Method for building road by using red mud, phosphogypsum and waste sludge

Abstract

The application discloses a method for road construction by using red mud, phosphogypsum and waste sludge, which pours the roadbed by adopting the method of layered paving and pouring, and the roadbed construction material comprises paving mixture and pumping mixture; the phosphogypsum coarse aggregate, the red mud fine aggregate and the cement dry powder are mixed and uniformly vibrated, so that the cement is uniformly distributed on the surface of the phosphogypsum coarse aggregate and the red mud fine aggregate, and the mixture serves as the paving mixture; and the waste sludge, water, cement, water glass and water reducing agent are uniformly mixed to obtain the high-fluidity waste sludge slurry as the pumping mixture. The application can realize large-scale utilization of industrial solid wastes, and saves the cost without rolling construction. The material is selected by taking the advantage of acid-base neutralization of the acidic phosphogypsum and the alkaline curing agent, and the chemical activity of the dredged sludge is fully improved by the phosphogypsum sulfur excitation and the red mud alkali excitation.

Description

Technical Field

[0001] This invention belongs to the field of road paving technology, specifically relating to a method for road construction using red mud, phosphogypsum and waste silt. Background Technology

[0002] Red mud is an alkaline waste residue produced in the aluminum industry during the extraction of alumina. It is named for its red color due to its high iron oxide content. Producing one ton of alumina generates 0.7 to 1.8 tons of red mud. Currently, the world produces approximately 120 million tons of red mud annually, with my country accounting for about half. The accumulated stockpile reaches hundreds of millions of tons, almost entirely stored in the open. Large-scale stockpiling of red mud also leads to a series of problems, including soil salinization and groundwater pollution.

[0003] Phosphogypsum is a solid waste produced during the treatment of phosphate rock with sulfuric acid in phosphoric acid production. Its main component is CaSO4·2H2O, and it also contains various heavy metals such as copper, lead, cadmium, and mercury, as well as other impurities. At full capacity, my country discharges approximately 20 million tons of phosphogypsum annually, resulting in a very low utilization rate. Most of the phosphogypsum remains in open-air storage.

[0004] Every year, my country conducts numerous river and lake dredging and marine dredging projects, generating large quantities of waste silt with high water content and low strength. Due to its poor engineering properties, much of this dredged silt is disposed of as waste. Inland dredged silt is typically stored by constructing dikes on requisitioned land, while marine dredged silt is disposed of near the coast. This waste disposal of dredged silt results in resource waste and poses a threat to the environment. Solidification is an effective method for the recycling of dredged silt. Through chemical modification, dredged silt can be transformed into high-quality soil for use in engineering filling and construction. However, solidification of dredged silt typically uses energy-intensive and high-emission materials such as cement and lime, resulting in high economic costs and significantly increasing carbon emissions.

[0005] The utilization of red mud and phosphogypsum is relatively difficult and limited in scale. The main problems lie in the low chemical activity of red mud and phosphogypsum as cementing materials. The aluminosilicates in red mud have very weak chemical activity, making it difficult to dissolve in cement systems and participate in pozzolanic reactions. Furthermore, phosphogypsum, due to its acidic impurities, has a significant negative impact on the early strength of cement-cured materials. Additionally, waste sludge, with its high liquid limit and clay content, is difficult to use as compacted subgrade filler, resulting in significant springy soil problems. As a fluid fill material, it often fails to meet the requirements for fluidity and self-compacting properties due to insufficient moisture content. Summary of the Invention

[0006] This invention proposes a method for road construction using red mud, phosphogypsum, and waste sludge, which solves the problems in the prior art where phosphogypsum and red mud, two industrial waste residues, and waste sludge cannot be effectively utilized, occupy large storage yards, and easily cause environmental pollution.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for road construction using red mud, phosphogypsum and waste silt, wherein the method employs a layered paving and pouring method to pour the roadbed, and the roadbed construction materials include paving mixture and pumped mixture, wherein the mass ratio of paving mixture to pumped mixture is 1:1 to 1:3;

[0009] The raw materials of the paving mixture include, by weight, 20-30 parts of phosphogypsum coarse aggregate, 10-20 parts of red mud fine aggregate, and 6-10 parts of cement dry powder;

[0010] The raw materials of the pumped mixture include, by weight, 10-30 parts waste sludge, 4-8 parts dry cement powder, 1-2 parts water glass, and 0.05-0.2 parts water-reducing agent.

