Garbage incineration fly ash artificial aggregate and preparation method thereof

Abstract

The invention relates to a waste incineration fly ash artificial aggregate and a preparation method thereof. The method comprises the following steps: uniformly mixing the waste incineration fly ash, cement and fly ash, then adding water, and uniformly stirring to obtain an aggregate mixture; placing the aggregate mixture in a mold for compression molding to obtain a molded product; the compression molding comprises the following steps: pre-pressing for 10-20 seconds at 6-10 MPa, then pressing for 20-40 seconds at a medium pressure of 12-18 MPa, then uniformly increasing the pressure to a high pressure of 22-28 MPa, and maintaining the pressure for 4-6 seconds at the high pressure of 22-28 MPa; and performing standard curing on the molded product, demolding to obtain a demolded sample, and sequentially performing crushing treatment and steam curing to obtain the waste incineration fly ash artificial aggregate. The prepared waste incineration fly ash artificial aggregate is low in crushing value, low in water absorption rate, high in strength and high in heavy metal curing capacity, a feasible path is provided for resource utilization of waste incineration fly ash, and the waste incineration fly ash artificial aggregate has important environmental protection value and economic value.

Description

Technical Field

[0001] This invention belongs to the field of building material resource utilization technology of waste incineration fly ash, and particularly relates to an artificial aggregate made from waste incineration fly ash and its preparation method. Background Technology

[0002] The rapid urbanization and rising consumption capacity of residents in my country are driving a surge in the total amount of urban household waste. Data shows that in recent years, the annual output of urban household waste nationwide has exceeded 200 million tons, and continues to grow at a rate of 8%-10% annually. The increasing production of fly ash from household waste incineration not only occupies a large amount of land resources but also poses a potential threat to the environment. The increasingly serious problem of "garbage surrounding cities" makes the resource utilization and harmless treatment of waste a critical challenge that urgently needs to be addressed, creating an urgent need for technologies for the safe disposal and resource utilization of fly ash from waste incineration. Among various treatment methods, waste-to-energy incineration can significantly reduce the volume of waste by about 90% through high-temperature incineration. Compared with traditional landfill methods, it requires less land and effectively alleviates the pressure on urban land resources. Simultaneously, the heat energy generated during incineration can be converted into electricity, achieving resource recycling. Therefore, waste-to-energy incineration, as a highly efficient and environmentally friendly treatment technology, has become a major approach to disposing of household waste in my country.

[0003] Waste-to-energy incineration produces fly ash as a byproduct. The incineration of municipal solid waste generates various secondary pollutants, including heavy metals, dioxins, and soluble chlorides. These pollutants typically accumulate in the fly ash, resulting in high levels of heavy metal leaching and highly toxic dioxins. Currently, landfilling remains the primary method for disposing of fly ash. Other treatment methods, such as cement solidification and chelating agent stabilization, are two major technologies for immobilizing heavy metals in fly ash. It is roughly estimated that over two-thirds of fly ash is treated with chelating agents, while less than one-third is solidified with cement, both ultimately ending up in landfills. However, chelated or cement-solidified fly ash has poor long-term sustainability in landfills, and heavy metals easily leach out, polluting surrounding soil and groundwater. Therefore, developing resource-based treatment methods for incineration fly ash is urgently needed.

[0004] Currently, with my country's sustained economic growth, infrastructure projects and major engineering projects have become development priorities, leading to a growing demand for construction sand and gravel. However, natural sand and gravel resources are dwindling due to long-term, large-scale mining, resulting in a shortage of aggregate supply. This severely impacts construction progress and causes significant environmental damage. Incineration fly ash shares similar physical properties with natural aggregates, making it a viable option for use in building materials. Therefore, research into environmentally friendly artificial aggregates is urgently needed. Domestic research on aggregates currently focuses on high-energy-consuming aggregates such as expanded clay aggregates. In contrast, using incineration fly ash to prepare artificial aggregates, employing compression molding technology, eliminates the need for high-temperature treatment, resulting in a simple, low-cost, and environmentally friendly artificial aggregate preparation technology that can effectively alleviate the shortage of natural aggregates. However, due to the loose particle size and high porosity of fly ash, traditional compression molding processes easily lead to internal gas retention or stress concentration, resulting in high porosity, high water absorption, high crushing value, low strength, and weak heavy metal solidification ability in the aggregates.

