Additive for enhancing compression resistance and fracture resistance of cement-based material as well as preparation method and application of additive
By using sodium calcium silicate nanosheets as admixtures in cement-based materials, the problem of difficulty in effectively improving the bending performance of cement-based materials in the prior art is solved, and significant improvement of compressive and flexural properties and optimization of material structure are achieved.
Patent Information
- Application Number
- CN202311563120.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-21
- Publication Date
- 2025-05-23
AI Technical Summary
The prior art is difficult to effectively improve the bending performance of cement-based materials, and the existing additive enhancement effect is limited and there are various difficulties in practical applications.
Using a new two-dimensional nanomaterial with a special morphology and can participate in cement hydration, namely, sodium calcium silicate nanosheets, the nanosheets are prepared by hydrothermal reaction and added to the cement-based material as an admixture. This nanosheet can not only physically enhance the cement-based material, but also induce cement hydration and improve the early strength and late toughness of the material.
It significantly improves the compressive and flexural resistance of cement-based materials, improves early strength and late toughness, and does not affect engineering applications, and has huge potential.
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Figure CN120025098A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of building material admixtures, and in particular, relates to an admixture for enhancing the compression and flexural properties of cement-based materials, a preparation method thereof, and application of the admixture in cement-based materials. Background Art
[0002] At present, cement-based materials have been widely used in construction projects. Despite its many advantages, such as high mechanical properties and durability, it is difficult for cement-based materials to obtain high flexural strength. In the past few decades, many researchers have used various methods to improve the flexural strength of Portland cement (PC). Many additives, such as fibers and rubber, have been used to improve the flexural properties of cement-based composites. For example, fixed-oriented carbon fibers with a volume fraction of 3% significantly increased the flexural strength of the composite by 13.4 times; at the same time, natural latex increased the cohesion between particles by forming a thick film, thereby enhancing the flexural strength of concrete. In addition, it is reported that by adding carbon nanotubes, the flexural and tensile strength of cement-based materials increased by 50%, and the compressive strength also increased by 30%. Although these materials improve the toughness of the cement matrix due to their special structure, they all lead to microstructural defects due to their inability to participate in the hydration reaction of cement.
[0003] In addition, nanoparticles, such as nano-SiO 2 and nano-Al 2 O 3 It has been shown to improve the flexural properties of cement, such as 1% nano-SiO 2 The self-compacting concrete with nano ZrO particles showed good flexural fatigue performance, and the flexural strength reduction factor increased by 1.5% to 5.0%. 2 It can also improve the flexural strength of concrete. After replacing 2% ordinary Portland cement (OPC), the strength increase after 3 days reached 19.9%. However, through these data, it was found that although nanoparticles can reduce cracks and improve mechanical properties by inducing hydration and filling pores, the strengthening effect is very limited.
[0004] It is reported that graphene oxide (GO), as a two-dimensional nanomaterial, can significantly improve the toughness of cement-based materials. 0.04% GO can increase the flexural strength of cement paste by 83%. The main reason is that GO affects the shape and aggregation state of hydration products by promoting the hydration of PC. However, due to its high cost, GO is difficult to be applied in practical engineering.
[0005] The two-dimensional layered montmorillonite obtained by the wet grinding process provides nucleation sites and promotes the formation of hydration products, refines the microstructure, reduces pores, and improves flexural strength. Studies have shown that layered montmorillonite not only promotes early strength enhancement because it can participate in hydration, but also makes the hydration products more regular and more orderly due to its special two-dimensional morphology. However, since the wet grinding process is a top-down synthesis method, it is difficult to obtain a smaller size, and there are also certain problems with its dispersion in cement-based materials.
[0006] In summary, although existing reports show that fibers, rubber, nanoparticles, GO and specific montmorillonite can enhance the flexural properties of cement-based materials, the enhancement effect is limited and there are various difficulties in practical applications, making it impossible to truly enhance the flexural properties of cement-based materials.
[0007] Therefore, it is urgent to develop new technologies for improving the bending properties of cement-based materials to promote the steady development of the performance and structure of cement-based materials. Summary of the invention
[0008] The inventors of the present invention have found in their long-term research on the performance improvement of cement-based materials that the various additives for improving the flexural strength of PC systems in the prior art have different mechanisms, but all have relatively weak effects and other application drawbacks. To this end, the inventors have studied a new type of two-dimensional nanomaterial with a special morphology that can participate in cement hydration, which can more effectively enhance the flexural properties of cement-based materials. When the admixture is applied to cement-based materials, it has the dual effects of physical enhancement and inducing cement hydration, giving cement-based materials better early strength, as well as better toughness and mechanical properties in the later stage, without affecting engineering applications, and has great potential.
