An admixture for improving the flexural strength of cement-based materials and its application

Abstract

This invention provides an admixture for improving the flexural strength of cement-based materials, comprising two components, A and B. Component A includes polymeric monomers and silica capsules, while component B includes a reducing initiator. The silica capsules are obtained by emulsifying and coating an oxidizing initiator with a silane precursor, which is a mixture of tetraethyl orthosilicate and a silane coupling agent. In the admixture of this application, the silica capsules in component A have a slow-release effect due to the nano-silica shell. After a period of hydration, the silica shell dissolves, releasing the oxidizing initiator, which then reacts with the reducing initiator to initiate acrylamide polymerization, minimizing the impact of the polymer on cement hydration. Nano-silica itself is an excellent reinforcing material; its unique pozzolanic activity allows it to react with cement-based materials, optimizing the structure and composition of hydration products and strengthening the cement-based materials.

Description

Technical Field

[0001] This invention relates to the field of admixtures for modifying cement-based materials, specifically to an admixture for improving the flexural strength of cement-based materials and its application. Background Technology

[0002] Cement concrete is a typical brittle material with high compressive strength but significantly insufficient flexural and tensile strength. In practical applications, it is prone to various cracks or damage due to stress concentration or uneven stress, leading to decreased durability and limiting its application. Currently, concrete toughening methods include fiber toughening, polymer toughening, and nanomaterial toughening, which adjust the microstructure of concrete at various scales to improve its tensile strength and fracture energy. However, these toughening methods all have shortcomings: among fiber toughening methods, steel fiber toughening is the most widely used and has an existing industrial application base, but steel fibers are prone to agglomeration and do not improve the matrix toughness of concrete; directly adding polymers for toughening can affect cement hydration and easily form defects in concrete; and nanomaterial toughening can lead to nanomaterial agglomeration and is difficult to industrialize.

[0003] Common and easy-to-operate cement-polymer paste mixing methods include directly mixing cement with polymers as binders or additives, or immersing hardened cement paste in polymer solutions. This single physical addition blending method has many drawbacks, preventing effective optimization and adjustment of the modified concrete's performance. Most experimental results show a significant improvement in flexural strength, but compressive strength decreases after polymer modification. Therefore, adding polymer solutions at high dosages leads to retardation, lower hydration levels, and insignificant strengthening effects; adding polymer emulsions, with organic polymer phase sizes ranging from 10 to 500 μm, creates "macroscopic defects" in the cement matrix, and the larger the polymer phase size, the more pronounced the strength-weakening effect. Therefore, current polymer addition methods for toughening concrete sacrifice compressive strength. These drawbacks severely limit its widespread application in modern concrete. Achieving improved concrete toughness is currently a research hotspot and challenge both domestically and internationally.

[0004] To address this challenge, in-situ polymerization is currently considered a highly feasible approach by researchers. Small monomers are added to concrete without polymerization, initiating polymer polymerization simultaneously with cement hydration, thus achieving in-situ polymerization in cement-based materials. However, current in-situ polymerization processes cannot control the polymerization process; the polymerization and hydration processes are difficult to match, making it impossible to prepare polymer / cement-based composite materials with adjustable and controllable properties.

[0005] Patent 202310083711.9 discloses an in-situ polymerized inorganic synergistic modified cement-based composite material and its preparation method. This organic in-situ polymerized-inorganic synergistic modified cement-based composite material utilizes in-situ polymerization of polymer monomers, combined with cost-effective inorganic additives and admixtures to improve the toughness and durability of the composite material. However, this patent does not control the in-situ polymerization process; the monomers and initiators are blended in the initial mixing stage, at which point the polymerization reaction has already occurred. The presence of polymers before the hydration of the cement-based material affects its hydration and is detrimental to compressive strength.

[0006] Patent 202010274758.X discloses a polymer cement-based material and its preparation method and application. The method involves mixing an initiation system with a mixed solution of acrylate monomers and a cement-based material, then allowing the acrylate monomers to polymerize in situ within the cement-based material, forming another network interwoven with the cement hydration products, thus obtaining the in-situ polymer cement-based material. This patent also points out that blending monomers with an initiator will prematurely initiate polymerization; therefore, using low-temperature (0-5°C) storage of the mixed precursor solution to suppress the polymerization reaction is impractical. Summary of the Invention

