Sulphoaluminate cement composite thickening time control agent and application thereof

Abstract

The invention provides a sulphoaluminate cement composite thickening time control agent and application thereof, and relates to the technical field of building materials. The sulphoaluminate cement composite thickening time control agent is prepared by mixing the following raw materials in parts by weight: 11-48 parts of sodium sulfate or calcium nitrate and 1-8 parts of citric acid. According to the invention, through the synergistic effect of the sodium sulfate-citric acid system and the calcium nitrate-citric acid system on the sulphoaluminate cement, the fluidity of the sulphoaluminate cement is improved, the setting time is prolonged, and the sulphoaluminate cement has high early strength.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a composite setting regulator for sulphoaluminate cement and application thereof. Background Art

[0002] Sulphoaluminate cement is regarded as a low-carbon cement because of its low sintering temperature during the manufacturing process. It has attracted widespread attention from scholars at home and abroad in recent years. The cement is made by calcining gypsum, limestone and bauxite at a temperature of about 1250°C. Its sintering temperature is about 200°C lower than that of ordinary Portland cement, thereby reducing CO2 emissions by about 20% to 30%. In addition, sulphoaluminate cement has a rapid strength development, excellent hourly service performance, and exhibits excellent properties such as low-temperature hardening, frost resistance and impermeability. However, due to its mineral composition characteristics, sulphoaluminate cement sets quickly, which brings certain difficulties to construction operations, which also limits its promotion and application in the engineering field to a certain extent.

[0003] In order to solve the problem that the setting time of sulphoaluminate cement is difficult to control in practical applications, researchers have tried to improve it by optimizing the raw material components. For example, modified cements such as alite-sulphoaluminate cement and high belite-sulphoaluminate cement have been developed. These modified cements can regulate the setting time to a certain extent, but there are still many limitations. The firing temperature of alite-sulphoaluminate cement is difficult to accurately control, while high belite-sulphoaluminate cement shows a lag in late strength growth and a high production cost. In order to more efficiently regulate the setting time and strength of sulphoaluminate cement, researchers began to explore ways to optimize performance by adding admixtures. Although the application of admixtures in ordinary Portland cement is very mature, due to the significant differences in the mineral clinker composition between sulphoaluminate cement and Portland cement, the existing admixtures suitable for Portland cement cannot be directly applied to the sulphoaluminate cement system. At the same time, the compatibility problem between admixtures and their complex mineral components in the sulphoaluminate cement system is also much more complicated than that of Portland cement. Therefore, how to control the setting time of sulphoaluminate cement is still an unresolved technical problem. Based on the above background, there is an urgent need to develop new admixtures suitable for sulphoaluminate cement to efficiently adjust its setting time, enable it to better adapt to the complex and changeable construction environment, and further promote its widespread application in the engineering field. Summary of the invention

[0004] In view of the above problems, the technical problem to be solved by the present invention is to provide a composite setting regulator and a preparation method thereof which can effectively regulate the setting time of sulphoaluminate cement and improve its working performance and mechanical properties.

[0005] The present invention is achieved by adopting the following technical solutions:

[0006] A composite setting regulator for sulphoaluminate cement is prepared by mixing the following raw materials in parts by weight:

[0007] 11-48 parts of sodium sulfate or calcium nitrate, 1-8 parts of citric acid.

[0008] In some embodiments, the composite sulphoaluminate cement setting regulator of the present invention is composed of the following raw materials in parts by weight: 11 to 23 parts of sodium sulfate and 1 to 7 parts of citric acid.

[0009] In some embodiments, the composite sulphoaluminate cement setting regulator of the present invention is composed of the following raw materials in parts by weight: 30 to 48 parts of calcium nitrate and 2 to 8 parts of citric acid.

[0010] In one embodiment, the composite sulphoaluminate cement setting regulator of the present invention is composed of the following raw materials in parts by weight: 13 parts of sodium sulfate and 1 part of citric acid.

[0011] In one embodiment, the composite sulphoaluminate cement setting regulator of the present invention is composed of the following raw materials in parts by weight: 16 parts of sodium sulfate and 1 part of citric acid.

