Circulating fluidized bed ash-based road base cementing material and preparation method thereof

Abstract

This invention belongs to the field of industrial solid waste resource utilization technology, and relates to a circulating fluidized bed ash-based cementitious material for road base courses and its preparation method. The raw materials for the road base course cementitious material are composed of the following mass parts: 29-43 parts of circulating fluidized bed ash, 16-27 parts of ground blast furnace slag, 3-6 parts of silica fume, 7-15 parts of P.O42.5 silicate cement, 0.1-0.4 parts of activator, and 27-30 parts of water. The circulating fluidized bed ash is prepared by mixing circulating fluidized bed fly ash and slag in a mass ratio of (2-5):(5-10). This invention effectively alleviates the problems of fast setting time and shrinkage cracking of traditional road base course cementitious materials by utilizing the characteristics of micro-expansion and long hydration time of circulating fluidized bed ash. The advantage of this invention is that it promotes the large-scale utilization of circulating fluidized bed ash and contributes to carbon emission reduction in the road sector.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial solid waste resource utilization and road base material technology, specifically relating to a cementitious material for circulating fluidized bed ash-based road base and its preparation method. Background Technology

[0002] As the lowest load-bearing component of the road structure, the road base course directly bears the dynamic and static loads transmitted from the pavement structure and evenly transfers them to the subgrade. It is the core supporting foundation ensuring pavement smoothness, load-bearing capacity, and service life, and its engineering performance directly determines the long-term stable operation of the entire road system. Therefore, the cementitious materials used in the road base course, as the core raw materials for the formation and strength development of the base course structure, must meet multiple performance requirements in engineering applications. These include sufficient compressive strength, flexural strength, and other mechanical properties to resist deformation and damage under load; good volume stability to avoid harmful deformations such as shrinkage and expansion during forming, curing, and use; and excellent durability properties such as frost resistance and water erosion resistance to adapt to the complex climate and hydrological environments of different regions and extend the service life of the road base course.

[0003] Currently, the cementitious materials used for road base courses are generally silicate cement. This type of cement has long dominated road base construction due to its mature production process and stable mechanical properties. However, the production process of silicate cement involves significant resource consumption and environmental impact. It requires the large-scale extraction of natural mineral resources such as limestone and clay, and emits substantial amounts of carbon dioxide. Furthermore, silicate cement has inherent performance defects as a cementitious material for road base courses. Its rapid setting and hardening speed and short setting time cause inconvenience in large-area road base construction, and improper control of the construction schedule can easily lead to poor base course quality. More importantly, cement-based base courses undergo volume shrinkage during hardening, easily forming surface cracks or internal micro-cracks. These cracks not only reduce the load-bearing capacity and integrity of the base course but also accelerate the penetration of moisture and harmful substances, exacerbating aging and damage, thus shortening the overall service life of the road and significantly increasing later maintenance and repair costs, resulting in a waste of resources and funds.

[0004] With the rapid development of my country's clean power generation industry, circulating fluidized bed combustion technology has been widely promoted and applied in the thermal power sector due to its advantages of efficient desulfurization and low pollutant emissions. However, the emissions of circulating fluidized bed slag (CFB slag) and fly ash have also increased year by year. Currently, the total annual emissions of CFB slag and fly ash in my country have exceeded 120 million tons and are still showing an increasing trend. The disposal of large amounts of slag and fly ash has become a prominent bottleneck for the industry's development. Due to the special physicochemical properties of circulating fluidized bed slag, its particles are loose and porous, with rough and irregular surfaces, and it contains high levels of calcium oxide, sulfides, and other components. It is highly hygroscopic and easily undergoes hydration reactions and self-hardening expansion when exposed to water, resulting in poor volume stability and making it difficult to directly use as an admixture in ordinary concrete for large-scale resource utilization.

[0005] Currently, most circulating fluidized bed slag and fly ash in my country are still disposed of through traditional landfill and stockpiling methods. This not only occupies a large amount of valuable farmland and forest land, but also poses serious ecological and environmental risks. The soluble salts, heavy metals, and other harmful substances contained in the slag and fly ash can easily seep into the soil and groundwater through rainwater leaching, causing soil and groundwater pollution, disrupting the balance of the surrounding ecosystem, and threatening crop growth and human health. Therefore, promoting the resource-based and high-value utilization of industrial solid waste such as circulating fluidized bed slag and fly ash, alleviating the environmental and land pressures of solid waste stockpiling, practicing the concept of green development, and promoting industrial transformation and upgrading have become urgent needs and important development directions for my country's industrial and infrastructure construction sectors.

[0006] In summary, existing technologies face two major challenges: First, traditional road base cementitious materials (silicate cement) suffer from high carbon emissions, high resource consumption, and susceptibility to shrinkage and cracking, making them unsuitable for green road construction and the "dual-carbon" strategy. Second, circulating fluidized bed slag and fly ash emissions are enormous and difficult to dispose of, their inherent characteristics limiting resource utilization and causing resource waste and environmental hazards. Providing a technological solution that synergistically addresses these two challenges, fully utilizing the potential value of circulating fluidized bed slag and fly ash while compensating for the performance and environmental deficiencies of traditional cement-based cementitious materials, would effectively overcome these technological bottlenecks.

[0007] Chinese invention patent application CN102442792A discloses a method for producing low-shrinkage-expansion cement using calcium-based desulfurization products and fluidized bed coal-fired boiler ash. The method involves mixing fluidized bed coal-fired boiler ash with calcium-based desulfurization products to produce low-shrinkage-expansion cement. However, this method only utilizes the active alumina in the fluidized bed coal-fired boiler ash, and such products cannot be used as gel materials for road base courses.