[0009] The present invention specifically adopts the following technical solutions:
[0010] A method for preparing an admixture for enhancing the compression and flexural properties of cement-based materials comprises the following steps:
[0011] S1, dispersing a silicon dioxide source into an alkaline solution to obtain a silicon dioxide dispersion;
[0012] S2, adding a water-soluble calcium salt dropwise to the silicon dioxide dispersion to obtain a suspension;
[0013] S3. Add an alcohol solvent to the suspension and perform a hydrothermal reaction at 150° C. to 180° C. for 4 h to 24 h to obtain sodium calcium silicate nanosheets, which are the additives for enhancing the compression and flexural properties of the cement-based material.
[0014] In the above step S1, the silica source is a substance having a silica content of more than 95% such as nano-silica, silica fume, and silica hydrosol.
[0015] The concentration of the alkali solution is controlled to be 0.3 mol / L to 0.5 mol / L. Conventional alkali solutions such as sodium hydroxide solution can be selected. The purpose is to convert silicon dioxide into silicates, which are not listed here one by one.
[0016] In the above step S2, the water-soluble calcium salt can be a conventional water-soluble calcium salt such as calcium nitrate or calcium chloride solution, and its purpose is to provide calcium ions, which are not listed here one by one.
[0017] The average drop rate is generally controlled to be 0.02 mass parts / min to 0.4 mass parts / min. The addition rate of the water-soluble calcium salt affects the size of the sodium calcium silicate nanosheets finally obtained. A faster drop rate generally makes it easier to obtain larger sodium calcium silicate nanosheets.
[0018] In the above step S3, the alcohol solvent is used to provide an anti-solvent to promote the precipitation of sheet-like calcium sodium silicate, which is essential for the synthesis of sheet-like materials. Generally, the alcohol solvent can be selected from alcohol solutions that are miscible with water, such as any one of small molecule alcohol solutions such as ethanol, propanol, isopropanol, or a mixture of at least two.
[0019] The amount of alcohol solvent used is important for finally obtaining flaky sodium calcium silicate, wherein the mass fraction of the alcohol solvent in the total solution obtained (i.e., the mixed solution of the alcohol solvent and the suspension) is 15wt% to 40wt%.
[0020] Therefore, the present invention also provides an admixture for enhancing the compression and flexural properties of cement-based materials obtained by the above preparation method, which is a sheet-like sodium calcium silicate material with a specific size of 1 μm to 12 μm and a thickness of less than 50 nm. It can be seen that the admixture belongs to a sodium calcium silicate nanosheet.
[0021] Moreover, in the sodium calcium silicate material, the hydrothermal reaction is fully carried out at a high temperature, and the relative contents of silicon and calcium in the sodium calcium silicate material are adjustable by adjusting the amounts of the silicon dioxide source and the water-soluble calcium salt in the preparation raw materials, and the molar ratio of silicon to calcium is controlled between 0.01:1 and 1:1; that is, at the above-mentioned relatively high hydrothermal temperature, the reactant raw materials corresponding to all the core components are basically reacted, so that the relative contents of silicon and calcium in the product sodium calcium silicate nanosheets are basically consistent with the relative contents of the two in the reactants.
[0022] The sodium calcium silicate nanosheet provided by the present invention has sodium calcium silicate as its main component, which is a sodium-doped calcium silicate substance. Its components are similar to those in cement-based materials and can be applied to cement-based materials.
[0023] The present invention also provides the use of the sodium calcium silicate nanosheets in cement-based materials, that is, adding the sodium calcium silicate nanosheets into cement-based materials at a dosage of 0.1% to 1% (based on the total amount of cementitious materials in the cement-based materials).
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] 1) The sodium calcium silicate nanosheets obtained by the above preparation method provided by the present invention are mainly composed of sodium calcium silicate, which is a sodium-doped calcium silicate material. When it is applied to cement-based materials, on the one hand, the presence of silicon, calcium and other elements can not only induce the formation of cement hydration products; but also have a strong interaction with calcium ions in the pore solution of cement-based materials. Due to its flaky morphology and thickness of less than 50nm, this inorganic material has a huge specific surface area, which makes it a kind of early strength material to improve the early strength; at the same time, it can be used as a nucleation site, so that the Ca ions dissolved in the cement can be used as a kind of early strength material. 2+ 、SiO 4 2- It is more inclined to deposit on its surface, allowing the flake morphology to grow further. The above multiple effects all induce changes in the hydration path of cement-based materials, thereby changing the overall internal structure of cement-based materials (changing the morphology of cement hydration products) and optimizing the pore structure. On the other hand, further growth under its flake morphology can make the hydration products inside the cement-based materials more likely to form densely stacked layered materials like shells, thereby improving the macroscopic mechanical properties and toughness of cement-based materials.
