Preparation and performance regulation and control method of cement expanding agent

Abstract

The invention belongs to the technical field of cement-based material admixtures, and particularly relates to a preparation and performance regulation and control method of a cement expanding agent. The technical problems of large component fluctuation, unstable performance and excessive expansion prevention at present are solved. According to the method, magnesium oxide is treated through low-temperature calcination, surface treatment and nano coating, an auxiliary expansion source high-activity magnesium silicate mineral is introduced, and meanwhile, a bio-based polymer crystal form regulating agent is doped to modify lignosulfonate to regulate the crystallization process of a hydration product, so that the expansion performance is controllable and stable and does not change drastically due to fluctuation of raw materials; excessive expansion is avoided while concrete shrinkage is effectively compensated, and cracking damage of a set cement structure is prevented.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cement-based material admixtures, and particularly relates to a cement expansion agent preparation and performance control method. BACKGROUND

[0002] Concrete has the risk of cracking due to volume shrinkage during hardening, which affects the structural durability. To compensate for shrinkage and prevent cracking, cement expansion agents are often added in engineering. The expansion agent generates crystalline expansion pressure through hydration, causing the concrete to produce a moderate volume increase, thereby offsetting the shrinkage strain.

[0003] There are three main types of expansion agents currently in use: calcium-based expansion agents, calcium sulphoaluminate-based expansion agents, and magnesium-based expansion agents. Calcium-based expansion agents rely on the volume expansion of calcium oxide hydration to generate calcium hydroxide to compensate for shrinkage, with the characteristics of large expansion and early occurrence. However, the hydration rate is difficult to control. In addition, calcium-based expansion agents are sensitive to curing conditions and require sufficient water for hydration. If the curing is not proper, the expansion reaction may not be complete, affecting the compensation effect. Calcium sulphoaluminate-based expansion agents are usually composed of calcium sulphoaluminate minerals and gypsum, which generate ettringite crystals during hydration, causing volume expansion. This type of expansion agent has stable and controllable expansion, mainly occurring in the early stage, and is often used to compensate for early concrete shrinkage. However, the expansion effect of calcium sulphoaluminate-based expansion agents gradually stops in the later stage, and the long-term shrinkage compensation effect is limited. If calcium sulphoaluminate-based expansion agents are used alone, they may provide expansion in the early stage but still exhibit some shrinkage in the later stage, which cannot completely offset the long-term shrinkage strain. Magnesium-based expansion agents use the volume increase of magnesium oxide hydration to magnesium hydroxide to compensate for shrinkage. Magnesium-based expansion agents have a relatively slow hydration expansion that can last for several months or even longer, making them suitable for compensating for late-stage shrinkage. However, due to the delayed expansion, the early-age shrinkage is often not fully compensated.

[0004] In the prior art, the performance of magnesium-based expansion agents is significantly affected by the quality of raw materials and the calcination process. Traditional magnesium-based expansion agents are usually made by calcining magnesite, but magnesite resources are limited and have varying grades, resulting in fluctuations in the activity of different batches, making the expansion performance unstable.

[0005] In summary, it is necessary to develop a new type of cement expansion agent preparation and performance control method, which innovatively designs from the aspects of raw material selection, preparation process, and component synergy, to ensure stable and controllable expansion agent performance, and to compensate for shrinkage without causing structural damage. SUMMARY

[0006] The application provides a cement expansion agent preparation and performance control method, aiming to solve the problems of existing expansion agent composition fluctuations, unstable performance, and excessive expansion leading to cement stone structure damage.

[0007] The specific technical solution is as follows: A cement expansion agent preparation and performance control method, as follows: S1: Magnesium oxide pretreatment.

[0008] S11: Low-temperature calcination is performed on the magnesium oxide powder, and then air cooling is performed to 200 DEG C, and finally natural cooling is performed to room temperature, to obtain the calcined magnesium oxide powder.

[0009] S12: 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 the 100 parts of the calcined magnesium oxide powder prepared in S1, to obtain the surface-modified magnesium oxide.

[0010] S13: The magnesium oxide powder prepared in S12, nano-silicon dioxide and nano-metakaolin are stirred and mixed, to obtain the nano-wrapped magnesium oxide particles, and then aging treatment is performed, to obtain the pretreated magnesium oxide powder.

[0011] S2: Preparation of an auxiliary expansion source.

[0012] S21: Serpentine or sepiolite minerals are crushed, and then dried to constant weight in an oven at 105 DEG C, to obtain magnesium silicate mineral powder.

[0013] S22: The magnesium silicate mineral powder prepared in S21 is calcined, and then naturally cooled to 200 DEG C, and finally moved to a desiccator to cool to room temperature, to obtain the heat-activated magnesium silicate mineral powder.

