate prepared in Example 1 below.

[0030] Figure 3 is a scanning electron microscope image of the crystalline phosphate prepared in Example 1 below.

[0031] Figure 4 shows a sample of crystalline phosphate prepared in Example 2 below.

[0032] Figure 5 is a scanning electron microscope image of the crystalline phosphate prepared in Example 2 below.

[0033] Figure 6 shows a modified hydrotalcite sample prepared in Example 2 below.

[0034] Figure 7 shows a sample of crystalline phosphate prepared in Example 3 below.

[0035] Figure 8 shows a modified hydrotalcite sample prepared in Example 3 below.

[0036] Figure 9 shows a sample of hydrotalcite powder used in Example 5 below.

[0037] Figure 10 shows a modified hydrotalcite sample prepared in Example 6 below.

[0038] Figure 11 shows a modified hydrotalcite sample prepared in Example 7 below.

[0039] Figure 12 shows a modified hydrotalcite sample prepared in Example 8 below. Detailed Implementation

[0040] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the invention. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as those skilled in the art. The preferred embodiments and materials described in this invention are for illustrative purposes only. The technical solutions of the present invention will now be further described with reference to specific embodiments.

[0041] Example 1: Preparation of a potassium magnesium phosphate cement-based material with high density and high salt erosion resistance, comprising the following steps: (1) according to K + Na + Mg 2+ :PO4 3- A molar ratio of 1:1:2:2, with K + Source (potassium chloride), Na + Source (sodium chloride), Mg 2+ Source (magnesium chloride), PO4 3- Potassium dihydrogen phosphate (KH2PO4) was added to water and stirred until homogeneous to obtain a mixture. Sodium hydroxide solution was then added to adjust the pH of the mixture to 10, and the mixture was heated to 50°C for 6 hours under stirring. After the reaction was complete, the solid product was separated, washed with water, and dried at 40°C for 48 hours. The product was then ground to obtain crystalline phosphate (KNaMg2(PO4)2·14H2O) with a particle size distribution between 5 and 100 μm, which was then used for later use. The physical sample of this crystalline phosphate is shown in Figure 1, and its XRD test results and scanning electron microscope microstructure are shown in Figures 2 and 3, respectively.

[0042] (2) Take the following raw materials in the following proportions: 35 parts by weight of calcined magnesium oxide powder, 18 parts by weight of potassium dihydrogen phosphate powder, 4 parts by weight of borax, 0.025 parts by weight of crystalline phosphate in this embodiment, 36 parts by weight of fine aggregate, and 11 parts by weight of mixing water; wherein the fine aggregate is river sand with a fineness of 10-20 mesh. Add the above raw materials to a planetary mixer and stir for 2 minutes to obtain the potassium magnesium phosphate cement-based material.

[0043] Performance Testing: The potassium magnesium phosphate cement-based material of this embodiment was poured into a mold, hardened for 5 hours, demolded, and then immersed in a 3.5 wt.% NaCl solution for 90 days to obtain specimens. The compressive strength and flexural strength of the specimens were then tested according to the "Test Method for Strength of Cement Mortar (ISO Method)" (GBT 17671-2021), with results of 34.6 MPa and 5.7 MPa, respectively. Additionally, the chloride ion migration coefficient of the potassium magnesium phosphate cement-based material of this embodiment was measured to be 7.2 × 10⁻⁶. - 12 m 2 / s.

[0044] Example 2: Preparation of a potassium magnesium phosphate cement-based material with high density and high salt erosion resistance, comprising the following steps: (1) according to K + Na + Mg 2+ :PO4 3- A molar ratio of 1:1:2:2, with K + Source (potassium sulfate), Na + Source (sodium sulfate), Mg 2+ Source (magnesium sulfate), PO4 3- Potassium dihydrogen phosphate (KH2PO4) was added to water and stirred until homogeneous to obtain a mixture. Sodium hydroxide solution was then added to adjust the pH of the mixture to 9, and the mixture was heated to 40°C for 6 hours under stirring. After the reaction was complete, the solid product was separated, washed with water, and dried at 45°C for 40 hours. The product was then ground to obtain crystalline phosphate (KNaMg2(PO4)2·14H2O) with a particle size distribution between 5 and 100 μm, which was then used for later use. The physical sample of this crystalline phosphate is shown in Figure 4, and its microstructure under a scanning electron microscope is shown in Figure 5.