[0008] Although the poor volume stability of circulating fluidized bed ash limits its application in concrete, its moderate expansion characteristics can compensate for the defects of traditional cement-based base courses that are prone to shrinkage and cracking. If the expansion amount can be controlled by reasonable technical means, so that the expansion effect cancels out the shrinkage effect of cement-based materials, the generation of road base course cracks can be effectively suppressed, thus giving it unique advantages and potential value for resource utilization in road base course engineering.

[0009] Chinese invention patent application CN114538808A discloses a circulating fluidized bed fly ash-based low-carbon cement and its preparation method. It involves mixing P·I type 42.5 grade silicate cement with circulating fluidized bed fly ash, microsilica, and diatomaceous earth to form a circulating fluidized bed fly ash base material. The addition of microsilica and diatomaceous earth enables high-proportion utilization of circulating fluidized bed fly ash solid waste in the building materials field. Microsilica and diatomaceous earth stabilize the unstable components f-CaO and SO3 in the circulating fluidized bed fly ash, improving the utilization rate of circulating fluidized bed fly ash in cement while reducing the use of cement clinker. However, its proportioning method and required performance indicators still cannot meet the requirements of gel materials for road base courses.

[0010] Therefore, there is an urgent need to propose a method for preparing cementitious materials for road base courses using circulating fluidized bed slag and fly ash. Through targeted technical means, this method can effectively activate the cementitious activity of circulating fluidized bed slag and precisely control its volume stability. This will provide a road base course cementitious material alternative with excellent construction performance, stable mechanical properties, better durability, and reasonable cost, while achieving resource utilization and high-value utilization of industrial solid waste, alleviating the pressure of solid waste disposal, and reducing carbon emissions. This will effectively overcome the shortcomings of existing silicate cement-based cementitious materials, solve the environmental problems of circulating fluidized bed slag storage, promote the green and low-carbon transformation of road construction, and meet the practical application needs of engineering projects. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention provides a cementitious material for road base courses prepared using circulating fluidized bed ash. This invention uses circulating fluidized bed ash as the main cementitious component, supplemented with finely ground blast furnace slag, a small amount of silica fume, P.O42.5 silicate cement, and sodium sulfate as raw materials. Employing design techniques of proportion optimization and activator control, the cementitious system generates an appropriate amount of ettringite during the hydration reaction to achieve a micro-expansion effect. Furthermore, it utilizes the volcanic ash reaction and micro-aggregate filling effect of multi-source solid waste, thereby solving the problems of short setting time leading to construction difficulties and poor durability due to shrinkage cracking in traditional road base materials during practical applications. This invention focuses on extending the setting time and controlling the expansion rate, successfully transforming circulating fluidized bed ash from industrial solid waste that is difficult to utilize on a large scale into a key component of cementitious materials for road base courses, ultimately obtaining a novel cementitious material for road base courses that combines slow setting, high strength, and volume stability.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A circulating fluidized bed ash-based road base cementitious material, comprising by weight: 29-43 parts circulating fluidized bed ash, 16-27 parts ground blast furnace slag, 3-6 parts silica fume, 7-15 parts P.O42.5 silicate cement, 0.1-0.4 parts activator, and 27-30 parts water; wherein the circulating fluidized bed ash has a specific surface area of ​​700-800 m². 2 / kg of circulating fluidized bed fly ash with an average particle size of 8~10µm and a specific surface area of ​​700~900m² 2 / kg of circulating fluidized bed slag is mixed in a mass ratio of (2~5):(5~10).

[0013] Preferably, the circulating fluidized bed fly ash is circulating fluidized bed fly ash with a SiO2 content of 35-40%, an Al2O3 content of 25-30%, a CaO content of 15-20%, and a SO3 content of 5-10%.

[0014] Preferably, the circulating fluidized bed slag is a circulating fluidized bed slag with a SiO2 content of 45-50%, an Al2O3 content of 25-30%, a CaO content of 10-15%, and a SO3 content of 5-10%.

[0015] Preferably, the activator is sodium sulfate.

[0016] Preferably, the circulating fluidized bed ash is a mixture of circulating fluidized bed fly ash and circulating fluidized bed slag in a mass ratio of (2~5):(5~8).

[0017] Preferably, the circulating fluidized bed slag is circulating fluidized bed slag powder that is ground from slag discharged from the circulating fluidized bed to an average particle size of 8~10µm and a fineness (screen residue percentage) of 3~7%.

[0018] Preferably, the finely ground blast furnace slag is of grade S95 and has a specific surface area of ​​600-700 m². 2 / kg.

[0019] Preferably, the specific surface area of ​​the silica fume is 20,000 to 21,000 m². 2 / kg.

[0020] Preferably, the specific surface area of ​​the PO 42.5 silicate cement is 350~400 m². 2 / kg.

[0021] Preferably, the particle size distribution of the finely ground blast furnace slag is: D10 is 1~1.5µm, D50 is 9.5~10µm, and D90 is 30~30.5µm.

[0022] Preferably, the silica fume has a particle size distribution of D50 of 0.1~0.3µm, and the silica fume has a SiO2 content of 90~95%.

[0023] A method for preparing a cementitious material for circulating fluidized bed ash-based road base courses, the method comprising the following steps: S1, take 14.5~34.4 parts by weight of circulating fluidized bed slag and put it into a ball mill for grinding for 40~60 minutes to obtain circulating fluidized bed slag powder with an average particle size of 8~10µm and a sieve residue percentage of 3~7%; then, take a specific surface area of ​​700~800m²... 2 / kg of circulating fluidized bed fly ash and the obtained circulating fluidized bed slag powder are mixed at a mass ratio of (2~5):(5~10) to obtain 29~43 parts by weight of circulating fluidized bed ash slag.

