Retarded fly ash-based geopolymer mortar as well as preparation method and application thereof

Abstract

The invention relates to the technical field of building materials, and discloses retarded fly ash-based geopolymer mortar as well as a preparation method and application thereof. The fly ash-based geopolymer mortar prepared by the method is prepared from the following components in parts by weight: 300-450 parts of fly ash, 50-200 parts of mineral powder, 25-60 parts of a solid alkali activator, 3-9 parts of silica fume, 9-20 parts of borax, 2-7 parts of a naphthalene water reducer, 10-20 parts of anhydrous sodium sulphate, 20-50 parts of steel slag powder, 180-230 parts of water and 1300-1400 parts of sand. The prepared fly ash-based geopolymer mortar has ideal setting time: initial setting is greater than or equal to 60 min, final setting is greater than or equal to 100 min, excellent durability and high strength are shown, the compressive strength exceeds 20 MPa in 3 days, and the compressive strength exceeds 67 MPa in 28 days. According to the invention, not only is the utilization rate of industrial wastes such as fly ash increased, but also the optimization of material performance is realized through accurate proportioning, and a high-performance and environment-friendly novel mortar material is provided for the building material industry.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and specifically to a retarding fly ash-based geopolymer mortar and its preparation method and application. Background Art

[0002] As a large amount of solid waste generated during industrial production processes such as coal-fired power plants, the large-scale accumulation of fly ash not only occupies land resources, but may also cause a series of environmental problems. Specifically, the open storage of fly ash will generate dust pollution, and its leachate contains harmful substances such as heavy metals, which may cause serious pollution to the surrounding soil and groundwater. With the in-depth development of the concept of resource recycling, the efficient utilization of fly ash as a secondary resource has become a current research hotspot. Research shows that fly ash contains a large amount of active components such as silicon and aluminum, and has the potential to prepare high-performance building materials, which highly coincides with the requirements of sustainable development.

[0003] As a new type of inorganic non-metallic material, geopolymers are formed by the polymerization reaction of aluminosilicate raw materials under the action of alkaline activators. Compared with traditional cement-based materials, geopolymers have significant performance advantages: rapid early strength development, excellent durability, outstanding high-temperature resistance, etc. These characteristics make them show broad application prospects in the fields of building structures, refractory materials, etc. However, in practical engineering applications, geopolymers, especially fly ash-based geopolymers, have a technical problem that needs to be solved urgently: their setting time is too short and the reaction speed is too fast, resulting in insufficient workable time. This problem is particularly prominent in large-scale concrete pouring projects. Due to the need for a long mixing, transportation and pouring time, the premature setting of geopolymers may cause the concrete to start hardening before it can reach the designated position smoothly, seriously affecting the project quality.

[0004] Regarding the retarding problem of geopolymers, the existing technologies mainly adopt methods such as adding organic retarders or adjusting the types and dosages of activators. However, these methods have obvious limitations: on the one hand, the addition of some organic retarders may cause a decrease in the later strength of geopolymers; on the other hand, the compatibility of some retarders with the geopolymer system is poor, which is likely to cause unstable material performance. Therefore, developing a retarding geopolymer mortar that can effectively extend the setting time and maintain stable material performance has important practical significance for giving full play to the performance advantages of fly ash-based geopolymers and promoting their large-scale application in the engineering field. Summary of the Invention

[0005] In order to solve the deficiencies of the prior art, the present invention provides a slow-setting fly ash-based polymer mortar and its preparation method and application. The polymer mortar achieves a significant slow-setting effect and precise setting time control by optimizing the material ratio and preparation process, and has excellent mechanical properties, durability and construction work performance. In addition, the present invention also provides a preparation method with stable process, high production efficiency and easy large-scale industrial application, which provides reliable technical support for the promotion of fly ash-based polymer mortar in the field of construction engineering.

