A modified magnesium phosphate cement solidifying agent for rapidly solidifying waste mud and a preparation method thereof

Abstract

This invention discloses a curing agent for rapidly solidifying waste mud using modified magnesium phosphate cement and its preparation method, belonging to the field of building materials technology. This method can treat waste mud generated during civil engineering construction and tunnel engineering. The curing agent, by weight, comprises the following components: 8-12 parts magnesium phosphate cement, 6-8 parts quicklime, 6-8 parts blast furnace slag, and 4-6 parts sodium silicate. Compared with existing technologies, this invention modifies the magnesium phosphate cement, giving the solidified waste mud higher strength. This invention, through mixing and stirring with the waste mud, achieves a series of hydration reactions over solidification times of 3, 7, 14, and 28 days, forming a large amount of hydration cementitious products. This approach utilizes the low cost of industrial solid wastes like blast furnace slag and quicklime, reducing the cost of solidification treatment. Furthermore, it improves the strength and water resistance of the solidified soil from the waste mud, rapidly increasing its strength and enhancing its resistance to water erosion in a short period.

Description

Technical Field

[0001] This invention relates to a curing agent for rapidly curing waste mud with modified magnesium phosphate cement and its preparation method, particularly a composite curing material used for curing waste mud generated in civil engineering construction, belonging to the field of building materials technology. Background Technology

[0002] Currently, the main method for treating construction waste mud is off-site transportation, leading to high processing and transportation costs. Improper handling can also cause serious environmental pollution and land occupation issues. This method is outdated, expensive, and inefficient, contradicting the national strategy of high efficiency and low resource consumption for sustainable development. Therefore, it is necessary to find a new technology for treating construction waste mud, specifically a method for solidifying and reusing it. This approach is gradually becoming the solution for construction waste mud in modern society. The working principle of solidifying agents lies in their ability to improve the pore structure of the soil through a series of physicochemical reactions, transforming loose soil into a denser structure and significantly enhancing its strength and durability.

[0003] Currently, commonly used silicate cement hardeners and lime-based hardeners generally require high costs and have high energy consumption during production. Magnesium phosphate cement, on the other hand, is a new type of inorganic cementitious material that achieves its strength through an acid-base neutralization reaction between recalcined MgO (alkaline oxide) and soluble phosphate hydrochloric acid. It features rapid setting and hardening, high early strength, good bonding properties, and high biocompatibility, and is widely used in both military and civilian fields, such as repairing public roads, bridges, structural engineering components, artificial teeth, and bones. Furthermore, due to its rapid hardening, early strength, good stability, and near-neutral pH, magnesium phosphate cement can also be used for military emergency repairs and construction, as well as nuclear waste treatment.

[0004] Patent CN201810317241.7, published on June 22, 2018, discloses a magnesium phosphate cement for emergency repair and construction in extremely cold environments. Its key features include the use of one or both of phosphoric acid and potassium formate as antifreeze components in the cement formulation; the use of bauxite as a heating material; the use of methylcellulose as a water-retaining component; and the use of potassium phosphate and Dynol-360 to improve the fluidity of the magnesium phosphate cement in extremely cold environments. A method for preparing the aforementioned magnesium phosphate cement for emergency repair and construction in extremely cold environments is also disclosed. During implementation, no special mixing equipment is required, making construction convenient. No special curing process is needed after preparation and molding. Tests have shown that the compressive strength of the obtained magnesium phosphate cement can reach over 20 MPa 2 hours after construction in extremely cold environments with temperatures below -20°C, meeting the requirements for early strength development of cementitious materials in emergency repair and construction projects in extremely cold environments.

[0005] The patent published on April 29, 2022, with publication number CN114409371A, discloses a water-resistant phosphate cement-based repair material. The material disclosed in the patent is prepared from the following raw materials: modified magnesium oxide, potassium dihydrogen phosphate, phosphoaluminate cement, silica fume, potassium chloride, and additives. It is a water-resistant phosphate cement-based repair material that can be used for rapid repair of buildings in long-term humid environments and coastal environments. It has early strength, high strength, and good water stability. Modified magnesium oxide is prepared according to the following steps: (1) Ethanol is added to a wet ball mill, and then calcium chloride, potassium carbonate and triethanolamine are added to the wet ball mill in a weight ratio of 1:1:20-200 and mixed evenly, with a solid-liquid ratio of 10-50%; (2) After wet milling, centrifugation and filtration are used to obtain a slurry. During the wet milling process, the outer wall temperature of the ball mill is controlled to be ≤50℃ by water cooling or liquid nitrogen; (3) Magnesium oxide and slurry are fully mixed in a weight ratio of 1:50 and then granulated to obtain modified magnesium oxide; wherein, the magnesium oxide is obtained by crushing recalcined magnesium oxide, and the specific surface area is 238-322m². 2 / kg.

