Method for improving dispersion performance of hydrated calcium silicate seed crystal and application thereof

Abstract

The invention discloses a method for improving the dispersion performance of a hydrated calcium silicate seed crystal and application thereof. The method comprises the following steps: S1, adding silica fume, carbide slag, fly ash, water and grinding balls into a sealed grinding tank; s2, standing for 24 hours, and then carrying out wet grinding at the speed of 600 revolutions per minute; and S3, the step S2 is repeated, the final grinding time is determined according to the target particle size, and the raw material ratio is determined according to the target calcium-silicon ratio. The hydrated calcium silicate seed crystal is used as an early strength agent of Portland cement. The method is beneficial for improving the early strength and the later strength of the cement-based material doped with the C-S-H seed crystal.

Description

Technical Field

[0001] The invention relates to the technical field of cement-based material admixtures, and in particular to a method for improving the dispersibility of calcium silicate hydrate crystal seeds and an application thereof. Background Art

[0002] Nano-calcium silicate hydrate (CSH) is a new type of cement-based material early strength agent. By exerting its nucleation effect in cement-based materials, it can accelerate the early hydration rate of cement and significantly improve the early mechanical properties of cement-based materials. It has great application potential in engineering fields such as oil well cementing, low-temperature concrete construction, cement mixed with auxiliary cementitious materials, and alkali-activated cementitious materials.

[0003] At present, the main methods for synthesizing CSH seeds are sol-gel method, chemical precipitation method and volcanic ash method. The CSH seeds prepared by sol-gel method have high purity and good uniformity, but the raw material ethyl orthosilicate required by this method is expensive and has adverse effects on human health, so it is not conducive to the industrial production of CSH seeds. The chemical precipitation method uses alkali silicate (Na2SiO3) and calcium salt (Ca(NO3)2 and CaCl2) as raw materials, and has the advantages of simple operation, short reaction time and low equipment requirements. However, this method requires high purity of raw materials and high preparation cost. The volcanic ash method is divided into hydrothermal synthesis method, direct mixing method and mechanochemical synthesis. Among them, mechanochemical synthesis is also called wet grinding method. Wet grinding method is an efficient ultrafine grinding technology that can refine raw materials with larger particle size to nanometer level, so there is a lot of room for the selection of raw materials. In recent years, the research on the preparation of nano-hydrated calcium silicate seeds by wet grinding has been continuously deepened. By optimizing the preparation process and conditions, researchers have successfully prepared nano-hydrated calcium silicate seeds with excellent performance using a variety of solid wastes.

[0004] At present, the biggest problem in the promotion and application of calcium silicate hydrate seeds prepared by mechanochemical synthesis (i.e., wet grinding) is that the prepared nano-sized calcium silicate hydrate is very easy to agglomerate, and the dispersibility in cement-based materials is poor, which seriously affects the early strength effect of nano calcium silicate hydrate seeds. At present, the methods for improving the dispersibility of calcium silicate hydrate seeds mainly include adding various polymer dispersants, ultrasonic dispersion, etc. However, polymer dispersants usually increase the preparation cost, ultrasonic dispersion increases energy consumption, and the dispersion effect is limited. Summary of the invention

[0005] The object of the present invention is to provide a method for improving the dispersibility of calcium silicate hydrate seeds and its application, which is beneficial to improving the later strength and durability of cement-based materials mixed with CSH seeds.

[0006] In one aspect of the present invention, the present invention provides a method for improving the dispersibility of calcium silicate hydrate seeds. According to an embodiment of the present invention, the method comprises the following steps:

[0007] S1. Add silica ash, carbide slag, fly ash, water and grinding balls into a sealed grinding tank;

[0008] S2, let it stand for 24 hours, then wet grind at 600 revolutions per minute;

[0009] S3. Repeat the above step S2, determine the final grinding time according to the target particle size, and determine the raw material ratio according to the target calcium-silicon ratio.

[0010] In addition, the method for improving the dispersibility of calcium silicate hydrate seeds according to the above embodiment of the present invention may also have the following additional technical features:

[0011] In some embodiments of the present invention, in step S1, the water is deionized water that is boiled to remove carbon dioxide.

[0012] In some embodiments of the present invention, in step S1, the mass ratio of silica ash, carbide slag, fly ash and water is (2.2:2.7:1:43.7) to (4.5:5.6:1:87.5).

[0013] In some embodiments of the present invention, in step S1, the ball-to-material ratio is (4.5:1) to (5:1).

[0014] In some embodiments of the present invention, in step S2, the mixture is allowed to stand for 1 day for every 1 hour of grinding.

[0015] In another aspect of the present invention, the present invention provides a calcium silicate hydrate seed prepared according to the method for improving the dispersibility of calcium silicate hydrate seed.

[0016] In another aspect of the present invention, the present invention provides an application of the calcium silicate hydrate seed crystals. According to an embodiment of the present invention, the calcium silicate hydrate seed crystals are used to prepare silicate cement.

