Anti-shrinkage polygeomer cementitious material and method of making

Abstract

The application provides an anti-shrinkage geopolymer cementing material and a preparation method thereof, and belongs to the technical field of geopolymer cementing materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of engineering materials, and particularly relates to an anti-shrinkage geopolymer cementitious material, and further provides a preparation method of the material. BACKGROUND

[0002] Geopolymer is a gel material formed by silicate material under the action of alkali activator, and has the advantages of high strength, fast setting, low pollution, high temperature resistance, high durability, etc. It does not need calcination and does not exist decomposition of carbonate minerals, so the emission of carbon dioxide is low. The use of geopolymer to prepare engineering materials can realize the secondary utilization of solid waste, but the high shrinkage of geopolymer is a key problem restricting its application. The shrinkage of geopolymer refers to the phenomenon of volume reduction during the setting and curing process. When the geopolymer material shrinks, if it is hindered and cannot freely shrink, it will form tension on the surface, and then cause the formation of cracks, affecting the safety and durability of the geopolymer structure. Moreover, the stress generated in the shrinkage process may cause the geopolymer material to deform before it is completely cured, so that the material deviates from the original design shape and size, affecting the service performance and service function of the structure formed by the material.

[0003] Coal gangue is composed of clay rock, sandstone, carbonate and aluminous rock, etc., and is rich in aluminosilicate, containing different amounts of inorganic substances such as Si2O, Al2O3, Fe2O3, CaO, MgO, K2O, etc. In an alkaline environment, the aluminosilicate raw material in coal gangue dissolves, the dissolved aluminum-silicon complex diffuses from the surface of solid particles to the interstitial space, forming a gel phase M {—(SiO2)z—AlO2}n·wH2O, and the polymerization occurs between the alkali silicate solution and the aluminum-silicon complex. Coal gangue can be used as a cementitious admixture, because the clay coal gangue mineral is decomposed at a certain temperature, and the clay mineral and mica are dehydrated and decomposed after heating, and kaolinite is decomposed into metakaolin and amorphous Si2O and Al2O3, so that the coal gangue has activity.

[0004] The coal gangue is used as an admixture to prepare the geopolymer cementitious material, which can delay the setting time of the geopolymer, improve the workability, and improve the mechanical properties of the geopolymer. Therefore, the coal gangue-slag is used as the raw material to prepare the geopolymer cementitious material, and the expansion agent is added, which is a common method to solve the problem of large shrinkage of the geopolymer. The expansion agent mainly resists shrinkage through the ways of crystallization growth after hydration reaction, water absorption swelling, or solid phase volume increase. The common expansion agents can be divided into calcium sulphoaluminate, CaO, MgO, and calcium sulphoaluminate-calcium oxide types according to the components. For example, in the invention CN201811520583.5, the MgO in the nickel slag is extracted by glycerol, strontium nitrate and water as the expansion agent, which has a complex process and high energy consumption. Therefore, if the natural substances can be directly used or modified as the expansion agent, it will provide a good solution to the shrinkage problem of the geopolymer. The hectorite is a layered clay mineral containing magnesium, lithium and silicon, belongs to the vermiculite subfamily of the montmorillonite and vermiculite families, and has a crystal structure of tri-octahedral type. It can swell when it meets water and form a gel containing a large number of water network structures. In addition, if it is added to the geopolymer cementitious material, it can generate magnesium-aluminum carbonate type hydrotalcite (Mg6Al2(OH) 16 CO3· 4H2O) in an alkali-activated environment, so that the solid phase volume of the cementitious material increases, and the hydrotalcite crystal density is smaller than that of the hydrated calcium silicate (C-S-H), which can fill the internal pores in the cementitious material, so that the cementation ability of the multiple cementitious groups is stronger. It not only can increase the compactness of the geopolymer cementitious material to improve the strength, but also can offset the alkali-activated shrinkage effect of the geopolymer cementitious material, and has the potential as a new type of expansion agent. SUMMARY

[0005] The application provides an anti-shrinkage geopolymer cementitious material and a preparation method thereof. The anti-shrinkage geopolymer cementitious material is prepared by using slag as the raw material, coal gangue powder as the admixture, and a low-dosage expansion agent to improve the anti-shrinkage performance of the material. The geopolymer cementitious material has excellent anti-shrinkage performance and mechanical properties, and at least one of the problems in the prior art, such as large shrinkage of the geopolymer, comprehensive utilization of coal gangue, and high energy consumption of the extraction and synthesis of the common expansion agent, is solved.