[0006] Due to its rapid hardening and early strength characteristics, magnesium phosphate cement has considerable development potential in special engineering scenarios. However, its inherent weakness in water resistance limits its application in engineering to some extent. In recent years, technologies for magnesium phosphate cement repair materials have largely focused on improving its water resistance. However, previous studies have had some shortcomings. These technologies either introduce admixtures or surfactants into the mature magnesium phosphate cement system to increase the density of the hardened paste and improve water resistance, or add polymers to improve surface properties and reduce surface wettability. Simply introducing admixtures or surfactants has no effect on the strength of magnesium phosphate cement, but the improvement in water resistance is insufficient; it will still suffer structural damage under long-term water erosion. Simply adding polymers to improve surface properties can significantly improve the water resistance of magnesium phosphate cement, but this technology will reduce the strength of magnesium phosphate cement using potassium dihydrogen phosphate and magnesium oxide as cementing materials. Summary of the Invention

[0007] The purpose of this invention is to provide a curing agent for rapidly solidifying waste mud with modified magnesium phosphate cement and its preparation method. This method can prepare magnesium phosphate cement with high early strength, while improving its water resistance to ensure that its strength is not lost. It has the effect of rapidly solidifying waste mud and realizes the efficient utilization of solid waste.

[0008] The purpose of this invention is to address the characteristics of waste mud, such as extremely high water content, high porosity, high compressibility, high fluidity, and low strength. Through extensive experimental research, the inventors have developed a highly efficient composite curing agent to overcome the problems of unstable effects and incomplete functions of single curing agents. At the same time, it can play a synergistic role in waste mud, improving the physical and mechanical properties and water resistance of waste mud.

[0009] The technical solution adopted in this invention is:

[0010] A curing agent for rapidly solidifying waste mud using modified magnesium phosphate cement and its preparation method, comprising the following components by mass: 8-12 parts magnesium phosphate cement, 6-8 parts quicklime, 6-8 parts blast furnace slag, and 4-6 parts sodium silicate.

[0011] Preferably, the recalcined magnesium oxide is obtained by calcining magnesite powder at a high temperature above 1400℃.

[0012] Preferably, the potassium dihydrogen phosphate is chemically analytical grade KH2PO4.

[0013] Preferably, the quicklime is industrial-grade CaO.

[0014] Preferably, the blast furnace slag is S95 slag powder.

[0015] Preferably, the sodium silicate is industrial-grade Na2SiO3.

[0016] This invention provides a curing agent for rapidly solidifying waste mud using modified magnesium phosphate cement and its preparation method, comprising the following steps:

[0017] (1) Mix calcined magnesium oxide and potassium dihydrogen phosphate in a mass ratio of 3:1 to 4:1, add water and stir evenly with a mixer to make magnesium phosphate cement slurry. After drying, magnesium phosphate cement is obtained.

[0018] (2) Mix 8-12 parts of magnesium phosphate cement, 6-8 parts of quicklime, 6-8 parts of blast furnace slag, and 4-6 parts of sodium silicate by mass to make waste mud solidification agent.

[0019] The stirring in steps (1) and (2) is carried out at a stirring rate of 80 r / min for 1 min.

[0020] The design concept of this invention is as follows:

[0021] This invention uses a smaller amount of quicklime and blast furnace slag in a certain proportion for compounding. Compared with previous magnesium phosphate cement repair materials that only contain quicklime or blast furnace slag, this invention has higher setting and hardening strength. Burnt magnesium oxide and potassium dihydrogen phosphate can undergo a hydration reaction to generate hydration products that provide strength, such as MgKPO4·6H2O (MgO + K2HPO4·3H2O + 3H2O → MgKPO4·6H2O). The addition of blast furnace slag and quicklime promotes rapid early strength development and further promotes the hydration reaction, increasing the MgKPO4·6H2O content and generating gel substances. The pozzolanic effect and micro-aggregate effect cement the soil pores and soil particles / aggregates, making the soil structure denser and ensuring the compactness of this repair material. This effectively improves the morphology of the hydration products, hinders water penetration, and enhances the water resistance of the slurry-stabilized soil. Meanwhile, unreacted blast furnace slag can serve as a micro-aggregate filler matrix to form an interfacial transition zone between the aggregate and quicklime, thereby increasing bonding performance.

