Method for preparing cement stabilized macadam mixture from detoxified fly ash and cement stabilized macadam mixture

Abstract

The invention discloses a method for preparing a cement stabilized macadam mixture by using detoxified fly ash and the cement stabilized macadam mixture, the cement stabilized macadam mixture comprises the following raw materials: a solid phase and water, the solid phase comprises the following components in parts by weight: 3-7 parts of cement; 52-71 parts of coarse aggregate; 19 to 29 parts of fine aggregate; 5 to 12 parts of detoxified fly ash; and the water accounts for 8-12% of the total weight of the solid phase. The cement stabilized macadam mixture with good performance is prepared from the detoxified fly ash, a large amount of detoxified fly ash can be treated and digested, the troubles of fly ash occupation and land pollution are solved, meanwhile, natural resources are saved, and the cement stabilized macadam mixture has remarkable environmental and economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization, and more particularly to a method for preparing a cement-stabilized gravel mixture by utilizing detoxified fly ash and the cement-stabilized gravel mixture. Background Art

[0002] Municipal solid waste incineration fly ash (hereinafter referred to as "fly ash") is a byproduct of municipal solid waste incineration. According to statistics, my country produces approximately 10 million tons of fly ash annually, and this figure is projected to reach 12 million tons by 2025. Currently, fly ash is primarily treated through "stabilization and solidification followed by landfilling." In recent years, limited landfill capacity and a shortage of land resources have created significant risks associated with landfilling. Therefore, the safe and effective disposal and resource utilization of incineration fly ash has become a hot topic of concern both domestically and internationally.

[0003] The "Technical Specification for Pollution Control of Municipal Waste Fly Ash" (HJ 1134-2020) explicitly states that after treated fly ash meets relevant requirements, it can be classified as general solid waste during co-disposal in cement kilns, rather than as hazardous waste. Detoxified fly ash from municipal waste incineration, after undergoing multiple treatment steps like washing and pyrolysis, has heavy metal leaching and dioxin concentrations far below standard requirements, making it feasible for use in the production of construction materials. However, research into the material properties and resource utilization of detoxified fly ash is still in its infancy, and there is a lack of approaches to its large-scale disposal and utilization.

[0004] In recent years, my country's road construction has rapidly developed, and the demand for road base materials has also increased. Cement-stabilized gravel mixtures have become the mainstream material for road bases due to their high strength, good stability, and convenient construction. Currently, cement-stabilized gravel mixtures are primarily composed of cement, coarse aggregate, and manufactured sand. There is no development or application of using detoxified fly ash as a raw material to replace manufactured sand in cement-stabilized gravel mixtures. Therefore, if detoxified fly ash were used as a raw material in cement-stabilized gravel mixtures, it would be possible to dispose of and consume large quantities of detoxified fly ash, solving the problem of fly ash occupation and land pollution. Summary of the Invention

[0005] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for preparing a cement-stabilized gravel mixture using detoxified fly ash and a cement-stabilized gravel mixture, which can dispose of and consume detoxified fly ash in large quantities, solve the problems of fly ash occupation and land pollution caused by incineration of domestic waste, save natural resources, and have significant environmental and economic benefits.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A first aspect of the present invention provides a cement-stabilized crushed stone mixture, the raw materials of which include a solid phase and water, wherein the solid phase is calculated in parts by weight as follows:

[0008]

[0009] The water accounts for 8-12% of the total weight of the solid phase.

[0010] Preferably, the weight proportion of the cement is 3 to 5 parts or 4 to 7 parts; and / or

[0011] The cement is P·O42.5 cement with a specific surface area greater than 300m 2 / kg, 28-day compressive strength ≥42.5MPa.

[0012] Preferably, the weight proportion of the coarse aggregate is 52 to 66 parts or 56 to 71 parts.

[0013] Preferably, the coarse aggregate is compounded by aggregate with a particle size of 16 to 31.5 mm and aggregate with a particle size of 5 to 16 mm;

[0014] The weight proportion of the aggregate with a particle size of 16 to 31.5 mm is 24 to 35 parts, and the weight proportion of the aggregate with a particle size of 5 to 16 mm is 28 to 36 parts.

