Fly ash-based paste admixture with early strength and chloride ion curing functions, its preparation method and application

Abstract

The present invention discloses a fly ash-based paste admixture with early strength and chloride ion curing functions, and its preparation method and application. In the present invention, high-aluminum fly ash is used as the aluminum source, calcium oxide is used as the supplementary calcium source, and polycarboxylate superplasticizer (PCE) is used as the anion intercalation modification material. By controlling the environmental pH with a pH buffer solution, a fly ash-based paste admixture containing abundant high-activity Ca-Al-PCE layered double hydroxides is prepared under the synergistic action of mechanical force and chemistry. It overcomes the defect of insufficient early activity of traditional fly ash, and has both excellent early strength effect and outstanding chloride ion curing ability. When it is used in concrete, the chloride ion curing rate at 28 days can be increased by 30-40%, and the compressive strength at 1 day can be increased by 30-50%.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly relates to a fly ash-based paste admixture with early strength and chloride ion curing functions, a preparation method thereof, and an application thereof. Background Art

[0002] In the construction of remote island reefs, coral sand is used as a concrete aggregate, which can achieve local material utilization, solve the problem of raw material transportation, and has important engineering significance. However, the chloride ions carried by coral sand can damage the passivation film on the surface of steel bars, induce steel bar corrosion, and easily cause risks such as expansion failure and structural failure of reinforced concrete. In view of the problem of endogenous chloride ion erosion, although methods such as fresh water washing and dechlorination, epoxy coating protection, steel bar corrosion inhibitor, and electrochemical protection have certain effects, there are still problems such as high cost and limited implementation conditions. Chloride ion curing can efficiently capture free chloride ions by using the hydration products of cement-based materials themselves. The method is simple and low-cost, and has received attention and recognition from many scholars. Chloride ion curing includes two action modes: chemical binding and physical adsorption. Among them, chemical binding mainly generates Friedel salt and Kuzel salt through the AFm phase transformation reaction, and realizes chloride ion curing through chemical reactions, and the curing effect is more stable and reliable.

[0003] Research shows that when fly ash is used as a mineral admixture, it not only has the advantages of energy conservation and environmental protection, but also can significantly improve the workability, mechanical properties, crack resistance, impermeability and durability of concrete, and is widely used in various engineering constructions. In addition, fly ash has a rich aluminum phase content. By generating the pozzolanic effect, it promotes the formation of Friedel salt in cement-based materials and can improve the chloride ion curing ability of cement-based materials. However, fly ash has a high vitreous content and low early activity. When used as an admixture, there are easily problems such as insufficient early mechanical properties and limited chloride ion curing ability. Summary of the Invention

[0004] In view of this, the present invention aims to provide a preparation method of a fly ash-based paste admixture with early strength and chloride ion curing functions to solve the problems of low activity of existing fly ash, resulting in insufficient early mechanical properties and limited chloride ion curing ability of cement-based materials.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] A preparation method of a fly ash-based paste admixture with early strength and chloride ion curing functions includes the following steps:

[0007] 1) Mix high-aluminum fly ash, sodium hydroxide, a surface modifier, and water evenly according to a mass ratio of 30:2:5:500 to 50:3:4:300, and then grind for a period of time to obtain an alkali-treated highly reactive fly ash slurry with a median particle size of 6 - 8 μm;

[0008] 2) Add calcium oxide, a polycarboxylate superplasticizer, and a glycine / sodium hydroxide buffer solution with a pH value of 9.0 to the alkali-treated highly reactive fly ash slurry in sequence according to a mass ratio of 8:3:20 to 10:3:20, and continue to grind for a period of time to obtain a composite-modified fly ash slurry with a median particle size of 2 - 4 μm;

[0009] 3) Place the composite-modified fly ash slurry at 50 - 60 °C and continuously stir for 2 - 4 h, then add welan gum accounting for 0.001% - 0.003% of the dry basis weight of the composite-modified fly ash slurry. After stirring evenly, obtain a fly ash-based paste admixture with early strength and chloride curing functions.

[0010] Optionally, the Al 2 O 3 content of the high-aluminum fly ash in step 1) is 42 - 50%, and the SiO 2 content is 30 - 35%.

[0011] Optionally, the grinding temperature in step 1) is 30 - 40 °C, the grinding time is 2 - 3 h, and the grinding speed is 600 - 800 r / min.

[0012] Optionally, the grinding ball material in step 1) is zirconia, and the grading is 5 mm:3 mm:1 mm:0.2 mm = 1:5:5:3 - 2:5:3:2, and the ball-to-material ratio is 5:3 - 3:1.

[0013] Optionally, the surface modifier in step 1) is composed of a compound admixture of sodium dodecylbenzenesulfonate and polyether-modified trisiloxane in a weight ratio of 1:6 - 2:5.