[0007] To address the problem that existing technologies cannot simultaneously achieve both toughness and compressive strength in cement-based materials, this invention provides an admixture for improving the flexural strength of cement-based materials and its application. It utilizes an alkali-activated capsule-type slow-release material as a carrier, introducing an active initiating component into the slow-release material. This component breaks down during the hydration process of the cement-based material (under alkaline conditions, silica exhibits pozzolanic activity and reacts with calcium hydroxide, thus breaking down to generate hydration products that can densify pores), thereby initiating polymerization in situ within the cement-based material and controlling the polymerization time. Based on coordination, electrostatic, hydrogen bonding, and chemical bond interactions, organic polymers are composited with CSH gel at the molecular scale, optimizing the size and packing mode of both the organic polymer and CSH gel. The polymer phase size is reduced to be similar to that of the hydration products, and the polymer induces optimization of the size and orientation of the hydration products, enhancing interfacial adhesion and filling of internal pores, thereby significantly improving the mechanical properties of the cement-based material.

[0008] An admixture for improving the flexural strength of cement-based materials, comprising two components, component A and component B:

[0009] The above-mentioned component A includes polymeric monomers and silica capsules.

[0010] The above-mentioned monomers are selected from acrylamide or sodium acrylate.

[0011] The mass ratio of the above-mentioned polymeric monomer to silica capsules is 30:(1-30).

[0012] The aforementioned silica capsules were obtained by emulsifying and coating an oxidizing initiator with a silane precursor.

[0013] The ratio of the above-mentioned silane precursor to the oxidizing initiator is 2:(5-6).

[0014] The above-mentioned silane precursor is a mixture of tetraethyl orthosilicate and silane coupling agent in a mass ratio of 1:(0-0.2);

[0015] The above-mentioned component B includes a reducing initiator.

[0016] The aforementioned reducing initiator is an amine initiator, and its mass is 0.2%-0.8% of the mass of the polymerizing monomer.

[0017] The above-mentioned silica capsules were prepared by the following steps: (1) Oil phase solution preparation: the emulsifier and the oil phase solvent were mixed evenly; (2) Aqueous phase solution preparation: water, alkaline substance and oxidizing initiator were mixed evenly; (3) the aqueous phase solution was poured into the oil phase solution for emulsification to obtain an emulsion; (4) a silane precursor was added to the emulsion and emulsification was continued; (5) the emulsion was allowed to stand; (6) the solution obtained after standing was centrifuged, washed and dried to obtain a solid powder.

[0018] In step (1) above, the emulsifier is either TEGOPREN 7008 or Tween 80; the oil phase solvent is either liquid paraffin or hexadecane. The amount of emulsifier used is approximately 1% of the amount of solvent used.

[0019] In step (2) above, the alkaline substance is any one of ammonia, sodium hydroxide, or potassium hydroxide, and its pH value is adjusted to 12.6; the oxidizing initiator is ammonium persulfate or sodium persulfate.

[0020] In step (3) above, emulsification is carried out under the action of an emulsifying shear machine, with an emulsification shear rate of 2000-5000 rpm and an emulsification time of 20-30 min; in step (4), the emulsification time is 5-10 min.

[0021] In step (5) above, the standing time is 24-48h, and the reaction is complete when all solid particles have settled; in step (6), the drying temperature is 40±0.5℃; in step (6), the centrifugation speed is 8000rpm, and cyclohexane is used for washing.

[0022] The amine initiator mentioned above is selected from any one of tetramethylethylenediamine, ethylenediamine, and diethanolmonoisopropanolamine.

[0023] The aforementioned silane coupling agent is either KH560 or KH570. The mass ratio between tetraethyl orthosilicate and the silane coupling agent is 1:(0-0.2). Because KH570 contains double bonds, the strong initiator used for coating will initiate polymerization, resulting in excessive KH570 dosage leading to gel formation and preventing capsule formation.

[0024] When the above-mentioned admixtures are applied to cement concrete systems, the water-cement ratio is 0.3-0.5, and the admixture dosage is 0.1%-1%.

[0025] The present invention has the following advantages over the prior art:

[0026] 1) In the admixture component A of this application, the silica capsules have a slow-release effect due to the nano-silica in the capsule shell. In the early stage of hydration, the oxidizing initiator is not released. After a period of hydration, that is, after the silica shell has dissolved for a period of time, the oxidizing initiator is released and, together with the reducing initiator, initiates the polymerization of acrylamide, thereby minimizing the impact of the polymer on cement hydration. Nano-silica itself is a very good reinforcing material. Its special pozzolanic activity can react with cement-based materials, optimize the structure and composition of hydration products, and enhance cement-based materials.

