Fly ash-based cementing material and preparation method thereof

Abstract

The preparation method comprises the following steps: weighing ultrafine fly ash, ardealite, red mud and RAP powder in parts by mass, putting into a mixer, and stirring for 10 minutes to obtain a multi-element solid waste composite base material; weighing a composite coagulant, uniformly mixing the composite coagulant with the C-S-H nanocrystalline seed aqueous dispersion, spraying the mixture into the obtained multi-element solid waste composite base material, and stirring for 5 minutes to obtain a pre-modified base material; adding a composite foaming agent into the pre-modified base material, and stirring at the rotating speed of 1500r / min for 3 minutes to form a microporous slurry precursor; the material disclosed by the invention can be rapidly hardened at a severe low temperature of-5 DEG C, the compressive strength can exceed 15MPa after the material is cured for 30 minutes, and the strength can reach 35MPa or above after the material is cured for 24 hours. The strength development bottleneck of the conventional cementing material in winter construction is broken through, and emergency engineering and rapid repair in a severe cold environment can be carried out without external heating.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering materials technology, and particularly relates to a fly ash-based cementitious material and its preparation method. Background Technology

[0002] With the continuous development of infrastructure construction, the performance requirements of engineering materials in special environments are increasing, especially for winter construction, cold-region engineering, and active road de-icing. Currently, related technology research and development mainly revolves around the following directions: First, low-temperature modification of traditional cement-based materials, through the addition of early-strength agents such as chlorides and nitrates or the use of special cements, aiming to achieve a certain early strength at low temperatures. However, the effect is often limited and may lead to durability issues. Second, for snow melting and de-icing needs, chloride-based de-icing agents or active heating technologies such as electric heating and heat pipes are widely used. While these methods can quickly melt ice, they have problems such as corrosion of reinforcing steel, high energy consumption, complex construction, and environmental unfriendliness. Third, industrial solid waste resource utilization technology, commonly using fly ash, slag, etc., as auxiliary cementing materials to partially replace cement, or using solid waste to prepare roadbed filling materials, aiming to reduce cement usage and the pressure of solid waste storage. Furthermore, phase change energy storage materials have been extensively studied in the fields of building energy conservation and temperature control due to their excellent thermal regulation capabilities. However, their compatibility with cementitious matrices, long-term stability, and maintenance of functionality under harsh environments remain technical challenges. Existing technologies are mostly solutions addressing single performance requirements, lacking systematic integration.

[0003] Despite numerous studies, existing technologies still have significant limitations and struggle to meet the current comprehensive demands for high-performance, multifunctional, and environmentally friendly cementitious materials. Specifically, traditional low-temperature construction materials exhibit severely delayed early strength development in environments of -5°C and below, hindering rapid repair and load-bearing capacity, and significantly restricting construction efficiency. Conventional snow-melting technologies are mostly passive or involve external intervention; for example, salting for ice melting corrodes infrastructure and pollutes the environment, while external heating is costly and energy-intensive, failing to achieve proactive and intelligent responses from the material itself. Regarding solid waste utilization, existing technologies are often limited to the use of single or small amounts of solid waste, with low dosages that typically negatively impact performance (especially early strength and durability), making it difficult to achieve efficient synergy and high-value transformation of large quantities of diverse solid waste. Furthermore, mature and reliable solutions are still lacking for designing material systems that combine early strength, freeze-thaw resistance, and ice-melting capabilities, as well as for ensuring the long-term stable and uniform dispersion of functional components (such as phase change microcapsules) in strongly alkaline cementitious environments. Therefore, developing a new type of cementitious material that can harden rapidly under severe cold conditions, possesses excellent freeze-thaw resistance and durability, and has an active ice-melting function, and can absorb a variety of industrial solid wastes on a large scale, has significant technological value and is an urgent practical need. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention provides a fly ash-based cementitious material and its preparation method, which solves the problem that it is difficult to achieve the material's ultra-early strength, active ice melting, high freeze resistance and efficient utilization of bulk solid waste under severe cold conditions.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A fly ash-based cementitious material and its preparation method, comprising, by mass parts: 40-60 parts ultrafine fly ash, 8-12 parts phosphogypsum, 8-12 parts red mud, 25-35 parts RAP powder, 0.5-2 parts composite coagulant, 0.5-2 parts CSH nanocrystal seed aqueous dispersion, 0.5-1.2 parts composite foaming agent, 5-10 parts alkali-resistant phase change microcapsules, and an appropriate amount of carbide slag leachate; The carbide slag leachate is prepared with a water-cement ratio of 0.25-0.30 and a pH of 11-11.5; the ultrafine fly ash has a specific surface area ≥850m² / kg, a loss on ignition ≤3%, and a water requirement ≤95%. The RAP powder has a particle size ≤75μm and a residual asphalt content ≤5%; The alkali-resistant phase change microcapsules have a polyurea-polyacrylate double-layer shell material and a fatty acid complex core material. The phase change temperature is 0~3℃, the latent heat is ≥80J / g, the particle size is 50~100μm, and the latent heat loss is ≤5% after soaking in an environment of pH=12 for 7 days. The fly ash-based cementitious material has a compressive strength ≥15MPa after curing at -5℃ for 30min and a compressive strength ≥35MPa after curing at -5℃ for 24h; the strength loss rate after 50 freeze-thaw cycles is ≤10%; and the melting rate of a 2cm thick layer of ice and snow at 0℃ for 2h is ≥80%.

