Preparation method of single-component geopolymer straw aggregate

Abstract

A method for preparing a single-component geopolymer straw aggregate comprises the following steps: crushing straw particles, wetting the straw particles by sprinkling water, spraying and mixing the straw particles with sodium hydroxide particles, stirring and mixing the straw particles with sodium silicate particles, vibrating and extruding the straw mixture to compact it into straw aggregate blocks, and sealing and packaging the straw aggregate blocks with polyethylene film and packing tape. The straw aggregate blocks serve as carriers for alkaline activators, thereby solving the corrosion risk caused by adding activators to traditional geopolymer composite materials at the construction site, solving the problems of inaccurate on-site mixing ratios and metering errors of single-component geopolymers, saving time and effort, and solving the problems of loose straw materials, large unit volume, and high loading and unloading and transportation costs.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and in particular relates to a method for preparing a single-component geopolymer straw aggregate. Background Art

[0002] Traditional geopolymers are made from precursor silicoaluminous raw materials such as kaolin, slag, and fly ash, followed by curing after dissolving and activating soluble alkali metal aluminosilicates. They are prepared by reacting and polymerizing aluminosilicate precursors with alkaline activator solutions such as sodium hydroxide, potassium hydroxide, and sodium silicate, or a combination thereof. Because they are prepared by mixing an activator solution with the precursor material, traditional geopolymers are also called two-component geopolymers. Commonly used activators for two-component geopolymers include solutions of sodium hydroxide, potassium hydroxide, sodium silicate, sodium carbonate, and sodium sulfate. Currently, the most common geopolymer activators are sodium hydroxide and sodium silicate solutions. Sodium silicate activation can produce high-performance, alkali-activated cementitious materials with high strength. However, these solution-based activators present numerous challenges, including process risks associated with highly alkaline solutions, rapid setting times, high mixture viscosity, and poor fluidity.

[0003] In the prior art, application number CN201710774873.1 discloses a geopolymer-based rice straw fiberboard and its preparation method, which is composed of liquid sodium water glass, metakaolin, and rice straw fibers. Application number CN202210128171.7 discloses a geopolymer mortar and its preparation method, whose raw materials include oil shale ash, silica fume, fine aggregate, composite activator, modified straw, zeolite powder, water reducer, retarder, and waterproofing agent. Application number CN201710460164.6 discloses a method for preparing a geopolymer material made from printing and dyeing sludge, which is prepared by treating printing and dyeing sludge with corn straw powder and then mixing it with saline-alkali soil leachate.

[0004] A one-component geopolymer is a mixture of a solid alkaline activator and an aluminum silicate precursor. This mixture can be directly mixed with water, similar to traditional cement concrete. Commonly used one-component geopolymers, like traditional two-component geopolymers, use aluminosilicate precursor materials such as kaolin, fly ash, and slag. The activator is a solid particle, unlike the solution-based activators used in two-component geopolymers. One-component geopolymers are typically synthesized using a solid Na2SiO3 activator.

[0005] When preparing geopolymers, the precursor fly ash, a raw material component, is a mixture of glassy and crystalline phases, with the former being the active component and the latter being the inert component. The activity of fly ash is related to the content, structure, and composition of the glassy phase. However, the glassy phase in fly ash is essentially inert in water and must be activated to exhibit gelling properties. Different material ratios and activator dosages in the precursor have varying effects on the fresh mix performance, workability, and mechanical properties of single-component geopolymers. Using fibers to toughen and strengthen single-component geopolymers can effectively improve their macroscopic mechanical properties, including the flow characteristics, compressive and flexural strength, and bending strength of geopolymer mortars. Summary of the Invention

[0006] The synthesis and preparation of traditional two-component geopolymers must be carried out on-site, causing construction inconvenience. Secondly, the alkaline solution is corrosive, and the construction process must be carried out under comprehensive protective measures, which hinders the large-scale use of geopolymers. Single-component geopolymers use solid activators to alleviate the above shortcomings. However, their on-site ingredients are not precise enough, and the quality of the mixing process of different activators is difficult to control, which reduces the efficiency of geopolymer mass production, affects project quality, and increases costs. In addition, there are also disadvantages such as insufficient material toughness and susceptibility to brittle failure. Using straw fiber as a base material for toughening is an inevitable choice.