[0014] S23: The magnesium silicate mineral powder treated in S22 is superfine ground, to obtain D 50 ≤5 mu m magnesium silicate powder.

[0015] S3: Lignosulfonate modification.

[0016] S31: Sodium lignosulfonate solid powder is slowly added into deionized water at 65 DEG C, and stirred until completely dissolved, to prepare a 25 wt% lignosulfonate solution.

[0017] S32: Hydrogen peroxide solution is added dropwise into the lignosulfonate solution prepared in S31, and stirred at 65-75 DEG C for 1-2 h, and then cooled to 50-60 DEG C, and sodium sulfite is added to adjust pH to 10, and continue to react for 2-3 h, to obtain the sulfonated lignosulfonate solution.

[0018] S33: Formaldehyde solution is added into the sulfonated lignosulfonate solution prepared in S32, and the pH is maintained at 11, and the temperature is increased to 80-85 DEG C, and reacted for 3-5 h. Then cooled to room temperature, and adjust the pH to 7, and finally the reaction solution is spray dried, to obtain the modified lignosulfonate powder.

[0019] S4: mixing preparation.

[0020] S41: mixing the activated magnesium silicate with part of the fly ash to obtain a magnesium silicate-fly ash mixture; mixing the pretreated magnesium oxide powder, calcium sulfoaluminate, and the remaining fly ash to obtain a basic mixture.

[0021] S42: mixing the magnesium silicate-fly ash mixture prepared in S41 with the basic mixture prepared in S41 to obtain an expansion agent premix; adding the modified lignosulfonate powder to the expansion agent premix, stirring and mixing at low speed, and sieving to obtain a cement expansion agent.

[0022] Further, the low-temperature calcination in S11 has the following parameters: temperature 1000-1200℃, heating rate 5-10℃ / min, holding time 30-60min, and oxygen excess 5-10%.

[0023] The spraying in S12 has the following parameters: temperature 80-110℃, and time 20-40min.

[0024] The nano-silicon dioxide and nano-metakaolin in S13 have the following proportions: nano-silicon dioxide 2-4% of the mass of magnesium oxide, and nano-metakaolin 3-5% of the mass of magnesium oxide.

[0025] The stirring in S13 has the following parameters: temperature 25℃, stirring speed 15rpm, and time 20min.

[0026] The aging treatment in S13 has the following parameters: temperature 50℃, relative humidity 60℃, and time 6 days.

[0027] Further, the calcination in S22 has the following parameters: temperature 600-750℃, heating rate 5-10℃ / min, and time 1.5-3h.

[0028] Further, the hydrogen peroxide solution in S32 has a mass ratio of 0.05:1-0.15:1 to the lignosulfonate.

[0029] The sodium sulfite in S32 has a mass ratio of 0.1:1-0.3:1 to the lignosulfonate.

[0030] The formaldehyde solution in S33 has a mass ratio of 0.08:1-0.2:1 to the lignosulfonate.

[0031] The spray drying in S33 has the following parameters: inlet temperature 180-200℃, and outlet temperature 90-100℃.

[0032] Further, the part of fly ash in S41 accounts for 20-30% of the total mass of fly ash.

[0033] The remaining fly ash in S41 accounts for 70-80% of the total mass of fly ash.

[0034] The low-speed mixing in S41 is parameterized as follows: rotation speed 15 rpm, time length 20 min.

[0035] The mixing in S42 is parameterized as follows: rotation speed 25 rpm, time length 30 min.

[0036] The low-speed stirring in S42 is parameterized as follows: rotation speed 10 rpm, time length 20 min.

[0037] Compared with the prior art, the present application has the following beneficial effects: 1. The present application solves the problem of large performance fluctuation of traditional magnesium oxide expansion agent by precisely regulating the activity of magnesium oxide and compounding multiple components, and by using low-temperature calcination-surface modification-nano coating.

[0038] 2. The present application avoids the situations of early uncompensation and late overcompensation by using calcium sulphoaluminate to form ettringite in early hydration and modified coated magnesium oxide to gradually hydrate in later period.

[0039] 3. The present application compensates for the strength loss caused by expansion by activating the secondary hydration reaction between active SiO2 in magnesium silicate minerals and Ca(OH)2 produced by cement hydration, and enhances the later strength. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A process flow chart of a cement expansion agent preparation and performance regulation method.

[0041] Figure 2 A comparison chart of the limited expansion rate, compressive strength, and magnesium oxide hydration rate of the cement expansion agent prepared in Examples 1-4 and Comparative Examples 1-3 after 7 days of internal cement permeation.

