Modified steel slag cooperates with iron tailings and straw asphalt concrete and preparation method

Abstract

The application discloses modified steel slag cooperated with iron tailings and straw asphalt concrete and a preparation method thereof. The raw materials of the asphalt concrete include aggregate dry base, modified straw fiber, straw fiber and asphalt. The modified straw fiber accounts for 0.14-0.33% of the total mass of the aggregate dry base, the asphalt accounts for 4.2-6.4% of the total mass of the aggregate dry base, and the straw fiber accounts for 0.75-1.75% of the mass of the asphalt. According to the mass percentage, the aggregate dry base includes modified steel slag coarse aggregate 60-70%, iron tailings fine aggregate 30-35% and steel slag powder 1-5%. The effective components in solid wastes such as steel slag, iron tailings and corn straw can be effectively utilized by the modifier, so that the steel waste and agricultural waste are effectively utilized, and the prepared asphalt concrete shows good working performance and physical and mechanical properties. The application can realize the cooperative utilization of industrial solid wastes, achieve the purpose of energy saving and environmental protection, and promote the comprehensive utilization of solid wastes to the development of high added value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of asphalt concrete, in particular to a modified steel slag cooperated with iron tailings and straw for asphalt concrete and a preparation method. BACKGROUND

[0002] Steel slag is a by-product of steelmaking, and its hardness, abrasion value and other properties are close to or better than those of natural minerals, making it a valuable resource that can replace natural minerals. However, the volume stability problem of steel slag limits its application and promotion. For example, Masoudi et al. found that steel slag can improve the short-term and long-term anti-aging performance of warm-mixed asphalt mixture, but slightly increases the consumption of asphalt. Arbani et al. found that the addition of steel slag effectively improves the Marshall stability (MS) and fatigue life of asphalt mixture, and reduces the permanent deformation of asphalt mixture, but does not consider the crack resistance of asphalt mixture. Waligora et al. found that the asphalt mixture pavement paved with steel slag completely replacing natural aggregate will crack prematurely, and the water-swelling property of steel slag leads to cracking of asphalt mixture. The existing methods for reducing the water-swelling rate and improving the stability of steel slag mainly focus on mechanical grinding, acid modification and high-temperature reconstruction. Although these modification methods can reduce the content of f-CaO in steel slag and have a certain digestion effect, they still have problems such as environmental pollution and complex operation process. Therefore, it is particularly important to explore a steel slag modification technology with good modification effect and simple process to promote the resource utilization of steel slag.

[0003] In addition to steel slag, under the background of large-scale mining of non-renewable resources such as sand and cement in transportation infrastructure, the application of new materials such as straw fiber and iron tailings not only saves resources but also improves the performance of transportation infrastructure. In recent years, many domestic and foreign studies have shown that iron tailings as coarse or fine aggregate have good application prospects in asphalt mixture. For example, Velasquez et al. explored the mechanical properties of iron tailings asphalt mixture and described the feasibility of its application in asphalt pavement as aggregate. Zhang Binlin et al. used high-dosage iron tailings sand waste and recycled materials as road base mixture, and verified through tests that it has the characteristics of easy compaction. Zhang Zhihao et al. studied the feasibility of improved iron tailings for pavement base, and showed that it is feasible to select appropriate inorganic binder and appropriate iron tailings dosage for road base. Although iron tailings have the advantage of replacing natural sand, their composition varies greatly due to different sources, resulting in unstable physical and chemical properties. In addition, iron tailings need to be pretreated by crushing and screening before use, which increases the complexity and cost of construction process, and restricts the large-scale application of iron tailings. Therefore, it is necessary to further explore the properties and treatment methods of iron tailings to fully utilize their performance while reducing the complexity of the process and saving costs.

[0004] Straw fiber has broad research prospects due to its low cost, good renewability and environmental friendliness. For example, Gao Qinghua studied the rheological properties, viscosity-temperature properties and low-temperature deformation properties of asphalt mortar after adding cotton straw fiber, and gave the optimal mixing amount. Li Zhenxia et al. studied the preparation process of corn straw fiber, the performance of asphalt mixture and the mechanism of fiber action. Liu Kaiping et al. prepared asphalt mortar with different fiber contents using cotton straw fiber, and evaluated its road performance by needle penetration test and dynamic shear rheological test. However, the unmodified straw fiber has poor effect on improving the road performance of asphalt mixture. The straw fiber modified by different materials can improve the compatibility with asphalt, and in turn improve the road performance of asphalt mixture to different degrees. However, the preparation process of modified straw fiber is relatively complicated, and the quality of finished product is not easy to control. Therefore, it is necessary to further study the mechanism and influencing factors of straw fiber in asphalt mixture, and explore more economical, effective and convenient modification methods and technologies to realize the efficient application of straw fiber in asphalt mixture.

[0005] Asphalt concrete is commonly used in road construction. Traditional asphalt concrete has the disadvantages of easy cracking, poor low-temperature resistance and poor ultraviolet aging resistance, which greatly reduces the service life of asphalt concrete. Chinese patent CN119661123A discloses an anti-cracking asphalt concrete material and a preparation method thereof. The asphalt concrete material is prepared by using coarse aggregate, fine aggregate, fly ash and reinforcing filler, mixing dry materials and composite aerogel. The reinforcing filler is based on the synergistic effect between modified lignin, diatomite and hydrotalcite, which improves the anti-cracking performance of the concrete. The modified lignin utilizes its fiber characteristics to enhance the compression resistance of the asphalt concrete. Although the asphalt concrete prepared by the above technical solution has excellent compression resistance and anti-cracking performance, lignin is mainly derived from wood, and large-scale application will cause damage to forest resources, which is not suitable for industrial production. How to reasonably and stably modify raw materials such as steel slag, iron tailings and straw fiber, and apply them in the preparation process of asphalt concrete to improve the comprehensive performance of asphalt concrete is the current research focus. SUMMARY

[0006] The present application provides a modified steel slag cooperated with iron tailings and straw asphalt concrete and a preparation method thereof, to solve the problem that the modification method of raw materials such as steel slag, iron tailings and straw fiber is unreasonable, which leads to insufficient improvement of the comprehensive performance of the concrete after being applied in asphalt concrete. The present application can effectively utilize the effective components in solid waste (steel slag, iron tailings and corn straw) by changing the modification method, so that steel waste and agricultural waste are effectively utilized. The prepared asphalt concrete shows good working performance and physical and mechanical properties. The present application can realize the cooperative utilization of bulk industrial solid waste, achieve the purpose of energy saving and environmental protection, and promote the comprehensive utilization of solid waste to develop in the direction of high added value.

[0007] To achieve the above object, the application provides a first aspect of a modified steel slag asphalt concrete cooperated with iron tailings and straw, raw materials of the asphalt concrete including aggregate dry base, modified straw fiber, straw fiber and asphalt; wherein the modified straw fiber accounts for 0.14-0.33% of the total mass of the aggregate dry base, the asphalt accounts for 4.2-6.4% of the total mass of the aggregate dry base, and the straw fiber accounts for 0.75-1.75% of the mass of the asphalt; the aggregate dry base includes modified steel slag coarse aggregate 60-70%, iron tailings fine aggregate 25-35% and steel slag powder 1-5% according to the mass percentage.

