CN111662024A - Geopolymer mortar based on fly ash and preparation method thereof - Google Patents

Abstract

The invention discloses a fly ash-based geopolymer mortar and a preparation method thereof, belonging to the technical field of construction mortar. The invention uses domestic waste incineration fly ash as a raw material for the preparation of geopolymer mortar, utilizes two alkaline excitations and controls the process parameters in the preparation process, and effectively stabilizes and solidifies the heavy metals in the fly ash. The leaching heavy metals of the geopolymer material can meet the application requirements, will not cause secondary pollution to the environment, have heavy metal environmental safety, and can better realize the treatment and resource utilization of waste incineration fly ash, and the prepared geological Polymer mortar has excellent mechanical strength and crack resistance. The preparation method of the invention is simple and feasible, and the production cost is low.

Description

A kind of geopolymer mortar based on fly ash and preparation method thereof

technical field

The invention relates to the technical field of construction mortar, in particular to a fly ash-based geopolymer mortar and a preparation method thereof.

Background technique

As a bonding and repairing material, traditional cement mortar is widely used in various engineering constructions due to its wide source of raw materials, low cost, strong mechanical properties, good corrosion resistance, strong fire resistance, and wide application range. , is one of the important building materials. However, in the process of cement production, a large amount of carbon dioxide will inevitably be generated, which will cause the greenhouse effect and cause great pressure on environmental protection.

Geopolymer materials (Geopolymers) are a new class of alkali-activated cementitious materials developed in recent years. This material has the characteristics of high strength, high corrosion resistance, high temperature resistance, and excellent environmental protection performance, and is currently a research hotspot. Geopolymeric materials have the properties of polymers, ceramics and cement and can be used as cementitious materials to prepare engineering materials such as concrete and mortar. Compared with cement-based building materials, their mechanical properties and anti-cracking properties are also better. Excellent, and will not cause environmental pollution in the production process.

At the same time, although environmental protection has become a common concern in the world, the current method of waste disposal in my country is still incineration, and waste incineration will lead to a huge increase in fly ash production. However, due to the potential pozzolanic properties of fly ash, active SiO ₂ and Al ₂ O ₃ can be released through certain chemical means, such as alkali activation, destruction of the glass body of the outer layer of fly ash, etc., and finally react to form hydraulic gels such as CSH and CAH. Substance is a substance that can be used as a cementitious material for construction, which can turn waste incineration fly ash into treasure.

However, since fly ash contains a large amount of heavy metals and harmful substances, if it is directly landfilled without special treatment, heavy metals in fly ash will seep out in large quantities under the acidic conditions of the landfill, pollute groundwater, soil and even air, and through heavy metals Migration and transformation in plants and animals further endanger human health.

At present, in the prior art, there is a process of using domestic waste incineration fly ash as a raw material for preparing geopolymer mortar, which can realize the resource utilization of domestic waste incineration fly ash, but has not yet achieved effective stabilization of heavy metals in fly ash. Solidification makes the heavy metals and harmful substances in the fly ash likely to be leached, which directly or indirectly pollutes the environment and affects human health, and the performance of the geopolymer mortar prepared by using the waste incineration fly ash still needs to be improved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a kind of geopolymer mortar based on fly ash and preparation method thereof, in order to solve the problems existing in the above-mentioned prior art, while the geopolymer mortar using fly ash as raw material has strong mechanical properties, It can effectively achieve stable solidification of heavy metals in fly ash.

For achieving the above object, the present invention provides the following scheme:

The present invention provides a method for preparing a fly ash-based geopolymer mortar, comprising the following steps:

(1) Dry and grind the fly ash for pretreatment;

(2) Place the metakaolin in a stirring tank, and at a rotating speed of 200-300 r/min, according to the mass ratio of fly ash: metakaolin: alkaline activator to be 1: (2-3): (0.05-0.25), first Add the pretreated fly ash, stir for 2-3 minutes, then add the alkaline activator by spraying, and stir for 5-10 minutes to obtain a mixture;

(3) adjusting the rotational speed to 400-500r/min, adding the fine aggregate to the mixture in step (3), adding the alkaline activator solution, and stirring for 1.5-2min;

(4) adding mixing water to the mixture in step (3), adjusting the rotational speed to 550-650r/min, and stirring for 2-3min to obtain a fly ash-based geopolymer mortar.