[0017] In another aspect of the present invention, a method for preparing silicate cement is provided. According to an embodiment of the present invention, the calcium silicate hydrate seed crystals are added to silicate cement in an amount of 0.5% to 2% by mass.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) The raw materials for preparing hydrated calcium silicate seeds in the present invention are silica fume, carbide slag and fly ash. All of them are solid wastes with low prices, which significantly reduce the preparation cost and realize the high added value utilization of silica fume, carbide slag and fly ash.

[0020] 2) The present invention makes the suspension more stable by adding fly ash, thereby improving the dispersibility of the wet-grinding nano calcium silicate hydrate seeds, making the calcium silicate hydrate seeds more dispersed in cement, and further improving the early strength of cement.

[0021] 3) The present invention improves the later strength and durability of cement-based materials mixed with nano-hydrated calcium silicate crystal seeds through the pozzolanic activity of fly ash.

[0022] 4) In the process of preparing CSH seeds by wet grinding of solid waste, fly ash is added as a dispersant for CSH seeds, so that CSH seeds grow on the surface of fly ash. This effectively reduces the agglomeration of CSH seeds, improves the dispersibility of seeds in cement, and thus improves the early strength effect of CSH seeds. In addition, high-intensity grinding is conducive to stimulating the pozzolanic activity of fly ash, which is conducive to improving the later strength and durability of cement-based materials mixed with CSH seeds. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a transmission electron microscope (TEM) image of the calcium silicate hydrate seed suspension in the comparative example of the present invention;

[0024] Figure 2 This is a transmission electron microscope (TEM) image of the calcium silicate hydrate seed suspension in Example 2 of the present invention;

[0025] Figure 3 It is the thermogravimetric (TG) analysis diagram of the products of "silica ash and carbide slag wet grinding for 3 hours" and "fly ash and carbide slag wet grinding for 3 hours" of the present invention;

[0026] Figure 4 The thermogravimetric (TG) analysis diagram of the products in Example 2 of the present invention and the comparative example;

[0027] Figure 5 The particle size distribution diagram of the suspension in Example 1, Example 2 and the comparative example of the present invention;

[0028] Figure 6 Graphs showing the absorbance of the calcium silicate hydrate seeds of Example 2 of the present invention and the comparative example. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] A method for improving the dispersibility of calcium silicate hydrate seeds comprises the following steps:

[0032] S1. Add 3.59g silica fume, 4.41g carbide slag (main component Ca(OH)2), 0.8g fly ash, water (deionized water, boiled to remove carbon dioxide, to fill the tank) and grinding balls into a sealed grinding tank at a ball-to-material ratio of 3.98:1 (grinding ball mass 35g, grinding material mass 8.8g).

[0033] S2. Wet grind at 600 rpm for 1 hour and then let stand for one day.

[0034] S3. Repeat S2 three times to obtain a target calcium silicate hydrate seed suspension with a particle size of 400 nm.

[0035] The calcium silicate hydrate seed suspension was added to silicate cement (cement grade P.O42.5) at a mass ratio of 2% and a water-cement ratio of 0.36. The strength of the cement paste was tested. The results showed that the 12h strength of the cement paste added with calcium silicate hydrate seeds was 16.5MPa; the compressive strength after 28 days was 53MPa.

[0036] The composition of Portland cement is shown in the following table:

[0037] Table 1 Portland cement components

[0038] raw materials <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[SO3]]> <![CDATA[K2O]]> <![CDATA[Na2O]]> other content 21.250％ 6.563％ 3.545％ 58.922％ 2.519％ 5.404％ 0.785％ 0.306％ 0.706％

[0039] Example 2

[0040] A method for improving the dispersibility of calcium silicate hydrate seeds comprises the following steps:

[0041] S1. Add 3.59g silica fume, 4.41g carbide slag, 1.6g fly ash, water (deionized water, boiled to remove carbon dioxide, to fill the tank) and grinding balls into a sealed grinding tank at a ball-to-material ratio of 3.65:1.

[0042] S2. Wet grind at 600 rpm for 1 hour and then let stand for one day.

[0043] S3. Repeat S2 three times to obtain a target calcium silicate hydrate seed suspension with a particle size of 400 nm.

[0044] The calcium silicate hydrate seed suspension was added to silicate cement (cement grade P.O42.5) at a mass ratio of 2% and a water-cement ratio of 0.36. The strength of the cement paste was tested. The results showed that the 12h strength of the cement paste added with calcium silicate hydrate seeds was 18.1MPa; the compressive strength after 28 days was 69MPa.

[0045] Comparative Example

[0046] A method for preparing a calcium silicate hydrate seed suspension comprises the following steps:

[0047] S1. Add 3.59g silica fume, 4.41g carbide slag, water (deionized water, boiled to remove carbon dioxide, to fill the tank) and grinding balls into a sealed grinding tank at a ball-to-material ratio of 4.375:1.