[0012] In one embodiment, the composite sulphoaluminate cement setting regulator of the present invention is composed of the following raw materials in parts by weight: 21 parts of sodium sulfate and 3 parts of citric acid.

[0013] In one embodiment, the composite setting regulator of sulphoaluminate cement of the present invention is composed of the following raw materials in parts by weight: 43 parts of calcium nitrate and 3 parts of citric acid.

[0014] In one embodiment, the composite sulphoaluminate cement setting regulator of the present invention is composed of the following raw materials in parts by weight: 44 parts of calcium nitrate and 4 parts of citric acid.

[0015] In one embodiment, the composite sulphoaluminate cement setting regulator of the present invention is composed of the following raw materials in parts by weight: 47 parts of calcium nitrate and 5 parts of citric acid.

[0016] The application of the composite setting regulator of sulphoaluminate cement described in the present invention is specifically to add the composite setting regulator to sulfate cement, wherein the amount of the composite setting regulator added accounts for 1% to 5% of the mass of the sulfate cement. In some embodiments, the amount of sodium sulfate in the sulphoaluminate cement is 1% to 5%, the amount of calcium nitrate in the sulphoaluminate cement is 1% to 5%, and the amount of citric acid in the sulphoaluminate cement is 0.1% to 1%.

[0017] The present invention uses a composite sodium sulfate-citric acid system and a composite calcium nitrate-citric acid system. In the sodium sulfate-citric acid system, sodium sulfate is used as an early strength agent. After dissolution, it quickly reacts with Ca(OH)2 to form dihydrate gypsum, and then reacts with anhydrous calcium sulfoaluminate to form calcium sulfoaluminite and aluminum gel, which significantly accelerates the hydration process, thereby achieving faster hardening and strength improvement. In addition, the addition of sodium sulfate can increase the ion concentration in the slurry, promote ion migration, and accelerate the hydration reaction; at the same time, sodium sulfate can also inhibit adverse reactions such as sulfate erosion, further improving the early strength.

[0018] In the calcium nitrate-citric acid system, calcium nitrate acts as an early strength agent, rapidly releasing Ca due to its high solubility. 2 +, increase the concentration of calcium ions in the paste, promote the rapid nucleation and crystallization of calcium sulfonate, and thus enhance the early strength. Calcium nitrate can also improve the density of cement paste by optimizing the pore structure, further improving the compressive performance. At the same time, calcium nitrate reduces the cohesion between cement particles through the electrolyte effect, increases the amount of free water in the paste, and thus significantly improves the fluidity of the cement paste.

[0019] Citric acid is used as a retarder in both systems, mainly through its weak acidity to moderately reduce the pH value of cement paste, thereby affecting the cement hydration process. Citric acid can form complexes with calcium, aluminum and other ions in cement, inhibiting the hydration reaction of cement, thereby achieving a retarding effect. At the same time, citric acid can also improve the fluidity of cement paste, facilitate construction, and make it better suitable for various engineering applications.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention provides a composite setting regulator for sulphoaluminate cement and its application. The setting regulator can effectively prolong the initial setting time of sulphoaluminate cement and significantly improve its working performance by compounding sodium sulfate and citric acid or calcium nitrate and citric acid. At the same time, the composite setting regulator also has a significant enhancing effect on the early strength of cement. Through the application of the setting regulator, the setting time and early strength of sulphoaluminate cement can be effectively regulated, so that it can better meet the actual engineering needs.

[0022] (2) The early strength agent and retarder used in the present invention are both relatively low-priced admixtures, which can effectively reduce the production cost. At the same time, the preparation process is simple, the construction quality is easy to control, and has broad prospects for practical engineering application.

