Method for preparing and performance control of cement expansion agent

Abstract

This invention belongs to the field of cement-based material admixture technology, specifically relating to a method for preparing and controlling the performance of a cement expansion agent. Addressing the current technical problems of large fluctuations in composition, unstable performance, and the need to prevent excessive expansion, this invention treats magnesium oxide through low-temperature calcination, surface treatment, and nano-encapsulation, introducing a highly active magnesium silicate mineral as an auxiliary expansion source. Simultaneously, it incorporates a bio-based polymer crystal form regulator to modify lignin sulfonate, used to control the crystallization process of hydration products. This achieves controllable and stable expansion performance, preventing drastic changes due to raw material fluctuations. While effectively compensating for concrete shrinkage, it avoids excessive expansion, preventing cracking and damage to the cement stone structure.

Description

Technical Field

[0001] This invention belongs to the field of cement-based material admixtures technology, specifically relating to a method for preparing and controlling the performance of a cement expansion agent. Background Technology

[0002] Concrete is prone to cracking during the hardening process due to volume shrinkage, affecting structural durability. To compensate for shrinkage and prevent cracking, cement expansion agents are often added in engineering projects. The expansion agent generates crystallization expansion pressure through hydration, causing the concrete to produce a moderate volume increase, thereby offsetting shrinkage strain.

[0003] Currently, there are three main types of commonly used expansive agents: calcium-based expansive agents, calcium sulfoaluminate-based expansive agents, and magnesium-based expansive agents. Calcium-based expansive agents compensate for shrinkage by expanding in volume when free calcium oxide hydrates to form calcium hydroxide. They are characterized by large expansion and early occurrence, but their hydration rate is difficult to control. Furthermore, calcium-based expansive agents are sensitive to curing conditions; sufficient water is required for hydration, and inadequate curing can lead to incomplete expansion reactions, affecting the compensation effect. Calcium sulfoaluminate-based expansive agents are usually composed of calcium sulfoaluminate minerals and gypsum, etc. During hydration, they generate ettringite crystals, causing volume expansion. This type of expansive agent has stable and controllable expansion, mainly occurring in the early stages, and is often used to compensate for early shrinkage of concrete. However, the expansion effect of calcium sulfoaluminate expansive agents gradually ceases in the later stages, limiting their effectiveness in compensating for long-term shrinkage. If calcium sulfoaluminate expansive agents are used alone, they may provide expansion in the early stages, but some shrinkage still occurs later, failing to completely offset long-term shrinkage strain. Magnesium-based expansive agents utilize the characteristic of increased volume when magnesium oxide hydrates to form magnesium hydroxide to compensate for shrinkage. Magnesium-based swelling agents undergo hydration and expansion relatively slowly, which can last for months or even longer. This makes them suitable for compensating for later shrinkage. However, due to their delayed expansion, early-age shrinkage is often not adequately compensated.

[0004] In the existing technology, the performance of magnesium-based expansive agents is significantly affected by the quality of raw materials and calcination process. Traditional magnesium-based expansive agents are mostly made by calcining magnesite, but the source of magnesite is limited and the grade is not uniform. The activity of different batches varies, making the expansion performance not stable enough.

[0005] In conclusion, it is necessary to develop a novel method for the preparation and performance control of cement expanding agents. This method should incorporate innovative designs in terms of raw material selection, preparation process, and component synergy to ensure stable and controllable performance of the expanding agent, compensating for shrinkage without causing structural defects. Summary of the Invention

[0006] This invention provides a method for preparing and controlling the performance of a cement expanding agent, aiming to solve the problems of large fluctuations in the composition of existing expanding agents, unstable performance, and damage to the cement stone structure caused by excessive expansion.

[0007] The specific technical solution is as follows:

[0008] A method for preparing and controlling the performance of a cement expanding agent is as follows:

[0009] S1: Magnesium oxide pretreatment.

[0010] S11: Magnesium oxide powder is calcined at low temperature, then rapidly cooled to 200°C by air cooling, and finally naturally cooled to room temperature to obtain calcined magnesium oxide powder.

[0011] S12: Using 100 parts of calcined magnesium oxide powder prepared in S1 as a base, 1.5 to 3.0 parts of aluminum dihydrogen phosphate solution and 0.5 to 1.5 parts of silane coupling agent are mixed and then sprayed onto the surface of magnesium oxide powder to obtain surface-modified magnesium oxide.

[0012] S13: The magnesium oxide powder prepared in S12, nano-silica and nano-kaolin are stirred and mixed to obtain nano-encapsulated magnesium oxide particles, which are then aged to obtain pretreated magnesium oxide powder.

[0013] S2: Preparation of auxiliary expansion source.

[0014] S21: Crush serpentine or sepiolite minerals and then dry them in an oven at 105°C to constant weight to obtain magnesium silicate mineral powder.