[0006] Specifically, the present invention provides a slow-setting fly ash-based polymer mortar, characterized in that it comprises the following components in parts by weight:

[0007] 300-450 parts of fly ash; 50-200 parts of mineral powder; 25-60 parts of solid alkali activator; 3-9 parts of silica fume; 9-20 parts of borax; 2-7 parts of naphthalene-based water reducer; 10-20 parts of sodium sulfate; 20-50 parts of steel slag powder; 180-230 parts of water; 1300-1400 parts of sand.

[0008] In some specific embodiments of the present invention, the solid base activator includes solid sodium silicate and an alkali metal compound;

[0009] The modulus of the solid sodium silicate is 1.0-2.3;

[0010] The alkali metal compound is one or more of sodium hydroxide, potassium hydroxide, sodium carbon or potassium carbonate;

[0011] The mass ratio of the solid sodium silicate to the alkali metal compound is (2-10):1.

[0012] In some specific embodiments of the present invention, the fly ash silicon-aluminum ratio is preferably between 1.5 and 3.0, and Fe 2 O 3 Content <15%, specific surface area 400-600m 2 / kg.

[0013] In some specific embodiments of the present invention, the mineral powder has a calcium oxide content of >30%, a sulfur trioxide content of ≤3%, a chloride ion content of ≤0.04%, a loss on ignition of ≤0.8%, and a specific surface area of ​​380-450m 2 / kg, water content ≤0.9%.

[0014] In some specific embodiments of the present invention, the silica fume has a specific surface area greater than 15000m 2 / kg of ultrafine powder, wherein the silica ash has a silicon dioxide content of more than 94% by mass.

[0015] In some specific embodiments of the present invention, the calcium oxide content in the steel slag powder is > 40%, the magnesium oxide content is between 5 - 10%, the free calcium oxide content is ≤ 3%, and the specific surface area is ≥ 350 m 2 / kg.

[0016] In some specific embodiments of the present invention, the fineness modulus of the sand is between 2 - 3, the mud content is ≤ 1%, and the apparent density is ≥ 2300 kg / m 3 .

[0017] In some specific embodiments of the present invention, the borax is sodium tetraborate decahydrate, the purity is > 90%, the heavy metal content does not exceed 0.001%, the particle size is between 80 - 220 mesh, the solubility at room temperature is ≥ 25 g / 100 g of water, and the pH after dissolving in water is between 8.9 - 10.2.

[0018] In some specific embodiments of the present invention, the naphthalene - based water - reducing agent has a purity > 92%, a water - reducing rate ≥ 9%, an air content ≤ 3%, and a pH between 7.5 - 9.5.

[0019] In some specific embodiments of the present invention, the content of sodium sulfate in the anhydrous sodium sulfate is > 98%, and the insoluble matter content is < 0.04%.

[0020] In some specific embodiments of the present invention, the water has a pH between 6 - 8, the chloride content is ≤ 500 mg / L, and the water temperature is preferably controlled between 5 - 30 °C.

[0021] In some specific embodiments of the present invention, it further includes the following preparation steps: Mix all components evenly, then pour the mixed components into a mold, and then obtain the retarding fly - ash - based geopolymer mortar after curing.

[0022] The present invention also provides a preparation method of the retarding fly - ash - based geopolymer mortar, which is characterized by including the following preparation steps:

[0023] S1. Mix fly ash, slag powder, solid alkali activator, silica fume, borax, naphthalene - based water - reducing agent, anhydrous sodium sulfate, steel slag powder, and water according to weight parts, and then stir at a low speed of 90 - 160 revolutions per minute for 60 - 80 s; Subsequently, add sand according to weight parts and stir at a low speed of 90 - 160 revolutions per minute for 20 - 40 s; Finally, stir at a high speed of 180 - 320 revolutions per minute for 80 - 100 s to make them fully mixed;

[0024] S2. Pour the mixed components into a mold, and under the curing conditions of a curing temperature of 20 - 80 °C and a relative humidity of 20 - 95%, cure for 5 - 24 h to obtain the retarding fly - ash - based geopolymer mortar.

[0025] The present invention also provides the application of the retarding fly ash-based geopolymer mortar or the retarding fly ash-based geopolymer mortar prepared by the preparation method of the retarding fly ash-based geopolymer mortar of the present invention in building materials.

