Preparation method and application of full-size steel slag gradient carbonized artificial aggregate suitable for ultra-thin asphalt wearing layer

Abstract

A method for preparing and applying a full-size steel slag gradient carbonized artificial aggregate suitable for ultra-thin asphalt wearing layers relates to the preparation and application of artificial aggregates. This method addresses the low strength of existing carbonized steel slag aggregates and their inability to comprehensively utilize diverse solid waste resources. This method involves crushing, magnetically separating, and screening steel slag to obtain particles of varying sizes. Each particle size is then subjected to pre-curing, granulation, curing, pre-curing, and post-curing to produce the full-size steel slag gradient carbonized artificial aggregate. This aggregate has an average carbon fixation content of 12.4%, an average free calcium oxide content of 0.32%, an average compressive strength of 54.32 MPa, and a volume expansion rate of 0.32% when maintained at 60°C for 5 days. This aggregate was used to prepare an ultra-thin SMA-10 asphalt mixture for wearing layers, achieving a dynamic stability of 13,285 times / mm, a water-immersion Marshall value of 96.5%, and an anti-skid BPN value of 0.76. This aggregate can be used in highway applications.

Description

Technical Field

[0001] The invention relates to a preparation method and application of artificial aggregate, and belongs to the technical field of solid waste utilization and road paving materials. Background Art

[0002] Steel slag, an industrial waste product generated during my country's steelmaking process, boasts high strength, wear resistance, and anti-skid properties, and has been used in asphalt pavements. However, a bottleneck limiting the widespread use of steel slag in asphalt pavements is the high concentration of free calcium oxide and other highly carbonizing substances within the slag. These substances readily expand in volume upon contact with water, causing cracking and other defects in asphalt concrete. Furthermore, highway construction consumes large quantities of high-quality natural aggregate, leading to a growing demand for alternatives to natural aggregates. Thoroughly carbonizing steel slag is a key approach to addressing CO2 sequestration, natural aggregate substitution, and the efficient resource utilization of steel slag.

[0003] In existing steel slag carbonization methods, as the carbonization product calcium carbonate increases during the carbonization process, a dense carbonized layer forms on the slag surface, hindering the further diffusion of carbon dioxide and ions. This slows the reaction rate in the later stages of slag carbonization, limiting the degree of carbonization in the core slag and resulting in poor strength. Furthermore, the use of only steel slag as a single solid waste hinders the comprehensive resource utilization of multiple solid wastes, such as fly ash and biochar. Summary of the Invention

[0004] The present invention aims to solve the technical problems of low strength of existing carbonized steel slag aggregates and the inability to fully utilize multiple solid waste resources, and to provide a preparation method and application of full-size steel slag gradient carbonized artificial aggregates suitable for asphalt ultra-thin wearing layers.

[0005] The method for preparing full-size steel slag gradient carbonized artificial aggregate suitable for ultra-thin asphalt wearing layer of the present invention is carried out according to the following steps:

[0006] 1. Crushing, magnetic separation and screening the steel slag in sequence to obtain steel slag with a particle size d in the following eight sizes: d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm and 4.75 ≤ d < 9.5 mm;

[0007] Use high-pressure water to flush the surface of steel slag with 6 particle sizes, namely 0.15≤d<0.3mm, 0.3≤d<0.6mm, 0.6≤d<1.18mm, 1.18≤d<2.36mm, 2.36≤d<4.75mm, and 4.75≤d<9.5mm, to remove dust and impurity layers attached to the surface of the steel slag;

[0008] Subsequently, steel slag aggregates with eight particle sizes, including d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm, and 4.75 ≤ d < 9.5 mm, were placed in an oven at 130-150°C for 8-12 hours for heating and drying.