[0023] (3) The setting regulator can give full play to the low-carbon, energy-saving and high-efficiency characteristics of sulphoaluminate cement, making it the most powerful high-performance supplementary material for sulphoaluminate cement under the high pressure of energy conservation and emission reduction in the future. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be fully and clearly described below in conjunction with specific embodiments, but the described embodiments are only some embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0025] In the specific implementation manner, the admixtures used in the examples are all purchased from Sinopharm Chemical Reagent Co., Ltd., and are sodium sulfate (early strength agent, purity ≥ 99.5%), calcium nitrate (early strength agent, purity ≥ 99.0%), and citric acid (retarder, purity ≥ 90.0%). Among them, sodium sulfate is in the form of colorless transparent powder, while calcium nitrate and citric acid are in the form of white powder. The sulphoaluminate cement used in the examples and comparative examples is 42.5 grade fast-hardening sulphoaluminate cement provided by Hubei Yicheng Anda Special Cement Co., Ltd. Its specific surface area is not less than 450m 2 kg -1 , C4A3S in its mineral composition - The content is not less than 45%, the C2S content is not less than 20%, and the C4AF content is not less than 10%.

[0026] Example 1

[0027] The composite setting regulator of sulphoaluminate cement proposed by the present invention is composed of the following raw materials and their weight proportions:

[0028] 13 parts of sodium sulfate, 1 part of citric acid.

[0029] Example 2

[0030] The composite setting regulator of sulphoaluminate cement proposed by the present invention is composed of the following raw materials and their weight proportions:

[0031] 16 parts of sodium sulfate, 1 part of citric acid.

[0032] Example 3

[0033] The composite setting regulator of sulphoaluminate cement proposed by the present invention is composed of the following raw materials and their weight proportions:

[0034] 21 parts of sodium sulfate, 3 parts of citric acid.

[0035] Example 4

[0036] The composite setting regulator of sulphoaluminate cement proposed by the present invention is composed of the following raw materials and their weight proportions:

[0037] 43 parts of calcium nitrate and 3 parts of citric acid.

[0038] Example 5

[0039] The composite setting regulator of sulphoaluminate cement proposed by the present invention is composed of the following raw materials and their weight proportions:

[0040] Calcium nitrate 44 parts, citric acid 4 parts.

[0041] Example 6

[0042] The composite setting regulator of sulphoaluminate cement proposed by the present invention is composed of the following raw materials and their weight proportions:

[0043] Calcium nitrate 47 parts, citric acid 5 parts.

[0044] 2.5g of the composite setting regulator prepared in Examples 1 to 6 were added to 100g of 42.5 grade rapid hardening sulphoaluminate cement and mixed evenly. A blank control group was set up at the same time, i.e., no setting regulator was added. The above cement was tested for performance according to the following method.

[0045] The cement setting time is determined according to GB / T 1346-2011. Before the test, the setting time measuring instrument is calibrated so that the pointer points to zero when the test needle touches the glass plate. After the cement paste is prepared with water of standard consistency, it is immediately placed in a standard curing box and then tested according to the specification. The fluidity of cement mortar is tested according to GB / T2419-2005.

[0046] According to GB / T 17671-2021 standard, cement mortar specimens with a size of 40mm×40mm×160mm were made. Then they were placed in a standard curing box for curing. After curing to the corresponding age, the compressive strength test was carried out according to the specification. The test results are shown in Table 1.

[0047] Table 1 Initial setting time, fluidity and strength of Examples 1-6 and the blank control group

[0048]

[0049] From the data of the blank control group in Table 1, it can be seen that when no admixture is added, the initial setting time of sulphoaluminate cement is only 14 minutes, the fluidity is 156 mm, the 4h strength is 7.2 MPa, and the 1d strength is 36.6 MPa.

[0050] From the compressive strength test results of Example 1, Example 2 and the blank control group, the compressive strength shows an increasing trend with the increase of sodium sulfate dosage, indicating that the addition of an appropriate amount of sodium sulfate can effectively improve the early strength of sulphoaluminate cement. This is because after the addition of sodium sulfate, it will react with the calcium hydroxide produced by cement hydration to generate gypsum and sodium hydroxide. Sodium hydroxide can increase the solubility of gypsum and aluminate substances in the system and accelerate the generation of ettringite. At the same time, the concentration of calcium hydroxide in the system is reduced, hydrated calcium silicate is generated, and the pore structure is filled with ettringite, which effectively improves the early strength.