Further, the moisture content of the pretreated fly ash in step (1) is not more than 1%.

Further, the specific surface area of the pretreated fly ash in step (1) is not less than 330 m ² /kg.

Further, the alkaline activator in step (2) is a mixed solution of water glass and NaOH solution.

Further, in the step (2), the concentration of the NaOH solution in the alkaline activator is 8-12 mol/L, and the modulus of the water glass is 1.5-1.8.

Further, the spraying speed in step (2) is 1.5-2ml/min.

Further, the alkaline activator described in step (3) is a mixed solution of water glass and sodium carbonate solution.

Further, the concentration of the sodium carbonate solution in the alkaline activator is 7-8 mol/L, and the modulus of the water glass is 2.4-2.8.

Further, in step (3), the mass ratio of the fine aggregate to the metakaolin and fly ash mixture is (0.4-2): 1; the fine aggregate is machine-made sand.

Further, in step (4), the mass ratio of mixing water to metakaolin and the total mass of fly ash is 1:(0.2-0.4).

The present invention discloses the following technical effects:

The invention uses domestic waste incineration fly ash as a raw material for the preparation of geopolymer mortar, utilizes two alkaline excitations and controls the process parameters in the preparation process, and effectively stabilizes and solidifies the heavy metals in the fly ash. The leaching heavy metals of the geopolymer material can meet the application requirements, will not cause secondary pollution to the environment, have heavy metal environmental safety, and can better realize the treatment and resource utilization of waste incineration fly ash, and the prepared geological Polymer mortar has excellent mechanical strength and crack resistance.

The preparation method of the invention is simple and feasible, and the production cost is low.

Detailed ways

Various exemplary embodiments of the present invention will now be described in detail, which detailed description should not be construed as a limitation of the invention, but rather as a more detailed description of certain aspects, features, and embodiments of the invention.

It should be understood that the terms described in the present invention are only used to describe particular embodiments, and are not used to limit the present invention. Additionally, for numerical ranges in the present disclosure, it should be understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated value or intervening value in that stated range is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention relates. Although only the preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials in connection with which the documents are referred. In the event of conflict with any incorporated document, the content of this specification controls.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the present invention. The description and examples of the present application are only exemplary.

As used herein, "comprising," "including," "having," "containing," and the like, are open-ended terms, meaning including but not limited to.

The "parts" described in the present invention are all in parts by mass unless otherwise specified.

The chemical composition of the waste incineration fly ash used in the present invention is shown in Table 1:

Table 1

According to the regulations of the environmental protection industry standard "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid Nitric Acid Method" HJ/T299-2007, the leachable heavy metals of the waste incineration fly ash used in the present invention are detected, and the results are as shown in Table 2:

Table 2

Example 1

(1) Dry and grind the fly ash for pretreatment, so that the moisture content of the pretreated fly ash is not more than 1%, and the specific surface area is not less than 330m ² /kg.

(2) Place the metakaolin in a stirring tank, and at a rotating speed of 200 r/min, according to the mass ratio of fly ash: metakaolin: alkaline activator to be 1:3:0.05, add the pretreated fly ash first, and stir for 2 min , and then the mixture of water glass and NaOH solution was added as an alkaline activator, and the concentration of NaOH solution in the alkaline activator was 12 mol/L, the modulus of water glass was 1.5, and the spray was controlled. The speed was 2 ml/min and the stirring was carried out for 10 min to obtain a mixture.

(3) Adjust the rotating speed to 400r/min, according to the mass ratio of the mixture of machine-made sand, metakaolin and fly ash is 0.4:1, add the machine-made sand to the mixture of step (3), and then use the mixture of water glass and sodium carbonate solution. The mixed solution was used as an alkaline activator, added in the form of a solution, and stirred for 2 min;

Wherein, the concentration of the sodium carbonate solution in the alkaline activator is 8 mol/L, and the modulus of the water glass is 2.4.

(4) be 1:0.2 according to the mass ratio of mixing water to metakaolin and the total mass of fly ash, add mixing water to the mixture of step (3), adjust the rotating speed to 650r/min, stir 3min, obtain based on fly ash geopolymer mortar.

