Method for preparing cement-stabilized bottom ash macadam by using incineration bottom ash artificial aggregate

Abstract

The invention relates to the field of solid waste resource utilization, and discloses a method for preparing cement-stabilized bottom ash gravel by using incineration bottom ash artificial aggregate, which comprises the following steps: pretreatment of incineration bottom ash: taking the part with the particle size of less than 4.75 mm as fine aggregate, and preparing the part with the particle size of greater than 4.75 mm into artificial coarse aggregate through ball milling; mixing the incineration bottom ash, a cementing material and water according to a proportion, and preparing artificial aggregate by adopting a cold bonding process through a disc granulator; performing water bath maintenance on the prepared artificial aggregate to form aggregate with certain strength; finally, the artificial aggregate, the incineration bottom ash fine aggregate, the natural aggregate and cement are mixed according to the mixing proportion, and the cement-stabilized bottom ash gravel is prepared through the design of the optimal water content and the maximum dry density. By optimizing the particle size distribution and interface transition zone characteristics of the artificial aggregate, the mechanical property, durability and environmental friendliness of the base material are improved, the production cost and carbon emission are reduced, and high-valued utilization of solid waste is realized.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste resource utilization, in particular to a method for preparing cement-stabilized bottom ash crushed stone by using incineration bottom ash artificial aggregate. Background Art

[0002] With the acceleration of urbanization, the amount of urban domestic waste is increasing year by year, becoming a major challenge to the sustainable development of cities. Incineration is widely used because it can effectively reduce the volume of waste and recover energy. The bottom ash (MSWIBA) produced after incineration accounts for about 20%-30% of the total amount of waste and is the main by-product of the waste incineration process. At present, most MSWIBA is landfilled, but landfill not only occupies a large amount of land resources, but also may cause serious environmental pollution due to the leaching of heavy metals in the bottom ash. At the same time, the traditional landfill method does not meet the needs of sustainable development.

[0003] MSWIBA has certain gelling and volcanic ash activity, mainly composed of SiO 2 , CaO and Al 2 O 3 The composition of MSWIBA is similar to that of building materials, so its resource utilization has become a hot topic of research. However, due to the porous particles, high water absorption, low density and poor mechanical properties of bottom ash, its performance is not enough to meet the requirements of engineering applications when used directly as building materials or roadbed materials. In addition, the application of MSWIBA as coarse aggregate is also limited by its high crushing value, and its fragility makes it difficult to meet the strength and durability requirements of road base materials.

[0004] On the other hand, highway construction has a huge demand for natural aggregates, but the over-exploitation of natural aggregates has had a serious impact on the environment and has led to the gradual depletion of resources. Therefore, the resource utilization of MSWIBA to replace part of the natural aggregate can not only reduce the dependence on natural aggregates, but also effectively solve the environmental problems caused by the landfill treatment of MSWIBA. However, the existing technology still has shortcomings in improving the performance of MSWIBA, lacks an effective method to modify the bottom ash to meet the needs of engineering applications, and fails to take into account both performance optimization and environmental protection requirements in the process design. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing cement-stabilized bottom ash gravel using artificial aggregate from incineration bottom ash, which solves the problem that the performance of incineration bottom ash is not sufficient to be directly applied to road base materials. It provides a method for efficiently resource-using incineration bottom ash and replacing part of natural aggregate through artificial aggregate preparation and reasonable proportion design, thereby improving the mechanical properties, durability and environmental protection of the base material.

[0006] To achieve the above object, the present invention is implemented by the following technical scheme: A method for preparing cement-stabilized bottom ash gravel using incineration bottom ash artificial aggregate, comprising the following steps:

[0007] (1) Pretreatment of incineration bottom ash: The incineration bottom ash of municipal solid waste is processed and sieved according to particle size. The part with particle size less than 4.75 mm is used as fine aggregate, and the part with particle size greater than 4.75 mm is used to make artificial coarse aggregate;

[0008] (2) Preparation of artificial aggregate: Mix the bottom ash from the incineration of municipal solid waste, cementitious materials and water in proportion, and form them through a granulation device to obtain artificial aggregate;

[0009] (3) Curing: Curing the artificial aggregate to form an artificial aggregate with a certain strength;

[0010] (4) Preparation of cement-stabilized bottom ash gravel: artificial aggregate, fine aggregate from municipal solid waste incineration bottom ash, natural aggregate and cement are mixed in proportion, the optimum moisture content and maximum dry density are determined, and cement-stabilized bottom ash gravel is prepared through a molding process.

[0011] Preferably, the municipal solid waste incineration bottom ash is pretreated by magnetic separation and water washing to remove metal impurities and pollutants.

[0012] Preferably, the mix ratio of the artificial aggregate includes:

[0013] The cement content is 10%,

[0014] Ground blast furnace slag as auxiliary cementitious material,

[0015] The content of bottom ash from incineration of urban domestic waste is 60%-80%.

[0016] Preferably, the artificial aggregate is made by a granulator.

[0017] Preferably, the curing of the artificial aggregate includes:

[0018] Initial sealing and curing for 1 day;

[0019] Then carry out water bath curing, the water bath temperature is 20±2℃, and the curing age is 7-120 days.

[0020] Preferably, the content of fine aggregate from the incineration bottom ash of municipal solid waste in the cement-stabilized bottom ash gravel is 25%.

[0021] Preferably, the mass ratio of coarse aggregate to fine aggregate in the cement-stabilized bottom ash crushed stone is 62:38, and the cement content is 5%.