[0024] S2, the circulating fluidized bed ash obtained in step S1, 16-27 parts by weight of finely ground blast furnace slag, 3-6 parts by weight of silica fume, and 7-15 parts by weight of PO 42.5 silicate cement are mixed to obtain a solid mixed powder.

[0025] S3, mix 0.1 to 0.4 parts by weight of activator with 27 to 30 parts by weight of water and dissolve them completely to obtain a liquid mixture.

[0026] S4. The solid mixed powder obtained in step S2 and the liquid mixed material obtained in step S3 are poured into the mixing unit and stirred evenly to ensure complete mixing. The mixing process is roughly divided into three stages: In the initial stage of mixing, the stirring speed is set to 140~160 rpm, the cement particles are fully dispersed and hydrated, the volume of the cementitious mixture begins to shrink and Ca(OH)2 is generated; In the middle stage of mixing, the stirring speed is set to a high speed of 290~310 rpm, which allows the circulating fluidized bed ash and the generated Ca(OH)2 to react rapidly to generate ettringite, the cementitious mixture undergoes micro-expansion, and the generated ettringite coats the surface of the cement particles; In the later stage of mixing, a low speed of 65~85 rpm is used, the finely ground blast furnace slag and silica fume continue to dissolve under the activation of Ca(OH)2, continuously dissolve and polymerize to generate C-(A)-SH gel and ettringite hydration products, forming a dense network structure, and the generated ettringite continues to coat the surface of the cement particles; The initial stage of mixing takes 4~6 minutes, the middle stage takes 8~12 minutes, and the later stage takes 4~6 minutes.

[0027] S5, the slurry that was completely mixed in step S4 is poured into a mold for curing to obtain the cementitious material for road base.

[0028] Preferably, in step S3, the complete dissolution is achieved by stirring with a magnetic stirrer at a speed of 240-260 rpm for 5-10 minutes.

[0029] Preferably, in step S4, the uniform stirring is performed at a speed of 150 rpm for 5 minutes, followed by high-speed stirring at 300 rpm for 10 minutes, and finally low-speed stirring at 75 rpm for 5 minutes.

[0030] As a preferred option, the initial setting time of the cementitious material for road base courses is ≥300 min, and the final setting time is 360~720 min; the 7-day linear expansion rate is ≥0.1%, and the 28-day linear expansion rate is ≤0.5%; the 3-day flexural strength is ≥4.0 MPa, the compressive strength is ≥17.0 MPa, and the 28-day flexural strength is ≥6.5 MPa, and the compressive strength is ≥42.5 MPa.

[0031] The technical effects of this invention are as follows: 1. This invention involves pulverizing circulating fluidized bed slag to a specific particle size, mixing it with circulating fluidized bed fly ash to form a complete mixture, then mixing it with specific amounts of finely ground blast furnace slag, silica fume, P.O42.5 silicate cement, and finally mixing it with a specific activator and water. Because the CaO content of the circulating fluidized bed ash obtained through this specific proportion does not exceed 20% and the SO3 content does not exceed 10%, under the alkaline environment of the activator and water, the active components of the circulating fluidized bed ash react with the Ca(OH)2 generated during cement hydration. The reaction generates hydration products such as C-(A)SH gel and ettringite, producing certain strength and expansion stress, effectively improving the volume stability of the cementitious material. At the same time, the ettringite generated in the reaction coats the surface of cement particles, delaying the cement hydration reaction and thus extending the setting time of the cementitious system. In other words, by specifically selecting and proportioning the raw materials, the efficient use of circulating fluidized bed ash, a difficult-to-use solid waste, to prepare cementitious materials for road base courses is achieved. This reduces raw material costs while significantly reducing cement usage, thereby effectively saving production energy and reducing carbon emissions.

[0032] By rationally selecting the specific surface area of ​​blast furnace slag and silica fume, a highly active auxiliary cementitious material is formed. Under the stimulation of Ca(OH)2, the internal silica-alumina components of blast furnace slag and silica fume will continuously dissolve and polymerize to generate hydration products such as C-(A)SH and ettringite, which can improve the strength and durability of the cementitious material. Furthermore, by specifically limiting the particle size of each raw material, raw materials with different specific particle sizes form a good particle size distribution in the cementing system, effectively reducing the internal porosity, thereby significantly improving the density and structural stability of the cementitious material.

[0033] By selecting a specific surface area of ​​350~400 m² 2 / kg of PO 42.5 silicate cement serves as the main active component and strength source in the cementitious system. Through its rapid hydration, it can provide the early strength required for road base courses, meeting the requirements of construction progress and initial load-bearing capacity. At the same time, through synergistic reaction with blast furnace slag, silica fume, and circulating fluidized bed ash in the established alkaline environment, it can effectively activate the potential activity of other cementitious materials, thereby achieving a synergistic effect of multi-source solid waste.

[0034] The preferred method is to select sodium sulfate as the activator, which can accelerate and enhance the hydration reaction of the system. In particular, in synergy with finely ground blast furnace slag, it can enhance the activation of the potential activity of finely ground blast furnace slag and the dissolution of anhydrite in circulating fluidized bed ash, promote the large-scale generation of ettringite, and significantly improve the mid-to-late stage strength of cementitious materials used in road base courses, thereby further promoting the efficient utilization of industrial solid waste.