[0011] Preferably, the coarse aggregate of phosphogypsum has a particle size of 16-30 mm. The phosphogypsum in the paving mixture should be selected from fully compacted lumps for crushing to ensure that the large particles retain their particle size after crushing.

[0012] Preferably, the particle size of the red mud fine aggregate is mainly 4~16mm. The red mud should have moderate alkalinity, with a pH between 11 and 12.

[0013] In one embodiment of the present invention, the method for preparing the paving mixture is as follows:

[0014] 1) Samples of the compacted phosphogypsum in the stockpile were taken and crushed to obtain well-graded phosphogypsum coarse aggregate;

[0015] 2) Samples of the compacted red mud from the red mud stockpile were taken and crushed to obtain well-graded red mud fine aggregate;

[0016] 3) Mix the phosphogypsum coarse aggregate, red mud fine aggregate, and cement powder, and vibrate them evenly so that the cement is evenly distributed on the surface of the phosphogypsum coarse aggregate and red mud fine aggregate.

[0017] Preferably, the mixing time for the phosphogypsum coarse aggregate, red mud fine aggregate, and cement dry powder is not less than 150 seconds. A vibrating mixer should be used to ensure that the cement, phosphogypsum coarse aggregate, and red mud fine aggregate are fully mixed, have good gradation, and that the cement dry powder is fully adhered to the surface of the aggregate.

[0018] Optionally, the paving mixture can be stockpiled or sold as a composite material, stored in a dry environment, and transported to the paving site when there is a need for road construction.

[0019] By adopting the above technical solution, the skeletal filling function of phosphogypsum and red mud can be effectively utilized. Furthermore, the mixing of coarse and fine particles increases the intergranular embedding effect, resulting in a better overall structure. Simultaneously, the alkalinity of the red mud compensates for the negative effects of the acidic impurities in phosphogypsum. The presence of cement powder in the aggregate voids, phosphogypsum powder on the phosphogypsum surface, and red mud powder on the red mud surface effectively forms a sulfur-activated and alkali-activated cementitious cementitious system.

[0020] Preferably, the natural moisture content of the waste sludge is between 0.5 and 1.5 times the liquid limit, and needs to be increased to 2 times the liquid limit by adding water and mixing.

[0021] Preferably, the liquid limit of the waste sludge is between 30% and 60%, and the clay content should not exceed 30%.

[0022] Preferably, the modulus of the water glass is 2 to 3, and the Baume degree is 30 to 45 Bé°.

[0023] Preferably, the flowability of the pumped mixture is around 22cm, not less than 20cm, and not more than 24cm, to meet the flowability requirements without adding too much water-reducing agent and increasing costs.

[0024] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0025] In one embodiment of the present invention, the method for preparing the pumped mixture is as follows:

[0026] 1) Determine the natural moisture content and liquid limit of the waste sludge, and make the moisture content of the waste sludge reach twice the liquid limit by adding water and stirring.

[0027] 2) Mix the well-stirred waste sludge slurry with cement and water glass until homogeneous;

[0028] 3) Add water-reducing agent according to the pumping flow requirements and stir evenly to obtain pumpable mixture.

[0029] After the pumping mixture is prepared, it should be poured within half an hour to prevent excessive loss of fluidity, which could cause pumping difficulties or poor self-compacting ability.

[0030] In this invention, the roadbed is laid and poured in three layers (subbase, intermediate base, and top base), and three pumped mixtures with different cement content can be configured, with the cement content increasing sequentially from the subbase to the top base.