Example 2

(1) Dry and grind the fly ash for pretreatment, so that the moisture content of the pretreated fly ash is not more than 1%, and the specific surface area is not less than 330m ² /kg.

(2) Place the metakaolin in a stirring tank, at 300r/min rotating speed, according to the mass ratio of fly ash:metakaolin:alkaline activator is 1:2:0.25, first add the pretreated fly ash, and stir for 3min , and then the mixture of water glass and NaOH solution is added as an alkaline activator, and the concentration of NaOH solution in the alkaline activator is 8 mol/L, the modulus of water glass is 1.8, and the spray is controlled. The speed was 1.5 ml/min and the stirring was carried out for 5 min to obtain a mixture.

(3) Adjust the rotating speed to 500r/min, according to the mass ratio of the mixture of machine-made sand, metakaolin and fly ash is 2:1, add the machine-made sand to the mixture of step (3), and then use the mixture of water glass and sodium carbonate solution. The mixed solution was added as an alkaline activator in the form of a solution and stirred for 1.5 min;

Wherein, the concentration of the sodium carbonate solution in the alkaline activator is 7 mol/L, and the modulus of the water glass is 2.8.

(4) be 1:0.4 according to the mass ratio of mixing water and metakaolin and the total mass of fly ash, add mixing water to the mixture of step (3), adjust the rotating speed to 550r/min, stir 2min, obtain based on fly ash geopolymer mortar.

Example 3

(1) Dry and grind the fly ash for pretreatment, so that the moisture content of the pretreated fly ash is not more than 1%, and the specific surface area is not less than 330m ² /kg.

(2) Place the metakaolin in a stirring tank, at 300r/min rotating speed, according to the mass ratio of fly ash:metakaolin:alkaline activator is 1:2.5:0.2, first add the pretreated fly ash, stir for 2.5 min, and then the mixture of water glass and NaOH solution was added as an alkaline activator by spraying, wherein the concentration of NaOH solution in the alkaline activator was 10 mol/L, the modulus of water glass was 1.6, and the control The spray rate was 1.8 ml/min, and the mixture was stirred for 8 min.

(3) Adjust the rotating speed to 450r/min, according to the mass ratio of the mixture of machine-made sand, metakaolin and fly ash is 1:1, add the machine-made sand to the mixture of step (3), and then use the mixture of water glass and sodium carbonate solution. The mixed solution was added as an alkaline activator in the form of a solution and stirred for 1.8 min;

Wherein, the concentration of the sodium carbonate solution in the alkaline activator is 7.5 mol/L, and the modulus of the water glass is 2.5.

(4) be 1:0.3 according to the mass ratio of mixing water and metakaolin and the total mass of fly ash, add mixing water to the mixture of step (3), adjust the rotating speed to 600r/min, stir 2.5min, obtain based on fly ash Ash geopolymer mortar.

Example 4

(1) Dry and grind the fly ash for pretreatment, so that the moisture content of the pretreated fly ash is not more than 1%, and the specific surface area is not less than 330m ² /kg.

(2) Place the metakaolin in a stirring tank, and at a rotating speed of 280 r/min, according to the mass ratio of fly ash: metakaolin: alkaline activator to be 1:3:0.15, add the pretreated fly ash first, and stir for 3 min , and then add the mixture of water glass and NaOH solution as an alkaline activator by spraying, wherein the concentration of NaOH solution in the alkaline activator is 11 mol/L, the modulus of water glass is 1.7, and the spray is controlled. The speed was 1.8 ml/min, and the mixture was stirred for 8 min.

(3) Adjust the rotating speed to 450r/min, according to the mass ratio of the mixture of machine-made sand, metakaolin and fly ash to be 1.5:1, add the machine-made sand to the mixture of step (3), and then use the mixture of water glass and sodium carbonate solution. The mixed solution was added as an alkaline activator in the form of a solution and stirred for 1.8 min;

Wherein, the concentration of the sodium carbonate solution in the alkaline activator is 8 mol/L, and the modulus of the water glass is 2.5.

(4) be 1:0.3 according to the mass ratio of mixing water and metakaolin and the total mass of fly ash, add mixing water to the mixture of step (3), adjust the rotating speed to 600r/min, stir 2.5min, obtain based on fly ash Ash geopolymer mortar.