[0015] S22: The magnesium silicate mineral powder prepared in S21 is calcined, then naturally cooled to 200°C, and finally transferred to a desiccator to cool to room temperature to obtain thermally activated magnesium silicate mineral powder.

[0016] S23: The magnesium silicate mineral powder treated in S22 is subjected to ultrafine grinding to obtain D. 50 Magnesium silicate powder with a particle size of ≤5μm.

[0017] S3: Lignosulfonate modified.

[0018] S31: Slowly add sodium lignosulfonate solid powder to deionized water at 65°C and stir until completely dissolved to prepare a lignosulfonate solution with a concentration of 25wt%.

[0019] S32: Add hydrogen peroxide solution dropwise to the lignin sulfonate solution prepared in S31, stir and react at 65-75℃ for 1-2 hours, then cool to 50-60℃, add sodium sulfite, adjust pH to 10, and continue the reaction for 2-3 hours to obtain the sulfonated lignin sulfonate solution.

[0020] S33: Add formaldehyde solution to the sulfonated lignin sulfonate solution prepared in S32, maintain pH at 11, raise the temperature to 80-85℃, and react for 3-5 hours. Then cool to room temperature, adjust pH to 7, and finally spray dry the reaction solution to obtain modified lignin sulfonate powder.

[0021] S4: Mixed preparation.

[0022] S41: Premix the milled and activated magnesium silicate with a portion of fly ash to obtain a magnesium silicate-fly ash mixture; mix the pretreated magnesium oxide powder, calcium sulfoaluminate, and the remaining fly ash at a medium-low speed to obtain a basic mixture.

[0023] S42: Mix the magnesium silicate-fly ash mixture prepared in S41 with the base mixture prepared in S41 to obtain an expansion agent premix; add the modified lignin sulfonate powder to the expansion agent premix, stir and mix at low speed, and sieve to obtain the cement expansion agent.

[0024] Furthermore, the low-temperature calcination described in S11 has the following parameter settings: temperature 1000~1200℃, heating rate 5~10℃ / min, holding time 30~60min, and atmosphere with 5~10% excess oxygen.

[0025] The spraying parameters described in S12 are: temperature 80-110℃, duration 20-40min.

[0026] The nano-silica and nano-meta-kaolin described in S13, wherein the mass of nano-silica is 2-4% of the mass of magnesium oxide, and the mass of nano-meta-kaolin is 3-5% of the mass of magnesium oxide.

[0027] The stirring described in S13 has the following parameters: temperature 25℃, speed 15rpm, and duration 20min.

[0028] The aging process described in S13 has the following parameters: temperature 50℃, relative humidity 60℃, and duration 6 days.

[0029] Furthermore, the calcination described in S22 has the following parameters: temperature 600–750°C, heating rate 5–10°C / min, and duration 1.5–3 hours.

[0030] Furthermore, the hydrogen peroxide solution described in S32 has a mass ratio of 0.05:1 to 0.15:1 with lignin sulfonate.

[0031] The sodium sulfite described in S32 has a mass ratio of 0.1:1 to 0.3:1 with lignin sulfonate.

[0032] The formaldehyde solution described in S33 has a mass ratio of 0.08:1 to 0.2:1 with lignin sulfonate.

[0033] The spray dryer described in S33 has the following parameter settings: inlet temperature 180-200℃, outlet temperature 90-100℃.

[0034] Furthermore, the fly ash described in S41 accounts for 20-30% of the total fly ash mass.

[0035] The remaining fly ash mentioned in S41 accounts for 70-80% of the total fly ash mass.

[0036] The low-to-medium speed mixing described in S41 has the following parameter settings: speed 15 rpm, duration 20 min.

[0037] The mixing described in S42 has the following parameter settings: rotation speed 25 rpm, duration 30 min.

[0038] The low-speed stirring described in S42 has the following parameters: speed 10 rpm, duration 20 min.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. This invention solves the problem of large performance fluctuations in traditional magnesium oxide expanders by precisely controlling the activity of magnesium oxide and using multi-component composites, and by utilizing low-temperature calcination-surface modification-nano-encapsulation.

[0041] 2. This invention utilizes the combined action of calcium sulfoaluminate and magnesium oxide, with calcium sulfoaluminate undergoing early hydration to form ettringite, while the modified and coated magnesium oxide undergoes gradual hydration in the later stages, thus avoiding both uncompensated early stages and overcompensated later stages.

[0042] 3. This invention compensates for the strength loss caused by expansion and enhances the later strength by activating the active SiO2 in magnesium silicate minerals to undergo a secondary hydration reaction with Ca(OH)2 produced by cement hydration. Attached Figure Description

[0043] Figure 1 This is a process flow diagram of a method for preparing and controlling the performance of a cement expanding agent.