[0042] Figure 3 A comparison chart of the limited expansion rate, compressive strength, and magnesium oxide hydration rate of the cement expansion agent prepared in Examples 1-4 and Comparative Examples 1-3 after 28 days of internal cement permeation.

[0043] Figure 4 A comparison chart of the limited expansion rate, compressive strength, and magnesium oxide hydration rate of the cement expansion agent prepared in Examples 1-4 and Comparative Examples 1-3 after 60 days of internal cement permeation. DETAILED DESCRIPTION

[0044] The following examples further explain and illustrate the technical solutions of the present application. It is particularly pointed out that each specific embodiment is a specific embodiment and explanation of the technical solutions, and should not be regarded as a limitation on the scope of protection of the present application. Those skilled in the art still have the right to modify the technical solutions of these examples, to make equivalent replacements to some or all of the technical features, and these modifications or replacements do not change the essence of the corresponding technical solutions, and do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions described in the present application.

[0045] The present application proposes a cement expansion agent preparation and performance control method, which provides early moderate expansion by calcium sulfoaluminate, provides sustained expansion in the middle and late stages by specially treated magnesium oxide, provides micro-expansion and improves strength by magnesium silicate minerals, and ensures stable and orderly expansion by high molecular weight control agents. The synergistic effect of each component enables the expansion agent to function throughout the curing period. As shown in the accompanying Figure 1 The detailed technical solutions are as follows: 1. Pretreatment of magnesium oxide 1.1 Low-temperature calcination The low-temperature calcination of magnesium oxide enables the obtained magnesium oxide to have a moderate active content, and then air-cooling and rapid cooling to below 200℃, and finally natural cooling to room temperature. Rapid cooling can maintain the crystal structure and activity under high temperature, preventing the reduction of activity during slow cooling.

[0046] 1.2 Surface modification Take 100 parts of low-temperature calcined magnesium oxide powder as the base, mix 1.5-3.0 parts of aluminum dihydrogen phosphate solution and 0.5-1.5 parts of silane coupling agent, and then spray them onto the surface of the magnesium oxide powder to obtain surface-modified magnesium oxide. Aluminum dihydrogen phosphate reacts with the surface of magnesium oxide to form a dense and insoluble magnesium aluminum phosphate complex protective film, effectively blocking the initial contact of water molecules. The silanol group formed by the hydrolysis of the silane coupling agent condenses with the hydroxyl group on the surface of magnesium oxide to form a layer of hydrophobic organic silicon film, further delaying hydration and improving compatibility with the cement matrix.

[0047] 1.3 Nano-wrapping Mix the surface-modified magnesium oxide powder, nano-silicon dioxide, and nano-metakaolin to obtain nano-wrapped magnesium oxide particles. Nano-silicon dioxide and nano-metakaolin can react with magnesium hydroxide produced by magnesium oxide hydration and calcium hydroxide produced by cement hydration in the high alkalinity environment in the later stage of cement hydration to generate additional calcium silicate gel or magnesium-silicon hydrogen gel.

[0048] 1.4 Aging treatment The nano-wrapped magnesium oxide particles prepared above are subjected to aging treatment to stabilize the surface state of magnesium oxide and reduce the activity decay rate of the product during storage.

[0049] 2. Preparation of auxiliary expansion source 2.1 Pretreatment The serpentine or sepiolite mineral is crushed and then dried in an oven at 105°C to constant weight to remove free moisture, obtaining a magnesium silicate mineral powder, the serpentine or sepiolite being chosen because it has a layered or fibrous structure and is rich in magnesium oxide and silicon dioxide.

[0050] 2.2 Low-temperature thermal activation The dried magnesium silicate mineral powder is calcined and then naturally cooled to 200°C, and finally moved to a desiccator to cool to room temperature, preventing clumping of the product due to sudden cooling, obtaining a thermally activated magnesium silicate mineral powder.

[0051] 2.3 Ultrafine grinding The thermally activated magnesium silicate mineral powder is ultrafine ground, obtaining a magnesium silicate powder with a D 50 ≤ 5 μm, the ultrafine grinding destroying the stable crystal structure of the mineral and increasing the chemical activity.

[0052] 3. Modification of lignosulfonate 3.1 Preparation of lignosulfonate solution The sodium lignosulfonate solid powder is slowly added to deionized water at 65°C and stirred until completely dissolved, preparing a lignosulfonate solution with a concentration of 25 wt%, this concentration ensuring sufficient reactant concentration for the subsequent reaction and not affecting the mass transfer and mixing efficiency due to excessively high viscosity.

