Biomass coagulant for low-calcium fly ash geopolymer and application

Abstract

The invention discloses a biomass coagulant for a low-calcium fly ash geopolymer and application of the biomass coagulant. The construction method comprises the following steps: carrying out coarse grinding, screening, fine grinding and secondary screening on the low-calcium fly ash, compounding 10-15% of hydrophobic rock wool into the ground low-calcium fly ash, carrying out alkali excitation by adopting sodium silicate, adding 0.5-1.5% of a biomass coagulant, and finally carrying out high-temperature maintenance at 60-90 DEG C for 3-6 hours. Wherein the biomass coagulant is a mixture of cyclodextrin and carboxymethyl dextrin which are compounded according to a certain proportion, and the rock wool is hydrophobic rock wool. The low-calcium fly ash geopolymer prepared by the method can be used for road base materials, building wall materials, thermal insulation materials and the like. Compared with the prior art, the invention aims to overcome the defects of long coagulation time, low strength, high maintenance cost and limited application of the low-calcium fly ash geopolymer, and the coagulant is prepared from the biomass material dextrin, so that the coagulant is green, environment-friendly and low in cost; and the compounded hydrophobic rock wool accelerates gel curing of the geopolymer in the later period while toughening, the high-temperature maintenance period is shortened, and the overall strength of the geopolymer in the later period is improved. The method realizes resource utilization of the low-calcium fly ash, is low-carbon and environment-friendly, and is simple in preparation method, relatively low in cost and wide in application prospect.

Description

Technical Field

[0001] The present invention relates to the field of admixtures for civil engineering materials, and particularly to a biomass coagulant for low-calcium fly ash geopolymer and its application. Background Art

[0002] There are many problems in the practical application of low-calcium fly ash-based geopolymer. On the one hand, its setting time is long and its strength is low, making it difficult to be directly applied to engineering. In engineering scenarios such as road subbase construction, the long setting time will seriously affect the construction progress and increase the construction cost. Traditional industrial coagulants such as chlorides, sulfates, and formates are toxic and harmful and consume a large amount of natural resources. On the other hand, although high-temperature curing of low-calcium fly ash geopolymer can increase the later strength, the long curing cycle and high curing cost will limit the application scenarios of low-calcium fly ash geopolymer and hinder its application and promotion. Now, in order to improve the disadvantages of long curing time, low strength, and too long setting time of low-calcium fly ash geopolymer, a biomass coagulant for low-calcium fly ash geopolymer is adopted to broaden its application scenarios and improve the overall strength of the geopolymer. Summary of the Invention

[0003] Object of the Invention

[0004] Compared with the prior art, the present invention is committed to improving the disadvantages of long setting time, low strength, high curing cost, and limited application of low-calcium fly ash geopolymer. The object of the invention is to provide a biomass coagulant for low-calcium fly ash geopolymer and its application. Through innovative preparation processes and raw material combinations, while shortening the setting time of low-calcium fly ash-based geopolymer, the curing cycle is shortened, and its overall strength is improved to achieve the efficient resource utilization of low-calcium fly ash.

[0005] Technical Solution

[0006] A biomass coagulant for low-calcium fly ash geopolymer and its application, in parts by mass, includes the following components: 50-70 parts of low-calcium fly ash after classified grinding, 10-20 parts of sodium silicate, 5-15 parts of dextrin, and 5-15 parts of hydrophobic rock wool.

[0007] The preparation method of the above-mentioned low-calcium fly ash geopolymer includes the following steps:

[0008] S1. Classified grinding of low-calcium fly ash: The low-calcium fly ash is subjected to classified grinding. By controlling the grinding time and the parameters of the grinding equipment, the particle size of the low-calcium fly ash is regulated to meet certain particle size distribution requirements, and the low-calcium fly ash after classified grinding is obtained;

[0009] S2. Mixing of raw materials: According to the above mass ratio, the low-calcium fly ash after classified grinding, sodium silicate, dextrin, and hydrophobic rock wool are sequentially added to a stirring device, and stirred and mixed evenly to obtain a mixed material;

[0010] S3, Alkali activation and coagulation promotion reaction: Add an appropriate amount of water to the mixed materials to cause the alkali activation reaction of sodium silicate. At the same time, dextrin plays a role in promoting coagulation, promoting the coagulation reaction of low-calcium fly ash geopolymer;

[0011] S4, High-temperature curing: Put the reacted materials into a high-temperature curing environment and cure them under certain temperature and time conditions to improve the overall strength of the low-calcium fly ash geopolymer.