[0026] 2) The flaky sodium calcium silicate material obtained by the above-mentioned preparation method provided by the present invention has components similar to those in cement-based materials. When it is applied to cement-based materials, the two have good compatibility; and they are all inorganic components and do not contain organic matter, and their application will not have an adverse effect on cement hydration.
[0027] 3) The preparation method provided by the present invention has a wide range of raw material sources, is safe and environmentally friendly, and the preparation process is simple and easy to control. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 is a SEM image of the product prepared according to Example 7 of the present invention;
[0029] Figure 2 is the XRD pattern of the product prepared according to Example 7 of the present invention;
[0030] Figure 3 is a SEM image of the product prepared according to Comparative Example 1 of the present invention;
[0031] Figure 4is a SEM image of the product prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION
[0032] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with embodiments. However, these embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.
[0033] It should be noted that, in each embodiment and comparative example, "part" refers to part by mass.
[0034] Example 1
[0035] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0036] (1) Disperse 0.1 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0037] (2) 1.6 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion over a period of 5 minutes to obtain a suspension.
[0038] (3) 16 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0039] (4) The mixed reaction liquid is placed in a reactor, subjected to a hydrothermal reaction at 180° C. for 4 h, and the supernatant is removed by centrifugation to obtain sodium calcium silicate nanosheets S01.
[0040] Characterization shows that its size ranges from 8μm to 12μm and its thickness is less than 50nm.
[0041] Example 2
[0042] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0043] (1) Disperse 0.2 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0044] (2) 0.8 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0045] (3) 16 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0046] (4) The mixed reaction liquid is placed in a reactor, and a hydrothermal reaction is carried out at 180° C. for 4 h. The supernatant is removed by centrifugation to obtain sodium calcium silicate nanosheets S02.
[0047] Characterization shows that its size ranges from 6μm to 10μm and its thickness is less than 50nm.
[0048] Example 3
[0049] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0050] (1) Disperse 0.3 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0051] (2) 0.4 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0052] (3) 16 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0053] (4) The mixed reaction liquid is placed in a reactor, subjected to a hydrothermal reaction at 180° C. for 4 h, and the supernatant is removed by centrifugation to obtain sodium calcium silicate nanosheets S03.
[0054] Characterization shows that its size ranges from 4μm to 7μm and its thickness is less than 50nm.
[0055] Example 4
[0056] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0057] (1) Disperse 0.4 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0058] (2) 0.2 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0059] (3) 16 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0060] (4) The mixed reaction liquid is placed in a reactor, and a hydrothermal reaction is carried out at 180° C. for 4 h. The supernatant is removed by centrifugation to obtain sodium calcium silicate nanosheets S04.
[0061] Characterization shows that its size ranges from 2μm to 6μm and its thickness is less than 50nm.
[0062] Example 5
[0063] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0064] (1) Disperse 0.5 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0065] (2) 0.1 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0066] (3) 16 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0067] (4) placing the mixed reaction liquid in a reactor, performing a hydrothermal reaction at 180° C. for 4 h, and removing the supernatant by centrifugation to obtain sodium calcium silicate nanosheets S05.
[0068] Characterization shows that its size ranges from 1μm to 5μm, and its thickness is less than 50nm.
[0069] Example 6
[0070] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0071] (1) Disperse 0.5 parts of nano-silicon dioxide into 25 parts of 0.4 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0072] (2) 0.4 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0073] (3) 16 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0074] (4) placing the mixed reaction liquid in a reactor, performing a hydrothermal reaction at 180° C. for 4 h, and removing the supernatant by centrifugation to obtain sodium calcium silicate nanosheets S06.
[0075] Characterization shows that its size ranges from 2μm to 7μm and its thickness is less than 50nm.