[0006] The hectorite is a layered clay mineral containing magnesium, lithium and silicon, belongs to the vermiculite subfamily of the montmorillonite and vermiculite families, and has a crystal structure of tri-octahedral type. It can swell when it meets water and form a gel containing a large number of water network structures. In addition, if it is added to the geopolymer cementitious material, it can generate magnesium-aluminum carbonate type hydrotalcite (Mg6Al2(OH) 16CO3· 4H2O), so that the solid phase volume of the cementitious material increases, and the density of the hydrotalcite crystal is smaller than that of the calcium silicate hydrate (C-S-H), which can fill the internal pores in the cementitious material, so that the cementitious material has stronger cementation ability, not only can increase the density of the geopolymer cementitious material to improve the strength, but also can offset the alkali activation shrinkage effect of the geopolymer cementitious material, and has the potential to be used as a new type of expansive agent; the use of hectorite as the expansive agent and the coal gangue and hectorite together to increase the mechanical properties not only consumes the solid waste of the coal gangue, but also prepares the geopolymer cementitious material with mechanical strength and shrinkage resistance.

[0007] The powder component is 100 parts, the dry powder alkali activator component is 10.0-15.0 parts, the expansive agent component is 1.8-2.4 parts, and the water is 45.0-55.0 parts.

[0008] The expansive agent is high-purity layered hectorite, wherein the content of MgO is ≥25%; preferably 2.1 parts.

[0009] The powder component is composed of 65-75 parts of 100-200 mesh coal gangue powder and 25-35 parts of slag; the mass fraction of the slag is preferably 70.0 parts, and the slag is S95 grade slag; the fineness of the coal gangue powder is 100-200 mesh, preferably 140 mesh.

[0010] The dry powder alkali activator component is composed of sodium silicate powder and sodium hydroxide powder, and the mass ratio is 1:1-1:1.5; preferably 1:1.25; the modulus of the sodium silicate powder is 2.10-2.75, preferably 2.43.

[0011] 1) Take the powder component, the expansive agent, the dry powder alkali activator, and the water according to the above proportions;

[0012] 2) Pour the dry powder alkali activator into the water and stir until it is completely dissolved to obtain an alkali activator solution for standby;

[0013] 3) Dry stir the weighed powder component and the expansive agent in a stirrer to mix them uniformly to obtain a mixed dry powder for standby;

[0014] 4) Mix and stir the mixed dry powder and the alkali activator solution, low-speed stir for 110-130 s, stop stirring and scrape the wall, then high-speed stir for not less than 90 s, and the whole process should not exceed 300 s, to obtain the shrinkage-resistant geopolymer gel material;

[0015] 5) Pour the shrinkage-resistant geopolymer cementitious material into a mold, vibrate to form, demold, and continue to cure to obtain the shrinkage-resistant geopolymer cementitious body.

[0016] The anti-shrinkage geopolymer cementing material is developed on mineral resources, and the swelling agent hectorite is added in the base material, and the anti-shrinkage performance is excellent: the hectorite generates a new substance hydrotalcite in the hydration reaction process, on the one hand, the hydrotalcite can fill the micro-cracks and pores in the material, so that the material is more dense, on the other hand, the hydrotalcite grows in the material and generates the outward constraint reaction force to resist the shrinkage in the setting and curing process, and the anti-shrinkage of the material is improved, and with the change of time, the pores and micro-cracks in the material are filled by the hydrotalcite and the gel material, and the material becomes dense and the connection is more compact; the free CaO and MgO in the coal gangue powder and the slag are used together with the hectorite to produce a composite anti-shrinkage effect, and the shrinkage of the geopolymer material is significantly inhibited, and the problem of large shrinkage of the geopolymer is effectively alleviated.

