A fully solid waste environmentally friendly road structure containing a steel slag wearing layer and its construction method

Abstract

The present invention provides a fully solid waste environmentally friendly road structure containing a steel slag wearing layer and a construction method thereof, belonging to the technical field of road engineering. Coral sand is used to pave a precipitate absorption layer on the roadbed, and modified red mud or modified phosphogypsum is used to fill the roadbed in layers on top of the precipitate absorption layer. Under the condition that the bearing capacity requirements are met, an asphalt structure combination layer of a certain thickness is directly paved on the roadbed, and the anti-skid wear layer in the asphalt structure combination layer is paved with steel slag aggregate instead of part of the stone. The pavement structure has a simple construction process and low cost, and can avoid soil and groundwater pollution caused by the infiltration of residual harmful substances in red mud or phosphogypsum solid waste, while realizing large-scale road use and high-value utilization of materials such as steel slag, red mud, phosphogypsum, and coral sand.

Description

Technical Field

[0001] The present invention relates to the technical field of road engineering, and in particular to an all-solid waste environmentally friendly road structure containing a steel slag wearing layer and a construction method thereof. Background Art

[0002] With the continued development of highway construction, high-quality road construction materials are becoming increasingly scarce. Industrial solid wastes, such as red mud and phosphogypsum, are gradually coming into the public eye. At the same time, the harmless, large-scale, road-use disposal of industrial solid wastes has become a current research hotspot. Steel slag, a byproduct of the steelmaking process, is composed of oxides produced by the oxidation of Ca, Fe, Si, Mg, and a small amount of Al; impurities introduced by corroded furnace linings, furnace patching materials, and metal charge; and slag-forming fillers such as limestone, dolomite, and iron ore. Steel slag is characterized by its angular shape and hard texture. Red mud, produced during the production of alumina from bauxite, is a highly alkaline, extremely fine-grained solid material rich in rare earth and rare metals, and exhibits a certain degree of radioactivity. Phosphogypsum, a solid waste generated during the wet process of producing phosphoric acid, is fine-grained and contains residual phosphoric acid, fluoride, acid-insoluble matter, and organic matter. Industrial solid waste represented by red mud and phosphogypsum cannot be fully and effectively utilized at present and can only be stored in storage yards, which occupies a large amount of land and causes great pollution to the environment. If red mud, phosphogypsum, etc. are directly used for highway roadbed filling, they will penetrate into the surrounding environment and have certain harmful effects on the soil and groundwater, which hinders their large-scale application in highway construction.

[0003] At present, the anti-seepage treatment of solid waste fill roadbed usually adopts the method of laying high-density polyethylene geomembrane under the solid waste roadbed. For example, the Chinese invention patent application with the announcement number "CN115262307A" discloses a red mud-based lightweight roadbed construction method, wherein a geogrid and an anti-seepage geomembrane are provided on the top of the red mud-based lightweight roadbed, the geogrid is laid under the anti-seepage geomembrane, the anti-seepage geomembrane and the geogrid are both laid horizontally, and the top and bottom surfaces of the red mud-based lightweight roadbed are wrapped with a composite geomembrane; this process has the disadvantages of high cost of the anti-seepage membrane, complex construction process, easy breakage of the anti-seepage membrane under the action of uneven settlement of the roadbed, non-degradability, and impact on the groundwater level.

[0004] Coral sand, made of coral or shell fragments, is extremely abundant in my country. It is lightweight, porous, and highly absorbent, making it a natural lightweight aggregate. Leveraging its rich micropores and strong absorbency, we intend to use coral sand as a precipitate absorption layer beneath roadbeds filled with solid wastes such as red mud and phosphogypsum. This will absorb harmful substances precipitated from these solid wastes. At the same time, we will utilize the high skid and wear resistance of steel slag to replace some stone in the construction of an anti-skid wear layer, thereby constructing a fully solid waste, environmentally friendly road structure containing a steel slag wear layer. This will not only enhance the overall performance of the pavement structure, but also address the challenges of reducing and reusing industrial solid wastes such as steel slag, red mud, and phosphogypsum. Summary of the Invention

[0005] In order to address the deficiencies in the prior art, the present invention provides a fully solid waste environmentally friendly road structure containing a steel slag wearing layer and a construction method thereof. When this structure is used for construction, it can ensure that the environmental protection requirements are met when using industrial solid waste such as red mud and phosphogypsum to fill the roadbed, while achieving large-scale road use and high-value utilization of materials such as steel slag, red mud, phosphogypsum, and coral sand.

[0006] The technical solution specifically adopted in the present invention is:

[0007] A fully solid waste environmentally friendly road structure containing a steel slag wearing layer comprises a precipitate absorption layer paved with coral sand on the roadbed, and a roadbed filled with modified red mud or modified phosphogypsum on top of the precipitate absorption layer to obtain a modified red mud roadbed or a modified phosphogypsum roadbed. Under the condition that the bearing capacity requirements are met, an asphalt structure composite layer of a certain thickness is paved on the roadbed, and the anti-skid wear layer in the asphalt structure composite layer is paved with steel slag.

