CN116283102A - A method of regulating the coagulation time of geopolymers by using magnesium ions - Google Patents

Abstract

The invention relates to a method for regulating the coagulation time of a geopolymer by using magnesium ions, and belongs to the technical field of geopolymer materials. By adding magnesium ions to the sodium silicate or potassium silicate alkali excitation solution, the pH value of the solution and the polymerization degree of silicon in the solution are changed, thereby reducing the dissolution rate of metakaolin and the early condensation reaction rate, and making the setting time of the geopolymer slurry A significant increase. This method belongs to an indirect method of regulating the coagulation time. The Si/Al ratio in the condensation reaction process of the geopolymer can be indirectly regulated without changing the mixing ratio, which can significantly slow down the condensation reaction without affecting the later performance. It effectively solves the problem that the early coagulation of low-calcium geopolymers is difficult to control.

Description

A method of regulating the coagulation time of geopolymers by using magnesium ions

technical field

The invention relates to the technical field of geopolymer materials, and more specifically, relates to a method for regulating the coagulation time of geopolymers by using magnesium ions.

Background technique

Geopolymer is an amorphous cementitious material formed by stimulating silica-alumina precursors (such as metakaolin _, fly ash, slag, etc.) It is only about 20% of traditional Portland cement, and hardly produces harmful gases such as nitrogen oxides and sulfur oxides, which can effectively solve the environmental problems caused by cement production. At the same time, in addition to having the same mechanical strength as traditional Portland cement, it also has better properties such as high temperature resistance and acid and alkali corrosion resistance. In addition, geopolymer raw materials have a wide range of sources, such as fly ash, slag and other industrial waste can not only reduce the cost, but also solve the environmental pollution caused by industrial waste. Therefore, geopolymer is an economical and environmentally friendly cementitious material, and is considered to be the most potential cement substitute in the 21st century. However, as a new type of cementitious material, the admixtures widely used in Portland cement are not well compatible with geopolymers due to their high alkalinity and different reaction mechanisms. Especially for low-calcium geopolymers represented by metakaolin or fly ash, the research and development of admixtures is seriously insufficient. The regulation of the early setting time can only depend on changing the mix ratio, but the change of the mix ratio will affect the later performance. This has greatly restricted the promotion and application of geopolymers. Therefore, there is an urgent need to develop corresponding admixtures to control the setting time of low-calcium geopolymers, so as to meet the requirements of the current geopolymer production and application.

Contents of the invention

Based on the problem that the early coagulation time of geopolymers is difficult to be flexibly adjusted, a method for regulating the coagulation time of geopolymers is provided. The invention utilizes magnesium ions to react with the alkali excitation solution to change the pH value of the alkali excitation solution and the degree of polymerization of the sodium silicate solution, thereby reducing the dissolution rate and condensation reaction rate of the precursor and achieving a significant retarding effect.

According to the purpose of the present invention, a kind of method utilizing magnesium ion to control the coagulation time of ground polymer is provided, comprising the following steps:

(1) adding magnesium salt to the alkali excitation solution, the alkali excitation solution is sodium silicate solution or potassium silicate solution;

(2) Mix the alkali-activated solution regulated by magnesium ions in step (1) with the geopolymer precursor, so that the dissolution rate and condensation reaction rate of the precursor are reduced, thereby increasing the coagulation time of the geopolymer slurry.

Preferably, the magnesium salt is MgCl ₂ , MgSO ₄ or Mg(NO ₃ ) ₂ .

Preferably, the amount of the magnesium ion is 10%-20% of the amount of the sodium element in the sodium silicate solution or the potassium element in the potassium silicate solution.

Preferably, the reaction time of step (1) is greater than 24 hours.

Preferably, the precursor is metakaolin or fly ash.

Preferably, in step (2), the mass ratio of the alkaline excitation solution regulated by magnesium ions to the precursor is 1.3-1.6.

Preferably, the preparation method of the sodium silicate solution is: dissolving nano SiO ₂ and NaOH in water to prepare the sodium silicate solution.

Preferably, the ratio of SiO ₂ to NaOH is 1-2.

Preferably, the preparation method of the potassium silicate solution is: dissolving nano-SiO ₂ and KOH in water to prepare the potassium silicate solution.

