CN116535147B - Method for preparing self-compacting concrete by utilizing tailing sand and application - Google Patents

Abstract

The invention belongs to the technical field of concrete, and particularly relates to a method for preparing self-compacting concrete by utilizing tailing sand and application thereof. The self-compacting concrete comprises 600-800 parts of raw material components of modified cement, 200-300 parts of modified iron tailing sand, 100-200 parts of phosphorus tailing sand, 150-200 parts of limestone tailing sand, 50-100 parts of quartz tailing sand, 60-80 parts of fly ash, 12-18 parts of water reducer, 10-20 parts of waterproof agent, 5-10 parts of anti-corrosion antirust agent and 200-300 parts of water. The self-compacting concrete prepared by fully utilizing the tailing sand and optimizing the ingredients and the preparation method has the advantages of excellent compressive strength, high anti-seepage grade, good filling property, good fluidity, low segregation rate and bleeding rate, good durability, excellent overall performance and low cost, and can be applied to the technical field of bridge and pier manufacturing.

Description

A method and application of preparing self-compacting concrete using tailings sand

Technical Field

The invention belongs to the technical field of concrete, and particularly relates to a method for preparing self-compacting concrete by utilizing tailings sand and application thereof.

Background Art

Self-compacting concrete refers to concrete that can flow and compact under its own gravity, can completely fill the formwork even in the presence of dense steel bars, and has good homogeneity and does not require additional vibration. With the development of construction technology, self-compacting concrete has become increasingly popular due to its advantages such as good compactness, production efficiency, and working environment. However, self-compacting concrete still has poor durability after hardening, is not cold-resistant, and shrinks when drying, which directly affects its application.

Tailings sand is a solid mineral waste formed by natural dehydration of tailings slurry discharged from the ore dressing plant. It is a composite silicate or carbonate mineral material. There are various types of tailings sand, including quartz sand tailings sand, iron tailings sand, phosphate tailings sand, etc. With the continuous development of my country's mineral resources, the amount of tailings waste is also increasing. If it is not utilized, it will not only require a large number of storage yards but also cause certain pollution. If tailings sand is used in concrete, it can not only be comprehensively utilized to alleviate the shortage of sand and gravel resources, but also effectively solve the pollution problems caused by it.

At present, there are more and more reports on the use of tailings sand in concrete. For example, the patent with application number 202110427223.6 discloses a radiation-proof self-compacting concrete, whose components include radiation-proof cement, admixtures, iron tailings sand, barite crushed stone, high-efficiency water reducer, rheological agent, stabilizer and water. It uses iron tailings sand as fine aggregate, which absorbs industrial solid waste and saves natural mineral resources; the patent with application number 201811414174.7 discloses a self-compacting composite concrete, including component A, component B and component C, wherein component B is made of the following raw materials in parts by weight: 40-50 parts of slag, 12-15 parts of steel slag, and 30-35 parts of iron tailings sand. Specific slag, steel slag and iron tailings sand are compounded as aggregate components to make full use of industrial waste slag, save ingredients, and maintain the strength of concrete bricks formed by concrete. The above two patents both use iron tailings as raw materials, and the amount used is relatively small. Although they can solve the problem of iron tailings accumulation, the amount used is limited, and they cannot solve other tailings problems. In view of this, it is necessary to develop a method for preparing self-compacting concrete using a variety of tailings.

Summary of the invention

In view of the deficiencies in the prior art, the present invention provides a method and application of preparing self-compacting concrete using tailings sand. The self-compacting concrete uses tailings sand as the main raw material. After pretreatment and optimization of ingredients and preparation method, the obtained self-compacting concrete has excellent compressive strength, high impermeability grade, good filling and fluidity, low segregation rate and water bleeding rate, good durability, excellent overall performance, low cost, and can be applied to the field of bridge and pier manufacturing.