[0008] Preferably, the precipitate absorption layer is coral sand of different particle sizes.

[0009] Preferably, the precipitate absorption layer comprises, by weight: 15 to 35 parts of coral sand with a diameter of 0 to 5 mm, 5 to 20 parts of coral sand with a diameter of 5 to 10 mm, 20 to 40 parts of coral sand with a diameter of 10 to 20 mm, 10 to 35 parts of coral sand with a diameter of 20 to 30 mm, and 3 to 15 parts of water.

[0010] The precipitate absorption layer uses coral sand aggregates of different particle sizes to form a skeleton-dense mixture. The mixture structure has a large number of coarse aggregates to form a spatial skeleton, and at the same time has enough fine aggregates to fill the gaps in the skeleton. It has high structural strength, rich pores and strong adsorption capacity.

[0011] Preferably, the thickness of the precipitate absorption layer is greater than 30 cm, and the layer is constructed in layers, with a maximum thickness of ≤20 cm and a minimum thickness of ≥10 cm in single-layer construction, and a compaction degree of >90%.

[0012] Preferably, the resilience modulus of the precipitate absorbing layer is ≥400 MPa.

[0013] Preferably, the modified red mud roadbed is constructed in layers, with a maximum thickness of a single layer of ≤30 cm, a minimum thickness of ≥15 cm, a compaction degree of >92%, and an overall stiffness requirement of >100 MPa.

[0014] Preferably, the modified phosphogypsum roadbed is constructed in layers, with a maximum thickness of ≤30 cm and a minimum thickness of ≥15 cm for a single layer, a compaction degree of >92%, and an overall stiffness requirement of >100 MPa.

[0015] Preferably, the thickness of the modified red mud roadbed or modified phosphogypsum roadbed is 50 to 300 cm.

[0016] Preferably, in order to ensure the overall performance of the pavement structure, the asphalt structure composite layer is a semi-rigid base asphalt structure composite layer, which includes, from top to bottom, an anti-skid wear layer, a bonding layer, an anti-fatigue layer, a durable anti-cracking layer and a cement-stabilized gravel base.

[0017] Preferably, the anti-skid wear layer comprises, by weight: 30 to 85 parts of steel slag aggregate, 10 to 30 parts of stone chips, 2 to 6 parts of filler, and 5 to 11 parts of modified asphalt; wherein the steel slag aggregate adopts one or more of the particle sizes of 2.36 mm to 4.75 mm, 4.75 mm to 9.5 mm, and 9.5 to 13.2 mm, and the free calcium oxide content of each specification is ≤3%; the stone chips are limestone or basalt, with a particle size of 0 to 2.36 mm and a sand equivalent of ≥60%; wherein the binder is SBS modified asphalt; the thickness of the anti-skid wear layer is 3 to 6 cm, and the porosity is 3 to 4%.

[0018] Preferably, the bonding layer adopts AC-20 grade asphalt mixture, wherein the binder is SBS modified asphalt; the bonding layer has a thickness of 3 to 6 cm and a porosity of 4 to 6%.

[0019] Preferably, the anti-fatigue layer adopts AC-25 grade asphalt mixture, wherein the binder is 70# matrix asphalt; the thickness of the anti-fatigue layer is 6 to 10 cm, and the porosity is 4 to 6%.

[0020] Preferably, the durable anti-cracking layer adopts ATB-25 grade asphalt mixture, wherein the binder is SBS modified asphalt; the durable anti-cracking layer has a thickness of 16 to 32 cm, is constructed in layers, and has a porosity of 3.5 to 4.5%.

[0021] Preferably, the cement-stabilized gravel base layer adopts a cement-stabilized gravel mixture, in which the binder is P.O42.5 ordinary Portland cement; the cement-stabilized gravel base layer is constructed in 3 layers, each layer is 18 cm, in which the cement dosage of the bottom base cement-stabilized gravel mixture is 3.5% (external admixture), and the cement dosage of the upper base or lower base cement-stabilized gravel mixture is 4.5% (external admixture).

[0022] Preferably, the modified red mud is obtained by modifying red mud with a red mud modifier in an amount of 5 to 10% by mass of the red mud, and the modified phosphogypsum is obtained by modifying phosphogypsum with a phosphogypsum modifier in an amount of 5 to 15% by mass of the phosphogypsum; wherein the red mud modifier comprises, in parts by weight: 40 to 80 parts of phosphogypsum, 5 to 30 parts of fly ash, 3 to 25 parts of cement, and 1 to 10 parts of asphalt; and the phosphogypsum modifier comprises, in parts by weight: 2 to 10 parts of a silane coupling agent, 5 to 15 parts of an aluminate coupling agent, and 10 to 23 parts of quicklime.