[0012] A biomass coagulation promoter of the present invention is carried out according to the following steps:

[0013] S1, Preparation of the mixture of cyclodextrin and carboxymethyl dextrin: First, prepare the two kinds of dextrins separately and then mix them according to a ratio;

[0014] S2, When preparing carboxymethyl dextrin, disperse starch in an ethanol-water mixed solution, alkalize with sodium hydroxide for 30 - 60 minutes, and control the temperature at 30 - 40 °C. Then add monochloroacetic acid or its sodium salt and carry out carboxymethylation reaction at 40 - 60 °C for 2 - 4 hours. After the reaction, neutralize, filter, wash, and dry to obtain carboxymethyl starch, and then obtain carboxymethyl dextrin through hydrolysis, separation, purification, and drying;

[0015] S3, Preparation of cyclodextrin: Prepare a 10% - 20% starch slurry from starch, gelatinize at 80 °C - 95 °C, and add cyclodextrin glucosyltransferase after cooling to 40 - 60 °C and react for 8 - 24 hours. Inactivate the enzyme after the reaction and purify to obtain cyclodextrin through methods such as chromatographic separation and crystallization;

[0016] S4, Taking 100 grams as an example, 70 grams of cyclodextrin and 30 grams of carboxymethyl dextrin, with a ratio of 7:3. After weighing, stir or grind evenly in a dry container, or dissolve them separately and then mix the solutions to ensure uniform mixing.

[0017] Principle of the invention

[0018] The present invention compound cyclodextrin and carboxymethyl dextrin as a biomass coagulation promoter. The main role of cyclodextrin is to accelerate the setting and hardening of low-calcium fly ash geopolymer by promoting the formation of silica-aluminum gel and adsorption catalysis. The compounded carboxymethyl dextrin promotes coagulation by increasing viscosity through ion exchange and complexation reactions. During the ion exchange process of carboxymethyl dextrin molecules, the carboxymethyl group (-CH2COO - ) undergoes an ion exchange reaction with metal cations in the low-calcium fly ash geopolymer, and cations such as calcium ions (Ca 2+ ), aluminum ions (Al 3+ ) can exchange ions with sodium ions (Na +)Ion exchange is carried out. Since the radii of cations such as calcium ions and aluminum ions are different from that of sodium ions, and the number of charges carried also varies, this ion exchange changes the distribution and concentration of ions in the reaction, thus affecting the kinetic process of the geopolymer reaction of low-calcium fly ash, and ultimately promoting setting and hardening.

[0019] Since the carboxymethyl dextrin molecule has multiple oxygen atoms that can act as coordination atoms, it can form stable complexes with metal ions in the low-calcium fly ash geopolymer during complexation, such as aluminum ions (Al 3+ ), iron ions (Fe 3+ ) and other ions. Through this reaction, the chemical activity of metal ions can be changed, and the existing form of metal ions can be affected, accelerating the formation of silicate-aluminate polymers in the low-calcium fly ash geopolymer, promoting the formation of silica-aluminum gel, and accelerating setting and hardening.

[0020] The disadvantage of carboxymethyl dextrin is that it has a certain viscosity. If the addition ratio is too high, it will cause the geopolymer to be too viscous, which is not conducive to construction, and the too intense ion exchange and complexation will affect the uniformity and stability of the geopolymer structure; while if the addition ratio of cyclodextrin is too high, it will cause the premature formation of silica-aluminum gel. Although the early strength increases rapidly, the later strength growth will be relatively weak.

[0021] Taking into account the advantages and disadvantages of both, in the application of low-calcium fly ash-based geopolymers, the mass ratio of cyclodextrin to carboxymethyl dextrin set in the range of 3:1 to 1:1 is more reasonable. Within this range, it can not only accelerate the formation of silicate-aluminate gel through cyclodextrin, but also form a dense gel with a more stable structure through the ion exchange and complexation of carboxymethyl dextrin, thereby improving the early strength and setting and hardening speed of the geopolymer, and also ensuring the continuous growth of the later strength to make it have good construction performance.

[0022] Beneficial effects

[0023] 1. By compounding hydrophobic rock wool, the present invention can not only play a toughening role, but also absorb and accelerate the evaporation of moisture inside the geopolymer, which is beneficial to chemical reactions and gel curing, enhancing the strength of the low-calcium fly ash geopolymer while accelerating hardening.

[0024] 2. The present invention compounds cyclodextrin and carboxymethyl dextrin as biomass coagulants. Cyclodextrin can effectively promote the formation of silicate-aluminate gel. By compounding carboxymethyl dextrin, through ion exchange and complexation, the gel formed later is denser and has a more stable structure. Thereby improving the early strength of the low-calcium fly ash geopolymer and accelerating its setting and hardening speed, ensuring the stable growth of the later strength, and making it have good construction performance.