To achieve the above object, the present invention provides a method for preparing self-compacting concrete using tailings sand, comprising the following specific steps:

S1. Raw material preparation: prepare 600-800 parts by weight of raw material components of modified cement, 200-300 parts of modified iron tailings, 100-200 parts of phosphate tailings, 150-200 parts of limestone tailings, 50-100 parts of quartz tailings, 60-80 parts of fly ash, 12-18 parts of water reducer, 10-20 parts of waterproofing agent, 5-10 parts of anticorrosion and rust inhibitor, 200-300 parts of water, set aside;

S2. Preparation of modified cement: Phosphorus tailings powder, limestone tailings powder, cement clinker, iron tailings powder, and clay were added to a mixer, stirred at a speed of 300-500r/min for 1-2h, an appropriate amount of water was added, stirring was continued for 0.5-1h, and the mixture was fed into a molding machine to form a rectangular block, and then fed into a rotary kiln at 500-800°C for calcination for 3-5h, cooled, and crushed to obtain modified cement;

S3. Preparation of modified iron tailings: The iron tailings were added to a ball mill, ball milled for 1-2 h, then added to a 30% hydrochloric acid solution and soaked for 2-4 h, rinsed with water, added to a fluorosilane ethanol solution and soaked for 0.5-1 h, filtered and dried to obtain modified iron tailings;

S4. The modified cement and the anticorrosion and rust inhibitor are first mixed in a mixer according to the ratio, and then water is added and stirred. After standing for 0.5-1h, modified iron tailings, phosphorus tailings, limestone tailings, quartz tailings, and fly ash are added and stirred to obtain a sand and gravel slurry;

S5. Add the water reducing agent and waterproofing agent to the sand and gravel slurry obtained in S4 in sequence according to the proportion, stir evenly, pour into a mold, and make self-compacting concrete.

The invention uses tailings as the main raw material, and makes full use of various tailings by using different tailings for proportioning. At the same time, certain phosphorus tailings powder, limestone tailings powder and iron tailings powder are mixed with cement clinker to make modified cement. The beneficial elements in the tailings increase the fluxing effect, and the components such as limestone and phosphogypsum can effectively improve the strength, adhesion and quality of cement. Since the iron tailings sand has many edges and corners and a large meshing force, the iron tailings sand is ball-milled to increase its rheological properties, and is treated with acid to dissolve part of the ferric chloride substance, forming gaps on its surface, and finally By soaking in fluorosilane, certain groups are formed in the gaps and surface of the concrete, increasing its surface activity and combining well with other substances to obtain modified iron tailings sand with good rheology, no segregation and water seepage, and stability. The anti-corrosion and rust inhibitor is pre-mixed with the modified cement, and the anti-corrosion and rust inhibitor is fully infiltrated and combined with the cement, which can effectively improve the anti-corrosion performance of the concrete. By adding a water reducer, the dispersion effect can be improved while effectively preventing particle agglomeration, which can reduce water seepage and effectively improve the self-compactness and durability of the concrete. By adding a waterproofing agent, the waterproof performance and anti-corrosion of the concrete are improved, and the durability is increased.

Further, in the above technical scheme, in step S2, the modified cement is composed of the following components by weight: 20-30 parts of phosphorus tailings powder, 20-30 parts of limestone tailings powder, 30-40 parts of cement clinker, 2-4 parts of iron tailings powder, and 3-6 parts of clay. In this technical scheme, phosphorus tailings powder and limestone tailings powder are mixed with cement clinker, and the phosphogypsum in the phosphorus tailings powder and the limestone in the limestone tailings are fully utilized to form cementitious materials, thereby improving the quality, strength and heat resistance of cement clinker; the main component of clay is silicate, and the particles are small, but it is generally in the form of flakes, tubes or rods, which can improve the crack resistance of concrete, and at the same time, due to its high viscosity, it can improve the bonding performance and compactness of concrete, thereby improving salt resistance; the obtained modified cement not only has comprehensive properties such as high bonding and strength, but also can greatly reduce costs.

Furthermore, in the above technical solution, in step S2, after adding water, the moisture content of the mixture is 35-45%. In this technical solution, by controlling the moisture content of the mixture, a molding material with certain control is formed, the reaction is more sufficient during the sintering process, and the obtained modified cement has good stability.

Furthermore, in the above technical solution, the particle size of the modified cement is 5-20 μm.

Furthermore, in the above technical solution, in step S3, the concentration of fluorosilane in the fluorosilane ethanol solution is 1-2%.