[0007] The present invention uses sodium hydroxide and sodium silicate as activators. Based on the requirements for the fluidity, setting time, and strength of the geopolymer composite material, a certain mass fraction of the activators is mixed with straw aggregate in batches. The straw aggregate serves as an activator carrier to produce activator-containing straw particle aggregate blocks. Later, during on-site geopolymer preparation, the straw particle aggregate blocks, precursor materials, and sand aggregate are directly added according to the designed proportions, and water is added for stirring.

[0008] The technical solution adopted by the present invention to solve its technical problems is: a preparation method of a single-component geopolymer straw aggregate, the production process of which includes crushing straw particles, spraying and moistening the straw particles, spraying and mixing the straw particles and sodium hydroxide particles, stirring and mixing the straw particles and sodium silicate particles, vibrating and extruding the straw mixture to form a straw aggregate block, and sealing and packaging the straw aggregate block with a polyethylene film and a packing tape.

[0009] A method for preparing a single-component geopolymer straw aggregate, wherein the geopolymer components include a precursor, an activator, aggregate, and water. The precursor material is slag, fly ash, or kaolin; the activator material is sodium hydroxide and sodium silicate; the aggregate is sand and straw particles; and the water is tap water.

[0010] Straw particle fibers play a reinforcing and toughening role in geopolymer composites, effectively solving the defects of pure geopolymers such as high brittleness and easy cracking. Therefore, the addition of straw enhances the strength of the composite material, and the ratio of straw fibers should be appropriate. As the straw fiber content is too high, the volume proportion of the fiber increases and the volume proportion of the matrix decreases relatively, resulting in the composite material not being tightly bonded and the strength decreasing. Sodium hydroxide and sodium silicate should not be excessive, and excessive alkaline activators are not conducive to the hardening of the composite material. The sugars in the straw fibers are easily hydrolyzed under the action of alkali, and the dissolved substances have an anti-coagulation effect on the hardening of the composite material. In addition, straw fibers are easily corroded in the alkaline matrix, resulting in a decrease in strength.

[0011] A method for preparing a single-component geopolymer straw aggregate uses straw aggregate as a carrier for a geopolymer activator to form a straw aggregate block containing the activator. The straw aggregate block is composed of straw pellets, sodium hydroxide and sodium silicate activators, and water. The preparation method includes the following steps:

[0012] A. Crushing straw to prepare straw pellets. Fresh, dry straw is crushed by a crusher in a crushing bin and sieved to obtain straw pellets.

[0013] B. Spraying and wetting the straw pellets. The crushed and sieved straw pellets are sprayed into the upper part of the wetting chamber through the nozzle outlet of the grinder. At the same time, water is sprayed upward from the lower part of the wetting chamber through the spray pipe to fully wet the straw pellets and form moistened straw pellets.

[0014] C. Mixing straw pellets with sodium hydroxide pellets. The moistened straw pellets enter the mixing bin through a collection conveyor belt. At the same time, sodium hydroxide pellets are sprayed into the mixing bin through a nozzle to fully mix the straw pellets and sodium hydroxide pellets to form alkali-pretreated straw pellets.

[0015] D. The alkali-pretreated straw particles mixed with sodium hydroxide in the mixing bin are output through a collecting conveyor belt and enter the mixer bin in the mixing equipment;

[0016] E. The feed pipe on the upper part of the mixer chamber inputs sodium silicate particles into the mixing chamber of the machine body, and fully stirs and mixes them with the alkali-pretreated straw particles mixed with sodium hydroxide particles, so that the alkali-treated straw particles and the sodium silicate particles are mixed to form a straw particle mixture;

[0017] F. The straw pellet mixture is transferred to an extrusion molding machine through a collection conveyor belt, and is extruded and molded by mechanical vibration to form a block of straw pellets of a certain size, i.e., a straw aggregate block;

[0018] G. The straw aggregate blocks are packed with polyethylene film and packing tape through a packing machine.

[0019] Furthermore, in step C, sodium hydroxide is mixed with the moistened straw particles, so that the surface of the straw particles can achieve an alkaline pretreatment effect.