[0022] Preferably, the molding process uses a heavy compaction method to determine the optimum moisture content and the maximum dry density.

[0023] Preferably, the strength of the artificial aggregate is optimized by adjusting the content of bottom ash from the incineration of municipal solid waste, the curing time and the proportion of cementitious materials.

[0024] Preferably, the cement-stabilized bottom ash gravel is suitable for the road base of secondary and lower grade highways.

[0025] The invention provides a method for preparing cement-stabilized bottom ash crushed stone by using incineration bottom ash artificial aggregate.

[0026] It has the following beneficial effects:

[0027] 1. The present invention utilizes municipal solid waste incineration bottom ash (MSWIBA) to prepare artificial aggregate, which partially replaces natural aggregate and is applied to cement stabilized bottom ash gravel, which not only effectively reduces the occupation of land resources and potential environmental pollution caused by landfill, but also provides a practical solution for the resource utilization of incineration bottom ash.

[0028] 2. By using artificial aggregate prepared from incinerated bottom ash to partially replace natural aggregate, the present invention significantly reduces the demand for natural sand and gravel resources in road construction, helps alleviate the problem of sand and gravel resource shortage, and reduces the damage to the ecological environment caused by aggregate mining.

[0029] 3. The artificial aggregate prepared by the present invention not only meets the requirements of the road base such as the crushing value, but also improves the mechanical properties of the cement-stabilized bottom ash gravel, such as the unconfined compressive strength and splitting strength, by optimizing the structure of the interface transition zone, thereby ensuring the service life and engineering performance of the base material.

[0030] 4. The artificial aggregate is prepared by cold bonding process, without high temperature sintering, which significantly reduces carbon emissions in the production process. At the same time, experimental verification shows that the material prepared by the present invention meets national environmental standards, has no risk of heavy metal leaching, and is friendly to the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the method flow of the present invention;

[0032] Figure 2 This is a microscopic morphology image of MSWIBA of Example 1 of the present invention;

[0033] Figure 3 XRF and XRD analysis diagrams of the gelling material of Example 1 of the present invention;

[0034] Figure 4 This is a particle gradation diagram of artificial aggregate according to Example 2 of the present invention;

[0035] Figure 5 This is a physical property diagram of the artificial aggregate of Example 2 of the present invention;

[0036] Figure 6 This is a single particle crushing strength diagram of Example 2 of the present invention;

[0037] Figure 7 This is a graph showing the unconfined compression test results of Example 3 of the present invention;

[0038] Figure 8 This is a diagram showing the splitting test results of Example 3 of the present invention;

[0039] Fig. 9 The microscopic morphology of natural aggregates in Example 3 of the present invention, wherein (a) natural aggregate ITZ, (b) artificial aggregate ITZ;

[0040] Fig.10 The nanoindentation test results of different ITZs and their adjacent substrates in Example 3 of the present invention are shown;

[0041] Fig.11 This is a diagram of the leaching test results of Example 3 of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Please see attached Figure 1 The present invention provides a method for preparing cement-stabilized bottom ash gravel using incineration bottom ash artificial aggregate.

[0044] like Figure 1 As shown, the method for preparing cement-stabilized bottom ash gravel using incinerated bottom ash artificial aggregate of the present invention may include the following steps:

[0045] S1. Pretreatment of incineration bottom ash;

[0046] S2. Preparation of artificial aggregates;

[0047] S3. Maintenance of artificial aggregates;

[0048] S4. Preparation of cement stabilized bottom ash gravel.

[0049] For step S1, in this embodiment, necessary pretreatment is performed on the municipal solid waste incineration bottom ash (MSWIBA) to meet the performance requirements of subsequent aggregate preparation.

[0050] In some embodiments, MSWIBA, as the residue after incineration, usually contains metal impurities, dust, salt and other components that are not conducive to gelling performance. Therefore, in this embodiment, MSWIBA needs to be processed through two steps of magnetic separation and water washing.

[0051] Specifically, the magnetic separation process uses special equipment to remove metal impurities such as iron and aluminum from the incineration bottom ash. These metal components are not completely melted during the incineration process and usually exist in block or granular form. Magnetic separation can effectively reduce the heavy metal content in subsequent products and reduce the wear of granulation equipment. As an option, the magnetic separation equipment can use a permanent magnetic drum magnetic separator, whose drum diameter and magnetic field strength can be adjusted according to the composition of the bottom ash.

[0052] In a possible implementation, the water washing step is mainly used to remove dust, salt and soluble impurities in the bottom ash. Exemplarily, clean water or low-concentration diluted alkali solution is used for soaking and stirring to reduce the influence of water-soluble chloride ions and other pollutants on the subsequent gelation reaction. It should be noted that the bottom ash after water washing needs to be dehydrated or dried naturally to avoid affecting the operating efficiency due to excessive moisture in the subsequent screening and ball milling process.

[0053] It is understandable that the particle size of the incineration bottom ash is uneven and contains a large number of irregularly shaped particles. Therefore, in some embodiments, particle size screening of MSWIBA is a necessary step. Specifically, the bottom ash is graded by a vibrating screen, and the part with a particle size less than 4.75 mm is directly used as fine aggregate for the preparation of cement-stabilized bottom ash gravel, while the part with a particle size greater than 4.75 mm needs to be ball-milled for the production of artificial coarse aggregate.