[0005] In summary, it is essential to provide an artificial aggregate from waste incineration fly ash and its preparation method. Summary of the Invention

[0006] To address one or more technical problems existing in the prior art, this invention provides an artificial aggregate from waste incineration fly ash and its preparation method. The artificial aggregate from waste incineration fly ash prepared by this invention is more dense, has a lower crushing value, lower water absorption, higher aggregate strength, and stronger heavy metal solidification ability. It can solve the problem of large-scale fly ash disposal and achieve resource recycling, showing broad development prospects. This invention can replace traditional methods of landfilling fly ash to alleviate urban land resource pressure and the shortage of natural aggregate resources, providing a new way to utilize waste incineration fly ash resources, and has significant environmental and economic value. This invention solves the problems of high energy consumption and high carbon emissions in the preparation of artificial aggregate from fly ash in existing technologies, and also solves the performance defects of artificial aggregates prepared by existing technologies, such as high water absorption, low strength, and weak heavy metal solidification ability.

[0007] The present invention provides a method for preparing artificial aggregate from waste incineration fly ash in a first aspect, the method comprising the following steps: (1) Mix the fly ash from waste incineration, cement and fly ash evenly to obtain a mixture, then add water to the mixture and stir evenly to obtain an aggregate mixture; (2) The aggregate mixture is placed in a mold and pressed to obtain a molded product; the pressing is first pre-pressed at 6~10MPa for 10~20s, then pressed at 12~18MPa for 20~40s, and then uniformly increased to a high pressure of 22~28MPa and held at 22~28MPa for 4~6s. (3) After the molded material is initially cured, it is demolded to obtain a demolded pattern. Then the demolded pattern is crushed and steam cured in sequence to obtain artificial aggregate of waste incineration fly ash.

[0008] Preferably, the mixture contains 30-70% by mass of waste incineration fly ash; and / or the amount of cement accounts for 55-65% of the sum of the mass of the cement and the fly ash, preferably 60%.

[0009] Preferably, the cement is PO42.5 ordinary Portland cement; and / or the fly ash is Grade I fly ash.

[0010] Preferably, the aggregate mixture contains 6-10% water by mass.

[0011] Preferably, the pre-pressing pressure and / or the intermediate-pressure pressing pressure are applied at a constant pressure; the uniform pressurization is performed by uniformly increasing the pressure at a rate of 0.2 MPa / s to 0.3 MPa / s.

[0012] Preferably, the pressing process involves first pre-pressing at 8MPa for 10-20s, then pressing at 15MPa for 20-40s, and then uniformly increasing the pressure to a high of 25MPa and holding at 25MPa for 4-6s.

[0013] Preferably, the preliminary curing is performed for 22-26 hours at a temperature of 18-22℃ and a relative humidity of ≥90%; and / or the steam curing is performed for 10-15 hours at a temperature of 78-82℃ and a relative humidity of 100%.

[0014] Preferably, the pressure difference between the intermediate pressure and the pre-pressure is 5~8MPa; the pressure difference between the high pressure and the intermediate pressure is 9~12MPa.

[0015] Preferably, the crushing value of the artificial aggregate from the waste incineration fly ash is less than 19%, and the water absorption rate is not greater than 8%.

[0016] In a second aspect, the present invention provides an artificial aggregate of waste incineration fly ash prepared by the preparation method described in the first aspect of the present invention.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: (1) This invention provides a new way to safely dispose of and utilize fly ash from waste incineration. Untreated fly ash from waste incineration (such as fly ash from municipal solid waste incineration) can be directly used to prepare artificial aggregates, which can replace sand and gravel aggregates in concrete in construction projects, reduce the mining of natural aggregates, and the amount of fly ash in the raw material ratio proposed in this invention can be no less than 50%, with high fly ash utilization rate, effectively realizing the resource utilization of solid waste, thereby significantly reducing the production cost and carbon emissions of artificial aggregates.

[0018] (2) The present invention adopts gradient pressure control technology, which divides the aggregate compression molding stage into pre-compression stage (low pressure), medium pressure stage, high pressure stage and pressure holding stage. The present invention found that by controlling the pressure and time in stages, the aggregate mixture can be de-vented and compacted, which is conducive to achieving the densification molding of aggregate. The gradient pressure control technology in the present invention can effectively expel closed pore air, improve compaction degree, reduce microcracks, improve aggregate strength and compactness, and ultimately significantly reduce the crushing value and water absorption rate of fly ash artificial aggregate, and significantly improve cylinder compression strength.

[0019] (3) The artificial aggregate prepared by the present invention using fly ash from waste incineration as the main raw material has a crushing value of less than 19%, which meets the standard of (II) aggregate. At the same time, the water absorption rate is controlled within 8.0%, which meets the technical requirements of (III) aggregate. Furthermore, the heavy metal leaching concentration (Zn, Pb, Cd, Ni, Cu) of the artificial aggregate prepared by the present invention is lower than the national standard limit, the environmental risk is controllable, and it has the potential for practical engineering application.