[0017] The dry powder alkali activator is composed of alkali metal silicate powder and caustic alkali hydroxide powder, on the one hand, the activation effect is better than that of single alkali activator and liquid alkali activator, and the dry powder alkali activator is easier to store and transport, on the other hand, the composite activation has more excellent mechanical properties than the single alkali activation geopolymer, and the durability is more excellent, and the service life of the material is prolonged. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The figure is a typical SEM graph of the test piece of the present application after curing for 3d;

[0019] Figure 2 The figure is a typical SEM graph of the test piece of the present application after curing for 28d. EMBODIMENT

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below, obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the present application.

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below. The specific conditions are not marked in the embodiments, and the conventional conditions or the conditions suggested by the manufacturer are carried out. The reagents or instruments used are not marked by the manufacturer, and are conventional products that can be purchased in the market. EMBODIMENT

[0022] 1. The following raw materials are weighed: 140 mesh coal gangue powder 23.0 kg, slag powder 70.0 kg, hectorite 1.8 kg, sodium silicate powder 5.5 kg, sodium hydroxide powder 7.0 kg, and water 50.0 kg;

[0023] 2. Pour the weighed sodium silicate powder and sodium hydroxide powder into water and stir until completely dissolved to obtain an alkali activator solution;

[0024] 3. Stir the weighed coal gangue powder, slag powder and hectorite in a blender at 100 r / min for 6 min to mix uniformly to obtain a mixed dry powder for standby;

[0025] 4. Pour the mixed dry powder and alkali activator solution into a stirring pot, stir at low speed for 120 s, stop stirring and scrape the wall for 90 s, then stir at high speed for 90 s to obtain an anti-shrinkage geopolymer gel material; place half of the anti-shrinkage geopolymer gel material in a mold, vibrate the vibration table for 60 times, then place the other half in the mold, vibrate the vibration table for 60 times, then scrape it flat, and cure for 24 h under the condition of temperature 20℃ and relative humidity ≥90% to form, demold, and continue to cure to obtain an anti-shrinkage geopolymer gel body;

[0026] 5. Test the shrinkage values of the prepared geopolymer material at 3d, 7d, 14d, 21d and 28d, the flexural strength at 3d, 7d and 28d, and the compressive strength at 3d, 7d and 28d. Example

[0027] 1. Weigh the following raw materials: 140 mesh coal gangue powder 30.0 kg, slag powder 70.0 kg, hectorite 2.1 kg, sodium silicate powder 5.5 kg, sodium hydroxide powder 7.0 kg, and water 50.0 kg;

[0028] 2. Pour the weighed sodium silicate powder and sodium hydroxide powder into water and stir until completely dissolved to obtain an alkali activator solution;

[0029] 3. Stir the weighed coal gangue powder, slag powder and hectorite in a blender at 100 r / min for 6 min to mix uniformly to obtain a mixed dry powder for standby;

[0030] 4. Pour the mixed dry powder and alkali activator solution into a stirring pot, stir at low speed for 120 s, stop stirring and scrape the wall for 90 s, then stir at high speed for 90 s to obtain an anti-shrinkage geopolymer gel material; place half of the anti-shrinkage geopolymer gel material in a mold, vibrate the vibration table for 60 times, then place the other half in the mold, vibrate the vibration table for 60 times, then scrape it flat, and cure for 24 h under the condition of temperature 20℃ and relative humidity ≥90% to form, demold, and continue to cure to obtain an anti-shrinkage geopolymer gel body;

[0031] 5. Test the shrinkage values of the prepared geopolymer material at 3d, 7d, 14d, 21d and 28d, the flexural strength at 3d, 7d and 28d, and the compressive strength at 3d, 7d and 28d. Example

[0032] 1. Take the following raw materials: 140 mesh coal gangue powder 30.0 kg, slag powder 70.0 kg, hectorite 2.4 kg, sodium silicate powder 5.5 kg, sodium hydroxide powder 7.0 kg, water 50.0 kg.