[0045] (2) Add hydrotalcite powder (Mg6Al2(OH)) 16The product was heated to 350℃ and calcined for 3 hours using CO3·4H2O, then cooled to room temperature. The calcined product was added to a mixed solution containing boric acid (borax) and phosphate (dipotassium hydrogen phosphate) in a ratio of 1g:20mL, with the boric acid concentration at 0.2mol / L and the phosphate concentration at 0.3mol / L. The mixture was then stirred at 25℃ for 8 hours. After reaction, the solid product was filtered out and dried at 60℃ for 12 hours to obtain the modified hydrotalcite-like material (as shown in Figure 6), which was then set aside for later use.

[0046] (3) Take the following raw materials in the following proportions: 30 parts by weight of calcined magnesium oxide powder, 15 parts by weight of potassium dihydrogen phosphate powder, 3 parts by weight of sodium citrate, 0.01 parts by weight of crystalline phosphate in this embodiment, 0.5 parts by weight of modified hydrotalcite in this embodiment, 30 parts by weight of fine aggregate, and 8 parts by weight of mixing water; wherein the fine aggregate is river sand with a fineness of 10-20 mesh. Add the above raw materials to a planetary mixer and stir for 2 minutes to obtain the potassium magnesium phosphate cement-based material.

[0047] Performance testing: The compressive strength, flexural strength, and chloride ion migration coefficient of the potassium magnesium phosphate cement-based material in this embodiment were tested using the same method as in Example 1 above. The results were 52.8 MPa, 8.7 MPa, and 2.8 × 10⁻⁶ MPa, respectively. -12 m 2 / s.

[0048] Example 3: Preparation of a potassium magnesium phosphate cement-based material with high density and high salt erosion resistance, comprising the following steps: (1) according to K + Na + Mg 2+ :PO4 3- A molar ratio of 1:1:2:2, with K + Source (potassium nitrate), Na + Source (sodium nitrate), Mg 2+ Source (magnesium nitrate), PO4 3- The source (dipotassium hydrogen phosphate) was added to water and stirred until homogeneous to obtain a mixture. Then, ammonia water was added to adjust the pH of the mixture to 11, and the mixture was heated to 60°C for 5 hours under stirring. After completion, the solid product was separated, washed with water, and dried at 45°C for 42 hours. The product was then ground to obtain crystalline phosphate (KNaMg2(PO4)2·14H2O) with a particle size distribution between 5 and 100 μm, as shown in Figure 7, for later use.

[0049] (2) Take 200-mesh hydrotalcite powder (Mg6Al2(OH)2) 16The modified hydrotalcite (CO3·4H2O) was heated to 450℃ and calcined for 0.5 hours, then cooled to room temperature. The calcined product was added to a mixed solution containing boric acid (boric acid) and phosphate (sodium hexametaphosphate) in a ratio of 1 g:30 mL, with the concentration of boric acid (0.02 mol / L) and phosphate (0.05 mol / L) in the mixed solution. The mixture was then heated to 60℃ and stirred for 0.5 hours. After the reaction was completed, the solid product was filtered out and dried at 40℃ for 48 hours to obtain the modified hydrotalcite-like material (as shown in Figure 8) for later use.