[0022] The beneficial effects of this invention are:

[0023] The waste mud solidifier of this invention is based on magnesium phosphate cement. Magnesium phosphate cement can rapidly increase strength in a short period of time, and also has excellent properties such as high early strength after solidification, wear resistance and frost resistance. The modified magnesium phosphate cement has strong durability in treating waste mud and can meet the requirements of roadbed filling and other projects. It can solve the problem of large-scale waste mud stockpiling and land occupation, as well as the problem of high waste mud treatment costs. It reduces the cost of engineering construction and treatment and realizes the resource utilization of waste mud, which has environmental and economic benefits and is in line with the national concept of sustainable development. Attached Figure Description

[0024] Figure 1 This is a water stability effect diagram of waste mud after soaking in water for 1 day with the curing agent of this invention added;

[0025] Figure 2 This is a water stability effect diagram of waste mud after soaking in water for 5 days with the curing agent of this invention added;

[0026] Figure 3 This is a water stability effect diagram of waste mud after soaking in water for 9 days with the solidifying agent of this invention added;

[0027] Figure 4 The image shows the water stability effect of waste mud after soaking in water for 14 days with the curing agent of this invention added to it.

[0028] Figure 5 The image shows the water stability effect of adding the curing agent of this invention to waste mud and soaking it in water for 28 days. Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the content of the present invention is not limited to the following embodiments.

[0030] Example 1: A modified magnesium phosphate cement waste mud solidifier, comprising the following components by mass: 12 kg magnesium phosphate cement, 8 kg quicklime, 6 kg blast furnace slag, and 5 kg sodium silicate.

[0031] Mix magnesium phosphate cement, quicklime, blast furnace slag, and sodium silicate evenly according to the above proportions.

[0032] The quicklime is industrial-grade CaO.

[0033] The blast furnace slag is S95 slag powder.

[0034] The sodium silicate is industrial grade Na2SiO3.

[0035] A method for preparing a curing agent for rapidly solidifying waste mud using modified magnesium phosphate cement includes the following steps:

[0036] Step 1: Mix calcined magnesium oxide and potassium dihydrogen phosphate in a mass ratio of 3:1, add a small amount of water and stir evenly to make magnesium phosphate cement slurry. After drying, magnesium phosphate cement is obtained.

[0037] Step 2: Mix the above-mentioned parts by weight of magnesium phosphate cement, quicklime, blast furnace slag, and sodium silicate evenly and stir thoroughly to prepare waste mud solidification agent.

[0038] Example 2: A modified magnesium phosphate cement waste mud solidifier, comprising the following components by mass: 10 kg magnesium phosphate cement, 6 kg quicklime, 7 kg blast furnace slag, and 4 kg sodium silicate.

[0039] Mix magnesium phosphate cement, quicklime, blast furnace slag, and sodium silicate evenly according to the above proportions.

[0040] The quicklime is industrial-grade CaO.

[0041] The blast furnace slag is S95 slag powder.

[0042] The sodium silicate is industrial grade Na2SiO3.

[0043] A method for preparing a curing agent for rapidly solidifying waste mud using modified magnesium phosphate cement includes the following steps:

[0044] Step 1: Mix calcined magnesium oxide and potassium dihydrogen phosphate at a mass ratio of 4:1, add a small amount of water and stir evenly to make magnesium phosphate cement slurry. After drying, magnesium phosphate cement is obtained.

[0045] Step 2: Mix the above-mentioned parts by weight of magnesium phosphate cement, quicklime, blast furnace slag, and sodium silicate evenly and stir thoroughly to prepare waste mud solidification agent.

[0046] Example 3: A modified magnesium phosphate cement waste mud solidifier, comprising the following components by mass: 8 kg magnesium phosphate cement, 7 kg quicklime, 8 kg blast furnace slag, and 6 kg sodium silicate.

[0047] Mix magnesium phosphate cement, quicklime, blast furnace slag, and sodium silicate evenly according to the above proportions.

[0048] The quicklime is industrial-grade CaO.

[0049] The blast furnace slag is S95 slag powder.

[0050] The sodium silicate is industrial grade Na2SiO3.

[0051] A method for preparing a curing agent for rapidly solidifying waste mud using modified magnesium phosphate cement includes the following steps:

[0052] Step 1: Mix calcined magnesium oxide and potassium dihydrogen phosphate at a mass ratio of 5:1, add a small amount of water and stir evenly to make magnesium phosphate cement slurry. After drying, magnesium phosphate cement is obtained.