[0053] 3.2 Oxidative degradation and sulfonation modification Hydrogen peroxide solution is added dropwise to the lignosulfonate solution and stirred at 65-75°C for 1-2 h, hydrogen peroxide being chosen because it is green and environmentally friendly and does not introduce harmful impurities, the temperature being 65-75°C because at this temperature hydrogen peroxide decomposes to produce hydroxyl radicals, which can effectively break the chains and degrade lignin, while avoiding excessive boiling; the temperature is then lowered to 50-60°C, sodium sulfite is added, and the pH is adjusted to 10, and the reaction is continued for 2-3 h, obtaining a sulfonated lignosulfonate solution, the alkaline environment being conducive to the occurrence of the sulfonation reaction and effectively introducing sulfonic acid groups into the benzene ring or side chain of the lignin molecule.

[0054] 3.3 Polycondensation modification Formaldehyde solution is added to the above sulfonated lignosulfonate solution, the pH is maintained at 11, the temperature is raised to 80-85°C, and the reaction is continued for 3-5 h, the formaldehyde carbonyl group reacting with the phenolic hydroxyl group of the lignin molecule to form a methylene bridge, reconnecting the small lignin fragments, the alkaline and higher temperature being necessary conditions for the condensation reaction to occur, thereby precisely controlling the molecular weight of the final product (5000-20000 Da).

[0055] 3.4 Post-treatment The solution after the above polycondensation modification is cooled to room temperature and neutralized to pH = 7 with dilute sulfuric acid. The reaction solution is spray dried to obtain modified lignin sulfonate powder. Spray drying can quickly dehydrate and prevent the product from agglomeration or property change during long-time drying.

[0056] 4. Mixed preparation 4.1 Proportioning The mass proportion of pretreated magnesium oxide is 20-40%, the mass proportion of calcium sulfoaluminate is 15-30%, the mass proportion of pulverized and activated magnesium silicate powder is 10-20%, the mass proportion of modified lignin sulfonate powder is 1-3%, and the rest is fly ash.

[0057] 4.2 Premixing The pulverized and activated magnesium silicate is premixed with part of the fly ash to obtain a magnesium silicate-fly ash mixture. This step is to wrap and disperse the easily dusting and agglomerating magnesium silicate powder with fly ash to prevent the agglomeration of magnesium silicate powder. The pretreated magnesium oxide, calcium sulfoaluminate, and the remaining fly ash are mixed at medium-low speed to obtain a basic mixture. This step is to achieve uniform distribution of modified magnesium oxide powder, calcium sulfoaluminate, and fly ash with similar densities.

[0058] 4.3 Mixing The magnesium silicate-fly ash mixture is added to the basic mixture and mixed to obtain an expansion agent premix. This step ensures the macroscopic uniform mixing of all solid particles. The modified lignin sulfonate powder is added to the expansion agent premix and stirred at low speed. The cement expansion agent is obtained after sieving.

[0059] Example 1 A method for preparing and performance control of a cement expansion agent is as follows: Table 1 Main raw materials S1: Pretreatment of magnesium oxide.

[0060] S11: The magnesium oxide powder is calcined at low temperature, then air-cooled to 200℃, 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 oxygen excess 8%.

[0061] S12: 100g of calcined magnesium oxide powder prepared in S1 is used as a substrate. 2.5g of aluminum dihydrogen phosphate solution and 1g of silane coupling agent are mixed and then sprayed onto the surface of the magnesium oxide powder to obtain surface-modified magnesium oxide. The spraying parameters are set as follows: temperature 95℃, and time 30min.

[0062] S13: The magnesium oxide powder prepared in S12, nano-silicon dioxide and nano-metakaolin are stirred and mixed to obtain nano-coated magnesium oxide particles, and then aging treatment is performed to obtain pretreated magnesium oxide powder, wherein the mass of nano-silicon dioxide is 3% of the mass of magnesium oxide, the mass of nano-metakaolin is 4% of the mass of magnesium oxide, the stirring parameters are set as follows: temperature 25℃, rotation speed 15 rpm, time length 20 min, and the aging treatment parameters are set as follows: temperature 50℃, relative humidity 60℃, time length 6 days.

[0063] S2: Preparation of an auxiliary expansion source.

[0064] S21: Serpentine or sepiolite minerals are crushed, and then dried to constant weight in an oven at 105℃ to obtain magnesium silicate mineral powder.

[0065] S22: The magnesium silicate mineral powder prepared in S21 is calcined, and then naturally cooled to 200℃, and finally moved to a desiccator to cool to room temperature to obtain heat-activated magnesium silicate mineral powder, wherein the calcination parameters are set as follows: temperature 675℃, heating rate 8℃ / min, time length 2.5h.