[0054] As an option, the ball milling process can use a planetary ball mill or a drum ball mill, and the specific choice is determined according to the hardness, shape and subsequent granulation requirements of the particle size greater than 4.75 mm. For example, for the bottom ash component with high hardness, the speed of the ball mill can be set between 60-100 revolutions per minute, and the ball milling time is 5-15 minutes to ensure that the particle shape is more uniform.

[0055] It should be noted that the particle size of the fine aggregate after screening is mainly concentrated in the range of 0.075mm to 4.75mm, and the particle shape is mostly irregular. For example, these fine aggregates have a large specific surface area, which is conducive to the gelation reaction of the cement matrix. For the bottom ash part larger than 4.75mm, after ball milling, its particle size range is usually 4.75mm to 19mm, and the shape of the particles tends to be rounded, which has a significant performance improvement effect on the subsequent granulation process of artificial aggregate.

[0056] In this embodiment, the pretreated MSWIBA has the following typical physical properties: apparent density is 2.305 g / cm 3 , water absorption is 14.51%, methylene blue value is 1.2g / kg, and crushing value is 34%. It should be noted that these physical properties fluctuate within a certain range, and the specific values ​​may vary slightly depending on the source of the incineration bottom ash and its treatment process.

[0057] In some embodiments, in order to improve the applicability of fine aggregate, the fine aggregate may be further dried. Specifically, the sieved fine aggregate is heated to 40-60°C in a constant temperature oven to reduce its initial moisture content and avoid an imbalance in the water-cement ratio during subsequent mixing. In addition, for incineration bottom ash that may contain a high salt content, salt testing and desalination treatment steps may be added, such as repeated washing or ultrasonic oscillation methods, to further reduce the adverse effects of salt on subsequent reactions.

[0058] For step S2, in this embodiment, incineration bottom ash (MSWIBA) is used as the main raw material, and cementitious materials and water are added to prepare artificial aggregate using a granulation device. The step aims to improve the particle properties of the incineration bottom ash so that it meets the application requirements of cement stabilized bottom ash gravel.

[0059] In some embodiments, the preparation of artificial aggregates is based on a specific mix design. Specifically, the cementitious material includes ordinary Portland cement and ground blast furnace slag (GGBFS). Exemplarily, the cement content is set to 10% of the total solid mass, and GGBFS is used as an auxiliary cementitious material, with a content of 10%-30%, and the specific proportion depends on the cementitious properties of the bottom ash from incineration. The content of MSWIBA is usually 60%-80%, and the rest is water, with the proportion of water being 20% ​​of the total mass. The mix designs are marked as B60, B70 and B80, corresponding to the content of MSWIBA of 60%, 70% and 80% respectively. It should be noted that the combination of cement and GGBFS can not only meet the strength requirements, but also reduce carbon emissions and energy consumption in the production process.

[0060] In one possible implementation, the raw materials need to be fully weighed according to the particle size distribution and mix ratio requirements before mixing. MSWIBA raw materials need to be screened to ensure that particles with a particle size greater than 4.75 mm are used for granulation, while the smaller particles are directly used as fine aggregate. In order to improve the mixing uniformity, the cementitious materials used need to be pre-dried to avoid the decrease in granulation efficiency due to uneven moisture content of the materials.

[0061] In this embodiment, the granulation process is carried out using a disc granulation device. Specifically, the parameters of the disc granulator are set as follows: an inclination angle of 45°, a disc diameter of 100 cm, a height of 12 cm, and an operating speed of 35 rpm. As an option, in order to ensure granulation efficiency and particle shape, the inner wall of the disc granulator can be coated with a polyurethane coating to reduce friction loss.

[0062] Exemplarily, the granulation step includes the following process: the mixed dry powder is divided into two parts, one of which is first added to the granulator. When the equipment is running, atomizing nozzles are used to evenly spray clean water into the dry powder, and the amount of water sprayed is 20% of the total mass of the powder. This process allows the powder to reach an over-wet state and initially form particle agglomerates. Subsequently, the remaining powder is slowly added, and the particles gradually grow and form under the action of rolling and friction. It should be noted that excessive water spraying may cause adhesion of the particle surface, while insufficient water spraying will prevent the particles from agglomerating, so the amount of water spraying should be dynamically adjusted according to the water absorption rate of the powder.

[0063] In some embodiments, in order to improve the uniformity and sphericity of the particles, the particles need to be rolled for 10 minutes during the granulation process to make the surface smoother and reduce the generation of cracks. After the particles are formed, they need to be sieved through a 4.75 mm screen. The fine particles under the screen can be used as nucleation points for the next granulation, and the particles on the screen are used as coarse aggregates for subsequent maintenance and application.

[0064] It is important to understand that the performance of artificial aggregates is significantly affected by the granulation process and mix ratio. In an optimized implementation, the ratio of cement to GGBFS can be adjusted according to the physical properties and cementitious activity of MSWIBA. For example, for incineration bottom ash with high pozzolanic activity, the amount of GGBFS can be appropriately reduced and the amount of cement can be increased to improve the particle strength; while for low-activity bottom ash, the proportion of GGBFS needs to be increased to enhance the hydration reaction effect.

[0065] In this embodiment, the artificial aggregate after granulation generally has the following typical physical properties: apparent density is 1600-1800kg / m 3 , water absorption is 10%-15%, and particle strength can be evaluated by single particle crushing strength test, usually reaching 2.5MPa-4.0MPa within 28 days. It should be noted that these performance indicators may vary slightly due to the source of incineration bottom ash, the proportion of cementitious materials and the granulation process.