Preferably, the ratio of SiO ₂ to KOH is 1-2.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

(1) The present invention utilizes the reaction of magnesium ions and the alkali excitation solution to change the pH value of the alkali excitation solution and the degree of polymerization of the sodium silicate solution, thereby reducing the dissolution rate and condensation reaction rate of the precursor, and having a significant retarding effect.

(2) The present invention uses magnesium ions and alkali to stimulate the reaction of the solution. This process can generate nano-hydrated magnesium silicate (M-S-H) gel to be adsorbed on the surface of the precursor (metakaolin) particles, thereby further reducing the dissolution rate of the precursor.

(3) The present invention utilizes the method for regulating and controlling the coagulation time of geopolymers by magnesium ions to change the coagulation time of geopolymers by regulating the degree of polymerization of the alkali-activated solution, which belongs to a mode of indirect regulation and control of coagulation time, without changing the mixing ratio On the premise of indirectly controlling the Si/Al ratio in the process of geopolymer condensation reaction, the later performance can be guaranteed to meet the requirements.

(4) The magnesium ion used in the present invention to regulate the coagulation time of the geopolymer has wide sources and low cost.

(5) The present invention does not require complicated operations, and the process is simple, which is beneficial to practical application.

Description of drawings

Figure 1 is the influence curve of magnesium ions on the coagulation time of the geopolymer (specifically, the coagulation time of the geopolymer is tested using a Vicat instrument, and the relationship curve between the curing time and the penetration of the geopolymer is drawn, 5% Mg sample).

Figure 2 is the influence curve of magnesium ions on the early reaction heat of geopolymer (5% Mg sample).

Figure 3 is a graph showing the effect of magnesium ions on the strength development of geopolymers (5% Mg sample).

Fig. 4 is the effect curve of magnesium ions on the coagulation time of the geopolymer (specifically, the coagulation time of the geopolymer is tested using a Vicat instrument, and the relationship curve between the curing time of the geopolymer and the penetration is drawn, 10% Mg sample).

Fig. 5 is the influence curve of magnesium ions on the early reaction heat of geopolymer (10% Mg sample).

Figure 6 is a graph showing the effect of magnesium ions on the strength development of geopolymers (10% Mg sample).

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not constitute a conflict with each other.

The invention adjusts the pH value and polymerization degree of the alkali excitation solution by adding magnesium ions in the alkali excitation solution, thereby affecting the dissolution and condensation reaction rate of the precursor, and finally achieves the purpose of regulating the coagulation time of the geopolymer. The geopolymer obtained by this method can significantly prolong the setting time under the premise that the later performance is guaranteed.

The object of the present invention is achieved through the following technical steps:

Step 1: Prepare an alkali excitation solution, and prepare a sodium silicate alkali excitation solution with a required modulus according to actual needs. Specifically, the chemical formula of sodium silicate is Na ₂ O·nSiO ₂ , n is the modulus of the sodium silicate solution, and NaOH can be added to the sodium silicate solution to adjust the modulus of the sodium silicate solution.

Step 2: Add magnesium salt (such as MgCl ₂ ) to the sodium silicate alkali excitation solution to provide the required magnesium ions, and react with the alkali excitation solution at room temperature for more than 24 hours. During this process, keep stirring at a speed of 300 rpm. , so that it can fully react. This step is used to regulate the pH value of the alkali excitation solution and the degree of polymerization of the sodium silicate solution. This process is the key to achieve the purpose of regulation.

Step 3: Mix and stir the prepared alkali-activated solution and the precursor (such as metakaolin) for 3-5 minutes. Specifically, first stir slowly for 1 minute, then stir rapidly for 3 minutes to make it evenly mixed. Since the alkali-activated solution is alkaline The reduction and the increase of the degree of polymerization can significantly reduce the dissolution rate and condensation reaction rate of the precursor, and the reaction of magnesium ions and sodium silicate alkali to stimulate the solution can generate nano-hydrated magnesium silicate (M-S-H) adsorbed on the surface of the precursor, thereby The dissolution rate of the precursor is further reduced to obtain a geopolymer slurry with obvious retarded results.

Step 4: Test the heat of reaction of the geopolymer and its setting time.

Step 5: Put the prepared geopolymer slurry into the mould, vibrate and compact it, put it in the curing box at 20°C for two days, remove the mold, and continue curing until the specified age to test the compressive strength.

