A composite functional admixture with early strength and long-term collapse protection, and its preparation method and application

Abstract

The present invention belongs to the technical field of building material admixtures and discloses a composite functional admixture for early strength and long-term collapse protection, its preparation method, and application. The preparation method comprises the following steps: 1) adding tricalcium aluminate, an activator, and a grinding medium to water, adjusting the pH and then grinding, and removing the grinding medium after grinding to obtain a suspension A; 2) adding the suspension A and a water reducer to a reactor, passing an inert gas through the reactor for protection, and reacting under heating and pressure to obtain a suspension B; 3) stirring and mixing the suspension B with a surfactant and limestone powder, and then ultrasonically dispersing the mixture to obtain the composite functional admixture for early strength and long-term collapse protection. When the composite functional admixture of the present invention is applied to supersulfated cement, it not only has excellent early strength performance, but also can achieve water reduction and long-term collapse protection, providing effective technical support for the large-scale application of supersulfated cement.

Description

Technical Field

[0001] The invention belongs to the technical field of building material admixtures, and particularly relates to an early-strength and long-lasting collapse-preserving composite functional admixture, a preparation method and an application thereof. Background Art

[0002] The cement and building materials industry is gradually transitioning towards a low-carbon industry. Among them, using low-carbon cementitious materials to replace traditional Portland cement is one of the main ways to achieve "carbon emission reduction". Supersulfated cement (SSC) is generally composed of 70-90wt% slag, 10-20wt% sulfate activator (phosphogypsum, anhydrite, etc.) and 0-5wt% alkaline activator (cement clinker, calcium hydroxide, etc.). Its hydration products are mainly ettringite (AFt) and C(A)-SH gel. Considering its extremely high utilization rate of industrial by-products, supersulfated cement is a recognized low-carbon cement, and has the advantages of low hydration heat, excellent resistance to sulfate erosion and volume stability.

[0003] However, due to the low CaO content, high SiO2 content, and high degree of polymerization in slag, depolymerization is difficult. Consequently, supersulfated cement commonly suffers from low slag hydration, poor early mechanical strength, and slow strength development. In recent years, numerous studies have demonstrated that the addition of ultrafine nanoparticles can effectively promote the pozzolanic reaction of materials such as slag, accelerating their hydration process. However, the addition of ultrafine powders inevitably affects the performance of SSC. Furthermore, as one of the main hydration products of SSC, the rapid formation of AFt in the early stages of hydration can also lead to rapid coagulation, affecting its performance and causing construction difficulties. Furthermore, commercially available nanomaterials inevitably suffer from poor dispersion stability. Therefore, developing admixtures that can address the low early strength of supersulfated cement while also improving its workability, achieving ultra-long slump retention, and exhibiting excellent dispersion stability is of great practical value. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies in the existing technology and provide a composite functional admixture for early strength and long-term collapse protection, as well as a preparation method and application thereof. When the composite functional admixture is applied to supersulfate cement, it not only has excellent early strength performance, but can also achieve water reduction and long-term collapse protection, providing effective technical support for the large-scale application of supersulfate cement.

[0005] In order to solve the technical problem raised by the present invention, the present invention provides a preparation method of a composite functional admixture with early strength and long-term collapse protection, comprising the following steps:

[0006] 1) adding tricalcium aluminate, an activator, and a grinding medium to water, adjusting the pH of the solution and then grinding, and removing the grinding medium after grinding to obtain a suspension A;

[0007] 2) adding suspension A and a water reducing agent into a reactor, and reacting under heating and pressure under inert gas protection to obtain suspension B;

[0008] 3) The suspension B is first stirred and mixed with the surfactant and limestone powder, and then ultrasonically dispersed to obtain an early strength and long-term collapse-preserving composite functional admixture.

[0009] In the above solution, the purity of the tricalcium aluminate is ≥95%, and the residue on a 75 μm sieve is ≤10%.