[0044] Figure 2 This is a comparison chart of the restricted expansion rate, compressive strength, and magnesium oxide hydration rate of cement infiltrated with cement prepared in Examples 1-4 and Comparative Examples 1-3 after 7 days.

[0045] Figure 3 This is a comparison chart of the data on the restricted expansion rate, compressive strength, and magnesium oxide hydration rate of the cement expansion agents prepared in Examples 1-4 and Comparative Examples 1-3 after 28 days of infiltration into the cement.

[0046] Figure 4 This is a comparison chart of the data on the restricted expansion rate, compressive strength, and magnesium oxide hydration rate of cement infiltrated with the cement expansion agents prepared in Examples 1-4 and Comparative Examples 1-3 after 60 days. Detailed Implementation

[0047] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0048] This invention proposes a method for preparing and regulating the performance of a cement expanding agent. Calcium sulfoaluminate provides moderate early-stage expansion, specially treated magnesium oxide provides sustained mid-to-late-stage expansion, magnesium silicate minerals assist in micro-expansion and enhance strength, and a polymeric regulator ensures stable and orderly expansion. The synergistic effect of these components allows the expanding agent to function effectively throughout the entire curing period. (See attached diagram) Figure 1 The diagram shows a method for preparing and controlling the performance of a cement expanding agent. The detailed technical solution is as follows:

[0049] 1. Magnesium oxide pretreatment

[0050] 1.1 Low-temperature calcination

[0051] Magnesium oxide is calcined at low temperature to obtain magnesium oxide with a suitable activity content. Then, it is rapidly cooled to below 200°C by air cooling and finally cooled naturally to room temperature. Rapid cooling can maintain the crystal structure and activity at high temperature and prevent the activity from decreasing during slow cooling.

[0052] 1.2 Surface finishing

[0053] Using 100 parts of calcined magnesium oxide powder as a base, 1.5-3.0 parts of aluminum dihydrogen phosphate solution and 0.5-1.5 parts of silane coupling agent are mixed and then sprayed onto the surface of magnesium oxide powder to obtain surface-modified magnesium oxide. The aluminum dihydrogen phosphate reacts with the magnesium oxide surface to form a dense and insoluble magnesium aluminum phosphate double salt protective film, which effectively blocks the initial contact of water molecules. The silanol groups formed after the hydrolysis of the silane coupling agent condense with the hydroxyl groups on the magnesium oxide surface to form a hydrophobic organosilicon film, which further delays hydration and improves compatibility with cement matrix.

[0054] 1.3 nanometer encapsulation

[0055] Surface-modified magnesium oxide powder, nano-silica, and nano-kaolin are mixed to obtain nano-encapsulated magnesium oxide particles. In the high alkalinity environment of the later stage of cement hydration, nano-silica and nano-kaolin can react with magnesium hydroxide produced by magnesium oxide hydration and calcium hydroxide, a cement hydration product, to generate additional hydrated calcium silicate gel or magnesium silicate hydrogel.

[0056] 1.4 Aging treatment

[0057] The nano-encapsulated magnesium oxide particles prepared above are aged to stabilize the surface state of magnesium oxide and reduce the rate of activity decay of the product during storage.

[0058] 2. Preparation of auxiliary expansion source

[0059] 2.1 Preprocessing

[0060] The serpentine or sepiolite minerals are crushed and then dried in an oven at 105°C to constant weight to remove free moisture, resulting in magnesium silicate mineral powder. Serpentine or sepiolite is chosen because it has a layered or fibrous structure and is rich in magnesium oxide and silicon dioxide.

[0061] 2.2 Low-temperature thermal activation

[0062] The dried magnesium silicate mineral powder was calcined, then naturally cooled to 200°C, and finally transferred to a dryer to cool to room temperature to prevent the product from agglomerating due to sudden cooling, thus obtaining thermally activated magnesium silicate mineral powder.

[0063] 2.3 Ultrafine grinding

[0064] The thermally activated magnesium silicate mineral powder was ultrafine ground to obtain D. 50 Magnesium silicate powder with a particle size of ≤5μm is ultra-finely ground to disrupt the stable crystal structure of the mineral and enhance its chemical activity.

[0065] 3. Lignosulfonate modification

[0066] 3.1 Preparation of lignin sulfonate solution

[0067] Sodium lignosulfonate solid powder was slowly added to deionized water at 65°C and stirred until completely dissolved to prepare a lignosulfonate solution with a concentration of 25 wt%. This concentration ensures that the subsequent reaction has a sufficient concentration of reactants, while avoiding the impact of excessive viscosity on mass transfer and mixing efficiency.