[0008] The application provides a second aspect of a preparation method of the modified steel slag asphalt concrete cooperated with iron tailings and straw, including the following steps:

[0009] S1: pretreatment of steel slag

[0010] After screening, crushing, carbonization, drying, shaping and screening of the steel slag, steel slag coarse particles and steel slag fine particles are obtained; after washing and drying of the steel slag coarse particles, modified steel slag coarse particles are obtained;

[0011] S2: preparation of steel slag powder

[0012] After powder grinding, magnetic separation and secondary powder grinding of the steel slag fine particles, steel slag powder is obtained and is ready for use;

[0013] S3: preparation of iron tailings fine aggregate

[0014] After water washing, drying, screening, shaping, magnetic separation and secondary shaping of the iron tailings, iron tailings fine aggregate is obtained;

[0015] S4: pretreatment of straw fiber

[0016] After peeling, intercepting, drying, crushing and screening of the corn straw, corn straw fragments are obtained, and then the corn straw fragments are disc milled to obtain straw fiber;

[0017] S5: preparation of modifier

[0018] (1) pretreatment of bean curd wastewater:

[0019] The bean curd wastewater is filtered to obtain bean curd wastewater filtrate;

[0020] (2) pretreatment of corn straw fragments

[0021] After the corn stalk fragments in step S4 are crushed and dried, corn stalk residues are obtained, and then the corn stalk residues are added to a mixed solvent of kerosene and concentrated sulfuric acid under heating, and after cooling to room temperature, the solvent is separated, neutralized with a NaOH solution, filtered, and corn stalk residue solution one is obtained, and then an aminosulfonic acid-based aromatic aminosulfonic acid polymer is added, and corn stalk residue solution two is obtained after stirring;

[0022] (3) The soybean wastewater filtrate is mixed with the corn stalk residue solution two to prepare a modifier;

[0023] S6: Preparation of modified steel slag coarse aggregate

[0024] The modified steel slag coarse particles prepared in step S1 are immersed in the modifier, and after filtration and drying, modified steel slag coarse aggregate is obtained.

[0025] S7: Preparation of modified straw fiber

[0026] The straw fiber obtained in step S4 is immersed in the modifier, and then an aluminum hydroxide flame retardant is added and mixed and stirred, and after drying, modified straw fiber is obtained.

[0027] S8: Mixing of aggregate dry base and modified straw fiber

[0028] The modified steel slag coarse aggregate obtained in step S6, the steel slag powder obtained in step S2, and the iron tailings fine aggregate obtained in step S3 are dried and kept warm, and then mixed in proportion to obtain an aggregate dry base, and then the modified straw fiber is added in proportion and stirred to obtain a dry-mixed aggregate.

[0029] S9: Preparation of asphalt concrete

[0030] The dry-mixed aggregate prepared in step S8 and asphalt are mixed in proportion, and then the straw fiber in step S4 is added and mixed, and finally asphalt concrete is obtained.

[0031] Preferably, in step S1, the specific steps of steel slag pretreatment are as follows:

[0032] First, the steel slag is screened to remove impurities in the steel slag, and then the screened steel slag is crushed to 5-25 mm to obtain steel slag particles, and then the steel slag particles are laid flat and carbonized, and the carbonized steel slag particles are dried to constant weight, and then the dried steel slag particles are placed in a ball mill for shaping, and then the shaped steel slag particles are screened to obtain steel slag coarse particles of 4.75-19 mm and steel slag fine particles with a particle size of less than 4.75 mm; and then the steel slag coarse particles of 4.75-19 mm are washed and dried to constant weight to obtain modified steel slag coarse particles.

[0033] Preferably, in step S1, the main mineral composition of the steel slag is RO phase, cementitious mineral phase (C2S, C3S) and C2F phase, and the main chemical composition and content are as follows: SiO2 15-25%, Al2O3 1.5-6%, Fe2O3 2-28%, MgO 1-11%, CaO 28-52%, FeO 2-13%, Na2O 0.01-1%, K2O 0.01-1%, SO3 0.01-0.28%, P2O5 0.1-5%, and loss on ignition 3-9%.

[0034] Preferably, in step S1, the carbonization condition is as follows: CO2 concentration 20±3%, temperature 20±3℃, and humidity 70±5%.

[0035] Preferably, in step S2, the specific process for preparing the steel slag powder is as follows:

[0036] The steel slag fine particles with particle size <4.75 mm are put into a ball mill for grinding, to obtain steel slag fine powder with specific surface area of 150-200 m 2 / kg, and then dry slag-iron separation is performed by using a strong magnetic separator, and the steel slag fine powder is put into the ball mill again for secondary grinding, to obtain steel slag powder with surface area of 500-700 m 2 / kg, for standby use.

[0037] Preferably, in step S1, the grinding speed of the ball mill used for shaping is 48 r / min.

[0038] Preferably, in step S2, the grinding speed of the strong magnetic separator used for magnetic separation is 15-25 r / min, and the magnetic field strength is 1.5-2.5 T.

[0039] Preferably, in step S3, the specific process for preparing the iron tailings fine aggregate is as follows:

[0040] First, the impurities in the iron tailings are screened out by using a water washing method, and the water content is dried, and then the large particles are removed by screening, so that the particle size is mainly distributed in the range of 1.18 mm-4.75 mm, and then the screened iron tailings are put into a ball mill for shaping, and magnetic separation is performed by using a strong magnetic separator, and the iron tailings after magnetic separation are continuously put into the ball mill for secondary shaping, to obtain the iron tailings fine aggregate.

[0041] Preferably, in step S4, the specific process for pretreating the straw fiber is as follows:

[0042] Firstly, the corn stalks with a diameter of 12-15 mm are peeled, and the corn stalks with a length of 30-40 cm are dried to a moisture content of less than or equal to 10%; then the corn stalks are put into a rubbing machine for crushing, and then corn stalk fragments with a diameter of 4-8 cm are obtained through screening; then the corn stalk fragments are put into a disc mill for disc milling, and corn stalk fibers with a diameter of 40-70 um and a length of 1-3 cm are obtained.

[0043] Preferably, in step S4, the main chemical elements of the corn stalks are: C 40-46%, H 5-6%, O 43-50%, N 0.6-1.1%, S 0.1-0.2, and ash 4.14%. The main chemical composition is: total cellulose 40-50%, lignin 15-20%, and alpha-cellulose 30-40%.

[0044] Preferably, in step S5, the specific process for preparing the modifier is as follows:

[0045] (1) Pretreatment of tofu wastewater:

[0046] The tofu wastewater is refrigerated at 1-5°C, and a tofu wastewater filtrate is obtained by filtration;

[0047] (2) Pretreatment of corn stalk residue:

[0048] The corn stalk fragments in step S4 are crushed to a diameter of less than 0.5 mm to obtain corn stalk residue, which is then dried to a constant weight. Then, 11% kerosene and 96% concentrated sulfuric acid are mixed in a volume ratio of 2-3:1 to obtain a mixed solvent. The corn stalk residue accounts for 25-30% of the mass of the mixed solvent, and the mixture is stirred at 45-55°C. After cooling to room temperature, the solvent is separated, neutralized with a NaOH solution with a mass percentage of 25-28%, filtered, and a corn stalk residue solution one with a solid content of 54-58% is obtained. Then, an amino sulfonic acid-aromatic amino sulfonic acid polymer is added, which accounts for 70-80% of the weight of the corn stalk residue solution one, to obtain a corn stalk residue solution two with a solid content of 35-45%.

[0049] (3) The tofu wastewater filtrate and the corn stalk residue solution two are mixed in a volume ratio of 1-2:1-2 to prepare the modifier.

[0050] Preferably, in step S6, the soaking time is 4-6h; in step S7, the soaking time is 3-5h, the amount of aluminum hydroxide flame retardant added is 10-13% of the weight of the stalk fibers, and the stirring time is 5-10 min.

[0051] Preferably, in step S6, the main technical indexes of the aluminum hydroxide flame retardant are: Al2O3≥64.5%, particle size 7000 meshes, attached water ≤0.5%, density 2.42g / cm 3 , average particle size 2.03-4um, whiteness 97%, pH value 8.5.