[0066] In some embodiments, different types of granulation equipment may be selected to further improve granulation efficiency and particle strength. For example, a rotary drum granulator or a vibrating granulator may be used as an alternative, and its operating parameters may be optimized according to the particle characteristics of the incineration bottom ash. In addition, other mineral admixtures (such as silica fume and fly ash) may be added to improve the cohesiveness and strength distribution of the particles.

[0067] As for step S3, in this embodiment, by performing a curing step for the artificial aggregate, it is ensured that the artificial aggregate has sufficient strength and durability after being formed, so as to meet the subsequent preparation requirements of cement-stabilized bottom ash gravel.

[0068] In some embodiments, the curing process includes two main stages: initial seal curing and water bath curing. The combination of the two is intended to optimize the internal structure of the aggregate and improve the mechanical properties by controlling the hydration conditions.

[0069] As an option, after the artificial aggregate is granulated, it is first subjected to preliminary sealing and curing. Specifically, the freshly prepared aggregate is sealed in a plastic container or an environment covered with a waterproof film, maintained at a constant temperature of 20±2°C, and left to stand for 1 day. The purpose of this process is to prevent the particles from being washed by water during the subsequent water bath curing due to insufficient hardening, resulting in particle breakage or dispersion. It should be noted that the preliminary sealing and curing can provide an environment that is moist but not in direct contact with water, thereby promoting the initial hydration of cement, generating a certain amount of hydration products (such as CSH gel and calcium aluminate), and providing initial structural strength for the aggregate.

[0070] In one possible implementation, after the initial sealing and curing, the aggregate needs to enter the water bath curing stage. For example, the aggregate is immersed in a water bath at 20±2°C, and the curing age can be set to 7 days, 14 days, 28 days, 56 days or 120 days according to actual needs. In this process, the sufficient water in the water bath provides the necessary environmental conditions for the hydration reaction, further promotes the hydration reaction of cement and slag powder, generates more hydration products inside the aggregate, fills the pores between the particles, and improves the density and compressive strength of the aggregate.

[0071] It is understandable that the waterbath curing time has a significant impact on the performance of aggregates. Taking the artificial aggregate with B70 mix ratio as an example, when the curing age is 7 days, the single particle crushing strength of the aggregate is about 2.42MPa; when the age is extended to 28 days, the strength can be increased to 3.09MPa; and 120 days of curing can further increase the strength to 4.00MPa. This shows that the longer the curing age, the higher the strength and stability of the aggregate, but at the same time, the extension of the curing time will also increase the project cost, so in practical applications, it is necessary to balance the strength increase and the construction period requirements.

[0072] It should be noted that the temperature control of water bath curing is very critical. In some embodiments, the water temperature can be maintained at 20±2°C by a constant temperature water bath device to ensure the stability of the hydration reaction. For some special engineering needs, such as rapid construction or applications in low temperature environments, the water bath temperature can be increased to 40°C-60°C for accelerated curing, but the generation rate of hydration products and the long-term performance of aggregates need to be verified.

[0073] In an optimized implementation, in order to further improve the hydration efficiency, a small amount of chemical activators, such as alkaline sulfate or sodium hydroxide solution, can be added to the water bath. These chemicals can stimulate the potential activity of GGBFS and promote the formation of more CSH gel, thereby improving the internal structure of the aggregate. However, the concentration of the activator needs to be controlled to avoid excessive reaction and the precipitation of unstable products on the surface of the aggregate.

[0074] It should be understood that the water absorption rate and apparent density of aggregates will gradually change during the curing process as the hydration reaction proceeds. Taking B70 as an example, its water absorption rate is 12.1% at the 28-day curing age, and its apparent density is 1733.4kg / m 3 After 120 days of curing, the water absorption rate decreased to 6.9% and the apparent density increased to 1838.5kg / m 3 This change reflects that the pores inside the aggregate are gradually filled and the density is significantly improved.

[0075] In some embodiments, other curing methods can be selected to meet specific engineering requirements. For example, dry-wet alternating curing is used, that is, the aggregate is placed in a water bath and a constant humidity environment alternately to simulate the natural climatic conditions in actual engineering. This method can further improve the crack resistance and durability of the aggregate. In addition, steam curing or microwave curing can also be used to accelerate the hydration process, which is particularly suitable for construction scenarios with tight schedules or low temperature environments.

[0076] For step S4, in this embodiment, artificial aggregate, incineration bottom ash fine aggregate, natural aggregate and cement are mixed in proportion and a reasonable molding process is adopted to prepare cement stabilized bottom ash macadam (ACSBAM), thereby meeting the mechanical and durability requirements of the road base material.

[0077] In some embodiments, the mix design of cement-stabilized bottom ash gravel is a key link, and the source, performance and engineering requirements of the aggregate must be considered comprehensively. Specifically, the mix design includes the following components:

[0078] Fine aggregate: It is composed of incineration bottom ash (MSWIBA) fine aggregate with a particle size of less than 4.75 mm, and the dosage is set at 25%. This proportion is determined on the premise of balancing resource utilization and performance.

[0079] Coarse aggregate: It is composed of natural aggregate and 28-day-old artificial aggregate, with the mass ratio of coarse aggregate to fine aggregate being 62:38. The amount of artificial aggregate can be adjusted to 5%, 10% or 15%.