[0068] 3.2 Oxidative Degradation and Sulfonation Modification

[0069] Hydrogen peroxide solution is added dropwise to the lignin sulfonate solution, and the mixture is stirred at 65-75℃ for 1-2 hours. Hydrogen peroxide is chosen because it is environmentally friendly and does not introduce harmful impurities. The temperature of 65-75℃ is chosen because at this temperature, hydrogen peroxide decomposes to produce hydroxyl radicals, which can effectively break the chain and degrade lignin, while avoiding excessive boiling. Then, the temperature is lowered to 50-60℃, sodium sulfite is added, the pH is adjusted to 10, and the reaction continues for 2-3 hours to obtain the sulfonated lignin sulfonate solution. The alkaline environment is conducive to the occurrence of the sulfonation reaction and can effectively introduce sulfonic acid groups into the benzene ring or side chain of the lignin molecule.

[0070] 3.3 Polycondensation Modification

[0071] Formaldehyde solution is added to the sulfonated lignin sulfonate solution, the pH is maintained at 11, the temperature is raised to 80-85℃, and the reaction is carried out for 3-5 hours. The formaldehyde carbonyl group can react with the phenolic hydroxyl group of the lignin molecule to form a methylene bridge, which reconnects the small lignin fragments. Alkalinity and high temperature are necessary conditions for promoting the condensation reaction, thereby precisely controlling the molecular weight of the final product (5000-20000 Da).

[0072] 3.4 Post-processing

[0073] The above-described condensation-modified solution was cooled to room temperature and neutralized with dilute sulfuric acid to pH 7. The reaction solution was then spray-dried to obtain modified lignin sulfonate powder. Spray drying allows for rapid dehydration, preventing agglomeration or property changes in the product during prolonged drying.

[0074] 4. Mixed preparation

[0075] 4.1 Proportioning

[0076] The pretreated magnesium oxide accounts for 20-40% of the mass, calcium sulfoaluminate accounts for 15-30% of the mass, milled and activated magnesium silicate powder accounts for 10-20% of the mass, modified lignin sulfonate powder accounts for 1-3% of the mass, and the remainder is fly ash.

[0077] 4.2 Premixing

[0078] The milled and activated magnesium silicate is premixed with a portion of fly ash to obtain a magnesium silicate-fly ash mixture. This step uses fly ash to coat and disperse the magnesium silicate powder, which is highly prone to dust generation and agglomeration, preventing agglomeration. The pretreated magnesium oxide, calcium sulfoaluminate, and the remaining fly ash are then mixed at medium to low speeds to obtain a basic mixture. This step aims to achieve a uniform distribution of modified magnesium oxide powder, calcium sulfoaluminate, and fly ash with similar densities.

[0079] 4.3 Mixing

[0080] The magnesium silicate-fly ash mixture is added to the base mixture and mixed to obtain the expansion agent premix. This step ensures that all solid particles are macroscopically uniformly mixed. Modified lignin sulfonate powder is added to the expansion agent premix, stirred at low speed, and sieved to obtain the cement expansion agent.

[0081] Example 1

[0082] A method for preparing and controlling the performance of a cement expanding agent is as follows:

[0083] Table 1 Main Raw Materials

[0084]

[0085] S1: Magnesium oxide pretreatment.

[0086] S11: Magnesium oxide powder is calcined at low temperature, then rapidly cooled to 200℃ by air cooling, and finally naturally cooled to room temperature to obtain calcined magnesium oxide powder. The low temperature calcination parameters are set as follows: temperature 1100℃, heating rate 8℃ / min, holding time 45min, and atmosphere with 8% excess oxygen.

[0087] S12: Using 100g of calcined magnesium oxide powder prepared in S1 as a base, 2.5g of aluminum dihydrogen phosphate solution and 1g of silane coupling agent are mixed and then sprayed onto the surface of magnesium oxide powder to obtain surface-modified magnesium oxide. The spraying parameters are set as follows: temperature 95℃, duration 30min.

[0088] S13: The magnesium oxide powder prepared in S12, nano-silica, and nano-kaolin are stirred and mixed to obtain nano-coated magnesium oxide particles, which are then aged to obtain pretreated magnesium oxide powder. The mass of nano-silica is 3% of the mass of magnesium oxide, and the mass of nano-kaolin is 4% of the mass of magnesium oxide. The stirring parameters are set as follows: temperature 25℃, speed 15rpm, time 20min. The aging parameters are set as follows: temperature 50℃, relative humidity 60℃, time 6 days.

[0089] S2: Preparation of auxiliary expansion source.

[0090] S21: Crush serpentine or sepiolite minerals and then dry them in an oven at 105°C to constant weight to obtain magnesium silicate mineral powder.

[0091] S22: The magnesium silicate mineral powder prepared in S21 is calcined, then naturally cooled to 200℃, and finally transferred to a desiccator to cool to room temperature to obtain thermally activated magnesium silicate mineral powder. The calcination parameters are set as follows: temperature 675℃, heating rate 8℃ / min, and duration 2.5h.