[0048] S2. Wet grind at 600 rpm for 1 hour and then let stand for one day.

[0049] S3. Repeat S2 three times to obtain a calcium silicate hydrate seed crystal suspension.

[0050] The calcium silicate hydrate seed suspension was added to silicate cement (cement grade P.O42.5) at a mass ratio of 2% and a water-cement ratio of 0.36. The strength of the cement paste was tested. The results showed that the 12h strength of the cement paste added with calcium silicate hydrate seeds was 13.2MPa; the compressive strength after 28 days was 47.2MPa.

[0051] The calcium silicate hydrate seed suspension was added to silicate cement (cement grade P.O42.5) at a mass ratio of 2%. The cement slurry formulations of Examples 1-2 and Comparative Example are shown in the following table:

[0052] Table 2 Cement slurry ratios of Examples 1-2 and Comparative Examples

[0053] Cement / g Water / g Calcium silicate hydrate seed suspension Pure Portland Cement 200 72 -- Comparative Example 200 53 20 Example 1 200 53 20 Example 2 200 53 20

[0054] The compressive strength of the silicate cement of Examples 1-2 and Comparative Example 2 was compared, and the results are shown in Table 3.

[0055] Table 3 Comparison of compressive strength of silicate cement of Examples 1-2 and Comparative Examples

[0056] Group 12h compressive strength Percentage increase 28d compressive strength Percentage increase Portland cement 8MPa / 46MPa / Comparative Example 13.2MPa 65％ 47.2MPa 2％ Example 1 16.5MPA 106％ 53MPa 15％ Example 2 18.1MPa 126％ 69MPa 50％

[0057] Note: Table 3 is the comparison results of cement paste strength after 12 hours and 28 days, where the increase percentage is compared with that of silicate cement.

[0058] The suspensions obtained in the comparative example and example 2 were subjected to thermogravimetric analysis and DLS detection.

[0059] like Figure 3-4 As shown in the figure, silica fume and carbide slag (set aside for 2 days) can fully react to form CSH when wet-grinded for 3 hours, while fly ash and carbide slag hardly react when wet-grinded for 3 hours ( Figure 3 ), and the final suspension dispersibility of the latter is significantly better than that of silica fume and carbide slag.

[0060] The calcium silicate hydrate seeds of Example 2 and Comparative Example 1 were subjected to a particle size analysis experiment. Figure 5 As shown, the particle size analysis experiment shows that the median particle size D(50) of the hydrated calcium silicate seeds in the control group without fly ash is 4989nm, while the median particle size of the hydrated calcium silicate seeds added with fly ash is reduced to 1097nm.

[0061] The absorbance of the hydrated calcium silicate seeds of Example 2 and the comparative example was measured by a violet photometer. First, compared with the control group without fly ash, the absorbance value of Example 2 mixed with 20% fly ash in the saturated calcium hydroxide solution was higher at any time, and the decay rate of the absorbance in the first 5 minutes was significantly reduced. See the attached absorbance graph Figure 6 .

[0062] The above experimental data all prove that the addition of fly ash improves the stability of the suspension.

[0063] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for improving the dispersibility of calcium silicate hydrate seeds, characterized in that: The following steps are involved: S1. Add silica ash, carbide slag, fly ash, water and grinding balls into a sealed grinding tank; S2, after standing for 24 hours, wet-grind at a speed of 600 revolutions per minute; S3. Repeat step S2, determine the final grinding time according to the target particle size, and determine the raw material ratio according to the target calcium-silicon ratio.

2. A method for improving the dispersibility of calcium silicate hydrate seeds according to claim 1, characterized in that: In step S1, the water is deionized water that is boiled to remove carbon dioxide.

3. A method for improving the dispersibility of calcium silicate hydrate seeds according to claim 1, characterized in that: In step S1, the mass ratio of silica ash, carbide slag, fly ash and water is (2.2:2.7:1:43.7) to (4.5:5.6:1:87.5).

4. A method for improving the dispersibility of calcium silicate hydrate seeds according to claim 1, characterized in that: In the step S1, the ball-to-material ratio is (4.5:1) to (5:1).

5. A method for improving the dispersibility of calcium silicate hydrate seeds according to claim 1, characterized in that: In the step S2, the mixture is left to stand for 1 day after grinding for 1 hour.

6. Calcium silicate hydrate seeds prepared according to the method for improving the dispersibility of calcium silicate hydrate seeds according to claim 1.

7. An application of the calcium silicate hydrate seed crystal according to claim 6, characterized in that: The hydrated calcium silicate seed crystals are used for preparing silicate cement.

8. A method for preparing silicate cement, characterized in that: The calcium silicate hydrate seed crystals according to claim 6 are added into silicate cement in an amount of 0.5% to 2% by mass.

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