[0080] Cement: The addition amount of ordinary Portland cement is 5% of the total mass of aggregate to provide the bonding strength of the foundation.

[0081] It should be noted that the mix ratio is designed based on the recommended gradation in the "Test Code for Stabilized Materials with Inorganic Binders for Highway Engineering" (JTGE51-2009), and is optimized in combination with the characteristics of MSWIBA to ensure that the gradation of the mixture meets the standard requirements.

[0082] In one possible implementation, after the mix ratio is designed, the optimal moisture content and maximum dry density need to be determined through a heavy compaction test. For example, after the aggregate, cement and water after the adjusted ratio are evenly mixed, 5 different moisture contents (with a difference of 0.5%) are preset respectively, and the heavy compaction test method is used for testing to obtain the optimal moisture content and the corresponding maximum dry density. For example, the optimal moisture content of the mixture containing 5% artificial aggregate is 10.9%, and the maximum dry density is 2.000g / cm 3 ; For the artificial aggregate mixture with a dosage of 15%, its optimum moisture content is 12.3% and its maximum dry density is 1.941g / cm 3 .

[0083] In this embodiment, the mixture is formed by static pressure method to prepare standard specimens. Specifically, the mixture mixed evenly according to the optimal water content is loaded into a Φ150mm×150mm mold, and compacted layer by layer to the designed density using hydraulic equipment at a specified pressure to obtain a cylindrical specimen. It should be noted that the formed specimen needs to be sealed and cured in a standard curing room (20±2℃, relative humidity 96%) for 28 days to ensure sufficient hydration reaction.

[0084] It is understandable that the mechanical properties of cement-stabilized bottom ash gravel are mainly determined by the hydration strength of the cement paste, the interlocking effect between aggregates, and the bonding effect of the interface transition zone (ITZ). In some embodiments, the performance of the specimens is evaluated by an unconfined compressive strength test. For example, the 28-day unconfined compressive strength of cement-stabilized bottom ash gravel containing 5%, 10% and 15% artificial aggregates are 4.97MPa, 4.60MPa and 4.49MPa, respectively, which all meet the requirements of secondary and below highway base materials. It should be noted that although the increase in the amount of artificial aggregate reduces the early strength of the mixture, due to the continuous hydration of artificial aggregates during the curing period, the increase in its later strength is better than that of natural aggregates.

[0085] In an optimized implementation, in order to further improve the splitting strength of the mixture, an appropriate amount of fiber material, such as polyester fiber or basalt fiber, can be added to the aggregate. The addition of fiber can enhance the crack resistance of the specimen and effectively delay the propagation of cracks. In addition, by adjusting the ratio of artificial aggregate to natural aggregate, the structure of the interface transition zone can be optimized and the overall strength can be improved.

[0086] It should be noted that the quality of the interfacial transition zone (ITZ) directly affects the durability of the mixture. In some embodiments, the rough surfaces of the incineration bottom ash fine aggregate and the artificial aggregate can provide more bonding points for the cement paste, thereby enhancing the bonding effect of the interfacial zone. For example, compared with natural aggregates, the CSH gel generated by the volcanic ash activity reaction on the surface of artificial aggregates can further fill the pores and improve the density of the ITZ. In addition, the higher water absorption rate of artificial aggregates can provide an "internal curing" effect in sealing curing, promote the hydration of the cement matrix, and further improve the overall performance.

[0087] It is understandable that the performance of the cement-stabilized bottom ash gravel in this embodiment is affected by multiple factors such as the mix ratio, aggregate properties, and molding process. For example, for a high humidity or high temperature construction environment, the cement content may be adjusted or mineral admixtures (such as silica fume or fly ash) may be added to improve the crack resistance and durability of the mixture.

[0088] To meet the needs of special projects, cement stabilized bottom ash gravel can also introduce admixtures, such as water reducers or retarders, to optimize working performance and adapt to different construction conditions. At the same time, the amount of incineration bottom ash can be increased to 30%-50%, further improving the efficiency of waste resource utilization.

[0089] The present invention prepares artificial aggregate by magnetic separation, water washing and particle size screening of incineration bottom ash (MSWIBA), and mixes cement and slag fine powder (GGBFS) in proportion, and finally prepares cement-stabilized bottom ash crushed stone suitable for road base through reasonable maintenance and mix ratio optimization. The present invention can significantly improve the resource utilization rate of incineration bottom ash, reduce dependence on natural aggregates, and ensure that the prepared materials have good mechanical properties and durability, and meet environmental friendliness requirements, and are suitable for the construction of base engineering of secondary and lower-level highways.

[0090] In order to better understand the present invention, the above method is described in detail below in conjunction with specific embodiments.

[0091] Example 1: Study of raw materials and their physical properties

[0092] In this embodiment, municipal solid waste incineration bottom ash (MSWIBA), ordinary Portland cement (OPC), ground blast furnace slag (GGBFS) and natural aggregate (NA) are selected as the main raw materials for preparing artificial aggregate and cement stabilized bottom ash gravel. The sources, characteristics and physical properties of each raw material are described in detail below.

[0093] 1.1 Municipal solid waste incineration bottom ash (MSWIBA)

[0094] In this embodiment, MSWIBA is derived from incineration bottom ash produced in Dongguan, China, and has been pre-treated by magnetic separation and water washing before leaving the factory. Its main components include slag, glass, ceramics, bricks and other waste mixtures, which are heterogeneous mixtures.