[0092] S23: The magnesium silicate mineral powder treated in S22 is subjected to ultrafine grinding to obtain D. 50 Magnesium silicate powder with a particle size of ≤5μm.

[0093] S3: Lignosulfonate modified.

[0094] S31: Slowly add 100g of sodium lignosulfonate solid powder to deionized water at 65℃ and stir until completely dissolved to prepare a lignosulfonate solution with a concentration of 25wt%.

[0095] S32: Add hydrogen peroxide solution dropwise to the lignin sulfonate solution prepared in S31, stir and react at 70℃ for 1.5h, then cool to 55℃, add sodium sulfite, adjust pH=10, and continue the reaction for 2.5h to obtain the sulfonated lignin sulfonate solution, wherein the mass ratio of lignin sulfonate to hydrogen peroxide is 1:0.1, and the mass ratio of lignin sulfonate to sodium sulfite is 1:0.2.

[0096] S33: Add formaldehyde solution to the sulfonated lignin sulfonate solution prepared in S32, maintain pH at 11, raise the temperature to 83℃, and react for 4 hours. Then cool to room temperature, adjust pH to 7, and finally spray dry the reaction solution to obtain modified lignin sulfonate powder. The mass ratio of lignin sulfonate to formaldehyde is 1:0.14. Spray drying parameters are set as follows: inlet temperature 190℃, outlet temperature 95℃.

[0097] S4: Mixed preparation.

[0098] S41: Premix the milled and activated magnesium silicate with a portion of fly ash to obtain a magnesium silicate-fly ash mixture; mix the pretreated magnesium oxide powder, calcium sulfoaluminate, and the remaining fly ash at a medium-low speed to obtain a basic mixture. The proportions of each component are set as follows: the mass percentage of pretreated magnesium oxide is 30%, the mass percentage of calcium sulfoaluminate is 22.5%, the mass percentage of milled and activated magnesium silicate powder is 15%, the mass percentage of modified lignin sulfonate powder is 2%, and the remainder is fly ash, with the portion of fly ash accounting for 25% of the total mass of fly ash and the remaining fly ash accounting for 75% of the total mass of fly ash.

[0099] S42: The magnesium silicate-fly ash mixture prepared in S41 is mixed with the base mixture prepared in S41 to obtain an expansive agent premix; the mixing parameters are set as follows: rotation speed 25 rpm, time 30 min. Modified lignin sulfonate powder is added to the expansive agent premix, stirred at low speed, and sieved to obtain a cement expansive agent; the low-speed stirring parameters are set as follows: rotation speed 10 rpm, time 20 min.

[0100] Example 2

[0101] The composition and preparation process are the same as in Example 1, except that:

[0102] The parameters for the low-temperature calcination of S11 in the preparation process are set as follows: temperature 1000℃, heating rate 5℃ / min, holding time 30min, atmosphere with 5% excess oxygen, and other steps are the same.

[0103] In the preparation process, the mass of aluminum dihydrogen phosphate solution in S12 is 1g, the mass of silane coupling agent is 0.5g, and other components are the same.

[0104] Spraying in step S12 of the preparation process, with the following parameters: temperature 80℃, duration 20min, and other steps are the same.

[0105] In the preparation process S13, nano-silica and nano-meta-kaolin are used. The mass of nano-silica is 2% of the mass of magnesium oxide, and the mass of nano-meta-kaolin is 3% of the mass of magnesium oxide. Other components are the same.

[0106] The calcination in S22 of the preparation process is set with the following parameters: temperature 600℃, heating rate 5℃ / min, duration 1.5h, and other steps are the same.

[0107] In the preparation process S32, the mass ratio of lignin sulfonate to hydrogen peroxide is 1:0.05, the mass ratio of lignin sulfonate to sodium sulfite is 1:0.1, and other components are the same.

[0108] In step S32 of the preparation process, hydrogen peroxide solution is added dropwise, and the mixture is stirred at 65°C for 1 hour. Then, the temperature is lowered to 50°C, sodium sulfite is added, and the reaction continues for 2 hours. The other steps are the same.

[0109] In the preparation process S33, the mass ratio of lignin sulfonate to formaldehyde is 1:0.08, and the other components are the same.

[0110] In step S33 of the preparation process, the temperature is raised to 80℃ and the reaction is carried out for 3 hours. The spray drying parameters are set as follows: inlet temperature 180℃, outlet temperature 90℃, and other steps are the same.

[0111] The proportions of each component in S41 of the preparation process are set as follows: pretreated magnesium oxide accounts for 20% of the mass, calcium sulfoaluminate accounts for 15% of the mass, milled and activated magnesium silicate powder accounts for 10% of the mass, modified lignin sulfonate powder accounts for 1% of the mass, and the remainder is fly ash. Part of the fly ash accounts for 20% of the total fly ash mass, and the remaining fly ash accounts for 80% of the total fly ash mass. Other proportions are the same.

