A retarder-free magnesium phosphate repair material based on organic waste liquid and its preparation method

Abstract

This invention belongs to the field of new building materials technology, specifically relating to a retarder-free magnesium phosphate repair material based on organic waste liquid and its preparation method. The retarder-free magnesium phosphate repair material based on organic waste liquid of this invention is mainly composed of the following raw materials in parts by weight: 100 parts of recalcined magnesium oxide, 130-180 parts of phosphate, 10-20 parts of fly ash, 190-300 parts of aggregate, and 43-63 parts of water; the recalcined magnesium oxide is prepared by grinding sintered magnesia under the condition of a grinding aid; the grinding aid is organic waste liquid. This invention utilizes the continuous role of organic waste liquid in both stages of the magnesium phosphate repair material's life cycle, forming a closed-loop process. Magnesium oxide treated by this grinding process can be directly used to prepare magnesium phosphate cement with excellent workability and a clear retarding effect.

Description

Technical Field

[0001] This invention belongs to the field of new building materials technology, specifically relating to a retarder-free magnesium phosphate repair material based on organic waste liquid and its preparation method. Background Technology

[0002] The scale of urban renewal projects for old buildings in China is currently enormous, typically measured by the number of projects and investment. According to data from the Ministry of Housing and Urban-Rural Development, since 2023, over 66,000 urban renewal projects have been implemented nationwide, with a total investment of 2.6 trillion yuan. In the renovation of old buildings, corrosion prevention and repair of reinforced concrete (RC) structures is one of the key aspects of maintaining structural stability. Therefore, effectively addressing the corrosion problem of reinforcing steel in old buildings, effectively reducing the rate of corrosion spread, effectively reducing the internal stress caused by corrosion, and ensuring the structural stability of the building have become urgent problems to be solved in the field of reinforcing steel corrosion prevention and repair.

[0003] Magnesium phosphate repair compound (MPC) is prepared by an acid-base chemical reaction between recalcined magnesium oxide and soluble phosphate. Compared with traditional concrete, MPC has many superior properties, such as high early strength, high bond strength with old concrete and steel, low permeability, and good durability. Therefore, given its rapid setting characteristics and good steel corrosion inhibition ability, magnesium phosphate repair compound has great potential as a rapid repair material for reinforced concrete structures.

[0004] Extensive research into the composition and hydration process of magnesium phosphate repair materials revealed that even with the use of recalcined magnesium oxide as a magnesium raw material to slow down the hydration reaction, the hydration rate remained relatively fast, resulting in insufficient operational time for engineering applications. Borax, sodium chloride, and other components must be used as retarders to regulate the setting time of magnesium phosphate cementitious materials, thereby expanding their application scenarios. However, existing retarders all have certain problems. For example, the most commonly used borax has a high cost for industrial-grade products, and its large dosage (5%–20%) directly increases the overall cost of magnesium phosphate repair materials, limiting their application. Sodium chloride, when used as a retarder in magnesium phosphate repair materials, introduces chloride ions, which, if applied to the repair of old buildings, can exacerbate the corrosion of reinforcing steel, posing a safety hazard. Therefore, how to control the setting time of magnesium phosphate repair materials while avoiding the cost problems or safety hazards caused by existing retarders has become an urgent technical problem to be solved in this field.

[0005] On the other hand, the recalcined magnesium oxide in magnesium phosphate repair materials is usually obtained by calcining purified magnesite at high temperatures and then grinding it. After calcination at 1700℃~1800℃, the magnesium oxide crystal structure becomes denser, resulting in a high Mohs hardness of 5.5~6.0, but also greater brittleness. This makes it prone to re-agglomeration after breakage, requiring a large amount of energy during grinding; when grinding to several hundred mesh, the power consumption can reach over 60 kWh per ton. Grinding aids can accelerate the grinding process and reduce energy consumption. However, the commonly used triethanolamine grinding aid can reduce the strength of magnesium phosphate repair materials and should be used with caution.

[0006] Organic waste liquids from biomass processing, such as molasses and alcoholic beverage mash, are inexpensive and rich in organic components like sugars, proteins, and alcohols, making them highly promising for application in the field of magnesium phosphate repair materials. Through certain technical means, they can be used as grinding aids in the grinding process of recalcined magnesium oxide to reduce grinding energy consumption. Furthermore, their organic components can also act as retarders during the reaction process of magnesium phosphate repair materials. This not only solves the problems of high energy consumption in recalcined magnesium oxide grinding, high cost of existing retarders for magnesium phosphate repair materials, and potential safety hazards, but also achieves high-value resource utilization of waste liquids.

