Multi-stage slow-release targeted control agent aiming at sulfate erosion expansion of cement-based material as well as preparation method and application of multi-stage slow-release targeted control agent

Abstract

The invention discloses a multistage slow-release targeted control agent aiming at sulfate erosion expansion of a cement-based material as well as a preparation method and application of the multistage slow-release targeted control agent. The multistage slow-release targeted control agent comprises an active aluminum-based inner core, a PVA-boric acid hydrogel (PBH) inner shell layer coating the surface of the inner core, and a hydrogel outer shell layer (PPH) which coats the inner shell layer and can be dissociated in an alkaline environment. The multi-stage slow-release targeted control agent can promote accurate growth of the expansive hydration product in preset micropores of a cement-based material, the strength of the generated expansive hydration product is high, and the problem of stress concentration damage caused by defects caused by insufficient strength at pores is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cement materials, and particularly relates to a multi-stage slow-release targeted control agent for sulfate attack expansion of cement-based materials and a preparation method and application thereof. BACKGROUND

[0002] In building engineering, cement-based materials often face the problem of sulfate attack. When the cement-based material is in an environment with high sulfate content (such as some groundwater, soil, industrial wastewater, marine engineering, etc.), sulfate ions will react with the hydration product Ca(OH)2 in the cement to generate CaSO4. In addition, sulfate ions will cause the hydration product monosulfate type hydrated calcium sulphoaluminate (AFm) in the cement to transform into trisulfate type hydrated calcium sulphoaluminate (AFt). The progress of the two reactions is accompanied by volume expansion, that is, it will cause the internal expansion stress of the cement-based material, and when it exceeds the cracking stress threshold of the cement-based material itself, it will induce microstructure damage. Therefore, reducing the excessive expansion stress in the cement-based body caused by sulfate attack is the key to improving the sulfate resistance of cement-based materials.

[0003] The most common strategies to alleviate the expansion pressure caused by sulfate attack include: (1) reducing the content of Ca(OH)2 in the cement-based material to prevent the generation of subsequent expansion products. At present, it is mainly achieved by adding supplementary cementitious materials (SCMs) to replace part of the cement clinker, and utilizing the pozzolanic reaction of SCMs to consume calcium hydroxide. However, this method will significantly reduce the compressive strength of the cement-based material due to the reduction of the content of cement clinker, thereby increasing the risk of damage to the cement-based body during service. (2) Adding air entraining agents (AEA) in the cement-based body to introduce micropores, thereby providing additional space for the expansion of the hydration product generated after sulfate attack, so as to reduce the expansion stress in the cement-based body. However, due to the poor matching degree of the micropores introduced by the AEA and the position of the expansion hydration product, the effectiveness of this strategy is still limited. SUMMARY

[0004] The present application provides a multi-stage slow-release targeted control agent for sulfate attack expansion of cement-based materials and a preparation method and application thereof, which can promote the accurate growth of the expansion hydration product in the pre-set micropores of the cement-based material, and the strength of the generated expansion hydration product is high, thereby avoiding the stress concentration damage problem caused by the defects due to insufficient strength at the pores.

[0005] Technical scheme: the multi-stage slow-release targeted control agent for sulfate attack expansion of cement-based materials, comprising: an active aluminum-based inner core, a PVA-boric acid hydrogel (PBH) inner shell layer coated on the surface of the inner core, and a hydrogel outer shell layer capable of dissociating in an alkaline environment coated on the inner shell layer.

[0006] Further, the material of the active aluminum-based inner core comprises at least one of boehmite powder, γ-Al2O3 powder, etc. Optionally, the particle size of the active aluminum-based inner core is 0.2-1.0 μm.

[0007] Further, the PVA-boric acid hydrogel is a gel formed by cross-linking of polyvinyl alcohol (PVA) under the action of boric acid and / or borax.

[0008] Further, the hydrogel shell layer comprises poly N-isopropyl acrylamide (NIPAm), sodium acrylate (SA), N,N-methylene bisacrylamide (Bis), tetramethyl ethylenediamine (TEMED) cross-linking.

