Stress gradient absorption type self-toughening high-bearing phosphogypsum pavement structure

Abstract

This invention discloses a stress gradient absorbing, self-toughening, high-load-bearing phosphogypsum pavement structure, relating to the field of road construction materials technology. From top to bottom, it comprises a high-strength load-bearing layer, a stress transmission layer, and a stress dispersion layer. The raw materials for the high-strength load-bearing layer, stress transmission layer, and stress dispersion layer include modified phosphogypsum, cement, admixtures, a complexing water-resistant crosslinking agent, a water-reducing agent, and water. The modified phosphogypsum is prepared by adjusting the pH value of phosphogypsum waste to 7-8. The admixtures are blast furnace slag and / or metakaolin. The pavement structure provided by this invention achieves improved base layer strength and modulus, as well as gradient distribution, effectively transferring pavement stress to the underlying layer while reducing fatigue stress in the base layer material and increasing the fatigue life of the pavement base layer.

Description

Technical Field

[0001] This invention relates to the field of road construction materials technology, and in particular to stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure. Background Technology

[0002] Phosphogypsum is a byproduct of the wet process for producing phosphoric acid and is a solid waste generated by phosphate chemical enterprises. Statistics show that approximately 4-5 tons of phosphogypsum are produced for every 1 ton of phosphoric acid produced, and the amount of phosphogypsum discharged is increasing year by year. Since 2000, the growth rate of my country's phosphate fertilizer industry has consistently remained above 10%, and the current annual discharge of phosphogypsum is comparable to the annual production of natural gypsum. According to statistics from my country's Ministry of Industry and Information Technology in 2019, the current annual production of phosphogypsum in my country is approximately 75 million tons, but the comprehensive utilization rate is less than 40%. Phosphogypsum contains harmful substances such as phosphorus, fluorine, and heavy metal ions. Its indiscriminate discharge and accumulation not only pollute groundwater resources but also waste land resources, seriously harming the natural environment.

[0003] The base course is the main load-bearing layer of asphalt pavement, serving as the structural layer for distributing loads and regulating water temperature in cement concrete pavements. Academician Sha Qinglin of the Chinese Academy of Engineering emphasized that a high-quality base course is crucial; therefore, the load-bearing capacity, crack resistance, and erosion resistance of the base course are vital to the service quality and lifespan of the road. The subgrade, located below the surface layer and above the soil layer, primarily serves to indirectly bear or distribute pavement loads and transfer stress. Cement-stabilized semi-rigid base asphalt pavements possess characteristics such as good stability, high overall strength, high stiffness, strong resistance to permanent deformation, and resistance to fatigue failure under traffic loads, making them suitable for heavy traffic and the most widely used type of subgrade in my country. However, in recent years, the problems of semi-rigid base asphalt pavement defects, especially early-stage defects, have become very common, attracting widespread attention. Some researchers attribute many defects in semi-rigid base asphalt pavements to inherent defects in material properties, among which shrinkage cracking is one of the most common and far-reaching defects.

[0004] Currently, the common pavement structure for urban roads and highways typically employs a semi-rigid base course combined with an asphalt surface course. For roads with high traffic volume, the base course usually consists of a 16-20cm thick asphalt concrete surface course and a 18-20cm thick, three-layer cement-stabilized crushed stone base course. The strength of the cement-stabilized crushed stone base course is typically less than 10MPa, and it is usually constructed using materials with similar or identical strength and modulus. Under actual traffic loads, insufficient strength and modulus of the upper layer lead to inadequate load-bearing capacity and stress transmission ability. Using cement-stabilized crushed stone as a semi-rigid base course material also presents the problem of insufficient flexural strength. For pavement slab structures, improving flexural strength can significantly enhance the pavement's load-bearing capacity. Cement-stabilized crushed stone is a shrinking material, especially in the high-strength upper base course where shrinkage is particularly pronounced. Often, cement-stabilized crushed stone shrinks and cracks before reaching its fatigue cracking life. These cracks are transmitted to the surface course under traffic dynamics, causing cracking of the asphalt concrete. Rainwater entering the base course along the asphalt concrete further exacerbates the damage to the water-stabilized layer, leading to a significant reduction in the pavement's service life. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure, which is specifically achieved through the following technologies.