[0112] Example 3

[0113] The composition and preparation process are the same as in Example 1, except that:

[0114] The parameters for the low-temperature calcination of S11 in the preparation process are set as follows: temperature 1200℃, heating rate 10℃ / min, holding time 60min, atmosphere with 10% excess oxygen, and other steps are the same.

[0115] In the preparation process, the mass of aluminum dihydrogen phosphate solution in S12 is 3g, the mass of silane coupling agent is 1.5g, and other components are the same.

[0116] Spraying in step S12 of the preparation process, with the following parameters: temperature 110℃, duration 40min, and other steps are the same.

[0117] In the preparation process S13, nano-silica and nano-meta-kaolin are used. The mass of nano-silica is 4% of the mass of magnesium oxide, and the mass of nano-meta-kaolin is 5% of the mass of magnesium oxide. Other components are the same.

[0118] The calcination in S22 of the preparation process is set with the following parameters: temperature 750℃, heating rate 10℃ / min, duration 3h, and other steps are the same.

[0119] In the preparation process S32, the mass ratio of lignin sulfonate to hydrogen peroxide is 1:0.15, the mass ratio of lignin sulfonate to sodium sulfite is 1:0.3, and other components are the same.

[0120] In the preparation process, hydrogen peroxide solution was added dropwise to S32, and the mixture was stirred at 75°C for 2 hours. Then, the temperature was lowered to 60°C, sodium sulfite was added, and the reaction was continued for 3 hours. The other steps were the same.

[0121] In the preparation process S33, the mass ratio of lignin sulfonate to formaldehyde is 1:0.02, and the other components are the same.

[0122] In step S33 of the preparation process, the temperature is raised to 85℃ and the reaction is carried out for 5 hours. The spray drying parameters are set as follows: inlet temperature 200℃, outlet temperature 100℃, and other steps are the same.

[0123] The proportions of each component in S41 of the preparation process are set as follows: 40% by mass of pretreated magnesium oxide, 30% by mass of calcium sulfoaluminate, 20% by mass of milled and activated magnesium silicate powder, 3% by mass of modified lignin sulfonate powder, and the remainder is fly ash. Part of the fly ash accounts for 30% of the total fly ash mass, and the remaining fly ash accounts for 70% of the total fly ash mass. Other proportions are the same.

[0124] Example 4

[0125] The composition and preparation process are the same as in Example 1, except that:

[0126] The S11 low-temperature calcination parameters for the preparation process are set as follows: temperature 1050℃, heating rate 9℃ / min, holding time 50min, atmosphere with 7% excess oxygen, and other steps are the same.

[0127] In the preparation process, the mass of aluminum dihydrogen phosphate solution in S12 is 2g, the mass of silane coupling agent is 0.9g, and other components are the same.

[0128] The spraying process in step S12 of the preparation process is set with the following parameters: temperature 105℃, duration 35min, and other steps are the same.

[0129] In the preparation process S13, nano-silica and nano-meta-kaolin are used. The mass of nano-silica is 2.5% of the mass of magnesium oxide, and the mass of nano-meta-kaolin is 4.5% of the mass of magnesium oxide. Other components are the same.

[0130] The calcination in S22 of the preparation process is set with the following parameters: temperature 700℃, heating rate 7℃ / min, duration 2.6h, and other steps are the same.

[0131] In the preparation process S32, the mass ratio of lignin sulfonate to hydrogen peroxide is 1:0.13, the mass ratio of lignin sulfonate to sodium sulfite is 1:0.25, and other components are the same.

[0132] In the preparation process, hydrogen peroxide solution was added dropwise to S32, and the mixture was stirred at 72°C for 1.8 h. Then the temperature was lowered to 60°C, sodium sulfite was added, and the reaction was continued for 2.2 h. The other steps were the same.

[0133] In the preparation process S33, the mass ratio of lignin sulfonate to formaldehyde is 1:0.02, and the other components are the same.

[0134] In the preparation process, the temperature in step S33 is increased to 84℃, and the reaction is carried out for 3.5 hours. The spray drying parameters are set as follows: inlet temperature 195℃, outlet temperature 92℃, and other steps are the same.

[0135] The proportions of each component in S41 of the preparation process are set as follows: pretreated magnesium oxide accounts for 35% of the mass, calcium sulfoaluminate accounts for 27% of the mass, milled and activated magnesium silicate powder accounts for 13% of the mass, modified lignin sulfonate powder accounts for 1.5% of the mass, and the remainder is fly ash. Part of the fly ash accounts for 22% of the total fly ash mass, and the remaining fly ash accounts for 78% of the total fly ash mass. Other proportions are the same.

[0136] Comparative Example 1

[0137] The composition and preparation process are the same as in Example 1, except that:

[0138] In step S4 of the preparation process, pretreated magnesium oxide is removed, and unmodified magnesium oxide calcined at 1200℃ is directly used for mixing. The other steps are the same.