[0023] After the overall asphalt pavement structure combination and thickness are determined, the tensile strain at the bottom of the layer must be verified to ensure the durability of the pavement structure under the design load. The total thickness verification of the semi-rigid base asphalt structure combination layer should meet the requirement that the bending tensile strain at the bottom of the asphalt structure combination layer is less than 70 microstrain (μm) under the design load. If the requirement is not met, the layer thickness and design modulus will be adjusted; the microstrain at the bottom of the semi-rigid base asphalt structure combination layer is calculated using the continuous elastic layer theory. The structural modulus of the modified red mud roadbed or modified phosphogypsum roadbed and the semi-rigid base asphalt structure combination layer is determined through actual test measurements, and the value range is as follows:

[0024] Precipitation absorption layer: 400-800 MPa, Poisson's ratio 0.35;

[0025] Modified red mud roadbed or modified phosphogypsum roadbed: 120-400 MPa, Poisson's ratio 0.4;

[0026] Cement-stabilized gravel base: 18,000-28,000 MPa, Poisson's ratio 0.25;

[0027] Durable anti-cracking layer: 7000Mpa~9000Mpa, Poisson's ratio 0.25;

[0028] Anti-fatigue layer: 8000~10000Mpa, Poisson's ratio 0.25;

[0029] Connection layer: 13000-15000, Poisson's ratio 0.25;

[0030] Anti-slip wear layer: 7500~9500Mpa, Poisson's ratio 0.25.

[0031] Beneficial effects of the present invention:

[0032] 1) The present invention provides a coral sand precipitate absorption layer under the modified red mud roadbed or modified phosphogypsum roadbed. The layer has high structural strength, abundant pores, strong adsorption capacity, and low cost. It can effectively prevent residual harmful substances in the red mud or phosphogypsum from polluting the soil and groundwater, thus meeting environmental protection requirements.

[0033] 2) The present invention utilizes the high anti-skid and high wear-resistant properties of steel slag to replace part of the stone to pave the anti-skid wear layer, greatly improving the anti-skid performance of the anti-skid wear layer and extending the service life of the wear layer, while achieving high-value utilization of steel slag waste;

[0034] 3) The road structure provided by the present invention can consume a large amount of industrial solid waste such as steel slag, red mud, phosphogypsum and low-value raw materials such as coral sand, thereby realizing the recycling of waste and saving resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the pavement structure of the present invention;

[0036] 1. Anti-skid wear layer; 2. Bonding layer; 3. Anti-fatigue layer; 4. Durable anti-cracking layer; 5. Cement-stabilized gravel base; 6. Solid waste roadbed; 7. Precipitate absorption layer; 8. Roadbed. DETAILED DESCRIPTION

[0037] The following describes the process in conjunction with specific embodiments:

[0038] Example 1:

[0039] 1. Determine the road structure combination plan

[0040] According to the design elevation of the road surface, the topsoil of the original road base is removed, and the roadbed 8 is compacted with a roller. The road structure designed on the compacted roadbed 8 is: 40 cm precipitate absorption layer 7 (constructed in two layers, 20 cm per layer) + 200 cm modified red mud roadbed 6 (constructed in 10 layers, 20 cm per layer) + 54 cm cement stabilized gravel base 5 (constructed in 3 layers, 18 cm per layer) + 18 cm durable anti-cracking layer 4 (ATB-25, constructed in 2 layers, 9 cm per layer) + 8 cm anti-fatigue layer 3 (AC-25) + 6 cm bonding layer 2 (AC-20) + 4 cm anti-skid wear layer 1 (SMA-13).

[0041] 2. Road surface pouring on site

[0042] 1. Precipitate absorption layer

[0043] 0-5mm coral sand, 5-10mm coral sand, 10-20mm coral sand, 20-30mm coral sand and water with a mass ratio of 32:19:24:25:5 are mixed and produced using continuous mixing equipment, spread by a paver, and compacted by a heavy roller. The construction is divided into two layers, each layer is 20cm, and the compaction degree reaches 91%.

[0044] Before paving the modified red mud roadbed thereon, the overall stiffness index was tested, and the representative value of the modulus of the precipitate absorption layer 7 was detected to be 450 MPa.

[0045] 2. Modified red mud roadbed

[0046] Red mud is used as the main paving material, and a mixture of phosphogypsum, fly ash, cement and asphalt with a mass ratio of 70:18:10:2 is used as the modifier, with the modifier dosage being 10% of the red mud mass;

[0047] The modified red mud roadbed was constructed in 10 layers, with each layer being 20 cm thick and a compaction degree of 92%.