Furthermore, in the above technical solution, in step S3, the particle size range of the modified iron tailings sand is 5-10 mm, the particle size range of the phosphate tailings sand is 0.5-5 mm, the particle size range of the limestone tailings sand is 15-20 mm, and the particle size range of the quartz tailings sand is 8-15 mm.

In the technical solution, different particle sizes are used for proportioning according to the characteristics of each tailings, which can not only achieve higher fluidity during use according to the density, but also can fill each other during the mixing process to improve the density; the particle size of the tailings sand is controlled below 20mm, which can effectively reduce the possibility of slurry-bone separation; in the process of preparing concrete, fly ash with a smaller particle size is combined at the same time to obtain concrete with good density and viscosity, and the strength is improved while the anti-seepage and anti-segregation properties are improved.

Furthermore, in the above technical solution, the water reducer is a mixture of a polycarboxylate water reducer and a naphthalene-based water reducer in a mass ratio of 1:2-3.

In the technical scheme, naphthalene-based water-reducing agent is used as the main water-reducing agent, which has good compatibility, dispersibility and fluidity, has little effect on the setting time, and has high cost performance. However, due to its fast slump loss, the present invention can effectively solve the problem of fast slump loss by simultaneously combining with polycarboxylate water-reducing agent and utilizing its molecular characteristics, while further improving its dispersion stability, improving durability and reducing the probability of shrinkage deformation.

Further, in the above technical solution, the waterproofing agent is a mixture of inorganic aluminum salt and octadecylamine in a mass ratio of 5-8:1. In the present technical solution, an inorganic aluminum salt having the advantages of waterproofing, water reduction, crack resistance, tensile strength, bending resistance, early strength, impermeability, leakage resistance, moisture resistance, acid and alkali resistance, etc. is used as the main ingredient of the waterproofing agent, which can form a dense hydrophobic substance, fill and block the capillary pores and water channels formed in the hardening process of concrete and mortar, and has extremely strong hydrophobicity and moisture repellency, good waterproof and anti-corrosion performance, and combined with a small amount of octadecylamine surfactant, it can not only form a hydrophobic film on the surface to improve waterproofness, but also increase antifreeze performance. Specifically, the inorganic aluminum salt is any one of aluminum sulfate, aluminum chloride, alum, and polyaluminum chloride.

Furthermore, in the above technical solution, the anticorrosion and rust preventive agent is triethanolamine borate. As an additive, triethanolamine borate can not only increase the dispersion effect of the system, but also form a protective film on the surface of metal when encountering metal to block the erosion of corrosive substances, and has good anticorrosion and rust preventive effects.

The present invention also provides an application of the self-compacting concrete prepared by the preparation method in the manufacture of bridges and bridge piers.

The present invention has the following beneficial effects:

The invention uses various tailings as main raw materials, pre-treats and optimizes the ingredients and preparation method, and the obtained self-compacting concrete has excellent fluidity and viscosity, good density after solidification, good waterproof and antifreeze properties, good durability, and realizes the resource utilization of waste at low cost.

The invention prepares modified cement by mixing certain phosphorus tailing powder, limestone tailing powder and iron tailing powder with cement clinker. The beneficial elements in the tailings increase the fluxing effect, and the components such as limestone and phosphogypsum can effectively improve the strength, adhesion and quality of the cement, further utilize the resources and reduce the production cost. The iron tailing sand is modified by combining physical and chemical methods to effectively improve the rheology and water seepage. The composite water reducing agent is added to improve the compatibility and dispersibility, while the fluidity and slump are maintained for a long time and the durability is improved. The waterproofing agent, anticorrosion and rust-proof agent and other additives are added to further improve the waterproofing, anticorrosion and rust-proof functions of the concrete and improve the durability.

The preparation method of the invention is simple and easy to implement. The obtained concrete has excellent fluidity and viscosity, good density after solidification, good waterproof and frost resistance, good durability, and can be applied to the field of bridge and pier manufacturing.