[0076] Example 7
[0077] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0078] (1) Disperse 0.5 parts of nano-silicon dioxide into 25 parts of 0.5 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0079] (2) 0.4 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0080] (3) 16 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0081] (4) placing the mixed reaction liquid in a reactor, performing a hydrothermal reaction at 180° C. for 4 h, and removing the supernatant by centrifugation to obtain sodium calcium silicate nanosheets S07.
[0082] The above products obtained in this example were characterized by SEM and XRD, and the test results were as follows: Figure 1 and Figure 2 shown.
[0083] from Figure 1 It can be seen that the above product has a flaky morphology, a size range of 2 μm to 7 μm, and a thickness of less than 50 nm, and is a flaky nanomaterial.
[0084] from Figure 2 It can be seen that the main component of the solid phase product is sodium calcium silicate, which is also doped with a small amount of incompletely reacted calcium silicate and silicon dioxide.
[0085] Example 8
[0086] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0087] (1) Disperse 0.5 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0088] (2) 0.4 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0089] (3) Add 5 parts of ethanol solvent to the suspension and stir evenly to obtain a mixed reaction liquid.
[0090] (4) placing the mixed reaction liquid in a reactor, performing a hydrothermal reaction at 180° C. for 4 h, and removing the supernatant by centrifugation to obtain sodium calcium silicate nanosheets S08.
[0091] Characterization shows that its size ranges from 2μm to 7μm and its thickness is less than 50nm.
[0092] Example 9
[0093] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0094] (1) Disperse 0.5 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0095] (2) 0.4 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0096] (3) Add 10 parts of ethanol solvent to the suspension and stir evenly to obtain a mixed reaction liquid.
[0097] (4) placing the mixed reaction liquid in a reactor, performing a hydrothermal reaction at 180° C. for 4 h, and removing the supernatant by centrifugation to obtain sodium calcium silicate nanosheets S09.
[0098] Characterization shows that its size ranges from 2μm to 7μm and its thickness is less than 50nm.
[0099] Example 10
[0100] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0101] (1) Disperse 0.5 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0102] (2) 0.4 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 30 seconds to obtain a suspension.
[0103] (3) 12 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0104] (4) placing the mixed reaction liquid in a reactor, performing a hydrothermal reaction at 150° C. for 24 h, and removing the supernatant by centrifugation to obtain sodium calcium silicate nanosheets S10.
[0105] Characterization shows that its size ranges from 2μm to 7μm and its thickness is less than 50nm.
[0106] Embodiment 11
[0107] The sodium calcium silicate nanosheets provided in this embodiment are prepared by the following method:
[0108] (1) Disperse 0.5 parts of nano-silicon dioxide into 25 parts of 0.3 mol / L sodium hydroxide solution, and obtain a silicon dioxide dispersion by ultrasonic treatment.
[0109] (2) 0.4 parts of 25 wt% calcium nitrate tetrahydrate solution was added dropwise to the above silicon dioxide dispersion for 3 minutes to obtain a suspension.
[0110] (3) 12 parts of ethanol solvent was added to the suspension and stirred evenly to obtain a mixed reaction liquid.
[0111] (4) The mixed reaction liquid was placed in a reactor, and a hydrothermal reaction was carried out at 165° C. for 8 h. The supernatant was removed by centrifugation to obtain sodium calcium silicate nanosheets S11.
[0112] Characterization shows that its size ranges from 2μm to 7μm and its thickness is less than 50nm.
[0113] In order to reflect the importance of the amount of alcohol solvent added in the above preparation method of the present invention, the following comparative experiment was carried out.
[0114] Comparative Example 1
[0115] The similarities between this comparative example and Example 8 are not described here, and only the differences from Example 8 are described. The difference between this comparative example and Example 8 is that, in the third step, 2 parts of ethanol solvent are added to the suspension, and stirred evenly to obtain a mixed reaction liquid; and in the fourth step, the hydrothermal reaction time is extended to 8 hours, and the supernatant is removed by centrifugation to obtain the product S12.
[0116] Comparative Example 2
[0117] The similarities between this comparative example and Example 7 are not described here, and only the differences from Example 7 are described. The difference between this comparative example and Example 7 is that in the third step, 25 more parts of ethanol solvent are added to the suspension and stirred evenly to obtain a mixed reaction liquid; and in the fourth step, the hydrothermal reaction time is extended to 8 hours, and the supernatant is removed by centrifugation to obtain the product S13.
