Additive suitable for geopolymer concrete and preparation method thereof

Abstract

The invention relates to the field of building materials, and discloses an additive suitable for geopolymer concrete and a preparation method thereof, the additive is composed of overburnt quicklime, sepiolite, a thixotropic lubricant, a dispersant, a system stabilizer, an early strength agent, a water reducer, lignosulfonate, gypsum and water. Through reasonable proportioning and a preparation process, the admixture has delayed coagulation, water reduction, shrinkage compensation and thixotropic properties, and the constructability, volume stability and mechanical properties of the geopolymer concrete are remarkably improved. The admixture prepared by the invention can optimize the flowability and strength of the geopolymer concrete, solves the problem of adaptability of the existing Portland cement admixture in a geopolymer system, and provides technical support for application of the geopolymer concrete in repair and reinforcement projects.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, in particular to an admixture suitable for geopolymer concrete and a preparation method thereof. Background Art

[0002] With the continuous improvement of my country's urbanization level, my country's new urbanization construction has achieved remarkable results, and the urbanization rate has reached 65.22% in 2022. According to international experience, when the urbanization rate is close to or exceeds 70%, its development model will gradually shift from "high-speed development" to "high-quality development". In this context, urban development faces many challenges, such as improving ecological quality, strengthening safety and resilience, and optimizing governance capabilities. There is still much room for improvement. The 2023 National Housing and Urban-Rural Construction Work Conference clearly proposed to focus on building livable, resilient and smart cities by implementing urban renewal actions. my country's urban development has thus entered a critical stage of urban renewal, gradually shifting from "large-scale incremental construction" to a model of "giving equal importance to stock quality improvement and incremental structural adjustment". Urban renewal with the transformation of existing buildings as the main content has become the core direction of current construction.

[0003] By the end of 2022, the existing building area in my country is close to 70 billion square meters, and a considerable part of these buildings have been in service for many years. Compared with new buildings, the renovation of existing buildings is subject to more restrictions, is more difficult to implement, and faces the challenge of inconsistent new and old technical standards. As the main material for civil engineering, concrete has been significantly reduced in structural safety and durability due to long-term influences from the external environment (such as temperature changes, chemical erosion, etc.) and internal factors (such as design defects, improper maintenance or aging). The consequences of insufficient durability of concrete structures are very serious. The cost of repairing and reinforcing old buildings has increased year by year, and even in many developed countries it has exceeded the investment in new buildings. In my country, at least 50% of the existing concrete buildings have a service life of more than 20 years and need reinforcement and maintenance. The reinforcement and maintenance of concrete has become an important branch of structural engineering.

[0004] Geopolymers are a new type of alkali-activated cementitious material. They use natural minerals, solid waste or artificial silicon-aluminum compounds as raw materials. Through the action of alkali activators, they undergo reactions such as dissolution, monomer reconstruction and polycondensation to form a hardened body with a three-dimensional network structure. Geopolymer materials have excellent mechanical properties and durability, low energy consumption in the production process, can effectively utilize solid waste, and have good environmental friendliness. In the field of waterproofing and plugging, the anti-permeability of geopolymer materials is far superior to that of ordinary silicate concrete, showing significant repair potential. However, geopolymers are essentially different from traditional silicate cement, and they are different in production process, reaction process and hydration products. For example, geopolymers do not require the high-energy consumption process of "two grindings and one burning", and the typical hydration products of silicate cement such as CSH gel, calcium hydroxide and calcium sulfonate are not generated during the reaction process.

[0005] At present, the applicability of silicate cement-based admixtures in geopolymer systems is poor, which is specifically manifested in the following problems: Failure of retarder: Admixtures that have a retarding effect on silicate cement (such as sucrose, sodium gluconate, citric acid, etc.) cannot delay its rapid reaction in geopolymers, resulting in insufficient construction time and failure to meet engineering requirements.

[0006] The water-reducing agent has poor effect: the aliphatic water-reducing agent and aminosulfonate-based high-efficiency water-reducing agent commonly used in silicate cement cannot significantly improve the fluidity in the geopolymer system, making it difficult to meet the high fluidity requirements of waterproof plugging materials, and cannot further improve the strength of geopolymer repair materials.

[0007] Insufficient adaptability of expansive agents: Calcium sulfoaluminate or magnesium oxide expansive agents commonly used in silicate cement-based repair materials generate expansive calcium sulfonate crystals through chemical reactions to compensate for shrinkage, but they cannot change the flow properties of the geopolymer concrete system.