[0006] Preferably, the phosphogypsum is a by-product of the phosphate fertilizer industry, with a moisture content ≤10%, a CaSO4・2H2O content ≥85%, and a pH of 2~3.

[0007] Preferably, the red mud is Bayer process red mud with a moisture content ≤5%, a sum of SiO2 and Al2O3 content ≥40%, and a pH of 11~12.

[0008] Preferably, the composite coagulant is composed of sodium carbonate and calcium chloride mixed in a mass ratio of 1:1, and the purity of both sodium carbonate and calcium chloride is ≥98%.

[0009] Preferably, the CSH nanocrystal seed aqueous dispersion has a nanocrystal seed particle size ≤100nm and a solid content of 30%.

[0010] Preferably, the composite foaming agent is composed of anionic surfactant and foam stabilizer mixed at a mass ratio of 3:1, with a foaming ratio of ≥20 times.

[0011] Preferably, the calcium carbide slag leachate is prepared by mixing calcium carbide slag and water at a mass ratio of 1:5, stirring for 30 minutes, and then filtering after standing.

[0012] Preferably, the ultrafine fly ash is obtained by air jet milling of Grade I fly ash.

[0013] Preferably, the core material fatty acid complex of the alkali-resistant phase change microcapsule is a mixture of decanoic acid and stearic acid in a mass ratio of 2~3:1, so that the phase change temperature is stabilized at 0~3℃.

[0014] Preferably, a method for preparing a fly ash-based cementitious material according to any one of claims 1 to 9 includes the following steps: S1. Weigh out the ultrafine fly ash, phosphogypsum, red mud and RAP powder according to the mass fraction, put them into a mixer, and stir at 1500 r / min for 10 min to obtain a multi-element solid waste composite material. S2. Weigh the composite coagulant, mix it evenly with the CSH nanocrystal seed aqueous dispersion, and spray it onto the multi-element solid waste composite substrate obtained in step S1. Stir at 500 r / min for 5 min to obtain the pre-modified substrate. S3. Add a composite foaming agent to the pre-modified substrate obtained in step S2, and stir at 1500 r / min for 3 min to form a microporous slurry precursor; S4. Add alkali-resistant phase change microcapsules to the microporous slurry precursor obtained in step S3, and adsorb them for 3 minutes under a vacuum of -0.08 MPa to allow the microcapsules to be loaded into the microporous structure. S5. Add carbide slag leachate to the system obtained in step S4, control the water-cement ratio to be 0.25~0.30, stir at 500 r / min for 30 s to obtain cementitious material slurry; S6. Pour the cementitious material slurry obtained in step S5 into the area to be repaired, vibrate it with a plate vibrator for 10~15s until it is dense, and then cure it naturally in an environment of -5~10℃.

[0015] The technical effects and advantages of the fly ash-based cementitious material and its preparation method of the present invention are as follows: 1. This invention allows the material to harden rapidly at a harsh low temperature of -5℃. After 30 minutes of curing, its compressive strength exceeds 15MPa, and after 24 hours, it reaches over 35MPa. This overcomes the strength development bottleneck of conventional cementitious materials during winter construction, enabling emergency projects and rapid repairs in frigid environments without the need for external heating.

[0016] 2. The phase change unit built into the material can release latent heat near the freezing point, enabling active and rapid melting of surface ice and snow (melting rate ≥80% in 2 hours). At the same time, its internal microporous structure and dense matrix can effectively buffer frost heave stress, so that the strength loss of the material is still less than 10% after 50 freeze-thaw cycles, combining ice-melting function with structural durability.

[0017] 3. The raw materials of this invention contain more than 90% solid waste. Through collaborative formulation design, typical industrial solid wastes such as fly ash, phosphogypsum, red mud, RAP powder and carbide slag are transformed into high-performance cementitious components, which greatly reduces production costs and environmental impact, and has significant resource utilization benefits.