[0048] 3. Asphalt structural composite layer

[0049] ①Asphalt surface layer:

[0050] The steel slag anti-skid wear layer 1 adopts SMA-13 ​​grade asphalt mixture, in which the binder is SBS modified asphalt; the thickness of the anti-skid wear layer 1 is 4 cm and the porosity is 3.5%; 9.5-13.2mm steel slag aggregate, 4.75-9.5mm steel slag aggregate, 2.36-4.75mm steel slag aggregate, 0-2.36mm limestone, filler, and modified asphalt with a mass ratio of 15:38:22:14:5:6 are mixed and produced using a continuous mixing equipment, spread by a paver, and compacted by a heavy roller.

[0051] The connecting layer 2 uses AC-20 grade asphalt mixture, and the binder is SBS modified asphalt; the thickness of the connecting layer 2 is 6 cm and the porosity is 4%.

[0052] The anti-fatigue layer 3 is made of AC-25 asphalt mixture, and the binder is 70# matrix asphalt; the thickness of the anti-fatigue layer 3 is 8 cm, and the porosity is 4%.

[0053] The durable anti-cracking layer 4 uses ATB-25 grade asphalt mixture, and the binder is SBS modified asphalt; the thickness of the durable anti-cracking layer 4 is 18 cm, and it is constructed in layers, with a porosity of 3.6%.

[0054] ②Cement stabilized gravel base:

[0055] The cement-stabilized gravel base layer 5 adopts a cement-stabilized gravel mixture, in which the binder is P.O42.5 ordinary Portland cement; the cement-stabilized gravel base layer 5 is constructed in 3 layers, each layer is 18 cm, in which the cement dosage of the bottom base cement-stabilized gravel mixture is 3.5% (externally mixed), and the cement dosage of the upper or lower base cement-stabilized gravel mixture is 4.5% (externally mixed).

[0056] 3. Analysis of anti-seepage and anti-alkali data

[0057] The red mud filler of the modified red mud roadbed on the precipitate absorption layer and the roadbed soil of the roadbed below the precipitate absorption layer were sampled respectively, and the engineering and environmental indicators were compared. The results are shown in Table 1:

[0058] Table 1. Test results of various indicators in Example 1

[0059] Test items Red mud filler roadbed soil pH 8.2 7.1 Hexavalent chromium (mg / L) 0.48 0.023 Arsenic (mg / L) 0.008 0.002 Cyanide (mg / L) 0.04 0.01 Fluoride (mg / L) 0.8 0.1

[0060] As shown in Table 1, the pH value of the roadbed soil dropped to 7.1, and the contents of harmful substances such as hexavalent chromium, arsenic, cyanide, and fluoride all decreased. This shows that the coral sand precipitate absorption layer effectively prevented the pollution of soil and groundwater by harmful substances in red mud.

[0061] Example 2:

[0062] 1. Determine the road structure combination plan

[0063] According to the design elevation of the road surface, the topsoil of the original road base is removed, and the roadbed 8 is compacted with a roller. The road structure designed on the compacted roadbed 8 is: 40 cm precipitate absorption layer 7 (constructed in two layers, 20 cm per layer) + 200 cm modified red mud roadbed 6 (constructed in 10 layers, 20 cm per layer) + 54 cm cement stabilized gravel base 5 (constructed in 3 layers, 18 cm per layer) + 18 cm durable anti-cracking layer 4 (ATB-25, constructed in 2 layers, 9 cm per layer) + 8 cm anti-fatigue layer 3 (AC-25) + 6 cm bonding layer 2 (AC-20) + 4 cm anti-skid wear layer 1 (AC-13).

[0064] 2. Road surface pouring on site

[0065] 1. Precipitate absorption layer

[0066] 0-5mm coral sand, 5-10mm coral sand, 10-20mm coral sand, 20-30mm coral sand and water with a mass ratio of 28:20:27:25:5 are mixed and produced using continuous mixing equipment, spread by a paver, and compacted by a heavy roller. The construction is divided into two layers, each layer is 20cm, and the compaction degree reaches 92%.

[0067] Before paving the modified red mud roadbed thereon, the overall stiffness index was tested, and the representative value of the modulus of the precipitate absorption layer 7 was detected to be 490 MPa.

[0068] 2. Modified red mud roadbed

[0069] Red mud is used as the main paving material, and a mixture of phosphogypsum, fly ash, cement and asphalt with a mass ratio of 68:19:11:2 is used as the modifier, with the modifier dosage being 10% of the red mud mass;

[0070] The modified red mud roadbed was constructed in 10 layers, with each layer being 20 cm thick and a compaction degree of 92%.

[0071] 3. Asphalt structural composite layer

[0072] ①Asphalt surface layer:

[0073] The steel slag anti-skid wear layer 1 uses AC-13 grade asphalt mixture, in which the binder is SBS modified asphalt; the thickness of the anti-skid wear layer 1 is 4 cm and the porosity is 3.5%; 9.5-13.2mm steel slag aggregate, 4.75-9.5mm steel slag aggregate, 2.36-4.75mm steel slag aggregate, 0-2.36mm limestone, filler, and modified asphalt with a mass ratio of 22:21:29:17:4:7 are mixed and produced using a continuous mixing equipment, spread by a paver, and compacted by a heavy-duty roller.