[0009] The present application also includes a preparation method of a multi-stage slow-release targeted control agent for sulfate corrosion expansion of cement-based materials, comprising the following steps:

[0010] (1) adding a boric acid solution to a polyvinyl alcohol (PVA) aqueous solution for cross-linking reaction, and obtaining a PVA-boric acid hydrogel (PBH) after completion.

[0011] (2) mixing an active aluminum-based inner core with the PBH, and then coating to obtain a single-layer composite particle (PBH@Al) formed by coating the PBH on the surface of the inner core.

[0012] (3) forming a gelatinous liquid phase (PPH hydrogel) by using poly N-isopropyl acrylamide (NIPAm), sodium acrylate (SA), N,N-methylene bisacrylamide (Bis), tetramethyl ethylenediamine (TEMED), and an initiator, and then mixing with the single-layer composite particle and coating to coat the single-layer composite particle with a hydrogel shell layer capable of dissociating in an alkaline environment. The multi-stage slow-release targeted control agent is obtained after drying the obtained gelatinous phase product.

[0013] Further, in step (1), the mass ratio of polyvinyl alcohol (PVA) provided by the polyvinyl alcohol aqueous solution to boric acid provided by the boric acid solution is (7-13):(0.5-1.3). Optionally, the mass fraction of the polyvinyl alcohol (PVA) aqueous solution is 5-10%, and the mass fraction of the boric acid solution is 0.5-1%.

[0014] Further, in step (2), the mass ratio of the active aluminum-based inner core to the PVA-boric acid hydrogel is (0.2-0.7):(7.5-14.3).

[0015] Further, in step (2), the obtained mixture is extruded through a microporous filter membrane under negative pressure and dropped into anhydrous ethanol for receiving, so as to obtain single dispersed PBH@Al.

[0016] Further, in step (3), the mass ratio of the poly-N-isopropyl acrylamide, sodium acrylate, N,N-methylene bisacrylamide, tetramethyl ethylenediamine, initiator and water is (0.7-0.9):(0.1-0.3):(0.010-0.014):(0.010-0.015):(0.010-0.014):(7-15).

[0017] Further, in step (3), the initiator includes at least one of ammonium persulfate, potassium persulfate and the like.

[0018] Further, in step (3), the mass ratio of the gelled liquid phase (PPH hydrogel) and the single-layer composite particles is (1-2):(7-15).

[0019] Further, in step (3), the gelled liquid phase is mixed with the single-layer composite particles, and then extruded through a microporous filter membrane under the action of negative pressure and dropped into anhydrous ethanol for receiving.

[0020] Further, in steps (2) and (3), the drying method is to first place in a vacuum environment at room temperature for 8-24 hours, and then air-dry for 15-45 min.

[0021] In a third aspect, the application provides application of the multi-stage slow-release targeted control agent for sulfate attack expansion of cement-based materials in cement-based materials containing Ca(OH)2, such as Portland cement-based materials and the like. Optionally, the addition amount of the multi-stage slow-release targeted control agent is 0.05-0.2% of the mass of the cement-based material.

[0022] Advantages: Compared with the prior art, the application has the following remarkable advantages:

[0023] After the multi-stage slow-release targeted control agent of the present application is incorporated into the cement-based material, the hydrogel shell layer absorbs the mixing water in the cement-based material and then swells, and as the cement-based material gradually hydrates and hardens, the hydrogel shell layer loses water first, and the volume originally occupied due to swelling becomes a micropore. The characteristics of the hydrogel shell layer, i.e., high water content and low stress in the micropore, make the calcium hydroxide hydration product enriched on the inner surface of the micropore, thereby laying a foundation for the directional formation of the swelling product generated due to subsequent sulfate attack. In addition, since the water release process of the hydrogel shell layer (PPH) is mainly concentrated in the later hydration stage of the cement-based material, it plays a role in supplementing water and promoting the progress of the later hydration and improving the development of the later strength. After encountering water-soluble sulfate attack, it first forms calcium sulfate with the calcium hydroxide enriched on the inner surface of the micropore, thereby directing the invasion of the sulfate into the preset micropore. At the same time of the sulfate invasion, the PBH inner shell layer in the multi-stage slow-release targeted control agent also starts to dissociate in the alkaline cement pore solution, thereby exposing the active aluminum-based inner core, which reacts with the invading sulfate, the calcium sulfate to generate high-strength hydration product AFt. The volume expansion of this hydration product gradually fills the preset micropore, not only achieving the purpose of directing the invasion of the sulfate into the preset micropore, but also reducing the risk of stress concentration at defects due to the high strength of the hydration product, thereby creating a new solution for sulfate attack. This is because the strength of the newly generated swelling hydration product in the preset pore needs to be as high as possible to match the strength of the cement-based material matrix, so as to avoid the defect caused by the insufficient strength of the pore at the later stage, which causes stress concentration and damage. The multi-stage slow-release targeted control agent of the present application can well achieve the above purpose. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 SEM image of the multi-stage slow-release targeted control agent sample prepared for the following Example 1.