[0050] (3) Take the following raw materials in the following proportions: 40 parts by weight of calcined magnesium oxide powder, 20 parts by weight of potassium dihydrogen phosphate powder, 5 parts by weight of sodium citrate, 0.03 parts by weight of crystalline phosphate in this embodiment, 2 parts by weight of modified hydrotalcite in this embodiment, 40 parts by weight of fine aggregate, and 13 parts by weight of mixing water; wherein the fine aggregate is river sand with a fineness of 10-20 mesh. Add the above raw materials to a planetary mixer and stir for 2 minutes to obtain the potassium magnesium phosphate cement-based material.

[0051] Performance testing: The compressive strength, flexural strength, and chloride ion migration coefficient of the potassium magnesium phosphate cement-based material in this embodiment were tested using the same method as in Example 1 above. The results were 56.0 MPa, 9.4 MPa, and 2.1 × 10⁻⁶ MPa, respectively. -12 m 2 / s.

[0052] Example 4: Preparation of a potassium magnesium phosphate cement-based material, comprising the following steps: taking the following raw materials in the following proportions: 35 parts by weight of recalcined magnesium oxide powder, 18 parts by weight of potassium dihydrogen phosphate powder, 4 parts by weight of borax, 36 parts by weight of fine aggregate, and 11 parts by weight of mixing water; wherein the fine aggregate is river sand with a fineness of 10-20 mesh. Adding the above raw materials to a planetary mixer and stirring for 2 minutes yields the potassium magnesium phosphate cement-based material.

[0053] Performance testing: The compressive strength, flexural strength, and chloride ion migration coefficient of the potassium magnesium phosphate cement-based material in this embodiment were tested using the same method as in Example 1 above. The results were 31.3 MPa, 5.1 MPa, and 9.3 × 10⁻⁶ MPa, respectively. -12 m 2 / s.

[0054] Example 5: Preparation of a potassium magnesium phosphate cement-based material with high density and high resistance to salt erosion, comprising the following steps: taking the following raw materials in the following proportions: 30 parts by weight of recalcined magnesium oxide powder, 15 parts by weight of potassium dihydrogen phosphate powder, 3 parts by weight of sodium citrate, 0.01 parts by weight of the crystalline phosphate from Example 2 above, and 200-mesh hydrotalcite powder (Mg6Al2(OH)). 16The following ingredients are added to a planetary mixer and stirred for 2 minutes to obtain the potassium magnesium phosphate cement-based material: 0.5 parts by weight of CO3·4H2O (as shown in Figure 9), 30 parts by weight of fine aggregate, and 8 parts by weight of mixing water; wherein the fine aggregate is river sand with a fineness of 10-20 mesh.

[0055] Performance testing: The compressive strength, flexural strength, and chloride ion migration coefficient of the potassium magnesium phosphate cement-based material in this embodiment were tested using the same method as in Example 1 above. The results were 38.3 MPa, 6.3 MPa, and 6.1 × 10⁻⁶, respectively. -12 m 2 / s.

[0056] Example 6: Preparation of a potassium magnesium phosphate cement-based material with high density and high salt erosion resistance, comprising the following steps: (1) preparing hydrotalcite powder (Mg6Al2(OH)2) 16 The product was heated to 350℃ and calcined for 3 hours using CO3·4H2O, then cooled to room temperature. The calcined product was added to a phosphate (dipotassium hydrogen phosphate) solution at a ratio of 1 g: 20 mL, with the phosphate concentration in the solution being 0.3 mol / L. The mixture was then stirred at 25℃ for 8 hours. After the reaction was complete, the solid product was filtered out and dried at 60℃ for 12 hours to obtain the modified hydrotalcite-like material (as shown in Figure 10), which was then set aside for later use.

[0057] (2) Take the following raw materials in the following proportions: 30 parts by weight of calcined magnesium oxide powder, 15 parts by weight of potassium dihydrogen phosphate powder, 3 parts by weight of sodium citrate, 0.01 parts by weight of the crystalline phosphate from Example 2 above, 0.5 parts by weight of the modified hydrotalcite of this example, 30 parts by weight of fine aggregate, and 8 parts by weight of mixing water; wherein the fine aggregate is river sand with a fineness of 10-20 mesh. Add the above raw materials to a planetary mixer and stir for 2 minutes to obtain the potassium magnesium phosphate cement-based material.