[0066] S23: The magnesium silicate mineral powder treated in S22 is superfine ground to obtain D 50 ≤5μm magnesium silicate powder.

[0067] S3: Lignosulfonate modification.

[0068] S31: 100g of sodium lignosulfonate solid powder is slowly added to deionized water at 65℃, and stirred until completely dissolved to prepare a lignosulfonate solution with a concentration of 25wt%.

[0069] S32: Hydrogen peroxide solution is added dropwise to the lignosulfonate solution prepared in S31, and stirred at 70℃ for 1.5h, then cooled to 55℃, sodium sulfite is added, the pH is adjusted to 10, and the reaction is continued for 2.5h to obtain sulfonated lignosulfonate solution, wherein the mass ratio of lignosulfonate to hydrogen peroxide is 1:0.1, and the mass ratio of lignosulfonate to sodium sulfite is 1:0.2.

[0070] S33: Formaldehyde solution is added to the sulfonated lignosulfonate solution prepared in S32, the pH is maintained at 11, the temperature is raised to 83℃, and the reaction is carried out for 4h. Then cooled to room temperature, adjust the pH to 7, and finally the reaction solution is spray dried to obtain modified lignosulfonate powder, wherein the mass ratio of lignosulfonate to formaldehyde is 1:0.14, and the spray drying parameters are set as follows: inlet temperature 190℃, outlet temperature 95℃.

[0071] S4: Mixing preparation.

[0072] S41: The ground and activated magnesium silicate is premixed with part of the fly ash to obtain a magnesium silicate-fly ash mixture; the pretreated magnesium oxide powder, calcium sulfoaluminate, and the remaining fly ash are mixed at a low speed to obtain a basic mixture, wherein the mass ratio of each component is set as follows: the mass ratio of the pretreated magnesium oxide is 30%, the mass ratio of the calcium sulfoaluminate is 22.5%, the mass ratio of the ground and activated magnesium silicate powder is 15%, the mass ratio of the modified lignosulfonate powder is 2%, and the rest is fly ash, the mass ratio of part of the fly ash is 25% of the total mass of the fly ash, and the mass ratio of the remaining fly ash is 75% of the total mass of the fly ash.

[0073] S42: The magnesium silicate-fly ash mixture prepared in S41 is mixed with the basic mixture prepared in S41 to obtain an expansion agent premix; wherein the mixing parameters are set as follows: the rotation speed is 25 rpm, and the time length is 30 min. The modified lignosulfonate powder is added to the expansion agent premix, and low-speed stirring and mixing are performed, and sieving is performed to obtain a cement expansion agent, wherein the low-speed stirring and mixing parameters are set as follows: the rotation speed is 10 rpm, and the time length is 20 min.

[0074] Example 2 Referring to the composition and preparation process of Example 1, the difference lies in that: In the low-temperature calcination of S11 of the preparation process, the temperature is set to 1000℃, the heating rate is set to 5℃ / min, the holding time is set to 30 min, the atmosphere is set to an excess of 5% oxygen, and the other steps are the same.

[0075] In S12 of the preparation process, the mass of the aluminum dihydrogen phosphate solution is 1g, and the mass of the silane coupling agent is 0.5g, and the other components are the same.

[0076] In S12 of the preparation process, the parameters for spraying are set as follows: the temperature is 80℃, and the time length is 20 min, and the other steps are the same.

[0077] In S13 of the preparation process, the mass of the nano-silicon dioxide is 2% of the mass of the magnesium oxide, and the mass of the nano-metakaolin is 3% of the mass of the magnesium oxide, and the other components are the same.

[0078] In S22 of the preparation process, the parameters for calcination are set as follows: the temperature is 600℃, the heating rate is 5℃ / min, the time length is 1.5h, and the other steps are the same.

[0079] In S32 of the preparation process, the mass ratio of the lignosulfonate to hydrogen peroxide is 1:0.05, and the mass ratio of the lignosulfonate to sodium sulfite is 1:0.1, and the other components are the same.

[0080] In S32 of the preparation process, the hydrogen peroxide solution is added dropwise, stirred and reacted at 65℃ for 1h, then cooled to 50℃, added with sodium sulfite, and continued to react for 2h, and the other steps are the same.

[0081] The mass ratio of lignin sulfonate to formaldehyde in S33 of the preparation process is 1:0.08, and the other compositions are the same.

[0082] In S33 of the preparation process, the temperature was raised to 80°C, the reaction was carried out for 3 hours, and the spray drying parameters were set as follows: inlet temperature 180°C, outlet temperature 90°C, and the other steps were the same.