[0008] Lack of thixotropic agent function: The thixotropic agents commonly used in silicate cement systems (such as calcium sulfate system or aluminum sulfate / ferrous sulfate system) cannot generate corresponding calcium aluminum vanadium crystals in the geopolymer system due to the lack of C3A participation, resulting in the slurry being unable to obtain thixotropic properties.

[0009] Therefore, the present invention provides an admixture suitable for geopolymer concrete and a preparation method thereof to solve the deficiencies of the prior art. Summary of the invention

[0010] In view of the problem of insufficient adaptability of geopolymer concrete admixtures in the prior art, the present invention provides an admixture suitable for geopolymer concrete and a preparation method thereof. The admixture can effectively solve the technical problems of poor retarding effect, insufficient water reduction performance, poor shrinkage compensation effect and lack of thixotropic performance in the prior art, and significantly improve the construction performance, mechanical properties and volume stability of geopolymer concrete.

[0011] To achieve the above object, the present invention is implemented by the following technical scheme: an admixture suitable for geopolymer concrete, the admixture consisting of the following components in parts by weight: Burnt quicklime: 5-10 parts Overburned quicklime has the characteristics of dense structure and small porosity, and its surface is covered with glass glaze formed by melting clay impurities. In the geopolymer concrete system, overburned quicklime can react with water to form calcium hydroxide in the early stage, and its chemical reaction is: CaO+H 2 O→Ca(OH) 2 During the reaction, the volume of the generated calcium hydroxide solid increases and expands, thereby compensating for the shrinkage of the geopolymer. The volume expansion provided by this reaction matches the shrinkage time of the geopolymer during curing, which helps to improve the volume stability of the material.

[0012] Sepiolite: 5-10 parts Sepiolite has a special porous structure, large specific surface area and pore volume, and can absorb a large amount of water. During the hardening process of geopolymer concrete, the water absorbed by the sepiolite can be slowly released to compensate for the water consumed by the reaction between the overburned quicklime and water, while avoiding the self-shrinkage caused by the decrease in internal relative humidity. This water replenishment property is crucial to improving the stability of geopolymer concrete.

[0013] Thixotropic lubricant: 5-10 parts The thixotropic lubricant is a compound of one or more of magnesium aluminum silicate, polymerized thixotropic lubricant, montmorillonite or viren gum. These lubricants form a dynamic network structure in the system through the physical action of their polymer chains, so that the slurry has excellent fluidity and thixotropy, thereby ensuring the construction performance of geopolymer concrete. The lubricant can also reduce the viscous resistance of the material during the construction process and improve the construction efficiency.

[0014] Dispersant: 5-10 parts The dispersant is a compound of one or more of tannic acid, sodium linoleate or sodium oxalate. The main function of the dispersant is to reduce the agglomeration phenomenon between particles and improve the dispersibility of particles through electrostatic repulsion and steric hindrance effect. This good dispersibility not only improves the fluidity of the material, but also optimizes the contact effect between the particles and the alkali activator, thereby improving the reaction efficiency of the geopolymer.

[0015] System stabilizer: 5-12 parts The system stabilizer is calcium carbonate. Calcium carbonate has a filling effect and can improve the uniformity and stability of the geopolymer concrete slurry. It physically fills fine pores in the system, reduces water seepage, and further improves the volume stability and impermeability of the material.

[0016] Early strength agent: 0-12 parts The early strength agent is calcium formate. Calcium formate can quickly release calcium ions, accelerate the reaction process of geopolymer, and improve early strength. Since calcium formate has good adaptability to alkaline environment, it can significantly increase the hardening speed of geopolymer concrete in the early stage.

[0017] Water reducing agent: 25-50 parts The water reducer is a composite polycarboxylic acid water reducer, which includes an air entraining component and a retarding component. The polycarboxylic acid water reducer combines with the aggregate surface through the adsorption groups on the molecular chain, produces a dispersion effect in the material system, reduces the water consumption and ensures the high fluidity of the slurry. Its retarding component can moderately delay the reaction process of the geopolymer to meet the construction operation time requirements, while the air entraining component improves the antifreeze performance and durability of the material by introducing tiny bubbles.

[0018] Lignin sulfonate: 0-20 parts Lignin sulfonate has good dispersibility. When compounded with polycarboxylic acid water reducer, it can further enhance the water-reducing effect and improve the cohesiveness of the material, which helps to improve the workability of geopolymer concrete.