[0014] Optionally, the grinding temperature in step 2) is 40 - 50 °C, the grinding time is 1 - 2 h, and the grinding speed is 600 - 800 r / min.

[0015] Optionally, the grinding ball material in step 2) is zirconia, and the grading is 5 mm:3 mm:1 mm:0.2 mm = 1:5:5:3 - 2:5:3:2, and the ball-to-material ratio is 5:3 - 3:1.

[0016] Optionally, the total mass of the calcium oxide, the polycarboxylate superplasticizer, and the glycine / sodium hydroxide buffer solution in step 2) is 50% - 60% of the mass of the alkali-treated highly reactive fly ash slurry.

[0017] Optionally, the fly ash-based paste admixture with early strength and chloride ion curing functions is prepared by the preparation method of the fly ash-based paste admixture with early strength and chloride ion curing functions according to any one of claims 1 to 7.

[0018] Optionally, the dry basis dosage of the fly ash-based paste admixture with early strength and chloride ion curing functions is 20%-30% of the total amount of cementitious materials in the cement concrete.

[0019] The preparation mechanism of the present invention is as follows:

[0020] In the present invention, high-aluminum fly ash is used as the aluminum source, calcium oxide is used as the supplementary calcium source, and polycarboxylate superplasticizer (PCE) is used as the anion intercalation modification material. By controlling the environmental pH with a pH buffer solution, a fly ash-based paste admixture (Ca-A1-PCE layered double hydroxide / fly ash composite structure material) containing rich high-activity Ca-A1-PCE layered double hydroxides is prepared under the synergistic action of mechanical force and chemistry. In the obtained fly ash-based paste admixture, the Ca-A1-PCE layered double hydroxides adhere to the surface of the fly ash structure. Due to the action of the dispersant PCE, the high-activity Ca-Al-PCE layered double hydroxides overcome the defects of poor dispersibility and easy agglomeration of conventional Ca-A1-PCE. And under the action of mechanical force and chemistry, the particle size of fly ash is refined, and its activity is significantly enhanced. Its micro-aggregate filling effect and pozzolanic effect in cement-based materials are enhanced. Synergistically with the high-activity Ca-Al-PCE layered double hydroxides adsorbed on the surface, the early strength and chloride ion curing ability of cement-based materials are greatly improved.

[0021] Compared with the prior art, the preparation method of the fly ash-based paste admixture with early strength and chloride ion curing functions of the present invention has the following advantages:

[0022] 1. The fly ash-based paste admixture prepared by the present invention contains rich high-activity Ca-A1-PCE layered structure materials, overcomes the defect of insufficient early activity of traditional fly ash, and has both excellent early strength effect and outstanding chloride ion curing ability. In the early stage of hydration, it can react with the sulfate ions of gypsum in cement to generate AFt, improving the early strength of cement-based materials. As the gypsum is gradually consumed, AFt gradually transforms into AFm, which can cure chloride ions to generate Friedel salt and Kuzel salt, improving the chloride ion curing ability of cement-based materials.

[0023] 2. The Ca-A1-PCE in the fly ash-based paste admixture prepared by the present invention has the advantages of high dispersibility and high stability, making it have more reliable chloride ion curing ability and early strength performance.

[0024] 3. The present invention uses industrial waste fly ash as raw material to prepare a high-performance admixture, which has significant advantages such as energy conservation, environmental protection, low cost, and easy mass production. Moreover, compared with the traditional hydrothermal synthesis method, it is simple, energy-saving, environmentally friendly, low-cost, and easy for mass production. Detailed Embodiments

[0025] To enable those skilled in the art to better understand the technical solutions and technical effects of the present invention, several embodiments will be provided below. Obviously, what is described below is only an embodiment, which does not limit the protection scope of the present invention.

[0026] Embodiment 1

[0027] A preparation method of a fly ash-based paste admixture with early strength and chloride ion curing functions specifically includes the following steps:

[0028] 1) Mix high-aluminum fly ash (Al 2 O 3 content is 42%, SiO 2 content is 35%), sodium hydroxide, a surface modifier, and water evenly according to a mass ratio of 30∶2∶5∶500, and then grind them in a temperature environment of 30°C for 2 h. During the grinding process, the ball-to-material ratio is 5∶3, the rotation speed is 600 r / min, the material of the grinding balls used is zirconia, and the grinding ball gradation is 5 mm∶3 mm∶1 mm∶0.2 mm = 1∶5∶5∶3 to obtain an alkali-treated highly active fly ash slurry with a median particle size of 8 μm. Among them, the surface modifier is composed of a compound admixture of sodium dodecylbenzenesulfonate and polyether-modified trisiloxane at a weight ratio of 1∶6;

