A water-resistant and freeze-resistant magnesium phosphate cement repair mortar and its preparation method

Abstract

This invention belongs to the field of building repair materials technology and provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar and its preparation method. The raw materials of the water-resistant and freeze-resistant magnesium phosphate cement repair mortar include: modified magnesium oxide, potassium dihydrogen phosphate, admixture, retarder, fine aggregate, water-reducing agent and water. The preparation method includes: (1) dry mixing: the modified magnesium oxide, potassium dihydrogen phosphate, admixture, fine aggregate and retarder are dry mixed to obtain a dry material system; (2) wet mixing and molding: half the mass of water is added to the dry material system, and after stirring, the remaining mass of water and water-reducing agent are added, and stirring is continued to obtain the water-resistant and freeze-resistant magnesium phosphate cement repair mortar. The repair mortar has excellent water resistance, freeze resistance and mechanical properties. The preparation method has a simplified preparation process, low production cost, and can realize the high-value utilization of solid waste, meeting the needs of rapid repair of building projects in harsh environments such as dampness and cold.

Description

Technical Field

[0001] This invention belongs to the field of building repair materials technology, specifically relating to a water-resistant and freeze-resistant magnesium phosphate cement repair mortar and its preparation method. Background Technology

[0002] Magnesium phosphate cement repair mortar, as a special building repair material, has outstanding advantages such as rapid hardening and early strength, high bonding strength, good micro-expansion, and low-temperature construction. It is widely used in various concrete structure defect repair projects such as roads, bridges, tunnels, industrial floors, and ancient building restoration. It can quickly restore the structural function, shorten the construction period, and reduce maintenance costs.

[0003] However, in practical engineering applications, especially in harsh environments such as open-air, humid, cold, or repeated freeze-thaw cycles, existing magnesium phosphate cement repair mortar still has some obvious problems that limit its applicability and service life, becoming an obstacle to its large-scale industrial promotion. These problems are also interconnected and mutually influential, making it difficult to achieve a breakthrough through a single improvement.

[0004] First, insufficient water resistance is the most critical shortcoming of existing products. The main cementitious component of magnesium phosphate cement is the hydration product generated by the reaction of magnesium oxide and phosphate. This hydration product itself has a certain degree of hydrophilicity and easily forms capillary pores inside. Water can easily penetrate into the mortar through the pores, causing the hydration product to decompose and soften, thereby destroying the internal structure of the mortar and causing a significant decrease in interfacial bonding strength. After long-term immersion in water, the mortar strength decreases significantly, and the strength retention rate is generally low. It often cannot meet the long-term use requirements of humid environments, underwater repairs, or rainy areas, and is prone to failure problems such as repair layer peeling and cracking.

[0005] Secondly, the frost resistance is poor. During the preparation process of existing mortars, the cementitious reaction rate is difficult to control precisely, which easily leads to the formation of a large number of interconnected and unevenly sized pores. These pores will be filled with water in low-temperature environments. When the temperature drops below freezing point repeatedly, the water in the pores will freeze and expand, generating large volume stress. Under repeated action, the internal structure of the mortar will be gradually destroyed, leading to cracking, powdering, and peeling. Ultimately, it will lose its repair function and be difficult to adapt to the engineering needs of cold northern regions and high-altitude freeze-thaw regions, significantly shortening the service life of the repair structure.

[0006] Furthermore, existing repair mortars often present a contradiction: "improving water resistance at the expense of frost resistance" and "enhancing mechanical properties at the expense of water resistance and frost resistance." If the density is simply increased to improve water resistance, the internal pore structure of the mortar will become too dense, and the expansion stress during freeze-thaw cycles cannot be released, resulting in a decrease in frost resistance. If the pore structure is simply optimized to improve frost resistance, the density of the mortar will be reduced, leading to damage to both water resistance and mechanical properties. It is difficult to achieve a simultaneous improvement in overall performance.

[0007] In addition, the utilization rate of raw materials is low, and the functions of some raw materials are not fully utilized. On the one hand, ordinary magnesium oxide has high activity and reacts with phosphate too quickly, which not only affects the workability of construction, but also leads to insufficient hydration reaction and waste of raw materials. On the other hand, existing products mostly use high-purity raw materials, which not only increases production costs, but also makes it difficult to maximize the utilization of raw material functions. At the same time, existing products have obvious shortcomings in balancing water resistance and frost resistance with workability and economy. Either the water resistance and frost resistance meet the standards but the construction is difficult and the cost is high, or the cost is low and the construction is convenient but the performance cannot meet the needs of harsh environments, and cannot fully adapt to the diverse repair needs in different harsh environments.

[0008] Therefore, developing a water-resistant and freeze-resistant magnesium phosphate cement repair mortar and its preparation method that can simultaneously improve water resistance, freeze resistance and mechanical properties, while taking into account workability and economy, has a simple process, can be industrialized, and can be adapted to harsh environments such as dampness and cold has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] In view of the above-mentioned shortcomings in the prior art, the first objective of the present invention is to provide a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which has excellent water resistance, freeze resistance and mechanical properties.

[0010] To address the aforementioned shortcomings of the existing technology, a second objective of this invention is to provide a method for preparing water-resistant and freeze-resistant magnesium phosphate cement repair mortar. This preparation method simplifies the process, reduces production costs, and enables the high-value utilization of solid waste, meeting the needs for rapid repair of building projects in harsh environments such as dampness and cold.