[0035] In other words, this invention achieves the synergistic combination of multiple solid waste sources through the specific setting and synergistic cooperation of various materials, thereby obtaining a gel material for road base that meets the usage conditions.

[0036] 2. In the preparation process of this invention, by specifically setting the mixing steps and parameters, and combining the screening and proportioning of specific raw materials, a multi-stage hydration reaction is formed during the hydration process: The first stage is that cement reacts rapidly when it comes into contact with water, the volume of the cementitious material begins to shrink and a certain amount of Ca(OH)2 is generated; the second stage is that the circulating fluidized bed ash is hydrolyzed and reacts with the Ca(OH)2 generated by the cement to quickly generate ettringite, causing the cementitious material to undergo micro-expansion. The micro-expansion effect of the circulating fluidized bed ash cancels out the shrinkage of the cement hydration, effectively improving the volume stability of the cementitious material. At the same time, a certain amount of ettringite covers the cement surface, delaying further hydration of the cement, thereby effectively extending the setting time of the cementitious material; the third stage is that the slag particles and silica fume continuously dissolve under the activation of Ca(OH)2, and the internal silica-alumina components continuously dissolve and polymerize to generate hydration products such as C-(A)SH with a dense network structure, which continuously enhances the mechanical properties of the cementitious material. By specifically designing each stage of the reaction process, the synergistic hydration reaction of different solid wastes is utilized to optimize the performance of cementitious materials for road base layers, further effectively alleviating the technical problems of short setting time, high construction difficulty, and easy shrinkage and cracking of traditional road base layer materials.

[0037] 3. The technical effect of this invention does not emphasize the performance and superiority of the obtained product, but rather emphasizes the use of traditionally considered solid wastes such as circulating fluidized bed ash and finely ground blast furnace slag as the main raw materials to prepare road base cementitious materials that meet the requirements. The utilization rate of solid waste in the raw material ratio of this invention exceeds 80%, thus truly realizing the transformation of waste into treasure. While achieving large-scale disposal of multi-source industrial solid waste, it effectively reduces the construction cost of road engineering, thereby improving the comprehensive technical effect of economic and environmental benefits. Attached Figure Description

[0038] Figure 1 This is a SEM electron microscope scan result of Example 1 of the present invention after a maintenance period of 3 days.

[0039] Figure 2 This is a SEM electron microscope scan result of Example 1 of the present invention, after a maintenance period of 28 days.

[0040] Figure 3 This is a SEM electron microscope scan result of Example 5 of the present invention, after a maintenance period of 3 days.

[0041] Figure 4 This is a SEM electron microscope scan result of Example 5 of the present invention, after a maintenance period of 28 days.

[0042] In the diagram: 101 - pores; 102 - unreacted substance; 103 - ettringite; 104 - C-(A)SH hydration product; 105 - calcium hydroxide. Detailed Implementation

[0043] The process technology solution of the present invention will be further described below with reference to embodiments and accompanying drawings. Unless otherwise specified, each feature is merely one example of a series of equivalent or similar features. These embodiments are merely for the purpose of aiding understanding the present invention and should not be considered as specific limitations thereof.

[0044] In a specific embodiment of this invention, the industrial solid waste is circulating fluidized bed ash, comprising a specific ratio of circulating fluidized bed fly ash and circulating fluidized bed slag, wherein the CaO content of the ash does not exceed 20% and the SO3 content does not exceed 10%. Under alkaline conditions, the active components of the circulating fluidized bed ash react with Ca(OH)2 produced by cement hydration to generate C-(A)SH gel and ettringite, producing certain strength and expansion stress, effectively improving the volume stability of the cementitious material. Simultaneously, the generated ettringite coats the surface of cement particles, delaying the cement hydration reaction and thus prolonging the setting time of the cementitious system. The efficient use of circulating fluidized bed ash in the preparation of cementitious materials for road base courses significantly reduces raw material costs and cement usage, thereby effectively saving production energy and reducing carbon emissions.

[0045] The mineral admixtures in this embodiment of the invention are blast furnace slag and silica fume, with specific surface areas of 500-600 m², respectively. 2 / kg and 20000~21000 m 2 / kg. Both raw materials are highly active auxiliary cementitious materials. Under the stimulation of Ca(OH)2, the internal silica-alumina components continuously dissolve and polymerize, generating hydration products such as C-(A)SH and ettringite, which can improve the strength and durability of the cementitious material. The different particle sizes of the raw materials form a good particle size distribution in the cementing system, effectively reducing the internal porosity, thereby significantly improving the density and structural stability of the cementitious material.

[0046] The PO 42.5 silicate cement selected in this embodiment of the invention has a specific surface area of ​​350~400 m². 2 P.O42.5 silicate cement, at a concentration of / kg, is the main active component and strength source in the cementitious system. Due to its rapid hydration rate, it can provide the early strength required for road base courses, meeting construction schedule and initial load-bearing requirements. Simultaneously, by establishing an alkaline environment, it can effectively activate the potential activity of other cementitious materials, achieving a synergistic effect from multiple solid waste sources.

[0047] In this embodiment of the invention, sodium sulfate is selected as the activator. Sodium sulfate is added to the cementitious material for road base courses, mainly to accelerate and enhance the hydration reaction of the system, especially to activate the potential activity of finely ground blast furnace slag and dissolve anhydrite in circulating fluidized bed ash, promote the large-scale generation of ettringite, significantly improve the mid-to-late stage strength of the cementitious material for road base courses, and promote the efficient utilization of industrial solid waste.