[0029] 2) Add calcium oxide, a commercially available polycarboxylate water reducer with a solid content of 39%, and a glycine / sodium hydroxide buffer solution with a pH value of 9.0 to the alkali-treated highly active fly ash slurry in step 1) in sequence according to a mass ratio of 8∶3∶20, and continue to grind at a temperature of 40°C for 1 h. During the grinding process, the ball-to-material ratio is 5∶3, the rotation speed is 600 r / min, the material of the grinding balls used is zirconia, and the grinding ball gradation is 5 mm∶3 mm∶1 mm∶0.2 mm = 1∶5∶5∶3 to obtain a composite-modified fly ash slurry with a median particle size of 4 μm. Among them, the total mass of calcium oxide, polycarboxylate water reducer, and glycine / sodium hydroxide buffer solution is 50% of the mass of the alkali-treated highly active fly ash slurry;

[0030] 3) Take out the composite-modified fly ash slurry in step 2), place it at a temperature of 50°C and continuously stir for 2 h, then add 0.001% of xanthan gum based on the dry weight of the composite-modified fly ash slurry to stabilize the slurry. After stirring evenly, a fly ash-based paste admixture with early strength and chloride ion curing functions is obtained.

[0031] The fly ash-based paste admixture with early strength and chloride ion solidification functions obtained in this example is used to replace the cementitious material in cement concrete. Among them, the dry basis dosage of the fly ash-based paste admixture with early strength and chloride ion solidification functions is 20% of the total amount of cementitious materials.

[0032] Example 2

[0033] A preparation method of a fly ash-based paste admixture with early strength and chloride ion solidification functions specifically includes the following steps:

[0034] 1) Mix high-aluminum fly ash (with an Al 2 O 3 content of 50% and an SiO 2 content of 30%), sodium hydroxide, a surface modifier, and water in a mass ratio of 50∶3∶4∶300. After mixing evenly, grind them in a temperature environment of 40°C for 3 hours. During the grinding process, the ball-to-material ratio is 3∶1, the rotation speed is 800 r / min, the material of the grinding balls used is zirconia, and the grinding ball gradation is 5mm∶3mm∶1mm∶0.2mm = 2∶5∶3∶2 to obtain an alkali-treated highly active fly ash slurry with a median particle size of 6 μm. Among them, the surface modifier is composed of a compound admixture of sodium dodecylbenzenesulfonate and polyether-modified trisiloxane in a weight ratio of 2∶5;

[0035] 2) Add calcium oxide, a commercially available polycarboxylate water reducer with a solid content of 41%, and a glycine / sodium hydroxide buffer solution with a pH value of 9.0 to the alkali-treated highly active fly ash slurry in step 1) in a mass ratio of 10∶3∶20. Continue to grind at a temperature of 50°C for 2 hours. During the grinding process, the ball-to-material ratio is 3∶1, the rotation speed is 800 r / min, the material of the grinding balls used is zirconia, and the grinding ball gradation is 5mm∶3mm∶1mm∶0.2mm = 2∶5∶3∶2 to obtain a composite-modified fly ash slurry with a median particle size of 2 μm. Among them, the total mass of calcium oxide, polycarboxylate water reducer, and glycine / sodium hydroxide buffer solution is 60% of the mass of the alkali-treated highly active fly ash slurry;

[0036] 3) Take out the composite-modified fly ash slurry in step 2), place it at a temperature of 60°C and continuously stir for 4 hours, then add 0.003% of xanthan gum based on the dry basis weight of the composite-modified fly ash slurry to stabilize the slurry. After stirring evenly, a fly ash-based paste admixture with early strength and chloride ion solidification functions is obtained.

[0037] The fly ash-based paste admixture with early strength and chloride ion solidification functions obtained in this example is used to replace the cementitious material in cement concrete. Among them, the dry basis dosage of the fly ash-based paste admixture with early strength and chloride ion solidification functions is 30% of the total amount of cementitious materials.

[0038] The fly ash-based paste admixtures obtained in Examples 1-2 were applied to concrete. To simulate a certain amount of chloride ions in the concrete, sodium chloride was introduced as the chloride ion source, and the chloride ion content was 0.12% of the mass of the sand. Then, according to the water conservancy industry standard SL352-2006 "Test Regulations for Hydraulic Concrete", the chloride ion curing rate of the concrete was measured by the Mohr method. The mechanical properties of the concrete specimens in each example were operated according to the relevant regulations of GB / T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", and the size of the test specimens was 150mm×150mm×150mm.