[0020] Furthermore, the straw aggregate block in step F contains straw aggregate and a certain proportion of sodium hydroxide and sodium silicate activators, so that the straw aggregate block becomes an activator carrier.

[0021] Furthermore, straw aggregate blocks with different contents of sodium hydroxide and sodium silicate alkaline activators can be prepared according to design requirements.

[0022] The present invention has the following beneficial effects: using straw aggregate blocks as carriers for alkaline activators eliminates the corrosion risk associated with adding activators to conventional geopolymer composites during construction. It also addresses the issues of inaccurate on-site mixing and metering errors associated with single-component geopolymers, saving time and effort. It also addresses the issues of loose straw materials, large unit volume, and high loading, unloading, and transportation costs. The use of polyethylene film for sealed packaging prevents alkaline corrosion and reaction with atmospheric carbon dioxide during transportation. The use of crop straw waste significantly reduces material costs, is energy-efficient and environmentally friendly, and can be mass-produced in factories, simplifying the construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A process flow chart of a method for preparing single-component geopolymer straw aggregate.

[0024] 1. Crush the straw into pellets; 2. Spray the straw pellets with water to moisten them; 3. Mix the straw pellets with sodium hydroxide pellets; 4. Stir and mix the straw pellets with sodium silicate pellets; 5. Form the straw mixture into straw aggregate blocks; 6. Pack the straw aggregate blocks; 7. Straw pellet spray pipe; 8. Water spray pipe; 9. Sodium hydroxide pellet spray pipe; 10. Sodium silicate pellet feed pipe; 11. Aggregate conveyor belt. Implementation Method

[0025] The straw aggregate is made of fresh, dried corn stalks, industrial-grade sodium hydroxide pellets (content ≥ 95.0%), and industrial solid sodium silicate pellets (content ≥ 95.0%). The mass ratio of the components is: 16 parts sodium hydroxide, 63 parts sodium silicate, 16 parts straw pellets, and 5 parts water.

[0026] A method for preparing a single-component geopolymer straw aggregate, the components of which include straw particles, sodium hydroxide particles, sodium silicate particles, and water. The preparation method comprises the following steps:

[0027] A. Crushing straw to prepare straw pellets. Fresh and dry straw is crushed by a crusher in the crushing bin and sieved to obtain 20-40 mesh straw pellets. The bulk density of the straw pellets is 80-120 kg / cm 3 ;

[0028] B. Spraying and wetting the straw pellets. The crushed and sieved straw pellets are sprayed into the upper part of the wetting chamber through the nozzle outlet of the grinder. At the same time, water is sprayed upward from the lower part of the wetting chamber through the spray pipe to fully wet the straw pellets and form moistened straw pellets.

[0029] C. Mixing straw pellets with sodium hydroxide pellets. The moistened straw pellets enter the mixing bin through a collection conveyor belt. At the same time, sodium hydroxide pellets are sprayed into the mixing bin through a nozzle to fully mix the straw pellets and sodium hydroxide pellets to form alkali-pretreated straw pellets.

[0030] D. The alkali-pretreated straw particles mixed with sodium hydroxide in the mixing bin are output through a collecting conveyor belt and enter the mixer bin in the mixing equipment;

[0031] E. The feed pipe on the upper part of the mixer chamber inputs sodium silicate particles into the mixing chamber of the machine body, and fully stirs and mixes them with the alkali-pretreated straw particles mixed with sodium hydroxide particles, so that the alkali-treated straw particles and the sodium silicate particles are mixed to form a straw particle mixture;

[0032] F. The straw pellet mixture is transferred to the extrusion molding machine through the aggregate conveyor belt and extruded by mechanical vibration to form a 62.5mm×125mm×250mm block of straw pellet extrusion, namely the straw aggregate block. The compaction density of the straw aggregate block is 200kg / cm 3

[0033] G. The straw aggregate blocks are packed using a baler, polyethylene film and packing tape. The packing volume is 1000mm×1000mm×1000mm, and each pack contains 512 straw aggregate blocks.

[0034] The present invention provides a method for preparing a single-component geopolymer straw aggregate. The geopolymer composite material finally prepared by the present invention comprises a precursor material, an activator material, medium sand aggregate, straw aggregate, and water.