[0048] This embodiment illustrates a cementitious material for road base prepared using circulating fluidized bed ash, comprising the following components by mass: 32.6 parts of circulating fluidized bed ash (obtained by mixing circulating fluidized bed fly ash and circulating fluidized bed slag at a mass ratio of 1:4), 26.1 parts of finely ground blast furnace slag, 5.1 parts of silica fume, 8.7 parts of PO 42.5 silicate cement, 0.11 parts of sodium sulfate activator, and 27.5 parts of water.

[0049] The preparation method of the cementitious material for road base course in this embodiment is as follows: The above-proportioned circulating fluidized bed slag is fed into a ball mill and ground for 50 minutes until the specific surface area is 820 m². 2 / kg, with an average particle size of 9.12 μm. Then, the above-mentioned amounts of circulating fluidized bed fly ash, circulating fluidized bed slag, finely ground blast furnace slag, silica fume, and PO 42.5 silicate cement were premixed to obtain a solid mixed powder. At the same time, the above-mentioned amounts of sodium sulfate were added as an activator to tap water and fully dissolved to obtain a liquid mixed water (in this embodiment, a magnetic stirrer was used to stir at a speed of 250 rpm for 8 minutes). The powder and water were added to a mixer and stirred evenly (in this embodiment, the stirring process is roughly divided into three stages: in the initial stirring stage of 0-5 minutes, the stirring speed is set to 150 rpm, the cement particles are fully dispersed and hydrated, the volume of the cementitious mixture begins to shrink and Ca(OH)2 is generated; then in the stage of 5-15 minutes, the stirring speed is set to a high speed of 300 rpm, at which time the circulating fluidized bed ash reacts with the generated Ca(OH)2 to rapidly generate ettringite, the cementitious mixture undergoes micro-expansion, and the generated ettringite coats the surface of the cement particles; finally, a low speed of 75 rpm is used for stirring for 20 minutes, the finely ground blast furnace slag and silica fume continue to dissolve under the activation of Ca(OH)2, continuously dissolving and polymerizing to generate C-(A)-SH gel and ettringite hydration products, forming a dense network structure, and the generated ettringite continues to coat the surface of the cement particles), ensuring complete mixing. Then it is poured into a steel mold for standard curing, and finally the road base material is obtained. The SEM electron microscope scanning results after 3 days of curing are shown in the figure. Figure 1 As shown in the figure, the SEM electron microscope scan results after 28 days of curing are as follows. Figure 2 As shown. (Through) Figure 1As can be seen, the microstructure after 3 days of curing contains a large number of unreacted raw material particles with clear edges. Although short rod-shaped or needle-shaped ettringite particles are formed, their distribution is relatively loose, and there are pores and cracks of varying sizes between the particles. These characteristics indicate that the hydration reaction is in its initial stage, the amount of hydration products is limited, and the slurry structure is loose and porous, which is consistent with the slow macroscopic performance of early strength development. At 28 days of hydration, the amount of unreacted material decreases continuously, the number of ettringite crystals increases continuously, and the flaky hydration products overlap, covering the particle surface and filling the pores. A small number of pores are visible in some local areas, indicating that the hydration reaction is relatively complete at 28 days, but the microstructure is not yet fully dense.

[0050] The performance indicators of the cementitious material for road base obtained in this embodiment were tested, and the results are shown in Table 1.

[0051] Example 2 This embodiment illustrates a road base cementitious material prepared using circulating fluidized bed ash with different proportions. By mass, it comprises the following components: 29.0 parts circulating fluidized bed ash, 23.2 parts ground blast furnace slag, 5.8 parts silica fume, 14.5 parts PO 42.5 silicate cement, 0.15 parts sodium sulfate activator, and 27.5 parts water. The mass ratio of circulating fluidized bed fly ash to circulating fluidized bed slag in the circulating fluidized bed ash is 1:3.

[0052] Preparation method of cementitious material for road base course: The circulating fluidized bed slag is fed into a ball mill and ground for 40 minutes until the specific surface area is 760 m². 2 / kg, with an average particle size of 9.69 μm. The subsequent preparation steps are the same as in Example 1.

[0053] The performance indicators of the cementitious material for road base obtained in Example 2 were tested, and the results are shown in Table 1.

[0054] Example 3 This embodiment illustrates a road base cementitious material prepared using circulating fluidized bed ash with different proportions. By mass, it comprises the following components: 42.9 parts circulating fluidized bed ash, 17.9 parts ground blast furnace slag, 3.6 parts silica fume, 7.1 parts PO 42.5 silicate cement, 0.29 parts sodium sulfate activator, and 28.6 parts water. The mass ratio of circulating fluidized bed fly ash to circulating fluidized bed slag in the circulating fluidized bed ash is 1:2.

[0055] The preparation method of cementitious materials for road base courses differs in that: the circulating fluidized bed slag is fed into a ball mill and ground for 60 minutes until the specific surface area is 870 m². 2 / kg, with an average particle size of 8.34 μm. The subsequent preparation method steps are the same as in Example 1.

[0056] The performance indicators of the cementitious material for road base obtained in Example 3 were tested, and the results are shown in Table 1.

[0057] Example 4 This embodiment illustrates a road base cementitious material prepared using circulating fluidized bed ash with different proportions. By mass, it comprises the following components: 42.2 parts circulating fluidized bed ash, 17.6 parts ground blast furnace slag, 3.5 parts silica fume, 7.0 parts PO 42.5 silicate cement, 0.4 parts sodium sulfate activator, and 29.6 parts water. The mass ratio of circulating fluidized bed fly ash to circulating fluidized bed slag in the circulating fluidized bed ash is 1:1.