[0118] The product S12 obtained above was characterized by SEM. Figure 3 As shown. From the characterization results, it can be seen that when the amount of alcohol solvent is insufficient, even if the hydrothermal time is extended, no sheet-like nanomaterials can be obtained. This is because the amount of ethanol solvent added is small, and at a high temperature of 180°C, the amount of ethanol present in the solution will be even smaller, and at this time, the solution does not tend to form sheet-like materials. At the same time, SEM characterization of product S13 is performed as shown Figure 4 This result shows that when the alcohol solvent is excessive, the nanomaterial has a higher crystallinity and tends to form granular crystals.
[0119] The performance of the flaky sodium calcium silicate material obtained in the above embodiments was tested in terms of the performance considered during application. Specifically, the flaky sodium calcium silicate material was added to a cement-based material and the relevant performance of the corresponding cement-based material was measured.
[0120] Test method for fluidity of cement mortar
[0121] The fluidity of cement mortar was tested according to the national standard GB / T 8077-2012 “Test method for homogeneity of concrete admixtures”, using naphthalene-based high-efficiency water reducer. The comparison results are shown in Table 1.
[0122] Table 1 Comparison of mortar fluidity test
[0123]
[0124]
[0125] It can be seen from the data in Table 1 that after adding the sodium calcium silicate micro-nano flakes of the present invention, the fluidity of the corresponding cement-based material does not change significantly, proving that the inorganic admixture has no effect on the working performance of cement.
[0126] Application Examples
[0127] The mortar was prepared by adding the sodium calcium silicate nanosheets provided in the above embodiments in the proportions shown in Table 2.
[0128] Table 2 Mortar mix ratio
[0129]
[0130] The mechanical properties of each mortar at different admixture dosages and ages were tested. The test method can be found in the existing literature (Construction and Building Materials, 2013, 49:121) and will not be repeated here. The test results are as follows:
[0131] Table 3 Mechanical properties of mortar (dosage based on cement mass)
[0132]
[0133]
[0134] As can be seen from Table 3, the cement test block added with the sodium calcium silicate nanosheets provided by the present invention has significantly improved flexural and compressive data at 12h and 28d, and the influence of different dosages on mechanical properties is relatively small. Among them, the 12h compressive and flexural resistance can be improved by 45%, and the 28d flexural and compressive resistance can be improved by 25%.
[0135] The above application examples prove that the sodium calcium silicate nanosheets obtained under the above conditions provided by the present invention can be used to enhance the mechanical properties of cement-based materials.
[0136] In summary, the sodium calcium silicate nanosheets provided by the present invention, when used as an admixture in cement-based materials, not only improve the mechanical properties of cement-based materials due to the specificity of their components, but also do not have an adverse effect on the hydration process and working performance of cement-based materials compared to other similar admixtures in the prior art.
Claims
1. A method for preparing an admixture for enhancing the compressive and flexural properties of cement-based materials, It is characterized in that The steps include: S1, dispersing a silicon dioxide source into an alkaline solution to obtain a silicon dioxide dispersion; S2, adding a water-soluble calcium salt dropwise to the silicon dioxide dispersion to obtain a suspension; S3, adding an alcohol solvent to the suspension, and performing a hydrothermal reaction at 150° C. to 180° C. for 4 h to 24 h to obtain sodium calcium silicate nanosheets; Wherein, in the step S3, the mass fraction of the alcohol solvent in the mixed solution of the alcohol solvent and the suspension is 15wt% to 40wt%.
2. The preparation method according to claim 1, It is characterized in that The alcohol solvent is an alcohol solvent miscible with water.
3. The preparation method according to claim 2, It is characterized in that The alcohol solvent is selected from any one of ethanol, propanol, isopropanol, or a mixture of at least two of them.
4. The preparation method according to any one of claims 1 to 3, It is characterized in that In the step S2, the average dropping speed of the water-soluble calcium salt is 0.02 mass parts / min to 0.4 mass parts / min.
5. The preparation method according to claim 4, It is characterized in that The water-soluble calcium salt is selected from calcium nitrate or calcium chloride solution.
6. The preparation method according to claim 1, It is characterized in that The concentration of the alkali solution is 0.3 mol / L to 0.5 mol / L.
7. An admixture for enhancing the compressive and flexural properties of cement-based materials obtained by the preparation method according to any one of claims 1 to 6, It is characterized in that The component of the additive is sodium calcium silicate nanosheets with a size of 1 μm to 12 μm and a thickness of less than 50 nm.
8. Use of the admixture as claimed in claim 7, It is characterized in that The admixture is added to the cement-based material in an amount of 0.1% to 1%, wherein the amount is based on the total amount of cementitious materials in the cement-based material.