[0025] Figure 2 SEM image of the multi-stage slow-release targeted control agent incorporated into the cement-based material after the following Example 1. DETAILED DESCRIPTION

[0026] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application. The experimental methods not specified in the following examples are usually carried out according to the conventional conditions or according to the conditions recommended by the manufacturer.

[0027] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art. The reagents or materials used in the present application can be purchased through conventional routes, and unless otherwise specified, the reagents or materials used in the present application are used according to the conventional manner in the art or according to the product instructions. In addition, any method and material similar or equivalent to those described can be applied to the method of the present application. The technical solutions of the present application are further described in conjunction with specific examples.

[0028] Example 1

[0029] A preparation method of a multi-stage slow-release targeted control agent for sulfate attack expansion of cement-based materials, comprising the following steps:

[0030] (1) PVA powder is added to water at 90°C and stirred until fully dissolved to obtain a PVA solution with a mass fraction of 8%. Then, according to a mass ratio of PVA:boric acid of 10:1.1, a 0.7% boric acid solution is slowly added to the PVA solution with continuous stirring, and a crosslinking reaction is carried out. After completion, a PVA-boric acid hydrogel (PBH) is obtained and reserved.

[0031] (2) The active aluminum-based inner core (boehmite powder with a particle size distribution of 0.2-1.0 μm) is mixed with the PVA-boric acid hydrogel according to a mass ratio of 0.5:10 and stirred uniformly. Then, the obtained mixture is placed in a microporous filter (with a pore size of 5 microns). Then, under the action of negative pressure, the micropores on the filter membrane are extruded, and the droplets are received in anhydrous ethanol. Then, after being placed in a vacuum environment at room temperature for 12 hours, air blowing is performed for 30 min to obtain single-layer composite particles (PBH@Al) with the inner core coated with PBH, which are reserved.

[0032] (3) According to a mass ratio of poly-N-isopropyl acrylamide (NIPAm), sodium acrylate (SA), N,N-methylene bisacrylamide (Bis), initiator (potassium persulfate), tetramethyl ethylenediamine (TEMED), and water = 0.8:0.2:0.012:0.012:0.012:10, the raw materials are weighed. Then, the NIPAm, SA, Bis, and initiator are added to water and stirred until completely dissolved. Then, the TEMED is added to gel the solution, and a PPH hydrogel is obtained and reserved.

[0033] (4) The single-layer composite particles are mixed with PPH hydrogel at a mass ratio of 10:1.5, and then stirred uniformly to make the single-layer composite particles coated with a hydrogel shell layer again. Then the obtained mixture is placed in a microporous filter (the pore size of the microporous filter is 50 microns). Then the particles are squeezed out from the micropores on the filter under the action of negative pressure, and then dropped into anhydrous ethanol for receiving. Then the particles are placed in a vacuum environment at room temperature for 12 hours, and then air-dried for 30 min to obtain a multi-stage slow-release targeted control agent, as shown in Figure 1 .

[0034] Figure 2 The SEM image of the test piece obtained after the multi-stage slow-release targeted control agent prepared in this embodiment is incorporated into the cement-based material. It can be seen that the high-strength expansive hydration product AFt generated by the reaction of the invading sulfate and calcium sulfate fills the pre-designed micropores made by the hydrogel shell layer of the multi-stage slow-release targeted control agent.