[0006] The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure consists of a high-strength load-bearing layer, a stress transmission layer, and a stress dispersion layer from top to bottom.

[0007] The raw materials of the high-strength load-bearing layer include, by weight, 1100-1300 parts of modified phosphogypsum, 120-150 parts of cement, 260-280 parts of admixture, 10-50 parts of complexing water-resistant crosslinking agent, 10-20 parts of water-reducing agent, 20-30 parts of self-toughening resin, and 190-230 parts of water.

[0008] The raw materials of the stress transmission layer include, by weight, 1350-1450 parts of modified phosphogypsum, 75-95 parts of cement, 190-210 parts of admixture, 5-15 parts of complexing water-resistant crosslinking agent, 10-20 parts of water-reducing agent, 20-30 parts of self-toughening resin, and 150-190 parts of water.

[0009] The raw materials of the stress dispersion layer include, by weight, 1100-1300 parts of modified phosphogypsum, 120-150 parts of cement, 155-175 parts of admixture, 5-15 parts of complexing water-resistant crosslinking agent, 10-20 parts of water-reducing agent, 20-30 parts of self-toughening resin, and 130-150 parts of water.

[0010] The modified phosphogypsum is prepared by adjusting the pH value of phosphogypsum waste residue (e.g., by adjusting with quicklime powder) to 7-8; the admixture is blast furnace slag and / or metakaolin.

[0011] Optionally, the specific preparation method of modified phosphogypsum is as follows: take phosphogypsum particles with a particle size of no more than 0.6 mm, and use one or more of carbide slag, calcium hydroxide, and sodium hydroxide to adjust the pH value to 7-8 to obtain modified phosphogypsum.

[0012] Alternatively, commercially available cement can be used, such as PO42.5 ordinary Portland cement, etc.

[0013] Alternatively, commercially available water-reducing agents can be used, such as polycarboxylate water-reducing agents, naphthalene-based water-reducing agents, etc.

[0014] Preferably, the preparation method of the complexed water-resistant crosslinking agent includes: taking 300-400 parts of hot water at 60°C, 5-6 parts of sodium hydroxide and 3-5 parts of sodium carbonate by weight and stirring evenly; adding 42-52 parts of oleic acid and stirring evenly until the oleic acid dissolves; adding 600-700 parts of water and continuing to stir evenly; after the mixture cools to ≤35°C, adding 24-30 parts of ammonia water and 50-100 parts of water glass and stirring evenly to form the complexed water-resistant crosslinking agent product.

[0015] More preferably, the preparation method of the complexed water-resistant crosslinking agent includes: taking 350 parts of hot water at 60°C, 4.45 parts of sodium hydroxide and 3 parts of sodium carbonate by mass, stirring evenly, heating to 60°C, adding 47 parts of oleic acid, and stirring evenly until the oleic acid dissolves, adding 551.55 parts of water and continuing to stir evenly; after the mixture cools to ≤35°C, adding 27 parts of ammonia water and 10 parts of water glass, and stirring evenly to obtain the crosslinking agent product.

[0016] Optionally, in the preparation method of the complexed water-resistant crosslinking agent, the water glass has a modulus of 3.1-3.3 and an effective solid content of 28-32%.

[0017] Preferably, the specific surface area of ​​the admixture is ≥400m². 2 / kg.

[0018] Preferably, the raw materials of the high-strength load-bearing layer include, by weight, 1182 parts modified phosphogypsum, 133 parts cement, 268 parts admixture, 12 parts crosslinking agent, 14.5 parts water-reducing agent, 24 parts self-toughening resin, and 208 parts water.

[0019] Preferably, the raw materials of the stress transmission layer include, by weight, 1320 parts modified phosphogypsum, 100 parts cement, 200 parts admixture, 11 parts crosslinking agent, 15.0 parts water-reducing agent, 24 parts self-toughening resin, and 169 parts water.

[0020] Preferably, the raw materials of the stress dispersion layer include, by mass, 1389 parts modified phosphogypsum, 84 parts cement, 166 parts admixture, 8 parts crosslinking agent, 15 parts water-reducing agent, 24 parts self-toughening resin, and 149 parts water.