[0020] (4) The present invention adopts a low-temperature heat curing process (that is, steam curing the crushed fly ash aggregate at 80℃±2℃), which generates more CSH gel in a short time compared with the standard curing conditions, improves early strength, and shortens curing time; the active substances in fly ash are glassy SiO2 and Al2O3, and the SO4 in fly ash 2- It reacts more readily with the cement hydration product Ca(OH)2 to generate additional CSH gel and / or ettringite (AFt), filling pores and increasing density; it accelerates moisture migration and evaporation, reducing internal defects, while the generated CSH gel is denser, reducing total porosity; under standard curing conditions, the hydration products are mainly CSH gel and Ca(OH)2, while steam curing may promote the transformation of CSH gel into CSH crystals with a higher degree of polymerization, and even generate tobermorite, significantly improving strength and durability.

[0021] (5) The present invention uses fly ash aggregate prepared by some preferred technical solutions to replace natural aggregate in the preparation of concrete, which can make the compressive strength of concrete after 28 days of standard curing reach more than 49.3 MPa (meeting the C40 requirement), which is high-performance concrete, and can exhibit excellent resistance to sulfate attack and carbonation. Heavy metal leaching test shows that the heavy metal leaching concentration of the artificial aggregate of waste incineration fly ash in the present invention and the concrete is lower than the national standard limit, and the environmental safety is good. The present invention provides a feasible path for the resource utilization of waste incineration fly ash, and has important environmental and economic value. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the preparation process of the present invention; Figure 2 This is a physical image of the artificial aggregate made from waste incineration fly ash prepared in Example 1 of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] This invention provides a method for preparing artificial aggregates using waste incineration fly ash, and the resulting waste incineration fly ash artificial aggregates. The performance of these fly ash artificial aggregates and environmental risk assessments were also conducted.

[0026] In its first aspect, this invention provides a method for preparing artificial aggregate from waste incineration fly ash, including a preparation flow chart, for example... Figure 1 As shown, the method includes the following steps: (1) Mix the waste incineration fly ash, cement, and fly ash evenly to obtain a mixture. Then add water to the mixture and stir evenly to obtain an aggregate mixture. The waste incineration fly ash in this invention is untreated incineration fly ash. In this invention, waste incineration fly ash can be simply referred to as incineration fly ash. In this invention, the operation of adding water to the mixture and stirring evenly is performed in... Figure 1The process is referred to as uniform mixing. Specifically, step (1) is as follows: fly ash from waste incineration, cement, and fly ash are placed in a mixing pot according to the mass ratio of the mixture and dry-mixed for 40-80 seconds to obtain a mixture. Then, water is added to the mixture in the mixing pot while stirring. The stirring is continued for 2-4 minutes until the mixture is uniform and a homogeneous mixture is formed, which is the uniformly mixed aggregate mixture. The present invention does not specifically limit the speed of the dry mixing and the stirring. Those skilled in the art can choose conventionally, for example, 400-800 r / min. (2) The aggregate mixture is placed in a mold and pressed to obtain a molded product; the pressing is performed by first pre-pressing at 6~10MPa (e.g., 6, 7, 8, 9 or 10MPa) for 10~20s (e.g., 10, 15 or 20s), then pressing at 12~18MPa (e.g., 12, 13, 14, 15, 16, 17 or 18MPa) for 20~40s (e.g., 20, 25, 30, 35 or 40s), then uniformly increasing the pressure to a high pressure of 22~28MPa (e.g., 22, 23, 24, 25, 26, 27 or 28MPa) and holding the pressure at 22~28MPa (e.g., 22, 23, 24, 25, 26, 27 or 28MPa) for 4~6s. (e.g., 4, 5 or 6 s); In this invention, the pressure is applied by a pressure testing machine for pressing and molding. This invention does not specifically limit the pressure testing machine and mold used, and those skilled in the art can make conventional selections as needed; The mold can be, for example, a cylindrical steel mold with an inner diameter of 150 mm and a height of 130 mm, and the pressure testing machine can be, for example, a 3000 kN pressure testing machine; In this invention, the pressure is increased from the medium pressure to the high pressure of 22~28 MPa, which is called the high pressure stage. The high pressure stage is the slow loading of pressure, for example, the pressure can be uniformly increased to the high pressure of 22~28 MPa within 30~90 s; Specifically, step (2) is, for example, mixing the uniformly mixed aggregate. The aggregate mixture is loaded into a steel mold and placed in a pressure testing machine for pressing and molding. Gradient pressure control technology is used to perform staged venting and compaction of the aggregate mixture. This invention reveals that during the pre-compression stage, a constant pressure of 6-10 MPa is applied to the aggregate mixture for 10-20 seconds, which helps to expel air between particles and reduce closed pores. During the medium-compression stage, a constant pressure of 12-18 MPa is applied to the aggregate mixture for 20-40 seconds, which can initially compact the particle skeleton. During the high-compression stage, a slow pressure application of 12-18 MPa to 22-28 MPa (e.g., slow pressure application completed within 30-90 seconds) is beneficial for achieving plastic deformation and bonding of the particles. During the holding pressure stage, a pressure of 22-28 MPa is applied... The pressure is maintained for 4-6 seconds, which helps the particles to fully recombine. After maintaining the pressure for 4-6 seconds, the load is removed to complete the densification of the aggregate. In addition to pressure control at each pressure stage, the time control of each pressure stage is also crucial. If the pre-compression and intermediate pressure stages are not long enough, the gas will not be completely discharged, resulting in more closed pores inside. If the high pressure and holding time are too short, elastic rebound and loose structure may occur, which are not conducive to reducing water absorption and / or crushing value. If the pre-compression, intermediate pressure and high pressure times are too long, it will also affect the overall particle shape of the aggregate. In fact, if the high pressure stage is too long, it may easily cause excessive crushing of particles, which is also not conducive to reducing water absorption and / or crushing value. (3) After the molded material is initially cured, it is demolded to obtain a demolded pattern. Then, the demolded pattern is crushed and cured with aggregate (i.e., steam curing) to obtain waste incineration fly ash artificial aggregate (abbreviated as fly ash artificial aggregate). The present invention adopts the form of crushing the aggregate mixture into aggregate after gradient pressure pressing and initial curing. This can make the aggregate particles have more edges and rough surfaces, which is beneficial to improving the bonding ability with cement paste and improving the performance of fly ash artificial aggregate. Specifically, step (3) is, for example: initial curing (curing with mold): the molded specimen (molded material) together with the mold is placed in a constant temperature and humidity curing chamber (temperature 20℃±2℃, relative humidity ≥90%) and left to stand for 24 hours±2 hours for initial curing. Then, the sample is demolded to obtain a demolded sample (demolded sample); Crushing treatment: The demolded sample (demolded sample) is crushed to obtain aggregate particles that meet the particle size requirements. In this invention, the particle size of the aggregate particles is 5~25mm; Aggregate curing: The crushed aggregate particles are steam cured. The steam curing process is as follows: The aggregate particles are placed in a steam curing chamber, the temperature is set to 80℃±2, the relative humidity is 100%, and the curing time is 10~15h to obtain artificial aggregate from waste incineration fly ash with excellent performance. The artificial aggregate from waste incineration fly ash obtained by this invention has a low crushing value, low water absorption, high strength, and strong heavy metal solidification ability. This invention provides a feasible path for the resource utilization of waste incineration fly ash and has important environmental and economic value.