[0035] Performance test: (1) The multi-stage slow-release targeted control agent prepared in this embodiment is incorporated into 42.5 ordinary Portland cement mortar (the amount of incorporation is 0.1% of the mass of the cement component) to make a test piece, and then the expansion rate and the corrosion resistance coefficient of the test piece at ages of 28d, 56d, 100d, 150d and 200d are tested according to the “Cement Sulfate Resistance Test Method” (GB / T 749-2008), and the results are shown in the following table. (2) According to the “Standard Test Methods for Basic Properties of Building Mortar” (JGJ / T 70-2009), the test piece with an age of 28d (referred to as the initial test piece) is immersed in a 10% mass fraction sodium sulfate solution, and the compressive strength of the test piece after immersion for 28d, 56d, 100d, 150d and 200d is tested, and then the compressive strength change rate relative to the initial test piece is calculated, and the results are shown in Table 1 below. “+” means increase, and “-” means decrease.

[0036] Table 1

[0037]

[0038] Example 2

[0039] A preparation method of a multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials, comprising the following steps:

[0040] (1) PVA powder is added to water at 85°C and stirred until it is fully dissolved to obtain a PVA solution with a mass fraction of 10%. Then, according to the mass ratio of PVA to boric acid of 13:1.3, a 1.0% mass fraction boric acid solution is slowly added to the PVA solution while stirring continuously, and a cross-linking reaction is carried out. After completion, a PVA-boric acid hydrogel (PBH) is obtained for standby use.

[0041] (2) The active aluminum-based inner core (boehmite powder with a particle size distribution of 0.2-1.0 μm) is mixed with the PVA-boric acid hydrogel at a mass ratio of 0.2:7.5, and then stirred uniformly. The obtained mixture is then placed in a microporous filter (the microporous filter has a pore size of 5 microns). Then, under the action of negative pressure, the micropores on the filter membrane are extruded, and the particles falling are received in anhydrous ethanol. Then, after being placed in a vacuum environment at room temperature for 12 hours, the particles are air-dried for 30 min, to obtain single-layer composite particles (PBH@Al) formed by the inner core coated with PBH, which are ready for use.

[0042] (3) Each raw material is weighed according to the mass ratio of poly-N-isopropyl acrylamide (NIPAm), sodium acrylate (SA), N,N-methylene bisacrylamide (Bis), initiator (potassium persulfate), tetramethyl ethylenediamine (TEMED), and water = 0.7:0.1:0.010:0.010:0.010:7. Then, the NIPAm, SA, Bis, and initiator are first added to water and stirred until completely dissolved. Then, the TEMED is added to gel the solution, to obtain a PPH hydrogel, which is ready for use.

[0043] (4) The single-layer composite particles are mixed with the PPH hydrogel at a mass ratio of 7:1, and then stirred uniformly, so that the single-layer composite particles are coated with a hydrogel outer shell layer again. Then, the obtained mixture is placed in a microporous filter (the microporous filter has a pore size of 50 microns). Then, under the action of negative pressure, the micropores on the filter membrane are extruded, and the particles falling are received in anhydrous ethanol. Then, after being placed in a vacuum environment at room temperature for 24 hours, the particles are air-dried for 15 min, to obtain a multi-stage slow-release targeted control agent.

[0044] The test piece doped with the multi-stage slow-release targeted control agent prepared in this example is tested by the same method as in Example 1, to obtain the expansion rate and the corrosion resistance coefficient of the test piece at ages of 28d, 56d, 100d, 150d, and 200d, and the change rate of the compressive strength of the test piece soaked in 10% sodium sulfate solution for 28d, 56d, 100d, 150d, and 200d, and the results are shown in Table 2.

[0045] Table 2

[0046]

[0047] Example 3

[0048] A preparation method of a multi-stage slow-release targeted control agent for sulfate erosion expansion of cement-based materials, comprising the following steps:

[0049] (1) PVA powder was added to water at 90°C and stirred until fully dissolved to obtain a PVA solution with a mass fraction of 5%. Then, a borax solution with a mass fraction of 0.5% was slowly added to the PVA solution in a mass ratio of PVA:borax = 7:0.5, and stirring was continued, and the cross-linking reaction was completed to obtain a PVA-borax hydrogel (PBH), which was ready for use.