[0010] In the above scheme, the activator is one of sodium lactate, sodium propionate, sodium carboxymethyl cellulose, and polyaspartic acid.

[0011] In the above solution, the grinding medium is zirconia balls with a diameter of 0.3 to 1 mm.

[0012] In the above scheme, in step 1), the mass ratio of tricalcium aluminate, activator and water is 1: (0.05-0.25): (5-25).

[0013] In the above scheme, in step 1), the ball-to-material ratio during grinding is (2.4-5):1.

[0014] In the above scheme, in step 1), the pH of the solution is adjusted to 10.5-13, more preferably 11.5-12.5.

[0015] In the above scheme, in step 1), the pH regulator used to adjust the pH of the solution is sodium hydroxide solution with a concentration of 0.2 to 10 mol / L.

[0016] In the above scheme, in step 1), the grinding rate is 200-800 rpm, and the grinding time is 0.5-6 h.

[0017] In the above scheme, the water reducer is maleic anhydride polycarboxylic acid water reducer (MAHPC), which has a molecular weight of 20,000 to 36,000 and a molecular structure of:

[0018]

[0019] In the formula, a:b:c:d=1:(1.5~4.5):(0.5~1.5):(1~3.5), 8≤n≤35, and n is an integer.

[0020] In the above scheme, the preparation method of the water reducer is:

[0021] a) dissolving acrylic acid, maleic anhydride, sodium sulfonate and a chain transfer agent in water to obtain liquid A;

[0022] b) Ethylene glycol monovinyl polyoxyethylene ether (EPEG) is mixed with water, and an initiator is first added under stirring, and then the reaction temperature is adjusted to obtain a water reducing agent. Liquid A is added dropwise thereto, and the reaction is continued with stirring after the addition is complete. After the reaction is completed, water is added to adjust the solid content to obtain a water reducing agent.

[0023] Furthermore, the molar ratio of acrylic acid, maleic anhydride, sodium sulfonate, and ethylene glycol monovinyl polyoxyethylene ether is 2:(2-6):(1-2):(3-9).

[0024] Furthermore, the molecular weight of the ethylene glycol monovinyl polyoxyethylene ether is 500 to 3000.

[0025] Furthermore, the chain transfer agent is one of isopropyl alcohol, sodium methacrylate sulfonate, thioglycolic acid, and mercaptopropionic acid.

[0026] Furthermore, the mass of the chain transfer agent is 0.2 to 1.2% of the mass of ethylene glycol monovinyl polyoxyethylene ether.

[0027] Furthermore, the initiator is a redox initiator.

[0028] Furthermore, the mass of the initiator is 0.5 to 1% of the mass of ethylene glycol monovinyl polyoxyethylene ether.

[0029] Furthermore, in step b), the stirring rate is 150-500 rpm, the reaction temperature is 20-45° C., the dropwise addition of solution A is completed over 0.5-1.5 h, and the stirring reaction is continued for 2-8 h after the dropwise addition is completed.

[0030] Furthermore, the amount of water in step a) is only required to uniformly dissolve acrylic acid, maleic anhydride, sodium sulfonate and chain transfer agent. The mass ratio of ethylene glycol monovinyl polyoxyethylene ether to water in step b) is (1-4):1. After the reaction is completed, water is added to adjust the solid content of the water reducer to 35-43%.

[0031] In the above solution, the inert gas is one of nitrogen, argon and helium.

[0032] In the above scheme, the mass ratio of the suspension A to the water reducer is 40:(1-5).

[0033] In the above scheme, in step 2), the reaction temperature is 40-95° C., the reaction pressure is 0.5-4 MPa, and the reaction time is 12-48 h.

[0034] In the above scheme, the median particle size of the suspended matter in the suspension B is 50 to 350 nm.

[0035] In the above scheme, the surfactant is one of methyl cellulose ether, sodium alginate, and sodium polyacrylate.