[0018] 4. This invention employs a specific dry-mixing foaming process, vacuum loading, and alkaline liquid activation to ensure foam stability, uniformity of functional components, and good workability of the slurry. The material exhibits strong operability under low-temperature conditions, is easy to pour and compact, and is particularly suitable for rapid repair and anti-icing layer laying in road and bridge projects. Attached Figure Description

[0019] Figure 1 This is a flowchart of a fly ash-based cementitious material and its preparation method proposed in this invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include," "contain," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "includes..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0022] refer to Figure 1This invention belongs to the field of building materials technology, specifically relating to a multifunctional fly ash-based cementitious material suitable for extremely cold environments and its preparation method. The material uses ultrafine fly ash, phosphogypsum, red mud, and RAP powder, among other bulk industrial solid wastes, as main raw materials. It incorporates functional components such as a synergistic ratio of composite coagulant accelerator, CSH nanocrystals, composite foaming agent, and alkali-resistant phase change microcapsules. Calcium carbide slag leachate is used as the alkaline activation and mixing medium, and the material is prepared through specific processes including dry mixing, vacuum loading, and alkaline activation. The core advantage of this material is its ability to achieve ultra-early high strength development at -5℃, while also possessing multiple functions such as active snow melting and ice removal, and high freeze-thaw resistance and durability. This effectively solves the technical problems of slow strength development in winter construction materials, the corrosive environment or high energy consumption of conventional snow melting technologies, and the difficulty in the synergistic high-value utilization of bulk solid wastes. It is particularly suitable for rapid repair of roads and bridges in cold regions, anti-icing coatings, and emergency engineering construction.

[0023] Raw materials and general preparation basics: Raw material specifications and sources: All embodiments and comparative examples used raw materials of the following specifications, whose performance indicators form the basis for achieving the final material properties: Ultrafine fly ash: It is made from Grade I fly ash by fluidized bed air jet milling, with a specific surface area controlled at 920±20m² / kg, loss on ignition ≤2.5%, and water requirement ratio of 92%.

[0024] Phosphogypsum: An industrial byproduct that has been washed and dried, with a moisture content of 8%, a calcium sulfate dihydrate (CaSO4·2H2O) content of 88%, and a pH value of 2.5.

[0025] Red mud: Bayer process red mud was used, with a moisture content of 4% after drying, a total silica and alumina content of 45%, and a pH value of 11.5.

[0026] RAP powder: Recycled asphalt pavement material obtained through crushing, grinding and screening, with a maximum particle size ≤75μm and an asphalt residue content of 4.2%.

[0027] Composite coagulant: prepared by mechanically mixing analytical grade sodium carbonate and calcium chloride at a mass ratio of 1:1.

[0028] CSH nanocrystal seed aqueous dispersion: commercially available, average particle size approximately 50 nm, solid content 30%.

[0029] Composite foaming agent: It is made by compounding anionic surfactant sodium dodecyl sulfate and foam stabilizer hydroxypropyl methylcellulose in a mass ratio of 3:1, and the measured foaming ratio is 22 times.

[0030] Alkali-resistant phase change microcapsules: self-made, synthesized using interfacial polymerization with a polyurea-polyacrylate double shell. The core material is a fatty acid complex of decanoic acid and stearic acid mixed in a mass ratio of 2.5:1. The finished product has a phase change temperature of 1.8℃, a latent heat value of 83J / g, and a particle size distribution mainly in the range of 60-90μm. After soaking in a saturated calcium hydroxide solution at pH=12 for 7 days, the latent heat retention rate reaches 96.5%.

[0031] Leachate from carbide slag: Carbide slag and deionized water are mixed at a mass ratio of 1:5, stirred for 30 minutes, and allowed to stand for 24 hours. The supernatant is then filtered, and the resulting solution has a pH value of 11.3. This solution is used as the sole mixing and activation liquid.

[0032] Water: Ordinary tap water, used only in the comparison ratio.

[0033] General performance testing methods: Compressive strength: 40mm×40mm×160mm prism specimens were prepared according to the national standard GB / T17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)". After curing in a specified low temperature environment for a specified time, the compressive strength was immediately tested using a pressure testing machine.

[0034] Freeze-thaw cycle test: The test was conducted according to the "rapid freezing method" in the national standard GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". After 28 days of standard curing, the specimens were subjected to 50 freeze-thaw cycles, and the rate of loss of compressive strength before and after the freeze-thaw cycle was calculated.