DETAILED DESCRIPTION

The experimental methods in the following examples are conventional methods unless otherwise specified. The raw materials involved in the following examples are common commercial products unless otherwise specified and can be purchased from the market. The present invention is further described in detail below in conjunction with the examples:

Example 1

A method for preparing self-compacting concrete using tailings sand comprises the following specific steps:

S1. Raw material preparation: prepare 600 parts by weight of raw material components of modified cement, 200 parts of modified iron tailings, 150 parts of phosphate tailings, 150 parts of limestone tailings, 80 parts of quartz tailings, 60 parts of fly ash, 12 parts of water reducer, 12 parts of waterproofing agent, 5 parts of anticorrosion and rust inhibitor, 200 parts of water, and set aside;

S2. Preparation of modified cement: Phosphorus tailings powder, limestone tailings powder, cement clinker, iron tailings powder and clay were added to a mixer, stirred at a speed of 300r/min for 2h, an appropriate amount of water was added to make the moisture content of the mixture 35-45%, and stirring was continued for 0.5h. The mixture was sent to a molding machine to form a rectangular block, and then sent to a rotary kiln for high temperature roasting at 500°C for 5h. After cooling, the mixture was crushed to obtain modified cement; wherein, by weight, the modified cement is composed of the following ingredients: 20 parts of phosphorus tailings powder, 20 parts of limestone tailings powder, 30 parts of cement clinker, 3 parts of iron tailings powder and 3 parts of clay;

S3. Preparation of modified iron tailings: adding the iron tailings to a ball mill, ball milling for 1 h, then adding it to a 30% hydrochloric acid solution and soaking it for 4 h, rinsing it with water, adding it to a fluorosilane ethanol solution and soaking it for 0.5 h, filtering it to obtain modified iron tailings; wherein the concentration of fluorosilane in the fluorosilane ethanol solution is 1-2%;

S4. The modified cement and the anticorrosion and rust inhibitor are first mixed in a mixer according to the ratio, and then water is added and stirred. After standing for 0.5h, modified iron tailings, phosphorus tailings, limestone tailings, quartz tailings, and fly ash are added and stirred to obtain a sand and gravel slurry;

S5. Add the water reducing agent and waterproofing agent to the sand and gravel slurry obtained in S4 in sequence according to the proportion, stir evenly, pour into a mold, and make self-compacting concrete.

The water reducer is a mixture of a polycarboxylate water reducer and a naphthalene water reducer in a mass ratio of 1:2;

The waterproofing agent is a mixture of inorganic aluminum salt and octadecylamine in a mass ratio of 5:1;

The anticorrosion and rust inhibitor is triethanolamine borate.

Example 2

A method for preparing self-compacting concrete using tailings sand comprises the following specific steps:

S1. Raw material preparation: prepare 700 parts by weight of raw material components of modified cement, 250 parts of modified iron tailings, 100 parts of phosphate tailings, 170 parts of limestone tailings, 50 parts of quartz tailings, 70 parts of fly ash, 15 parts of water reducer, 10 parts of waterproofing agent, 7 parts of anticorrosion and rust inhibitor, 250 parts of water, and set aside;

S2. Preparation of modified cement: Phosphorus tailings powder, limestone tailings powder, cement clinker, iron tailings powder and clay were added to a mixer, stirred at a speed of 400r/min for 1.5h, an appropriate amount of water was added to make the moisture content of the mixture 35-45%, and stirring was continued for 1h. The mixture was sent to a molding machine to form rectangular blocks, and then sent to a rotary kiln for high temperature roasting at 600°C for 4h. After cooling, the blocks were crushed to obtain modified cement; wherein, by weight, the modified cement is composed of the following ingredients: 25 parts of phosphorus tailings powder, 30 parts of limestone tailings powder, 40 parts of cement clinker, 2 parts of iron tailings powder and 6 parts of clay;

S3. Preparation of modified iron tailings: adding the iron tailings to a ball mill, ball milling for 1.5 h, then adding it to a 30% hydrochloric acid solution and soaking it for 3 h, rinsing it with water, adding it to a fluorosilane ethanol solution and soaking it for 0.5 h, filtering it to obtain modified iron tailings; wherein the concentration of fluorosilane in the fluorosilane ethanol solution is 1-2%;

S4. The modified cement and the anticorrosion and rust inhibitor are first mixed in a mixer according to the ratio, and then water is added and stirred. After standing for 1h, modified iron tailings, phosphorus tailings, limestone tailings, quartz tailings, and fly ash are added and stirred to obtain a sand and gravel slurry.