[0036] In the above solution, the mass of the surfactant is 0.001 to 0.01% of the mass of the suspension B.

[0037] In the above solution, the limestone powder is ultrafine limestone powder with a median particle size of 500 to 1500 nm.

[0038] In the above solution, the mass of the limestone powder is 3-5% of the mass of the suspension B.

[0039] In the above scheme, in step 3), the stirring rate is 200-500 rpm, the stirring time is 2-6 h, and the ultrasonic dispersion time is 0.5-1.5 h.

[0040] The present invention also provides an early strength and long-term collapse-preserving composite functional admixture, which is prepared by the above scheme.

[0041] In the above solution, the water reduction rate of the composite functional admixture is 25-36%, and no obvious sedimentation will occur within 30 days of storage.

[0042] The present invention also provides an application of an early strength and long-term collapse-preserving composite functional admixture in supersulfate cement. The application method is: after uniformly mixing the powder of the supersulfate cement, the composite functional admixture is mixed with mixing water and then added thereto and mixed uniformly.

[0043] In the above solution, the dosage of the composite admixture is 2-4% of the mass of the supersulfate cement.

[0044] The technical concept of the present invention is as follows:

[0045] The original intention of the present invention is to hydrate tricalcium aluminate in an alkaline polycarboxylate water-reducing agent solution to generate calcium-aluminum double hydroxide intercalated with the polycarboxylate water-reducing agent. On the one hand, the admixture is nanosized to improve the early strength performance, and on the other hand, the release of polycarboxylate water-reducing agent molecules is regulated to improve the working performance. However, most commercially available polycarboxylate water-reducing agents have a large molecular weight and a long side chain structure, resulting in a low intercalation loading rate, making it difficult to achieve the desired effect. To this end, the present invention first uses a negatively charged small molecule salt such as sodium lactate to react with OH - The ion exchange between the two expands the OH-AFm generated by the hydration of tricalcium aluminate, increasing its interlayer spacing and facilitating the entry of subsequent water reducers. Secondly, the structure of the water reducer is redesigned, and the functional groups of the polycarboxylate water reducer are replaced by sulfonate and maleic anhydride to synthesize MAHPC; among them, the sulfonate increases the overall charge of the polycarboxylate water reducer, improving the interaction between the water reducer and OH -The ion exchange capacity of the maleic anhydride group is high; due to its slow hydrolysis rate, it has a sustained release effect, achieving ultra-long collapse retention; MAHPC will undergo another ion exchange with low-electronegative small-molecule salts, with MAHPC entering the interlayers and small-molecule salts such as sodium lactate entering the solution. Furthermore, high temperature and high pressure are used to increase the ion exchange rate, significantly enhancing the probability of MAHPC entering the interlayers, resulting in a high-loading nano-MAHPC-AFm. Combined with the subsequent addition of surfactants and ultrafine limestone powder, this nano-MAHPC-AFm material can achieve no significant sedimentation within 30 days, giving the admixture excellent dispersion stability.

[0046] The working principle of the admixture of the present invention when applied to supersulfated cement is:

[0047] When the admixture is added to the supersulfated cement, the MAHPC molecules between the MAHPC-AFm layers exchange ions with the sulfate in the system, releasing MAHPC molecules; the calcium-aluminum main layer reacts with sulfate and water molecules to form AFt. The released MAHPC molecules adjust the working properties of the slurry and achieve water reduction in the initial mixing process. The presence of maleic anhydride groups makes COO - It has a slow release effect, thereby achieving ultra-long slump retention in the later stages. The generated AFt acts as a nucleation site for the hydration reaction, reducing the Gibbs free energy of AFt nucleation, promoting AFt formation, accelerating slag hydration, and generating more hydration products, significantly improving the early mechanical properties of supersulfated cement. Furthermore, the filling effect of small molecule salts such as sodium lactate and ultrafine limestone powder further enhances the mechanical properties of the supersulfated cement system. The combined action of these multiple components achieves the combined benefits of high early strength, efficient water reduction, and high slump retention.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention utilizes the ion exchangeability between layers of tricalcium aluminate hydration products, such as AFm phases. Small molecule salts are first used to expand the interlayer spacing, followed by the introduction of MAHPC with a specific structure for intercalation. High temperature and high pressure are then used to improve the intercalation efficiency, resulting in a high-loading nano-MAHPC-AFm. This admixture is then combined with a surfactant and ultrafine limestone powder to form a composite admixture with early strength and long-term collapse protection. This admixture has stable performance, exhibits no significant settling within 30 days, and exhibits excellent storage and transportation stability. When applied to supersulfated cement, this admixture achieves water reduction by releasing MAHPC molecules, achieves ultra-long collapse protection through the maleic anhydride groups in the MAHPC molecules, and achieves early strength through the generation of AFt combined with the filling effect of small molecule salts such as sodium lactate and ultrafine limestone powder, demonstrating excellent composite properties. DETAILED DESCRIPTION

[0050] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0051] In the following examples, the purity of the tricalcium aluminate used was 98%, with a 75 μm sieve residue of 5%; the grinding medium was zirconia balls with a diameter of 0.5 mm; and the limestone powder was ultrafine limestone powder with a median particle size of 1500 nm.

[0052] Example 1

[0053] A method for preparing an early strength and long-term collapse-preserving composite functional admixture comprises the following steps:

[0054] 1) adding tricalcium aluminate, sodium lactate, and zirconium oxide balls to water in a mass ratio of 1:0.05:5; a balls-to-material ratio of 2.4:1; adjusting the pH of the solution to 11.5 with a 0.2 mol / L sodium hydroxide solution; and milling at 200 rpm for 0.5 h. After milling, removing the zirconium oxide balls to obtain a suspension A;

[0055] 2) Suspension A and maleic anhydride polycarboxylate water-reducing agent were added to a reactor in a mass ratio of 40:1, and nitrogen was passed through the reactor for protection. The reaction was carried out at 0.5 MPa and 40° C. for 12 h to obtain suspension B. The median particle size of the suspended matter in the obtained suspension B was 350 nm.

[0056] 3) Suspension B, 0.001% by weight of methyl cellulose ether of suspension B, and 3% by weight of limestone powder of suspension B were stirred and mixed at a rate of 200 rpm for 2 h, and then ultrasonically dispersed for 0.5 h to obtain a composite functional admixture with early strength and long-term collapse protection.

[0057] Wherein, the preparation method of maleic anhydride polycarboxylic acid water reducer is:

[0058] a) dissolving acrylic acid, maleic anhydride, sodium sulfonate and thioglycolic acid in a small amount of water to obtain liquid A;

[0059] b) EPEG (molecular weight 2000) was mixed with water in a mass ratio of 2:1, and an initiator (ascorbic acid and hydrogen peroxide in a molar ratio of 1:1) was added under stirring at 150 rpm. The temperature was then adjusted to 40±2° C., and solution A was added dropwise thereto. The addition of solution A was completed within 0.5 h, and the reaction was continued with stirring for 2 h. After the reaction was completed, water was added to adjust the solid content to obtain a maleic anhydride polycarboxylate water-reducing agent with a solid content of 39%;

[0060] During the preparation process, the molar ratio of acrylic acid, maleic anhydride, sodium sulfonate, and EPEG is 2:2:1:9, the mass of thioglycolic acid is 0.2% of the mass of EPEG, and the mass of the initiator is 0.5% of the mass of EPEG;

[0061] The molecular weight of the obtained maleic anhydride polycarboxylic acid water reducer is 36,000, and the molecular structure is:

[0062]

[0063] Wherein, a:b:c:d=1:4.5:0.5:2, n=30.