[0050] (2) The active aluminum-based inner core (γ-Al2O3 powder with a particle size distribution of 0.2-1.0 μm) was mixed with the PVA-borax hydrogel in a mass ratio of 0.7:14.3, and then stirred until uniform. The obtained mixture was then placed in a microporous filter (the pore size of the microporous filter was 5 microns). Then, under the action of negative pressure, the micropores on the filter membrane were extruded, and the dripping particles were received in anhydrous ethanol. After being placed in a vacuum environment at room temperature for 12 hours, the particles were air-dried for 30 min to obtain single-layer composite particles (PBH@Al) with the inner core coated with PBH, which were ready for use.

[0051] (3) The raw materials were weighed according to the mass ratio of poly-N-isopropyl acrylamide (NIPAm), sodium acrylate (SA), N,N-methylene bisacrylamide (Bis), initiator (ammonium persulfate), tetramethyl ethylenediamine (TEMED), and water = 0.9:0.3:0.014:0.015:0.014:15. Then, the NIPAm, SA, Bis, and initiator were added to water and stirred until fully dissolved. Then, the TEMED was added to gel the solution to obtain a PPH hydrogel, which was ready for use.

[0052] (4) The single-layer composite particles were mixed with the PPH hydrogel in a mass ratio of 15:2, and then stirred until uniform to coat the surface of the single-layer composite particles with an additional hydrogel shell layer. Then, the obtained mixture was placed in a microporous filter (the pore size of the microporous filter was 50 microns). Then, under the action of negative pressure, the micropores on the filter membrane were extruded, and the dripping particles were received in anhydrous ethanol. After being placed in a vacuum environment at room temperature for 8 hours, the particles were air-dried for 45 min to obtain a multi-stage slow-release and targeted control agent.

[0053] The test piece doped with the multi-stage slow-release and targeted control agent prepared in this example was tested for the expansion rate and the erosion resistance coefficient at ages of 28d, 56d, 100d, 150d, and 200d, and the change rate of the compressive strength after being soaked in a 10% sodium sulfate solution for 28d, 56d, 100d, 150d, and 200d, using the same method as in Example 1, and the results are shown in Table 3.

[0054] Table 3

[0055]

[0056] Example 4

[0057] A preparation method of a multi-stage slow-release targeted control agent for sulfate attack expansion of cement-based materials, comprising the following steps:

[0058] (1) PVA powder is added to water at 90°C and stirred until fully dissolved to obtain a PVA solution with a mass fraction of 8%. Then, a 0.7% boric acid solution is slowly added to the PVA solution in a mass ratio of PVA:boric acid = 10:1.1, and stirring is continued, and a cross-linking reaction is carried out, and after completion, a PVA-boric acid hydrogel (PBH) is obtained and reserved.

[0059] (2) An active aluminum-based inner core (boehmite powder with a particle size distribution of 0.2-1.0 μm) is mixed with the PVA-boric acid hydrogel in a mass ratio of 0.5:10, and then stirred uniformly. Then, the obtained mixture is placed in a microporous filter (with a pore size of 5 microns). Then, under the action of negative pressure, the micropores on the filter membrane are extruded, and the droplets are received in anhydrous ethanol. Then, after being placed in a vacuum environment at room temperature for 12 hours, air blowing drying is carried out for 30 min, and a single-layer composite particle (PBH@Al) formed by coating the inner core with PBH is obtained, which is used as a multi-stage slow-release targeted control agent.

[0060] The same method as in Example 1 is used to test the expansion rate and corrosion resistance coefficient of the test piece doped with the multi-stage slow-release targeted control agent prepared in this example at ages of 28d, 56d, 100d, 150d, and 200d, and the change rate of the compressive strength of the test piece soaked in 10% sodium sulfate solution for 28d, 56d, 100d, 150d, and 200d, and the results are shown in Table 4.