[0007] In view of this, this application provides a retarder-free magnesium phosphate repair material based on organic waste liquid and its preparation method. Summary of the Invention

[0008] In view of the problems and shortcomings of the existing technology, the purpose of this invention is to provide a retarder-free magnesium phosphate repair material based on organic waste liquid and its preparation method.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention provides a retarder-free magnesium phosphate repair material based on organic waste liquid, mainly composed of the following raw materials in parts by weight: The mixture comprises 100 parts of recalcined magnesium oxide, 130-180 parts of phosphate, 10-20 parts of fly ash, 190-300 parts of aggregate, and 43-63 parts of water; the recalcined magnesium oxide is prepared by grinding sintered magnesia under the condition of a grinding aid; the grinding aid is an organic waste liquid.

[0010] Preferably, the organic waste liquid contains organic matter, and the organic matter contains hydroxyl and / or carboxyl functional groups.

[0011] Preferably, the organic waste liquid is at least one of waste molasses and waste alcohol mash.

[0012] Preferably, the chemical oxygen demand of the organic waste liquid is 60,000 to 100,000 mg / L; the amount of organic waste liquid added is 0.5% to 1% of the mass of sintered magnesia.

[0013] Preferably, the phosphate is at least one of ammonium dihydrogen phosphate and potassium dihydrogen phosphate.

[0014] Preferably, the aggregate is quartz sand.

[0015] More preferably, the particle size of the quartz sand is 40-70 mesh.

[0016] Preferably, the particle size of the fly ash is 3–10 μm.

[0017] Preferably, the particle size of the recalcined magnesium oxide is 25–50 μm.

[0018] The second aspect of this invention provides a method for preparing the retarder-free magnesium phosphate repair material based on organic waste liquid as described in the first aspect above, comprising the following steps: (1) Add phosphate to water and stir evenly to obtain phosphate slurry; (2) Add fly ash and recalcined magnesium oxide to the phosphate slurry, stir evenly to obtain a mixed slurry; (3) Add aggregate to the mixed slurry and stir evenly to obtain magnesium phosphate repair material without retarder based on organic waste liquid.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In the grinding stage of sintered magnesia, this invention utilizes organic waste liquid such as waste molasses as a grinding aid to improve the grinding process of recalcined magnesia. This allows organic molecules to be adsorbed on the surface of microcracks in the recalcined magnesia material, reducing its surface energy and thus preventing the microcracks from reclosing and reducing the agglomeration of fine particles, thereby saving grinding energy. On the other hand, in the hydration stage of magnesium phosphate repair material, the adsorption of organic molecules on the surface of the recalcined magnesia material can be regarded as a physical coating modification of recalcined magnesia. During the hydration reaction, it can hinder the diffusion and dissolution of MgO, thereby playing a role in regulating the setting time and realizing the preparation of magnesium phosphate repair material without retarder.

[0020] (2) This invention utilizes organic waste liquid to play a continuous role in two stages of the life cycle of magnesium phosphate repair material, forming a closed-loop process. Magnesium oxide treated by this grinding process can be directly used to prepare magnesium phosphate cement with excellent workability and clear retarding effect. This not only realizes the high-value resource utilization of organic waste liquid, which is in line with the circular economy policy, but also allows the use of low-cost or even negative-cost waste liquid to replace expensive special grinding aids and retarders on the market, resulting in a huge cost advantage and achieving good economic and social benefits at the same time. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below through embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] (I) Effect of grinding aid dosage on the performance of magnesium phosphate repair material Example 1: A retarder-free magnesium phosphate repair material based on organic waste liquid, comprising the following raw materials in parts by weight: The mixture comprises 100 parts of recalcined magnesium oxide, 150 parts of phosphate, 10 parts of fly ash, 210 parts of quartz sand, and 53 parts of water; wherein the phosphate is potassium dihydrogen phosphate; the particle size of the recalcined magnesium oxide is 25-50 μm, the particle size of the ultrafine fly ash is 3-10 μm, and the particle size of the quartz sand is 40-70 mesh. The recalcined magnesium oxide is prepared by grinding sintered magnesia for 3 hours under the condition of using organic waste liquid as a grinding aid; the organic waste liquid is waste molasses, which comes from the sugarcane sugar industry and has a chemical oxygen demand of 81300 mg / L. The amount of waste molasses added is 0.7% of the mass of sintered magnesia.