[0011] To achieve the above objectives, the solution adopted by the present invention is as follows:

[0012] A water-resistant and freeze-resistant magnesium phosphate cement repair mortar, the raw materials of which, by weight, include: 100 parts modified magnesium oxide, 60-70 parts potassium dihydrogen phosphate, 30-45 parts admixture, 4-6 parts retarder, 150-180 parts fine aggregate, 0.8-1.2 parts water-reducing agent, and 22-26 parts water; the modified magnesium oxide is obtained by sequentially coating magnesium oxide with a silane layer and a polyurethane layer; the mass ratio of magnesium oxide, silane layer and polyurethane layer is 1:0.024:0.016.

[0013] Furthermore, in a preferred embodiment of this application, the admixture includes magnesium slag powder, ceramic powder, and metakaolin in a mass ratio of 5:3:2.

[0014] Furthermore, in a preferred embodiment of this application, the retarder comprises sodium citrate, aminotrimethylene phosphonic acid, and nano-calcium carbonate modified with a silane coupling agent in a mass ratio of 4:3:3.

[0015] Further, in a preferred embodiment of this application, the preparation of modified magnesium oxide includes: placing recalcined magnesium oxide in an oven and drying it at 100-110℃ for 2-3 hours, then cooling it to room temperature for later use; placing the dried magnesium oxide in a high-speed mixer and adding a methyltrimethoxysilane solution dropwise at a speed of 800-1000 r / min and a rate of 1-2 mL / min; the methyltrimethoxysilane solution includes silane: anhydrous ethanol: water in a mass ratio of 1:4:1; after the addition is complete, stirring is continued for 30-40 minutes to obtain a mixed system; adding a polyurethane emulsion with a solid content of 40% to the mixed system, maintaining a speed of 800-1000 r / min, and continuing to stir for 20-30 minutes to obtain coated magnesium oxide; placing the coated magnesium oxide in a forced-air drying oven and drying it at 75-85℃ for 4-5 hours, then cooling it to room temperature and passing it through a 100-mesh sieve to obtain modified magnesium oxide.

[0016] Furthermore, in a preferred embodiment of this application, the preparation of the admixture includes: placing magnesium slag powder, ceramic powder, and metakaolin into a high-speed mixer, adjusting the speed to 600-800 r / min, stirring for 15-20 min, mixing evenly, and then passing through an 80-mesh sieve to obtain the admixture.

[0017] Furthermore, in a preferred embodiment of this application, the magnesium slag powder needs to be activated before mixing: the industrial magnesium slag is crushed, ball-milled to a particle size of less than or equal to 50 μm, placed in a muffle furnace, activated at 780-820℃ for 2 hours, and then cooled to room temperature for later use.

[0018] Furthermore, in a preferred embodiment of this application, the ceramic powder needs to be pretreated before mixing: the waste building ceramics are crushed, ball-milled to a particle size of less than or equal to 45 μm, placed in an oven, dried at 100-110°C for 2 hours, and cooled to room temperature for later use.

[0019] Further, in a preferred embodiment of this application, the preparation of the retarder includes: placing nano-calcium carbonate with a particle size of 50-100 nm into a high-speed mixer, adding 0.5% of its own mass of silane coupling agent KH-550, adjusting the speed to 1200-1500 r / min, and stirring for 10-15 min to obtain modified nano-calcium carbonate; placing sodium citrate, aminotrimethylene phosphonic acid, and modified nano-calcium carbonate into a mixer, adjusting the speed to 400-600 r / min, and stirring for 10 min to obtain the retarder.

[0020] A method for preparing the above-mentioned water-resistant and freeze-resistant magnesium phosphate cement repair mortar includes: (1) dry mixing: modified magnesium oxide, potassium dihydrogen phosphate, admixture, fine aggregate and retarder are put into a forced mixer and dry mixed to obtain a dry material system; (2) wet mixing and molding: half the mass of water is added to the dry material system, and the mixture is stirred for 2-3 minutes. Then the remaining mass of water and water-reducing agent are added, and the rotation speed is maintained at 300-400 r / min. The mixture is stirred for 3-4 minutes to obtain water-resistant and freeze-resistant magnesium phosphate cement repair mortar.

[0021] Furthermore, in a preferred embodiment of this application, in step (1), the mixture is dry-mixed for 3-5 minutes at a rotation speed of 300-400 r / min.

[0022] The beneficial effects of the water-resistant and freeze-resistant magnesium phosphate cement repair mortar and its preparation method provided by this invention are:

[0023] (1) The water-resistant and freeze-resistant magnesium phosphate cement repair mortar provided by this invention forms a complete synergistic system among its raw material components. In particular, through the synergistic cooperation between the three core components—modified magnesium oxide, admixtures, and retarder—and other auxiliary components, the functions of each component are complementary and their effects are superimposed, without functional conflicts. This simultaneously solves the technical problems in the prior art, such as insufficient water resistance, poor freeze-resistant performance, and the contradiction between mechanical properties and water resistance and freeze-resistant performance. Theoretical verification shows that the mortar of this invention has significantly improved long-term immersion strength retention rate, freeze-resistant grade, 28-day compressive strength, and 28-day bond strength, while significantly reducing 28-day shrinkage rate and acid corrosion resistance strength loss, demonstrating excellent comprehensive performance.

[0024] (2) The preparation method of the water-resistant and freeze-resistant magnesium phosphate cement repair mortar provided by the present invention is simple, requires no complicated pretreatment, has a high solid waste utilization rate, low raw material cost, no ammonia release, is green and environmentally friendly, can be industrialized on a large scale, and is suitable for building repair needs in various harsh environments such as dampness and cold, and is extremely practical. Attached Figure Description

[0025] Figure 1 This is a production process flow chart provided in Embodiment 1 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] The following is a detailed description of a water-resistant and freeze-resistant magnesium phosphate cement repair mortar and its preparation method provided by an embodiment of the present invention.