[0019] Gypsum: 0-12 parts The main function of gypsum is to adjust the setting time. Gypsum reacts with geopolymers in an alkaline environment, slowly releasing sulfate ions, which moderately inhibits the early reaction rate of the system, thereby extending the construction time.

[0020] Water: 30-60 parts As a basic solvent, water provides the necessary medium conditions for the dissolution, reconstruction and polycondensation of geopolymers. By precisely controlling the amount of water, the fluidity and coagulation properties of the system can be guaranteed to meet the design requirements.

[0021] Preferably, the thixotropic lubricant is a compound of one or more of magnesium aluminum silicate, polymeric thixotropic lubricant, montmorillonite or viren gum.

[0022] One or more of magnesium aluminum silicate, polymerized thixotropic lubricant, montmorillonite or viren gum are compounded to enhance the thixotropy of the slurry through physical cross-linking, thereby effectively improving the construction performance of the material.

[0023] Preferably, the dispersant is a compound of one or more of tannic acid, sodium linoleate or sodium oxalate.

[0024] One or more of tannic acid, sodium linoleate or sodium oxalate are compounded, and their dispersing effect realizes stable dispersion of particles through electrostatic repulsion and adsorption effect, thereby improving the fluidity and uniformity of the slurry.

[0025] Preferably, the system stabilizer is calcium carbonate.

[0026] Calcium carbonate improves the material's resistance to water seepage by physically filling fine pores, while also enhancing the concrete's impermeability and stability.

[0027] Preferably, the early strength agent is calcium formate.

[0028] Calcium formate can quickly release calcium ions, accelerate the curing reaction of geopolymers, and significantly improve the early strength.

[0029] Preferably, the water reducer is a composite polycarboxylic acid-based water reducer comprising an air entraining component and a retarding component.

[0030] The compound polycarboxylic acid-based water reducer reduces water demand through adsorption and dispersion effects and spatial steric hindrance effects. At the same time, the retarding component moderately adjusts the reaction time to meet construction requirements.

[0031] Preferably, a method for preparing an admixture suitable for geopolymer concrete comprises the following steps: S1. Heat water to 45-55°C; S2, add dispersant, early strength agent, water reducer and lignin sulfonate, and stir until uniformly dispersed; S3, add burnt quicklime, sepiolite, thixotropic lubricant, system stabilizer and gypsum, and continue stirring until the dispersion is uniform; S4, dispersing the suspension in an ultrasonic disperser; S5. Seal and store the obtained admixture.

[0032] Preferably, the stirring time in step S2 and step S3 is 10 minutes, and the system temperature is maintained between 45°C and 55°C.

[0033] Preferably, the ultrasonic dispersion time in step S4 is 5 minutes.

[0034] Preferably, the water reducing agent added in step S2 is a polycarboxylic acid water reducing agent, and the dispersant is a tannic acid solution; and the thixotropic lubricant added in step 3 is a compound of magnesium aluminum silicate and a polymeric thixotropic lubricant.

[0035] The present invention provides an admixture suitable for geopolymer concrete and a preparation method thereof, which has the following beneficial effects: 1. The present invention uses a synergistic admixture containing overburned quicklime and sepiolite to give the geopolymer concrete good fluidity during the construction stage, ensuring that the material is still easy to construct under low water consumption. Once the material solidifies and hardens, the overburned quicklime reacts with water to generate calcium hydroxide in the early stage, providing a volume expansion effect to compensate for the volume shrinkage of the geopolymer material during the curing process. And sepiolite, with its special porous structure and water absorption and release characteristics, can gradually release water during the material hardening process, maintain the internal humidity balance of the system, avoid the problem of self-shrinkage caused by internal drying, and thus significantly improve the volume stability of the geopolymer concrete.

[0036] 2. The present invention adopts a polycarboxylic acid water reducer and lignin sulfonate synergistic design to ensure a high water reduction rate of the geopolymer repair material, so that it has excellent fluidity during the construction stage, while greatly reducing fluidity loss. The polycarboxylic acid water reducer has good adaptability to the geopolymer system, and can improve the strength of the material while reducing water consumption through adsorption, dispersion, wetting and lubrication. In addition, the present invention also moderately delays the reaction speed of the geopolymer through the retarding effect of the polycarboxylic acid water reducer, optimizes the construction operation time, and overcomes the limitation of a short construction window caused by the rapid coagulation of the geopolymer material.