[0058] Preparation method of cementitious material for road base course: The circulating fluidized bed slag is fed into a ball mill and ground for 55 minutes until the specific surface area is 850 m². 2 / kg, with an average particle size of 8.77 μm. The subsequent preparation steps are the same as in Example 1.

[0059] The performance indicators of the cementitious material for road base obtained in Example 4 were tested, and the results are shown in Table 1.

[0060] Example 5 This embodiment illustrates road base cementitious materials prepared using circulating fluidized bed ash in different proportions. By mass, it comprises the following components: 35.2 parts circulating fluidized bed ash, 16.9 parts ground blast furnace slag, 4.2 parts silica fume, 14.1 parts PO 42.5 silicate cement, 0.36 parts sodium sulfate activator, and 28.6 parts water. The mass ratio of circulating fluidized bed fly ash to circulating fluidized bed slag in the circulating fluidized bed ash is 1:1.

[0061] The preparation method of the cementitious material for road base course in this embodiment is as follows: the circulating fluidized bed slag is fed into a ball mill and ground for 55 min until the specific surface area is 850 m². 2 / kg, with an average particle size of 8.77 μm. Subsequent preparation steps were the same as in Example 1. The final road base cementitious material was obtained. SEM analysis was performed on the obtained road base cementitious material at different curing ages. The SEM scan results at a curing age of 3 days are shown below. Figure 3 As shown in the figure, the SEM electron microscope scan results after 28 days of curing are as follows. Figure 4 As shown. Overall, the microstructure mainly consists of C-(A)SH gel, ettringite, and unreacted Ca(OH)₂. Observation Figure 3It can be seen that at 3 days of hydration, Ca(OH)₂ crystals are clearly visible, and a small amount of flocculent C-(A)SH gel is formed on the particle surface and in the pores, but a continuous network structure has not yet been formed; the microstructure at 28 days of hydration is as follows: Figure 4 As shown, unreacted particles almost completely disappeared, and ettringite and a large number of continuous and dense C-(A)-SH gels interpenetrated each other, with the pores fully filled, forming a dense three-dimensional network structure. Figure 3 and Figure 1 The difference is Figure 3 With relatively fewer mesopores, the amount of C-(A)-SH gel formed is slightly higher than that of other gels. Figure 1 ;contrast Figure 4 and Figure 2 Discover, Figure 4 Less than Figure 2 The C-(A)-SH gel and ettringite are more evenly and densely distributed, and the pore structure is also more refined. The reason for the above-mentioned differences in microstructure is that the circulating fluidized bed slag in Example 5 was ground for a longer time and had a higher fineness than that in Example 1, which improved the early reaction activity and filling effect of the system. In addition, the amount of sodium sulfate activator in Example 5 was increased from 0.11 parts to 0.15 parts, which further promoted the pozzolanic reaction and the generation of hydration products, ultimately forming a microsystem with fewer pores and a more dense structure.

[0062] The performance indicators of the cementitious material for road base obtained in Example 5 were tested, and the results are shown in Table 1.

[0063] Example 6 This embodiment illustrates road base cementitious materials prepared using circulating fluidized bed ash and slag in different proportions. By mass, it comprises the following components: 32.6 parts circulating fluidized bed ash and slag, 26.1 parts ground blast furnace slag, 5.1 parts silica fume, 8.7 parts PO 42.5 silicate cement, 0.15 parts sodium sulfate activator, and 27.5 parts water. The mass ratio of circulating fluidized bed fly ash to circulating fluidized bed slag is 1:4. Same as Example 1.

[0064] Preparation method of cementitious material for road base course: The circulating fluidized bed slag is fed into a ball mill and ground for 60 minutes until the specific surface area is 870 m². 2 / kg, with an average particle size of 8.34 μm. The subsequent preparation method steps are the same as in Example 1.

[0065] The performance indicators of the cementitious material for road base obtained in Example 6 were tested, and the results are shown in Table 1.

[0066] Comparative Example 1 This comparative example serves as a comparative test demonstrating preparation without an alkaline environment (i.e., without the addition of an activator). The raw materials in this comparative example comprise the following components by mass: 32.6 parts circulating fluidized bed fly ash, 26.1 parts ground blast furnace slag, 5.1 parts silica fume, 8.7 parts PO 42.5 silicate cement, and 27.5 parts water. The mass ratio of circulating fluidized bed fly ash to circulating fluidized bed slag is 1:4. That is, the other component proportions in this comparative example are exactly the same as in Example 6, the only difference being the absence of the activator sodium sulfate.

[0067] The preparation method of the cementitious material for road base in this comparative example is as follows: the circulating fluidized bed slag is fed into a ball mill and ground for 60 min until the specific surface area is 870 m². 2 / kg, with an average particle size of 8.34 μm. The subsequent preparation steps are the same as in Example 1.

[0068] The performance indicators of the cementitious material for road base obtained in Comparative Example 1 were tested, and the results are shown in Table 1.

[0069] Comparative Example 2 This comparative example illustrates a comparative test conducted without the addition of ground blast furnace slag and silica fume. The difference between this comparative example and Example 1 is the absence of ground blast furnace slag and silica fume; all other settings are identical to Example 1. The performance indicators of the cementitious material for road base obtained in Comparative Example 2 were tested, and the results are shown in Table 1.

[0070] Comparative Example 3 This comparative example is used to demonstrate a comparative test without the addition of P.O42.5 silicate cement. The difference between this comparative example and Example 1 is that P.O42.5 silicate cement was not added; all other settings are exactly the same as in Example 1. The performance indicators of the road base cementitious material obtained in Comparative Example 3 were tested, and the results are shown in Table 1.