[0009] 2. Placing the steel slag aggregates of the eight particle sizes treated in step 1 in a curing box isolated from a carbon dioxide environment for steel slag pre-curing treatment, spraying deionized water mist on the steel slag of each particle size and stirring the slag to allow the steel slag to undergo sufficient hydration reaction before carbonization; wherein, the amount of deionized water sprayed into the steel slag of 4.75≤d<9.5mm is 15%-20% of the mass of the steel slag, and the amount of deionized water sprayed increases by 0.5% for each particle size reduction;

[0010] 3. Granulation and curing treatment of steel slag with eight particle sizes were carried out under normal temperature and pressure: first, steel slag aggregate of any particle size, biochar powder, fly ash powder and ammonium carbonate powder were placed in a disc granulation device, and the granulation device was rotated for 5-10 minutes under the conditions of an inclination angle of 45° and a stirring speed of 15-20r / min for granulation treatment. During the entire granulation process, a water mist composed of deionized water and sodium bicarbonate was sprayed onto the mixture in the disc device, and carbon dioxide gas with a volume percentage concentration of 85%-95% was applied simultaneously, thereby obtaining carbonized steel slag artificial aggregate with a particle size of one grade higher;

[0011] Among them, when steel slag with a particle size of d < 0.075 mm is granulated and cured to prepare steel slag aggregate with a particle size of 0.075 ≤ d < 0.15 mm, the mass of biochar powder, fly ash powder, and ammonium carbonate powder is 3% to 10% of the mass of the steel slag, and the mass of sodium bicarbonate is 3.5% to 5.0% of the mass of the steel slag; when the particle size of the steel slag is increased by one level, the mass of the biochar powder, fly ash powder, and ammonium carbonate powder increases by 0.5%, and the mass of the sodium bicarbonate increases by 0.3%;

[0012] 4. Pre-curing the carbonized steel slag artificial aggregate: The carbonized steel slag artificial aggregate of different particle sizes obtained in step 3 is placed in an environment of normal pressure, temperature of 25°C, and relative humidity of 60% to 70% for pre-curing, so that the carbonized steel slag artificial aggregate has initial strength;

[0013] Among them, the pre-curing time of carbonized steel slag artificial aggregate with a particle size of 9.5≤d<13.2mm is 15~18h; the pre-curing time increases by 3h for each decrease in the particle size of carbonized steel slag artificial aggregate;

[0014] 5. Post-curing the carbonized steel slag artificial aggregate: placing the pre-cured carbonized steel slag artificial aggregate of different particle sizes in a supercritical carbon dioxide reactor, introducing carbon dioxide gas at a pressure of 8-10 MPa, a temperature of 40-60° C., and a relative humidity of 60%-70% for carbonization; wherein the carbon dioxide concentration is 95%-100%, and the carbon dioxide gas flow rate is 5-15 L / min; during the post-curing process of the carbonized steel slag artificial aggregate of each particle size, turning the carbonized steel slag artificial aggregate multiple times (4-6 times) to achieve uniform carbonization;

[0015] Among them, the post-curing time of carbonized steel slag artificial aggregate with a particle size of 9.5≤d<13.2mm is 15~20min; the pre-curing time increases by 3min for each decrease in the particle size of carbonized steel slag artificial aggregate;

[0016] After the post-curing treatment is completed, full-size steel slag gradient carbonized artificial aggregate suitable for asphalt ultra-thin wearing layer is obtained.

[0017] Furthermore, the steel slag in step 1 is any one or more of converter slag, electric furnace slag, and ladle refining slag.

[0018] The method for preparing an asphalt mixture for an ultra-thin asphalt wearing layer using full-size steel slag gradient carbonized artificial aggregate is carried out in the following steps:

[0019] First, the full-size steel slag gradient carbonized artificial aggregate is crushed and screened to obtain carbonized steel slag artificial aggregate with a particle size d in the following eight sizes: d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm, and 4.75 ≤ d < 9.5 mm. The purpose is to make the carbonized steel slag artificial aggregates of different particle sizes irregular in shape, which is more consistent with the shape of natural aggregates.