[0035] Snow melting performance test: The material was cast into a 2 cm thick plate-shaped specimen and kept at a constant temperature of 0°C for 24 hours. Then, a 2 cm thick layer of artificial snow and ice (made from a mixture of crushed ice and a small amount of water, with an initial temperature of -2°C) was evenly spread on the surface of the specimen. The mass of snow and ice melted into water after 2 hours was recorded, and the percentage of melted mass to the total mass of snow and ice was calculated; this is the 2-hour melting rate.

[0036] Other characterizations: The specific surface area of ​​the raw materials was determined by nitrogen adsorption BET method, the chemical composition was analyzed by X-ray fluorescence spectroscopy, and the microstructure was observed by scanning electron microscopy.

[0037] Example 1 This embodiment provides a fly ash-based cementitious material and its preparation method for benchmark mix ratio comprehensive performance verification. Specific implementation details include: Objective: To verify whether the material can fully achieve the set core performance indicators under the optimized central ratio, including -5℃ ultra-early strength, high frost resistance and efficient snow melting ability, and to establish performance benchmarks.

[0038] Implementation ingredients (parts by weight): Ultrafine fly ash: 50 parts; Phosphogypsum: 10 parts; Red mud: 10 parts; RAP powder: 30 servings; Compound coagulant: 1 part; CSH nanocrystal seed aqueous dispersion: 1 part (0.3 parts by solid mass); Composite foaming agent: 0.8 parts; Alkali-resistant phase change microcapsules: 7.5 parts; Calcium carbide slag leachate: The amount added should be based on controlling the total system water-cement ratio to be 0.28 (approximately 23.5 parts).

[0039] Implementation steps: S1. Premixing of solid waste substrate: Weigh out all the ultrafine fly ash, phosphogypsum, red mud and RAP powder into a planetary cement mortar mixer, turn on the high speed (corresponding to a blade linear speed of about 1500 r / min) and dry mix for 10 minutes until the color is uniform to obtain a multi-element solid waste composite dry powder substrate.

[0040] S2. Functional component pre-modification: The composite coagulant and CSH nanocrystal seed aqueous dispersion are mixed evenly in a small beaker with a glass rod to form a suspension. Under the low speed setting (about 500 r / min) of the mixer, the suspension is slowly added to the dry powder substrate of step S1 in a spray form. After the addition is complete, the mixture is stirred at low speed for 5 minutes to ensure that the liquid is evenly attached to the surface of the powder particles, thus obtaining the pre-modified substrate.

[0041] S3. Microporous Structure Prefabrication: Add all the composite foaming agent to the pre-modified substrate, switch the mixer back to high speed, and continue mixing for 3 minutes. Observe that the dry powder mixture expands significantly in volume, becomes loose like sand, and forms a "dry foam mortar" precursor rich in uniform and stable microbubbles.

[0042] S4. Phase Change Microcapsule Loading: Alkali-resistant phase change microcapsules are added to the above precursor, and then the entire material is transferred to a vacuum-sealed container. The vacuum pump is started, and the pressure inside the container is reduced to -0.08 MPa and maintained for 3 minutes. During this process, the microcapsules are effectively adsorbed into the microporous network.

[0043] S5. Liquid-to-Pulp Combination and Slurry Preparation: The vacuum-treated material is returned to the mixing tank. Under low-speed stirring, the pre-calculated mass of carbide slag leachate is slowly added. The addition time is controlled within 30 seconds. After the addition is complete, stirring continues for another 30 seconds to finally obtain a cementitious material slurry with suitable fluidity and uniform color.

[0044] S6. Molding and Curing: Quickly inject the slurry into the mold and vibrate it on a vibrating table for 12 seconds to compact it. Then, immediately transfer the mold to a constant temperature and humidity curing chamber set at -5℃ and relative humidity ≥95% and cure it in the mold for the specified time.

[0045] Implementation results: Ultra-early strength performance: After curing at -5℃ for 30 minutes and then demolding, the compressive strength reached 16.8 MPa; after curing for 24 hours, the compressive strength increased to 38.5 MPa. This indicates that the material has an extremely rapid solidification and hardening rate and early strength development capability under extremely cold conditions.

[0046] Long-term strength and freeze resistance: After curing some specimens at -5℃ for 24 hours, they were transferred to a standard curing room at 20℃ for further curing for 28 days, and their compressive strength was 52.3 MPa. After 50 rapid freeze-thaw cycles, the specimens remained intact, with a compressive strength loss rate of only 7.2%, demonstrating excellent freeze-thaw durability.