[0027] This invention provides a new approach for the safe disposal and resource utilization of waste incineration fly ash. Untreated waste incineration fly ash (e.g., municipal solid waste incineration fly ash) can be directly used in the preparation of artificial aggregates, replacing sand and gravel aggregates in concrete construction, reducing the mining of natural aggregates. Furthermore, the fly ash content in the raw material mix proposed in this invention can be no less than 50%, resulting in high fly ash utilization and effectively realizing the resource utilization of solid waste. This significantly reduces the production cost and carbon emissions of artificial aggregates. This invention employs gradient pressure control technology, dividing the aggregate compression molding stage into a pre-compression stage (low pressure), a medium pressure stage, a high pressure stage, and a holding pressure stage. This invention discovers that staged pressure and time control can degas and compact the aggregate mixture, facilitating the densification of the aggregate. The gradient pressure control technology in this invention effectively removes closed pore air, increases compaction, reduces microcracks, and improves aggregate strength and density. Ultimately, it significantly reduces the crushing value and water absorption rate of fly ash artificial aggregates and significantly improves cylinder compressive strength. This invention produces artificial aggregate using fly ash from waste incineration as the main raw material. The crushing value is less than 19%, meeting the standards for Class II aggregates. Simultaneously, the water absorption rate is controlled within 8.0%, meeting the technical requirements for Class III aggregates. Furthermore, the heavy metal leaching concentrations (Zn, Pb, Cd, Ni, Cu) of the artificial aggregate prepared by this invention are all below the national standard limits, indicating controllable environmental risks and potential for practical engineering applications. This invention employs a low-temperature thermal curing process (steam curing the crushed fly ash aggregate at 80℃±2℃). Compared to standard curing conditions, this process generates more CSH gel in a shorter time, improving early strength and shortening curing time. This saves energy and yields artificial aggregates from waste incineration fly ash with superior performance. The active substances in fly ash, such as the glassy SiO2 and Al2O3, and the SO4 in fly ash... 2- It reacts more readily with the cement hydration product Ca(OH)2 to generate additional CSH gel and / or ettringite (AFt), filling pores and increasing density; it accelerates moisture migration and evaporation, reducing internal defects, while the generated CSH gel is denser, reducing total porosity; under standard curing conditions, the hydration products are mainly CSH gel and Ca(OH)2, while steam curing may promote the transformation of CSH gel into CSH crystals with a higher degree of polymerization, and even generate tobermorite, significantly improving strength and durability.