[0015] Preferably, the coarse aggregate is natural crushed stone or recycled aggregate, and the crushing value of the coarse aggregate is less than 30%;

[0016] The weight proportion of the aggregate with a particle size of 16 to 31.5 mm is 24 to 30 parts or 27 to 35 parts;

[0017] The weight proportion of the aggregate with a particle size of 5 to 16 mm is 28 to 34 parts or 20 to 36 parts.

[0018] Preferably, the weight percentage of the fine aggregate is 19 to 25 parts or 23 to 29 parts; and / or

[0019] The fine aggregate is machine-made sand with a particle size of ≤5 mm and a crushing value of <30%.

[0020] Preferably, the weight proportion of the detoxified fly ash is 5 to 10 parts or 6 to 12 parts.

[0021] Preferably, the particle size of the detoxified fly ash is ≤5 mm;

[0022] The detoxified fly ash meets the following requirements: dioxin content ≤ 50ng-TEQ / kg, soluble chlorine content ≤ 2%, and heavy metal leaching concentration not exceeding the maximum allowable discharge concentration limit specified in GB8978 "Integrated Sewage Discharge Standard" (the maximum allowable discharge concentration of Class II pollutants shall be implemented in accordance with the first-level standard).

[0023] Preferably, the cement-stabilized crushed stone mixture has the following properties: 7-day unconfined compressive strength ≥4.0 MPa, and compaction degree is 95-98%.

[0024] The second aspect of the present invention provides a method for preparing the cement-stabilized gravel mixture as described in the first aspect of the present invention using detoxified fly ash, comprising the following steps:

[0025] S1. Determine the weight proportions of coarse aggregate, fine aggregate and detoxified fly ash based on the recommended crushed stone gradation for highway pavement base;

[0026] S2, adding cement and water of different proportions to the coarse aggregate, fine aggregate and detoxified fly ash prepared in step S1, determining the optimum moisture content and maximum dry density of the raw materials through compaction tests, and determining the weight ratios of cement and water accordingly;

[0027] S3, weighing raw materials according to the weight proportions determined in step S1 and step S2, and mixing the raw materials in sequence to obtain a cement-stabilized gravel mixture.

[0028] Preferably, in step S1, the recommended crushed stone gradations for the highway pavement base layer include CB-1, CB-2, CB-3, CC-1, CC-2 and CC-3.

[0029] Preferably, in step S3, the mixing time is 60 to 90 seconds.

[0030] The effects of the present invention are as follows:

[0031] 1. In the present invention, each ton of cement-stabilized crushed stone mixture can absorb 50-120 kg of detoxified fly ash, opening up a technical approach for large-scale disposal and utilization of detoxified fly ash;

[0032] 2. The present invention can unleash the high calcium and sulfate content of detoxified fly ash. Under the same cement content, the 7-day unconfined compressive strength of the cement-stabilized gravel mixture containing detoxified fly ash is higher than that of the ordinary cement-stabilized gravel mixture. Other properties meet the requirements of engineering applications.

[0033] 3. The method of the present invention for preparing cement-stabilized gravel mixture by using detoxified fly ash has simple process and meets safety standards, and is worthy of promotion and application. DETAILED DESCRIPTION

[0034] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below with reference to embodiments.

[0035] The present invention provides a cement-stabilized gravel mixture, the raw materials of which include a solid phase and water, and the solid phase is calculated in parts by weight as follows:

[0036]

[0037]

[0038] Water accounts for 8-12% of the total weight of the solid phase.

[0039] The functions of the components in the above solid phase are as follows: cement plays a bonding role, and the hydration products form a bonding layer between the gravel particles, firmly bonding the gravel particles together to form a whole mixture; coarse aggregate and fine aggregate are the main components of cement-stabilized gravel, providing a strength skeleton; detoxified fly ash replaces part of the fine aggregate, plays a filling role, and further improves the density of the mixture.

[0040] In a specific embodiment, the weight of cement is 3 to 5 parts or 4 to 7 parts, such as 4 parts or 5 parts; the cement is P·O42.5 cement with a specific surface area greater than 300m 2 / kg, 28-day compressive strength ≥42.5MPa.