[0064] Example 2

[0065] 1) tricalcium aluminate, sodium propionate, and zirconium oxide balls were added to water in a mass ratio of tricalcium aluminate, sodium propionate, and water of 1:0.15:15; the ball-to-material ratio was 4:1; the solution was adjusted to pH 12.0 with a 5 mol / L sodium hydroxide solution, and then ground at 500 rpm for 2 h. After grinding, the zirconium oxide balls were removed to obtain a suspension A;

[0066] 2) Suspension A and maleic anhydride polycarboxylate water reducer were added to a reactor in a mass ratio of 40:2.5, and nitrogen was passed through the reactor for protection. The reaction was carried out at 2 MPa and 65° C. for 36 hours to obtain suspension B; the median particle size of the suspended matter in the obtained suspension B was 200 nm;

[0067] 3) Suspension B, 0.005% sodium alginate by weight of suspension B, and 4% limestone powder by weight of suspension B were stirred and mixed at a rate of 350 rpm for 4 hours, and then ultrasonically dispersed for 1 hour to obtain an early strength and long-term collapse-preserving composite functional admixture.

[0068] Wherein, the preparation method of maleic anhydride polycarboxylic acid water reducer is:

[0069] a) dissolving acrylic acid, maleic anhydride, sodium sulfonate and sodium methacrylate sulfonate in water to obtain liquid A;

[0070] b) EPEG (molecular weight 1500) was mixed with water in a mass ratio of 3:1, and an initiator (ascorbic acid and hydrogen peroxide in a molar ratio of 1:1) was added first under stirring at 350 rpm. The temperature was then adjusted to 30±2° C., and solution A was added dropwise thereto. The addition of solution A was completed within 1 hour, and the reaction was stirred for 5 hours. After the reaction was completed, water was added to adjust the solid content to obtain a maleic anhydride polycarboxylate water-reducing agent with a solid content of 40%;

[0071] During the preparation process, the molar ratio of acrylic acid, maleic anhydride, sodium sulfonate, and EPEG is 2:5:2:6, the mass of sodium methacrylate sulfonate is 0.8% of the mass of EPEG, and the mass of the initiator is 0.8% of the mass of EPEG;

[0072] The molecular weight of the obtained maleic anhydride polycarboxylic acid water reducer is 30,000, and the molecular structure is:

[0073]

[0074] In the formula, a:b:c:d=1:3:1:2.5, n=25.

[0075] Example 3

[0076] A method for preparing an early strength and long-term collapse-preserving composite functional admixture comprises the following steps:

[0077] 1) adding tricalcium aluminate, sodium carboxymethyl cellulose, and zirconium oxide balls to water in a mass ratio of 1:0.25:25 to water; and a balls-to-material ratio of 5:1; adjusting the pH of the solution to 12.5 with a 10 mol / L sodium hydroxide solution; and milling at 800 rpm for 6 h. After milling, removing the zirconium oxide balls to obtain a suspension A;

[0078] 2) Suspension A and maleic anhydride polycarboxylate water-reducing agent were added to a reactor in a mass ratio of 40:5, and nitrogen was passed through the reactor for protection. The reaction was carried out at 4 MPa and 95° C. for 48 hours to obtain suspension B. The median particle size of the suspended matter in the obtained suspension B was 50 nm.

[0079] 3) Suspension B, 0.01% sodium polyacrylate by weight of suspension B, and 5% limestone powder by weight of suspension B were stirred and mixed at a rate of 500 rpm for 6 hours, and then ultrasonically dispersed for 1.5 hours to obtain an early strength and long-term collapse-preserving composite functional admixture.