[0025] 3. Due to the addition of hydrophobic rock wool in the early stage, during the high-temperature curing process, the hydrophobic rock wool is added to the low-calcium fly ash-based geopolymer, which can increase the strength while shortening the curing cycle and improving the curing efficiency. The hydrophobic rock wool absorbs and accelerates the evaporation of moisture inside the geopolymer, facilitating chemical reactions and gel curing. It can also regulate the temperature to ensure the smooth progress of the reaction, thereby shortening the curing cycle and reducing the curing cost.

[0026] 4. The present invention makes full use of the industrial solid waste low-calcium fly ash, realizing the resource utilization of waste, and adopts the biomass coagulant dextrin, which is low-cost and environmentally friendly compared with industrial coagulants. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the embodiments. Figure 1 It is the preparation process of the biomass coagulant for low-calcium fly ash geopolymer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following will further illustrate the present invention with specific examples, but not limited to the following examples.

[0028] In the following specific examples, the method for measuring the setting time of the low-calcium fly ash geopolymer refers to the "Technical Specification for the Application of Geopolymer Concrete"; the strength test method refers to the "Test Method for the Strength of Cement Mortar (ISO Method)".

[0029] Example 1

[0030] Take low-calcium fly ash and use a grinding device for classification grinding, control the grinding time to be 30 minutes, and obtain the classified and ground low-calcium fly ash. Weigh 50 g of the classified and ground low-calcium fly ash, 6 g of sodium silicate, 0.5 g of dextrin, and 5 g of thermal insulation material rock wool, and add them to the stirring device in sequence, stir for 15 minutes to make the raw materials fully mixed and uniform, and obtain the mixed material.

[0031] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction, and the dextrin admixture plays a coagulation-promoting role. Put the reacted material into a high-temperature curing box and cure it at a temperature of 80 °C for 5 hours to obtain the low-calcium fly ash geopolymer.

[0032] Example 2

[0033] Take low-calcium fly ash and use a grinding device for classification grinding, control the grinding time to be 30 minutes, and obtain the classified and ground low-calcium fly ash. Weigh 50 g of the classified and ground low-calcium fly ash, 6 g of sodium silicate, and add 0.5 g of dextrin, and add them to the stirring device in sequence, stir for 15 minutes to make the raw materials fully mixed and uniform, and obtain the mixed material.

[0034] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction, and the dextrin admixture plays a role in promoting coagulation. Place the reacted material in a high-temperature curing box and cure it at a temperature of 80°C for 5 hours to obtain a low-calcium fly ash geopolymer.

[0035] Example 3

[0036] Take low-calcium fly ash and use a grinding device for classified grinding, controlling the grinding time to be 30 minutes to obtain classified ground low-calcium fly ash. Weigh 50 g of the classified ground low-calcium fly ash, 6 g of sodium silicate, and 5 g of the thermal insulation material rock wool, and add them to a stirring device in sequence, and stir for 15 minutes to fully mix the raw materials evenly to obtain a mixed material.

[0037] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction. Place the reacted material in a high-temperature curing box and cure it at a temperature of 80°C for 5 hours to obtain a low-calcium fly ash geopolymer.

[0038] Example 4

[0039] Take low-calcium fly ash and use a grinding device for classified grinding, controlling the grinding time to be 30 minutes to obtain classified ground low-calcium fly ash. Weigh 50 g of the classified ground low-calcium fly ash, 6 g of sodium silicate, add 0.5 g of dextrin, and 5 g of the thermal insulation material rock wool, and add them to a stirring device in sequence, and stir for 15 minutes to fully mix the raw materials evenly to obtain a mixed material.

[0040] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction, and the dextrin admixture plays a role in promoting coagulation. Place the reacted material in a high-temperature curing box and cure it at a temperature of 80°C for 4.5 hours to obtain a low-calcium fly ash geopolymer.

[0041] Example 5

[0042] Take low-calcium fly ash and use a grinding device for classified grinding, controlling the grinding time to be 30 minutes to obtain classified ground low-calcium fly ash. Weigh 50 g of the classified ground low-calcium fly ash, 6 g of sodium silicate, and 0.5 g of dextrin, and add them to a stirring device in sequence, and stir for 15 minutes to fully mix the raw materials evenly to obtain a mixed material.

[0043] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction, and the dextrin admixture plays a role in promoting coagulation. Place the reacted material in a high-temperature curing box and cure it at a temperature of 80°C for 4.5 hours to obtain a low-calcium fly ash geopolymer.