[0020] 2. Use carbonized steel slag artificial aggregate as the coarse and fine aggregate of the asphalt mixture, use a mixture of carbonized steel slag powder with the same particle size as the basalt mineral powder and basalt mineral powder in a volume ratio of 1:1 as the filler of the asphalt mixture, add asphalt and fiber, and prepare an ultra-thin wearing layer asphalt mixture.

[0021] Furthermore, the mass of asphalt in the asphalt mixture is 4 to 6% of the mass of the asphalt mixture.

[0022] Furthermore, the fibers in the asphalt mixture are steel slag fibers, and the mass of the steel slag fibers is 0.2-0.4% of the mass of the asphalt mixture.

[0023] Furthermore, the gradation of the ultra-thin wearing layer asphalt mixture is SMA-10, OGFC-10 or AC-10 asphalt mixture.

[0024] The present invention performs crushing-curing-synthesis treatment on steel slag of all particle sizes, especially adds biochar, fly ash and ammonium carbonate in the granulation curing process, and adopts different carbonization process parameters for steel slag of different particle sizes, thereby fully ensuring the carbonization quality of steel slag of different particle sizes, achieving uniform carbonization of the outside and inside of steel slag of different particle sizes, improving the performance of steel slag, and increasing the resource utilization rate of waste; at the same time, as the carbonization process of steel slag proceeds, carbonization can reduce the carbonization activity of the internal materials of the steel slag and increase the hydration activity, while the carbonization activity of the internal materials of the steel slag is reduced. The reduction can alleviate the risk of steel slag volume instability, and the increase in hydration activity can promote the formation of gelled products, thereby improving the strength of carbonized steel slag. Therefore, the present invention realizes a coordinated balance design of steel slag carbonization and hydration activity during the steel slag carbonization process, significantly improving the stability and strength of carbonized steel slag artificial aggregate; in addition, spraying deionized water mist in the pre-curing stage and performing preliminary strength curing in the pre-curing stage also realizes a coordinated balance design of carbonization and hydration activity of steel slag with different particle sizes, further promoting the stability and strength of carbonized steel slag artificial aggregate.

[0025] The full-grained steel slag gradient carbonized artificial aggregate suitable for use in ultra-thin asphalt wear layers prepared by the present invention has an average carbon fixation content of 12.4%, an average free calcium oxide content of 0.32%, and an average compressive strength of 54.32 MPa; the volume expansion rate of the artificial aggregate when maintained at a temperature of 60°C for 5 days is 0.32%. The ultra-thin wear layer SMA-10 asphalt mixture prepared using this full-grained steel slag gradient carbonized artificial aggregate has a dynamic stability of 13,285 times / mm, a water Marshall of 96.5%, and an anti-skid performance BPN value of 0.76. The present invention fully utilizes the role of solid waste materials such as biochar and fly ash in improving the carbonization degree of steel slag, achieving the preparation of carbonized steel slag artificial aggregate synergistically stimulated by multiple solid wastes such as steel slag, biochar, and fly ash, thereby improving the efficient resource utilization rate of different types of bulk solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic diagram of the preparation process of full-size steel slag gradient carbonized artificial aggregate suitable for ultra-thin asphalt wearing layer. DETAILED DESCRIPTION

[0027] The beneficial effects of the present invention are demonstrated with the following examples.

[0028] Example 1: The preparation method of the full-size steel slag gradient carbonized artificial aggregate suitable for the ultra-thin asphalt wearing layer of this embodiment is carried out according to the following steps:

[0029] 1. Crushing, magnetic separation and screening the steel slag in sequence to obtain steel slag aggregate with a particle size d in the following eight sizes: d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm and 4.75 ≤ d < 9.5 mm;

[0030] Use high-pressure water to flush the surface of steel slag with 6 particle sizes, namely 0.15≤d<0.3mm, 0.3≤d<0.6mm, 0.6≤d<1.18mm, 1.18≤d<2.36mm, 2.36≤d<4.75mm, and 4.75≤d<9.5mm, to remove dust and impurity layers attached to the surface of the steel slag;

[0031] Subsequently, steel slag aggregates with eight particle sizes (d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm, and 4.75 ≤ d < 9.5 mm) were placed in an oven at 135°C for 12 hours.