[0052] Preferably, in step S8, the specific process of mixing the aggregate dry base and the modified straw fiber is:

[0053] The modified steel slag coarse aggregate obtained in step S6, the steel slag powder obtained in step S2 and the iron tailings fine aggregate obtained in step S3 are respectively placed in an oven and dried for 4-6h, and after drying, they are kept in the oven for 2-3h; then the modified steel slag coarse aggregate, the iron tailings fine aggregate and the steel slag powder are respectively taken according to the proportion, put into a preheated mixing pot and fast mixed for 20-40s, then the modified straw fiber is added, slowly mixed along the clockwise direction for 20-40s, and then mixed counterclockwise for 20-40s, to obtain dry mixed aggregate, which is ready for use.

[0054] Preferably, in step S9, the specific process of preparing asphalt concrete is:

[0055] A groove is dug in the middle of the dry mixed aggregate prepared in step S8, the depth of which is not more than 1 / 3 of the thickness, and asphalt with a temperature of 170-180℃ is added, and after mixing for 3-5min, the straw fiber is added in three times, each time accounting for 0.25%-0.58% of the total mass of asphalt, and the interval time is 30s, and after uniform mixing, the asphalt concrete is obtained.

[0056] Therefore, the asphalt concrete prepared by using the modified steel slag, the iron tailings and the straw fiber and the preparation method thereof have the following beneficial effects:

[0057] (1) The asphalt concrete is prepared by using industrial waste steel slag and agricultural waste corn straw, and has the advantages of good volume stability, crack resistance and the like, and greatly reduces the production cost, so that the application of the asphalt concrete roadbed is inhibited, the expansion and extension of cracks are inhibited, and the efficient and stable control of the asphalt concrete production process is realized.

[0058] (2) The asphalt concrete prepared by the application utilizes multi-industry waste, and the waste used in the preparation includes steel industry waste (steel slag, iron tailings, steel slag powder) and agricultural waste (corn straw), and the performance indexes of the prepared asphalt concrete all meet the test index requirements in the Highway Engineering Asphalt and Asphalt Mixture Test Regulation JTG E20-2011, and the radioactivity meets the test index requirements in the Building Material Radioactive Nuclide Limitation GB 6566-2010, the utilization rate of the industrial solid waste raw material is improved, the production cost of enterprises can be significantly reduced, and the economic benefit and social environmental benefit are remarkable.

[0059] (3) The aggregate in the asphalt concrete uses 100% of the steel industry solid waste, uses steel slag as coarse aggregate, uses iron tailings as fine aggregate, and uses steel slag powder as filler, the steel slag powder filler is prepared by adopting a strong magnetic separator for dry slag-iron separation, and the grindability of the steel slag is improved. In the application, the aggregate content and the fineness of the filler are designed according to the particle closest packing theory and the Fuller integration distribution model, the consumption of asphalt in the asphalt concrete is reduced, and the comprehensive performance of the asphalt concrete is improved.

[0060] (4) The coarse aggregate steel slag used in the asphalt concrete provided by the application is first pretreated through screening, crushing, drying, shaping, washing and other processes, and then is impregnated with a modifier to obtain modified steel slag coarse aggregate, the performance indexes such as water absorption, crushing value, abrasion value and adhesion grade with asphalt of the modified steel slag coarse aggregate are improved to a certain extent, the stability of the modified steel slag is improved, the volume stability of the asphalt concrete doped with the modified steel slag is good, the wear resistance is improved, and the performance indexes of the modified steel slag meet the requirements in the Road Steel Slag (GB / T 25824-2010) and the Steel Slag for Wear-Resistant Asphalt Pavement (GB / T 24765-2009).

[0061] (5) The agricultural waste corn straw is used as fiber in the preparation of the asphalt concrete provided by the application, the shear resistance and tensile resistance of the road surface can be improved, the durability of the road surface is improved, the wear and tear of the road surface and the repair frequency are reduced, the corn straw fiber can also be used as a mechanical reinforcing agent to improve the service life and durability of the asphalt concrete, and in the ice and snow weather, the fiber can prevent the road surface from icing and traffic accidents. The straw fiber and the asphalt interact through adsorption, physical and chemical anchoring force, form a three-dimensional network structure, increase the strength and toughness of the mixture, effectively absorb the stress energy of the asphalt, and form a strength enhanced area in the asphalt to prevent the spread of cracks and damage.

[0062] (6) The asphalt concrete provided by the application, the agricultural waste corn straw fiber used in the preparation of the asphalt concrete is additionally added with a flame retardant, the fire resistance of the asphalt concrete is improved, fire accidents in the process of highway construction and use are avoided, the flame retardant forms a protective film in the asphalt concrete, the asphalt concrete is difficult to ignite or not easy to ignite, and when a fire occurs, the flame spreading speed can be effectively delayed, the fire expansion is avoided, the safety of the road is improved, the service life is prolonged, and the environmental protection is also improved.

[0063] The technical solutions of the application are described in further detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 The preparation flowchart of the modified steel slag coarse particles of the application;

[0065] Figure 2 The preparation flowchart of the steel slag powder filler of the application;

[0066] Figure 3 The preparation flowchart of the modified corn straw fiber of the application;

[0067] Figure 4 The preparation flowchart of the modifier of the application;

[0068] Figure 5 The preparation flowchart of the asphalt concrete of the application;

[0069] Figure 6(a) is an XRD diagram of steel slag;

[0070] Figure 6(b) is an XRD diagram of iron tailings;

[0071] Figure 7 Figures are SEM diagrams of the steel slag of example 2 and modification conditions 1-3, wherein (a) is the unmodified steel slag; (b) is the steel slag in modification condition 1; (c) is the steel slag in modification condition 2; (d) is the steel slag in modification condition 3;

[0072] Figure 8 Figures are the volume expansion rates of the steel slag of example 2 and modification conditions 1-3 under the same particle size and different modification conditions;

[0073] Figure 9 Figures are the volume stability curves of the steel slag asphalt concrete of example 2 and modification conditions 1-3;

[0074] Figure 10 Figures are the Marshall test result diagrams of the steel slag asphalt concrete of example 2 and modification conditions 1-3;

[0075] Figure 11 Figures are the asphalt mixture optimum oil stone ratio test result diagrams of example 2 and modification conditions 1-3. Detailed Implementation

[0076] The present invention will be further described below. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the present invention is not limited to this embodiment.

[0077] Example 1

[0078] like Figures 1-5 As shown, a method for preparing asphalt concrete using modified steel slag in conjunction with iron tailings and straw includes the following specific steps:

[0079] S1. Pretreatment of steel slag coarse aggregate:

[0080] First, the steel slag is screened to remove impurities. Then, the screened steel slag is crushed to 5-25mm using a jaw crusher to obtain steel slag particles. These 5-25mm particles are then spread evenly on a pallet and placed in a carbonization chamber for 60 hours under the following conditions: CO2 concentration 20±3%, temperature 20±3℃, and humidity 70±5%. The carbonized steel slag particles are then placed in a 105℃ drying oven and dried to constant weight. Finally, the dried steel slag particles are placed in a container without steel balls and... The steel slag particles were shaped in a hollow ball mill for 15 minutes at a speed of 48 r / min. The shaped steel slag particles were then sieved in a vibrating screen to obtain coarse steel slag particles of 4.75–19 mm and fine steel slag particles with a particle size <4.75 mm. The coarse steel slag particles of 4.75–19 mm were then washed and placed in a drying oven at 105℃ to dry to constant weight, yielding modified steel slag coarse particles of 4.75–19 mm.

[0081] As shown in Figure 6(a), the main mineral composition of the steel slag, after testing, is RO phase, cementing mineral phase (C2S, C3S) and C2F phase, etc., and the main chemical components and contents are: SiO2 23.48%, Al2O3 4.54%, Fe2O3 10.16%, MgO 5.24%, CaO 43.53%, FeO 4.84%, Na2O 0.16%, K2O 0.09%, SO3 0.17%, P2O5 2.47%, and loss on ignition 5.32%.