[0033] 2. Pour the weighed sodium silicate powder and sodium hydroxide powder into water and stir until completely dissolved to obtain an alkali activator solution;

[0034] 3. Mix the weighed coal gangue powder, slag powder and hectorite in a blender at 100 r / min for 6 min to obtain a mixed dry powder for standby;

[0035] 4. Pour the mixed dry powder and alkali activator solution into a stirring pot, stir at low speed for 120 s, stop stirring and scrape the wall for 90 s, then stir at high speed for 90 s to obtain an anti-shrinkage geopolymer gel material; Place half of the anti-shrinkage geopolymer gel material in a mold, vibrate the vibration table for 60 times, then place the other half in the mold, vibrate the vibration table for 60 times, then scrape it flat, and then cure it at a temperature of 20℃ and a relative humidity of ≥90% for 24h to form, demold, and continue to cure to obtain an anti-shrinkage geopolymer gel body;

[0036] 5. Test the shrinkage value of the prepared geopolymer material at 3d, 7d, 14d, 21d and 28d, the flexural strength at 3d, 7d and 28d, and the compressive strength at 3d, 7d and 28d.

[0037] 1. Take the following raw materials: 140 mesh coal gangue powder 30.0 kg, slag powder 70.0 kg, hectorite 0 parts, sodium silicate powder 5.5 kg, sodium hydroxide powder 7.0 kg, water 50.0 kg.

[0038] 2. Pour the weighed sodium silicate powder and sodium hydroxide powder into water and stir until completely dissolved to obtain an alkali activator solution;

[0039] 3. Mix the weighed coal gangue powder, slag powder and hectorite in a blender at 100 r / min for 6 min to obtain a mixed dry powder for standby;

[0040] 4. Pour the mixed dry powder and alkali activator solution into a stirring pot, stir at low speed for 120 s, stop stirring and scrape the wall for 90 s, then stir at high speed for 90 s to obtain an anti-shrinkage geopolymer gel material; Place half of the anti-shrinkage geopolymer gel material in a mold, vibrate the vibration table for 60 times, then place the other half in the mold, vibrate the vibration table for 60 times, then scrape it flat, and then cure it at a temperature of 20℃ and a relative humidity of ≥90% for 24h to form, demold, and continue to cure to obtain an anti-shrinkage geopolymer gel body.

[0041] 5. Test the shrinkage values of the prepared geopolymer materials 3d, 7d, 14d, 21d and 28d, the flexural strength of 3d, 7d, 28d, and the compressive strength of 3d, 7d, 28d.

[0042] 1. Weigh the following raw materials: 140 mesh coal gangue powder 25.0 kg, slag powder 75.0 kg, hectorite 2.1 kg, sodium silicate powder 5.5 kg, sodium hydroxide powder 7.0 kg, and water 50.0 kg.

[0043] 2. Pour the weighed sodium silicate powder and sodium hydroxide powder into water and stir until completely dissolved to obtain an alkali activator solution;

[0044] 3. Mix the weighed coal gangue powder, slag powder and hectorite in a blender at 100 r / min for 6 min to obtain a mixed dry powder for standby;

[0045] 4. Pour the mixed dry powder and the alkali activator solution into a stirring pot, stir at low speed for 120 s, stop stirring and scrape the wall for 90 s, then stir at high speed for 90 s to obtain an anti-shrinkage geopolymer gel material; Place half of the anti-shrinkage geopolymer gel material in a mold, vibrate the vibration table for 60 times, then place the other half in the mold, vibrate the vibration table for 60 times, then scrape it flat, and then cure it at a temperature of 20℃ and a relative humidity of ≥90% for 24h to form, demold, and continue to cure to obtain an anti-shrinkage geopolymer body.

[0046] 5. Test the shrinkage values of the prepared geopolymer materials 3d, 7d, 14d, 21d and 28d, the flexural strength of 3d, 7d, 28d, and the compressive strength of 3d, 7d, 28d.