[0032] Second, the steel slag aggregates of the eight particle sizes treated in step one were placed in a curing box isolated from a carbon dioxide environment for steel slag pre-curing treatment. Deionized water mist was sprayed on the steel slag of each particle size and stirred to allow the steel slag to undergo sufficient hydration reaction before carbonization. The amount of deionized water sprayed into the steel slag aggregates of each particle size is shown in Table 1.

[0033] Table 1 The amount of deionized water injected into the slag of different particle sizes

[0034] 3. Granulation and curing treatment of steel slag of eight particle sizes were carried out under normal temperature and pressure: steel slag aggregate of any particle size, biochar powder, fly ash powder, and ammonium carbonate powder were first placed in a disc granulation device, and the granulation device was rotated for 10 minutes under the conditions of an inclination angle of 45° and a stirring speed of 20r / min for granulation treatment. During the entire granulation process, a water mist formed by a mixed solution of deionized water and sodium bicarbonate was sprayed onto the mixture in the disc device, and carbon dioxide with a volume percentage concentration of 90% was simultaneously applied to obtain carbonized steel slag artificial aggregate with a particle size of one grade higher. The mass percentage of biochar powder, fly ash powder, and ammonium carbonate powder in the steel slag of each particle size grade to the mass of the steel slag is shown in Table 2;

[0035] Among them, when steel slag with a particle size of d < 0.075 mm is granulated and cured to prepare steel slag aggregate with a particle size of 0.075 ≤ d < 0.15 mm, the mass of biochar powder, fly ash powder, and ammonium carbonate powder is 6% of the mass of the steel slag, and the mass of sodium bicarbonate is 4.0% of the mass of the steel slag. For each increase in the particle size of the steel slag, the mass of biochar powder, fly ash powder, and ammonium carbonate powder increases by 0.5%, and the mass of sodium bicarbonate increases by 0.3%. The specific quantities are shown in Table 2.

[0036] Table 2 The percentage of each substance added during the granulation and curing of steel slag of different particle size grades

[0037] 4. Pre-curing treatment of carbonized steel slag artificial aggregate: The carbonized steel slag artificial aggregate of different particle sizes obtained above was placed in an environment of normal pressure, temperature of 25°C, and relative humidity of 65% for pre-curing treatment to ensure that the carbonized steel slag artificial aggregate has initial strength; among them, the pre-curing time of carbonized steel slag artificial aggregate with a particle size of 9.5≤d<13.2mm is 16h; the pre-curing time increases by 3h for each decrease in particle size of the carbonized steel slag artificial aggregate; the pre-curing time of carbonized steel slag artificial particles of each particle size is shown in Table 3.

[0038] Table 3 Pre-curing time of carbonized steel slag artificial particles of different particle sizes

[0039] 5. Post-curing treatment of the carbonized steel slag artificial aggregate treated in step 4: placing the carbonized steel slag artificial aggregate after pre-curing treatment in a supercritical carbon dioxide reactor, and introducing carbon dioxide gas for carbonization at a pressure of 10 MPa, a temperature of 50°C, and a relative humidity of 65%; wherein the carbon dioxide concentration is 95% and the carbon dioxide gas flow rate is 15 L / min; during the post-curing treatment of the carbonized steel slag artificial aggregate of each particle size grade, the carbonized steel slag artificial aggregate is turned over 4 times to achieve uniform carbonization; wherein, the post-curing time of the carbonized steel slag artificial aggregate with a particle size of 9.5~13.2 mm is 18 min; for each decrease in the particle size of the carbonized steel slag artificial aggregate, the pre-curing time is increased by 3 min; the post-curing time of the carbonized steel slag artificial aggregate of each particle size grade is shown in Table 4; after the post-curing treatment is completed, a full-size steel slag gradient carbonized artificial aggregate suitable for an ultra-thin asphalt wearing layer is obtained.