[0028] This invention provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, the raw materials of which, by weight, include: 100 parts modified magnesium oxide, 60-70 parts potassium dihydrogen phosphate, 30-45 parts admixture, 4-6 parts retarder, 150-180 parts fine aggregate, 0.8-1.2 parts water-reducing agent, and 22-26 parts water. In this application, the fine aggregate and water-reducing agent can be common varieties in this technical field.

[0029] The modified magnesium oxide is prepared by sequentially coating magnesium oxide with a silane layer and a polyurethane layer; the mass ratio of magnesium oxide, silane layer and polyurethane layer is 1:0.024:0.016. Specifically, the preparation of modified magnesium oxide includes: placing recalcined magnesium oxide in an oven and drying it at 100-110℃ for 2-3 hours, then cooling it to room temperature for later use; placing the dried magnesium oxide in a high-speed mixer and adding a methyltrimethoxysilane solution dropwise at a speed of 800-1000 r / min and a rate of 1-2 mL / min; the methyltrimethoxysilane solution includes silane: anhydrous ethanol: water in a mass ratio of 1:4:1; after the addition is complete, continue stirring for 30-40 minutes to obtain a mixed system; add a polyurethane emulsion with a solid content of 40% to the mixed system, maintain a speed of 800-1000 r / min, and continue stirring for 20-30 minutes to obtain coated magnesium oxide; placing the coated magnesium oxide in a forced-air drying oven and drying it at 75-85℃ for 4-5 hours, then cooling it to room temperature and passing it through a 100-mesh sieve to obtain modified magnesium oxide.

[0030] In this application, the modified magnesium oxide prepared under the aforementioned specific technical conditions serves as the core raw material for cementitious mortar. Its surface is coated with a double-layer gradient layer of inorganic silane and organic polyurethane, which can form a synergistic reaction system with potassium dihydrogen phosphate. This system not only inhibits water intrusion through the dense barrier effect of the inorganic silane layer, preventing the decomposition of hydration products generated by the reaction of potassium dihydrogen phosphate and magnesium oxide by water, thus improving the water resistance of the mortar, but also regulates the reaction rate between magnesium oxide and potassium dihydrogen phosphate through the flexible buffering effect of the organic polyurethane layer, preventing excessively vigorous reactions that could lead to excessive porosity within the mortar. Simultaneously, potassium dihydrogen phosphate provides stable phosphate ions to magnesium oxide, promoting a full hydration reaction and generating structurally stable hydration products. This synergistic effect with the double-layer coating layer optimizes the internal structure of the mortar, reduces interconnected pores, and improves both the mechanical properties and freeze-thaw resistance of the mortar, solving the core problem of insufficient water and freeze-thaw resistance in existing cementitious mortar systems.

[0031] The admixture comprises magnesium slag powder, ceramic powder, and metakaolin in a mass ratio of 5:3:2. Specifically, the preparation of the admixture includes: Activated magnesium slag powder: Industrial magnesium slag is crushed, ball-milled to a particle size of ≤50μm, placed in a muffle furnace, activated at 780-820℃ for 2 hours, and cooled to room temperature for later use. Pretreated ceramic powder: Waste building ceramics are crushed, ball-milled to a particle size of ≤45μm, placed in an oven, dried at 100-110℃ for 2 hours, and cooled to room temperature for later use. Then, the activated magnesium slag powder, treated ceramic powder, and metakaolin are placed in a high-speed mixer at a mass ratio of 5:3:2, the speed is adjusted to 600-800 r / min, and stirred for 15-20 minutes. After uniform mixing, the mixture is passed through an 80-mesh sieve to obtain the admixture.

[0032] The admixture prepared under the specific technical conditions described above can form a synergistic reinforcing system with modified magnesium oxide and potassium dihydrogen phosphate. Specifically, the activated magnesium slag powder can supplement cementitious activity, undergo a secondary hydration reaction with potassium dihydrogen phosphate to generate an additional hydration strength phase, which synergistically intertwines with the hydration products of the composite-coated modified magnesium oxide to improve mortar density. The fine particle size of the waste ceramic powder can fill the capillary pores inside the mortar, reducing porosity and cutting off pore connectivity. It synergistically optimizes the mortar pore structure with the magnesium slag powder, reducing water intrusion and expansion damage during freeze-thaw cycles, enhancing freeze-thaw resistance, and simultaneously improving the mortar's water resistance. The pozzolanic activity of metakaolin can undergo a secondary reaction with the hydration products to generate a dense CSH gel, filling interfacial gaps, improving the interfacial bonding force between the cementitious matrix and fine aggregates. Synergistically working with the coating layer of modified magnesium oxide, it further blocks water penetration, while simultaneously enhancing the mortar's mechanical properties and freeze-thaw durability. The admixture not only realizes the high-value utilization of solid waste, but also works synergistically with the cementitious matrix to improve the water resistance, freeze resistance and mechanical properties of mortar, while reducing the amount of high-purity magnesium oxide used, reducing production costs, and simultaneously achieving environmental protection and performance.

[0033] The retarder comprises sodium citrate, aminotrimethylene phosphonic acid, and silane coupling agent-modified nano-calcium carbonate in a mass ratio of 4:3:3. Specifically, the preparation of the retarder includes: placing nano-calcium carbonate with a particle size of 50-100 nm into a high-speed mixer, adding 0.5% of its own mass of silane coupling agent KH-550, adjusting the speed to 1200-1500 r / min, and stirring for 10-15 min to obtain modified nano-calcium carbonate; placing sodium citrate, aminotrimethylene phosphonic acid, and modified nano-calcium carbonate into a mixer, adjusting the speed to 400-600 r / min, and stirring for 10 min to obtain the retarder.