S5. Add the water reducing agent and waterproofing agent to the sand and gravel slurry obtained in S4 in sequence according to the proportion, stir evenly, pour into a mold, and make self-compacting concrete.

The water reducer is a mixture of a polycarboxylate water reducer and a naphthalene water reducer in a mass ratio of 1:2.5;

The waterproofing agent is a mixture of inorganic aluminum salt and octadecylamine in a mass ratio of 6:1; the anticorrosion and rust preventive agent is triethanolamine borate.

Example 3

A method for preparing self-compacting concrete using tailings sand comprises the following specific steps:

S1. Raw material preparation: prepare 800 parts by weight of raw material components of modified cement, 300 parts of modified iron tailings, 200 parts of phosphate tailings, 200 parts of limestone tailings, 100 parts of quartz tailings, 60 parts of fly ash, 18 parts of water reducer, 20 parts of waterproofing agent, 10 parts of anticorrosion and rust inhibitor, 300 parts of water, and set aside;

S2. Preparation of modified cement: Phosphorus tailings powder, limestone tailings powder, cement clinker, iron tailings powder and clay were added to a mixer, stirred at a speed of 500r/min for 2h, an appropriate amount of water was added to make the moisture content of the mixture 35-45%, and stirring was continued for 1h. The mixture was sent to a molding machine to form rectangular blocks, and then sent to a rotary kiln for high temperature roasting at 800°C for 3h. After cooling, the blocks were crushed to obtain modified cement; wherein, by weight, the modified cement is composed of the following ingredients: 30 parts of phosphorus tailings powder, 25 parts of limestone tailings powder, 35 parts of cement clinker, 4 parts of iron tailings powder and 4 parts of clay;

S3. Preparation of modified iron tailings: adding the iron tailings to a ball mill, ball milling for 1-2 hours, then adding to a 30% hydrochloric acid solution and soaking for 2-4 hours, rinsing with water, adding to a fluorosilane ethanol solution and soaking for 0.5-1 hours, filtering and drying to obtain modified iron tailings; wherein the concentration of fluorosilane in the fluorosilane ethanol solution is 1-2%;

S4. The modified cement and the anticorrosion and rust inhibitor are first mixed in a mixer according to the ratio, and then water is added and stirred. After standing for 0.5-1h, modified iron tailings, phosphorus tailings, limestone tailings, quartz tailings, and fly ash are added and stirred to obtain a sand and gravel slurry;

S5. Add the water reducing agent and waterproofing agent to the sand and gravel slurry obtained in S4 in sequence according to the proportion, stir evenly, pour into a mold, and make self-compacting concrete.

The water reducer is a mixture of a polycarboxylate water reducer and a naphthalene water reducer in a mass ratio of 1:3;

The waterproofing agent is a mixture of inorganic aluminum salt and octadecylamine in a mass ratio of 8:1;

The anticorrosion and rust inhibitor is triethanolamine borate.

Comparative Example 1

A method for preparing self-compacting concrete using tailings sand is different from Example 2 in that:

Cement clinker replaces modified cement in S1.

Comparative Example 2

A method for preparing self-compacting concrete using tailings sand is different from Example 2 in that:

Iron tailings are not modified.

Comparative Example 3

A method for preparing self-compacting concrete using tailings sand is different from Example 2 in that:

The water reducer is only a single naphthalene-based water reducer.

Comparative Example 4

A method for preparing self-compacting concrete using tailings sand is different from Example 2 in that:

The waterproofing agent is only inorganic aluminum salt.