[0058] Performance testing: The compressive strength, flexural strength, and chloride ion migration coefficient of the potassium magnesium phosphate cement-based material in this embodiment were tested using the same method as in Example 1 above. The results were 45.2 MPa, 7.4 MPa, and 4.3 × 10⁻⁶ MPa, respectively. -12 m 2 / s.

[0059] Example 7: Preparation of a potassium magnesium phosphate cement-based material with high density and high salt erosion resistance, comprising the following steps: (1) 200 mesh hydrotalcite powder (Mg6Al2(OH) 16The modified hydrotalcite (CO3·4H2O) was heated to 450℃ and calcined for 0.5 hours, then cooled to room temperature. The calcined product was added to a boric acid (borax) solution at a ratio of 1 g: 30 mL, with a boric acid concentration of 0.02 mol / L. The mixture was then heated to 60℃ and stirred for 0.5 hours. After the reaction was complete, the solid product was filtered out and dried at 40℃ for 48 hours to obtain the modified hydrotalcite-like material (as shown in Figure 11), which was then set aside for later use.

[0060] (2) Take the following raw materials in the following proportions: 40 parts by weight of calcined magnesium oxide powder, 20 parts by weight of potassium dihydrogen phosphate powder, 5 parts by weight of sodium citrate, 0.03 parts by weight of crystalline phosphate from Example 3 above, 2 parts by weight of modified hydrotalcite from this example, 40 parts by weight of fine aggregate, and 13 parts by weight of mixing water; wherein the fine aggregate is river sand with a fineness of 10-20 mesh. Add the above raw materials to a planetary mixer and stir for 2 minutes to obtain the potassium magnesium phosphate cement-based material.

[0061] Performance testing: The compressive strength, flexural strength, and chloride ion migration coefficient of the potassium magnesium phosphate cement-based material in this embodiment were tested using the same method as in Example 1 above. The results were 47.8 MPa, 7.9 MPa, and 3.6 × 10⁻⁶ MPa, respectively. -12 m 2 / s.

[0062] Example 8: Preparation of a potassium magnesium phosphate cement-based material with high density and high salt erosion resistance, comprising the following steps: (1) 200 mesh hydrotalcite powder (Mg6Al2(OH) 16 CO3·4H2O was added to a mixed solution containing boric acid (borax) and phosphate (sodium hexametaphosphate) in a ratio of 1g:30mL, with the concentration of boric acid at 0.02mol / L and the concentration of phosphate at 0.05mol / L. The mixture was then heated to 60℃ and stirred for 0.5 hours. After the reaction was complete, the solid product was filtered out and dried at 40℃ for 48 hours to obtain the modified hydrotalcite-like substance (as shown in Figure 12), for later use.

[0063] (2) Take the following raw materials in the following proportions: 40 parts by weight of calcined magnesium oxide powder, 20 parts by weight of potassium dihydrogen phosphate powder, 5 parts by weight of sodium citrate, 0.03 parts by weight of crystalline phosphate from Example 3 above, 2 parts by weight of modified hydrotalcite from this example, 40 parts by weight of fine aggregate, and 13 parts by weight of mixing water; wherein the fine aggregate is river sand with a fineness of 10-20 mesh. Add the above raw materials to a planetary mixer and stir for 2 minutes to obtain the potassium magnesium phosphate cement-based material.

[0064] Performance testing: The compressive strength, flexural strength, and chloride ion migration coefficient of the potassium magnesium phosphate cement-based material in this embodiment were tested using the same method as in Example 1 above. The results were 41.2 MPa, 6.8 MPa, and 5.4 × 10⁻⁶ MPa, respectively. -12 m 2 / s.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention.