The invention changes the coagulation time of the geopolymer by regulating the degree of polymerization of the alkali-activated solution, which belongs to a method of indirectly regulating the coagulation time, and indirectly regulates the Si/Al ratio in the condensation reaction process of the geopolymer without changing the mixing ratio. , which can ensure that the later performance meets the requirements.

The present invention will be further explained below in conjunction with specific embodiments.

Example 1

The present invention prepares a geopolymer using sodium silicate solution as an alkali activator and metakaolin as a precursor, and its chemical molar ratio is Na ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O=1:1 :4:11, this ratio has excellent mechanical properties, choose MgCl ₂ to provide the required Mg ions. The specific implementation steps are as follows:

Step 1: preparing an alkali excitation solution, dissolving 65g nano-SiO ₂ (purity 99.8%) and 45.9g NaOH (purity 98.7%) in 102.8g water to prepare a sodium silicate alkali excitation solution.

Step 2: 5.18g MgCl ₂ (purity 99.5%, equivalent to 5% of Na ₂ O moles) was added to the sodium silicate solution, and reacted for 24 hours under normal temperature conditions, and the process was kept stirring (about 300 rpm/min ), pay attention to sealing during the stirring process to prevent water loss.

Step 3: Mix 134.38g of metakaolin with the alkali-activated solution added with magnesium ions, and set the stirring time to 4 minutes to make them completely mixed uniformly to obtain a geopolymer slurry. At the same time, geopolymers without magnesium ions were prepared by the same method for comparison.

Step 4: Test the coagulation time of the slurry with a Vicat instrument at an ambient temperature of 20°C, draw a relationship curve between the depth of the Vicat instrument probe and the curing time at 30 seconds, and compare the coagulation time. In addition, about 16g of geopolymer samples were prepared, and the effect of magnesium ions on the heat of reaction of geopolymers was tested by isothermal calorimeter.

Step 5: Prepare the geopolymer slurry in the same way and put it into the mold, vibrate evenly, prepare a cube test block of 40mm×40mm×40mm, and maintain it at an ambient temperature of 20°C for 3 days, 5 days and 28 days. The compressive strength was tested to characterize the effect of magnesium ions on the mechanical properties of geopolymers.

Fig. 1 is the relationship curve between the penetration depth of the geopolymer and the curing time (Control in the figure is the reference sample, 5Mg is the sample added with 5% magnesium ions, and each sample is measured 3 times). It can be found that the addition of 5% magnesium ions delays the initial setting time for about 4 hours, and the overall penetration curve shifts to the right obviously, indicating that the addition of magnesium ions has a significant retarding effect.

Figure 2 is the influence curve of magnesium ions on the early reaction heat of geopolymer slurry. It can be found that the addition of 5% magnesium ions significantly reduces the early heat release rate and the total heat release. For example, after curing for 24 hours, the addition of magnesium ions reduces the total heat release by 28%, indicating that the addition of magnesium ions changes the geopolymer. Exothermic properties of slurries.

Fig. 3 is a curve showing the effect of magnesium ions on the strength development of geopolymers. The three-day strength of the geopolymer added with magnesium ions is lower than that of the reference sample, but with the increase of age, the strength gap gradually narrows, and the strength is basically the same at 28 days, which has no obvious impact on the later performance.

Example 2

The present invention prepares a geopolymer using sodium silicate solution as an alkali activator and metakaolin as a precursor, and its chemical molar ratio is Na ₂ O:Al ₂ O ₃ :SiO ₂ :H ₂ O=1:1 :4:11, this ratio has excellent mechanical properties, choose MgCl ₂ to provide the required Mg ions. The specific implementation steps are as follows:

Step 1: preparing an alkali excitation solution, dissolving 65g nano-SiO ₂ (purity 99.8%) and 45.9g NaOH (purity 98.7%) in 102.8g water to prepare a sodium silicate alkali excitation solution.

Step 2: 10.36g MgCl ₂ (purity 99.5%, equivalent to 10% of Na ₂ O moles) was added to the sodium silicate solution, and reacted for 24 hours under normal temperature conditions, and the process was kept stirring (about 300 rpm/min ), pay attention to sealing during the stirring process to prevent water loss.