[0083] The distribution ratio of each group in S41 of the preparation process is set as follows: the mass proportion of pretreated magnesium oxide is 20%, the mass proportion of calcium sulfoaluminate is 15%, the mass proportion of ground activated magnesium silicate powder is 10%, the mass proportion of modified lignin sulfonate powder is 1%, and the rest is fly ash. The proportion of part of the fly ash is 20% of the total mass of the fly ash, and the remaining fly ash accounts for 80% of the total mass of the fly ash. The other proportions are the same.

[0084] Example 3 The composition and preparation process are the same as in Example 1, except that: The low-temperature calcination parameter settings of S11 in the preparation process are as follows: temperature 1200°C, heating rate 10°C / min, holding time 60 min, atmosphere with 10% excess oxygen, and other steps are the same.

[0085] In S12 of the preparation process, the mass of the aluminum dihydrogen phosphate solution is 3 g, the mass of the silane coupling agent is 1.5 g, and the other compositions are the same.

[0086] The spraying parameters in S12 of the preparation process are set as follows: temperature 110° C., duration 40 min, and other steps are the same.

[0087] In the preparation process S13, the mass of nano-silicon dioxide and nano-metakaolin is 4% of the mass of magnesium oxide, and the mass of nano-metakaolin is 5% of the mass of magnesium oxide. Other compositions are the same.

[0088] The calcination parameters in S22 of the preparation process are set as follows: temperature 750°C, heating rate 10°C / min, duration 3h, and the other steps are the same.

[0089] In S32 of the preparation process, 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 compositions are the same.

[0090] In S32 of the preparation process, hydrogen peroxide solution is added dropwise, and the mixture is stirred and reacted at 75° C. for 2 hours. The temperature is then lowered to 60° C., sodium sulfite is added, and the reaction is continued for 3 hours. The other steps are the same.

[0091] The mass ratio of lignin sulfonate to formaldehyde in S33 of the preparation process is 1:0.02, and the other compositions are the same.

[0092] The temperature in S33 of the preparation process is increased to 85℃, the reaction is performed for 5h, the spray drying parameters are set as: inlet temperature 200℃, outlet temperature 100℃, and the other steps are the same.

[0093] In S41 of the preparation process, the proportion of each component is set as: the mass proportion of pretreated magnesium oxide is 40%, the mass proportion of calcium sulfoaluminate is 30%, the mass proportion of activated magnesium silicate powder is 20%, the mass proportion of modified lignosulfonate powder is 3%, and the rest is fly ash, and the proportion of part of the fly ash is 30% of the total mass of fly ash, and the proportion of the remaining fly ash is 70% of the total mass of fly ash, and the other proportions are the same.

[0094] Example 4 Referring to the composition and preparation process of Example 1, the difference is that: In S11 of the preparation process, the low-temperature calcination parameters are set as: temperature 1050℃, heating rate 9℃ / min, holding time 50min, and atmosphere oxygen excess 7%, and the other steps are the same.

[0095] In S12 of the preparation process, the mass of aluminum dihydrogen phosphate solution is 2g, and the mass of silane coupling agent is 0.9g, and the other components are the same.

[0096] In S12 of the preparation process, spraying is performed, and the parameters are set as: temperature 105℃, time 35min, and the other steps are the same.

[0097] In S13 of the preparation process, the mass of nano-silicon dioxide is 2.5% of the mass of magnesium oxide, and the mass of nano-metakaolin is 4.5% of the mass of magnesium oxide, and the other components are the same.

[0098] In S22 of the preparation process, calcination is performed, and the parameters are set as: temperature 700℃, heating rate 7℃ / min, time 2.6h, and the other steps are the same.

[0099] In S32 of the preparation process, the mass ratio of lignosulfonate to hydrogen peroxide is 1:0.13, and the mass ratio of lignosulfonate to sodium sulfite is 1:0.25, and the other components are the same.

[0100] In S32 of the preparation process, hydrogen peroxide solution is added dropwise, stirred at 72℃ for 1.8h, then cooled to 60℃, sodium sulfite is added, and the reaction is continued for 2.2h, and the other steps are the same.

[0101] In S33 of the preparation process, the mass ratio of lignosulfonate to formaldehyde is 1:0.02, and the other components are the same.

[0102] In S33 of the preparation process, the temperature is increased to 84℃, the reaction is performed for 3.5h, the spray drying parameters are set as: inlet temperature 195℃, outlet temperature 92℃, and the other steps are the same.

[0103] The proportioning of each component in S41 of the preparation process is as follows: the mass proportion of pretreated magnesium oxide is 35%, the mass proportion of calcium sulfoaluminate is 27%, the mass proportion of activated magnesium silicate powder is 13%, the mass proportion of modified lignosulfonate powder is 1.5%, and the rest is fly ash, part of which accounts for 22% of the total mass of fly ash, and the rest accounts for 78% of the total mass of fly ash, and other proportions are the same.