[0028] According to some preferred embodiments, the mixture contains 30-70% (e.g., 30%, 40%, 50%, 60% or 70%) of the mass percentage of waste incineration fly ash; the amount of cement used accounts for 55-65% (e.g., 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64% or 65%) of the sum of the mass of the cement and the fly ash, preferably 60%.

[0029] According to some preferred embodiments, the cement is PO42.5 ordinary Portland cement; and / or the fly ash is Grade I fly ash.

[0030] According to some preferred embodiments, the aggregate mixture contains 6 to 10% water by mass (e.g., 6%, 7%, 8%, 9% or 10%); for example, in some specific embodiments, the mass ratio of water in the aggregate mixture to the mixture formed from waste incineration fly ash, cement and fly ash is 1:12, that is, the water-to-material ratio is 1:12.

[0031] According to some preferred embodiments, the pre-compression pressure and / or the intermediate-compression pressure are applied at a constant pressure; the uniform pressure increase is performed at a pressure loading rate of 0.2 MPa / s to 0.3 MPa / s (e.g., 0.2, 0.25, or 0.3 MPa / s); in this invention, it is preferred to use constant pressure loading during the pre-compression and intermediate-compression stages, and then uniformly increase the pressure to 22 to 28 MPa at a pressure loading rate of 0.2 MPa / s to 0.3 MPa / s and hold the pressure. This is beneficial for gradually densifying the bonding between particles inside the aggregate during the molding process, effectively avoiding stress concentration and microcracks caused by instantaneous high-pressure loading, thereby improving structural uniformity and stability. This not only enables the artificial aggregate made from waste incineration fly ash to achieve higher molding density during the compression process, but also significantly improves the internal pore structure of the aggregate, reducing the formation of interconnected pores and / or macropores. Therefore, the crushing value of the resulting artificial aggregate made from fly ash is reduced, and the water absorption rate is significantly reduced. This invention improves the compressive strength and durability of the aggregate, resulting in superior mechanical and performance properties. The invention also finds that controlling the high-pressure stage within a suitable loading speed range allows for a balance between sufficient plastic deformation and bonding of particles and uniform stress transfer, ensuring high density and excellent mechanical properties of the formed aggregate. If the pressure loading speed is too fast, the aggregate mixture will be subjected to sudden high external forces in a short time, easily causing uneven stress distribution between particles, resulting in microcracks or localized breakage. This, in turn, reduces the overall density and mechanical strength of the formed product. It may also prevent moisture from migrating internally, forming localized water pockets and increasing the porosity and water absorption rate of the aggregate. Conversely, if the pressure loading speed is too slow, the aggregate mixture may experience excessive particle breakage during prolonged high-pressure operation, leading to localized relaxation, low pressing efficiency, and insufficient forming density. Excessive moisture removal may also cause shrinkage cracks, ultimately reducing the performance of the fly ash-based artificial aggregate.

[0032] According to some preferred embodiments, the pressing process involves first pre-pressing at 8 MPa for 10-20 seconds, then pressing at 15 MPa for 20-40 seconds, and then uniformly increasing the pressure to a high pressure of 25 MPa and holding at 25 MPa for 4-6 seconds, preferably 5 seconds. In this invention, the pressing process is carried out at room temperature, for example, room temperature of 15-35°C.

[0033] According to some preferred embodiments, the preliminary curing is performed at a temperature of 18~22℃, preferably 20℃, and a relative humidity of ≥90% for 22~26h, preferably 24h; and / or the steam curing is performed at a temperature of 78~82℃, preferably 80℃, and a relative humidity of 100% for 10~15h, preferably 12h.

[0034] According to some preferred embodiments, the pressure difference ΔP1 between the intermediate pressure pressing and the pre-pressing is 5~8MPa (e.g., 5, 6, 7 or 8MPa); the pressure difference ΔP2 between the high pressure and the intermediate pressure pressing is 9~12MPa (e.g., 9, 10, 11 or 12MPa). In this invention, preferably, 5MPa≤ΔP1≤8MPa and 9MPa≤ΔP2≤12MPa, to better ensure sufficient gas discharge, which is conducive to promoting plastic bonding of aggregate particles, thereby significantly reducing crushing value and water absorption, improving the structural density of artificial aggregate, and obtaining high-performance waste incineration fly ash artificial aggregate. This invention has found that if ΔP1<5MPa, insufficient venting is likely to form closed pores; if ΔP2<9MPa, the plastic compaction effect is not obvious; and if ΔP2>12MPa, local pulverization and aggregate surface cracking may easily occur.