[0026] The present invention has the following remarkable advantages and effects compared with the prior art:

[0027] (1) Synergy of multi-component composite: Innovatively, various industrial wastes such as fly ash, slag powder, and steel slag powder are compositely utilized, not only realizing the resource utilization of waste, but also the components cooperate with each other. Fly ash provides the basic framework, slag powder optimizes the microstructure, and steel slag powder supplements the strength, synergistically improving the overall performance of fly ash-based geopolymer mortar, which is the key difference from traditional single-component cementitious materials.

[0028] (2) Precise design of retarding system: A retarding system is constructed by specific proportions of silica fume, borax, naphthalene-based water reducer, etc. Silica fume gives full play to the role of fine particles and fills the voids accumulated by slag and fly ash. The activator released thereby increases the liquid film thickness on the surface of solid particles, thus improving the fluidity of the geopolymer, reducing the thixotropy, yield stress, and plastic viscosity of the paste; in addition, due to the high activity of silica fume, the silica fume added to the system reacts with the solid alkali activator preferentially, resulting in a decrease in the alkalinity of the system and an increase in the concentration of silicate ions, slowing down the reaction rate of precursor substances (such as fly ash and slag powder) and the formation rate of calcium silicoaluminate hydrate, manifested as an extended setting time. At the same time, borax can also play a role in regulating the setting process, and the naphthalene-based water reducer aids in dispersion, precisely controlling the setting time, solving the problem of too fast setting of geopolymer mortar, and meeting the requirements of complex construction durations.

[0029] (3) Microstructure strengthening: Silica fume can not only play a role in extending the setting time, but also fill pores during the retarding process, generating dense reaction products and enhancing durability. Sodium sulfate promotes the early strength development and increases the dosage of multi-component solid waste precursors. During the setting and hardening process of the retarding fly ash-based geopolymer mortar, due to the retarding effect, the water evaporation and volume shrinkage are more uniform, reducing the internal stress concentration and the possibility of crack generation.

[0030] (4) Optimization of water-binder ratio adaptation: The water-binder ratio is optimized according to the characteristics of multi-components. Corresponding to a specific solid material ratio with 180 - 230 parts of water, considering both workability and strength, ensuring good fluidity of the mortar for easy construction operation, and not sacrificing the later hardening strength, overcoming the dilemma of difficult balance of the water-binder ratio of traditional materials. Specific embodiments

[0031] The present invention will be further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by this application.

[0032] Example 1:

[0033] Raw material preparation: The following parts are calculated by weight fraction. Fly ash: 300 parts, with a silica-alumina ratio of 1.5, Fe 2 O 3 content of 10%, specific surface area of 400 m 2 / kg of fly ash. Ground granulated blast-furnace slag: 150 parts, with a calcium oxide content of 32%, sulfur trioxide content of 2%, chloride ion content of 0.03%, loss on ignition of 0.5%, specific surface area of 380 m 2 / kg, and water content of 0.5%. Alkali activator: 36 parts, with a sodium silicate modulus of 1.0, and sodium hydroxide as an alkali metal compound, where the mass ratio of sodium silicate to sodium hydroxide is 9:1. Silica fume: 7 parts, which is an ultra-fine powder with a specific surface area as high as 15000 m 2 / kg, and a silica content of 95%. Borax: 18 parts, which is sodium tetraborate decahydrate, with a purity of 92%, heavy metal content of 0.0008%, particle size between 80 - 180 mesh, solubility at room temperature of 28 g / 100 g of water, pH of 9.0 after dissolving in water. Naphthalene-based water reducer: 2 parts, with a purity of 93%, water reduction rate of 9%, air content of 2%, and pH of 7.5. Sodium sulfate: 10 parts, with a sodium sulfate content of 98.5% and insoluble matter content of 0.03%. Steel slag powder: 20 parts, with a calcium oxide content of 42%, magnesium oxide content of 6%, free calcium oxide content of 2%, and specific surface area of 350 m 2 / kg. Water: 200 parts, with a pH of 6, chloride content of 300 mg / L, and water temperature of 20 °C of ordinary tap water. Sand: 1300 parts, with a fineness modulus of 2, mud content of 0.5%, and apparent density of 2300 kg / m 3 , and river sand is selected.