[0040] Table 4 Post-curing time of carbonized steel slag artificial particles at different particle sizes

[0041] Comparative Example 1: The pretreatment method of the carbonized steel slag in this comparative example is consistent with that in Example 1, but the carbonization method is different. That is, the comparative carbonized steel slag does not undergo a pre-curing process, and the process parameters for carbonizing the carbonized steel slag of different particle size ranges are consistent. The carbonization process parameters of the comparative carbonized steel slag of different particle size ranges are mainly based on the carbonization parameters of the carbonized steel slag artificial aggregate of 2.36≤d<4.75mm in the embodiment. The preparation method of the carbonized steel slag artificial aggregate in this comparative example is specifically carried out as follows:

[0042] 1. Crushing, magnetic separation and screening the steel slag in sequence to obtain steel slag with a particle size d in the following eight sizes: d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm and 4.75 ≤ d < 9.5 mm;

[0043] Use high-pressure water to flush the surface of steel slag with 6 particle sizes, namely 0.15≤d<0.3mm, 0.3≤d<0.6mm, 0.6≤d<1.18mm, 1.18≤d<2.36mm, 2.36≤d<4.75mm, and 4.75≤d<9.5mm, to remove dust and impurity layers attached to the surface of the steel slag;

[0044] Subsequently, steel slag aggregates with eight particle sizes (d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm, and 4.75 ≤ d < 9.5 mm) were placed in an oven at 135°C for 12 hours.

[0045] 2. Granulation and curing treatment of steel slag with eight particle sizes were carried out under normal temperature and pressure: first, steel slag aggregate of any particle size, biochar powder, fly ash powder and ammonium carbonate powder were placed in a disc granulation device, and the granulation device was rotated for 10 minutes under the conditions of an inclination angle of 45° and a stirring speed of 20r / min for granulation treatment. During the entire granulation process, water mist formed by a mixed solution of deionized water and sodium bicarbonate was sprayed onto the mixture in the disc device, and carbon dioxide with a volume percentage concentration of 90% was applied at the same time to obtain carbonized steel slag artificial aggregate with a higher particle size. Among them, during the granulation and curing process of steel slag aggregates with different particle sizes, the mass of biochar powder, fly ash powder and ammonium carbonate powder was 9% of the mass of steel slag, and the mass of sodium bicarbonate was 5.8% of the mass of steel slag.

[0046] Carburized steel slag artificial aggregate is pre-cured: Carburized steel slag artificial aggregate of all particle sizes is placed in an environment of normal pressure, temperature of 25°C, and relative humidity of 65% for pre-curing for 22 hours to give the carburized steel slag artificial particles initial strength;

[0047] 4. The carbonized steel slag artificial aggregate was post-cured: the carbonized steel slag artificial aggregate of all particle sizes after pre-curing treatment was placed in a supercritical carbon dioxide reactor, and carbon dioxide gas was introduced at a pressure of 10 MPa, a temperature of 50°C, and a relative humidity of 65% for carbonization for 24 minutes; wherein the carbon dioxide concentration was 95% and the carbon dioxide gas flow rate was 15 L / min; during the post-curing treatment of the carbonized steel slag artificial aggregate of each particle size, the carbonized steel slag artificial aggregate was turned over 4 times to achieve uniform carbonization, thereby obtaining the carbonized steel slag artificial aggregate for comparison.