[0082] S2. Preparation of steel slag powder filler:

[0083] Fine steel slag particles with a particle size <4.75mm were ground in a ball mill equipped with steel balls and forged steel. The ball mill speed was 48 r / min, resulting in a specific surface area of ​​150 m². 2 / kg of steel slag fine powder, and then dry slag-iron separation was performed using a high-intensity magnetic separator at a speed of 20 r / min and a magnetic field strength of 2 T. The obtained steel slag fine powder was then put into a ball mill for secondary grinding until the specific surface area reached 500 m 2 / kg, to obtain steel slag powder for standby use.

[0084] S3, Pretreatment of iron tailings fine aggregate:

[0085] First, the impurities in the iron tailings were screened out by water washing method, and then dried in an oven at 105°C. Large particles were removed by screening to make the particle size mainly distributed between 1.18 mm and 4.75 mm. The screened iron tailings were put into a ball mill for shaping at a speed of 48 r / min for 22 min. Magnetic separation was performed using a high-intensity magnetic separator at a speed of 20 r / min and a magnetic field strength of 2 T. After magnetic separation, the iron tailings were put into a ball mill for secondary shaping for 18 min to obtain iron tailings fine aggregate. FIG. 6(b) is an XRD pattern of the iron tailings raw material.

[0086] S4, Preparation of straw fiber:

[0087] First, the 13 mm diameter corn stalks were surface peeled and dried in a 70°C air drying oven to a moisture content of ≤10%. Then the corn stalks were put into a rubbing machine for breaking, and then corn stalk fragments with a diameter of 5 cm were obtained by screening. Then the corn stalk fragments were put into a disc mill for disc milling (disc milling gap is 0.35 mm) to obtain corn straw fibers with a diameter of 45 um and a length of 1 cm.

[0088] S5, Preparation of steel slag modifier:

[0089] (1) Pretreatment of tofu wastewater: The tofu wastewater was refrigerated at 2°C, and the tofu wastewater filtrate was obtained by filtration.

[0090] (2) Pretreatment of corn straw residue: The corn straw fragments in step S4 were broken into corn straw residue with a diameter of less than 0.5 mm using a jaw crusher, and then dried to constant weight in a 70°C air drying oven. Then, a mixed solvent was obtained by uniformly mixing 11% kerosene and 96% concentrated sulfuric acid at a volume ratio of 2:1. The mixed solvent was added with 25% corn straw residue by mass ratio at 45°C and stirred. After cooling to room temperature, the solvent was separated out, then neutralized with a 25% NaOH solution by mass percentage, filtered, and the filtrate was suction filtered to obtain a corn straw residue solution one with a solid content of 55%. Then, 75% of the weight of the obtained corn straw residue solution one was added with an aminosulfonic acid-aromatic aminosulfonic acid polymer (purchased from Beijing Mu Lake New Material Technology Co., Ltd.), stirred for 40 min, and adjusted to obtain a corn straw residue solution two with a solid content of 35%.

[0091] (3) The tofu wastewater filtrate and the corn straw residue solution are mixed in a ratio of 1:2 by volume to prepare a modifier.

[0092] It is detected that the main chemical elements of the corn straw are C 41.14%, H 6.28%, O 43.25%, N 5.06%, S 0.13%, and ash 4.14%. The main chemical components are total cellulose 44.58%, lignin 18.35%, and α-cellulose 37.07%.

[0093] S6, modification of the steel slag coarse aggregate:

[0094] The modified steel slag coarse particles in step S1 are put into the impregnation container containing the modifier in step S5 for impregnation for 4 h. Then, the impregnated and modified steel slag coarse particles are filtered out, and are put into a tray and then are placed into a 70℃ air drying oven for drying until constant weight to obtain modified steel slag coarse aggregate for standby use.

[0095] S7, modification of the straw fiber:

[0096] The straw fiber in step S4 is put into the impregnation container containing the modifier in step S5 for impregnation for 4 h. Then, the aluminum hydroxide flame retardant is added and mixed for 6 min, and the added amount of the aluminum hydroxide flame retardant is 12% of the weight of the straw fiber. The impregnated and modified straw fiber is put into a tray and then is placed into a 70℃ air drying oven for drying until constant weight for standby use.

[0097] The main technical indexes of the aluminum hydroxide flame retardant are Al2O3≥64.5%, particle size 7000 mesh, attached water ≤0.5%, density 2.42 g / cm 3 , average particle size 2.03-4 um, whiteness 97%, and pH value 8.5. The aluminum hydroxide flame retardant is purchased from Dongguan Daoer New Material Technology Co., Ltd. and the model is Doher-6521.

[0098] S8, mixing of the aggregate and the straw fiber:

[0099] The modified steel slag coarse aggregate treated in step S6, the steel slag powder filler treated in step S2 and the iron tailings fine aggregate treated in step S3 are respectively placed in an oven for drying for 4h, the drying temperature of the oven is 105℃±5℃, the holding temperature is 160±5℃, and after drying, the oven is kept for 2h. Then, the modified steel slag coarse aggregate, the iron tailings fine aggregate and the steel slag powder filler (the modified steel slag coarse aggregate accounts for 60%, the iron tailings fine aggregate accounts for 35% and the steel slag powder accounts for 5%) are respectively taken according to the proportion, put into a preheated mixing pot and fast stirred for 20s, the preheating temperature of the mixing pot is 180℃, then 0.16% of the modified straw fiber in the total dry aggregate is added into the mixing pot, slowly stirred for 20s in the clockwise direction, then counterclockwise stirred for 20s, and the dry-mixed aggregate obtained is ready for use.

[0100] S9, Preparation of asphalt concrete:

[0101] A groove is dug in the middle of the dry-mixed aggregate mixed in S8, the depth is not more than 1 / 3 of the thickness, 4.6% of the total dry aggregate is added into the matrix asphalt (temperature 170℃), then the straw fiber is added in 3 times (0.30% of the total mass of the matrix asphalt is added each time), the interval time is 30s each time, and the asphalt concrete is obtained after slow mixing at 48r / min.

[0102] The unmodified steel slag coarse aggregate in step S1 and the modified steel slag coarse aggregate obtained in step S6 are respectively tested for performance, and the test results are shown in Tables 1 and 2. The straw fiber before and after modification in step S7 is tested for performance, and the test results are shown in Table 3. The asphalt concrete in step S9 is tested for performance, and the test results are shown in Table 4.

[0103] Table 1 Basic performance index of steel slag before and after modification in S6 of Example 1

[0104]

[0105] Table 2 Performance index of steel slag before and after modification in S6 of Example 1

[0106]

[0107]

[0108] Note 1: The test index requirement in “Technical Specification for Construction of Highway Asphalt Pavement” JTG F40-2004

[0109] Table 3 Performance index of straw fiber before and after modification in S7 of Example 1

[0110]

[0111] Note 2: Test index requirement in JTT533-2004 Wood Fiber for Bituminous Pavement

[0112] Table 4 Performance index of asphalt concrete in Example 1-S9

[0113]

[0114] Note 3: Test index requirement in JTG E20-2011 Test Regulation of Asphalt and Asphalt Mixture for Highway Engineering

[0115] Example 2

[0116] A preparation method of modified steel slag cooperated with iron tailings and straw of asphalt concrete, the specific steps are as follows:

[0117] S1, pretreatment of steel slag coarse aggregate:

[0118] Firstly, the steel slag is screened to remove impurities in the steel slag; then the screened steel slag is crushed to 5-25mm by a jaw crusher to obtain steel slag particles; then the 5-25mm steel slag particles are placed in a tray and carbonized in a carbonization box for 70h, and the carbonization conditions are as follows: CO2 concentration 20±3%, temperature 20±3℃, humidity 70±5%; then the carbonized steel slag is placed in a 105℃ drying oven for air drying to constant weight; then the dried steel slag particles are placed in a cavity ball mill without steel balls and steel hammers for shaping, and the shaping time is 25min and the rotation speed of the ball mill is 48r / min; then the shaped steel slag particles are screened in a vibrating screen to obtain 4.75-19mm steel slag coarse particles and steel slag fine particles with particle size <4.75mm; then the 4.75-19mm steel slag coarse particles are washed, and the washed steel slag coarse particles are placed in a 105℃ drying oven for air drying to constant weight to obtain 4.75-19mm modified steel slag coarse particles. The steel slag raw material is the same as that in Example 1.