[0080] Wherein, the preparation method of maleic anhydride polycarboxylic acid water reducer is:

[0081] a) dissolving acrylic acid, maleic anhydride, sodium sulfonate and thioglycolic acid in a small amount of water to obtain liquid A;

[0082] b) EPEG (molecular weight 1200) was mixed with water in a mass ratio of 4:1, and an initiator (ascorbic acid and hydrogen peroxide in a molar ratio of 1:1) was added under stirring at 500 rpm. The temperature was then adjusted to 20° C., and solution A was added dropwise thereto. The addition of solution A was completed within 1.5 h, and the reaction was continued with stirring for 8 h. After the reaction was completed, water was added to adjust the solid content to obtain a maleic anhydride polycarboxylate water-reducing agent with a solid content of 40%;

[0083] During the preparation process, the molar ratio of acrylic acid, maleic anhydride, sodium sulfonate, and EPEG is 2:6:3:3, the mass of thioglycolic acid is 1.2% of the mass of EPEG, and the mass of the initiator is 1.0% of the mass of EPEG;

[0084] The molecular weight of the obtained maleic anhydride polycarboxylic acid water reducer is 20,000, and the molecular structure is:

[0085]

[0086] In the formula, a:b:c:d=1:1.5:1.5:3, n=17.

[0087] Comparative Example 1

[0088] The only difference between Comparative Example 1 and Example 1 is that the maleic anhydride polycarboxylic acid water reducer in step 2) is replaced with a common polycarboxylic acid water reducer with a molecular weight of 40,000 to 60,000 and a structural formula of:

[0089] Wherein, n=45.

[0090] Comparative Example 2

[0091] The only difference between Comparative Example 2 and Example 1 is that no activator is added in step 1), and the reaction in step 2) is carried out at normal temperature and pressure.

[0092] Comparative Example 3

[0093] Tricalcium aluminate, sodium lactate, maleic anhydride polycarboxylic acid water reducer, methyl cellulose ether, limestone powder and water were directly mixed according to the proportions in Example 1 to form a composite functional admixture.

[0094] Performance Test 1

[0095] The properties of the composite functional admixtures prepared in each embodiment and each comparative example were measured.

[0096] The method for determining the water reducer intercalation rate is as follows: take 80mL of suspension B and centrifuge it at 20,000rpm for 10 minutes. Take the supernatant and measure the water reducer content. The intercalation rate is calculated according to the following formula:

[0097]

[0098] The test of water reduction rate is carried out in accordance with GB8077-2012 "Test method for homogeneity of concrete admixtures". The specific method is: cement paste with the same fluidity (180±5mm) is prepared at different water-binder ratios for the test samples with and without composite functional admixtures. The percentage of the difference in water consumption between the two and the water consumption without composite functional admixtures is the water reduction rate of the composite functional admixture.

[0099] The sedimentation rate is determined by taking 80 mL of the admixture and placing it in a sealed container. At 0, 10, 20, and 30 days, approximately 50 mL of liquid is removed from the upper layer of the sample to test for total organic carbon content. The sedimentation rate is calculated using the following formula:

[0100]

[0101] Table 1

[0102]

[0103]

[0104] As can be seen from Table 1, the water-reducing agent intercalation rate of each embodiment is significantly higher than that of the comparative example, so that the water-reducing rate of the composite functional admixture obtained is significantly higher than that of the comparative example, and the sedimentation rate is significantly lower than that of the comparative example, showing excellent water-reducing performance and stability. Comparative Example 1 adopts ordinary polycarboxylate water-reducing agent, which has a larger molecular weight and a longer side chain structure, resulting in a low intercalation load rate, so that the water-reducing rate of the composite functional admixture obtained is reduced, and the sedimentation rate increases. Although Comparative Example 2 adopts maleic anhydride polycarboxylate water-reducing agent, there is no small molecule salt for layer expansion, and there is no heating and pressurizing condition to improve the exchange rate, so the effect is not as expected. Comparative Example 3 directly uses several raw materials mixed as a composite admixture. When used, the water-reducing agent can be partially adsorbed on the ultrafine limestone powder, resulting in its low water-reducing rate, and it is easy to settle when stored after direct mixing, and the stability is poor.