Step 3: Mix 134.38g of metakaolin with the alkali-activated solution added with magnesium ions, and set the stirring time to 4 minutes to make them completely mixed uniformly to obtain a geopolymer slurry. At the same time, geopolymers without magnesium ions were prepared by the same method for comparison.

Step 4: Test the coagulation time of the slurry with a Vicat instrument at an ambient temperature of 20°C, draw a relationship curve between the depth of the Vicat instrument probe and the curing time at 30 seconds, and compare the coagulation time. In addition, about 16g of geopolymer samples were prepared, and the effect of magnesium ions on the heat of reaction of geopolymers was tested by isothermal calorimeter.

Step 5: Prepare the geopolymer slurry in the same way and put it into the mold, vibrate evenly, prepare a cube test block of 40mm×40mm×40mm, and maintain it at an ambient temperature of 20°C for 3 days, 5 days and 28 days. The compressive strength was tested to characterize the effect of magnesium ions on the mechanical properties of geopolymers.

Fig. 4 is the relationship curve between the penetration depth of the geopolymer and the curing time (Control in the figure is the reference sample, 10Mg is the sample added with 10% magnesium ions, and each sample is measured at least twice). It can be found that the addition of 10% magnesium ions delays the initial setting time by about 11 hours, and the overall penetration curve shifts to the right obviously, indicating that the addition of magnesium ions has a significant retarding effect.

Fig. 5 is a curve showing the effect of magnesium ions on the early reaction heat of geopolymer slurry. It can be found that the addition of 10% magnesium ions significantly reduces the early heat release rate and the total heat release. For example, after curing for 24 hours, the addition of magnesium ions reduces the total heat release by 46%, indicating that the addition of magnesium ions changes the geopolymer. Exothermic properties of slurries.

Figure 6 is a graph showing the effect of magnesium ions on the strength development of geopolymers. The three-day strength of the geopolymer added with magnesium ions is lower than that of the reference sample, but with the increase of age, the strength gap gradually narrows, and the strength is slightly stronger than the reference sample at 28 days, which has no obvious impact on the later performance.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. A method for regulating the coagulation time of a geopolymer by using magnesium ions, which comprises the following steps:

(1) Adding magnesium salt into alkali excitation solution, wherein the alkali excitation solution is sodium silicate solution or potassium silicate solution;

(2) And (3) uniformly mixing the alkali excitation solution regulated and controlled by the magnesium ions in the step (1) with the geopolymer precursor, so that the dissolution rate and the condensation reaction rate of the precursor are reduced, and the coagulation time of the geopolymer slurry is prolonged.

2. The method for regulating the clotting time of a polymer by magnesium ions of claim 1, wherein said magnesium salt is MgCl ₂ 、MgSO ₄ Or Mg (NO) ₃ ) ₂ 。

3. The method for controlling the setting time of a polymer using magnesium ions according to claim 1 or 2, wherein the amount of the substance of magnesium ions is 10% to 20% of the amount of the substance of sodium element in the sodium silicate solution or potassium element in the potassium silicate solution.

4. The method for regulating the clotting time of a polymer by magnesium ions of claim 1, wherein the time of said reaction of step (1) is greater than 24 hours.

5. The method for controlling the setting time of a geopolymer by using magnesium ions according to claim 1, wherein the precursor is metakaolin or fly ash.

6. The method for controlling coagulation time of a polymer by using magnesium ions according to claim 1 or 5, wherein in the step (2), the mass ratio of the alkali excitation solution and the precursor after the magnesium ions are controlled is 1.3 to 1.6.

7. The method for controlling the coagulation time of a polymer by using magnesium ions according to claim 1, wherein the sodium silicate solution is prepared by the following steps: nano SiO ₂ And NaOH are dissolved in water to prepare sodium silicate solution.

8. The method for controlling coagulation time of a polymer with magnesium ions as set forth in claim 7, wherein said SiO ₂ The ratio of the amount of the substance to NaOH is 1-2.

9. The method for controlling the coagulation time of a polymer by using magnesium ions according to claim 1, wherein the potassium silicate solution is prepared by the following steps: nano SiO ₂ And KOH is dissolved in water to prepare the potassium silicate solution.

10. The method for controlling coagulation time of a polymer with magnesium ions as set forth in claim 9, wherein said SiO ₂ The ratio of the amount of the material to KOH is 1 to 2.

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