[0041] In a specific embodiment, the weight proportion of the coarse aggregate is 52 to 66 parts or 56 to 71 parts, such as 55 parts, 60 parts, 65 parts, 70 parts, or a range consisting of any two of 55 parts, 60 parts, 65 parts, and 70 parts.

[0042] In a specific embodiment, the coarse aggregate is a compound of aggregate with a particle size of 16 to 31.5 mm and aggregate with a particle size of 5 to 16 mm; wherein the weight percentage of the aggregate with a particle size of 16 to 31.5 mm is 24 to 35 parts, and the weight percentage of the aggregate with a particle size of 5 to 16 mm is 28 to 36 parts. In a specific embodiment, the weight percentage of the aggregate with a particle size of 16 to 31.5 mm is 24 to 30 parts or 27 to 35 parts, such as 25 parts, 28 parts, 32 parts, or a range consisting of any two of 25 parts, 28 parts, and 32 parts; the weight percentage of the aggregate with a particle size of 5 to 16 mm is 28 to 34 parts or 20 to 36 parts, such as 30 parts, 32 parts, 36 parts, or a range consisting of any two of 30 parts, 32 parts, and 36 parts. The above-mentioned coarse aggregate is natural crushed stone or recycled aggregate, and the crushing value of the coarse aggregate is less than 30%;

[0043] In a specific embodiment, the weight percentage of fine aggregate is 19 to 25 parts or 23 to 29 parts; for example, 22 parts, 25 parts, or 28 parts, or a range consisting of any two of 22 parts, 25 parts, or 28 parts. The fine aggregate is manufactured sand with a particle size of ≤5 mm and a crushing value of <30%.

[0044] In a specific embodiment, the weight percentage of the detoxified fly ash is 5 to 10 parts or 6 to 12 parts; for example, 6 parts, 8 parts, or 12 parts, or a range consisting of any two of 6 parts, 8 parts, or 12 parts. The detoxified fly ash has a particle size of ≤5mm and is the product of washed and pyrolyzed fly ash from municipal solid waste incineration. Its soluble chlorine content, heavy metal leaching concentration, and dioxin concentration meet the pollution control requirements specified in HJ1134 "Technical Specifications for Pollution Control of Municipal Solid Waste Incineration Fly Ash." Specifically, the detoxified fly ash meets the following requirements: dioxin content ≤50ng-TEQ / kg, soluble chlorine content ≤2%. In a preferred embodiment, the soluble chlorine content ≤1%, and the heavy metal leaching concentration does not exceed the maximum allowable discharge concentration limit specified in GB8978 "Integrated Wastewater Discharge Standard" (the maximum allowable discharge concentration of Class II pollutants shall be implemented in accordance with the first-level standard).

[0045] The cement-stabilized crushed stone mixture of the present invention has the following properties: 7-day unconfined compressive strength of ≥4.0 MPa, and a compaction degree of 95-98%.

[0046] The present invention also provides a method for preparing a cement-stabilized gravel mixture using detoxified fly ash, comprising the following steps:

[0047] S1. Determine the weight proportions of coarse aggregate, fine aggregate and detoxified fly ash based on the recommended crushed stone gradation for highway pavement base;

[0048] In this step, the recommended crushed stone gradations for the highway pavement base include CB-1, CB-2, CB-3, CC-1, CC-2, and CC-3. The recommended crushed stone gradations for the highway pavement base are met by adjusting the content of aggregate and detoxified fly ash of different gradations.

[0049] S2, adding cement and water of different proportions to the coarse aggregate, fine aggregate and detoxified fly ash prepared in step S1, determining the optimum moisture content and maximum dry density of the raw materials through compaction tests, and determining the weight ratios of cement and water accordingly;

[0050] In this step, cement and water are weighed in different proportions, added to the coarse aggregate, fine aggregate and detoxified fly ash proportioned in step S1 and mixed evenly; a fitting curve of moisture content and dry density is drawn through multiple compaction tests to determine the optimal moisture content and maximum dry density of the raw materials. The weight proportions of cement and water are then determined based on the optimal moisture content and maximum dry density. The compaction test can be carried out with reference to the experiments in standard T0804 "Test Procedures for Stabilized Materials of Inorganic Binders for Highway Engineering", for example, the compaction test can be carried out 6 to 7 times; in the fitting curve of moisture content and dry density, the cement content can be fixed and the amount of water added can be adjusted to obtain it. S3, weigh the raw materials according to the weight proportions determined in steps S1 and S2, and mix the raw materials evenly to obtain a cement-stabilized gravel mixture.