[0119] S2, preparation of steel slag powder filler:

[0120] The steel slag fine particles with particle size <4.75mm are placed in a ball mill equipped with steel balls and steel hammers for grinding to obtain steel slag fine powder with specific surface area of 180m 2 / kg, and then dry iron slag separation is carried out by using a strong magnetic separator, the rotation speed of the strong magnetic separator is 20r / min and the magnetic field strength is 2T, and the obtained steel slag fine powder is placed in a ball mill for secondary grinding to a specific surface area of 600m 2 / kg to obtain steel slag powder for standby use.

[0121] S3, pretreatment of iron tailings fine aggregate:

[0122] Firstly, the impurities in the iron tailings are screened out by water washing method, then dried in an oven at 105℃, and then screened to remove large particles, so that the particle size is mainly distributed between 1.18mm and 4.75mm. The screened iron tailings are put into a ball mill for shaping, the rotation speed of the ball mill is 48r / min, the shaping time is 20min, and then the shaped iron tailings are put into a strong magnetic separator for magnetic separation, the rotation speed of the strong magnetic separator is 20r / min, and the magnetic field strength is 2T. After magnetic separation, the iron tailings are put into a ball mill for secondary shaping, the shaping time is 25min, and the iron tailings fine aggregate is obtained. The iron tailings used are the same as those in Example 1.

[0123] S4, preparation of straw fiber:

[0124] Firstly, the 14mm diameter corn stalks are surface peeled and treated, and the corn stalks with a length of 35cm are placed in a 70℃ air drying oven to dry to a moisture content of ≤10%. Then the corn stalks are put into a rubbing machine for crushing, and then the corn stalks with a diameter of 6cm are obtained by screening. Then the corn stalk pieces are put into a disc mill for disc milling (disc milling gap is 0.35mm), and corn straw fibers with a diameter of 50um and a length of 2cm are obtained.

[0125] S5, preparation of steel slag modifier:

[0126] (1) Pretreatment of tofu wastewater: The tofu wastewater is refrigerated at 2℃, and the tofu wastewater filtrate is obtained by filtration.

[0127] (2) Pretreatment of corn stalk residue: The corn stalk pieces in step S4 are crushed to a diameter of less than 0.5mm in a jaw crusher, and then placed in a 70℃ air drying oven to dry to a constant weight. Then, 11% kerosene and 96% concentrated sulfuric acid are mixed in a volume ratio of 2.5:1 to obtain a mixed solvent. The mixed solvent is added with 27% corn stalk residue by mass ratio at 50℃ and stirred. After cooling to room temperature, the solvent is separated, neutralized with a 26% NaOH solution by mass fraction, filtered, and the filtrate is extracted to obtain a corn stalk residue solution one with a solid content of 56%. Then, 75% of the weight of the obtained corn stalk residue solution one is added with an amino sulfonic acid-aromatic amino sulfonic acid polymer (purchased from Beijing Mu Lake New Material Technology Co., Ltd.), stirred for 45min, and adjusted to obtain a corn stalk residue solution two with a solid content of 40%.

[0128] (3) The tofu wastewater filtrate and the corn stalk residue solution two are mixed in a volume ratio of 1:1 to prepare a modifier. The corn stalk used is the same as that in Example 1.

[0129] S6, modification of steel slag coarse aggregate:

[0130] The modified steel slag coarse particles in step S1 are put into the impregnation container containing the modifier in step S5 for impregnation for 5h, and then the impregnated modified steel slag coarse particles are filtered out, placed in a tray, and then placed in a 70°C air drying oven for drying until constant weight to obtain modified steel slag coarse aggregate, which is ready for use.

[0131] S7, modification of straw fiber:

[0132] The straw fiber in step S4 is put into the impregnation container containing the modifier in step S5 for impregnation for 4h; then aluminum hydroxide flame retardant is added and mixed for 7min, the addition amount of the aluminum hydroxide flame retardant is 10% of the weight of the straw fiber, and then the impregnated modified straw fiber is placed in a tray and then placed in a 70°C air drying oven for drying until constant weight for use. The indexes, purchasing manufacturer and model of the aluminum hydroxide flame retardant are the same as those in Example 1.

[0133] S8, mixing of aggregate and straw fiber:

[0134] The modified steel slag coarse aggregate treated in step S6, the steel slag powder filler treated in step S2 and the iron tailings fine aggregate treated in step S3 are respectively placed in an oven for drying for 5h, the drying temperature of the oven is 105±5°C, the holding temperature is 160±5°C, and after drying, the oven is kept for 2.5h. Then the modified steel slag coarse aggregate, the iron tailings fine aggregate and the steel slag powder filler are respectively taken in proportion (the modified steel slag coarse aggregate accounts for 67%, the iron tailings fine aggregate accounts for 30% and the steel slag powder accounts for 3%), put into a preheated mixing pot and fast stirred for 30s, the preheating temperature of the mixing pot is 180°C, then 0.20% of the modified straw fiber based on the total dry weight of the aggregate is poured into the mixing pot in the clockwise direction, slowly stirred for 30s at 48r / min, and then counterclockwise stirred for 30s, and then the dry mixed aggregate is obtained and ready for use.

[0135] S9, preparation of asphalt concrete:

[0136] A groove is dug in the middle of the dry mixed aggregate in S8, the depth is not more than 1 / 3 of the thickness, 5.0% of the total dry aggregate is added, the temperature is 175°C, and then the straw fiber is added in three times (0.40% of the total mass of the base asphalt each time), the interval time is 30s, and then the asphalt concrete is obtained after slow mixing at 48r / min.

[0137] The unmodified steel slag coarse aggregate in step S1 and the modified steel slag coarse aggregate obtained in step S6 in this example are respectively tested for performance, and the test results are shown in Tables 5 and 6. The straw fiber before and after modification in step S7 in this example is tested for performance, and the test results are shown in Table 7. The asphalt concrete in step S9 in this example is tested for performance, and the test results are shown in Table 8.

[0138] Table 5 Basic performance index of steel slag before and after modification in Example 2-S6

[0139]

[0140]

[0141] Table 6 Performance index of steel slag before and after modification in Example 2-S6

[0142]

[0143] Note 4: The test index requirement in “Technical Specification for Construction of Highway Asphalt Pavement” JTG F40-2004

[0144] Table 7 Performance index of straw fiber before and after modification in Example 2-S7

[0145]

[0146] Note 5: The test index requirement in “Wood Fiber for Asphalt Pavement” JTT533-2004

[0147] Table 8 Performance index of asphalt concrete in Example 2-S9

[0148]

[0149] Note 6: The test index requirement in “Test Regulation of Highway Engineering Asphalt and Asphalt Mixture” JTG E20-2011

[0150] Example 3

[0151] A preparation method of modified steel slag cooperated with iron tailings and straw asphalt concrete, the specific steps are as follows:

[0152] S1, pretreatment of steel slag coarse aggregate:

[0153] Firstly, the steel slag is screened to remove impurities in the steel slag; then the screened steel slag is crushed to 5-25 mm by a jaw crusher to obtain steel slag particles; then the 5-25 mm steel slag particles are placed in a tray and carbonized in a carbonization box for 80 h, and the carbonization conditions are: CO2 concentration 20±3%, temperature 20±3℃, humidity 70±5%; then the carbonized steel slag is placed in a 105℃ drying oven for air drying to constant weight; then the dried steel slag particles are placed in a cavity ball mill without steel balls and steel hammers for shaping, and the shaping time is 35 min and the speed of the ball mill is 48 r / min; then the shaped steel slag particles are screened in a vibrating screen to obtain 4.75-19 mm steel slag coarse particles and steel slag fine particles with a particle size of less than 4.75 mm; then the 4.75-19 mm steel slag coarse particles are washed, and the washed steel slag coarse particles are placed in a 105℃ drying oven for air drying to constant weight to obtain 4.75-19 mm modified steel slag coarse particles. The steel slag raw material is the same as that in Example 1.