[0027] 2) The admixture used in this application is a small molecule monomer rather than a polymer, which has little impact on cement-based materials and can improve flexural strength without affecting the hydration of cement-based materials.

[0028] 3) The preparation method provided by this invention has a wide range of raw material sources, is safe and environmentally friendly, and the preparation process is simple and easy to control. Attached Figure Description

[0029] Figure 1 SEM image of the silica capsules prepared in Example 1;

[0030] Figure 2 Infrared spectrum of the silica capsule prepared in Example 1;

[0031] Figure 3 Release curve of the silica capsule prepared in Example 1 in solution. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] In the following examples and comparative examples, the vacuum drying temperature during the preparation of silica capsules was 40°C; the alkaline substance was used to adjust the pH to 12.6, and the oxidizing initiator was generally in excess. The mass ratio of the oil phase to the water phase was 63:22, i.e., water in an oil emulsion, and the water content should not be too high.

[0034] Example 1

[0035] (1) Preparation of oil phase solution: Mix 1g T7008 with 62g hexadecane until homogeneous;

[0036] (2) Preparation of aqueous solution: Mix 2g of ammonium persulfate with 20g of ammonia water with pH 12.6 until homogeneous;

[0037] (3) Under the action of a 3000rpm emulsifying shearing machine, the aqueous phase solution is poured into the oil phase solution and emulsified for 30 minutes;

[0038] (4) Add 5g of TEOS to the obtained emulsion and continue emulsifying for 5min.

[0039] (5) Let the obtained emulsion stand for 48 hours.

[0040] (6) The solution obtained by standing was centrifuged and washed with cyclohexane and then vacuum dried to obtain solid powder sample S1.

[0041] Example 2

[0042] (1) Preparation of oil phase solution: Mix 1g T7008 with 62g hexadecane until homogeneous;

[0043] (2) Preparation of aqueous solution: Mix 2g of ammonium persulfate with 20g of ammonia water with pH 12.6 until homogeneous;

[0044] (3) Under the action of a 5000rpm emulsifying shearing machine, the aqueous phase solution is poured into the oil phase solution and emulsified for 20 minutes;

[0045] (4) Add 5g of TEOS to the obtained emulsion and continue emulsifying for 5min.

[0046] (5) Let the obtained emulsion stand for 48 hours.

[0047] (6) The solution obtained by standing was centrifuged and washed with cyclohexane and then vacuum dried to obtain solid powder sample S2.

[0048] Example 3

[0049] (1) Preparation of oil phase solution: Mix 1g T7008 with 62g hexadecane until homogeneous;

[0050] (2) Preparation of aqueous solution: Mix 2g of ammonium persulfate with 20g of ammonia water with pH 12.6 until homogeneous;

[0051] (3) Under the action of a 5000rpm emulsifying shearing machine, the aqueous phase solution is poured into the oil phase solution and emulsified for 20 minutes;

[0052] (4) Add 5g TEOS + 1g KH570 to the obtained emulsion and continue emulsifying for 5min.

[0053] (5) Let the obtained emulsion stand for 48 hours.

[0054] (6) The solution obtained by standing was centrifuged and washed with cyclohexane and then vacuum dried to obtain solid powder sample S3.

[0055] Example 4

[0056] (1) Preparation of oil phase solution: Mix 1g T7008 with 62g hexadecane until homogeneous;

[0057] (2) Preparation of aqueous solution: Mix 2g of ammonium persulfate with 20g of sodium hydroxide solution with pH 12.6 until homogeneous;

[0058] (3) Under the action of a 5000rpm emulsifying shearing machine, the aqueous phase solution is poured into the oil phase solution and emulsified for 20 minutes;

[0059] (4) Add 5g TEOS + 1g KH570 to the obtained emulsion and continue emulsifying for 5min.

[0060] (5) Let the obtained emulsion stand for 48 hours.

[0061] (6) The solution obtained by standing was centrifuged and washed with cyclohexane and then vacuum dried to obtain solid powder sample S4.

[0062] Example 5

[0063] (1) Preparation of oil phase solution: Mix 1g T7008 with 62g hexadecane until homogeneous;

[0064] (2) Preparation of aqueous solution: Mix 2g of ammonium persulfate with 20g of sodium hydroxide solution with pH 12.6 until homogeneous;

[0065] (3) Under the action of a 5000rpm emulsifying shearing machine, the aqueous phase solution is poured into the oil phase solution and emulsified for 20 minutes;

[0066] (4) Add 5g TEOS + 0.1g KH570 to the obtained emulsion and continue emulsifying for 10min.