[0051] According to the setting time and fluidity test results of Example 1, Example 3 and the blank control group, with the addition of the retarder citric acid, the setting time and fluidity of the cement mortar both showed an increasing trend, showing the significant role of citric acid in regulating the setting time and working performance of the cement paste. This phenomenon can be attributed to the weak acidity of citric acid, which will affect the pH value in the cement mortar system, thereby regulating the hydration process of cement. At the same time, citric acid will form a complex with calcium ions and aluminum ions in cement, further inhibiting the hydration reaction of cement, reducing the interaction between cement particles, and improving the fluidity of the mortar while achieving a retarding effect.

[0052] The fluidity and compressive strength test results of Example 4, Example 5, Example 6 and the blank control group show that the performance of sulphoaluminate cement is significantly improved after calcium nitrate is added, mainly manifested in the increase of fluidity and the improvement of early strength. Calcium nitrate has high solubility and can quickly release Ca 2+ and NO3 - ions. These ions reduce the cohesion between cement particles through the electrolyte effect and increase the free water content in the paste, thereby significantly improving the fluidity of the cement paste. In terms of compressive strength, calcium nitrate promotes hydration reaction to produce more and more stable hydration products (such as NO3 - -AFm phase), optimizes the microstructure of the slurry, refines the pore distribution, makes the cement paste more compact, and significantly enhances the bearing capacity. In addition, the addition of calcium nitrate also makes the early hydration products have higher crystallinity and denser crystal structure. This improvement in microstructure further improves the early strength of cement.

[0053] In summary, the present invention provides a composite setting regulator for sulphoaluminate cement. The setting regulator effectively solves the problem that the setting time of sulphoaluminate cement is difficult to regulate, and can significantly improve its early strength and fluidity. The sulphoaluminate cement can better adapt to more complex construction environments. In addition, the composite regulator is not only effective, but also low in cost, economical and environmentally friendly, and has broad application prospects.

[0054] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solution and its improved conception within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A composite setting regulator for sulphoaluminate cement, characterized in that: It is made by mixing the following raw materials in parts by weight: 11-48 parts of sodium sulfate or calcium nitrate, 1-8 parts of citric acid.

2. The composite setting regulator of sulphoaluminate cement according to claim 1, characterized in that: The invention is composed of the following raw materials in parts by weight: 11 to 23 parts of sodium sulfate and 1 to 7 parts of citric acid.

3. The composite setting regulator of sulphoaluminate cement according to claim 1, characterized in that: The invention is composed of the following raw materials in parts by weight: 30 to 48 parts of calcium nitrate and 2 to 8 parts of citric acid.

4. The composite setting regulator of sulphoaluminate cement according to claim 2, characterized in that: The invention is composed of the following raw materials in parts by weight: 13 parts of sodium sulfate and 1 part of citric acid.

5. The composite setting regulator of sulphoaluminate cement according to claim 2, characterized in that: The invention is composed of the following raw materials in parts by weight: 16 parts of sodium sulfate and 1 part of citric acid.

6. The composite setting regulator for sulphoaluminate cement according to claim 2, characterized in that: The invention is composed of the following raw materials in parts by weight: 21 parts of sodium sulfate and 3 parts of citric acid.

7. The composite setting regulator of sulphoaluminate cement according to claim 3, characterized in that: The invention is composed of the following raw materials in parts by weight: 43 parts of calcium nitrate and 3 parts of citric acid.

8. The composite setting regulator for sulphoaluminate cement according to claim 3, characterized in that: The invention is composed of the following raw materials in parts by weight: 44 parts of calcium nitrate and 4 parts of citric acid.

9. The composite setting regulator of sulphoaluminate cement according to claim 3, characterized in that: The invention is composed of the following raw materials in parts by weight: 47 parts of calcium nitrate and 5 parts of citric acid.

10. The use of a composite setting regulator for sulphoaluminate cement according to any one of claims 1 to 9, characterized in that: The composite setting regulator is added into sulfate cement, wherein the amount of the composite setting regulator added accounts for 1% to 5% of the mass of the sulfate cement.

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