[0074] The connecting layer 2 uses AC-20 grade asphalt mixture, and the binder is SBS modified asphalt; the thickness of the connecting layer 2 is 5 cm and the porosity is 4%.

[0075] The anti-fatigue layer 3 is made of AC-25 asphalt mixture, and the binder is 70# matrix asphalt; the thickness of the anti-fatigue layer 3 is 9 cm, and the porosity is 4%.

[0076] The durable anti-cracking layer 4 uses ATB-25 grade asphalt mixture, and the binder is SBS modified asphalt; the thickness of the durable anti-cracking layer 4 is 20 cm, and it is constructed in layers, with a porosity of 3.6%.

[0077] ②Cement stabilized gravel base:

[0078] The cement-stabilized gravel base layer 5 adopts a cement-stabilized gravel mixture, in which the binder is P.O42.5 ordinary Portland cement; the cement-stabilized gravel base layer 5 is constructed in 3 layers, each layer is 18 cm, in which the cement dosage of the bottom base cement-stabilized gravel mixture is 3.5% (externally mixed), and the cement dosage of the upper or lower base cement-stabilized gravel mixture is 4.5% (externally mixed).

[0079] 3. Analysis of anti-seepage and anti-alkali data

[0080] The red mud filler of the modified red mud roadbed on the precipitate absorption layer and the roadbed soil of the roadbed below the precipitate absorption layer were sampled respectively, and the engineering and environmental indicators were compared. The results are shown in Table 2:

[0081] Table 2. Test results of various indicators in Example 2

[0082] Test items Red mud filler roadbed soil pH 8.1 7.1 Hexavalent chromium (mg / L) 0.45 0.020 Arsenic (mg / L) 0.007 0.001 Cyanide (mg / L) 0.03 0.01 Fluoride (mg / L) 0.9 0.2

[0083] Example 3:

[0084] 1. Determine the road structure combination plan

[0085] According to the design elevation of the road surface, the topsoil of the original road base is removed and the roadbed 8 is compacted with a roller. The road structure designed on the compacted roadbed 8 is: 40 cm precipitate absorption layer 7 (constructed in two layers, 20 cm per layer) + 200 cm modified phosphogypsum roadbed 6 (constructed in 10 layers, 20 cm per layer) + 54 cm cement stabilized gravel base 5 (constructed in 3 layers, 18 cm per layer) + 20 cm durable anti-cracking layer 4 (ATB-25, constructed in 2 layers, 10 cm per layer) + 8 cm anti-fatigue layer 3 (AC-25) + 6 cm bonding layer 2 (AC-20) + 4 cm anti-skid wear layer 1 (AC-13).

[0086] 2. Road surface pouring on site

[0087] 1. Precipitate absorption layer

[0088] 0-5mm coral sand, 5-10mm coral sand, 10-20mm coral sand, 20-30mm coral sand and water in a mass ratio of 20:24:30:26:5 are mixed and produced using continuous mixing equipment, spread by a paver, and compacted by a heavy roller. The construction is divided into two layers, each layer is 20cm, and the compaction degree reaches 91%.

[0089] Before paving the modified red mud roadbed thereon, the overall stiffness index was tested, and the representative value of the modulus of the precipitate absorption layer 7 was detected to be 490 MPa.

[0090] 2. Modified phosphogypsum roadbed

[0091] Phosphogypsum is used as the main paving material, and a mixture of silane coupling agent, aluminate coupling agent and quicklime with a mass ratio of 7:5:12 is used as the modifier, and the modifier dosage is 10% of the red mud mass.

[0092] The modified phosphogypsum roadbed is constructed in 10 layers, with each layer being 20 cm thick and a compaction degree of 92%.

[0093] 3. Asphalt structural composite layer

[0094] ①Asphalt surface layer:

[0095] The steel slag anti-skid wear layer 1 utilizes an AC-13 grade asphalt mixture with SBS modified asphalt as the binder. The anti-skid wear layer 1 is 4 cm thick and has a porosity of 3.5%. A mixture of 9.5-13.2 mm steel slag aggregate, 4.75-9.5 mm steel slag aggregate, 2.36-4.75 mm steel slag aggregate, 0-2.36 mm limestone, filler, and modified asphalt in a mass ratio of 20:23:28:18:5:6 is mixed using a continuous mixing plant, spread by a paver, and compacted by a heavy-duty roller.

[0096] The connecting layer 2 uses AC-20 grade asphalt mixture, and the binder is SBS modified asphalt; the thickness of the connecting layer 2 is 5 cm and the porosity is 4%.