[0105] Application Examples

[0106] Supersulfated cement was prepared using a raw material ratio of slag: phosphogypsum: steel slag of 16:3:1 (mass ratio), and a water-binder ratio of 0.35. The composite functional admixtures prepared in each of the Examples and Comparative Examples were applied to the supersulfated cement. The application method was as follows: slag, phosphogypsum, and steel slag were uniformly mixed, and then the composite functional admixture was mixed with mixing water and added to the mixture, mixing uniformly. The composite functional admixture was added in an amount of 2% by mass of the supersulfated cement.

[0107] Performance Test 2

[0108] The properties of supersulfated cement after application of the composite functional admixtures prepared in each Example and Comparative Example were tested. The time-dependent fluidity of the cement paste was tested according to GB 8077-2012, "Test Method for Homogeneity of Concrete Admixtures." Mechanical properties were tested according to GB / T 17671-2021, "Test Method for Strength of Cement Mortar (ISO Method)." The specimen dimensions were 40 × 40 × 40 mm.

[0109] Table 2

[0110]

[0111]

[0112] As can be seen from Table 2, the blank group without the addition of the composite functional admixture has the lowest fluidity and compressive strength. After adding the composite functional admixture in the embodiment, the MAHPC molecules between the MAHPC-AFm layers exchange ions with the sulfate in the system, releasing MAHPC molecules, which significantly improves the initial fluidity of the cement slurry compared with the blank group, and the fluidity remains at this level at 2h and 4h. This is because the maleic anhydride groups in the MAHPC molecules make the COO - Slow release, thereby achieving ultra-long collapse retention; in addition, after the MAHPC molecules between the MAHPC-AFm layers are released, the calcium-aluminum main layer reacts with sulfate and water molecules to generate Aft. The generated AFt can serve as a nucleation site for the hydration reaction, reducing the Gibbs free energy of AFt nucleation to promote the generation of AFt, accelerate the hydration of slag, generate more hydration products, and significantly increase the early mechanical properties of supersulfate cement. At the same time, the filling effect of small molecule salts such as sodium lactate and ultrafine limestone powder can further improve the mechanical properties of the supersulfate cement system. Therefore, the 3d, 7d, and 28d compressive strengths of each embodiment are significantly higher than those of the blank group. The composite functional admixture of Comparative Example 1 uses ordinary polycarboxylate water-reducing agent intercalation, which has a low intercalation loading rate and is easy to settle. Therefore, the improvement of fluidity and strength after adding supersulfate cement is not obvious. Although the composite functional admixture of Comparative Example 2 utilizes a maleic anhydride polycarboxylate water-reducing agent, it lacks a small molecule salt for layer expansion and lacks heating and pressurization to enhance the exchange rate. Consequently, its intercalation rate is reduced. While the effect is improved compared to the experimental group and Comparative Example 1, it still falls far short of the Example. Comparative Example 3 directly mixes several raw materials to form a composite admixture. During use, the water-reducing agent partially adsorbs onto the ultrafine limestone powder, resulting in poor fluidity improvement. More importantly, due to the lack of an intercalation structure, the C3A particle size is larger when directly added, resulting in low activity when reacting with sulfate to form AFt, low early AFt production, and low early strength.

[0113] The above embodiments are merely examples for clarification and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications may be made based on the above descriptions. It is not necessary and impossible to enumerate all implementation methods here, and any obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for preparing an early strength and long-term collapse-preserving composite functional admixture, characterized in that: The following steps are involved: 1) adding tricalcium aluminate, an activator, and a grinding medium to water, adjusting the solution pH to 10.5-13, and then grinding. After grinding, removing the grinding medium to obtain a suspension A; the activator is one of sodium lactate, sodium propionate, and sodium carboxymethyl cellulose; 2) Suspension A and maleic anhydride polycarboxylate water reducer are added to a reactor, and reacted under inert gas protection with heating and pressure to obtain suspension B; the maleic anhydride polycarboxylate water reducer has a molecular weight of 20,000 to 36,000 and a molecular structure of: ； Wherein, a:b:c:d=1:(1.5~4.5):(0.5~1.5):(1~3.5), 8≤n≤35, n is an integer; 3) The suspension B is first stirred and mixed with the surfactant and limestone powder, and then ultrasonically dispersed to obtain a composite functional admixture with early strength and long-term collapse protection.