[0154] S2, preparation of steel slag powder filler:

[0155] The steel slag fine particles with a particle size of less than 4.75 mm are placed in a ball mill equipped with steel balls and steel hammers for grinding to obtain steel slag fine powder with a specific surface area of 200 m 2 / kg, and then dry slag-iron separation is performed by a high-intensity magnetic separator with a speed of 20 r / min and a magnetic field strength of 2T, and the obtained fine powder is placed in a ball mill for secondary grinding to a specific surface area of 700 m 2 / kg to obtain steel slag powder for standby use.

[0156] S3, pretreatment of iron tailings fine aggregate:

[0157] Firstly, impurities in the iron tailings are removed by water washing method, and then dried in a 105℃ oven, and then screened to remove large particles to make the particle size mainly distributed between 1.18 mm and 4.75 mm; the screened iron tailings are placed in a ball mill for shaping, the speed of the ball mill is 48 r / min, the shaping time is 25 min, and magnetic separation is performed by a high-intensity magnetic separator with a speed of 20 r / min and a magnetic field strength of 2T, and then placed in a ball mill for secondary shaping for 20 min to obtain iron tailings fine aggregate. The iron tailings raw material used is the same as that in Example 1.

[0158] S4, preparation of straw fiber:

[0159] Firstly, the 15mm diameter corn stalks were surface peeled, and corn stalks of 35cm in length were placed in a 70℃ air drying oven to dry to a moisture content of ≤10%; then the corn stalks were placed in a rubbing machine for crushing, and then sieving was performed to obtain corn stalk fragments of 7cm in diameter; then the corn stalk fragments were placed in a disc mill for disc milling (disc milling gap of 0.35mm) to obtain corn stalk fibers of 60um in diameter and 3cm in length.

[0160] S5, preparation of a steel slag modifier:

[0161] (1) Pretreatment of tofu wastewater: the tofu wastewater was refrigerated at 4℃, and filtration was performed to obtain a tofu wastewater filtrate.

[0162] (2) Pretreatment of corn stalk residues: the corn stalk fragments in step S4 were placed in a jaw crusher for crushing to corn stalk residues of less than 0.5mm in diameter, and then placed in a 70℃ air drying oven to dry to a constant weight; then a mixed solution was obtained by uniformly mixing 11% kerosene and 96% concentrated sulfuric acid at a volume ratio of 3:1, and then 30% of the corn stalk residues by mass ratio of the mixed solvent were added to the mixed solution for stirring at 55℃, and then the solvent was separated after cooling to room temperature, and then neutralization was performed using a 28% NaOH solution by mass fraction, and then filtration was performed, and then the filtrate was suction filtered to obtain a corn stalk residue solution one with a solid content of 57%; then 75% of the weight of the corn stalk residue solution one was added to an aminosulfonic acid-aromatic aminosulfonic acid polymer (purchased from Beijing Mu Lake New Material Technology Co., Ltd.), and then stirring was performed for 50min, and then a corn stalk residue solution two with a solid content of 45% was obtained.

[0163] (3) The tofu wastewater filtrate and the corn stalk residue solution two were mixed at a volume ratio of 2:1 to prepare a modifier; the corn stalks used were the same as in Example 1.

[0164] S6, modification of steel slag coarse aggregate:

[0165] The modified steel slag coarse particles in step S1 were placed in the impregnation container containing the modifier in step S4 for impregnation for 6h, and then the modified steel slag coarse particles after impregnation were filtered out, and then placed in a tray and placed in a 70℃ air drying oven to dry to a constant weight to obtain modified steel slag coarse aggregate, which was ready for use.

[0166] S7, modification of straw fibers:

[0167] The straw fiber in step S4 is put into the impregnation container containing the modifier in step S5 for impregnation for 4h; then the aluminum hydroxide flame retardant is added and mixed for 8min, the addition amount of the aluminum hydroxide flame retardant is 13% of the weight of the straw fiber, the straw fiber after impregnation and modification is put into a tray and placed in a 70°C air drying oven for drying to constant weight for standby use. The indexes, purchasing manufacturer and model of the aluminum hydroxide flame retardant are the same as those in Example 1.

[0168] S8, mixing of aggregate and straw fiber:

[0169] The modified steel slag coarse aggregate in step S6, the steel slag powder filler in step S2 and the iron tailings fine aggregate in step S3 are respectively placed in an oven for drying for 6h, the drying temperature of the oven is 105±5°C, the holding temperature is 160±5°C, after drying, the materials are placed in the oven for holding for 3h. Then the modified steel slag coarse aggregate, the iron tailings fine aggregate and the steel slag powder filler are respectively taken according to the proportion (the modified steel slag coarse aggregate accounts for 70%, the iron tailings fine aggregate accounts for 25% and the steel slag powder accounts for 5%), and are put into a preheated mixing pot for fast mixing for 40s, the preheating temperature of the mixing pot is 180°C, then 0.25% of the modified straw fiber based on the total dry aggregate is poured into the mixing pot in the clockwise direction, slowly stirred at 48r / min for 40s, then counterclockwise stirred for 40s, and then the dry mixed aggregate is obtained for standby use.

[0170] S9, preparation of asphalt concrete:

[0171] A groove is dug in the middle of the dry mixed aggregate in S8, the depth is not more than 1 / 3 of the thickness, 5.5% of the total dry aggregate is added, the base asphalt (temperature 180°C) is added, the mixing machine is fast mixed at 80r / min for 3min, then the straw fiber is added in 3 times (each time the amount is 0.50% of the total mass of the base asphalt), the interval time of each time is 30s, the asphalt concrete is obtained after slow mixing at 48r / min.

[0172] The unmodified steel slag coarse aggregate in step S1 and the modified steel slag coarse aggregate in step S6 in this example are respectively tested for performance, and the test results are shown in Tables 9 and 10. The straw fiber before and after modification in step S7 in this example is tested for performance, and the test results are shown in Table 11. The asphalt concrete in step S9 in this example is tested for performance, and the test results are shown in Table 12.

[0173] Table 9 basic performance indexes of steel slag before and after modification in S6 in Example 3

[0174]

[0175] Table 10 performance indexes of steel slag before and after modification in S6 in Example 3

[0176]

[0177] Note 7: Testing index requirement in Technical Specification for Construction of Highway Asphalt Pavement JTG F40-2004

[0178] Table 11 Performance index of straw fiber before and after modification in Example 3-S7

[0179]

[0180] Note 8: Testing index requirement in Wood Fiber for Asphalt Pavement JTT533-2004

[0181] Table 12 Performance index of asphalt concrete in Example 3-S9

[0182]

[0183] Note 9: Testing index requirement in Test Rules of Asphalt and Asphalt Mixture for Highway Engineering JTG E20-2011

[0184] Modification Condition 1

[0185] The difference between this modification condition and Example 2 is that in step S5, the volume ratio of kerosene and concentrated sulfuric acid is 2:1, and the rest of the conditions remain unchanged.

[0186] Modification Condition 2

[0187] Modification Condition 2 is Example 2.

[0188] Modification Condition 3

[0189] The difference between this modification condition and Example 2 is that in step S2, the volume ratio of kerosene and concentrated sulfuric acid is 3:1, and the rest of the conditions remain unchanged.