[0139] Comparative Example 2

[0140] The composition and preparation process are the same as in Example 1, except that:

[0141] Magnesium silicate powder is not added in step S4 of the preparation process; the other steps are the same.

[0142] Comparative Example 3

[0143] The composition and preparation process are the same as in Example 1, except that:

[0144] In step S4 of the preparation process, the modified lignin sulfonate is removed and replaced with unmodified lignin sulfonate; the other steps remain the same.

[0145] Based on Examples 1-4 and Comparative Examples 1-3, a restricted expansion rate test was conducted: cement mortar with internal expansion agent was made into specimens of specified size, cured under constant temperature and humidity conditions, and the length change at different ages was measured using a length comparator to obtain the expansion rate, referring to standard GB / T 23439-2017 "Concrete Expansion Agent".

[0146] Combining Examples 1-4 and Comparative Examples 1-3, compressive strength tests were conducted: Prismatic specimens were prepared from cement mortar containing a specified proportion of expanding agent and cured under standard conditions to the specified age. Using a standard flexural and compressive strength testing machine, half of the specimen was compressed at a specified loading rate until failure. The pressure values ​​were recorded, and the strength was calculated, referring to standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0147] Based on Examples 1-4 and Comparative Examples 1-3, the hydration rate of magnesium oxide was tested using chemical titration, referring to standard GB / T 176-2017 "Chemical Analysis Methods for Cement".

[0148] The specific test results are shown in Tables 2, 3, and 4. Figure 2 , Figure 3 , Figure 4 As shown:

[0149] Table 2. 7-day performance comparison of Examples 1-4 and Comparative Examples 1-3

[0150]

[0151] Table 3. 28-day performance comparison of Examples 1-4 and Comparative Examples 1-3

[0152]

[0153] Table 4. 60-day performance comparison of Examples 1-4 and Comparative Examples 1-3

[0154]

[0155] The comparison results above show that Example 1 exhibits the best overall performance, with an ideal development of its limited expansion rate, reaching 0.038% at 7 days, effectively compensating for the maximum early shrinkage of cement; it shows stable growth at 28 days and tends to stabilize at 60 days, achieving stable compensation without excessive expansion in the later stages. Its compressive strength is the highest at all ages, proving that its expansion process is well-coordinated with the cement hydration process, without damaging the structure. The magnesium oxide hydration rate is moderate in the early stages and steadily increases in the later stages, indicating that its activity is stable and controllable, ensuring sufficient expansion sources while avoiding explosive hydration. This demonstrates that Example 1 solves the problem of performance instability caused by large component fluctuations. Example 2's parameters are at the minimum range, resulting in slightly slower early expansion and hydration rates, and slightly lower strength and final expansion. Example 3's parameters are at the maximum range, resulting in faster early expansion and hydration rates. The rate was slightly faster, with a slight increasing trend in expansion over 60 days, and a slight negative impact on later strength. The overall performance of Examples 2 to 4 was slightly lower than that of Example 1, but within a reasonable range, indicating that excellent extraction results were still achieved under a wide range of parameter variations. Comparative Example 1, due to the lack of modified magnesium oxide, resulted in severely insufficient early expansion, huge later expansion, and strength shrinkage in the later stages. Comparative Example 2, without the addition of an auxiliary expansion source, showed significantly insufficient expansion at each stage, with poor shrinkage compensation. Although it had the highest strength, this was because insufficient expansion failed to effectively offset the shrinkage stress generated by cement hydration, and microcracks may exist inside the concrete. Comparative Example 3, using unmodified lignin sulfonate, resulted in uncontrolled expansion, with expansion rates at each stage far exceeding those of other groups and continuing to increase rapidly. At the same time, its strength development was extremely poor. Figure 4 Since magnesium oxide is almost completely hydrated within 60 days, the examples and comparative examples are within its scope.

[0156] In summary, it can be clearly seen from the above embodiments and comparative examples that the method for preparing and controlling the performance of cement expanding agent provided by the present invention solves the technical problems of large fluctuations in composition, unstable performance, and prevention of excessive expansion.