[0034] The retarder prepared under the specific technical conditions described above can further form a synergistic regulatory system with modified magnesium oxide and admixtures. Specifically, sodium citrate and aminotrimethylenephosphonic acid synergistically complex the active sites on the surface of modified magnesium oxide, slowly releasing active substances. In synergy with the polyurethane layer, the setting time of the mortar is regulated to ensure smooth construction while avoiding the negative impact of excessive retarder on mortar performance. After modification with a silane coupling agent, the modified nano-calcium carbonate, together with the silane layer of modified magnesium oxide and the CSH gel generated by metakaolin, acts as a crystal nucleus to promote the directional growth of hydration products, optimize the structure of hydration products, and fill pores in synergy with magnesium slag powder and ceramic powder, thereby improving the density of the mortar. At the same time, the modified nano-calcium carbonate, together with the admixtures, reduces the internal porosity of the mortar and enhances its freeze-thaw resistance. Together with the coating layer of modified magnesium oxide, it blocks moisture and improves water resistance. The complexation effect of sodium citrate and aminotrimethylene phosphonic acid can also inhibit the decomposition of hydration products, further enhancing the water resistance and freeze-thaw stability of the mortar. In synergy with the water-reducing agent, it can reduce water consumption and lower the water-cement ratio, further optimizing the mortar pore structure and improving overall performance.

[0035] The present invention also provides a method for preparing water-resistant and freeze-resistant magnesium phosphate cement repair mortar, comprising (1) dry mixing: placing modified magnesium oxide, potassium dihydrogen phosphate, admixture, fine aggregate and retarder into a forced mixer at a speed of 300-400 r / min and dry mixing for 3-5 min to obtain a dry material system; (2) wet mixing and molding: adding half the mass of water to the dry material system and stirring for 2-3 min, then adding the remaining mass of water and water-reducing agent, maintaining a speed of 300-400 r / min and continuing to stir for 3-4 min to obtain water-resistant and freeze-resistant magnesium phosphate cement repair mortar.

[0036] The above preparation method is simple, requires no complex pretreatment, has a high solid waste utilization rate, low raw material cost, releases no ammonia, is green and environmentally friendly, and can be industrialized for large-scale production.

[0037] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0038] Example 1

[0039] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, the raw materials of which include, by weight, 100 parts modified magnesium oxide, 65 parts potassium dihydrogen phosphate, 38 parts fly ash, 5 parts sodium citrate, 160 parts quartz sand, 1 part polycarboxylate-based high-efficiency water-reducing agent (PC-2000), and 24 parts water.

[0040] Modified magnesium oxide is prepared by sequentially coating magnesium oxide with a silane layer and a polyurethane layer; the mass ratio of the magnesium oxide, the silane layer, and the polyurethane layer is 1:0.024:0.016. The preparation of modified magnesium oxide includes: placing recalcined magnesium oxide in an oven and drying it at 105°C for 2.5 hours, then cooling it to room temperature; placing the dried magnesium oxide in a high-speed mixer and adding a methyltrimethoxysilane solution dropwise at a speed of 900 r / min and a rate of 1.5 mL / min; the methyltrimethoxysilane solution comprises silane:anhydrous ethanol:water in a mass ratio of 1:4:1; after the addition is complete, stirring is continued for 35 minutes to obtain a mixed system; adding a polyurethane emulsion with a solid content of 40% to the mixed system, maintaining a speed of 900 r / min, and continuing stirring for 25 minutes to obtain coated magnesium oxide; placing the coated magnesium oxide in a forced-air drying oven and drying it at 80°C for 4.5 hours, then cooling it to room temperature and passing it through a 100-mesh sieve to obtain modified magnesium oxide.

[0041] This embodiment also provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, including (1) dry mixing: put modified magnesium oxide, potassium dihydrogen phosphate, admixture, fine aggregate and retarder into a forced mixer at a speed of 350 r / min and dry mix for 4 min to obtain a dry material system; (2) wet mixing and molding: add half the mass of water to the dry material system, stir for 3 min, then add the remaining mass of water and water-reducing agent, keep the speed at 350 r / min and continue stirring for 3 min to obtain water-resistant and freeze-resistant magnesium phosphate cement repair mortar.

[0042] Example 2

[0043] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 1 in that its raw materials, by weight, include: 100 parts modified magnesium oxide, 60 parts potassium dihydrogen phosphate, 45 parts fly ash, 4 parts sodium citrate, 180 parts quartz sand, 0.8 parts polycarboxylate-based high-efficiency water-reducing agent (PC-2000), and 26 parts water.

[0044] Modified magnesium oxide is prepared by sequentially coating magnesium oxide with a silane layer and a polyurethane layer; the mass ratio of the magnesium oxide, the silane layer, and the polyurethane layer is 1:0.024:0.016. The preparation of modified magnesium oxide includes: placing recalcined magnesium oxide in an oven and drying it at 100°C for 3 hours, then cooling it to room temperature; placing the dried magnesium oxide in a high-speed mixer and adding a methyltrimethoxysilane solution dropwise at a speed of 800 r / min and a rate of 2 mL / min; the methyltrimethoxysilane solution comprises silane:anhydrous ethanol:water in a mass ratio of 1:4:1; after the addition is complete, stirring is continued for 30 minutes to obtain a mixed system; a polyurethane emulsion with a solid content of 40% is added to the mixed system, and stirring is continued for 20 minutes at a speed of 1000 r / min to obtain coated magnesium oxide; the coated magnesium oxide is placed in a forced-air drying oven and dried at 85°C for 4 hours, then cooled to room temperature and passed through a 100-mesh sieve to obtain modified magnesium oxide.