[0067] (5) Let the obtained emulsion stand for 24 hours.

[0068] (6) The solution obtained by standing was centrifuged and washed with cyclohexane and then vacuum dried to obtain solid powder sample S5.

[0069] Example 6

[0070] (1) Preparation of oil phase solution: Mix 1g Tween 80 with 62g liquid paraffin evenly;

[0071] (2) Preparation of aqueous solution: Mix 2g of ammonium persulfate with 20g of sodium hydroxide solution with pH 12.6 until homogeneous;

[0072] (3) Under the action of a 4000rpm emulsifying shearing machine, the aqueous phase solution is poured into the oil phase solution and emulsified for 30 minutes;

[0073] (4) Add 5g of TEOS to the obtained emulsion and continue emulsifying for 5min.

[0074] (5) Let the obtained emulsion stand for 48 hours.

[0075] (6) The solution obtained by standing was centrifuged and washed with cyclohexane and then vacuum dried to obtain solid powder sample S6.

[0076] Example 7

[0077] (1) Preparation of oil phase solution: Mix 1g T7008 with 62g liquid paraffin evenly;

[0078] (2) Preparation of aqueous solution: Mix 2g of sodium persulfate with 20g of sodium hydroxide solution with pH 12.6 until homogeneous;

[0079] (3) Under the action of a 4000rpm emulsifying shearing machine, the aqueous phase solution is poured into the oil phase solution and emulsified for 30 minutes;

[0080] (4) Add 5g of TEOS to the obtained emulsion and continue emulsifying for 5min.

[0081] (5) Let the obtained emulsion stand for 48 hours.

[0082] (6) The solution obtained by standing was centrifuged and washed with cyclohexane and then vacuum dried to obtain solid powder sample S7.

[0083] For example 1

[0084] (1) Preparation of oil phase solution: Mix 1g T7008 with 62g liquid paraffin evenly;

[0085] (2) Preparation of aqueous solution: 20g of sodium hydroxide solution with pH 12.6;

[0086] (3) Under the action of a 4000rpm emulsifying shearing machine, the aqueous phase solution is poured into the oil phase solution and emulsified for 30 minutes;

[0087] (4) Add 5g of TEOS to the obtained emulsion and continue emulsifying for 5min.

[0088] (5) Let the obtained emulsion stand for 48 hours.

[0089] (6) The solution obtained by standing was centrifuged and washed with cyclohexane and then vacuum dried to obtain solid powder sample DS1.

[0090] The performance of the silica capsules obtained in the above examples was tested in terms of application. Specifically, the samples obtained in the above examples were mixed with a polymer monomer solution (AM) to form component A solution, and a reducing initiator was used as component B solution. During the molding process, the mixture was added to the cement-based material, and the relevant properties of the corresponding cement-based material were measured.

[0091] Test Example 1: Cement Mortar Flowability Test

[0092] The flowability of cement mortar was tested according to the national standard GB / T 8077-2012 "Test Method for Homogeneity of Concrete Admixtures", using a naphthalene-based high-efficiency water-reducing agent. The comparison results are shown in Table 1. In the flowability test, no AM monomer was added to the sample; the dosage was the same as that of the slow-release capsules.

[0093] Table 1 Comparison of Mortar Flowability Tests

[0094]

[0095]

[0096] As can be seen from the data in Table 1, when the silica slow-release capsules (samples) in the above examples of the present invention were added, the fluidity of the corresponding cement-based materials did not change significantly, proving that the inorganic admixture has no effect on the workability of cement.

[0097] Test Example 2: Mortar Mechanical Property Test

[0098] Mortar was prepared using the mortar material proportions shown in Table 2, with the silica capsules provided in the examples above added. Specifically, 16.2g of acrylamide monomer was dispersed in 120g of aqueous solution to obtain solution A, and 0.033g of diethanol monoisopropanolamine was dispersed in 120g of water to obtain solution B. During mortar mixing and molding, solutions A and B were added simultaneously to replace the water required for molding, and then the mortar was cured at room temperature.

[0099] Meanwhile, a control group was set up. Control group 1 consisted of 0.033g ammonium persulfate, 16.2g acrylamide, and 0.033g diethanol monoisopropanolamine mixed for 30 minutes, then added to the mortar material shown in Table 2 and stirred to form a paste, which was then cured at room temperature.