[0035] According to some preferred embodiments, the crushing value of the waste incineration fly ash artificial aggregate is less than 19%, and the water absorption rate is not greater than 8%. The fly ash artificial aggregate prepared by the present invention using waste incineration fly ash as the main raw material has a crushing value of less than 19%, which meets the (II) aggregate standard. This indicates that the fly ash artificial aggregate prepared by the process of the present invention has good mechanical properties and durability, strong anti-crushing ability, dense internal structure, and a compressive strength of more than 10 MPa, which is significantly improved compared with conventional recycled aggregate (5~8 MPa). At the same time, the water absorption rate of the fly ash artificial aggregate prepared by the present invention is controlled within 8.0%, which meets the technical requirements of (III) aggregate. This indicates that the aggregate surface has good pore sealing and low water absorption. The fly ash artificial aggregate prepared by the present invention achieves a good balance between strength and water absorption performance, showing high potential for practical engineering applications.

[0036] In a second aspect, the present invention provides an artificial aggregate of waste incineration fly ash prepared by the preparation method described in the first aspect of the present invention.

[0037] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments. The present invention may have many other embodiments, and those skilled in the art can make various corresponding changes and modifications based on the present invention without departing from its spirit and essence; however, all such corresponding changes and modifications should fall within the scope of protection of the appended claims.

[0038] The waste incineration fly ash used in the following examples and comparative examples is waste incineration fly ash from a power plant in Boluo. The cement used in the following examples and comparative examples is silicate cement, specifically commercially available China Resources PO42.5 ordinary silicate cement. The fly ash used in the following examples and comparative examples is Grade I fly ash produced by a power plant in Zhengzhou.

[0039] Example 1 ① Place the waste incineration fly ash, cement, and fly ash in a mixing pot at a mass ratio of 1125:675:450 and dry mix for 60 seconds to obtain a mixture. Then, add water to the mixture in the mixing pot while stirring, and continue stirring for 3 minutes until the mixture is uniform and a homogeneous mixture is formed, which is the uniform aggregate mixture. The mixture contains 50% waste incineration fly ash by mass, and the cement content accounts for 60% of the total mass of cement and fly ash; the water-to-material ratio is 1:12.

[0040] ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing process involves first loading a constant pressure of 8MPa (pre-pressing) for 15s, then loading a constant pressure of 15MPa (medium-pressure pressing) for 30s, and then uniformly increasing the pressure from 15MPa to a high pressure of 25MPa at a pressure loading rate of 0.25MPa / s, and then unloading the load after holding the pressure at 25MPa for 5s.

[0041] ③ Place the molded material connected to the mold in a constant temperature and humidity curing chamber (temperature 20℃, relative humidity 90%) and let it stand (preliminary curing) for 24 hours, then remove the mold to obtain the demolded sample.

[0042] ④ The demolded pattern is crushed to obtain aggregate particles that meet the particle size requirements (particle size 5~25mm).

[0043] ⑤ The crushed aggregate particles are placed in a steam curing chamber at 80℃ and 100% relative humidity for 12 hours to produce artificial aggregate from waste incineration fly ash.

[0044] A physical image of the artificial aggregate made from waste incineration fly ash in this embodiment is shown below. Figure 2 As shown.

[0045] Example 2 Example 2 is basically the same as Example 1, except that: ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing process involves first loading a constant pressure of 8MPa for 15s, then loading a constant pressure of 15MPa for 30s, and then uniformly increasing the pressure from 15MPa to a high pressure of 25MPa at a pressure loading rate of 0.1MPa / s, and then unloading the load after holding the pressure at 25MPa for 5s.

[0046] Example 3 Example 3 is basically the same as Example 1, except that: ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing process involves first loading a constant pressure of 8MPa for 15s, then loading a constant pressure of 15MPa for 30s, and then uniformly increasing the pressure from 15MPa to a high pressure of 25MPa at a pressure loading rate of 0.5MPa / s, and then unloading the load after holding the pressure at 25MPa for 5s.

[0047] Example 4 Example 4 is basically the same as Example 1, except that: ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing process involves first loading a constant pressure of 8MPa for 15s, then loading a constant pressure of 12MPa for 30s, and then uniformly increasing the pressure from 12MPa to a high pressure of 28MPa at a pressure loading rate of 0.25MPa / s, and then unloading the load after holding the pressure at 28MPa for 5s.

[0048] Example 5 Example 5 is basically the same as Example 1, except that: ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing process involves first loading a constant pressure of 8MPa for 15s, then loading a constant pressure of 18MPa for 30s, and then uniformly increasing the pressure from 18MPa to a high pressure of 22MPa at a pressure loading rate of 0.25MPa / s, and then unloading the load after holding the pressure at 22MPa for 5s.