[0023] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is as follows: (1) Add phosphate to water and stir evenly to obtain phosphate slurry; (2) Add fly ash and recalcined magnesium oxide to the phosphate slurry, stir evenly to obtain a mixed slurry; (3) Slowly add quartz sand to the mixed slurry and stir evenly to obtain magnesium phosphate repair material without retarder based on organic waste liquid.

[0024] Example 2: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the amount of waste molasses added is 0.5% of the mass of sintered magnesia.

[0025] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0026] Example 3: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the amount of waste molasses added is 1.0% of the mass of sintered magnesia.

[0027] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0028] Comparative Example 1: A magnesium phosphate repair material has the same raw material composition as in Example 1, except that no organic waste liquid is added and the recalcined magnesium oxide is prepared by grinding sintered magnesium sand for 3 hours.

[0029] The preparation method of the above-mentioned magnesium phosphate repair material is the same as that in Example 1.

[0030] Comparative Example 2: A magnesium phosphate repair material has the same raw material composition as in Example 1, except that: no organic waste liquid is added, and the recalcined magnesium oxide is prepared by grinding sintered magnesium sand for 3 hours; in addition, 0.8 parts by weight of borax is added to the raw material as a retarder.

[0031] (1) Add phosphate to water and stir evenly to obtain phosphate slurry; (2) Add borax, fly ash and recalcined magnesium oxide to the phosphate slurry, stir evenly to obtain a mixed slurry; (3) Slowly add quartz sand to the mixed slurry and stir evenly to obtain magnesium phosphate repair material.

[0032] Performance testing: The performance of the reburned magnesium oxide and magnesium phosphate repair materials prepared in Examples 1-3 and Comparative Examples 1-2 was tested. The median particle size (D50) of the reburned magnesium oxide was determined using a laser particle size analyzer. The setting time of the magnesium phosphate repair material was determined according to the test methods specified in GB / T 1346-2011 "Standard Consistency Water Requirement, Setting Time and Soundness Test Methods for Cement". The 1-day compressive strength of the magnesium phosphate repair material was determined according to the test methods specified in JGJ / T70-2009 "Standard for Basic Performance Test Methods of Building Mortar". The test results are shown in Table 1.

[0033] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-2 As shown in Table 1, the median particle size (D50) of recalcined magnesium oxide in Examples 1-3 were 30 μm, 43 μm, and 31 μm, respectively, while the median particle size of Comparative Examples 1 and 2 was 85 μm. This is because waste molasses was used as a grinding aid in Examples 1-3, and its polar molecules can be strongly adsorbed on the surface of newly formed magnesium oxide particles, forming a monomolecular film. This significantly reduces the surface energy of the particles, weakens the tendency to agglomerate due to high surface energy, and allows grinding to continue towards finer particles. At the same time, organic molecules can be adsorbed on the tips of microcracks in the material particles, reducing their surface hardness, promoting crack expansion and propagation, thus making the particles easier to break and effectively reducing the "apparent hardness" of the material. On the other hand, the viscous components of molecules in organic waste liquids such as molasses can play a certain lubricating role between particles, reducing direct friction and adhesion between particles and grinding media, liners, and between particles themselves, improving the flowability of materials in the grinding chamber, increasing grinding efficiency, and reducing the "sticking" phenomenon. In Comparative Examples 1 and 2, due to the absence of grinding aids, the grinding efficiency of sintered magnesia decreased under the same grinding conditions, resulting in a larger median particle size of reburned magnesia. On the other hand, when the amount of waste molasses increased from 0.5% to 1.0%, the median particle size after grinding decreased from 43 μm to 30 μm, then slightly increased to 31 μm. This is because increasing the amount of waste molasses can improve grinding efficiency. However, when the amount of waste molasses is too large, its thick coating on the material produces excessive lubrication, negatively impacting the grinding effect.

[0034] Compared to Comparative Example 1, Examples 1-3 and Comparative Example 1 did not contain any retarder. However, Examples 1-3 exhibited longer setting times and higher compressive strength compared to Comparative Example 1. This is because the organic molecules in the molasses from Examples 1-3 form an organic polymer layer on the surface of the recalcined magnesium oxide powder during the grinding process. This layer slows down the reaction with phosphates, thus retarding the setting time and extending the setting time to meet the construction requirements.

[0035] Comparative Example 2 added borax as a retarder. No grinding aid was added, resulting in a larger median particle size of the reburned magnesium oxide. With the borax retarder, the retarding effect was the best, with a final setting time of up to 120 minutes. Correspondingly, its strength development was slower, with a 1-day compressive strength of only 26.7 MPa.