[0047] The anti-shrinkage geopolymer gel materials obtained in Examples 1-3 and the geopolymer gel materials prepared in Comparative Examples 1-2 are subjected to mechanical property detection and shrinkage performance detection, and the detection results are shown in Tables 1-2:

[0048] Table 1. Mechanical strength performance of different examples of the present application

[0049]

[0050] Table 2. Shrinkage performance of different examples of the present application

[0051]

[0052] Table 1 is the test results of the mechanical strength performance of different examples, and it can be seen that the anti-shrinkage geopolymer gel material of the present application has excellent mechanical properties, and by changing the content of hectorite, the material strength can be affected within a small range. Within a certain range, with the increase of the content of hectorite, the flexural and compressive strengths of the material first increase and then decrease.

[0053] Compared with Comparative Example 1, it can be seen that the addition of hectorite can obviously improve the mechanical properties of the geopolymer; compared with Comparative Example 2, it can be seen that the content of coal gangue plays an important role in the mechanical properties of the geopolymer.

[0054] Table 2 is the shrinkage performance test result of different examples, and it can be seen that the anti-shrinkage geopolymer cementing material of the application has excellent anti-shrinkage performance, and by changing the content of hectorite, the anti-shrinkage performance of the geopolymer cementing material is obviously improved, and within a certain range, the anti-shrinkage performance of the geopolymer material is improved with the increase of hectorite.

[0055] Compared with Comparative Example 1, it can be seen that hectorite has a significant effect on the anti-shrinkage performance of the material; compared with Comparative Example 2, it can be seen that the content of coal gangue also has a certain effect on the shrinkage performance of the geopolymer cementing material.

[0056] The application uses coal gangue and slag as raw materials to prepare an anti-shrinkage geopolymer cementing material, which has excellent mechanical properties: in the initial stage of hydration reaction, as shown in Figure 1 , the coal gangue powder and slag undergo hydration reaction under the action of alkali activator to generate small-sized hydrated calcium (aluminum) silicate (C-(A)-S-H) gel groups, and in the early stage, the gel groups in the material are few, and the cementation effect is limited, and with the continuous reaction, as shown in Figure 2 , the generated C-(A)-S-H gel increases, and the small-sized gel groups develop into large-sized gel groups, and the connection between them is more close, and the gel fills the internal pores to reduce the stress concentration phenomenon in the material, so that the strength of the material continues to grow.

Claims

1. An anti-shrinkage geopolymer cementitious material characterized in that it is It is prepared from the following raw materials in mass fraction: 100 parts of powder component, 10.0-15.0 parts of dry powder alkali activator component, 1.8-2.4 parts of expanding agent component, and 45.0-55.0 parts of water; The expanding agent is high-purity layered hectorite, wherein the content of MgO is ≥25%. The powder component is composed of 23 parts of 140-mesh coal gangue powder and 70 parts of slag powder.

2. The anti-shrinkage geopolymer gel material according to claim 1, characterized in that: The dry powder alkali activator component is composed of sodium silicate powder and sodium hydroxide powder, and the mass ratio is 1:1-1:1.

5.

3. The method according to any one of claims 1 to 2, characterized in that The method comprises the following steps: 1) The coal gangue particles are crushed, ground, and sieved to obtain 100-200-mesh coal gangue particles for standby use; the powder component, the expanding agent, the dry powder alkali activator, and the water are taken in the above mass fractions for standby use; 2) The dry powder alkali activator is weighed and poured into water for stirring until the dry powder alkali activator is completely dissolved to obtain an alkali activator solution for standby use; 3) The coal gangue powder, the slag powder, and the expanding agent are weighed and dry-stirred in a stirrer to obtain a mixed dry powder for standby use; 4) The mixed dry powder and the alkali activator solution are poured into a stirring pot, stirred at low speed for 110-130 s, and then stirred at high speed for not less than 90 s after stopping stirring and scraping the wall, and the whole process should not exceed 300 s, to obtain an anti-shrinkage geopolymer gel material; 5) The anti-shrinkage geopolymer gel material is poured into a mold, vibrated and formed, demolded after curing, and continuously cured to obtain an anti-shrinkage geopolymer gel body.

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