[0047] Active snow melting function: In the snow melting performance test at 0℃, the melting rate of a 2cm thick layer of ice and snow on the surface of the specimen reached 83% within 2 hours. After the specimen was cut open, it was found that the microcapsule part near the surface had undergone a phase change, confirming its mechanism of actively releasing latent heat to melt ice.

[0048] Comprehensive Analysis: This embodiment, serving as a benchmark, fully achieves all preset high-performance indicators. Microscopic analysis reveals a dense material structure, with hydration products (CSH gel, ettringite) well integrated with microcapsules and micropores, forming an organic-inorganic composite reinforced structure.

[0049] Example 2 This embodiment provides a fly ash-based cementitious material and its preparation method, used to verify the feasibility of the lower limit of the raw material ratio. Specific implementation details include: Objective: To investigate whether the key properties of the material can still meet the minimum requirements when the dosage of the main solid waste components is at the lower limit of the design range, so as to determine the boundary and feasibility of the proportion range.

[0050] Implementation ingredients (parts by weight): Ultrafine fly ash: 40 parts; phosphogypsum: 8 parts; Red mud: 8 parts; RAP powder: 35 servings; Composite coagulant: 1.2 parts; CSH nanocrystal seed aqueous dispersion: 0.8 parts (0.24 parts solid); Composite foaming agent: 0.5 parts; Alkali-resistant phase change microcapsules: 5 parts; Calcium carbide slag leachate: The amount added should be controlled so that the water-cement ratio is 0.30.

[0051] Implementation steps: Same as the general steps in Example 1.

[0052] Implementation results: Strength properties: The compressive strength at -5℃ / 30min is 15.3MPa, and the compressive strength at -5℃ / 24h is 36.1MPa. Although the total amount of cementitious components (fly ash, red mud, phosphogypsum) is reduced, due to the appropriate increase in the amount of accelerator and the maintenance of a low water-cement ratio, its early strength still stably exceeds the thresholds of 15MPa and 35MPa.

[0053] Functional performance: The snow and ice melting rate is 81% after 2 hours, and the strength loss rate after 50 freeze-thaw cycles is 9.5%. The snow melting rate meets the standard, and although the frost resistance is close to the critical line of 10%, it still meets the requirements.

[0054] Comprehensive Analysis: This embodiment demonstrates that even at the lower limit of economical raw material usage, materials with fully satisfactory performance can still be prepared by optimizing the ratio of functional additives (accelerators). This reflects the flexibility and practicality of the formulation, providing a feasible solution for cost control.

[0055] Example 3 This embodiment provides a fly ash-based cementitious material and its preparation method, used to verify the performance of the upper limit of the raw material ratio. Specific implementation details include: Objective: To investigate the performance trends of the material when the dosage of gelling active components and functional components is close to the upper limit of the design range, especially whether the snow melting and antifreeze properties can be further improved.

[0056] Implementation ingredients (parts by weight): Ultrafine fly ash: 60 parts; Phosphogypsum: 12 parts; Red mud: 12 parts; RAP powder: 25 servings; Composite coagulant: 0.8 parts; CSH nanocrystal seed aqueous dispersion: 1.5 parts (0.45 parts solid); Composite foaming agent: 1.0 part; Alkali-resistant phase change microcapsules: 10 parts; Calcium carbide slag leachate: The amount added should be controlled so that the water-cement ratio is 0.25.

[0057] Implementation steps: Same as the general steps in Example 1.

[0058] Implementation results: Strength properties: The compressive strength at -5℃ / 30min is 16.1MPa, and the compressive strength at -5℃ / 24h is 37.8MPa. The high content of active powder and the lower water-cement ratio ensure stable strength development.

[0059] Functional performance: The ice and snow melting rate was significantly improved to 86% within 2 hours, which is due to the increased content of phase change microcapsules and the enhanced heat storage capacity per unit volume. The strength loss rate after 50 freeze-thaw cycles was 8.1%, with the higher microcapsule content and richer microporous structure providing better buffering against frost heave stress.

[0060] Comprehensive Analysis: This embodiment demonstrates that when using the upper limit ratio, the material maintains excellent early strength properties while further enhancing its active snow melting and freeze-thaw resistance. This provides formulation guidance for applications with higher requirements for snow melting or freeze-thaw resistance.

[0061] Example 4 This embodiment provides a fly ash-based cementitious material and its preparation method, used for enhanced verification focusing on high early strength and high snow melting performance. Specific implementation details include: Objective: By simultaneously increasing the dosage of both the early-strength and phase-change functional components, this study aims to explore the performance limits of the material in both ultra-early strength and ultra-snow melting directions, and to demonstrate the flexibility of the formulation design.