[0045] Example 3

[0046] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 1 in that its raw materials, by weight, include: 100 parts modified magnesium oxide, 70 parts potassium dihydrogen phosphate, 30 parts fly ash, 6 parts sodium citrate, 150 parts quartz sand, 1.2 parts polycarboxylate-based high-efficiency water-reducing agent (PC-2000), and 22 parts water.

[0047] Modified magnesium oxide is prepared by sequentially coating magnesium oxide with a silane layer and a polyurethane layer; the mass ratio of the magnesium oxide, the silane layer, and the polyurethane layer is 1:0.024:0.016. The preparation of modified magnesium oxide includes: placing recalcined magnesium oxide in an oven and drying it at 110°C for 2 hours, then cooling it to room temperature; placing the dried magnesium oxide in a high-speed mixer and adding a methyltrimethoxysilane solution dropwise at a speed of 1000 r / min and a rate of 1 mL / min; the methyltrimethoxysilane solution comprises silane:anhydrous ethanol:water in a mass ratio of 1:4:1; after the addition is complete, stirring is continued for 40 minutes to obtain a mixed system; a polyurethane emulsion with a solid content of 40% is added to the mixed system, and stirring is continued for 30 minutes at a speed of 800 r / min to obtain coated magnesium oxide; the coated magnesium oxide is placed in a forced-air drying oven and dried at 75°C for 5 hours, then cooled to room temperature and passed through a 100-mesh sieve to obtain modified magnesium oxide.

[0048] Example 4

[0049] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 1 in that its raw materials, by weight, include: 100 parts modified magnesium oxide, 65 parts potassium dihydrogen phosphate, 38 parts admixture, 5 parts sodium citrate, 160 parts quartz sand, 1 part polycarboxylate-based high-efficiency water-reducing agent (PC-2000), and 24 parts water.

[0050] The admixture comprises magnesium slag powder, ceramic powder, and metakaolin in a mass ratio of 5:3:2. The preparation of the admixture includes: activating the magnesium slag powder: industrial magnesium slag is crushed, ball-milled to a particle size of ≤50μm, placed in a muffle furnace, activated at 800℃ for 2 hours, and cooled to room temperature for later use. Pre-treated ceramic powder: waste building ceramics are crushed, ball-milled to a particle size of ≤45μm, placed in an oven, dried at 105℃ for 2 hours, and cooled to room temperature for later use. Next, the activated magnesium slag powder, treated ceramic powder, and metakaolin are placed in a high-speed mixer, the speed is adjusted to 700r / min, and stirred for 18min. After uniform mixing, the mixture is passed through an 80-mesh sieve to obtain the admixture.

[0051] Example 5

[0052] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 4 in that the preparation of the admixture includes: activated magnesium slag powder: industrial magnesium slag is crushed, ball-milled to a particle size of less than or equal to 50 μm, placed in a muffle furnace, activated at 780°C for 2 hours, and cooled to room temperature for later use. Pretreated ceramic powder: waste building ceramics are crushed, ball-milled to a particle size of less than or equal to 45 μm, placed in an oven, dried at 100°C for 2 hours, and cooled to room temperature for later use. Then, the activated magnesium slag powder, the treated ceramic powder, and metakaolin are placed in a high-speed mixer, the speed is adjusted to 600 r / min, and stirred for 20 minutes. After being mixed evenly, the mixture is passed through an 80-mesh sieve to obtain the admixture.

[0053] Example 6

[0054] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 4 in that the admixture includes magnesium slag powder, ceramic powder, and metakaolin in a mass ratio of 5:3:2. The preparation of the admixture includes: activated magnesium slag powder: industrial magnesium slag is crushed, ball-milled to a particle size of less than or equal to 50 μm, placed in a muffle furnace, activated at 820°C for 2 hours, and cooled to room temperature for later use. Pretreated ceramic powder: waste building ceramics are crushed, ball-milled to a particle size of less than or equal to 45 μm, placed in an oven, dried at 110°C for 2 hours, and cooled to room temperature for later use. Then, the activated magnesium slag powder, treated ceramic powder, and metakaolin are placed in a high-speed mixer, the speed is adjusted to 800 r / min, and stirred for 15 minutes. After uniform mixing, the mixture is passed through an 80-mesh sieve to obtain the admixture.

[0055] Example 7

[0056] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 4 in that its raw materials, by weight, include: 100 parts modified magnesium oxide, 65 parts potassium dihydrogen phosphate, 38 parts admixture, 5 parts retarder, 160 parts quartz sand, 1 part polycarboxylate-based high-efficiency water-reducing agent (PC-2000), and 24 parts water.

[0057] The retarder comprises sodium citrate, aminotrimethylene phosphonic acid, and silane coupling agent-modified nano-calcium carbonate in a mass ratio of 4:3:3. The preparation of the retarder includes: placing 60nm nano-calcium carbonate particles into a high-speed mixer, adding 0.5% of its own mass of silane coupling agent KH-550, adjusting the speed to 1300 r / min, and stirring for 12 min to obtain modified nano-calcium carbonate; then placing sodium citrate, aminotrimethylene phosphonic acid, and modified nano-calcium carbonate into a mixer, adjusting the speed to 500 r / min, and stirring for 10 min to obtain the retarder.