[0034] Preparation process: First, add fly ash, ground granulated blast-furnace slag, steel slag powder, silica fume, borax, naphthalene-based water reducer, sodium sulfate, steel slag powder, and water into a mixer according to the weight parts in proportion, and stir at a low speed of 90 revolutions per minute for 80 s to make them preliminarily mixed evenly, and the raw materials start to react preliminarily. Then add sand and stir at a low speed of 90 revolutions per minute for 40 s to make the sand evenly dispersed in the mortar system. Finally, stir at a high speed of 180 revolutions per minute for 100 s to ensure that all components react and mix fully, and at this time, the chemical reaction in the system accelerates.

[0035] Curing process: Pour the mixed materials into the mold. Under the curing conditions of a curing temperature of 20°C and a relative humidity of 20%, the curing time is 24 h. This curing environment simulates a general indoor environment, which helps the mortar to react and harden slowly and stably, forming a stable structure, so as to obtain a fly ash-based geopolymer mortar with retarding properties.

[0036] Performance test: After testing, the initial setting time of this mortar is 63 min, and the final setting time is 103 min, meeting the retarding requirements and leaving sufficient time for construction operations. In terms of compressive strength, it reaches 20.8 MPa at 3 d and 70 MPa at 28 d, having good resistance to environmental erosion and extending the service life of the structure.

[0037] Example 2:

[0038] Raw material preparation: The following parts are by weight fraction. Fly ash: 375 parts, with a silicon-aluminum ratio of 1.5, Fe 2 O 3 content of 10%, specific surface area of 400 m 2 / kg. Ground granulated blast-furnace slag: 125 parts, calcium oxide content of 35%, sulfur trioxide content of 1.5%, chloride ion content of 0.02%, loss on ignition of 0.6%, specific surface area of 420 m 2 / kg, water content of 0.6%. Alkali activator: 40 parts, sodium silicate modulus of 1.2, with potassium hydroxide as an alkali metal compound, and the mass ratio of sodium silicate to potassium hydroxide is 10:1. Potassium hydroxide introduces different alkali metal ions, synergistically activating the raw material activity with sodium silicate and broadening the reaction path. Silica fume: 6 parts, specific surface area of 16000 m 2 / kg, silicon dioxide content of 96%. Borax: 14 parts, purity of 95%, heavy metal content of 0.0006%, particle size between 120 - 200 mesh, solubility at room temperature of 30 g / 100 g water, pH after dissolving in water of 9.2. Naphthalene-based water reducer: 4.5 parts, purity of 94%, water reduction rate of 10%, air content of 2.5%, pH of 8.0. Sodium sulfate: 15 parts, sodium sulfate content of 99%, insoluble matter content of 0.02%. Steel slag powder: 35 parts, calcium oxide content of 45%, magnesium oxide content of 8%, free calcium oxide content of 2.5%, specific surface area of 380 m 2 / kg. Water: 195 parts, pH of 7, chloride content of 300 mg / L, water temperature of 25°C. Sand: 1350 parts, fineness modulus of 2.5, mud content of 0.8%, apparent density of 2400 kg / m 3 .

[0039] Preparation process: Same as the stirring step in Example 1. First, mix fly ash, ground granulated blast-furnace slag, steel slag powder, silica fume, borax, naphthalene-based water reducer, sodium sulfate, steel slag powder, and water at low speed, and then add sand and stir at low speed first and then at high speed.

[0040] Curing process: Pour the mixed materials into the mold. Under the curing conditions of a curing temperature of 60 °C and a relative humidity of 20%, the curing time is 12 h. Appropriately increase the curing temperature to accelerate the early reaction of the mortar, shorten the curing cycle, and improve production efficiency.