[0095] Specifically, the physical properties of MSWIBA were tested according to the test method of JTGE42-2005, and the results are shown in Table 1. After the incineration bottom ash was screened, the part with a particle size of less than 4.75 mm was used as fine aggregate, and the part with a particle size of more than 4.75 mm was used to make artificial aggregate.

[0096] Table 1 Physical properties of MSWIBA

[0097] <![CDATA[Apparent relative density (g / cm 3 )]]> Water absorption (%) Methylene blue value (g / kg) Crushing value (%) 2.305 14.51 1.2 34

[0098] In one possible implementation, the microscopic morphology of MSWIBA was analyzed by scanning electron microscopy (SEM), such as Figure 2 The results show that the surface of MSWIBA is rough, there are many pores between particles, and its crystal morphology is mainly rod-shaped, agglomerated and granular, which is closely related to the uneven distribution of air and temperature and rapid cooling during the incineration process.

[0099] 1.2 Cementitious materials (OPC and GGBFS)

[0100] The OPC used in this embodiment is Conch brand P·O 42.5 ordinary Portland cement, which meets the GB 175-2007 standard. GGBFS is S95 grade mineral powder produced in Shenzhen, which meets the GB / T 18046-2017 standard. Its chemical composition is shown in Table 2.

[0101] Table 2 Chemical element composition of OPC and GGBFS

[0102]

[0103] It should be noted that the main components of cement and mineral powder are SiO 2 , CaO and Al 2 O 3 , the particle size distribution and crystal phase characteristics were analyzed by X-ray fluorescence spectrometer (XRF) and X-ray diffractometer (XRD), such as Figure 3 As shown in Figure 2, GGBFS has a higher activity due to its lower crystallinity and helps to improve the mechanical properties of artificial aggregates and cement stabilized bottom ash crushed stone.

[0104] 1.3 Natural Aggregate (NA)

[0105] The natural aggregates come from Jiujiang Jinlong Stone Factory and are classified into four specifications according to the particle size: 19-26.5mm, 9.5-19mm, 4.75-9.5mm and 0-4.75mm. The specific particle size distribution and physical properties such as apparent density, water absorption rate, crushing value, etc. are shown in Table 3.

[0106] Table 3 Test results of natural aggregate road performance

[0107]

[0108]

[0109] In one possible application scenario, natural aggregate is mainly used to mix with incineration bottom ash fine aggregate to optimize grading. Its relative density is significantly higher than MSWIBA, and its water absorption and crushing value are relatively low, which can provide higher strength and stability.

[0110] 1.4 Main conclusions

[0111] In this example, the physical properties and characteristics of each raw material were clarified through comprehensive testing and characterization of the raw materials, laying the foundation for subsequent mixing ratio design and performance optimization. 2 , CaO content, with certain cementitious activity and volcanic ash activity, suitable as fine aggregate or for preparing artificial aggregate. The high strength and low water absorption of cementitious materials and natural aggregates can effectively improve the overall performance of the mixture.

[0112] Example 2: Preparation and performance testing of artificial aggregate

[0113] In this embodiment, municipal solid waste incineration bottom ash (MSWIBA), ordinary Portland cement (OPC) and ground blast furnace slag (GGBFS) are used as raw materials to prepare artificial aggregate through cold bonding technology, and its physical and mechanical properties are tested and analyzed.

[0114] 2.1 Preparation of artificial aggregate

[0115] This embodiment adopts the disk granulation method to prepare artificial aggregate, and the specific steps are as follows:

[0116] 1. Mix design

[0117] According to the preliminary test results and literature reports, the cement content is set to 10%, the GGBFS content is 10%-30%, the MSWIBA content is 60%-80%, and the water content is 20% of the total mass. The mix ratio is shown in Table 4, where B60, B70 and B80 represent three mix ratios with MSWIBA content of 60%, 70% and 80%, respectively.

[0118] Table 4 Mix ratio of artificial aggregate

[0119]

[0120]

[0121] 2. Granulation process

[0122] The premixed materials were put into the granulator in batches using a disc granulator (parameters: inclination angle 45°, diameter 100 cm, height 12 cm, running speed 35 rap / min).

[0123] First, put 20% of the dry powder into the pan, spray water evenly to make the mixture enter the super-wet state, and then gradually add the remaining powder. After the granulation is completed, the finished aggregate with a particle size greater than 4.75mm is sieved out, and the material less than 4.75mm is recycled as the nucleation material for the next round of granulation.

[0124] 3. Maintenance methods

[0125] The initial sealing and curing is carried out for 1 day to form the initial strength, followed by water bath curing (20±2℃), and the curing age is set at 7, 28, 56, and 120 days. Water bath curing can provide sufficient water to accelerate the hydration reaction.

[0126] 2.2 Performance test of artificial aggregate

[0127] 2.2.1 Physical properties

[0128] The particle size distribution, water absorption rate and apparent density of three groups of artificial aggregates (B60, B70, B80) were tested, and the results of the particle size distribution of artificial aggregates are shown in Table 5. In addition, through the particle grading test and laser particle size analysis, the particle grading of artificial aggregates is as follows Figure 4 As shown, it is further confirmed that the particle size range of aggregate is concentrated in 4.75mm-19mm, which meets the requirements of road construction.

[0129] Table 5 Artificial aggregate particle size distribution

[0130]

[0131] Water absorption and apparent density:

[0132] like Figure 5 As shown in Figure 2, the water absorption rates of B60, B70 and B80 are 12.2%, 12.1% and 13.6% (28 days of curing age), and the apparent densities are 1765.9 kg / m 3 、1733.4kg / m 3 and 1681.7kg / m 3 With the increase of MSWIBA dosage, the water absorption of aggregate increases and the apparent density decreases.