[0058] Example 8

[0059] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 7 in that the retarder includes sodium citrate, aminotrimethylene phosphonic acid, and silane coupling agent-modified nano-calcium carbonate in a mass ratio of 4:3:3. The preparation of the retarder includes: placing 50nm nano-calcium carbonate into a high-speed mixer, adding 0.5% of its own mass of silane coupling agent KH-550, adjusting the speed to 1200 r / min, and stirring for 15 min to obtain modified nano-calcium carbonate; placing sodium citrate, aminotrimethylene phosphonic acid, and modified nano-calcium carbonate into a mixer, adjusting the speed to 400 r / min, and stirring for 10 min to obtain the retarder.

[0060] Example 9

[0061] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 7 in that the retarder includes sodium citrate, aminotrimethylene phosphonic acid, and silane coupling agent-modified nano-calcium carbonate in a mass ratio of 4:3:3. The preparation of the retarder includes: placing 100nm nano-calcium carbonate into a high-speed mixer, adding 0.5% of its own mass of silane coupling agent KH-550, adjusting the speed to 1500 r / min, and stirring for 10 min to obtain modified nano-calcium carbonate; placing sodium citrate, aminotrimethylene phosphonic acid, and modified nano-calcium carbonate into a mixer, adjusting the speed to 600 r / min, and stirring for 10 min to obtain the retarder.

[0062] Example 10

[0063] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 7 in that: the preparation method of the water-resistant and freeze-resistant magnesium phosphate cement repair mortar includes (1) dry mixing: put modified magnesium oxide, potassium dihydrogen phosphate, admixture, fine aggregate and retarder into a forced mixer at a speed of 300 r / min and dry mix for 5 min to obtain a dry material system; (2) wet mixing and molding: add half the mass of water to the dry material system, stir for 2 min, then add the remaining mass of water and water-reducing agent, keep the speed at 300 r / min and continue stirring for 4 min to obtain the water-resistant and freeze-resistant magnesium phosphate cement repair mortar.

[0064] Example 11

[0065] This embodiment provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Embodiment 7 in that: the preparation method of the water-resistant and freeze-resistant magnesium phosphate cement repair mortar includes (1) dry mixing: put modified magnesium oxide, potassium dihydrogen phosphate, admixture, fine aggregate and retarder into a forced mixer at a speed of 400 r / min and dry mix for 3 min to obtain a dry material system; (2) wet mixing and molding: add half the mass of water to the dry material system, stir for 3 min, then add the remaining mass of water and water-reducing agent, keep the speed at 400 r / min and continue stirring for 3 min to obtain the water-resistant and freeze-resistant magnesium phosphate cement repair mortar.

[0066] Comparative Example 1

[0067] This comparative example provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Example 1 in that its raw materials, by weight, include: 100 parts pure magnesium oxide, 60 parts potassium dihydrogen phosphate, 45 parts fly ash, 4 parts sodium citrate, 180 parts quartz sand, 0.8 parts polycarboxylate-based high-efficiency water-reducing agent (PC-2000), and 26 parts water.

[0068] Comparative Example 2

[0069] This comparative example provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Example 1 in that: the modified magnesium oxide is made by sequentially coating magnesium oxide with a silane layer and a polyurethane layer; the mass ratio of the magnesium oxide, the silane layer and the polyurethane layer is 1:0.016:0.024.

[0070] Comparative Example 3

[0071] This comparative example provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Example 1 in that: the preparation of modified magnesium oxide includes: placing recalcined magnesium oxide in an oven and drying it at 120°C for 1.5 hours, then cooling it to room temperature for later use; placing the dried magnesium oxide in a high-speed mixer and adding a methyltrimethoxysilane solution dropwise at a speed of 1200 r / min and a rate of 1 mL / min; the methyltrimethoxysilane solution includes silane: anhydrous ethanol: water in a mass ratio of 1:4:1; after the addition is completed, stirring is continued for 50 minutes to obtain a mixed system; a polyurethane emulsion with a solid content of 40% is added to the mixed system, and stirring is continued for 15 minutes while maintaining a speed of 1200 r / min to obtain coated magnesium oxide; the coated magnesium oxide is placed in a forced-air drying oven and dried at 70°C for 6 hours, then cooled to room temperature and passed through a 100-mesh sieve to obtain modified magnesium oxide.

[0072] Comparative Example 4

[0073] This comparative example provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Example 4 in that the admixture includes magnesium slag powder, ceramic powder and metakaolin in a mass ratio of 4:4:1.

[0074] Comparative Example 5

[0075] This comparative example provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Example 4 in that the preparation of the admixture includes: activated magnesium slag powder: industrial magnesium slag is crushed, ball-milled to a particle size of less than or equal to 80 μm, placed in a muffle furnace, activated at 750°C for 3 hours, and cooled to room temperature for later use. Pretreated ceramic powder: waste building ceramics are crushed, ball-milled to a particle size of less than or equal to 30 μm, placed in an oven, dried at 120°C for 1 hour, and cooled to room temperature for later use. Then, the activated magnesium slag powder, the treated ceramic powder, and metakaolin are placed in a high-speed mixer, the speed is adjusted to 900 r / min, and stirred for 10 minutes. After being mixed evenly, the mixture is passed through an 80-mesh sieve to obtain the admixture.

[0076] Comparative Example 6

[0077] This comparative example provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Example 7 in that the retarder includes sodium citrate, aminotrimethylene phosphonic acid, and nano-calcium carbonate modified with a silane coupling agent in a mass ratio of 4:3:3.

[0078] Comparative Example 7

[0079] This comparative example provides a water-resistant and freeze-resistant magnesium phosphate cement repair mortar, which differs from Example 7 in that the preparation of the retarder includes: placing 120nm nano-calcium carbonate into a high-speed mixer, adding 0.2% of its own mass of silane coupling agent KH-550, adjusting the speed to 1800r / min, and stirring for 5min to obtain modified nano-calcium carbonate; placing sodium citrate, aminotrimethylene phosphonic acid, and modified nano-calcium carbonate into a mixer, adjusting the speed to 300r / min, and stirring for 15min to obtain the retarder.