[0036] (II) The Influence of Grinding Aid Type on the Performance of Magnesium Phosphate Repair Material Example 4: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the organic waste liquid is alcohol waste mash, which comes from the corn fermentation industry and has a chemical oxygen demand of 65900 mg / L.

[0037] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0038] Example 5: A retarder-free magnesium phosphate repair material based on organic waste liquid has the same raw material composition as in Example 1, except that the organic waste liquid used is a mixture of waste molasses and alcohol waste mash. The amount of waste molasses added is 0.5% of the mass of sintered magnesia, and the amount of alcohol waste mash added is 0.2% of the mass of sintered magnesia. The waste molasses comes from the sugarcane sugar industry and has a chemical oxygen demand of 81,300 mg / L. The alcohol waste mash comes from the corn fermentation industry and has a chemical oxygen demand of 65,900 mg / L.

[0039] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0040] Example 6: A retarder-free magnesium phosphate repair material based on organic waste liquid has the same raw material composition as in Example 1, except that the organic waste liquid used is a mixture of waste molasses and alcohol waste mash. The amount of waste molasses added is 0.2% of the mass of sintered magnesia, and the amount of alcohol waste mash added is 0.5% of the mass of sintered magnesia. The waste molasses comes from the sugarcane sugar industry and has a chemical oxygen demand of 81,300 mg / L. The alcohol waste mash comes from the corn fermentation industry and has a chemical oxygen demand of 65,900 mg / L.

[0041] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0042] Comparative Example 3: A magnesium phosphate repair material has the same raw material composition as in Example 1, except that the grinding aid is triethanolamine, and the calcined magnesium oxide is prepared by grinding sintered magnesium sand for 3 hours under the condition of triethanolamine as a grinding aid.

[0043] The preparation method of the above-mentioned magnesium phosphate repair material is the same as that in Example 1.

[0044] Comparative Example 4: A magnesium phosphate repair material has the same raw material composition as in Example 1, except that: the grinding aid is triethanolamine, and the calcined magnesium oxide is prepared by grinding sintered magnesium sand for 3 hours under the condition of triethanolamine as a grinding aid; in addition, 0.8 parts by weight of borax is added to the raw material as a retarder.

[0045] The preparation method of the above-mentioned magnesium phosphate repair material is as follows: (1) Add phosphate to water and stir evenly to obtain phosphate slurry; (2) Add borax, fly ash and recalcined magnesium oxide to the phosphate slurry, stir evenly to obtain a mixed slurry; (3) Slowly add quartz sand to the mixed slurry and stir evenly to obtain magnesium phosphate repair material.

[0046] Performance testing: The performance of the reburned magnesium oxide and magnesium phosphate repair materials prepared in Examples 1, 4-6, and Comparative Examples 3-4 was tested. The median particle size (D50) of the reburned magnesium oxide was determined using a laser particle size analyzer. The setting time of the magnesium phosphate repair material was determined according to the test methods specified in GB / T 1346-2011 "Standard Test Methods for Water Requirement, Setting Time and Soundness of Cement". The 1-day compressive strength of the magnesium phosphate repair material was determined according to the test methods specified in JGJ / T70-2009 "Standard Test Methods for Basic Performance of Building Mortar". The test results are shown in Table 2.

[0047] Table 2 Performance test results of Examples 1, 4-6, and Comparative Examples 3-4 As shown in Table 2, the median particle size (D50) of the re-calcined magnesia in Examples 1 and 4-6 is between 28 and 33 μm. The median particle size of Comparative Examples 3 and 4 is 32 μm. This is because waste molasses, waste alcohol mash, and a mixture thereof were used as grinding aids in Examples 1 and 4-6. Due to film-forming and lubricating effects, the grinding efficiency of sintered magnesia can be improved. On the other hand, the median particle size varies depending on the type of grinding aid. In Example 5, waste molasses accounted for 0.5% of the mass ratio of sintered magnesia, and waste alcohol mash accounted for 0.2% of the mass ratio of sintered magnesia. The median particle size was the smallest at 28 μm, indicating that the synergistic effect of molasses and waste alcohol mash can further improve the grinding efficiency. In Comparative Examples 3 and 4, triethanolamine was added as a grinding aid. Under the same grinding conditions, the grinding efficiency of Comparative Examples 3 and 4 for sintered magnesia, measured by median particle size, is close to that of Examples 1 and 4-6.