[0053] Step 2: Mix the above-mentioned parts by weight of magnesium phosphate cement, quicklime, blast furnace slag, and sodium silicate evenly and stir thoroughly to prepare waste mud solidification agent.

[0054] The waste mud solidifiers obtained in Examples 1-3 were used for waste mud solidification: the waste mud solidifiers obtained in Examples 1-3 were added to the waste mud and cured for 3 days, 7 days, 14 days and 28 days to form solidified mud soil.

[0055] Since the waste mud solidifiers obtained in Examples 1 to 3 have similar performance, the following only describes in detail the test results of various performance indicators of the waste mud solidifier obtained in Example 1.

[0056] 1. Unconfined compressive strength test

[0057] The unconfined compressive strength of slurry-solidified soil at different curing ages was tested as follows: The obtained waste slurry solidifier and waste slurry with a moisture content of 45% were mixed at a mass ratio of 1:5, and the mixture was poured into a 38.1mm × 80mm (d × h) three-lobed membrane, covered with plastic wrap, and cured at room temperature. The unconfined compressive strength of the slurry-solidified soil at different curing ages was then tested. The test results are shown in Table 1.

[0058] Table 1 Unconfined compressive strength of solidified soil from waste mud during curing.

[0059] Curing agent / g Waste mud / g 3d / MPa 7d / MPa 14d / MPa 28d / MPa 80 400 1.4 1.8 2.0 2.1

[0060] 2. Water stability test

[0061] For the slurry-cured soil after 28 days of curing, immersion tests were conducted. Immersion days were 1 day, 5 days, 9 days, 14 days, and 28 days. K1 is the unconfined compressive strength after immersion, and K is the unconfined strength of the slurry-cured soil after 28 days. P1 is the strength loss rate, P1 = (K - K1) / K. Specific test data are shown in Table 2.

[0062] Table 2

[0063]

[0064] 3. Wet and dry cycle test

[0065] For the slurry-cured soil after 28 days of curing, a wet-dry cycle test was conducted with 2, 4, 6, and 8 cycles. K2 is the unconfined compressive strength after immersion in water, and K is the unconfined strength of the slurry-cured soil after 28 days. P2 is the strength loss rate, P2 = (K - K2) / K. Specific test data are shown in Table 3.

[0066] Table 3

[0067] Number of wet and dry cycles 2 4 6 8 Strength / MPa 1.945 1.867 1.578 1.496 Strength retention factor 0.93 0.89 0.75 0.71

[0068] In actual engineering projects, the strength requirement for backfill soil is much lower than 1MPa. From the data in the table above, it can be seen that the strength of the soil in the later stage of curing in this test is relatively high. After 28 days of curing and 8 cycles of wet and dry curing, its strength still meets the requirements, and its durability is good, which can meet the requirements of backfill soil.

[0069] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in the details for the sake of brevity.

[0070] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A solidification agent for rapidly solidifying waste mud by modifying magnesium phosphate cement, characterized by, According to the quality parts, including the following components: magnesium phosphate cement 8~12 parts, quicklime 6~8 parts, blast furnace slag 6~8 parts, sodium silicate 4~6 parts; The magnesium phosphate cement is made of dead-burned magnesia and potassium dihydrogen phosphate with a mass ratio of 3:1~5:1; The solidifying agent is used for solidifying waste mud, and the mixing mass ratio of the solidifying agent and the waste mud is 1:

5.

2. The solidifying agent for rapidly solidifying waste mud of modified magnesium phosphate cement according to claim 1, characterized in that, The dead-burned magnesia is made of magnesite powder calcined at a high temperature above 1400℃.

3. The solidifying agent for rapidly solidifying waste mud of modified magnesium phosphate cement according to claim 1, characterized in that, The blast furnace slag is S95 slag powder.

4. The solidifying agent for rapidly solidifying waste mud of modified magnesium phosphate cement according to claim 1, characterized by, The sodium silicate is industrial-grade powder instant sodium silicate.

5. A method for producing a solidifying agent for rapidly solidifying waste mud with modified magnesium phosphate cement, characterized by, The preparation method comprises the following steps: Step one: mix the dead-burned magnesia and the potassium dihydrogen phosphate with a mass ratio of 3:1~5:1, add water, and stir uniformly with a blender to make a magnesium phosphate cement slurry, and then dry the magnesium phosphate cement slurry to obtain the magnesium phosphate cement; Step two: mix and stir uniformly the magnesium phosphate cement 8~12 parts, the quicklime 6~8 parts, the blast furnace slag 6~8 parts, and the sodium silicate 4~6 parts according to the quality parts to make a waste mud solidifying agent.

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