[0104] Comparative Example 1 Referring to the composition and preparation process of Example 1, the difference is that: In S4 of the preparation process, the pretreated magnesium oxide is deleted, and unmodified magnesium oxide calcined at 1200℃ is directly mixed, and other steps are the same.

[0105] Comparative Example 2 Referring to the composition and preparation process of Example 1, the difference is that: In S4 of the preparation process, no magnesium silicate powder is added, and other steps are the same.

[0106] Comparative Example 3 Referring to the composition and preparation process of Example 1, the difference is that: In S4 of the preparation process, the modified lignosulfonate is deleted, and unmodified lignosulfonate is used instead, and other steps are the same.

[0107] Examples 1-4 and Comparative Examples 1-3 are combined to perform a limited expansion rate test: the cement mortar with internal expansion agent is made into a test body of a specified size, which is cured under constant temperature and humidity conditions, and the length change at different ages is measured using a length comparator to obtain the expansion rate, and the standard GB / T 23439-2017 “Concrete Expanding Agent” is referred to.

[0108] Examples 1-4 and Comparative Examples 1-3 are combined to perform a compressive strength test: the cement mortar with internal expansion agent of a specified proportion is made into a prism test piece, which is cured under standard conditions to a specified age. A standard bending and compression testing machine is used to press half of the test piece at a specified loading rate until failure, record the pressure value, and calculate the strength, and the standard GB / T 17671-2021 “Cement Mortar Strength Test Method (ISO Method)” is referred to.

[0109] Examples 1-4 and Comparative Examples 1-3 are combined to perform a magnesium oxide hydration rate test: a chemical titration method is used for testing, and the standard GB / T 176-2017 “Cement Chemical Analysis Method” is referred to.

[0110] The specific test results are shown in Tables 2, 3, 4, Figure 2 , Figure 3 , Figure 4 ​Table 2: 7-day performance comparison table of examples 1-4 and comparative examples 1-3 Table 3: 28-day performance comparison table of examples 1-4 and comparative examples 1-3 Table 4: 60-day performance comparison table of examples 1-4 and comparative examples 1-3 From the above comparison results, it can be seen that the comprehensive performance of example 1 is the best, the expansion rate is ideal, reaching 0.038% at 7 days, effectively compensating for the maximum shrinkage of cement in the early stage; it stably increases at 28 days and tends to be stable at 60 days, realizing stable compensation and no excessive expansion in the later period, and the compressive strength at each age is the highest, proving that the expansion process is well coordinated with the cement hydration process, the structure is not damaged, the magnesium oxide hydration rate is moderate in the early stage and steadily increases in the later stage, indicating that the activity is stable and controllable, which not only ensures sufficient expansion source but also avoids explosive hydration, indicating that example 1 solves the problem of unstable performance caused by large component fluctuations; the parameters of example 2 are the minimum values in the range, resulting in slightly slower early expansion and hydration rate, and slightly lower strength and final expansion; the parameters of example 3 are the maximum values in the range, resulting in slightly faster early expansion and hydration rate, a slight upward trend in 60-day expansion, and a slight negative impact on later strength; the comprehensive performance of examples 2 to 4 is slightly lower than that of example 1 but meets the reasonable range, which shows that excellent extraction effect is still achieved under large parameter variation; comparative example 1 does not use modified magnesium oxide, resulting in severe early expansion deficiency, huge later expansion, and strength reversal in the later period; comparative example 2 does not add auxiliary expansion source, and the expansion at each period is significantly insufficient, resulting in poor shrinkage compensation effect; although the strength is the highest, it is because the expansion is insufficient and cannot effectively offset the shrinkage stress generated by cement hydration, and there may be microcracks in the concrete; comparative example 3 uses unmodified lignosulfonate, resulting in uncontrolled expansion, with expansion rates at each period much higher than those of other groups and continuously and rapidly increasing, and its strength development is extremely poor; Figure Four Due to the 60-day time, magnesium oxide is almost completely hydrated, so the examples and comparative examples are within the range.

[0111] In summary, through the above examples and comparative examples, it can be clearly seen that the cement expansion agent preparation and performance control method provided by the present application solves the technical problems of large component fluctuations, unstable performance, and prevention of excessive expansion.