Example 5

(1) Dry and grind the fly ash for pretreatment, so that the moisture content of the pretreated fly ash is not more than 1%, and the specific surface area is not less than 330m ² /kg.

(2) Place the metakaolin in a stirring tank, and at a rotating speed of 300 r/min, according to the mass ratio of fly ash: metakaolin: alkaline activator to be 1:2.5:0.15, add the pretreated fly ash first, and stir for 2.5 min, then the mixture of water glass and NaOH solution was added as an alkaline activator by spraying, wherein the concentration of NaOH solution in the alkaline activator was 9 mol/L, the modulus of water glass was 1.6, and the control The spray rate was 2 ml/min, and the mixture was stirred for 9 min.

(3) Adjust the rotating speed to 480r/min, according to the mass ratio of the mixture of machine-made sand, metakaolin and fly ash is 1.8:1, add the machine-made sand to the mixture of step (3), and then use the mixture of water glass and sodium carbonate solution. The mixed solution was added as an alkaline activator in the form of a solution and stirred for 1.8 min;

Wherein, the concentration of the sodium carbonate solution in the alkaline activator is 7 mol/L, and the modulus of the water glass is 2.4.

(4) be 1:0.2 according to the mass ratio of mixing water and metakaolin and the total mass of fly ash, add mixing water to the mixture of step (3), adjust the rotating speed to 600r/min, stir 2min, obtain based on fly ash geopolymer mortar.

Comparative Example 1

Without adding the alkaline activator in step (2), the remaining steps are the same as in Example 1.

Comparative Example 2

The alkaline activator in step (2) is directly added in the form of a solution, and the remaining steps are the same as those in Example 1.

Comparative Example 3

Replace the basic activator in step (2) with the basic activator in step (3), and the remaining steps are the same as in Example 1.

1. Leachable heavy metal detection

For the geopolymer mortars prepared in Examples 1-5 and Comparative Examples 1-3, the leachable heavy metal project of the test piece 14d was carried out according to the environmental protection industry standard "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid Nitric Acid Method" HJ/T299-2007 The test results are shown in Table 3.

table 3

2. Compressive strength test

The compressive strength test refers to the provisions of "Standards for Testing Methods of Basic Properties of Building Mortars" (JGJT70-2009), and according to the preparation methods of Examples 1-5 and Comparative Examples 1-3, each poured 3 pieces with a size of 70.7mm × 70.7mm × 70.7mm cube specimen, after the specimen is cast and formed, it is placed horizontally at room temperature, demolded after 24 hours, and then placed in a standard curing room for curing. After 28 days, the specimen is taken out for the cube compressive strength test.

The formula for calculating the compressive strength of a cube is as follows:

In the formula: Rc—the compressive strength of the cube specimen (MPa);

Fc—the ultimate failure load of the specimen (N);

A—stressed area (mm ² );

According to formula (1), the compressive strength of the geopolymer mortar cubes of Examples 1-5 and Comparative Examples 1-3 was measured, and the results are shown in Table 4:

Table 4

3. Flexural strength test

The flexural strength test adopts the provisions of "Test Method for Mechanical Properties of Wire Mesh Cement Mortar" (GB/T7897-2008), according to the preparation methods of Examples 1-5 and Comparative Examples 1-3, each pouring 3 pieces with a size of 40mm × 40mm ×160mm specimens. After all specimens were cast and formed, they were placed horizontally at room temperature, demolded after 24 hours, and then placed in a standard curing room for curing. After reaching the age of 28 days, the specimens were taken out for flexural strength test.

The formula for calculating the flexural strength is as follows:

Formula: R _f - flexural strength (MPa);

F _f — load at failure (N);

L—the distance between the supporting cylinders, take 100mm;

b—the side length of the prismatic section, take 40mm

According to formula (2), the flexural strength of the geopolymer mortar cubes of Examples 1-5 and Comparative Examples 1-3 was measured, and the results are shown in Table 5:

table 5

4. Anti-cracking performance test

According to the crack width, the cracks are divided into five grades, and each grade corresponds to a weight value, as shown in Table 6. Multiply the length of each crack on the surface of the specimen by its corresponding weight value to obtain the cracking index corresponding to this crack, and add the cracking index of each crack to obtain the cracking index of the specimen, denoted as W, so as to obtain the cracking index of the specimen. Evaluate the cracking degree of mechanical sand geopolymer mortar specimens.