[0051] In this step, coarse and fine aggregates, detoxified fly ash, and cement are put into a forced mixer in a certain proportion and mixed, and then water is added. The mixing time is 60 to 90 seconds.

[0052] Example

[0053] Examples 1 to 5 use the following raw materials:

[0054] The cement used is P·O42.5 cement with a specific surface area of ​​370m 2 / kg, 28-day compressive strength is 55MPa;

[0055] The coarse aggregate is natural crushed stone with a crushing value of 18%;

[0056] The fine aggregate is machine-made sand with a particle size of 0-5 mm and a crushing value of 22%.

[0057] The particle size of the detoxified fly ash is 0-5mm; the detoxified fly ash meets the following requirements: dioxin content is 10ng-TEQ / kg, soluble chlorine content is 0.75%, and heavy metal leaching concentration is less than the maximum allowable emission concentration limit specified in GB8978 "Integrated Sewage Discharge Standard" (the maximum allowable emission concentration of Class II pollutants shall be implemented in accordance with the first-level standard).

[0058] Examples 1 to 5 employ the method of preparing cement-stabilized gravel mixture using detoxified fly ash of the present invention, as follows:

[0059] (1) Adjust the content of different graded aggregates (coarse aggregate, fine aggregate) and detoxified fly ash to meet the recommended crushed stone gradation range requirement CC-2 for highway pavement base, and determine the weight percentages of coarse aggregate, fine aggregate and detoxified fly ash, as shown in Table 1;

[0060] Table 1 Proportions of coarse aggregate, fine aggregate and detoxified fly ash (parts by weight)

[0061] Example 1 Example 2 Example 3 Example 4 Example 5 Coarse aggregate with a particle size of 16 to 31.5 mm 34 32 30 24 26 Coarse aggregate with a particle size of 5 to 16 mm 28 35 36 33 34 Fine aggregate with particle size ≤5mm 19 25 23 29 26 Detoxified fly ash 12 5 6 8 10

[0062] (2) Weigh cement and water in different proportions, add the weighed cement and water to the coarse aggregate, fine aggregate and detoxified fly ash in the weight proportions in (1), and mix them evenly. Determine the optimal moisture content and maximum dry density of the several raw materials in the weight proportions in (1) through multiple compaction tests, and determine the weight proportions of cement and water accordingly, as shown in Table 2;

[0063] Table 2 Cement and water ratio (parts by weight)

[0064] Example 1 Example 2 Example 3 Example 4 Example 5 Optimum moisture content 11.1％ 9.3％ 9.1％ 10.5％ 10.0％ <![CDATA[Maximum dry density (g / cm 3 )]]> 2.10 2.19 2.21 2.15 2.17 cement 7 3 5 6 4 water 12 8 10 11 8

[0065] (3) The raw materials determined in (1) and (2) were weighed and then placed into a mixer in a certain order and mixed for 60 to 90 seconds to prepare a cement-stabilized crushed stone mixture. The properties of the mixture are shown in Table 4.

[0066] Comparative Examples 1 to 5 are cement-stabilized gravel mixtures prepared without adding detoxified fly ash. The proportions thereof are shown in Table 3, and the properties are shown in Table 4.

[0067] Table 3 Raw material ratio of cement stabilized gravel mixture of comparative example (parts by weight)

[0068] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Coarse aggregate with a particle size of 16 to 31.5 mm 34 32 30 24 26 Coarse aggregate with a particle size of 5 to 16 mm 28 35 36 33 34 Fine aggregate with particle size ≤5mm 31 30 29 37 36 cement 7 3 5 6 4 water 12 8 10 11 8

[0069] Table 4 Performance of cement-stabilized crushed stone mixtures of Examples and Comparative Examples

[0070]

[0071]

[0072] As shown in Table 4, the 7-day unconfined compressive strength of the cement-stabilized gravel mixture prepared in the examples of the present invention is 4.1 to 5.1 MPa (average 4.6 MPa), which is higher than that of the cement-stabilized gravel mixture without detoxified fly ash (average 3.0 MPa). This shows that the high calcium and sulfate content of detoxified fly ash has a certain activity-stimulating effect, and at the same cement content, the performance of the prepared cement-stabilized gravel mixture is better. The compaction degree of the cement-stabilized gravel mixture prepared in the examples of the present invention is 95.4% to 97.8%, close to that of the comparative example, meeting the design requirements of the highway pavement base.