[0062] Implementation ingredients (parts by weight): Ultrafine fly ash: 55 parts; Phosphogypsum: 10 parts; Red mud: 10 parts; RAP powder: 28 servings; Composite coagulant: 2.0 parts; CSH nanocrystal seed aqueous dispersion: 2.0 parts (0.6 parts solid); Composite foaming agent: 1.2 parts; Alkali-resistant phase change microcapsules: 8 parts; Calcium carbide slag leachate: The amount added should be controlled so that the water-cement ratio is 0.26.

[0063] Implementation steps: Same as the general steps in Example 1.

[0064] Implementation results: Ultra-early strength performance: The compressive strength at -5℃ / 30min reached an astonishing 18.5MPa, the highest among all examples; the 24-hour strength also increased to 40.2MPa. This directly demonstrates the significant synergistic effect of the composite coagulant and nanocrystals in improving the early hydration rate at low temperatures.

[0065] High snow melting performance: The snow melting rate reaches 88% in 2 hours, demonstrating the powerful thermal effect of high-load phase change microcapsules.

[0066] Comprehensive Analysis: This embodiment successfully achieved targeted enhancement of specific properties (early strength, snow melting). Although the cost of functional additives increased, this formulation has significant application value for emergency rescue projects requiring extremely rapid traffic reopening or rapid ice melting.

[0067] Example 5 This embodiment provides a fly ash-based cementitious material and its preparation method for exploring adaptability to extreme low-temperature environments. Specific implementation details include: Purpose of implementation: To test the performance of the baseline formulation in extreme environments (-10°C) below the design temperature (-5°C) and to evaluate the application potential of the material under more severe climatic conditions.

[0068] Implementation ingredients (parts by mass): exactly the same as in Example 1.

[0069] Implementation steps: The preparation steps are the same as in Example 1, except that the curing environment in step S6 is changed to a constant temperature and humidity chamber at -10℃.

[0070] Implementation results: Low-temperature early strength performance: In an ultra-low temperature environment of -10℃, the compressive strength of the material still reaches 12.5MPa after 30 minutes and 30.1MPa after 24 hours.

[0071] Performance Analysis: Although the strength development rate slows down compared to -5°C, its 30-minute strength is sufficient to meet the early strength requirements of some temporary supports or rapid repairs, and its 24-hour strength is far higher than the almost zero strength value of ordinary Portland cement under the same conditions. This is mainly attributed to the sustained effect of the composite accelerator (lowering the freezing point of the solution and accelerating hydration) and nanocrystals (lowering the nucleation barrier) at extreme low temperatures, as well as the high freeze-thaw resistance of the low water-cement ratio system itself. This example demonstrates that the material formulation has a wider temperature adaptability range beyond -5°C.

[0072] Comparative Example 1 This comparative example provides a comparative experiment showing the absence of core functional components, specifically including: Objective: By deliberately omitting three key functional components—composite coagulant, CSH nanocrystal seeds, and alkali-resistant phase change microcapsules—and comparing the results with those using ordinary mixing water, this study aims to demonstrate the indispensability of these core components in achieving the material's low-temperature ultra-early strength, high freeze resistance, and active snow melting functions.

[0073] Implementation ingredients (parts by weight): Ultrafine fly ash: 50 parts; Phosphogypsum: 10 parts; Red mud: 10 parts; RAP powder: 30 servings; Composite foaming agent: 0.8 parts; Omitted: composite coagulant, CSH nanocrystal seed aqueous dispersion, alkali-resistant phase change microcapsules.

[0074] Mixing solution: Use ordinary tap water instead of calcium carbide slag leachate, and control the water-cement ratio to be 0.28.

[0075] Implementation steps: Dry mix fly ash, phosphogypsum, red mud, and RAP powder for 10 minutes.

[0076] Add the composite foaming agent and stir at high speed for 3 minutes.

[0077] Add tap water directly and stir until it becomes a paste.

[0078] After molding, it is cured at -5℃.

[0079] Implementation results: Setting and strength: The slurry failed to set for an extended period at -5°C, remaining in a loose, muddy state. After 24 hours, it could be barely demolded, but the specimen was extremely soft, with a compressive strength of only 2.1 MPa, indicating almost no load-bearing capacity.

[0080] Snow melting function: In the 0℃ snow melting test, the snow melting rate was less than 5% after 2 hours, which was no different from the blank control group, and it did not have an active snow melting function at all.

[0081] Freeze-thaw resistance: The specimens developed slowly under standard curing conditions, with a strength of less than 20 MPa after 28 days. During freeze-thaw cycle testing, the specimens showed severe peeling and cracking after only 3 cycles, and completely disintegrated after 5 cycles.