[0041] Performance test: The initial setting time is measured to be 60 min, and the final setting time is 100 min, meeting the retarder standard and ensuring the construction continuity. The compressive strength is 28 MPa at 3 d and 73 MPa at 28 d, with a significant strength increase, meeting the requirements of building projects with higher strength demands.

[0042] Example 3:

[0043] Raw material preparation: Fly ash: 400 parts, with a silicon-aluminum ratio of 1.5, an Fe 2 O3 content of 10%, and a specific surface area of 400 m 2 / kg. Ground granulated blast-furnace slag: 200 parts, with a calcium oxide content of 38%, a sulfur trioxide content of 1%, a chloride ion content of 0.01%, a loss on ignition of 0.7%, and a specific surface area of 450 m 2 / kg, and a water content of 0.8%. Alkali activator: 60 parts, with a sodium silicate modulus of 1.5, and potassium carbonate is used as the alkali metal compound, where the mass ratio of sodium silicate to potassium carbonate is 6:1. The unique chemical properties of potassium carbonate further expand the reaction space and stimulate the maximum activity of the raw materials. Silica fume: 9 parts, with a specific surface area of 18000 m 2 / kg, and a silicon dioxide content of 97%. Borax: 20 parts, with a purity of 98%, a heavy metal content of 0.0004%, a particle size between 160 - 220 mesh, a solubility of 32 g / 100 g water at room temperature, and a pH of 9.4 after being dissolved in water. Naphthalene-based water reducer: 7 parts, with a purity of 95%, a water reduction rate of 11%, an air content of 3%, and a pH of 9.0. Sodium sulfate: 20 parts, with a sodium sulfate content of 99.5% and an insoluble matter content of 0.01%. Steel slag powder: 50 parts, with a calcium oxide content of 48%, a magnesium oxide content of 9%, a free calcium oxide content of 3%, and a specific surface area of 400 m 2 / kg. Water: 180 parts, with a pH of 6, a chloride content of 300 mg / L, and ordinary tap water with a water temperature of 20 °C. Sand: 1400 parts, with a fineness modulus of 3, a mud content of 1%, and an apparent density of 2500 kg / m 3 .

[0044] Preparation process: Repeat the preparation process of Example 1 to ensure the full mixing and reaction of each component.

[0045] Curing process: Pour the mixed materials into the mold. Under the curing conditions of a curing temperature of 50°C and a relative humidity of 95%, the curing time is 5 hours. High-temperature and high-humidity curing accelerates the early strength development of the mortar, quickly reaches the usable state, and meets the needs of emergency projects.

[0046] Performance test: The initial setting time is 65 minutes, and the final setting time is 106 minutes, meeting the retarding requirements and providing sufficient construction time. The compressive strength is 25.5 MPa at 3 days and 76 MPa at 28 days, showing high strength and being able to undertake high-strength construction tasks.

[0047] Comparative example 1:

[0048] Raw material preparation: The following parts are in terms of weight fractions. Fly ash: 375 parts, with a silica-aluminum ratio of 1.5, an Fe 2 O 3 content of 10%, and a specific surface area of 400 m 2 / kg. Ground granulated blast-furnace slag: 125 parts, with a calcium oxide content of 35%, a sulfur trioxide content of 1.5%, a chloride ion content of 0.02%, a loss on ignition of 0.6%, a specific surface area of 420 m 2 / kg, and a water content of 0.6%. Alkali activator: 40 parts, with a sodium silicate modulus of 1.2, and potassium hydroxide is used as an alkali metal compound. The mass ratio of sodium silicate to potassium hydroxide is 10:1. Potassium hydroxide introduces different alkali metal ions, synergistically activates the raw material activity with sodium silicate, and broadens the reaction path. Silica fume: 0 parts. It is investigated that without silica fume, it may not be possible to fill the pores and effectively reduce the alkali content for the alkali activation reaction, and whether it may not be possible to effectively control the setting time and the development of later strength. Borax: 14 parts, with a purity of 95%, a heavy metal content of 0.0006%, a particle size between 120 - 200 mesh, a solubility of 30 g / 100 g water at room temperature, and a pH of 9.2 after being dissolved in water. Naphthalene-based water reducer: 4.5 parts, with a purity of 94%, a water reduction rate of 10%, an air content of 2.5%, and a pH of 8.0. Sodium sulfate: 15 parts. Steel slag powder: 35 parts, with a calcium oxide content of 45%, a magnesium oxide content of 8%, a free calcium oxide content of 2.5%, and a specific surface area of 380 m 2 / kg. Water: 195 parts, with a pH of 7, a chloride content of 300 mg / L, and a water temperature of 25°C. Sand: 1350 parts, with a fineness modulus of 2.5, a mud content of 0.8%, and an apparent density of 2400 kg / m 3 .