2. The preparation method of the early strength and long-term collapse-preserving composite functional admixture according to claim 1, characterized in that: The preparation method of the maleic anhydride polycarboxylic acid water reducer is: a) dissolving acrylic acid, maleic anhydride, sodium sulfonate and a chain transfer agent in water to obtain liquid A; b) Ethylene glycol monovinyl polyoxyethylene ether is mixed with water, and an initiator is added first under stirring. The temperature is then adjusted to the reaction temperature, and solution A is added dropwise thereto. After the addition is complete, stirring is continued for reaction. After the reaction is completed, water is added to adjust the solid content to obtain a maleic anhydride polycarboxylic acid water reducer.

3. The method for preparing the early strength and long-term collapse-preserving composite functional admixture according to claim 2, characterized in that: The molar ratio of acrylic acid, maleic anhydride, sodium sulfonate, and ethylene glycol monovinyl polyoxyethylene ether is 2:(2-6):(1-2):(3-9); in step b), the mass ratio of ethylene glycol monovinyl polyoxyethylene ether to water is (1-4):1, the stirring rate is 150-500 rpm, the reaction temperature is 20-45°C, and the A solution is added dropwise over 0.5-1.5 hours. After the addition is completed, the stirring reaction is continued for 2-8 hours.

4. The preparation method of the early strength and long-term collapse-preserving composite functional admixture according to claim 2, characterized in that: The molecular weight of the ethylene glycol monovinyl polyoxyethylene ether is 500-3000; the initiator is a redox initiator, and the mass of the initiator is 0.5-1% of the mass of the ethylene glycol monovinyl polyoxyethylene ether; the chain transfer agent is one of isopropyl alcohol, sodium methacrylate sulfonate, thioglycolic acid, and mercaptopropionic acid, and the mass of the chain transfer agent is 0.2-1.2% of the mass of the ethylene glycol monovinyl polyoxyethylene ether; the solid content of the maleic anhydride polycarboxylic acid water reducer is 35-43%.

5. The method for preparing the early strength and long-term collapse-preserving composite functional admixture according to claim 1, characterized in that: In step 1), the mass ratio of tricalcium aluminate, activator and water is 1: (0.05-0.25): (5-25), the grinding rate is 200-800 rpm, and the grinding time is 0.5-6 h.

6. The method for preparing the early strength and long-term collapse-preserving composite functional admixture according to claim 1, characterized in that: In step 2), the mass ratio of suspension A to maleic anhydride polycarboxylate water-reducing agent is 40:(1-5), the reaction temperature is 40-95°C, the reaction pressure is 0.5-4 MPa, the reaction time is 12-48 h, and the median particle size of the suspended matter in the obtained suspension B is 50-350 nm.

7. The method for preparing the early strength and long-term collapse-preserving composite functional admixture according to claim 1, characterized in that: The surfactant is one of methyl cellulose ether, sodium alginate, and sodium polyacrylate, and the mass of the surfactant is 0.001-0.01% of the mass of suspension B; the limestone powder is ultrafine limestone powder with a median particle size of 500-1500 nm, and the mass of the limestone powder is 3-5% of the mass of suspension B; the stirring rate in step 3) is 200-500 rpm, the stirring time is 2-6 hours, and the ultrasonic dispersion time is 0.5-1.5 hours.

8. An early strength and long-term collapse-preserving composite functional admixture prepared by the method according to any one of claims 1 to 7.

9. Use of the early strength and long-term collapse-preserving composite functional admixture according to claim 8 in super sulfated cement.

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