[0048] The full-size steel slag gradient carbonized artificial aggregate suitable for asphalt ultra-thin wearing layer prepared in Example 1 was compared with the carbonized steel slag artificial aggregate prepared in the comparative example in terms of average carbon fixation, average free calcium oxide content, average compressive strength, and average volume expansion rate. The results are as follows:

[0049] The average carbon fixation of the carbonized steel slag artificial aggregate is 3.2%; the average free calcium oxide content is 0.77%; the average compressive strength is 42.71 MPa; and the volume expansion rate is 0.75% when maintained at 60°C for 5 days.

[0050] The average carbon fixation content of the full-particle steel slag gradient carbonized artificial aggregate suitable for the ultra-thin asphalt wearing layer prepared in Example 1 is 12.4%, which is 3.9 times that of the comparative carbonized steel slag artificial aggregate; the average free calcium oxide content is 0.32%, which is only 41.6% of the comparative carbonized steel slag artificial aggregate; the average compressive strength is 54.32 MPa, which is 1.3 times that of the comparative carbonized steel slag artificial aggregate; the volume expansion rate when maintained at a temperature of 60°C for 5 days is 0.32%, which is only 42.7% of the comparative carbonized steel slag artificial aggregate.

[0051] It can be seen from this that the carbonized steel slag artificial aggregate prepared in Example 1 has a high carbon fixation amount, a low free calcium oxide content, a high average compressive strength, and a small volume expansion rate, which shows that the carbonized steel slag preparation method in Example 1 can significantly promote the carbonization degree of steel slag and improve its carbonized volume stability and strength.

[0052] Example 2: Asphalt mixture was prepared using the full-size steel slag gradient carbonized artificial aggregate prepared in Example 1. The specific method was carried out according to the following steps:

[0053] 1. The full-size steel slag gradient carbonized artificial aggregate prepared in Example 1 was crushed and sieved to obtain carbonized steel slag artificial aggregate with a particle size d in the following eight sizes: d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm, and 4.75 ≤ d < 9.5 mm. The purpose is to make the carbonized steel slag artificial aggregates of different particle sizes irregular in shape, which is more consistent with the shape of natural aggregates.

[0054] Second, based on the mineral gradation of the SMA-10 asphalt mixture, the carbonized steel slag artificial aggregate prepared in step 1 was used as the coarse and fine aggregate of the SMA-10 asphalt mixture. A mixture of carbonized steel slag powder with the same particle size as the basalt powder and basalt powder in a volume ratio of 1:1 was used as the filler of the SMA-10 asphalt mixture. Asphalt and fiber were added to prepare an ultra-thin wearing layer SMA-10 asphalt mixture. The asphalt mass accounted for 5.5% of the asphalt mixture, and the fiber was steel slag fiber, with a mass of 0.3% of the asphalt mixture. This resulted in an SMA-10 asphalt mixture containing full-size steel slag gradient carbonized artificial aggregate. The gradation composition of the SMA-10 asphalt mixture is shown in Table 5.

[0055] Table 5 SMA-10 asphalt mixture gradation composition Comparative Example 2: SMA-10 asphalt mixture was prepared using the carbonized steel slag artificial aggregate prepared in Comparative Example 1: According to the mineral gradation of SMA-10 asphalt mixture shown in Table 5, the carbonized steel slag artificial aggregate prepared in Comparative Example 1 was used as the coarse and fine aggregate of the SMA-10 asphalt mixture, basalt mineral powder was used as the filler of the SMA-10 asphalt mixture, asphalt and fiber were added to prepare an ultra-thin wearing layer SMA-10 asphalt mixture; the mass of the asphalt was 5.5% of the asphalt mixture, the fiber was steel slag fiber, and the mass of the steel slag fiber was 0.3% of the asphalt mixture, to obtain an SMA-10 asphalt mixture for comparison.

[0056] The high temperature stability, water damage resistance and anti-skid performance of the two asphalt mixtures were tested, and the results are as follows:

[0057] The dynamic stability of the SMA-10 asphalt mixture in comparison is 10572 times / mm; the immersion Marshall is 91.3%; and the anti-skid performance BPN value is 0.64.