[0044] Example 6

[0045] Take low-calcium fly ash and perform classified grinding using a grinding device, controlling the grinding time to be 30 minutes to obtain the classified ground low-calcium fly ash. Weigh 50 g of the classified ground low-calcium fly ash, 6 g of sodium silicate, 0.5 g of dextrin, and 5 g of the thermal insulation material rock wool, and sequentially add them to a stirring device and stir for 15 minutes to fully and evenly mix the raw materials to obtain a mixed material.

[0046] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction, and the dextrin admixture plays a coagulation-promoting role. Place the reacted material in a high-temperature curing box and cure it at a temperature of 80 °C for 4 hours to obtain a low-calcium fly ash geopolymer.

[0047] Example 7

[0048] Take low-calcium fly ash and perform classified grinding using a grinding device, controlling the grinding time to be 30 minutes to obtain the classified ground low-calcium fly ash. Weigh 50 g of the classified ground low-calcium fly ash, 6 g of sodium silicate, and 0.5 g of dextrin, and sequentially add them to a stirring device and stir for 15 minutes to fully and evenly mix the raw materials to obtain a mixed material.

[0049] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction, and the dextrin admixture plays a coagulation-promoting role. Place the reacted material in a high-temperature curing box and cure it at a temperature of 80 °C for 4 hours to obtain a low-calcium fly ash geopolymer.

[0050] Example 8

[0051] Take low-calcium fly ash and perform classified grinding using a grinding device, controlling the grinding time to be 30 minutes to obtain the classified ground low-calcium fly ash. Weigh 50 g of the classified ground low-calcium fly ash, 6 g of sodium silicate, 0.5 g of a chloride-based coagulation promoter, and 5 g of the thermal insulation material rock wool, and sequentially add them to a stirring device and stir for 15 minutes to fully and evenly mix the raw materials to obtain a mixed material.

[0052] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction, and the chloride-based coagulation promoter plays a coagulation-promoting role. Place the reacted material in a high-temperature curing box and cure it at a temperature of 80 °C for 5 hours to obtain a low-calcium fly ash geopolymer.

[0053] Example 9

[0054] Take low-calcium fly ash and perform classified grinding using a grinding device, controlling the grinding time to be 30 minutes to obtain the classified ground low-calcium fly ash. Weigh 50 g of the classified ground low-calcium fly ash, 6 g of sodium silicate, 0.5 g of a sulfate-based coagulation promoter, and 5 g of the thermal insulation material rock wool, and sequentially add them to a stirring device and stir for 15 minutes to fully and evenly mix the raw materials to obtain a mixed material.

[0055] Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction, and the sulfate coagulant plays a coagulation-promoting role. Put the reacted material into a high-temperature curing box and cure it at a temperature of 80°C for 4 hours to obtain a low-calcium fly ash geopolymer.

[0056] Reference group

[0057] Take low-calcium fly ash and use a grinding device for classification grinding. Control the grinding time to be 30 minutes to obtain the classified and ground low-calcium fly ash. Weigh 50 g of the classified and ground low-calcium fly ash, 6 g of sodium silicate (without adding dextrin and the thermal insulation material rock wool), and add them to a stirring device in sequence. Stir for 15 minutes to make the raw materials fully mixed and uniform to obtain a mixed material. Add an appropriate amount of water and stir evenly. Then, the sodium silicate undergoes an alkali activation reaction. Put the reacted material into a high-temperature curing box and cure it at a temperature of 80°C for 5 hours to obtain a low-calcium fly ash geopolymer. Measure the initial setting time and final setting time of the above Examples 1 to 9, and record the data in Table 1.

[0058] Comparison group

[0059] Take 50 g of fly ash (Class II fly ash), 6 g of sodium silicate, and 5 g of rock wool, and add them to a stirring device in sequence. Stir for 15 minutes to make the raw materials fully mixed and uniform to obtain a mixed material. Add an appropriate amount of water and stir evenly. Then, add sodium silicate for an alkali activation reaction. Put the reacted material into a high-temperature curing box and cure it at a temperature of 80°C for 5 hours to obtain an ordinary fly ash geopolymer.

[0060] Finally, the test items include flexural strength test, compressive strength test, and splitting tensile strength test to test the performance of the composite modified geopolymer material of the present invention and conduct a comparative analysis with an ordinary geopolymer material (Class II fly ash). Measure the flexural, compressive, and splitting tensile strengths of the above Examples 1 to the comparison group, and record the data in Table 2.