[0031] By adopting the above technical solution, silt can be effectively used for off-site construction. By adding water and water-reducing agents, high fluidity can be achieved, enabling pumping and pouring.

[0032] In this invention, the cement is ordinary Portland cement with a grade of 42.5.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) This invention breaks down the compacted lumps of phosphogypsum and red mud from stockpiles to form coarse phosphogypsum aggregate and fine red mud aggregate, which are used as aggregates for roadbed filling. This not only utilizes the filling function of phosphogypsum and red mud as aggregates but also leverages the role of the aggregate surface powder in the cementitious system. The surface layer of phosphogypsum aggregate can dissolve calcium sulfate, providing a large amount of calcium and sulfate ions, promoting the formation of ettringite in the cement system, thereby increasing density; while the surface layer of red mud aggregate can dissolve and release hydroxide ions, increasing the pH value of the system, thereby compensating for the negative effects of acidic impurities in phosphogypsum, promoting the dissolution of clay minerals in silt, and increasing the pozzolanic reaction rate.

[0035] (2) The present invention adopts the concept of flow solidification. By increasing the water content of waste sludge to twice the liquid limit and increasing the fluidity of the slurry by using a water-reducing agent, the waste sludge can be pumped for construction. It can also be self-compacted during pouring construction, fully filling the pores between red mud aggregate and phosphogypsum aggregate. Combined with vibration, high-quality filling can be achieved.

[0036] (3) The present invention adopts a two-step approach. Red mud and phosphogypsum aggregates can be industrialized and stockpiled for sale. When there is a need for roadbed filling, they can be transported to the road construction area and the mixture can be pumped on-site, thereby increasing flexibility and mobility. Attached Figure Description

[0037] Figure 1 A flowchart illustrating a method for road construction using red mud, phosphogypsum, and waste silt. Implementation

[0038] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0039] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0040] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0041] All raw materials used in the following examples are in parts by weight. Example

[0042] like Figure 1As shown in the figure, this embodiment discloses a method for road construction using red mud, phosphogypsum and waste sludge, including the preparation of paving mixture and the preparation of pumped mixture, as well as on-site paving, pouring and vibration curing, thereby reusing industrial solid waste red mud, phosphogypsum and waste sludge for roadbed filling.

[0043] A method for road construction using red mud, phosphogypsum, and waste silt includes the following steps:

[0044] S1: Prepare the paving mixture

[0045] S1a: Take the compacted phosphogypsum blocks from the phosphogypsum stockpile, crush them using a crusher, and then screen them to obtain coarse particles with a particle size between 16 and 30 mm.

[0046] S1b: Red mud lumps that have hardened in the red mud stockpile are crushed using a crusher. After crushing, they are screened to obtain fine particles with a particle size between 4 and 16 mm.

[0047] S1c: 25 parts coarse phosphogypsum particles, 12 parts fine red mud particles and 6 parts dry cement powder are vibrated and mixed to make the coarse and fine particles evenly mixed and well graded, and the surface of the phosphogypsum and red mud particles is coated with sufficient dry cement powder.

[0048] S1d: Transport the paving mixture to the road construction site.

[0049] S2: Configure pumpable mixture

[0050] Take 20 parts of waste sludge, 4 parts of dry cement powder, 1 part of water glass, and 0.05 parts of polycarboxylate superplasticizer for later use;

[0051] S2a: Determine the natural moisture content and liquid limit of the waste sludge, and calculate the amount of water that needs to be added for mixing;

[0052] S2b: By adding water and mixing, the water content of the waste sludge reaches twice the liquid limit;

[0053] S2c: The waste sludge slurry is mixed with cement dry powder and water glass to obtain a mixed slurry;

[0054] S2d: Determine the fluidity of freshly mixed slurry. Adjust the fluidity of the slurry by adding polycarboxylate superplasticizer to ensure that the fluidity of the slurry is greater than 20cm.