Table 6

Crack width d/mm Weight value A d≥3 3 3>d≥2 2 2>d≥1 1 1>d≥0.5 0.5 d＜0.5 0.25

The formula for calculating the cracking index is as follows:

W=∑Ai×Li (3)

In the formula: W—is the cracking index, the unit is mm;

Ai—the weight value corresponding to a crack;

Li—is the crack length corresponding to the weight value;

According to formula (3), the cracking indices of the geopolymer mortars of Examples 1-5 and Comparative Examples 1-3 were calculated, and the results were shown in Table 7:

Table 7

Cracking Index 1(mm) Cracking Index 2(mm) Cracking Index Average (mm) Example 1 183.3 185.5 184.4 Example 2 183.6 184.4 184.0 Example 3 186.5 183.4 185.0 Example 4 187.5 186.6 187.1 Example 5 186.5 184.9 185.7 Comparative Example 1 358.4 340.5 349.5 Comparative Example 2 320.5 318.9 319.7 Comparative Example 3 318.9 326.4 322.7

The above-mentioned embodiments are only to describe the preferred modes of the present invention, but not to limit the scope of the present invention. Without departing from the design spirit of the present invention, those of ordinary skill in the art can make various modifications to the technical solutions of the present invention. Variations and improvements should fall within the protection scope determined by the claims of the present invention.

Claims (10)

1. a preparation method based on the geopolymer mortar of fly ash, is characterized in that, comprises the following steps: (1) Dry and grind the fly ash for pretreatment; (2) Place the metakaolin in a stirring tank, and at a rotating speed of 200-300 r/min, according to the mass ratio of fly ash: metakaolin: alkaline activator to be 1: (2-3): (0.05-0.25), first Add the pretreated fly ash, stir for 2-3 minutes, then add the alkaline activator by spraying, and stir for 5-10 minutes to obtain a mixture; (3) adjusting the rotational speed to 400-500r/min, adding the fine aggregate to the mixture in step (3), adding the alkaline activator solution, and stirring for 1.5-2min; (4) adding mixing water to the mixture in step (3), adjusting the rotational speed to 550-650r/min, and stirring for 2-3min to obtain a fly ash-based geopolymer mortar. 2 . The preparation method of fly ash-based geopolymer mortar according to claim 1 , wherein the pretreated fly ash has a moisture content of not more than 1% in step (1). 3 . 3 . The preparation method of fly ash-based geopolymer mortar according to claim 1 , wherein the pretreated fly ash specific surface area in step (1) is not less than 330 m ² /kg. 4 . 4 . The preparation method of fly ash-based geopolymer mortar according to claim 1 , wherein the alkaline activator in step (2) is a mixed solution of water glass and NaOH solution. 5 . 5. the preparation method of the geopolymer mortar based on fly ash according to claim 4, is characterized in that, the concentration of NaOH solution in the alkaline activator described in step (2) is 8-12mol/L, water glass The modulus is 1.5-1.8. 6 . The preparation method of fly ash-based geopolymer mortar according to claim 1 , wherein the spraying speed in step (2) is 1.5-2 ml/min. 7 . 7 . The preparation method of fly ash-based geopolymer mortar according to claim 1 , wherein the alkaline activator in step (3) is a mixed solution of water glass and sodium carbonate solution. 8 . 8. The preparation method of fly ash-based geopolymer mortar according to claim 7, wherein the concentration of sodium carbonate solution in the alkaline activator is 7-8 mol/L, and the mold of the water glass is 7-8 mol/L. The number is 2.4-2.8. 9. the preparation method of the geopolymer mortar based on fly ash according to claim 1, is characterized in that, in step (3), the mass ratio of fine aggregate and metakaolin and fly ash mixture is (0.4-2): 1; the fine aggregate is machine-made sand. 10. the preparation method of the geopolymer mortar based on fly ash according to claim 1, is characterized in that, in step (4), the mass ratio of mixing water to metakaolin and total mass of fly ash is 1: (0.2- 0.4).