[0100] Control group 2 consisted of samples without the silica capsules obtained above, but with the addition of acrylamide monomer and diethanol monoisopropanolamine reducing initiator solution, in the same amounts as control group 1.

[0101] Table 2 Mortar Mix Proportion

[0102] Cement (PII 52.5) Standard sand water 600g 1350g 240g

[0103] The mechanical properties of various mortars at different silica capsule contents and curing ages were tested. The test methods are referenced (Construction and Building Materials, 2013, 49:121). The test results are shown in Table 3 below.

[0104] Table 3 Mechanical properties of mortar (dosage based on cement mass)

[0105]

[0106]

[0107] The results of the above embodiments show that adding capsules (DS1) without encapsulating the active ingredient does not improve flexural strength; neither flexural nor compressive strength is significantly improved. Meanwhile, when the pre-polymerized sample is added to the cement system (control group 1), the flexural strength is significantly improved due to the presence of the polymer, but the compressive strength decreases severely. Control group 2 indicates that without the addition of the oxidizing initiator, there is no significant effect on flexural and compressive strength. Cement specimens with the admixture provided in this application show significant improvements in flexural and compressive strength at 7 days and 28 days compared to the control group and the blank, with a dosage of 0.5% showing the best effect. Due to the retarding effect of the monomer, the compressive strength decreases slightly at 7 days, but not at 28 days. Specifically, the flexural strength improvement at 7 days reaches 24.75%, and the flexural strength improvement at 28 days reaches 33.19%.

[0108] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An admixture for improving the flexural strength of cement-based materials, characterized in that, It consists of two components, A and B: Component A comprises polymeric monomers and silica capsules. The mass ratio of the polymeric monomer to the silica capsule is 30:(1-30). The polymeric monomer is selected from acrylamide or sodium acrylate. The silica capsules are obtained by emulsifying and coating an oxidizing initiator with a silane precursor. The ratio of the silane precursor to the oxidizing initiator is 2:(5-6). The silane precursor is a mixture of tetraethyl orthosilicate and a silane coupling agent in a mass ratio of 1:(0-0.2); component B includes a reducing initiator. The reducing initiator is an amine initiator, and its mass is 0.2%-0.8% of the mass of the polymer monomer.

2. The admixture for improving the flexural strength of cement-based materials according to claim 1, characterized in that, The silica capsules are prepared by the following steps: (1) oil phase solution preparation: mix the emulsifier and the oil phase solvent evenly; (2) aqueous phase solution preparation: mix water, alkaline substance and oxidizing initiator evenly; (3) pour the aqueous phase solution into the oil phase solution for emulsification to obtain an emulsion; (4) add silane precursor to the emulsion and continue emulsification; (5) let the emulsion stand; (6) centrifuge, wash and dry the solution obtained after standing to obtain a solid powder.

3. An admixture for improving the flexural strength of cement-based materials according to claim 2, characterized in that: In step (1), the emulsifier is either T7008 or Tween 80; the oil phase solvent is either liquid paraffin or hexadecane.

4. An admixture for improving the flexural strength of cement-based materials according to claim 2, characterized in that: The alkaline substance in step (2) is any one of ammonia, sodium hydroxide, or potassium hydroxide; The oxidizing initiator is ammonium persulfate or sodium persulfate.

5. An admixture for improving the flexural strength of cement-based materials according to claim 2, characterized in that: In step (3), the speed of the emulsifying shear machine is 2000-5000 rpm, and the emulsification time is 20-30 min; The emulsification time in step (4) is 5-10 min.

6. An admixture for improving the flexural strength of cement-based materials according to claim 2, characterized in that: The standing time in step (5) is 24-48 hours; the drying temperature in step (6) is 40±0.5℃.

7. An admixture for improving the flexural strength of cement-based materials according to claim 1, characterized in that: The silane coupling agent is either KH560 or KH570.

8. An admixture for improving the flexural strength of cement-based materials according to claim 1, characterized in that: The amine initiator is selected from any one of tetramethylethylenediamine, ethylenediamine, and diethanolmonoisopropanolamine.

9. A method for applying an admixture for improving the flexural strength of cement-based materials according to any one of claims 1-8, characterized in that: When the admixture is applied to a cement concrete system, the water-cement ratio is 0.3-0.5, and the admixture dosage is 0.1%-1%.

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