Comparative Example 5

A method for preparing self-compacting concrete using tailings sand comprises the following specific steps:

S1. Raw material preparation: prepare 600 parts by weight of raw material components of modified cement, 200 parts of modified iron tailings, 150 parts of phosphate tailings, 150 parts of limestone tailings, 80 parts of quartz tailings, 60 parts of fly ash, 12 parts of water reducer, 12 parts of waterproofing agent, 5 parts of anticorrosion and rust inhibitor, 200 parts of water, and set aside;

S2. Preparation of modified cement: Phosphorus tailings powder, limestone tailings powder, cement clinker, iron tailings powder and clay were added to a mixer, stirred at a speed of 300r/min for 2h, an appropriate amount of water was added to make the moisture content of the mixture 35-45%, and stirring was continued for 0.5h. The mixture was sent to a molding machine to form a rectangular block, and then sent to a rotary kiln for high temperature roasting at 500°C for 5h. After cooling, the mixture was crushed to obtain modified cement; wherein, by weight, the modified cement is composed of the following ingredients: 20 parts of phosphorus tailings powder, 20 parts of limestone tailings powder, 30 parts of cement clinker, 3 parts of iron tailings powder and 3 parts of clay;

S3. Preparation of modified iron tailings: adding the iron tailings to a ball mill, ball milling for 1 h, then adding it to a 30% hydrochloric acid solution and soaking it for 4 h, rinsing it with water, adding it to a fluorosilane ethanol solution and soaking it for 0.5 h, filtering it to obtain modified iron tailings; wherein the concentration of fluorosilane in the fluorosilane ethanol solution is 1-2%;

S4. Add modified cement, modified iron tailings sand, phosphorus tailings sand, limestone tailings sand, quartz tailings sand, fly ash, water reducer, waterproofing agent, anticorrosion and rust inhibitor, and water into a mixer according to the proportion and mix them evenly, then pour into a mold to make self-compacting concrete.

The water reducer is a mixture of a polycarboxylate water reducer and a naphthalene water reducer in a mass ratio of 1:2.5;

The waterproofing agent is a mixture of inorganic aluminum salt and octadecylamine in a mass ratio of 6:1;

The anticorrosion and rust inhibitor is triethanolamine borate

Test example

The properties of the self-compacting concrete of Examples 1-3 and Comparative Examples 1-5 were tested respectively. The specific test methods were based on the relevant standard methods of GB/T 50080-2016, GB/T 50081-2019, GB/T 50082-2009, and JGJ/T283-2012. The test results are shown in Table 1.

Table 1 Performance test results

It can be seen from the results in Table 1 that the self-compacting concrete prepared by using tailings sand in the present invention has excellent compressive strength, high impermeability, good filling and fluidity, low segregation rate and water bleeding rate, and excellent overall performance.

Comparing Example 2 with Comparative Example 1, the cement used in Comparative Example 1 is all commercial cement, and the overall performance of the self-compacting concrete obtained is relatively good, but slightly lower than that of Example 3, indicating that the modified cement not only has the performance of commercial water-based cement, but also can further improve the strength of concrete and reduce costs.

Compared with Example 2 and Comparative Example 2, the iron tailings in Comparative Example 2 were not modified, and their performances were all reduced, especially the fluidity was poor, and the segregation rate and water seepage were significantly increased, indicating that modifying the iron tailings can effectively improve its rheological properties, as well as its anti-segregation and water seepage performance.

Compared with Example 2 and Comparative Example 3, the water reducer in Comparative Example 3 is only a naphthalene-based water reducer, and its slump is significantly reduced, and the rheological properties and impermeability are deteriorated, indicating that only using a single naphthalene-based water reducer, the concrete slump loss is fast, the stability is poor, thereby affecting other properties.

Compared with Example 2 and Example 4, the waterproofing agent in Example 4 is only inorganic aluminum salt, and its overall performance is significantly reduced, especially the water permeability and anti-seepage performance. This shows that the addition of a surfactant to the waterproofing agent of the present invention can significantly improve the waterproof performance of concrete, and improve durability and antifreeze properties.

Compared with Example 2 and Example 5, the overall performance of Example 5 was slightly reduced by mixing at one time during preparation compared with Example 2, but its resistance to chloride ions was significantly reduced, indicating that mixing the anti-corrosion and rust inhibitor with the modified cement in advance can effectively improve the anti-corrosion performance of concrete.