[0049] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that: ⑤ The crushed aggregate particles are soaked in water at 20℃ for standard curing for 24 hours to obtain artificial aggregate from waste incineration fly ash.

[0050] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that: ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing is performed by loading a constant pressure of 25MPa for 90s and then unloading the load.

[0051] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that: ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing is performed by loading a constant pressure of 15MPa for 90s and then unloading the load.

[0052] Comparative Example 4 Comparative Example 4 is basically the same as Example 1, except that: ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing is performed by loading a constant pressure of 8MPa for 90s and then removing the load.

[0053] Comparative Example 5 ① Place the waste incineration fly ash, cement, and fly ash in a mixing pot at a ratio (mass ratio) of 1125:675:450 and dry mix for 60 seconds to obtain a mixture. Then, add water to the mixture in the mixing pot while stirring, and continue stirring for 3 minutes until the mixture is uniform and a homogeneous mixture is formed, which is the uniform aggregate mixture. The mixture contains 50% waste incineration fly ash by mass, and the cement content accounts for 60% of the total mass of cement and fly ash; the water-to-material ratio is 1:12.

[0054] ② Granulate the aggregate mixture into aggregate particles that meet the particle size requirements (particle size 5~25mm).

[0055] ③ The granulated aggregate particles are placed in a steam curing chamber at 80℃ and 100% relative humidity for 12 hours to obtain artificial aggregate from waste incineration fly ash.

[0056] Comparative Example 6 ① Place the waste incineration fly ash, cement, and fly ash in a mixing pot at a ratio (mass ratio) of 1125:675:450 and dry mix for 60 seconds to obtain a mixture. Then, add water to the mixture in the mixing pot while stirring, and continue stirring for 3 minutes until the mixture is uniform and a homogeneous mixture is formed, which is the uniform aggregate mixture. The mixture contains 50% waste incineration fly ash by mass, and the cement content accounts for 60% of the total mass of cement and fly ash; the water-to-material ratio is 1:12.

[0057] ② The aggregate mixture is loaded into a steel mold and pressed to obtain a molded product; the pressing process involves first loading a constant pressure of 8MPa for 15s, then loading a constant pressure of 15MPa for 30s, and then uniformly increasing the pressure from 15MPa to a high pressure of 25MPa at a pressure loading rate of 0.25MPa / s, and then unloading the load after holding the pressure at 25MPa for 5s.

[0058] ③ Remove the molded material from the mold to obtain a demolded sample.

[0059] ④ The demolded pattern is crushed to obtain aggregate particles that meet the particle size requirements.

[0060] ⑤ The crushed aggregate particles are placed in a steam curing chamber at 80℃ and 100% relative humidity for 12 hours to produce artificial aggregate from waste incineration fly ash.

[0061] The present invention tested the crushing value, cylinder compressive strength and water absorption rate of the artificial aggregates of waste incineration fly ash prepared in each embodiment and each comparative example. The results are shown in Table 1. Among them, the water absorption rate test was carried out by soaking the sample in water for 24 hours until it reached the saturated surface dry state, weighing and calculating the percentage of the mass difference before and after water absorption to the mass before water absorption. The result was the average of two parallel tests, and the deviation did not exceed 0.2%.

[0062] Table 1 As shown in Table 1, the 80℃ steam curing in Example 1 is significantly better than the standard curing in Comparative Example 1. This indicates that fly ash artificial aggregate performs better under 80℃ steam curing than under standard curing. This is because under high-temperature curing conditions, the hydration reaction rate of C3S and C2S in silicate cement is significantly accelerated, generating more CSH gel in a short time and improving early strength. Secondly, the active substances in fly ash are more likely to react with the cement hydration product Ca(OH)2 at high temperatures, generating additional CSH gel and / or ettringite (AFt). Firstly, high-temperature curing fills pores and increases density. Secondly, it accelerates moisture migration and evaporation, filling the loose pore structure formed in the early stage of cement paste with rapidly growing CSH gel, causing the pore size distribution to concentrate into smaller nanoscale pores, reducing internal defects. At the same time, the generated CSH gel is more dense, reducing the total porosity. Finally, under standard curing conditions, the hydration products are mainly CSH gel and Ca(OH)2, while high temperature may promote the transformation of CSH gel into CSH crystals with a higher degree of polymerization, and even generate tobermorite, significantly improving strength and durability.

[0063] There is a significant correlation between the crushing value and cylinder compressive strength of fly ash artificial aggregate and the strength of concrete. A higher crushing value and lower cylinder compressive strength generally indicate poorer mechanical properties of the aggregate, negatively impacting the strength, durability, and crack resistance of the concrete. The water absorption rate of fly ash artificial aggregate directly reflects the pore structure characteristics of the aggregate, thus affecting the workability, mechanical properties, and durability of the concrete. This invention also uses the fly ash artificial aggregate sample prepared in Example 1 to prepare concrete (wherein, the fly ash artificial aggregate replaced 50% of the natural aggregate), and the compressive strength of the concrete after 28 days of standard curing reached over 49.3 MPa.