[0058] The dynamic stability of the SMA-10 asphalt mixture prepared using Example 2 is 13285 times / mm, which is 25.7% higher than that of the comparative SMA-13 ​​asphalt mixture; the immersion Marshall is 96.5%; and the anti-skid performance BPN value is 0.76, which is 18.8% higher than that of the comparative SMA-13 ​​asphalt mixture.

[0059] It can be seen that the SMA-10 asphalt mixture prepared using the full-particle steel slag gradient carbonized artificial aggregate prepared in Example 1 has good high-temperature stability, water damage resistance and anti-skid performance, which shows that the carbonized steel slag preparation method of the present invention can significantly improve the road performance of ultra-thin wearing layer asphalt mixture.

Claims

1. A method for preparing full-size steel slag gradient carbonized artificial aggregate suitable for ultra-thin asphalt wearing layer, characterized in that: The method proceeds as follows:

1. Crushing, magnetic separation and screening the steel slag in sequence to obtain steel slag with a particle size d in the following eight sizes: d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm and 4.75 ≤ d < 9.5 mm; Use high-pressure water to flush the surface of steel slag with 6 particle sizes, namely 0.15≤d<0.3mm, 0.3≤d<0.6mm, 0.6≤d<1.18mm, 1.18≤d<2.36mm, 2.36≤d<4.75mm, and 4.75≤d<9.5mm, to remove dust and impurity layers attached to the surface of the steel slag; Subsequently, steel slag aggregates with eight particle sizes, including d < 0.075 mm, 0.075 ≤ d < 0.15 mm, 0.15 ≤ d < 0.3 mm, 0.3 ≤ d < 0.6 mm, 0.6 ≤ d < 1.18 mm, 1.18 ≤ d < 2.36 mm, 2.36 ≤ d < 4.75 mm, and 4.75 ≤ d < 9.5 mm, were placed in an oven at 130-150°C for 8-12 hours for heating and drying.

2. Placing the steel slag aggregates of the eight particle sizes treated in step 1 in a curing box isolated from a carbon dioxide environment for steel slag pre-curing treatment, spraying deionized water mist on the steel slag of each particle size and stirring the slag to allow the steel slag to undergo sufficient hydration reaction before carbonization; wherein, the amount of deionized water sprayed into the steel slag of 4.75≤d<9.5mm is 15%-20% of the mass of the steel slag, and the amount of deionized water sprayed increases by 0.5% for each particle size reduction; 3. The eight particle size grades of steel slag obtained in step 2 are granulated and cured under normal temperature and pressure: first, steel slag aggregate of any particle size grade, biochar powder, fly ash powder and ammonium carbonate powder are placed in a disc granulation device, and the granulation device is rotated for 5 to 10 minutes under the conditions of an inclination angle of 45° and a stirring speed of 15 to 20 r / min for granulation treatment. During the entire granulation process, a water mist composed of deionized water and sodium bicarbonate is sprayed onto the mixture in the disc device, and carbon dioxide gas with a volume percentage concentration of 85% to 95% is simultaneously applied, thereby obtaining carbonized steel slag artificial aggregate with a higher particle size grade. Among them, the steel slag with a particle size of 4.75≤d<9.5mm is obtained after the above-mentioned granulation and curing treatment to obtain a particle size of 9.5≤d<13.2mm; When steel slag with a particle size of d < 0.075 mm is granulated and cured to prepare steel slag aggregate with a particle size of 0.075 ≤ d < 0.15 mm, the mass of biochar powder, fly ash powder, and ammonium carbonate powder is 3% to 10% of the mass of the steel slag, and the mass of sodium bicarbonate is 3.5% to 5.0% of the mass of the steel slag. For every increase in the particle size of the steel slag, the mass of the biochar powder, fly ash powder, and ammonium carbonate powder increases by 0.5%, and the mass of the sodium bicarbonate increases by 0.3%.