[0048] Compared with Examples 1, Examples 4-6, Comparative Examples 3 and 4, none of Examples 1, Examples 4-6 and Comparative Examples 3 added a retarder. However, Examples 1 and Examples 4-6 had longer setting times and higher compressive strengths than Comparative Example 3.

[0049] This is because the organic molecules contained in the examples act as a retarder. In Comparative Example 3, triethanolamine grinding aid was used without any retarder, resulting in smaller calcined magnesium oxide particles that could react violently with phosphates, leading to a very short setting time, larger internal defects in the prepared sample, and lower 1-day compressive strength. In Comparative Example 4, with the addition of triethanolamine grinding aid and borax retarder, the initial setting time was 35 min, the final setting time was 85 min, and the 1-day compressive strength was 56.9 MPa, which is close to the setting time and 1-day compressive strength of Examples 1 and 4-6.

[0050] (III) Effect of phosphate dosage on the performance of magnesium phosphate repair material Example 7: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the weight of potassium dihydrogen phosphate is 130.

[0051] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0052] Example 8: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the weight of potassium dihydrogen phosphate is 180.

[0053] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0054] Performance testing: The performance of the reburned magnesium oxide and magnesium phosphate repair materials prepared in Examples 1 and 7-8 was tested. The median particle size (D50) of the reburned magnesium oxide was determined using a laser particle size analyzer. The setting time of the magnesium phosphate repair material was determined according to the test methods specified in GB / T 1346-2011 "Standard Consistency Water Requirement, Setting Time and Soundness Test Methods for Cement". The 1-day compressive strength of the magnesium phosphate repair material was determined according to the test methods specified in JGJ / T70-2009 "Standard for Basic Performance Test Methods of Building Mortar". The test results are shown in Table 3.

[0055] Table 3 Performance test results of Examples 1 and 7-8 As shown in Table 3, the grinding process was the same in Examples 1 and 7-8, and the median particle size (D50) of recalcined magnesium oxide was 30 μm. The initial setting time and final setting time decreased with increasing weight of potassium dihydrogen phosphate, and the 1-day compressive strength showed a trend of rapid initial growth followed by a slower increase. This is because potassium dihydrogen phosphate, as one of the main cementitious components of magnesium phosphate repair material, directly affects the hydration reaction process. As its dosage increases, the hydration reaction becomes more intense, and the setting time decreases accordingly. The compressive strength shows a trend of rapid initial growth followed by a slower increase.

[0056] (iv) The effect of phosphate type on the performance of magnesium phosphate repair material Example 9: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the phosphate is ammonium dihydrogen phosphate.

[0057] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0058] Example 10: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the phosphate is a mixture of potassium dihydrogen phosphate and ammonium dihydrogen phosphate in a mass ratio of 1:1.

[0059] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0060] Performance testing: The performance of the reburned magnesium oxide and magnesium phosphate repair materials prepared in Examples 1 and 9-10 was tested. The median particle size (D50) of the reburned magnesium oxide was determined using a laser particle size analyzer. The setting time of the magnesium phosphate repair material was determined according to the test methods specified in GB / T 1346-2011 "Standard Consistency Water Requirement, Setting Time and Soundness Test Methods for Cement". The 1-day compressive strength of the magnesium phosphate repair material was determined according to the test methods specified in JGJ / T70-2009 "Standard for Basic Performance Test Methods of Building Mortar". The test results are shown in Table 4.

[0061] Table 4 Performance test results of Examples 1 and 9-10 As shown in Table 4, the grinding process was the same in Examples 1 and 9-10, and the median particle size (D50) of recalcined magnesium oxide was 30 μm. The shortest setting time and lowest compressive strength were achieved when ammonium dihydrogen phosphate was used as the phosphate type; the next shortest was achieved with a mixture of potassium dihydrogen phosphate and ammonium dihydrogen phosphate; and the longest setting time and highest compressive strength were achieved with potassium dihydrogen phosphate. This is because ammonium dihydrogen phosphate has higher solubility in water than potassium dihydrogen phosphate, allowing it to react quickly in aqueous solution and reducing setting time. Simultaneously, its hydration exothermic reaction accelerates the dissolution of recalcined magnesium oxide, further shortening the setting time. On the other hand, for the same mass, ammonium dihydrogen phosphate consumes less recalcined magnesium oxide, generates less struvite (the main strength component), and releases ammonia during its hydration reaction, resulting in more defects in the internal structure of the test block, leading to the lowest compressive strength in Example 9.