[0097] The anti-fatigue layer 3 is made of AC-25 asphalt mixture, and the binder is 70# matrix asphalt; the thickness of the anti-fatigue layer 3 is 8 cm, and the porosity is 4%.

[0098] The durable anti-cracking layer 4 uses ATB-25 grade asphalt mixture, and the binder is SBS modified asphalt; the thickness of the durable anti-cracking layer 4 is 19 cm, it is constructed in layers, and the porosity is 3.6%.

[0099] ②Cement stabilized gravel base:

[0100] The cement-stabilized gravel base layer 5 adopts a cement-stabilized gravel mixture, in which the binder is P.O42.5 ordinary Portland cement; the cement-stabilized gravel base layer 5 is constructed in 3 layers, each layer is 18 cm, in which the cement dosage of the bottom base cement-stabilized gravel mixture is 3.5% (externally mixed), and the cement dosage of the upper or lower base cement-stabilized gravel mixture is 4.5% (externally mixed).

[0101] 3. Analysis of anti-seepage and anti-alkali data

[0102] The phosphogypsum filler of the modified phosphogypsum roadbed on the precipitate absorption layer and the roadbed soil of the soil roadbed below the precipitate absorption layer were sampled respectively, and the engineering and environmental indicators were compared. The results are shown in Table 3:

[0103] Table 3. Test results of various indicators in Example 3

[0104] Test items Phosphogypsum filler roadbed soil pH 6.7 7.1 Hexavalent chromium (mg / L) 0.44 0.019 Arsenic (mg / L) 0.004 0.002 Lead and its compounds (mg / L) 0.013 0.004 Cadmium and its compounds (mg / L) 0.0008 0.0003

[0105] Example 4:

[0106] 1. Determine the road structure combination plan

[0107] According to the design elevation of the road surface, the topsoil of the original road base is removed and the roadbed 8 is compacted with a roller. The road structure designed on the compacted roadbed 8 is: 60cm precipitate absorption layer 7 (constructed in three layers, 20cm per layer) + 200cm modified phosphogypsum roadbed 6 (constructed in 10 layers, 20cm per layer) + 54cm cement-stabilized gravel base layer 5 (constructed in 3 layers, 18cm per layer) + 20cm durable anti-cracking layer 4 (ATB-25, constructed in 2 layers, 10cm per layer) + 8cm anti-fatigue layer 3 (AC-25) + 6cm bonding layer 2 (AC-20) + 4cm anti-skid wear layer 1 (AC-13).

[0108] 2. Road surface pouring on site

[0109] 1. Precipitate absorption layer

[0110] 0-5mm coral sand, 5-10mm coral sand, 10-20mm coral sand, 20-30mm coral sand and water in a mass ratio of 20:24:30:26:5 are mixed and produced using continuous mixing equipment, spread by a paver, and compacted by a heavy roller. The construction is divided into three layers, each layer is 20cm, and the compaction degree reaches 91%.

[0111] Before paving the modified phosphogypsum roadbed thereon, the overall stiffness index was tested, and the representative value of the modulus of the precipitate absorption layer 7 was detected to be 470 MPa.

[0112] 2. Modified phosphogypsum roadbed

[0113] Phosphogypsum is used as the main paving material, and a mixture of silane coupling agent, aluminate coupling agent and quicklime with a mass ratio of 8:15:18 is used as the modifier, and the modifier dosage is 10% of the red mud mass.

[0114] The modified phosphogypsum roadbed is constructed in 10 layers, with each layer being 20 cm thick and a compaction degree of 92%.

[0115] 3. Asphalt structural composite layer

[0116] ①Asphalt surface layer:

[0117] The steel slag anti-skid wear layer 1 utilizes an AC-13 grade asphalt mixture with SBS modified asphalt as the binder. The anti-skid wear layer 1 is 4 cm thick and has a porosity of 3.5%. A mixture of 9.5-13.2 mm steel slag aggregate, 4.75-9.5 mm steel slag aggregate, 2.36-4.75 mm steel slag aggregate, 0-2.36 mm limestone, filler, and modified asphalt in a mass ratio of 20:23:28:18:5:6 is mixed using a continuous mixing plant, spread by a paver, and compacted by a heavy-duty roller.

[0118] The connecting layer 2 uses AC-20 grade asphalt mixture, and the binder is SBS modified asphalt; the thickness of the connecting layer 2 is 6 cm and the porosity is 4%.

[0119] The anti-fatigue layer 3 is made of AC-25 asphalt mixture, and the binder is 70# matrix asphalt; the thickness of the anti-fatigue layer 3 is 9 cm, and the porosity is 4%.

[0120] The durable anti-cracking layer 4 uses ATB-25 grade asphalt mixture, and the binder is SBS modified asphalt; the thickness of the durable anti-cracking layer 4 is 20 cm, and it is constructed in layers, with a porosity of 3.6%.