4. Pre-curing the carbonized steel slag artificial aggregate: placing the carbonized steel slag artificial aggregate of different particle sizes obtained in step 3 in an environment of normal pressure, temperature of 25°C, and relative humidity of 60% to 70% for pre-curing treatment to ensure that the carbonized steel slag artificial aggregate has initial strength; Among them, the pre-curing time of carbonized steel slag artificial aggregate with a particle size of 9.5≤d<13.2mm is 15~18h; the pre-curing time increases by 3h for each decrease in the particle size of carbonized steel slag artificial aggregate; 5. Post-curing the carbonized steel slag artificial aggregate obtained in step 4: placing the pre-cured carbonized steel slag artificial aggregates of different particle sizes in a supercritical carbon dioxide reactor, and introducing carbon dioxide gas at a pressure of 8-10 MPa, a temperature of 40-60° C., and a relative humidity of 60%-70% for carbonization treatment; wherein the carbon dioxide concentration is 95%-100%, and the carbon dioxide gas flow rate is 5-15 L / min; during the post-curing treatment of the carbonized steel slag artificial aggregates of each particle size, the carbonized steel slag artificial aggregates are turned 4-6 times to achieve uniform carbonization; Among them, the post-curing time of carbonized steel slag artificial aggregate with a particle size of 9.5≤d<13.2mm is 15~20min; the post-curing time increases by 3min for each decrease in the particle size of carbonized steel slag artificial aggregate; After the post-curing treatment is completed, full-size steel slag gradient carbonized artificial aggregate suitable for asphalt ultra-thin wearing layer is obtained.

2. The method for preparing full-size steel slag gradient carbonized artificial aggregate suitable for ultra-thin asphalt wearing layer according to claim 1, characterized in that: The steel slag in step 1 is any one or more of converter slag, electric furnace slag, and ladle refining slag.

3. A method for preparing an asphalt mixture for an ultra-thin asphalt wearing layer using the full-size steel slag gradient carbonized artificial aggregate prepared by the method of claim 1, characterized in that: The method proceeds as follows: First, the full-size steel slag gradient carbonized artificial aggregate is crushed and sieved to obtain carbonized steel slag artificial aggregate with a particle size d in the following 8 sizes: d < 0.075mm, 0.075≤d < 0.15mm, 0.15≤d < 0.3mm, 0.3≤d < 0.6mm, 0.6≤d < 1.18mm, 1.18≤d < 2.36mm, 2.36≤d < 4.75mm, and 4.75≤d < 9.5mm. The purpose is to make the carbonized steel slag artificial aggregates of different particle sizes irregular in shape, which is more consistent with the shape of natural aggregates; 2. Use carbonized steel slag artificial aggregate as the coarse and fine aggregate of the asphalt mixture, use a mixture of carbonized steel slag powder with the same particle size as the basalt mineral powder and basalt mineral powder in a volume ratio of 1:1 as the filler of the asphalt mixture, add asphalt and fiber to prepare an ultra-thin wearing layer asphalt mixture.

4. The method for preparing an asphalt mixture with an ultra-thin asphalt wearing layer using full-size steel slag gradient carbonized artificial aggregate according to claim 3, characterized in that: The mass of asphalt in asphalt mixture is 4~6% of the mass of asphalt mixture.

5. The method for preparing an asphalt mixture with an ultra-thin asphalt wearing layer using full-size steel slag gradient carbonized artificial aggregate according to claim 3, characterized in that: The fiber in the asphalt mixture is steel slag fiber, and the mass of the steel slag fiber is 0.2~0.4% of the mass of the asphalt mixture.

6. The method for preparing an asphalt mixture with an ultra-thin asphalt wearing layer using full-size steel slag gradient carbonized artificial aggregate according to claim 3, characterized in that: The gradation of the ultra-thin wearing layer asphalt mixture is SMA-10, OGFC-10 or AC-10 asphalt mixture.

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