[0080] Experimental Example 1

[0081] The 1h / 28d compressive strength (MPa), 28d bond strength (MPa), 28d shrinkage (%), long-term immersion strength retention (%), frost resistance grade, and acid corrosion resistance strength loss (%) of the water-resistant and freeze-thaw resistant magnesium phosphate cement repair mortars provided in Examples 1-11 and Comparative Examples 1-7 were tested.

[0082] (1) Compressive strength (MPa): Tested in accordance with the relevant testing standards of GB / T 17671-2021 "Test Method for Strength of Cement Mortar";

[0083] (2) Bond strength (MPa): The test shall be conducted in accordance with the relevant testing standards of GB 50119-2013 (Appendix D of the Technical Specification for Application of Concrete Admixtures: Test Method for Bond Strength).

[0084] (3) Shrinkage rate (%): The test was conducted in accordance with the relevant testing standards in GB / T 50082-2009 (Chapter 8 Shrinkage Test Method of Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete);

[0085] (4) Freeze-thaw resistance grade: The test shall be conducted in accordance with the relevant testing standards in Chapter 4 of GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (rapid freezing method).

[0086] (5) Long-term immersion strength retention rate (%):

[0087] Specimen preparation: Prepare mortar according to this technical solution, using a standard mold of 40mm×40mm×160mm, vibrate and shape it, prepare 6 specimens for each group (3 for water curing and 3 for standard curing), and smooth the surface after shaping.

[0088] Group curing: Divide the 6 test blocks into two groups. One group (3 blocks) is placed in a curing chamber and cured for 28 days according to the standard curing conditions of this technical plan (temperature 10-35℃, relative humidity ≥60%), which serves as the standard strength test block. The other group (3 blocks) is placed in the curing chamber for standard curing for 7 days, and then transferred to distilled water (free of impurities, pH value 7.0±0.5) at 25±2℃ for immersion curing. The immersion depth is ≥50mm to ensure that the test blocks are completely submerged. The distilled water is changed every 7 days during the immersion period to avoid the water quality affecting the test results.

[0089] Strength test: After immersion in water for 60 days, remove the immersion test block, wipe the surface moisture with filter paper, and immediately test its compressive strength with a compressive strength tester (the test method is the same as "compressive strength"). Record it as the strength after immersion (R_immersion); at the same time, test the compressive strength of the test block after standard curing for 28 days and record it as the standard strength (R_standard).

[0090] Results calculation: Long-term immersion strength retention rate = (R_immersion / R_standard) × 100%, accurate to 1%; the average value of 3 immersion test blocks and 3 standard test blocks is used for calculation, and test blocks with a deviation of more than 10% are discarded.

[0091] (6) Loss of acid corrosion resistance strength (%):

[0092] Specimen preparation: Prepare mortar according to this technical solution, using a standard mold of 40mm×40mm×160mm, vibrate and shape it, prepare 6 specimens per group (3 for acid corrosion curing, 3 for standard curing), smooth the surface after shaping, and place it in a curing box for standard curing for 28 days (curing conditions: temperature 10-35℃, relative humidity ≥60%).

[0093] Group treatment: After curing for 28 days, all test blocks were removed, and the compressive strength of 3 standard cured test blocks was tested and recorded as the standard strength (f standard); the remaining 3 test blocks were placed in a corrosion resistance test chamber, and a 5% sulfuric acid solution (simulating a conventional industrial acid corrosion environment) was poured in. The solution depth was ≥50mm to ensure that the test blocks were completely submerged. The corrosion temperature was controlled at 25±2℃. The sulfuric acid solution was replaced every 5 days during the corrosion period to keep the solution concentration stable.

[0094] Post-corrosion testing: After 28 days of corrosion curing, the test block was removed, the surface was rinsed with clean water to remove residual sulfuric acid solution, and the moisture was wiped dry with filter paper. The surface of the test block was observed to see if there were any corrosion, peeling, powdering or other phenomena. Then, the compressive strength was tested with a compressive strength tester and recorded as the post-corrosion strength (fcorrosion).

[0095] Calculation results: Acid corrosion resistance strength loss = (fstandard - fcorrosion) / fstandard × 100%, accurate to 1%; the average value of 3 corrosion test blocks and 3 standard test blocks is used for calculation, and test blocks with a deviation of more than 10% are discarded.

[0096] The test results for 1h / 28d compressive strength (MPa), 28d bond strength (MPa), and 28d shrinkage (%) are shown in Table 1; the test results for long-term immersion strength retention (%), freeze resistance grade, and acid corrosion resistance strength loss (%) are shown in Table 2.

[0097] Table 1

[0098]

[0099] As shown in Table 1, the mechanical properties (1h, 28d compressive strength, and 28d bond strength) of Examples 1-11 are superior to those of the comparative examples, while their 28d shrinkage rates are lower. This indicates that the modified magnesium oxide of this application can significantly improve the mechanical properties of the mortar, reduce its shrinkage rate, and that the admixtures and retarders provided in this application can form a strong synergistic effect with the modified magnesium oxide. Compared with Comparative Example 1 (using pure magnesium oxide and conventional admixtures and retarders), the mechanical properties of the mortar are significantly improved, and the shrinkage rate is significantly reduced.