[0061] Table 4

[0062] Age 28d 56d 100d 150d 200d Swelling rate (‰) 12.14 15.57 26.08 28.33 31.12 Erosion resistance coefficient 1.03 0.95 0.89 0.82 0.77 Compressive strength change rate (%) +4.5 +1.2 -2.3 -3.5 -5.3

[0063] Example 5

[0064] A preparation method of a multi-stage slow-release targeted control agent for sulfate attack expansion of cement-based materials, comprising the following steps:

[0065] (1) The raw materials are weighed according to the mass ratio of poly-N-isopropyl acrylamide (NIPAm), sodium acrylate (SA), N,N-methylene bisacrylamide (Bis), initiator (potassium persulfate), tetramethyl ethylenediamine (TEMED), and water = 0.7:0.1:0.010:0.010:0.010:7. Then, the NIPAm, SA, Bis, and initiator are added to water and stirred until completely dissolved, and then the TEMED is added to gel the solution, and a PPH hydrogel is obtained and reserved.

[0066] (2) The active aluminum-based core (boehmite powder with a particle size distribution of 0.2-1.0 μm) is mixed with PPH hydrogel at a mass ratio of 7:1, and then stirred uniformly. The obtained mixture is then placed in a microporous filter (the pore size of the microporous filter is 50 microns). Then, under the action of negative pressure, the micropores on the filter membrane are extruded, and the dripping particles are received in anhydrous ethanol. Then, after being placed in a vacuum environment at room temperature for 24 hours, air blowing drying is performed for 15 min, to obtain a multi-stage slow-release targeted control agent.

[0067] The test piece doped with the multi-stage slow-release targeted control agent prepared in this example is tested by the same method as in Example 1 above, to obtain the expansion rate and the corrosion resistance coefficient of the test piece at ages of 28d, 56d, 100d, 150d, and 200d, and the change rate of the compressive strength of the test piece soaked in 10% sodium sulfate solution for 28d, 56d, 100d, 150d, and 200d, and the results are shown in Table 5 below.

[0068] Table 5

[0069]

[0070] Example 6

[0071] A preparation method of a multi-stage slow-release targeted control agent for sulfate attack expansion of cement-based materials, comprising the following steps:

[0072] (1) PVA powder is added to water at 90°C and stirred until fully dissolved, to obtain a PVA solution with a mass fraction of 8%. Then, according to a mass ratio of PVA:boric acid of 10:1.1, a boric acid solution with a mass fraction of 0.7% is slowly added to the PVA solution and stirring is continued, and a cross-linking reaction is performed. After completion, a PVA-boric acid hydrogel (PBH) is obtained and reserved.

[0073] (2) α-Al2O3 powder particles with a particle size distribution of 0.2-1.0 μm are mixed with the PVA-boric acid hydrogel at a mass ratio of 0.5:10, and then stirred uniformly. The obtained mixture is then placed in a microporous filter (the pore size of the microporous filter is 5 microns). Then, under the action of negative pressure, the micropores on the filter membrane are extruded, and the dripping particles are received in anhydrous ethanol. Then, after being placed in a vacuum environment at room temperature for 12 hours, air blowing drying is performed for 30 min, to obtain single-layer composite particles (PBH@Al) formed by coating the PBH on the surface of the core, which are reserved.

[0074] (3) Each raw material was weighed according to the mass ratio of poly-N-isopropyl acrylamide (NIPAm), sodium acrylate (SA), N,N-methylene bisacrylamide (Bis), initiator (potassium persulfate), tetramethyl ethylenediamine (TEMED), water = 0.8:0.2:0.012:0.012:0.012:10. Then the NIPAm, SA, Bis and initiator were first added to water and stirred until completely dissolved, then the TEMED was added to gel the solution, obtaining a PPH hydrogel, ready for use.

[0075] (4) The single-layer composite particles were mixed with the PPH hydrogel at a mass ratio of 10:1.5 and stirred uniformly, so that the single-layer composite particles were coated with a layer of hydrogel shell again. Then the obtained mixture was placed in a microporous filter (the pore size of the microporous filter was 50 microns). Then under the action of negative pressure, the particles dropped from the micropores on the filter membrane into anhydrous ethanol for receiving, and then placed in a vacuum environment at room temperature for 12 hours and then air-dried for 30 min, obtaining a multi-stage slow-release targeted control agent.