[0062] (v) The effect of chemical oxygen demand of organic waste liquid on the performance of magnesium phosphate repair material Example 11: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the chemical oxygen demand of the waste molasses is 71100 mg / L.

[0063] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0064] Example 12: A magnesium phosphate repair material without retarder based on organic waste liquid has the same raw material composition as in Example 1, except that the chemical oxygen demand of the waste molasses is 96800 mg / L.

[0065] The preparation method of the above-mentioned retarder-free magnesium phosphate repair material based on organic waste liquid is the same as that in Example 1.

[0066] Performance testing: The performance of the reburned magnesium oxide and magnesium phosphate repair materials prepared in Examples 1 and 11-12 was tested. The median particle size (D50) of the reburned magnesium oxide was determined using a laser particle size analyzer. The setting time of the magnesium phosphate repair material was determined according to the test methods specified in GB / T 1346-2011 "Standard Consistency Water Requirement, Setting Time and Soundness Test Methods for Cement". The 1-day compressive strength of the magnesium phosphate repair material was determined according to the test methods specified in JGJ / T70-2009 "Standard for Basic Performance Test Methods of Building Mortar". The test results are shown in Table 5.

[0067] Table 5 Performance test results of Examples 1 and 11-12 Table 4 shows that after grinding, the median particle size of recalcined magnesium oxide in Examples 1 and 11-12 were 32 μm, 30 μm, and 36 μm, respectively; the initial setting times were 25 min, 40 min, and 45 min, respectively; the final setting times were 65 min, 95 min, and 105 min, respectively; and the 1-day compressive strengths were 55.8 MPa, 48.2 MPa, and 51.5 MPa, respectively. With increasing chemical oxygen demand (COD), the median particle size distribution first decreased and then increased, while the setting time gradually increased, and the 1-day compressive strength first increased and then decreased. This is because COD represents the organic matter content in the waste molasses. When the organic matter content is low, it has little effect on grinding efficiency, thus affecting the development of magnesium phosphate strength. When the organic matter content is too high, the thicker organic film formed during grinding actually affects grinding efficiency; simultaneously, excessive organic matter reduces the reaction rate of magnesium phosphate during hydration, leading to a decrease in compressive strength.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Those skilled in the art can modify or make equivalent substitutions to the technical solutions of the present invention based on the concept of the present invention, without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An organic waste liquid-based magnesium phosphate repair material without a retarder, characterized by, It is mainly composed of the following raw materials in parts by weight: The mixture comprises 100 parts of recalcined magnesium oxide, 130-180 parts of phosphate, 10-20 parts of fly ash, 190-300 parts of aggregate, and 43-63 parts of water; the recalcined magnesium oxide is prepared by grinding sintered magnesia under the condition of a grinding aid; the grinding aid is an organic waste liquid.

2. The organic waste liquid-based magnesium phosphate repair material without retarder according to claim 1, characterized in that, The organic waste liquid contains organic matter, which contains hydroxyl and / or carboxyl functional groups.

3. The organic waste liquid-based magnesium phosphate repair material without retarder according to claim 2, characterized in that, The organic waste liquid is at least one of waste molasses and waste alcohol mash.

4. The organic waste liquid-based magnesium phosphate repair material without retarder according to any one of claims 1-3, characterized in that, The chemical oxygen demand of the organic waste liquid is 60,000 to 100,000 mg / L; the amount of organic waste liquid added is 0.5% to 1% of the mass of sintered magnesia.

5. The organic waste liquid-based magnesium phosphate repair material without retarder according to claim 4, characterized in that, The phosphate is at least one of ammonium dihydrogen phosphate and potassium dihydrogen phosphate.

6. The organic waste liquid-based magnesium phosphate repair material without retarder according to claim 5, characterized in that, The aggregate is quartz sand.

7. The organic waste liquid-based magnesium phosphate repair material without retarder according to claim 6, characterized in that, The particle size of the fly ash is 3–10 μm.

8. The organic waste liquid-based magnesium phosphate repair material without retarder according to claim 7, characterized in that, The particle size of the recalcined magnesium oxide is 25–50 μm.

9. The method for preparing the retarder-free magnesium phosphate repair material based on organic waste liquid according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Add phosphate to water and stir evenly to obtain phosphate slurry; (2) Add fly ash and recalcined magnesium oxide to the phosphate slurry, stir evenly to obtain a mixed slurry; (3) Add aggregate to the mixed slurry and stir evenly to obtain magnesium phosphate repair material without retarder based on organic waste liquid.

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