Claims

1. A method for preparing a cement expanding agent, characterized in that, Includes the following steps: S1: Magnesium oxide pretreatment; S11: Calcine magnesium oxide powder, then rapidly cool it to 200°C using air cooling, and finally allow it to cool naturally to room temperature to obtain calcined magnesium oxide powder. S12: Using 100 parts of calcined magnesium oxide powder prepared in S1 as a base, 1.5 to 3.0 parts of aluminum dihydrogen phosphate solution and 0.5 to 1.5 parts of silane coupling agent are mixed and then sprayed onto the surface of magnesium oxide powder to obtain surface-modified magnesium oxide. S13: The surface-modified magnesium oxide, nano-silica, and nano-kaolin prepared in S12 are stirred and mixed to obtain nano-encapsulated magnesium oxide particles, which are then aged to obtain pretreated magnesium oxide powder. S2: Preparation of auxiliary expansion source; S21: Crush serpentine or sepiolite minerals and then dry them in an oven at 105°C to constant weight to obtain magnesium silicate mineral powder. S22: The magnesium silicate mineral powder prepared in S21 is calcined, then naturally cooled to 200°C, and finally transferred to a desiccator to cool to room temperature to obtain thermally activated magnesium silicate mineral powder. S23: The magnesium silicate mineral powder treated in S22 is subjected to ultrafine grinding to obtain D. 50 Magnesium silicate powder with a particle size of ≤5μm; S3: Lignosulfonate modified; S31: Slowly add sodium lignosulfonate solid powder to deionized water at 65°C and stir until completely dissolved to prepare a lignosulfonate solution with a concentration of 25wt%. S32: Add hydrogen peroxide solution dropwise to the lignin sulfonate solution prepared in S31, stir and react at 65-75℃ for 1-2 hours, then cool to 50-60℃, add sodium sulfite, adjust pH=10, and continue the reaction for 2-3 hours to obtain the sulfonated lignin sulfonate solution. S33: Add formaldehyde solution to the sulfonated lignin sulfonate solution prepared in S32, maintain pH at 11, raise the temperature to 80-85℃, and react for 3-5 hours; then cool to room temperature, adjust pH to 7, and finally spray dry the reaction solution to obtain modified lignin sulfonate powder. S4: Mixed preparation; S41: Premix the milled and activated magnesium silicate with a portion of fly ash to obtain a magnesium silicate-fly ash mixture; mix the pretreated magnesium oxide powder, calcium sulfoaluminate, and the remaining fly ash at a medium-low speed to obtain a basic mixture; S42: Mix the magnesium silicate-fly ash mixture prepared in S41 with the base mixture prepared in S41 to obtain an expansion agent premix; add the modified lignin sulfonate powder to the expansion agent premix, stir and mix at low speed, and sieve to obtain the cement expansion agent.

2. The method for preparing a cement expanding agent according to claim 1, characterized in that: The calcination described in S11 has the following parameter settings: temperature 1000-1200℃, heating rate 5-10℃ / min, holding time 30-60min, and atmosphere with 5-10% excess oxygen. The spraying parameters described in S12 are: temperature 80-110℃, duration 20-40min.

3. The method for preparing a cement expanding agent according to claim 1, characterized in that: The nano-silica and nano-metakaolin described in S13, wherein the mass of nano-silica is 2-4% of the mass of magnesium oxide, and the mass of nano-metakaolin is 3-5% of the mass of magnesium oxide; The stirring described in S13 has the following parameters: temperature 25℃, speed 15rpm, duration 20min. The aging process described in S13 has the following parameters: temperature 50℃, relative humidity 60℃, and duration 6 days.

4. The method for preparing a cement expanding agent according to claim 1, characterized in that: The calcination described in S22 has the following parameters: temperature 600-750℃, heating rate 5-10℃ / min, and duration 1.5-3h.

5. The method for preparing a cement expanding agent according to claim 1, characterized in that: The hydrogen peroxide solution described in S32 has a mass ratio of 0.05:1 to 0.15:1 with lignin sulfonate. The sodium sulfite described in S32 has a mass ratio of 0.1:1 to 0.3:1 with lignin sulfonate.

6. The method for preparing a cement expanding agent according to claim 1, characterized in that, Includes the following steps: The formaldehyde solution described in S33 has a mass ratio of 0.08:1 to 0.2:1 with lignin sulfonate. The spray dryer described in S33 has the following parameter settings: inlet temperature 180-200℃, outlet temperature 90-100℃.

7. The method for preparing a cement expanding agent according to claim 1, characterized in that: The portion of fly ash mentioned in S41 accounts for 20-30% of the total mass of fly ash. The remaining fly ash mentioned in S41 accounts for 70-80% of the total fly ash mass. The low-to-medium speed mixing described in S41 has the following parameter settings: speed 15 rpm, duration 20 min.

8. The method for preparing a cement expanding agent according to claim 1, characterized in that: The mixing described in S42 has the following parameter settings: rotation speed 25 rpm, duration 30 min; The low-speed stirring described in S42 has the following parameters: speed 10 rpm, duration 20 min.

9. The method for preparing a cement expanding agent according to claim 1, characterized in that: The pretreated magnesium oxide accounts for 20-40% by mass, calcium sulfoaluminate accounts for 15-30% by mass, milled and activated magnesium silicate powder accounts for 10-20% by mass, modified lignin sulfonate powder accounts for 1-3% by mass, and the remainder is fly ash.

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