[0049] Preparation process: First, fly ash, mineral powder, steel slag powder, silica fume, borax, naphthalene-based water reducer, sodium sulfate, steel slag powder, and water are added to a mixer in proportion and stirred at a low speed of 80 revolutions per minute for 70 s to make a preliminary uniform mixture. Then sand is added and stirred at a low speed of 80 revolutions per minute for 30 s, and then stirred at a high speed of 160 revolutions per minute for 90 s.

[0050] Curing process: The mixed material is poured into a mold and cured for 12 h under the curing conditions of a curing temperature of 60 °C and a relative humidity of 20% to obtain a retarding fly ash-based geopolymer mortar. By appropriately increasing the curing temperature, can it accelerate the early reaction of the mortar, play a role similar to that of sodium sulfate, shorten the curing cycle, and improve production efficiency?

[0051] Performance test: After testing, the initial setting time of this mortar is 60 min, and the final setting time is 75 min. Borax only plays a role in retarding the initial setting. Without adding silica fume, the final setting time does not meet the retarding requirements, the construction operation time is tight, and construction quality problems are likely to occur. In terms of compressive strength, it reaches 28 MPa at 3 d and 38 MPa at 28 d. The strength is significantly lower than that of the standard mortar, and it is difficult to meet the load-bearing requirements of building structures.

[0052] Control Example 2:

[0053] Raw material preparation: The following parts are calculated by weight fraction. Fly ash: 400 parts, with a silica-aluminum ratio of 1.5, Fe 2 O 3 content of 10%, and a specific surface area of 400 m 2 / kg. Mineral powder: 200 parts, with a calcium oxide content of 38%, a sulfur trioxide content of 1%, a chloride ion content of 0.01%, a loss on ignition of 0.7%, a specific surface area of 450 m 2 / kg, and a water content of 0.8%. Alkali activator: 60 parts, with a sodium silicate modulus of 1.5, and potassium carbonate is used as an alkali metal compound. The mass ratio of sodium silicate to potassium carbonate is 6:1. Silica fume: 8 parts, with a specific surface area of 18000 m 2 / kg and a silica dioxide content of 97%. Borax: 25 parts, with a purity of 98%, a heavy metal content of 0.0004%, a particle size between 160 - 220 mesh, a solubility of 32 g / 100 g water at room temperature, a pH of 10.5 after being dissolved in water. The dosage of borax is on the high side, increasing production costs, and the too high pH may affect the reaction of other components. Naphthalene-based water reducer: 7 parts, with a purity of 95%, a water reduction rate of 11%, an air content of 3%, and a pH of 9.0. Sodium sulfate: 20 parts, with a sodium sulfate content of 99.5% and an insoluble matter content of 0.01%. Steel slag powder: 80 parts, with a calcium oxide content of 48%, a magnesium oxide content of 9%, a free calcium oxide content of 4%, and a specific surface area of 400 m 2 / kg. Water: 180 parts, ordinary tap water with a pH of 6, a chloride content of 300 mg / L, and a water temperature of 20 °C. Sand: 1400 parts, fineness modulus of 3, mud content of 1%, apparent density of 2500 kg / m 3 .

[0054] Preparation process: Same as the stirring step in Comparative Example 1. First, mix fly ash, slag powder, steel slag powder, silica fume, and other admixtures with water at a low speed, and then add sand and stir at a low speed first and then at a high speed.