[0039] To compare the effects of the fly ash-based paste admixture with early strength and chloride ion curing functions of the present invention on the chloride ion curing performance and early mechanical properties of concrete, the concrete specimens mixed with the fly ash-based paste admixtures of Examples 1 and 2 of the present invention were compared with the blank group without the fly ash-based paste admixture of the present invention. The specific formula is shown in Table 1, where the dosage of the fly ash-based paste admixture of the present invention is calculated by dry basis weight parts.

[0040] Table 1

[0041]

[0042] The test results of various indexes of the concrete with the above ratio are shown in Table 2.

[0043] Table 2

[0044]

[0045] It can be seen from the data in Table 2 that compared with the blank control group, after adding the fly ash-based paste admixtures prepared in Examples 1 and 2 of the present invention, the 28d chloride ion curing rate of the concrete increased by 30-40%, and the 1d compressive strength increased by 30-50%. It shows that the fly ash-based paste admixture with early strength and chloride ion curing functions prepared by the present invention can effectively improve the early mechanical properties of concrete, significantly enhance the chloride ion curing ability, effectively improve the service life of reinforced concrete in the chloride ion erosion environment, and has great economic and social benefits.

[0046] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a fly ash-based paste admixture with early strength and chloride ion curing functions, characterized in that, it comprises the following steps: 1) Mix high-aluminum fly ash, sodium hydroxide, a surface modifier and water evenly according to a mass ratio of 30∶2∶5∶500 - 50∶3∶4∶300, and then grind for a period of time to obtain an alkali-treated highly active fly ash slurry with a median particle size of 6 - 8 μm; 2) Add calcium oxide, a polycarboxylate water reducer and a glycine / sodium hydroxide buffer solution with a pH value of 9.0 to the alkali-treated highly active fly ash slurry in sequence according to a mass ratio of 8∶3∶20 - 10∶3∶20, and continue to grind for a period of time to obtain a composite modified fly ash slurry with a median particle size of 2 - 4 μm. The total mass of the calcium oxide, the polycarboxylate water reducer and the glycine / sodium hydroxide buffer solution is 50% - 60% of the mass of the alkali-treated highly active fly ash slurry; 3) Place the composite modified fly ash slurry at 50 - 60 °C and continuously stir for 2 - 4 h, then add xanthan gum accounting for 0.001% - 0.003% of the dry basis weight of the composite modified fly ash slurry. After stirring evenly, a fly ash-based paste admixture with early strength and chloride ion curing functions is obtained.

2. The preparation method of the fly ash-based paste admixture with early strength and chloride ion curing functions according to claim 1, characterized in that, The Al content of the high-aluminum fly ash described in step 1) 2 O 3 is 42-50%, and the SiO 2 content is 30-35%.

3. The preparation method of the fly ash-based paste admixture with early strength and chloride ion curing functions according to claim 1, characterized in that, in step 1), the grinding temperature of the grinding is 30 - 40 °C, the grinding time is 2 - 3 h, and the grinding speed is 600 - 800 r / min.

4. The preparation method of the fly ash-based paste admixture with early strength and chloride ion curing functions according to claim 1, characterized in that, in step 1), the grinding balls for the grinding are made of zirconia, the particle size distribution is 5 mm∶3 mm∶1 mm∶0.2 mm = 1∶5∶5∶3 - 2∶5∶3∶2, and the ball-to-material ratio is 5∶3 - 3∶1.

5. The preparation method of the fly ash-based paste admixture with early strength and chloride ion curing functions according to claim 1, characterized in that, in step 1), the surface modifier is composed of a compound admixture of sodium dodecylbenzenesulfonate and polyether-modified trisiloxane in a weight ratio of 1∶6 - 2∶5.

6. The preparation method of the fly ash-based paste admixture with early strength and chloride ion curing functions according to claim 1, characterized in that, in step 2), the grinding temperature of the grinding is 40 - 50 °C, the grinding time is 1 - 2 h, and the grinding speed is 600 - 800 r / min.

7. The preparation method of the fly ash-based paste admixture with early strength and chloride ion curing functions according to claim 1, characterized in that, in step 2), the grinding balls for the grinding are made of zirconia, the particle size distribution is 5 mm∶3 mm∶1 mm∶0.2 mm = 1∶5∶5∶3 - 2∶5∶3∶2, and the ball-to-material ratio is 5∶3 - 3∶1.

8. A fly ash-based paste admixture with early strength and chloride ion curing functions, characterized in that, The fly ash-based paste admixture with early strength and chloride ion solidification functions is prepared by the preparation method of the fly ash-based paste admixture with early strength and chloride ion solidification functions according to any one of claims 1 to 7.

9. Application of the fly ash-based paste admixture with early strength and chloride ion solidification functions according to claim 8 in cement concrete, characterized in that the dry basis admixture amount of the fly ash-based paste admixture with early strength and chloride ion solidification functions is 20%-30% of the total amount of cementitious materials in the cement concrete.

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