[0190] Test Example

[0191] (1) The morphology of the modified steel slag and the unmodified steel slag in Example 2 was analyzed.

[0192] As Figure 7 (a) It can be seen that the surface of the unmodified steel slag is rough, with many particles protruding and of different sizes, and has a large porosity. When it is mixed into asphalt mixture, it will increase the amount of asphalt used, and the large number of pores will also increase the contact area between the steel slag and moisture, increasing the water absorption and volume expansion rate. Figure 7(b), (c), (d) can be seen, after the modified steel slag surface is wrapped by the protective layer, the surface becomes smooth, the surface porosity is effectively filled, the modifier fully wrapped the steel slag after the surface forms a dense protective layer, can play a role in water, so as to reduce the expansion caused by steel slag hydration. But the SEM image in the modification condition 3 shows that the protective layer on the surface of the steel slag is thicker, which covers the particles on the surface of the steel slag and forms a uniform protective layer. The too uniform surface may weaken the interlocking ability between aggregates, resulting in insufficient internal structural stability of the specimen. Based on the above analysis, the modification effect of steel slag under modification condition 2 is optimal, forming a dense and rough surface, which can prevent the expansion of steel slag when it comes into contact with water, ensure the adhesion between steel slag and asphalt, and reduce the asphalt oil stone ratio.

[0193] (2) The performance of the modified steel slag in Example 2 was analyzed.

[0194] a. Water immersion expansion performance of modified steel slag

[0195] As shown in Figure 8 , the volume expansion rate of steel slag under different modification conditions was compared, and it was found that the four particle size steel slag aggregates treated by modification showed significant reduction in volume expansion rate compared with unmodified steel slag. Under the same particle size conditions, the volume expansion rate of steel slag showed the following rules: unmodified steel slag > steel slag treated by modification condition 3 > steel slag treated by modification condition 1 > steel slag treated by modification condition 2. Among them, the steel slag aggregate treated by modification condition 2 showed the lowest volume expansion rate, indicating that this modification condition had a significant improvement effect on the performance of steel slag. The ratio of kerosene to concentrated sulfuric acid is a key factor affecting the modification effect of steel slag. When the ratio of kerosene to concentrated sulfuric acid is 2.5:1, the modification effect of steel slag reaches the best state, which can effectively inhibit the volume expansion of steel slag.

[0196] b. Water immersion expansion performance of modified steel slag asphalt concrete

[0197] As shown in Figure 9 , the modified steel slag treated by different conditions was used to prepare asphalt concrete, and its water immersion expansion performance was tested. By comparing the water immersion expansion performance at 24h, 48h, 72h, 96h and 120h, the results showed that compared with unmodified steel slag asphalt concrete, the volume expansion rate of three kinds of modified steel slag asphalt concrete was significantly reduced. The water immersion expansion curve showed a trend of first rising and then tending to be flat, indicating that the volume expansion rate gradually decreased with the extension of water immersion time.

[0198] The difference between the preparation process of unmodified steel slag asphalt concrete and Example 2 is that the unmodified steel slag coarse particles are not modified by the modifier in step S7, and the unmodified steel slag coarse particles are directly added to step S8 to prepare dry mixing aggregate.

[0199] The reason is that in the initial stage of immersion, due to the protective effect of the asphalt film, the expansion trends of modified steel slag asphalt concrete and unmodified steel slag asphalt concrete are basically the same. As the immersion time increases, the asphalt film gradually peels off, and at this time, the modified protective layer on the surface of the steel slag begins to play a water-blocking role, thereby effectively inhibiting volume expansion. Due to slight differences in the proportion of modifier under different modification conditions, the effect of inhibiting expansion varies slightly, but the overall trend is basically the same. The test results show that the immersion expansion performance of steel slag asphalt concrete is significantly correlated with the volume expansion rate of modified steel slag, and the volume expansion rate is unmodified > modified condition 3 > modified condition 1 > modified condition 2, further verifying that the mix ratio corresponding to modified condition 2 is the optimal mix ratio, and its effect of inhibiting expansion is the most significant.

[0200] c. Optimal oil-stone ratio

[0201] This invention uses 70# petroleum asphalt as a binder to determine the optimal asphalt-aggregate ratio for modified asphalt concrete. The mixing temperature is 160℃, and the initial asphalt content is 3.8%, 4.3%, 4.8%, 5.3%, and 5.8%. The volumetric index design values ​​are as follows:

[0202]

[0203] Figure 10 The Marshall test diagram was used to determine the optimal oil-stone ratio. Figure 11 Four optimal asphalt-aggregate ratios for asphalt concrete were demonstrated. The asphalt concrete prepared under modification condition 2 had the lowest optimal asphalt-aggregate ratio, indicating that different modifier ratios affect the degree of reaction between the modifier and the steel slag surface and the asphalt. When the ratio is low, the modified layer is not completely covered, and the steel slag still retains some highly adsorbed surface, resulting in an increase in the amount of asphalt required. When the modifier ratio approaches saturation, increasing the ratio has no significant effect; on the contrary, excessive modifier residue will interfere with asphalt bonding and increase the amount of asphalt used. When the modifier ratio is appropriate (modification condition 2), it can partially fill the pores on the surface of the steel slag, inhibit the expansion of the steel slag, and at the same time retain the necessary roughness to enhance mechanical interlocking force, thereby reducing the amount of asphalt required.

[0204] Comparative Example 1

[0205] The difference between this comparative example and Example 2 is that: in step S7, the straw fiber was not impregnated with a modifier, and the straw fiber was directly mixed with aluminum hydroxide flame retardant and then added to the mixing pot in step S8 to form dry aggregate.

[0206] Comparative Example 2

[0207] The difference between this comparative example and Example 2 is that no aminosulfonic acid-aromatic aminosulfonic acid polymer was added to the modifier in step S5.

[0208] The results of the volume expansion rate of the asphalt concrete prepared in Comparative Examples 1 to 2 and Modification Condition 2 after immersion expansion for 120 h are shown in Table 13.

[0209] Table 13 Volume expansion rate of asphalt concrete of Comparative Examples 1 to 2 and Modification Condition 2

[0210]

[0211] Finally, it should be noted that the above examples are intended to illustrate the technical solutions of the present application but not to limit the same, and although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can still be modified or equivalently replaced, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A modified steel slag synergistic with iron tailings and straw asphalt concrete, characterized in that: The raw materials for asphalt concrete include aggregate dry basis, modified straw fiber, straw fiber, and asphalt; wherein modified straw fiber accounts for 0.14~0.33% of the total mass of aggregate dry basis, asphalt accounts for 4.2~6.4% of the total mass of aggregate dry basis, and straw fiber accounts for 0.75~1.75% of the mass of asphalt; by mass percentage, the aggregate dry basis includes 60~70% modified steel slag coarse aggregate, 25~35% iron tailings fine aggregate, and 1~5% steel slag powder; The method for preparing the modified straw fiber is as follows: After peeling, cutting, drying, crushing and sieving corn stalks, corn stalk fragments are obtained. Then, the corn stalk fragments are ground in a disc to obtain straw fibers. The obtained straw fibers are impregnated with a modifier, and then aluminum hydroxide flame retardant is added and mixed. After drying, modified straw fibers are obtained. The preparation method of the modified steel slag coarse aggregate is as follows: After screening, crushing, carbonizing, drying, shaping and sieving steel slag, coarse steel slag particles and fine steel slag particles are obtained; after washing and drying the coarse steel slag particles, modified steel slag coarse particles are obtained; the prepared modified steel slag coarse particles are added to a modifier for impregnation, and then filtered and dried to obtain modified steel slag coarse aggregate. The method for preparing the modifier is as follows: (1) Pretreatment of tofu wastewater: The tofu wastewater was filtered to obtain tofu wastewater filtrate; (2) Pretreatment of corn stalk fragments After crushing and drying the corn stalk fragments, corn stalk residue is obtained. Then, the corn stalk residue is added to a mixed solvent of kerosene and concentrated sulfuric acid under heating conditions. After cooling to room temperature, the solvent is separated, neutralized with NaOH solution, filtered, and corn stalk residue solution one is obtained. Then, aminosulfonic acid-aromatic aminosulfonic acid polymer is added and stirred to obtain corn stalk residue solution two. (3) Mix the tofu wastewater filtrate with the corn straw residue solution to prepare a modifier.

2. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 1, characterized in that: Includes the following steps: S1: Pretreatment of steel slag After screening, crushing, carbonizing, drying, shaping and sieving, steel slag is obtained into coarse steel slag particles and fine steel slag particles; after washing and drying, steel slag coarse particles for modification are obtained. S2: Preparation of steel slag powder After grinding, magnetic separation, and secondary grinding of fine steel slag particles, steel slag powder is obtained and set aside for later use. S3: Preparation of fine aggregate from iron tailings Iron tailings are washed, dried, screened, shaped, magnetically separated and reshaped to obtain fine iron tailings aggregate. S4: Pretreatment of straw fiber After peeling, cutting, drying, crushing and sieving corn stalks, corn stalk fragments are obtained. Then, the corn stalk fragments are ground in a disc to obtain straw fiber. S5: Preparation of Modifier (1) Pretreatment of tofu wastewater: The tofu wastewater was filtered to obtain tofu wastewater filtrate; (2) Pretreatment of corn stalk fragments After crushing and drying the corn stalk fragments in step S4, corn stalk residue is obtained. Then, corn stalk residue is added to a mixed solvent of kerosene and concentrated sulfuric acid under heating conditions. After cooling to room temperature, the solvent is separated, neutralized with NaOH solution, filtered, and corn stalk residue solution one is obtained. Then, aminosulfonic acid-aromatic aminosulfonic acid polymer is added and stirred to obtain corn stalk residue solution two. (3) Mix the tofu wastewater filtrate with corn straw residue solution to prepare a modifier; S6: Preparation of Modified Steel Slag Coarse Aggregate The modified steel slag coarse particles prepared in step S1 are added to the modifier for impregnation, and then filtered and dried to obtain modified steel slag coarse aggregate. S7: Preparation of Modified Straw Fiber The straw fiber obtained in step S4 is impregnated with a modifier, then aluminum hydroxide flame retardant is added and mixed, and then dried to obtain modified straw fiber. S8: Mixing of aggregate dry base and modified straw fiber The modified steel slag coarse aggregate obtained in step S6, the steel slag powder obtained in step S2, and the iron tailings fine aggregate obtained in step S3 are dried and kept warm. Then they are mixed in proportion to obtain aggregate dry base. Modified straw fiber is added in proportion and stirred to obtain dry aggregate. S9: Preparation of Asphalt Concrete The dry aggregate prepared in step S8 and asphalt are mixed in proportion, and then the straw fiber in step S4 is added and mixed again to finally obtain asphalt concrete.

3. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 2, characterized in that: In step S1, the specific steps for steel slag pretreatment are as follows: First, the steel slag is screened to remove impurities. Then, the screened steel slag is crushed to 5-25mm to obtain steel slag particles. The steel slag particles are then spread out and carbonized. The carbonized steel slag particles are dried to constant weight. The dried steel slag particles are then placed in a ball mill for shaping. The shaped steel slag particles are then screened to obtain coarse steel slag particles of 4.75-19mm and fine steel slag particles with a particle size <4.75mm. The coarse steel slag particles of 4.75-19mm are then washed and dried to constant weight to obtain modified steel slag coarse particles.

4. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 2, characterized in that: In step S2, the specific process for preparing steel slag powder is as follows: Fine steel slag particles with a particle size <4.75mm are ground in a ball mill to obtain a specific surface area of ​​150~200m². 2 Steel slag fine powder of / kg was then subjected to dry slag-iron separation using a high-intensity magnetic separator, followed by secondary grinding in a ball mill to obtain a powder with a surface area of ​​500~700m². 2 / kg, to obtain steel slag powder, for later use.

5. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 4, characterized in that: In step S3, the specific process for preparing fine aggregate from iron tailings is as follows: First, impurities in the iron tailings are removed by washing and drying. Then, large particles are removed by screening, so that the particle size is mainly distributed between 1.18mm and 4.75mm. The screened iron tailings are then put into a ball mill for shaping and magnetic separation by a high-intensity magnetic separator. The magnetically separated iron tailings are then put into the ball mill for secondary shaping to obtain fine iron tailings aggregate.

6. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 2, characterized in that: In step S4, the specific process of straw fiber pretreatment is as follows: First, the surface of corn stalks with a diameter of 12-15mm is peeled, and corn stalks with a length of 30-40cm are cut and dried until the moisture content is ≤10%. Then, the corn stalks are put into a shredder for crushing, and then screened to obtain corn stalk fragments with a diameter of 4-8cm. The corn stalk fragments are then put into a disc mill for disc milling to obtain corn stalk fibers with a diameter of 40-70um and a length of 1-3cm.

7. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 2, characterized in that: In step S5, the specific process for preparing the modifier is as follows: (1) Pretreatment of tofu wastewater: The tofu wastewater was refrigerated at 1-5℃ and then filtered to obtain tofu wastewater filtrate. (2) Pretreatment of corn straw residue: The corn stalk fragments from step S4 are crushed to a diameter of less than 0.5 mm to obtain corn stalk residue, which is then dried to constant weight. Then, 11% kerosene and 96% concentrated sulfuric acid are mixed evenly at a volume ratio of 2-3:1 to obtain a mixed solvent. Corn stalk residue, accounting for 25-30% of the mass of the mixed solvent, is added at 45-55°C and stirred. After cooling to room temperature, the solvent is separated and neutralized with a 25-28% NaOH solution. The mixture is then filtered to obtain corn stalk residue solution one with a solid content of 54-58%. An aminosulfonic acid-aromatic aminosulfonic acid polymer is then added, accounting for 70-80% of the weight of corn stalk residue solution one, to obtain corn stalk residue solution two with a solid content of 35-45%. (3) Mix the tofu wastewater filtrate with the corn straw residue solution at a volume ratio of 1~2:1~2 to prepare a modifier.

8. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 2, characterized in that: In step S6, the soaking time is 4-6 hours; in step S7, the soaking time is 3-5 hours, the amount of aluminum hydroxide flame retardant added is 10-13% of the weight of straw fiber, and the stirring time is 5-10 minutes.

9. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 2, characterized in that: In step S8, the specific process of mixing the dry aggregate and modified straw fiber is as follows: The modified steel slag coarse aggregate obtained in step S6, the steel slag powder obtained in step S2, and the iron tailings fine aggregate obtained in step S3 are dried in an oven for 4-6 hours. After drying, they are kept warm in the oven for 2-3 hours. Then, the modified steel slag coarse aggregate, iron tailings fine aggregate, and steel slag powder are taken in proportion and put into a preheated mixing pot and quickly stirred for 20-40 seconds. Then, the modified straw fiber is added and poured into the mixing pot in a clockwise direction and slowly stirred for 20-40 seconds, and then stirred counterclockwise for 20-40 seconds. The resulting dry-mixed aggregate is ready for use.

10. The method for preparing asphalt concrete using modified steel slag in combination with iron tailings and straw according to claim 2, characterized in that: In step S9, the specific process for preparing asphalt concrete is as follows: A groove is dug in the middle of the dry-mixed aggregate prepared in step S8, with a depth not exceeding 1 / 3 of the thickness. Asphalt at a temperature of 170℃~180℃ is added. After mixing for 3~5 minutes, straw fiber is added in 3 batches, with each batch accounting for 0.25%~0.58% of the total mass of asphalt, and the interval between each batch is 30 seconds. After mixing evenly, asphalt concrete is obtained.

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