[0035] The mass usage ratio of each component material is: 100 parts of precursor fly ash, 100 parts of straw aggregate block (containing 16 parts of sodium hydroxide, 63 parts of sodium silicate, 16 parts of straw particles, and 5 parts of water), 100 parts of medium sand, and 50 parts of water.

[0036] The construction process is:

[0037] A. Use a forced mixer, first add straw aggregate blocks, each mixing tank has 128 straw aggregate blocks, 0.25m 3 , 50kg;

[0038] B. After adding the straw aggregate block, add 1 / 2 of water (12.5 kg) and stir for 3 minutes to completely disperse the straw particles and activator particles in the straw aggregate block;

[0039] C. Add 50kg of fly ash, 50kg of medium sand, and the remaining 1 / 2 of water (12.5kg), and stir for 1 minute;

[0040] D. The straw particles, precursor, activator and water are fully mixed to form a geopolymer slurry for use.

[0041] Furthermore, in step A, there is no need to weigh the straw aggregate when adding it. The required amount per tank is added according to the number of pieces, which is simple, convenient and accurate.

[0042] Furthermore, in step A, the straw aggregate block is used as a carrier of the alkaline activator, and the corresponding amount of sodium hydroxide added to each mixing tank is 8 kg, the amount of sodium silicate added is 31.5 kg, the amount of straw particles added is 8 kg, and the amount of water added is 2.5 kg;

[0043] Furthermore, in step A, when preparing the geopolymer, straw aggregate blocks with different alkaline activator contents can be selected according to design requirements.

[0044] Although the present invention has been described in detail above, it is not limited thereto, and those skilled in the art can make various modifications based on the principles of the present invention. Therefore, any modifications based on the principles of the present invention should be understood to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a single-component geopolymer straw aggregate, characterized in that: An stimulant with a certain mass fraction is mixed with straw aggregate in batches, and the straw aggregate serves as a carrier of the stimulant to prepare a straw particle aggregate block containing the stimulant; the production process includes crushing the straw particles, spraying and moistening the straw particles, spraying and mixing the straw particles and sodium hydroxide particles, stirring and mixing the straw particles and sodium silicate particles, vibrating and extruding the straw mixture to form a straw aggregate block, and sealing and packaging the straw aggregate block with polyethylene film and packaging tape; after the straw aggregate block is added into water, the straw particles and stimulant particles in the straw aggregate block are completely dispersed.

2. The method for preparing a single-component geopolymer straw aggregate according to claim 1, wherein: According to the design requirements, straw aggregate blocks with different contents of sodium hydroxide and sodium silicate alkaline activators were prepared.

3. The method for preparing a single-component geopolymer straw aggregate according to claim 1, wherein: The preparation method comprises the following steps: A. Crushing straw to prepare straw pellets: fresh and dry straw is crushed by a crusher in a crushing bin and sieved to obtain straw pellets; B. Spraying and wetting the straw pellets: The crushed and sieved straw pellets are sprayed into the upper part of the wetting bin through the nozzle outlet of the grinder; at the same time, water is sprayed upward through the spray pipe at the lower part of the wetting bin to fully wet the straw pellets and form wet straw pellets; C. Mixing straw particles with sodium hydroxide particles; the moistened straw particles enter the mixing bin through a collecting conveyor belt. At the same time, sodium hydroxide particles are sprayed into the mixing bin through a nozzle to fully mix the straw particles with the sodium hydroxide particles to form alkali-pretreated straw particles; D. The alkali-pretreated straw particles mixed with sodium hydroxide in the mixing bin are output through a collecting conveyor belt and enter the mixer bin in the mixing equipment; E. The feed pipe on the upper part of the mixer chamber inputs sodium silicate particles into the mixing chamber of the machine body, and fully stirs and mixes them with the alkali-pretreated straw particles mixed with sodium hydroxide particles, so that the alkali-treated straw particles and the sodium silicate particles are mixed to form a straw particle mixture; F. The straw pellet mixture is transferred to an extrusion molding machine through a collection conveyor belt, and is extruded and molded by mechanical vibration to form a block of straw pellets of a certain size, i.e., a straw aggregate block; G. The straw aggregate blocks are packed with polyethylene film and packing tape through a baler.

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