[0082] Comparative Conclusion: The results of this comparative example stand in stark contrast to those of Examples 1-5. This fully demonstrates that: Under low-temperature conditions, the weak alkalinity of red mud and ordinary mixing water alone are insufficient to effectively activate the activity of solid wastes such as fly ash, and the system lacks sufficient driving force to initiate and sustain the hydration reaction. Composite coagulants and CSH nanocrystals are necessary conditions for achieving ultra-early strength at low temperatures.

[0083] Alkali-resistant phase change microcapsules are the only source of materials with active snow-melting function; their absence leads to the complete loss of this function.

[0084] The lack of early strength components leads to a loose structure, and the lack of temperature buffering effect of microcapsules results in extremely poor frost resistance of the material.

[0085] This comparative example powerfully demonstrates, from the opposite perspective, the inventiveness of the core functional component design and the completeness of the technical solution in this invention.

[0086] Compared to Examples 1-5 and Comparative Example 1, Examples 1-5 systematically verified the universality and superior performance of the fly ash-based cementitious material of this invention within the scope of the claims. At a harsh low temperature of -5℃, all examples exhibited ultra-early strength characteristics surpassing conventional materials: the compressive strength stabilized between 15.3 and 18.5 MPa after 30 minutes of curing, and reached 36.1 to 40.2 MPa after 24 hours, fully meeting and exceeding the preset strength thresholds (≥15 MPa, ≥35 MPa). This is attributed to the "low-temperature dual-engine" composed of the composite coagulant and CSH nanocrystals, which synergistically reduced the activation energy of the hydration reaction, strongly initiating and accelerating the formation of the cementitious network near the freezing point. Simultaneously, the material exhibited excellent freeze-thaw resistance and active snow-melting function. After 50 freeze-thaw cycles, the strength loss rate was only 7.2% to 9.5%, significantly lower than the requirement of ≤10%; in the snow-melting test at 0℃, the snow-ice melting rate reached as high as 81% to 88% after 2 hours. These properties are achieved through the combined effects of alkali-resistant phase change microcapsules (which actively melt snow and buffer thermal stress through latent heat of phase change), the elastic microporous structure constructed by composite foaming agents (providing space for frost heave buffering), and the dense alkali-activated system formed by carbide slag leachate and solid waste components. Examples 2 and 3 demonstrate the feasibility of the formulation within its upper and lower limits, Example 4 shows that performance can be targeted and enhanced by adjusting functional components, and Example 5 maintains considerable early strength even under extreme conditions of -10°C, fully demonstrating the reliability, flexibility, and broad low-temperature adaptability of this technical solution.

[0087] In stark contrast to the success of the examples, Comparative Example 1, by deliberately omitting the composite coagulant, CSH nanocrystals, and alkali-resistant phase change microcapsules, and using ordinary tap water instead of carbide slag leachate, resulted in the complete and utter failure of the material's properties. At -5°C, the slurry failed to solidify properly, with a 24-hour strength as low as 2.1 MPa, demonstrating that without a dedicated coagulant component and alkaline activating solution, the system lacks effective hydration reaction driving force at low temperatures, and the gelation framework cannot be established. Simultaneously, the material completely lost its active snow-melting ability (melting rate <5%) and exhibited extremely poor freeze resistance, structurally disintegrating after only three freeze-thaw cycles. This stark contrast irrefutably demonstrates, through contradiction, that the core functional components designed in this invention are not simple additives, but indispensable key elements for achieving the synergistic performance goal of "low-temperature ultra-early strength - high freeze resistance - active snow-melting." Their absence would cause the material to revert to a common, ineffective low-temperature solid waste mixture, thus powerfully demonstrating the non-obviousness and inventiveness of the technical solution of this invention, highlighting the breakthrough technical effect brought about by the innovative integration of a specific coagulation mechanism, nanonucleation technology, microcapsule phase change energy storage technology and a multi-component solid waste alkaline activation system.

[0088] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims.