[0071] Comparative Example 4 This comparative example illustrates a comparative test where the circulating fluidized bed slag is not fully ball-milled. The difference between this comparative example and Example 1 is that in step S1, the ball mill is used for 20 min to obtain circulating fluidized bed slag powder with an average particle size of 50 μm (i.e., the ball milling time and particle size of the circulating fluidized bed slag powder are not within the range defined by this invention). Other settings are exactly the same as in Example 1. The performance indicators of the road base cementitious material obtained in Comparative Example 4 were tested, and the results are shown in Table 1.

[0072] Performance testing 1. Setting time: The setting time is determined in accordance with GB / T 1346-2024 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement". To ensure the construction quality, the setting time of the cementitious material used for road base is extended compared with that of the general cement.

[0073] 2. Linear expansion rate: The linear expansion rate is determined in accordance with JC / T 313-2009 "Test Method for Expansion Rate of Expansive Cement". Operating method: The specimen size is 25 mm×25 mm×280 mm. After standing for 24 h, it is demolded, and the initial length reference line is immediately marked. The length change is measured after curing in water to the corresponding age. The linear expansion rate E x (%) calculation formula: E x =(L x -L1) / 250×100.

[0074] 3. Mechanical properties: The mechanical properties are determined by operating in accordance with GB / T 17671-2021 "Test Methods for Strength of Cement Mortar". Operating method: The specimen size is 40 mm×40 mm×160 mm. It is demolded within 20 - 24 h after the test block is formed and the flexural strength and compressive strength are tested after curing under standard conditions to the corresponding age. The strength grade of the cementitious material used for road base in this invention can reach grade 42.5.

[0075] 4. Soundness: The soundness is determined by referring to GB / T 1346-2024 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement", detected by the boiling method, and determined by the Le Chatelier method or the test piece method. The Le Chatelier method is adopted in this invention, and the increase value of the distance between the pointers of the Le Chatelier mold after boiling is measured. If it is ≤5.0 mm, it is regarded as qualified.

[0076] After detecting the performance of the above-mentioned examples and comparative examples, the results shown in Table 1 are obtained. Table 1 is a comparison table of the performance parameters of each example and comparative example.

[0077] Table 1 From the results of each item in Table 1, it can be concluded that: From the results of Example 1 and Example 6, it can be seen that by extending the grinding time of circulating fluidized bed slag, the degree of hydration reaction in the cementitious system can be deepened and the reaction process can be accelerated, promoting the full release of the expansion of the material in the early stage of hardening, effectively avoiding the risk of volume unsoundness in the later stage, and laying a solid foundation for improving the mechanical properties of the material.

[0078] By comparing Example 6 and Comparative Example 1, it can be seen that the strength of Example 6 is higher than that of Comparative Example 1, especially the flexural strength and compressive strength in the middle and later stages. This is because the raw materials of Example 6 contain sodium sulfate activator, which can significantly accelerate and enhance the hydration reaction of the cementitious system compared with Comparative Example 1, which does not contain sodium sulfate, so that the setting time meets the specification requirements. At the same time, it promotes the formation of ettringite in the system, thereby significantly improving the strength of the cementitious material in the middle and later stages.

[0079] By comparing Example 1 and Comparative Example 2, it was found that both the early and late strengths were reduced and the volume stability was decreased. This was because the lack of addition of finely ground blast furnace slag and silica fume led to a weakening of the pozzolanic reaction in the system, a lack of micro-aggregate filling effect, a reduction in the amount of hydration products generated, and a decrease in structural density.

[0080] By comparing Example 1 and Comparative Example 3, it was found that the setting time was prolonged, the early strength was almost non-existent, and the 28-day strength was reduced. This is because cement is the core component that provides the initial hydration products and alkaline environment. Without the addition of cement, the pH value in the system will be weakened, which will not effectively stimulate the pozzolanic activity of circulating fluidized bed ash and finely ground blast furnace slag, resulting in a low degree of early hydration and failure to form an effective cementitious structure.

[0081] Comparative analysis of Example 1 and Comparative Example 4 revealed that the strength at all ages was lower than that of Example 1, and the microstructure contained a large number of unreacted particles. This is because the slag of the circulating fluidized bed furnace has a larger particle size, resulting in insufficient surface active sites and inadequate inter-particle contact, which inhibits the reaction rate and degree of the pozzolanic material. Simultaneously, the coarse particles cannot effectively play the filling role of the micro-aggregates, leading to increased system porosity and decreased structural density, ultimately failing to reach the 42.5 strength grade.

[0082] As shown in Table 1, Examples 1 to 6 of this invention all exhibit a retarding effect, with initial setting time greater than 300 min and final setting time controlled between 360 min and 720 min, which is beneficial for actual construction operations. The expansion performance of the cementitious material is stable and controllable, with a 7-day linear expansion rate greater than 0.1% and a 28-day linear expansion rate less than 0.5%. The mechanical properties of each example meet the requirements of grade 42.5, and the stability test results are qualified. In summary, although this invention uses fluidized bed ash and ground slag as solid waste as raw materials, the cementitious material for road base courses prepared from these solid wastes meets the performance requirements for road base course gel materials, such as retarding effect and controllable expansion performance. It has excellent mechanical properties and good construction effect, thus demonstrating that this invention truly realizes the effective utilization of solid waste, turning harm into benefit and increasing the added value of solid waste utilization.