[0133] Effect of curing age on performance:

[0134] After the curing age was extended to 120 days, the water absorption of the three groups of aggregates decreased significantly (7.3% for B60, 6.9% for B70, and 7.8% for B80), and the apparent density gradually increased (1837.5 kg / m 3 , B70 is 1838.5kg / m 3 , B80 is 1766.7kg / m 3 ), indicating that the hydration reaction significantly improves the density of aggregate.

[0135] 2.2.2 Mechanical properties

[0136] The single particle crushing strength test of artificial aggregate shows that the crushing strength gradually decreases with the increase of MSWIBA content. Figure 6 shown.

[0137] At 7 days of age: the strengths of B60, B70 and B80 were 2.58 MPa, 2.42 MPa and 2.08 MPa respectively, and the strength of B80 was about 81% of that of B60.

[0138] At 28 days of age: the strength of the three groups of aggregates increased to 3.19MPa, 3.09MPa and 2.47MPa respectively.

[0139] At 120 days of age: the strengths reached 3.73MPa, 4.00MPa and 2.77MPa respectively, indicating that a moderate amount of MSWIBA (B70) can more significantly promote long-term strength development.

[0140] 2.2.3 Microstructure analysis

[0141] The micromorphology of artificial aggregates was observed by scanning electron microscopy (SEM). The B70 aggregate showed a more developed CSH gel and AFm crystal structure, a clearer network morphology, and significantly reduced microcracks.

[0142] In addition, the pore structure was tested using a mercury intrusion porosimeter (MIP). The results showed that the total pore volume of B70 was 0.163 mL / g, 0.158 mL / g and 0.114 mL / g at 7 days, 28 days and 120 days, respectively, and the total pore volume gradually decreased with the progress of the hydration reaction.

[0143] The pore distribution curve shows that the porosity of B80 is significantly higher than that of B70 and B60, and it has more microcracks, which may be an important reason for the limited long-term strength development of B80.

[0144] 2.3 Conclusion of this Example

[0145] Preparation of artificial aggregate: By optimizing the mix design of MSWIBA, cement and slag, cold-bonded artificial aggregate with a particle size of 4.75 mm-19 mm was successfully prepared, which is suitable for road engineering applications.

[0146] Performance optimization: B70 aggregate has the best comprehensive performance in water absorption, apparent density and mechanical properties, especially the significant increase in strength within the 120-day curing age, reflecting good long-term development potential.

[0147] Microstructure advantages: B70 aggregate has a high microstructure density and sufficient hydration reaction, which can significantly reduce pores and cracks and is the best mix ratio.

[0148] Example 3: Application of artificial aggregate in cement stabilized bottom ash crushed stone

[0149] In this example, cold-bonded artificial aggregate (B70) and municipal solid waste incineration bottom ash (MSWIBA) fine aggregate were used to prepare cement stabilized bottom ash crushed stone (ACSBAM). The feasibility and performance advantages of artificial aggregate in cement stabilized bottom ash crushed stone were verified through compaction tests, mechanical property tests and microstructure analysis of the interface transition zone.

[0150] 3.1 Preparation of cement stabilized bottom ash gravel

[0151] 1. Mix design

[0152] In this embodiment, B70 aggregate (28 days curing age) is selected as the coarse aggregate part, and natural coarse aggregate is replaced by 0%, 5%, 10% and 15%, and the numbers are 25S0L, 25S5L, 25S10L and 25S15L respectively.

[0153] The content of MSWIBA fine aggregate is fixed at 25%, and the mix ratio is shown in Table 6. The gradation design of ACSBAM refers to the CB-1 gradation recommended by JTGT F20-2015 to ensure a reasonable ratio of coarse aggregate to fine aggregate.

[0154] Table 6 ACSBAM mix ratio

[0155]

[0156]

[0157] 2. Compacting

[0158] According to the compaction test results (see Table 7), the optimum moisture content and maximum dry density of each group of samples were determined.

[0159] Table 7 Compaction test results

[0160] serial number Optimum moisture content (%) <![CDATA[Maximum dry density (g / cm 3 )]]> 25S0L 8.3 2.126 25S5L 10.9 2.000 25S10L 11.9 1.952 25S15L 12.3 1.941

[0161] According to the standard of JTG E51-2009, cylindrical specimens were prepared by static compaction method with the size of φ150mm×150mm, and sealed and cured (20±2℃, relative humidity 96%).

[0162] 3.2 Performance Testing

[0163] 3.2.1 Unconfined compressive strength

[0164] Test Results

[0165] The 7-day and 28-day unconfined compressive strength of ACSBAM are shown in the attached Figure 7 shown.

[0166] 7-day age: The increase in B70 substitution rate resulted in a slight decrease in compressive strength (0%-17.6%), but all groups met the strength requirements for heavy traffic base materials for secondary roads (3-5MPa).

[0167] At 28 days of age: the strength of each group was 4.68MPa (25S0L), 4.97MPa (25S5L), 4.60MPa (25S10L) and 4.49MPa (25S15L), respectively, which was 12.24%-30.79% higher than that at 7 days.

[0168] The strength is highest when the replacement rate is 5%, and the water absorption of B70 provides "internal maintenance" for ACSBAM, promoting long-term strength development.