Claims

1. A potassium magnesium phosphate cement-based material with high density and high resistance to salt erosion, characterized in that, The composition includes the following components in the following proportions: 30-40 parts by weight of calcined magnesium oxide, 15-20 parts by weight of potassium dihydrogen phosphate, 3-5 parts by weight of retarder, 0.01-0.03 parts by weight of crystalline phosphate, 30-40 parts by weight of fine aggregate, and 8-13 parts by weight of mixing water; wherein the molecular formula of the crystalline phosphate is KNaMg2(PO4)2·14H2O.

2. The potassium magnesium phosphate cement-based material with high density and high salt erosion resistance according to claim 1, characterized in that, The retarder includes at least one of borax, sodium citrate, sodium hexametaphosphate, and sodium tripolyphosphate.

3. The potassium magnesium phosphate cement-based material with high density and high salt erosion resistance according to claim 1, characterized in that, The crystalline phosphate was prepared according to the following method: [following K...] + Na + Mg 2+ :PO4 3- A molar ratio of 1:1:2:2, with K + Source, Na + Source, Mg 2+ Source, PO4 3- The source is added to water and mixed well. The resulting mixture is then adjusted to alkaline conditions and heated under stirring. After the reaction is complete, the solid product is separated, washed, and dried to obtain the crystalline phosphate.

4. The potassium magnesium phosphate cement-based material with high density and high salt erosion resistance according to claim 3, characterized in that, The K + The source includes at least one of potassium chloride, potassium sulfate, and potassium nitrate; or, the Na... + The source includes at least one of sodium chloride, sodium sulfate, and sodium nitrate; or, the Mg... 2+ The source includes at least one of magnesium chloride, magnesium sulfate, and magnesium nitrate; or, the PO4... 3- The source includes at least one of potassium dihydrogen phosphate and dipotassium hydrogen phosphate; or, the pH of the mixture is adjusted to 9-11.

5. The potassium magnesium phosphate cement-based material with high density and high salt erosion resistance according to claim 3, characterized in that, The heating reaction is carried out at a temperature of 40-60°C for 5-6 hours; or the drying is carried out at a temperature of 40-45°C for 40-48 hours; or the crystalline phosphate has a particle size of 5-100 μm.

6. The potassium magnesium phosphate cement-based material with high density and high salt erosion resistance according to any one of claims 1-5, characterized in that, The potassium magnesium phosphate cement-based material also includes 0.5 to 2 parts by weight of modified hydrotalcite, which is formed by the intercalation of borate ions and phosphate ions between the hydrotalcite layers.

7. The potassium magnesium phosphate cement-based material with high density and high salt erosion resistance according to claim 6, characterized in that, The modified hydrotalcite is prepared by the following method: carbonate-type Mg-Al hydrotalcite is calcined to remove its interlayer anions, and then the calcined product is added to a mixed solution containing boric acid and phosphate and stirred to react. After the reaction is completed, the solid product is separated and dried to obtain the modified hydrotalcite.

8. The potassium magnesium phosphate cement-based material with high density and high salt erosion resistance according to claim 7, characterized in that, The calcination temperature is 350~450℃ and the time is 0.5~3 hours; or, the ratio of carbonate-type Mg-Al hydrotalcite to the mixed solution is 1g:20~30mL, and the concentration of boric acid in the mixed solution is 0.02~0.2mol / L, and the concentration of phosphate is 0.05~0.3mol / L.

9. The potassium magnesium phosphate cement-based material with high density and high salt erosion resistance according to claim 7, characterized in that, The boric acid substance includes at least one of borax and boric acid; or, the phosphate includes at least one of dipotassium hydrogen phosphate, sodium hexametaphosphate, and sodium tripolyphosphate; or, the stirring reaction temperature is 25~60℃ and the time is 0.5~8 hours; or, the drying temperature is 40~60℃ and the time is 12~48 hours.

10. The application of the potassium magnesium phosphate cement-based material with high density and high salt erosion resistance as described in any one of claims 1-9 in the fields of roads, bridges, water conservancy or marine engineering.

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