[0121] ②Cement stabilized gravel base:

[0122] The cement stabilized gravel base 5 adopts a cement stabilized gravel mixture, in which the binder is P.O42.5 ordinary Portland cement; the cement stabilized gravel base 5 is constructed in 3 layers, each layer is 18 cm, in which the cement content of the bottom base is 3.5%, and the cement content of the upper base and lower base is 4.5%.

[0123] 3. Analysis of anti-seepage and anti-alkali data

[0124] The phosphogypsum filler of the modified phosphogypsum roadbed on the precipitate absorption layer and the roadbed soil of the soil roadbed below the precipitate absorption layer were sampled respectively, and the engineering and environmental indicators were compared. The results are shown in Table 4:

[0125] Table 4. Test results of various indicators in Example 4

[0126] Test items Phosphogypsum filler roadbed soil pH 6.6 7.0 Hexavalent chromium (mg / L) 0.46 0.008 Arsenic (mg / L) 0.003 0.001 Lead and its compounds (mg / L) 0.013 0.004 Cadmium and its compounds (mg / L) 0.0007 0.0002

[0127] Comparative Example 1:

[0128] The difference from Example 1 is that 0-5 mm coral sand, 5-10 mm coral sand, 10-20 mm coral sand, 20-30 mm coral sand, and water in a mass ratio of 40:21:19:15:5 are mixed by a continuous mixing device, spread by a paver, and compacted by a heavy roller; the other steps are the same as in Example 1;

[0129] The structural strength and adsorption capacity of the precipitate absorption layer in Comparative Example 1 were tested, and the comparison results were as follows:

[0130] ① The detected modulus representative value of the precipitate absorption layer 7 is 220 MPa, which is less than 450 MPa in Example 1 and does not meet the load-bearing capacity design requirements;

[0131] ② The red mud filler of the modified red mud roadbed on the precipitate absorption layer and the roadbed soil of the roadbed below the precipitate absorption layer were sampled respectively, and the engineering and environmental indicators were compared. The results are shown in Table 5:

[0132] Table 5. Test results of various indicators of comparative example 1

[0133] Test items Red mud filler Comparative Example 1 Roadbed Soil Example 1 Roadbed soil pH 8.2 7.6 7.1 Hexavalent chromium (mg / L) 0.48 0.15 0.023 Arsenic (mg / L) 0.008 0.005 0.002 Cyanide (mg / L) 0.04 0.02 0.01 Fluoride (mg / L) 0.8 0.4 0.1

[0134] As shown in Table 5, the pH value, hexavalent chromium content, arsenic content, cyanide content and fluoride content of the roadbed soil in Comparative Example 1 are all greater than those in Example 1, and the adsorption purification effect is poor.

[0135] Comparative Example 2:

[0136] The difference from Example 1 is that 0-5 mm coral sand, 5-10 mm coral sand, 10-20 mm coral sand, and water in a mass ratio of 40:26:29:5 are mixed by a continuous mixing device, spread by a paver, and compacted by a heavy roller; the other steps are the same as in Example 1;

[0137] The structural strength and adsorption capacity of the precipitate absorption layer in Comparative Example 1 were tested, and the comparison results were as follows:

[0138] ① The detected modulus representative value of the precipitate absorption layer 7 is 140 MPa, which is less than 450 MPa in Example 1 and does not meet the load-bearing capacity design requirements;

[0139] ② The red mud filler of the modified red mud roadbed on the precipitate absorption layer and the roadbed soil of the roadbed below the precipitate absorption layer were sampled respectively, and the engineering and environmental indicators were compared. The results are shown in Table 6:

[0140] Table 6. Test results of various indicators of comparative example 2

[0141] Test items Red mud filler Comparative Example 2 Roadbed Soil Example 1 Roadbed soil pH 8.2 7.5 7.1 Hexavalent chromium (mg / L) 0.48 0.23 0.023 Arsenic (mg / L) 0.008 0.004 0.002 Cyanide (mg / L) 0.04 0.03 0.01 Fluoride (mg / L) 0.8 0.3 0.1

[0142] As can be seen from Table 6, the pH value, hexavalent chromium content, arsenic content, cyanide content and fluoride content of the roadbed soil in Comparative Example 2 are all greater than those in Example 1, and its adsorption purification effect is poor.

[0143] In summary, the coral sand precipitate absorption layer set up in the present invention has high structural strength, rich pores and strong adsorption capacity, which can effectively prevent residual harmful substances in red mud or phosphogypsum from polluting the soil and groundwater, and meet environmental protection requirements; in addition, while ensuring the strength of the road, it realizes the recycling of waste and saves resources.