[0055] Curing process: Repeat the curing process in Example 3. High temperature and high humidity and too short a curing time may cause the surface of the mortar to harden rapidly, preventing internal moisture from escaping, forming internal stress, causing cracks, and affecting durability.

[0056] Performance test: The initial setting time was measured to be 60 min. Compared with Example 3, the initial setting time does not increase with the increase in the addition amount of borax. The final setting time is 90 min. Compared with Comparative Example 1, the time interval from initial setting to final setting has increased after adding silica fume, further verifying that silica fume is beneficial for extending the final setting time. The compressive strength at 3 days is 9 MPa. The addition of too much steel slag powder introduces an inactive calcium source into the system, resulting in a decrease in early strength. The compressive strength at 28 days is 26 MPa, with insufficient strength and a risk of cracking at the same time.

[0057] Comparative Example 3:

[0058] Raw material preparation: The following parts are by weight. Fly ash: 300 parts, with a silica-aluminum ratio of 1.5, an Fe 2 O 3 content of 10%, and a specific surface area of 400 m 2 / kg of fly ash. Slag powder: 150 parts, with a calcium oxide content of 32%, a sulfur trioxide content of 2%, a chloride ion content of 0.03%, a loss on ignition of 0.5%, a specific surface area of 380 m 2 / kg, and a water content of 0.5%. Alkali activator: 36 parts, using sodium silicate with a modulus of 1.0 and sodium hydroxide as an alkali metal compound, with a mass ratio of sodium silicate to sodium hydroxide of 9:1. Sodium silicate can effectively dissolve and provide the silicate ions required for the reaction, and sodium hydroxide adjusts the alkalinity to activate the activity, and the two act synergistically. Silica fume: 7 parts, with a specific surface area as high as 15000 m 2 / kg of ultrafine powder, with a silicon dioxide content of 95%. Borax: 18 parts, sodium tetraborate decahydrate, with a purity of 92%, a heavy metal content of 0.0008%, a particle size between 80-180 mesh, a solubility of 28g / 100g water at room temperature, and a pH of 9.0 after dissolving in water. Naphthalene-based water reducer: 2 parts, with a purity of 93%, a water reduction rate of 9%, a gas content of 2%, and a pH of 7.5. Sodium sulfate: 0 parts, without adding sodium sulfate, a sodium sulfate content of 98.5%, and an insoluble matter content of 0.03%. Steel slag powder: 20 parts, a calcium oxide content of 42%, a magnesium oxide content of 6%, a free calcium oxide content of 2%, and a specific surface area of ​​350m 2 / kg. Water: 200 parts, pH 6, chloride content 300mg / L, ordinary tap water at 20℃. Sand: 1300 parts, fineness modulus 2, mud content 0.5%, apparent density 2300kg / m 3 , choose river sand.

[0059] Preparation process: First, add fly ash, mineral powder, silica fume, borax, naphthalene water reducer, sodium sulfate, steel slag powder and water into the mixer in proportion, stir at a low speed of 90 rpm for 80s to make them preliminarily mixed and evenly mixed, and the raw materials begin to have a preliminary contact reaction. Then add sand and stir at a low speed of 90 rpm for 40s to evenly disperse the sand in the mortar system, and finally stir at a high speed of 180 rpm for 100s to ensure that all components are fully reacted and mixed, and the chemical reaction in the system is accelerated.

[0060] Curing process: Pour the mixed material into the mold and cure it for 24 hours at a temperature of 20°C and a relative humidity of 20%. This curing environment simulates the general indoor environment, which helps the mortar to react and harden slowly and steadily, forming a stable structure and obtaining a slow-setting fly ash-based polymer mortar.

[0061] Performance test: After testing, the initial setting time of the mortar was 63 minutes, and the final setting time was 103 minutes, which met the slow setting requirements and reserved sufficient time for construction operations. In terms of compressive strength, it reached 15MPa at 3 days and 70MPa at 28 days. Compared with Example 1, the early strength decreased without adding sodium sulfate, and the later strength had no obvious effect, indicating that sodium sulfate mainly stimulated and promoted the early reaction.