[0169] 3.2.2 Splitting strength

[0170] Test Results

[0171] The splitting strength at 28 days of age is shown in the attached Figure 8 shown.

[0172] The splitting strength increases first and then decreases with the increase of substitution rate. The highest value appears in the sample with substitution rate of 10% (25S10L), with a strength of 0.46MPa.

[0173] Splitting failure mainly occurs in the interface transition zone (ITZ), and the mechanical embedding and good interface bonding properties of B70 aggregate significantly improve the strength of ITZ.

[0174] 3.3 Microstructure analysis

[0175] 1. Interface transition zone morphology

[0176] Scanning electron microscopy (SEM) observations show that the boundary between natural aggregate and cement matrix is ​​obvious, and there are many pores and cracks in the interface transition zone (see Appendix Fig. 9 a).

[0177] The boundary between B70 aggregate and cement matrix is ​​fuzzy, the interface transition zone is dense, and there is an inlay zone (IZ) formed by cement paste embedded in the aggregate pores (see Appendix Fig. 9 b).

[0178] The existence of IZ significantly improves the bonding between aggregate and matrix and enhances the strength of the interface transition zone.

[0179] 2. Nanoindentation Analysis

[0180] The elastic modulus distribution of ITZ is shown in the attached figure. Fig.10 shown.

[0181] The ITZ modulus of natural aggregate is significantly lower than that of cement matrix, while that of B70 aggregate (20-30 GPa) is close to that of the matrix, indicating that the open pores of artificial aggregate significantly weaken the "wall effect" and promote the hydration reaction and interfacial bonding of the cement matrix.

[0182] 3.4 Toxicity leaching performance

[0183] Heavy metal leaching tests were conducted on B70 and 25S15L samples. The results are shown in the attached Fig.11 shown.

[0184] The heavy metal concentrations of all tested groups were lower than the limit values ​​of GB 18485-2014.

[0185] The use of MSWIBA does not pose significant risks to the environment.

[0186] 3.5 Conclusion of this Example

[0187] 1. Performance Verification

[0188] When the replacement rate is 5%-10%, the mechanical properties of ACSBAM are the best, especially the 28-day unconfined compressive strength and splitting strength are significantly improved.

[0189] 2. Interface advantages

[0190] The high-quality interface transition zone between artificial aggregate and cement matrix significantly improves the overall mechanical properties. The presence of the inlay zone (IZ) enhances the interfacial bonding and significantly weakens the "wall effect" of natural aggregate.

[0191] 3. Environmental advantages

[0192] The combined use of artificial aggregate and MSWIBA realizes resource utilization, and the environmental friendliness of the material is verified through toxicity leaching tests.

[0193] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing cement-stabilized bottom ash gravel using incinerated bottom ash artificial aggregate, characterized in that: The following steps are involved: (1) Pretreatment of incineration bottom ash: The incineration bottom ash of municipal solid waste is processed and sieved according to particle size. The part with particle size less than 4.75 mm is used as fine aggregate, and the part with particle size greater than 4.75 mm is used to make artificial coarse aggregate; (2) Preparation of artificial aggregate: Mix the bottom ash from the incineration of municipal solid waste, cementitious materials and water in proportion, and form them through a granulation device to obtain artificial aggregate; (3) Curing: Curing the artificial aggregate to form an artificial aggregate with a certain strength; (4) Preparation of cement-stabilized bottom ash gravel: artificial aggregate, fine aggregate from municipal solid waste incineration bottom ash, natural aggregate and cement are mixed in proportion, the optimum moisture content and maximum dry density are determined, and cement-stabilized bottom ash gravel is prepared through a molding process.

2. The method for preparing cement-stabilized bottom ash gravel using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The municipal solid waste incineration bottom ash is pre-treated by magnetic separation and water washing to remove metal impurities and pollutants.

3. The method for preparing cement-stabilized bottom ash crushed stone using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The mix ratio of the artificial aggregate includes: The cement content is 10%, Ground blast furnace slag as auxiliary cementitious material, The content of bottom ash from incineration of urban domestic waste is 60%-80%.

4. The method for preparing cement-stabilized bottom ash gravel using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The artificial aggregate is made by a granulator.

5. The method for preparing cement-stabilized bottom ash gravel using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The maintenance of the artificial aggregate includes: Initial sealing and curing for 1 day; Then carry out water bath curing, the water bath temperature is 20±2℃, and the curing age is 7-120 days.

6. The method for preparing cement-stabilized bottom ash crushed stone using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The content of fine aggregate from the incineration bottom ash of urban domestic waste in the cement-stabilized bottom ash gravel is 25%.

7. The method for preparing cement-stabilized bottom ash gravel using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The mass ratio of coarse aggregate to fine aggregate in the cement-stabilized bottom ash crushed stone is 62:38, and the cement content is 5%.

8. The method for preparing cement-stabilized bottom ash crushed stone using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The molding process adopts a heavy compaction method to determine the optimum moisture content and the maximum dry density.

9. The method for preparing cement-stabilized bottom ash crushed stone using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The strength of the artificial aggregate is optimized by adjusting the content of bottom ash from incineration of municipal solid waste, the curing time and the proportion of cementitious materials.

10. The method for preparing cement-stabilized bottom ash crushed stone using incineration bottom ash artificial aggregate according to claim 1, characterized in that: The cement stabilized bottom ash crushed stone is suitable for the road base of secondary and lower grade highways.

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