[0064] To evaluate the heavy metal leaching risk of the fly ash artificial aggregate prepared by this invention, the heavy metal leaching characteristics of the fly ash artificial aggregate were analyzed. The heavy metal leaching tests of the samples were conducted according to the following methods: HJ557-2010 "Leaching Toxicity of Solid Waste - Horizontal Oscillation Method", which uses pure water as the leaching agent to simulate the leaching process of harmful components when solid waste is soaked in water; and HJ / T299-2007 "Leaching Toxicity of Solid Waste - Sulfuric Acid and Nitric Acid Method", which uses a sulfuric acid / nitric acid mixture (pH 3.20±0.05) as the leaching agent to simulate the leaching process of harmful components in waste in an acidic environment (such as improper landfill or stockpiling).

[0065] The leaching concentrations of heavy metals (Zn, Pb, Cd, Ni, Cu) in the artificial aggregate prepared by this invention are all lower than the national standard limits, and the environmental risks are controllable. Table 2 below shows the results of testing the leaching concentrations of five heavy metal elements (Zn, Pb, Cd, Ni, and Cu) in the fly ash artificial aggregate of Example 1 of this invention, which used fly ash with a content of 50% and was steam-cured at 80℃ for 12 hours. According to the standards HJ / T299-2007 and HJ 557-2010, the leaching rates of heavy metals Zn, Pb, and Cd in the fly ash artificial aggregate prepared by this invention are much lower than those in the original fly ash, regardless of whether it is the HJ / T 299 standard or the HJ / T 557 standard. Specifically, the leaching rate of Zn is reduced by more than 98%, the leaching rate of Pb is reduced by more than 99%, and the leaching rate of Cd is reduced by more than 90%. The heavy metal leaching concentrations are all significantly lower than the standard limits, demonstrating reliable environmental safety.

[0066] Table 2 Heavy metal leaching concentration of fly ash artificial aggregate The parts of this invention not described in detail are techniques known to those skilled in the art.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing artificial aggregate from waste incineration fly ash, characterized in that, The method includes the following steps: (1) Mix the fly ash from waste incineration, cement and fly ash evenly to obtain a mixture, then add water to the mixture and stir evenly to obtain an aggregate mixture; (2) The aggregate mixture is placed in a mold and pressed to obtain a molded product; the pressing is first pre-pressed at 6~10MPa for 10~20s, then pressed at 12~18MPa for 20~40s, and then uniformly increased to a high pressure of 22~28MPa and held at 22~28MPa for 4~6s. (3) After the molded material is initially cured, it is demolded to obtain a demolded pattern. Then the demolded pattern is crushed and steam cured in sequence to obtain artificial aggregate of waste incineration fly ash.

2. The preparation method according to claim 1, characterized in that: The mixture contains 30-70% by mass of incineration fly ash; and / or The amount of cement used accounts for 55-65% of the total mass of the cement and the fly ash, preferably 60%.

3. The preparation method according to claim 1, characterized in that: The cement is PO42.5 ordinary Portland cement; and / or The fly ash is grade I fly ash.

4. The preparation method according to claim 1, characterized in that: The aggregate mixture contains 6-10% water by mass.

5. The preparation method according to claim 1, characterized in that: The pre-compression pressure and / or the intermediate-compression pressure are applied at a constant pressure. The uniform pressurization is performed by uniformly increasing the pressure at a rate of 0.2 MPa / s to 0.3 MPa / s.

6. The preparation method according to claim 1, characterized in that: The pressing process involves first pre-pressing at 8MPa for 10-20 seconds, then pressing at 15MPa for 20-40 seconds, and finally uniformly increasing the pressure to a high of 25MPa and holding at 25MPa for 4-6 seconds.

7. The preparation method according to claim 1, characterized in that: The initial curing is carried out for 22-26 hours at a temperature of 18-22℃ and a relative humidity of ≥90%; and / or The steam curing is carried out at a temperature of 78~82℃ and a relative humidity of 100% for 10~15 hours.

8. The preparation method according to claim 1, characterized in that: The pressure difference between the medium-pressure pressing and the pre-pressing is 5~8MPa; The pressure difference between the high pressure and the medium pressure is 9~12MPa.

9. The preparation method according to claim 1, characterized in that: The crushing value of the artificial aggregate from the fly ash of the waste incineration is less than 19%, and the water absorption rate is not greater than 8%.

10. Artificial aggregate from waste incineration fly ash prepared by any one of claims 1 to 9.

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