[0062] The relevant data of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0063] Table 1 Experimental conditions and corresponding results of the embodiments of the present invention

[0064]

[0065] It can be seen from the examples and comparative examples that the retarding fly ash-based geopolymer mortar provided by the present invention achieves significant retarding effects and precise control of the setting time, while also having excellent mechanical properties, durability, and construction workability. By optimizing the material ratio and process parameters, the present invention successfully solves the problems of short setting time and poor construction performance of traditional geopolymer mortar, providing a reliable solution for the engineering application of fly ash-based geopolymer mortar.

[0066] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A slow-setting fly ash-based polymer mortar, characterized in that: By weight, it includes the following components: 300-450 parts of fly ash; 50-200 parts of mineral powder; 25-60 parts of solid alkali activator; Silica fume 3-9 parts; Borax 9-20 parts; Naphthalene water reducer 2-7 parts; Sodium sulfate 10-20 parts; 20-50 parts of steel slag powder; 180-230 parts of water; 1300-1400 parts of sand.

2. The slow-setting fly ash-based polymer mortar according to claim 1, characterized in that: The solid base activator includes solid sodium silicate and an alkali metal compound; The modulus of the solid sodium silicate is 1.0-2.3; The alkali metal compound is one or more of sodium hydroxide, potassium hydroxide, sodium carbon or potassium carbonate; The mass ratio of the solid sodium silicate to the alkali metal compound is (2-10):

1.

3. The slow-setting fly ash-based polymer mortar according to claim 1, characterized in that: The fly ash preferably has a silicon-aluminum ratio between 1.5 and 3.0, a Fe2O3 content of less than 15%, and a specific surface area of ​​400-600m 2 / kg.

4. The slow-setting fly ash-based polymer mortar according to claim 1, characterized in that: The mineral powder has a calcium oxide content of >30%, sulfur trioxide ≤3%, chloride ion content ≤0.04%, loss on ignition ≤0.8%, and a specific surface area of ​​380-450m 2 / kg, water content ≤0.9%.

5. The slow-setting fly ash-based polymer mortar according to claim 1, characterized in that: The silica fume has a specific surface area greater than 15000m 2 / kg of ultrafine powder, wherein the silica fume has a silicon dioxide content of more than 94% by mass.

6. The slow-setting fly ash-based polymer mortar according to claim 1, characterized in that: The steel slag powder has a calcium oxide content of >40%, a magnesium oxide content of 5-10%, a free calcium oxide content of ≤3%, and a specific surface area of ​​≥350m 2 / kg.

7. The slow-setting fly ash-based polymer mortar according to claim 1, characterized in that: The sand fineness modulus is between 2-3, the mud content is ≤1%, and the apparent density is ≥2300kg / m 3 .

8. The slow-setting fly ash-based polymer mortar according to any one of claims 1 to 7, characterized in that: The method also includes the following preparation steps: mixing all components evenly, pouring the mixed components into a mold, and then curing to obtain slow-setting fly ash-based polymer mortar.

9. The method for preparing the slow-setting fly ash-based polymer mortar according to claims 1-8, characterized in that: The method comprises the following preparation steps: S1. Mix fly ash, mineral powder, solid alkali activator, silica fume, borax, naphthalene water reducer, sodium sulfate, slag powder and water according to weight proportion, and then stir at low speed 90-160 rpm for 60-80s; then add sand according to weight proportion, stir at low speed 90-160 rpm for 20-40s; finally stir at high speed 180-320 rpm for 80-100s to mix thoroughly; S2. Pour the mixed components into a mold, and under the curing conditions of a curing temperature of 20-80° C. and a relative humidity of 20-95% for a curing time of 5-24 hours, obtain a slow-setting fly ash-based polymer mortar.

10. Application of the slow-setting fly ash-based polymer mortar prepared by the slow-setting fly ash-based polymer mortar according to any one of claims 1 to 8 or the method for preparing the slow-setting fly ash-based polymer mortar according to claim 9 in building materials.

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