[0089] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fly ash-based cementitious material, characterized in that, The raw material composition includes, in mass fraction: superfine fly ash 40-60 parts, phosphogypsum 8-12 parts, red mud 8-12 parts, RAP powder 25-35 parts, composite coagulant 0.5-2 parts, C-S-H nanocrystal seed aqueous dispersion 0.5-2 parts, composite foaming agent 0.5-1.2 parts, alkali-resistant phase change microcapsule 5-10 parts, and calcium carbide slag leaching liquor in an appropriate amount; The calcium carbide slag leaching liquor is prepared by mixing calcium carbide slag and water in a mass ratio of 1:5, stirring for 30 minutes, and standing and filtering, and the water-binder ratio is controlled to be 0.25-0.30, and the pH value is 11-11.5; the superfine fly ash has a specific surface area of greater than or equal to 850 m² / kg, a loss on ignition of less than or equal to 3%, and a water requirement ratio of less than or equal to 95%; The RAP powder has a particle size of less than or equal to 75 μm, and an asphalt residue content of less than or equal to 5%; The alkali-resistant phase change microcapsule is a polyurea-polyacrylate double-shell material, the core material is a fatty acid compound, the phase change temperature is 0-3 ℃, the latent heat is greater than or equal to 80 J / g, the particle size is 50-100 μm, and the latent heat loss is less than or equal to 5% after soaking in a pH=12 environment for 7 days; The fly ash-based cementitious material has a compressive strength of greater than or equal to 15 MPa when cured at-5 ℃ for 30 minutes, a compressive strength of greater than or equal to 35 MPa when cured at-5 ℃ for 24 hours, a strength loss rate of less than or equal to 10% after 50 freeze-thaw cycles, and a 2-hour melting rate of greater than or equal to 80% for a 2-cm-thick ice and snow layer in a 0 ℃ environment.

2. A fly ash based cementitious material as claimed in claim 1, wherein, The phosphogypsum is a by-product of the phosphate fertilizer industry, has a water content of less than or equal to 10%, and a CaSO4·2H2O content of greater than or equal to 85%, and a pH value of 2-3.

3. A fly ash based cementitious material as claimed in claim 1, wherein, The red mud is a Bayer process red mud, has a water content of less than or equal to 5%, a SiO2 and Al2O3 content sum of greater than or equal to 40%, and a pH value of 11-12.

4. A fly ash based cementitious material as claimed in claim 1, wherein, The composite coagulant is prepared by mixing sodium carbonate and calcium chloride in a mass ratio of 1:1, and the purity of sodium carbonate and calcium chloride is greater than or equal to 98%.

5. A fly ash based cementitious material as claimed in claim 1, wherein, The C-S-H nanocrystal seed aqueous dispersion has a nanocrystal seed particle size of less than or equal to 100 nm, and a solid content of 30%.

6. A fly ash based cementitious material as claimed in claim 1, wherein, The composite foaming agent is prepared by mixing an anionic surfactant and a foam stabilizer in a mass ratio of 3:1, and has a foaming multiple of greater than or equal to 20 times.

7. A fly ash based cementitious material as claimed in claim 1, wherein, The calcium carbide slag leaching liquor is prepared by mixing calcium carbide slag and water in a mass ratio of 1:5, stirring for 30 minutes, and standing and filtering.

8. A fly ash based cementitious material as claimed in claim 1, wherein, The superfine fly ash is prepared by airflow pulverization of grade I fly ash.

9. A fly ash based cementitious material as claimed in claim 1, wherein, The core material fatty acid compound of the alkali-resistant phase change microcapsule is prepared by mixing capric acid and stearic acid in a mass ratio of 2-3:1, so that the phase change temperature is stabilized at 0-3 ℃.

10. A method of producing a fly ash-based cementitious material according to any one of claims 1 to 9, characterised in that, The method comprises the following steps: S1. The superfine fly ash, phosphogypsum, red mud, and RAP powder are weighed in mass fraction, and are put into a mixer and stirred at a speed of 1500 r / min for 10 minutes to obtain a multi-component solid waste composite base material; S2. The composite coagulant is mixed uniformly with the C-S-H nanocrystal seed aqueous dispersion, and is sprayed into the multi-component solid waste composite base material obtained in step S1, and is stirred at a speed of 500 r / min for 5 minutes to obtain a pre-modified base material; S3. The composite foaming agent is added to the pre-modified base material obtained in step S2, and is stirred at a speed of 1500 r / min for 3 minutes to form a microporous slurry precursor; S4. The alkali-resistant phase change microcapsule is added to the microporous slurry precursor obtained in step S3, and is adsorbed under a vacuum degree of-0.08 MPa for 3 minutes to load the microcapsule into the microporous structure. S5. Adding the carbide slag leaching solution to the system obtained in step S4, controlling the water-binder ratio to be 0.25-0.30, stirring at a speed of 500 r / min for 30 s to obtain a cementitious material slurry; S6. Pouring the cementitious material slurry obtained in step S5 into the part to be repaired, vibrating with a flat vibrator for 10-15 s until compacted, and naturally curing in an environment at-5-10 ℃, thereby obtaining the product.

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