In summary, the present invention utilizes tailings sand and optimizes the ingredients and preparation method to obtain a self-compacting concrete with excellent compressive strength, high impermeability, good filling and fluidity, low segregation rate and water bleeding rate, good durability, excellent overall performance, low cost, and can be applied to the field of bridge and pier manufacturing technology.

Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims (10)

1. The method for preparing the self-compacting concrete by utilizing the tailing sand is characterized by comprising the following specific steps of:

S1, preparing raw materials: 600-800 parts of modified cement, 200-300 parts of modified iron tailing sand, 100-200 parts of phosphate tailing sand, 150-200 parts of limestone tailing sand, 50-100 parts of quartz tailing sand, 60-80 parts of fly ash, 12-18 parts of water reducer, 10-20 parts of waterproof agent, 5-10 parts of anti-corrosion and rust inhibitor and 200-300 parts of water for standby;

S2, preparing modified cement: respectively adding the phosphorus tailing powder, the limestone tailing powder, the cement clinker, the iron tailing powder and the clay into a stirrer, stirring for 1-2 hours at a rotating speed of 300-500r/min, adding a proper amount of water, continuously stirring for 0.5-1 hour, sending into a forming machine to prepare rectangular blocks, sending into a rotary kiln for roasting for 3-5 hours at a high temperature of 500-800 ℃, cooling, and crushing to obtain modified cement;

S3, preparing modified iron tailing sand: adding iron tailing sand into a ball mill, ball milling for 1-2h, then adding the iron tailing sand into 30% hydrochloric acid solution, soaking for 2-4h, washing with water, adding the iron tailing sand into fluorosilane ethanol solution, soaking for 0.5-1h, and filtering to obtain modified iron tailing sand;

s4, uniformly stirring and mixing the modified cement and the anti-corrosion antirust agent in a stirrer according to the proportion, then adding water, continuously stirring, standing for 0.5-1h, adding modified iron tailing sand, phosphorus tailing sand, limestone tailing sand, quartz tailing sand and fly ash, and continuously and uniformly stirring to obtain sand and stone slurry;

s5, sequentially adding the water reducer and the waterproof agent into the sand slurry obtained in the step S4 according to the proportion, uniformly stirring, pouring into a mould, and preparing the self-compacting concrete.

2. The method for preparing self-compacting concrete using tailing sand as claimed in claim 1, wherein in step S2, the modified cement is composed of the following components in parts by weight: 20-30 parts of phosphate tailing powder, 20-30 parts of limestone tailing powder, 30-40 parts of cement clinker, 2-4 parts of iron tailing powder and 3-6 parts of clay.

3. The method for preparing self-compacting concrete using tailing sand as set forth in claim 1, wherein the moisture content of the mixture after adding water in step S2 is 35-45%.

4. The method for preparing self-compacting concrete using tailing sand as claimed in claim 1, wherein the particle size of the modified cement is 5-20 μm.

5. The method for preparing self-compacting concrete using tailing sand as claimed in claim 1, wherein in step S3, the concentration of fluorosilane in the fluorosilane ethanol solution is 1-2%.

6. The method for preparing self-compacting concrete using tailings sand as claimed in claim 1, wherein in the step S3, the modified iron tailings sand has a particle size ranging from 5 to 10mm, the phosphorus tailings sand has a particle size ranging from 0.5 to 5mm, the limestone tailings sand has a particle size ranging from 15 to 20mm, and the quartz tailings sand has a particle size ranging from 8 to 15mm.

7. The method for preparing self-compacting concrete by utilizing tailing sand as claimed in claim 5, wherein the water reducing agent is a mixture of polycarboxylate water reducing agent and naphthalene water reducing agent in a mass ratio of 1:2-3.

8. The method for preparing self-compacting concrete by using tailing sand as claimed in claim 1, wherein the waterproof agent is a mixture of inorganic aluminum salt and octadecylamine in a mass ratio of 5-8:1.

9. The method for preparing self-compacting concrete by utilizing tailing sand as claimed in claim 1, wherein the corrosion-resistant and rust-resistant agent is triethanolamine borate.

10. Use of self-compacting concrete prepared by the preparation method of any one of claims 1-9 in the manufacture of bridges and piers.