[0076] The test piece doped with the multi-stage slow-release targeted control agent prepared in the present example was tested by the same method as in the above example 1 to test the expansion rate and the erosion resistance coefficient of the test piece at the ages of 28d, 56d, 100d, 150d, 200d, and the change rate of the compressive strength of the test piece soaked in 10% sodium sulfate solution for 28d, 56d, 100d, 150d, 200d, and the results are shown in the following table 6.

[0077] Table 6

[0078]

[0079] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials, characterized in that: include: An active aluminum-based core, a PVA-boric acid hydrogel inner shell layer coated on the surface of the core, and a hydrogel outer shell layer coated on the inner shell layer and capable of dissociating in an alkaline environment.

2. The multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials according to claim 1, characterized in that: The material of the active aluminum-based core includes at least one of boehmite powder and γ-Al2O3 powder; the particle size of the active aluminum-based core is 0.2-1.0 μm.

3. The multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials according to claim 1, characterized in that: PVA-boric acid hydrogel is a gel formed by cross-linking polyvinyl alcohol under the action of boric acid and / or borax.

4. The multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials according to any one of claims 1 to 3, characterized in that: The hydrogel shell layer comprises poly N-isopropylacrylamide, sodium acrylate, N, N-methylenebisacrylamide and tetramethylethylenediamine through cross-linking.

5. A method for preparing a multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials, characterized in that: The steps include: (1) adding a boric acid solution to a polyvinyl alcohol aqueous solution to carry out a cross-linking reaction, and obtaining a PVA-boric acid hydrogel after completion; (2) The active aluminum-based core is mixed with PVA-boric acid hydrogel and then coated, and the resulting gel phase product is dried to obtain a single-layer composite particle formed by coating the core surface with PBH; (3) Poly (N-isopropylacrylamide), sodium acrylate, N,N-methylenebisacrylamide, tetramethylethylenediamine, an initiator, and water are used to form a gelled liquid phase; the liquid phase is then mixed with the monolayer composite particles and coated, and the obtained gel phase product is dried to obtain a multi-stage sustained-release targeted control agent.

6. The method for preparing a multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials according to claim 5, characterized in that: In step (1), the mass ratio of polyvinyl alcohol provided by the polyvinyl alcohol aqueous solution to boric acid provided by the boric acid solution is (7-13): (0.5-1.3); the mass fraction of the polyvinyl alcohol aqueous solution is 5-10%; and the mass fraction of the boric acid solution is 0.5-1%.

7. The method for preparing a multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials according to claim 5, characterized in that: In step (2), the mass ratio of the active aluminum-based core to the PVA-boric acid hydrogel is (0.2-0.7): (7.5-14.3), and the mixture is squeezed through a microporous filter membrane under negative pressure and dripped into anhydrous ethanol for reception.

8. The method for preparing a multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials according to claim 5, characterized in that: In step (3), the mass ratio of poly (N-isopropylacrylamide), sodium acrylate, N,N-methylenebisacrylamide, tetramethylethylenediamine, initiator, and water is: (0.7-0.9): (0.1-0.3): (0.010-0.014): (0.010-0.015): (0.010-0.014): (7-15); The initiator includes at least one of ammonium persulfate and potassium persulfate.

9. The method for preparing a multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials according to claim 5, characterized in that: In step (3), the mass ratio of the gelled liquid phase to the single-layer composite particles is (1-2): (7-15); the gelled liquid phase is mixed with the single-layer composite particles, extruded through a microporous filter membrane under negative pressure, and dripped into anhydrous ethanol for reception; the drying method in steps (2) and (3) is: first treat in a vacuum drying oven at 25°C for 8-24 hours, and then blow dry for 15-45 minutes.

10. Use of the multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials according to any one of claims 1 to 4, or the multi-stage slow-release targeted control agent for sulfate erosion and expansion of cement-based materials obtained by the preparation method according to any one of claims 5 to 9 in cement-based materials whose hydration products contain Ca(OH)2; the addition amount of the multi-stage slow-release targeted control agent is 0.05 to 0.2% of the mass of the cement-based material.

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