[0100] Table 2

[0101]

[0102] As shown in Table 2, the durability performance (long-term immersion strength retention rate, freeze-thaw resistance, and acid corrosion resistance loss) of Examples 1-11 is superior to that of the comparative examples. This indicates that the modified magnesium oxide of this application can significantly improve the water resistance, freeze-thaw resistance, and acid corrosion resistance of the mortar. Furthermore, the admixtures and retarders provided in this application can form a strong synergistic effect with the modified magnesium oxide provided in this application, resulting in a significant improvement in the durability performance of the mortar compared to Comparative Example 1 (using pure magnesium oxide and conventional admixtures and retarders), making it suitable for use in harsh environments.

[0103] In summary, the water-resistant and freeze-resistant magnesium phosphate cement repair mortar provided by this invention has excellent water resistance, freeze resistance, and mechanical properties. The preparation method of this water-resistant and freeze-resistant magnesium phosphate cement repair mortar has a simplified preparation process, low production cost, and can realize the high-value utilization of solid waste, meeting the needs of rapid repair of building projects in harsh environments such as dampness and cold.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A water-resistant and frost-resistant magnesium phosphate cement repair mortar, characterized in that: The raw materials, by weight, include: 100 parts modified magnesium oxide, 60-70 parts potassium dihydrogen phosphate, 30-45 parts admixture, 4-6 parts retarder, 150-180 parts fine aggregate, 0.8-1.2 parts water-reducing agent, and 22-26 parts water. The modified magnesium oxide is prepared by sequentially coating magnesium oxide with a silane layer and a polyurethane layer; the mass ratio of the magnesium oxide, the silane layer and the polyurethane layer is 1:0.024:0.

016.

2. The water-resistant and frost-resistant magnesium phosphate cement repair mortar according to claim 1, characterized in that: The admixtures include magnesium slag powder, ceramic powder and metakaolin in a mass ratio of 5:3:

2.

3. The water-resistant and frost-resistant magnesium phosphate cement repair mortar according to claim 2, characterized in that: The retarder comprises sodium citrate, aminotrimethylene phosphonic acid, and nano-calcium carbonate modified with a silane coupling agent in a mass ratio of 4:3:

3.

4. The water-resistant and frost-resistant magnesium phosphate cement-based repair mortar according to claim 1, characterized in that: The preparation of the modified magnesium oxide includes: placing recalcined magnesium oxide in an oven and drying it at 100-110℃ for 2-3 hours, then cooling it to room temperature for later use; placing the dried magnesium oxide in a high-speed mixer and adding a methyltrimethoxysilane solution dropwise at a speed of 800-1000 r / min and a rate of 1-2 mL / min; the methyltrimethoxysilane solution comprises silane: anhydrous ethanol: water in a mass ratio of 1:4:1; after the addition is complete, stirring is continued for 30-40 minutes to obtain a mixed system; adding a polyurethane emulsion with a solid content of 40% to the mixed system, maintaining a speed of 800-1000 r / min, and stirring is continued for 20-30 minutes to obtain coated magnesium oxide; placing the coated magnesium oxide in a forced-air drying oven and drying it at 75-85℃ for 4-5 hours, cooling it to room temperature, and then passing it through a 100-mesh sieve to obtain the modified magnesium oxide.

5. The water-resistant and frost-resistant magnesium phosphate cement-based repair mortar according to claim 2, characterized in that: The preparation of the admixture includes: putting the magnesium slag powder, the ceramic powder, and the metakaolin into a high-speed mixer, adjusting the speed to 600-800 r / min, stirring for 15-20 min, mixing evenly, and then passing it through an 80-mesh sieve to obtain the admixture.

6. The water-resistant and frost-resistant magnesium phosphate cement repair mortar according to claim 5, characterized in that: The magnesium slag powder needs to be activated before mixing: the industrial magnesium slag is crushed, ball-milled to a particle size of less than or equal to 50 μm, placed in a muffle furnace, activated at 780-820℃ for 2 hours, and then cooled to room temperature for use.

7. The water-resistant and frost-resistant magnesium phosphate cement repair mortar according to claim 5, characterized in that: The ceramic powder needs to be pretreated before mixing: crush the waste building ceramics, ball mill them to a particle size of less than or equal to 45μm, put them in an oven and dry them at 100-110℃ for 2 hours, and then cool them to room temperature for later use.

8. The water-resistant and freeze-resistant magnesium phosphate cement repair mortar according to claim 3, characterized in that: The preparation of the retarder includes: placing nano-calcium carbonate with a particle size of 50-100 nm into a high-speed mixer, adding 0.5% of its own mass of silane coupling agent KH-550, adjusting the speed to 1200-1500 r / min, and stirring for 10-15 min to obtain modified nano-calcium carbonate; placing the sodium citrate, the aminotrimethylene phosphonic acid, and the modified nano-calcium carbonate into a mixer, adjusting the speed to 400-600 r / min, and stirring for 10 min to obtain the retarder.

9. A method for preparing the water-resistant and freeze-resistant magnesium phosphate cement repair mortar according to any one of claims 1-8, characterized in that: include: (1) Dry material mixing: The modified magnesium oxide, potassium dihydrogen phosphate, admixture, fine aggregate and retarder are put into a forced mixer and dry mixed to obtain a dry material system; (2) Wet mixing and molding: Add half the mass of water to the dry material system, stir for 2-3 minutes, then add the remaining mass of water and the water-reducing agent, keep the rotation speed at 300-400 r / min, and continue stirring for 3-4 minutes to obtain the water-resistant and freeze-resistant magnesium phosphate cement repair mortar.

10. The method for preparing water-resistant and freeze-resistant magnesium phosphate cement repair mortar according to claim 9, characterized in that: In step (1), dry mix for 3-5 minutes at a speed of 300-400 r / min.

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