Claims

1. A method for preparing a cement expansion agent, characterized in that: The steps include: S1: magnesium oxide pretreatment; S11: calcining the magnesium oxide powder at a low temperature, then rapidly cooling it to 200° C. by air cooling, and finally naturally cooling it to room temperature to obtain calcined magnesium oxide powder; S12: Using 100 parts of the calcined magnesium oxide powder prepared in S1 as a substrate, 1.5 to 3.0 parts of aluminum dihydrogen phosphate solution and 0.5 to 1.5 parts of a silane coupling agent are mixed, and then sprayed onto the surface of the magnesium oxide powder to obtain surface-modified magnesium oxide; S13: stirring and mixing the surface-modified magnesium oxide prepared in S12, nano-silica, and nano-metakaolin to obtain nano-coated magnesium oxide particles, and then performing an aging treatment to obtain pretreated magnesium oxide powder; S2: Preparation of auxiliary expansion source; S21: crushing the serpentine or sepiolite mineral, and then drying it in an oven at 105° C. to a constant weight to obtain magnesium silicate mineral powder; S22: calcining the magnesium silicate mineral powder prepared in S21, then naturally cooling it to 200° C., and finally transferring it to a dryer and cooling it to room temperature to obtain thermally activated magnesium silicate mineral powder; S23: Ultrafine grinding of magnesium silicate mineral powder treated in S22 to obtain D 50 Magnesium silicate powder ≤5μm; S3: lignin sulfonate modification; S31: Slowly add sodium lignin sulfonate solid powder into deionized water at 65° C. and stir until completely dissolved to prepare a lignin sulfonate solution with a concentration of 25 wt%; S32: Add hydrogen peroxide solution dropwise to the lignin sulfonate solution prepared in S31, stir and react at 65-75°C for 1-2 hours, then cool to 50-60°C, add sodium sulfite, adjust the pH to 10, and continue the reaction for 2-3 hours to obtain a sulfonated lignin sulfonate solution; S33: adding the formaldehyde solution to the sulfonated lignin sulfonate solution prepared in S32, maintaining the pH at 11, raising the temperature to 80-85°C, and reacting for 3-5 hours; then cooling to room temperature, adjusting the pH to 7, and finally spray drying the reaction solution to obtain a modified lignin sulfonate powder; S4: Mixing preparation; S41: premixing the ground activated magnesium silicate with a portion of fly ash to obtain a magnesium silicate-fly ash mixture; and mixing the pretreated magnesium oxide powder, calcium sulfoaluminate, and the remaining fly ash at a medium to low speed to obtain a base mixture; S42: The magnesium silicate-fly ash mixture prepared in S41 is mixed with the basic mixture prepared in S41 to obtain an expansion agent premix; the modified lignin sulfonate powder is added to the expansion agent premix, stirred and mixed at a low speed, and sieved to obtain a cement expansion agent.

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

3. The method for preparing a cement expansion agent according to claim 1, wherein: The nano-silicon dioxide and nano-metakaolin described in S13, wherein the mass of the nano-silicon dioxide is 2-4% of the mass of the magnesium oxide, and the mass of the nano-metakaolin is 3-5% of the mass of the magnesium oxide; The stirring described in S13 has the following parameters: temperature 25°C, speed 15 rpm, and duration 20 min; The aging treatment described in S13 has the following parameter settings: temperature 50° C., relative humidity 60° C., and duration 6 days.

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

5. The method for preparing a cement expansion agent according to claim 1, wherein: The mass ratio of the hydrogen peroxide solution in S32 to the lignin sulfonate is 0.05:1 to 0.15:1; The mass ratio of the sodium sulfite described in S32 to the lignin sulfonate is 0.1:1 to 0.3:

1.

6. The method for preparing a cement expansion agent according to claim 1, wherein: The following steps are involved: The mass ratio of the formaldehyde solution in S33 to the lignin sulfonate is 0.08:1 to 0.2:1; The spray drying described in S33 has the following parameter settings: inlet temperature 180-200°C, outlet temperature 90-100°C.

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

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

9. The method for preparing a cement expansion agent according to claim 1, wherein: The mass of the pretreated magnesium oxide accounts for 20-40%, the mass of calcium sulfoaluminate accounts for 15-30%, the mass of the ground activated magnesium silicate powder accounts for 10-20%, the mass of the modified lignin sulfonate powder accounts for 1-3%, and the rest is fly ash.

10. A method for controlling the performance of a cement expansion agent, characterized in that: The cement expansive agent is characterized by its performance being regulated by calcium sulfoaluminate, specially treated magnesium oxide, magnesium silicate mineral, and polymer regulator. Calcium sulfoaluminate provides early expansion, specially treated magnesium oxide provides sustained expansion in the middle and late stages, magnesium silicate mineral provides micro-expansion and enhances strength, and the polymer regulator ensures smooth and orderly expansion. The synergistic effect of the components enables the expansive agent to function throughout the entire curing period.

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