Claims

1. A fully solid waste environmentally friendly road structure containing a steel slag wearing layer, characterized in that: A precipitate absorption layer is paved on the roadbed using coral sand, and a roadbed is filled with modified red mud or modified phosphogypsum on the precipitate absorption layer to obtain a modified red mud roadbed or a modified phosphogypsum roadbed. Under the condition that the bearing capacity requirements are met, an asphalt structure composite layer of a certain thickness is paved on the roadbed, and the anti-skid wear layer in the asphalt structure composite layer is paved with steel slag; wherein: The precipitate absorption layer is coral sand of different particle sizes; The asphalt structure composite layer is a semi-rigid base asphalt structure composite layer, which includes, from top to bottom, an anti-skid wear layer, a bonding layer, an anti-fatigue layer, a durable anti-cracking layer, and a cement-stabilized crushed stone base. The anti-skid wear layer includes: steel slag aggregate, stone chips, filler, and modified asphalt; The modified red mud is obtained by modifying red mud with a red mud modifier in an amount of 5 to 10% by mass of the red mud, and the modified phosphogypsum is obtained by modifying phosphogypsum with a phosphogypsum modifier in an amount of 5 to 15% by mass of the phosphogypsum; the red mud modifier comprises: phosphogypsum, fly ash, cement, and asphalt; the phosphogypsum modifier comprises: silane coupling agent, aluminate coupling agent, and quicklime.

2. The road structure according to claim 1, characterized in that: The coral sand comprises, by weight, 15 to 35 parts of coral sand with a diameter of 0 to 5 mm, 5 to 20 parts of coral sand with a diameter of 5 to 10 mm, 20 to 40 parts of coral sand with a diameter of 10 to 20 mm, 10 to 35 parts of coral sand with a diameter of 20 to 30 mm, and 3 to 15 parts of water.

3. The road structure according to claim 1, characterized in that: The thickness of the precipitate absorption layer is greater than 30 cm, and the layer construction is carried out in layers. The maximum thickness of a single layer is ≤ 20 cm, the minimum thickness is ≥ 10 cm, and the compaction degree is greater than 90%.

4. The road structure according to claim 1, characterized in that: The elastic modulus of the precipitate absorption layer is ≥400 MPa.

5. The road structure according to claim 1, characterized in that: The modified red mud roadbed is constructed in layers, with a maximum thickness of a single layer ≤ 30 cm, a minimum thickness ≥ 15 cm, a compaction degree > 92%, and an overall stiffness requirement > 100 MPa.

6. The road structure according to claim 1, characterized in that: The thickness of the modified red mud roadbed is 50-300 cm.

7. The road structure according to claim 1, characterized in that: The modified phosphogypsum roadbed is constructed in layers, with a maximum thickness of ≤30 cm for a single layer and a minimum thickness of ≥15 cm, a compaction degree of >92%, and an overall stiffness requirement of >100 MPa.

8. The road structure according to claim 1, characterized in that: The thickness of the modified phosphogypsum roadbed is 50-300 cm.

9. The road structure according to claim 1, characterized in that: The anti-skid wear layer comprises, by weight, 30 to 85 parts of steel slag aggregate, 10 to 30 parts of stone chips, 2 to 6 parts of filler, and 5 to 11 parts of modified asphalt; the steel slag aggregate adopts one or more of the particle sizes of 2.36 mm to 4.75 mm, 4.75 mm to 9.5 mm, and 9.5 to 13.2 mm, and the free calcium oxide content of each specification is ≤3%; the stone chips are limestone or basalt with a particle size of 0 to 2.36 mm and a sand equivalent of ≥60%; the binder is SBS modified asphalt, the thickness of the anti-skid wear layer is 3 to 6 cm, and the porosity is 3 to 4%.

10. The road structure according to claim 1, characterized in that: The bonding layer adopts AC-20 grade asphalt mixture, the binder is SBS modified asphalt, the bonding layer thickness is 3~6cm, and the porosity is 4~6%; the anti-fatigue layer adopts AC-25 grade asphalt mixture, the binder is 70# matrix asphalt, the anti-fatigue layer thickness is 6~10cm, and the porosity is 4~6%; the durable anti-cracking layer adopts ATB-25 grade asphalt mixture, the binder is SBS modified asphalt, the durable anti-cracking layer thickness is 16~32cm, and it is constructed in layers with a porosity of 3.5~4.5%; the cement-stabilized gravel base adopts cement-stabilized gravel mixture, the binder is P.O42.5 ordinary Portland cement, and the cement-stabilized gravel base is constructed in 3 layers, each layer is 18cm, of which the cement dosage of the bottom base cement-stabilized gravel mixture is 3.5%, and the cement dosage of the upper base or lower base cement-stabilized gravel mixture is 4.5%.

11. The road structure according to claim 1, characterized in that: The red mud modifier includes, by weight, 40 to 80 parts of phosphogypsum, 5 to 30 parts of fly ash, 3 to 25 parts of cement, and 1 to 10 parts of asphalt; the phosphogypsum modifier includes, by weight, 2 to 10 parts of silane coupling agent, 5 to 15 parts of aluminate coupling agent, and 10 to 23 parts of quicklime.

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