[0083] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A cementitious material for a recycled fluidized bed ash-based road base, characterized by, By weight parts include: circulating fluidized bed ash 29~43 parts, ground blast furnace slag 16~27 parts, silica fume 3~6 parts, P.O42.5 Portland cement 7~15 parts, activator 0.1~0.4 parts and water 27~30 parts; the circulating fluidized bed ash is the circulating fluidized bed fly ash with specific surface area of 700~800 m 2 / kg and the circulating fluidized bed slag with average particle size of 8~10 µm and specific surface area of 700~900 m 2 / kg are mixed in a mass ratio of (2~5):(5~10).

2. The cementitious material for a recycled fluidized bed ash-based road base layer according to claim 1, characterized by, The circulating fluidized bed fly ash has a SiO2 content of 35-40%, an Al2O3 content of 25-30%, a CaO content of 15-20%, and a SO3 content of 5-10%. The circulating fluidized bed fly ash has a SiO2 content of 35-40%, an Al2O3 content of 25-30%, a CaO content of 15-20%, and a SO3 content of 5-10%.

3. The cementitious material for a recycled fluidized bed ash-based road base layer according to claim 1 or 2, characterized by, The activator is sodium sulfate.

4. The cementitious material for a recycled fluidized bed ash-based road base layer according to claim 1 or 2, characterized by, The circulating fluidized bed ash is a mixture of the circulating fluidized bed fly ash and the circulating fluidized bed slag in a mass ratio of (2-5):(5-8).

5. The cementitious material for a recycled fluidized bed ash-based road base layer according to claim 1 or 2, characterized by, The circulating fluidized bed slag is a circulating fluidized bed slag powder having an average particle size of 8-10 µm and a fineness of 3-7%.

6. The cementitious material for a recycled fluidized bed ash-based road base layer according to claim 1 or 2, characterized by, The ground blast furnace slag is S95 grade, and the specific surface area is 600-700 m 2 / kg; The specific surface area of the silica fume is 20000-21000 m 2 / kg; The specific surface area of the P.O 42.5 Portland cement is 350-400 m 2 / kg.

7. The cementitious material for a recycled fluidized bed ash-based road base layer according to claim 6, characterized by, The ground blast furnace slag has a particle size distribution of D10 of 1-1.5 µm, D50 of 9.5-10 µm, and D90 of 30-30.5 µm. The silica ash has a particle size distribution D50 of 0.1-0.3 µm, and a SiO2 content of 90-95%.

8. A method for producing a cementitious material for a recycled fluidized bed ash-based road base, characterized by, The preparation method is a method for preparing the circulating fluidized bed ash-based cementitious material for road base layers according to any one of claims 1-7, comprising the following steps: S1, putting 14.5-34.4 parts by weight of the circulating fluidized bed slag into a ball mill for grinding for 40-60 min to obtain a circulating fluidized bed slag powder having an average particle size of 8-10 µm and a sieve residue percentage of 3-7%; The fly ash of circulating fluidized bed with specific surface area of 700~800 m 2 / kg is mixed with the obtained circulating fluidized bed slag powder according to the mass ratio of (2~5):(5~10) to obtain 29~43 parts by weight of circulating fluidized bed ash. S2, mixing the circulating fluidized bed ash obtained in step S1, 16-27 parts by weight of the ground blast furnace slag, 3-6 parts by weight of the silica ash, and 7-15 parts by weight of the P.O 42.5 Portland cement to obtain a solid mixed powder; S3, mixing 0.1-0.4 parts by weight of the activator with 27-30 parts by weight of water and fully dissolving to obtain a liquid mixture; S4, pouring the solid mixed powder obtained in step S2 and the liquid mixture obtained in step S3 into a stirring component for uniform stirring to fully mix the mixture, and the stirring process is divided into three stages: in the initial stirring stage, the stirring speed is 140-160 rpm, the cement particles are fully dispersed and hydrated, the volume of the cementitious mixture begins to shrink and Ca(OH)2 is generated; then in the middle stirring stage, the stirring speed is 290-310 rpm, so that the circulating fluidized bed ash reacts with the generated Ca(OH)2 to rapidly generate ettringite, the cementitious mixture produces micro-expansion, and the generated ettringite is coated on the surface of the cement particles; in the later stirring stage, the stirring speed is 65-85 rpm, the ground blast furnace slag and the silica ash continue to dissolve under the activation of Ca(OH)2, continuously dissolve and polymerize to generate C-(A)-S-H gel and ettringite hydration products, form a dense network structure, and the generated ettringite continues to be coated on the surface of the cement particles; the initial stirring stage lasts for 4-6 min, the middle stirring stage lasts for 8-12 min, and the later stirring stage lasts for 4-6 min. S5, the completely mixed slurry of step S4 is cast into a mold for curing to obtain the cementitious material for road base.

9. The method for producing a cementitious material for a recycled fluidized bed ash-based road base according to claim 8, characterized in that, In step S3, the sufficient dissolving is performed by a magnetic stirrer at a speed of 240-260 rpm for 5-10 min; In step S4, the uniform stirring is performed at a speed of 150 rpm for 5 min, then at a speed of 300 rpm for 10 min, and finally at a speed of 75 rpm for 5 min.

10. The method for producing a cementitious material for a recycled fluidized bed ash-based road base according to claim 8 or 9, characterized in that, The obtained cementitious material for road base has an initial setting time of not less than 300 min, a final setting time of 360-720 min, a linear expansion rate of not less than 0.1% at 7 d and not more than 0.5% at 28 d, a 3 d flexural strength of not less than 4.0 MPa and a 3 d compressive strength of not less than 17.0 MPa, a 28 d flexural strength of not less than 6.5 MPa and a 28 d compressive strength of not less than 42.5 MPa.

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