[0037] 3. The present invention significantly improves the dispersibility and uniformity of geopolymer slurry through the combined application of dispersant, system stabilizer and thixotropic lubricant. Among them, the dispersant reduces the particle agglomeration phenomenon and optimizes the rheological properties of the slurry through electrostatic repulsion and steric hindrance effect; the system stabilizer (such as calcium carbonate) improves the anti-bleeding performance of the slurry by filling the pores; the thixotropic lubricant gives the slurry moderate thixotropic properties, enhances the anti-segregation ability, and ensures the performance consistency of the material during the construction and hardening process.

[0038] 4. The present invention achieves a balanced optimization of early strength and delayed reaction process in the geopolymer material system by introducing calcium formate early strength agent and salt retarding component. Calcium formate releases calcium ions at an early stage, accelerating the reaction process of the geopolymer, thereby significantly improving the early strength; components such as polycarboxylic acid water reducer and lignin sulfonate further improve the later strength of the material by improving the uniformity of the internal structure of the material. Compared with the prior art, the admixture prepared by the present invention can make the geopolymer concrete show significant advantages in both high strength and high durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The present invention is a flow chart of a method for preparing an admixture suitable for geopolymer concrete. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Please refer to the attached Figure 1 : Example 1: Concrete admixture suitable for geopolymer concrete (standard type) Admixture formulation According to the technical solution of the present invention, an admixture suitable for geopolymer concrete is prepared, and the formulation is as follows (in parts by mass): Burnt quicklime: 5 parts Meerschaum: 7.5 parts Thixotropic lubricant: polymerized thixotropic lubricant and magnesium aluminum silicate, 2.5 parts each, a total of 5 parts Dispersant: Tannic acid solution, 1 mol / L, 5 parts System stabilizer: calcium carbonate, 6 parts Early strength agent: calcium formate, 5 parts Water reducer: Compound polycarboxylic acid water reducer, containing air entraining and retarding components, 35 parts Water: 31.5 parts Preparation method Weigh each raw material according to the formula ratio.

[0042] After heating the water to 45-55℃, add dispersant, early strength agent and water reducing agent, and stir until evenly dispersed.

[0043] Add burnt quicklime, sepiolite, thixotropic lubricant and system stabilizer, continue stirring for 10 minutes, and keep the system temperature stable.

[0044] The mixture was further dispersed using an ultrasonic disperser for 5 min to ensure a homogeneous slurry.

[0045] After preparation, seal the admixture and store it in a cool and dry place.

[0046] Application and Proportion Geopolymer concrete was prepared according to the following proportions (parts by mass) and its performance was tested: Example 2: Concrete admixture suitable for geopolymer concrete (slow-setting type) Admixture formulation According to the technical solution of the present invention, a geopolymer concrete admixture suitable for slow setting requirements is prepared, and the formula is as follows (in parts by mass): Burnt quicklime: 5 parts Seafoam: 5 parts Thixotropic lubricant: polymerized thixotropic lubricant and magnesium aluminum silicate, 2.5 parts each, a total of 5 parts Dispersant: Tannic acid solution, 1 mol / L, 5 parts System stabilizer: calcium carbonate, 5 parts Water reducer: Compound polycarboxylic acid water reducer, containing air entraining and retarding components, 30 parts Lignin sulfonate: 5 parts Gypsum: 8.5 parts Water: 31.5 parts Preparation method The preparation steps are the same as those in Example 1, except that the ratio of the raw materials is adjusted.