[0073] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A cement-stabilized gravel mixture, characterized in that: The raw materials include a solid phase and water, and the solid phase is calculated in parts by weight as follows:

2. The cement-stabilized crushed stone mixture according to claim 1, characterized in that: The weight proportion of the cement is 3 to 5 parts or 4 to 7 parts; and / or The cement is P·O42.5 cement with a specific surface area greater than 300m 2 / kg, 28-day compressive strength ≥42.5MPa.

3. The cement-stabilized crushed stone mixture according to claim 1, characterized in that: The weight proportion of the coarse aggregate is 52 to 66 parts or 56 to 71 parts.

4. The cement-stabilized crushed stone mixture according to claim 1, characterized in that: The coarse aggregate is compounded by aggregate with a particle size of 16 to 31.5 mm and aggregate with a particle size of 5 to 16 mm; The weight proportion of the aggregate with a particle size of 16 to 31.5 mm is 24 to 35 parts, and the weight proportion of the aggregate with a particle size of 5 to 16 mm is 28 to 36 parts.

5. The cement-stabilized crushed stone mixture according to claim 4, characterized in that: The coarse aggregate is natural crushed stone or recycled aggregate, and the crushing value of the coarse aggregate is less than 30%; The weight proportion of the aggregate with a particle size of 16 to 31.5 mm is 24 to 30 parts or 27 to 35 parts; The weight proportion of the aggregate with a particle size of 5 to 16 mm is 28 to 34 parts or 20 to 36 parts.

6. The cement-stabilized crushed stone mixture according to claim 1, characterized in that: The weight percentage of the fine aggregate is 19 to 25 parts or 23 to 29 parts; and / or The fine aggregate is machine-made sand with a particle size of ≤5 mm and a crushing value of <30%.

7. The cement-stabilized crushed stone mixture according to claim 1, characterized in that: The weight proportion of the detoxified fly ash is 5 to 10 parts or 6 to 12 parts.

8. The cement-stabilized crushed stone mixture according to claim 1, characterized in that: The particle size of the detoxified fly ash is ≤5mm; The detoxified fly ash meets the following requirements: dioxin content ≤ 50 ng-TEQ / kg, soluble chlorine content ≤ 2%.

9. The cement-stabilized crushed stone mixture according to claim 1, characterized in that: The cement-stabilized crushed stone mixture has the following properties: 7-day unconfined compressive strength ≥4.0 MPa, and compaction degree is 95-98%.

10. A method for preparing the cement-stabilized gravel mixture according to any one of claims 1 to 9 using detoxified fly ash, characterized in that: The following steps are involved: S1. Determine the weight proportions of coarse aggregate, fine aggregate and detoxified fly ash based on the recommended crushed stone gradation for highway pavement base; S2, adding cement and water of different proportions to the coarse aggregate, fine aggregate and detoxified fly ash prepared in step S1, determining the optimum moisture content and maximum dry density of the raw materials through compaction tests, and determining the weight ratios of cement and water accordingly; S3, weighing raw materials according to the weight proportions determined in step S1 and step S2, and mixing the raw materials in sequence to obtain a cement-stabilized gravel mixture.

11. The method for preparing cement-stabilized gravel mixture using detoxified fly ash according to claim 10, characterized in that: In step S1, the recommended crushed stone gradations for the highway pavement base layer include CB-1, CB-2, CB-3, CC-1, CC-2 and CC-3.

12. The method for preparing cement-stabilized gravel mixture using detoxified fly ash according to claim 9, characterized in that: In step S3, the mixing time is 60 to 90 seconds.

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