[0055] S3: Subgrade paving and pouring

[0056] S3a: Surveying and setting out, clarifying the target area for roadbed paving, clearing and leveling the ground surface, removing construction waste, etc.

[0057] S3b: The outer frame formwork is constructed according to the roadbed construction area. The height of the formwork is 1 / 3 of the total roadbed thickness. Reinforcing bars are installed at the rear end of the formwork to support the outer frame formwork, and support rods are set at an angle to assist in supporting the formwork.

[0058] S3c: The top of the mold serves as the elevation control line for paving. The paving mix should be slightly lower than the elevation control line, roughly leveled, and then poured in sections. The mass ratio of paved material to pumped material should be controlled at 1:2. Construction equipment and personnel should be allocated appropriately, and monitoring should be maintained to ensure the elevation control line at the top of the mold is reached. Pouring should be carried out generally horizontally until the elevation control line is reached. After pouring, vibration and manual leveling should be performed to ensure the smoothness of the poured surface.

[0059] S3d: After the base course mixture has initially set, proceed with the intermediate course construction. First, raise the mold to 2 / 3 of the roadbed height, and then pave and pour the intermediate course material as above. The mass ratio of the paving material to the pumped material is the same as that of the base course.

[0060] S3e: Raise the mold to the height of the roadbed and carry out the construction of the top and bottom layers, with the same mix proportions as above.

[0061] S3f: After the top layer of poured soil has initially set, remove the outer frame formwork and cover it for curing.

Claims

1. A method for road construction using red mud, phosphogypsum, and waste silt, characterized in that, The roadbed is constructed using a layered paving and pouring method. The roadbed construction materials include paving mixture and pumped mixture, with a mass ratio of paving mixture to pumped mixture of 1:1 to 1:

3. The raw materials of the paving mixture include, by weight, 20-30 parts of phosphogypsum coarse aggregate, 10-20 parts of red mud fine aggregate, and 6-10 parts of cement dry powder; The raw materials of the pumped mixture include, by weight, 10-30 parts waste sludge, 4-8 parts dry cement powder, 1-2 parts water glass, and 0.05-0.2 parts water-reducing agent.

2. The method according to claim 1, characterized in that, The particle size of the phosphogypsum coarse aggregate is 16~30mm.

3. The method according to claim 1, characterized in that, The particle size of the red mud fine aggregate is 4~16mm.

4. The method according to claim 1, characterized in that, The preparation method of the paving mixture is as follows: 1) Samples of the compacted phosphogypsum in the stockpile were taken and crushed to obtain well-graded phosphogypsum coarse aggregate; 2) Samples of the compacted red mud from the red mud stockpile were taken and crushed to obtain well-graded red mud fine aggregate; 3) Mix the coarse phosphogypsum aggregate, fine red mud aggregate, and dry cement powder, and vibrate them evenly so that the cement is evenly distributed on the surface of the coarse phosphogypsum aggregate and fine red mud aggregate to obtain the paving mixture.

5. The method according to claim 1, characterized in that, The natural moisture content of the waste sludge is between 0.5 and 1.5 times the liquid limit.

6. The method according to claim 1, characterized in that, The liquid limit of the waste sludge is between 30% and 60%, and the clay content should not exceed 30%.

7. The method according to claim 1, characterized in that, The water glass has a modulus of 2 to 3 and a Baume degree of 30 to 45 Bé°.

8. The method according to claim 1, characterized in that, The preparation method of the pumped mixture is as follows: 1) Determine the natural moisture content and liquid limit of the waste sludge, and make the moisture content of the waste sludge reach twice the liquid limit by adding water and stirring. 2) Mix the well-stirred waste sludge slurry with cement and water glass until homogeneous; 3) Add water-reducing agent according to the pumping flow requirements and stir evenly to obtain pumpable mixture.

9. The method according to claim 1, characterized in that, The layering consists of three layers.

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