[0047] Application and Proportion Geopolymer concrete was prepared according to the following proportions (parts by mass) and its performance was tested: Comparison of the effects of admixtures on the performance of geopolymer concrete: The performance of geopolymer concrete prepared with admixtures prepared in Example 1 and Example 2 and without admixtures is shown in the following table: Performance Indicators Example 1 Example 2 No additives added Water consumption 83.6kg 85.9kg 105kg Uniformity detection (△H, △L) 0mm,0mm 0mm,0mm 20mm,30mm Initial setting time 10min 30min 10min Final setting time 25min 55min 25min Slump out of machine 210mm 210mm 210mm Slump before initial setting 210mm(7min) 205mm(25min) 140mm(7min) Water bleeding rate 0.0085 0.0095 0.0324 1d compressive strength 35.8MPa 33.9MPa 30.2MPa 3d compressive strength 44.5MPa 42.5MPa 37.6MPa 7d compressive strength 59.6MPa 52.6MPa 48.3MPa 28d compressive strength 77.2MPa 68.8MPa 54.9MPa 28d positive tensile bond strength 3.1MPa 3.0MPa 1.7MPa 28d maximum water seepage pressure 3.0MPa no water seepage 3.0MPa no water seepage 1.8MPa water seepage Chloride ion migration coefficient <![CDATA[0.89×10-12m 2 / s]]> <![CDATA[0.63×10-12m 2 / s]]> <![CDATA[2.85×10-12m 2 / s]]> 28d shrinkage ratio -0.00013 0.00013 0.00032 Construction performance The admixtures in Example 1 and Example 2 significantly reduced the water consumption, so that the geopolymer concrete still had good fluidity and workability under the condition of low water-binder ratio. Compared with the control group without adding admixture, the slump loss was significantly reduced and the uniformity of concrete was greatly improved.

[0048] Durability By reducing the water seepage rate and enhancing the anti-seepage capacity, Example 1 and Example 2 significantly improved the water intrusion resistance and long-term durability of concrete, and no obvious water seepage occurred, which was far better than the control group.

[0049] Mechanical properties The geopolymer concrete prepared with the admixture of Example 1 has higher early and late strength, and the 28d compressive strength reaches 77.2MPa, which is more than 40% higher than the control group without admixture. The slow setting formula of Example 2 ensures the construction time while maintaining a high strength level.

[0050] Volume stability Geopolymer concrete with admixtures has excellent performance in shrinkage and bonding properties, with shrinkage close to zero or even slight expansion, which significantly solves the shrinkage cracking problem when no admixtures are added.

[0051] In summary, Example 1 is suitable for scenes requiring high strength and rapid construction, and Example 2 is suitable for scenes requiring longer construction time and higher slow setting requirements. Both formulations significantly improve the comprehensive performance of geopolymer concrete.

[0052] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An admixture suitable for geopolymer concrete, characterized in that: The admixture consists of the following components in parts by weight: composition: Burnt quicklime: 5-10 parts; Sepiolite: 5-10 parts; Thixotropic lubricant: 5-10 parts; Dispersant: 5-10 parts; System stabilizer: 5-12 parts; Early strength agent: 0-12 parts; Water reducing agent: 25-50 parts; Lignin sulfonate: 0-20 parts; Gypsum: 0-12 parts; Water: 30-60 parts.

2. An admixture suitable for geopolymer concrete according to claim 1, characterized in that: The thixotropic lubricant is a compound of one or more of magnesium aluminum silicate, polymeric thixotropic lubricant, montmorillonite or viren gum.

3. The admixture suitable for geopolymer concrete according to claim 1, characterized in that: The dispersant is a compound of one or more of tannic acid, sodium linoleate or sodium oxalate.

4. The admixture suitable for geopolymer concrete according to claim 1, characterized in that: The system stabilizer is calcium carbonate.

5. The admixture suitable for geopolymer concrete according to claim 1, characterized in that: The early strength agent is calcium formate.

6. The admixture suitable for geopolymer concrete according to claim 1, characterized in that: The water reducer is a composite polycarboxylic acid-based water reducer, comprising an air entraining component and a retarding component.

7. A method for preparing an admixture suitable for geopolymer concrete according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Heat water to 45-55°C; S2, add dispersant, early strength agent, water reducer and lignin sulfonate, and stir until uniformly dispersed; S3, add burnt quicklime, sepiolite, thixotropic lubricant, system stabilizer and gypsum, and continue stirring until the dispersion is uniform; S4, dispersing the suspension in an ultrasonic disperser; S5. Seal and store the obtained admixture.

8. The method for preparing an admixture suitable for geopolymer concrete according to claim 1, characterized in that: The stirring time in step S2 and step S3 is 10 minutes, and the system temperature is maintained between 45°C and 55°C.

9. The method for preparing an admixture suitable for geopolymer concrete according to claim 1, characterized in that: The ultrasonic dispersion time in step S4 is 5 minutes.

10. The method for preparing an admixture suitable for geopolymer concrete according to claim 1, characterized in that: The water reducing agent added in step S2 is a polycarboxylic acid water reducing agent, and the dispersant is a tannic acid solution; the thixotropic lubricant added in step 3 is a compound of magnesium aluminum silicate and a polymeric thixotropic lubricant.

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