[0061] Table 1 Comparison table of setting times of composite fly ash geopolymers with different components and the reference group

[0062]

[0063] Table 2 Comparison table of mechanical properties of composite fly ash geopolymers with different components

[0064]

[0065] According to the experimental data in Table 1, compared with the reference group, the method of adding biomass coagulant and compound hydrophobic rock wool can effectively shorten the setting time of low-calcium fly ash geopolymer, enabling it to harden quickly, and its coagulation-promoting ability is basically equivalent to that of industrial coagulants on the market. Comparing Example 1 with Examples 4 and 5, the setting time of the low-calcium fly ash geopolymer added with rock wool and dextrin did not change significantly after the curing period was shortened, indicating that the addition of hydrophobic rock wool can enable the fly ash geopolymer to complete setting within a shorter curing period, and to a certain extent broadens the application scenarios of low-calcium fly ash-based geopolymer.

[0066] As can be seen from Table 2, the 28-day flexural strength of the compound-modified low-calcium fly ash-based geopolymer is greater than that of ordinary geopolymer materials, indicating that the toughness of the compound-modified low-calcium fly ash geopolymer is stronger than that of ordinary geopolymer materials; the 28-day compressive strength of the compound-modified geopolymer material is greater than that of ordinary geopolymer materials, indicating that the hardness and compressive capacity of the compound-modified low-calcium fly ash geopolymer material are stronger than those of ordinary geopolymer materials, and their 28-day splitting tensile strengths are basically equivalent.

[0067] The compound-modified geopolymer material of this application meets the relevant requirements of GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0068] The compound-modified geopolymer material of this application meets the relevant requirements of GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" and JGJ / T 70-2009 "Test Methods for Basic Properties of Building Mortars". Its flexural strength and compressive performance indicators are significantly better than those of ordinary geopolymer materials, indicating that the geopolymer material of this invention has excellent properties that can replace ordinary geopolymer materials.

[0069] The above content has been analyzed in detail in combination with specific cases and experimental data. However, those skilled in this professional field should be aware that as long as it does not violate the design and invention concept of this patent, the materials and mix ratios in the above examples can be adjusted and changed, or some steps can be optimized and improved. A series of changes and modifications thus derived are all within the scope of the invention patent protection of this application, and will not be elaborated one by one here.

Claims

1. A biomass coagulant for low-calcium fly ash geopolymer and its application, characterized in that It includes the following steps: S1. Classification grinding: It includes four stages of primary grinding, screening, fine grinding, and secondary screening until all particles pass through a 30-μm sieve to obtain low-calcium fly ash meeting the particle size requirements. S2. Compound with rock wool: Hydrophobic rock wool, a thermal insulation material, is compounded into the ground low-calcium fly ash. The addition amount of the hydrophobic rock wool is 10% - 15% of the mass of the low-calcium fly ash. The hydrophobic rock wool absorbs and accelerates the evaporation of internal moisture in the geopolymer, facilitating chemical reactions and gel curing, regulating temperature, ensuring the smooth progress of the reaction, and shortening the curing duration. S3. Alkali activation and coagulation promotion: Sodium silicate is used for alkali activation, and a biomass coagulant is added. The addition amount of the biomass coagulant is 0.5% - 1.5% of the mass of the low-calcium fly ash to improve the drawback of the long setting time of the low-calcium fly ash. S4. High-temperature curing: The mixture after the above treatment is subjected to high-temperature curing. The curing temperature is 60°C - 90°C, and the curing time is 3h - 6h to improve the overall strength and shorten the curing cycle.

2. The preparation method of a biomass coagulant for low-calcium fly ash geopolymer according to claim 1, characterized in that The biomass coagulant is a mixture of cyclodextrin and carboxymethyl dextrin.

3. A biomass coagulant and its application for low-calcium fly ash geopolymer according to claim 1, characterized in that The rock wool is hydrophobic rock wool, with a length of 1200 mm, a width of 600 mm, a thickness of 30 - 100 mm, and a bulk density of 80 - 120 kg / m 3 , and a fiber diameter of 3 - 9 microns.

4. The low-calcium fly ash geopolymer according to any one of claims 1 to 4, characterized in that, The low-calcium fly ash geopolymer is used as one or more of road base materials, building wall materials, and thermal insulation materials.

5. The preparation of the cyclodextrin and carboxymethyl dextrin mixture according to claim 1, characterized in that, It includes the following steps: S1. Preparation of the mixture of cyclodextrin and carboxymethyl dextrin: First, the two kinds of dextrins need to be prepared separately and then mixed in proportion. S2. When preparing carboxymethyl dextrin, starch is dispersed in an ethanol-water mixed solution, alkalized with sodium hydroxide for 30 - 60 minutes, and the temperature is controlled at 30 - ​ ​ 6. A biomass coagulant for low-calcium fly ash geopolymer and its application, characterized in that, ​

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