[0021] The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure provided by this invention is not laid directly on the subgrade (roadbed), but needs to be used in conjunction with other pavement structures. For example, wear-resistant materials such as crushed stone asphalt need to be laid on top of the high-strength load-bearing layer, and a graded crushed stone subbase needs to be laid below the stress dispersion layer.

[0022] The stress gradient absorbing self-toughening high-load-bearing phosphogypsum pavement structure provided by this invention features a gradient distribution of strength and elastic modulus of the semi-rigid base material, which can reasonably transmit and disperse stress caused by traffic loads. The high-strength load-bearing layer improves compressive and flexural strength and elastic modulus to increase load-bearing capacity and stress transmission ability. The stress transmission layer has a lower strength and modulus, effectively absorbing internal stress in the upper base layer and reasonably transmitting stress caused by traffic loads. The stress dispersion layer has a strength and modulus comparable to cement-stabilized crushed stone, effectively dispersing the stress transmitted by the two upper layers. The bottom graded crushed stone subbase completely absorbs residual stress in the pavement.

[0023] In stress gradient absorbing self-toughening high-load-bearing phosphogypsum pavement structures, the addition of self-toughening resin, along with the complexing water-resistant crosslinking agent, not only enhances the strength of phosphogypsum and supersulfurized cementitious materials but also provides the necessary reaction environment for the hydration of the self-toughening resin. During the phosphogypsum mixing process, the self-toughening resin monomers form a microfilamentous structure in the slurry, creating a self-toughening effect similar to that achieved with added fibers. This toughening effect not only improves the flexural strength of the pavement base material but also reduces its volumetric expansion deformation, creating internal prestress and further increasing its flexural strength.

[0024] The synergistic use of phosphogypsum powder, admixtures, and complexing water-resistant crosslinking agents produces a product that not only has high mechanical strength (especially flexural strength) and elastic modulus, but also a certain degree of micro-expansion. This can completely eliminate cracks caused by the drying shrinkage of cement-stabilized crushed stone (a commonly used road base construction material). At the same time, because the complexing water-resistant crosslinking agent has high hydrophobicity, even if surface moisture enters the base layer, it can significantly reduce the damage that leads to a reduction in road surface life.

[0025] Preferably, the self-toughening resin is prepared by mixing cashew phenol and phenolic resin in a mass ratio of 2:1.

[0026] Preferably, the thickness of the high-strength load-bearing layer is 18-20cm, the stress transmission layer is 18-20cm, and the stress dispersion layer is 18-20cm.

[0027] Preferably, it further includes an anti-slip and wear-resistant layer and a drainage stress-absorbing layer, wherein the anti-slip and wear-resistant layer is located above the high-strength load-bearing layer, and the drainage stress-absorbing layer is located below the stress-dispersing layer.

[0028] Optionally, the anti-skid and wear-resistant layer is generally made of asphalt material containing wear-resistant aggregate, or other materials commonly used in other industries (such as diabase, basalt, high-viscosity asphalt, etc.); the drainage stress-absorbing layer is generally made of graded crushed stone with a maximum particle size ≤31.5mm.

[0029] The method for preparing the high-strength load-bearing layer / stress transmission layer / stress dispersion layer in the stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure provided by the present invention includes the following steps:

[0030] Accurately weigh each raw material; first, dry mix the modified phosphogypsum powder, cement, and admixtures for 60-80 seconds; then add water, complexing water-resistant crosslinking agent, and water-reducing agent and wet mix for 60 seconds; then add self-toughening resin and stir for 60 seconds (this step can be omitted if the raw materials do not contain self-toughening resin); finally, a high-strength load-bearing layer / stress transmission layer / stress dispersion layer with good workability and road base material mixture is obtained.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] 1. The road structure provided by this invention improves the strength and modulus of the base layer and enhances its gradient distribution, effectively transferring road stress to the underlying layer while reducing fatigue stress in the base layer material and increasing the fatigue life of the road base layer.

[0033] 2. The base material used in this invention has greater compressive strength, flexural strength and elastic modulus than ordinary cement-stabilized crushed stone, so the road surface has better load-bearing capacity and significantly improves the service life of the road in overloaded and heavy traffic environments.

[0034] 3. The base material used in this invention has micro-expansion and hydrophobic properties, which can reduce or even eliminate shrinkage cracking of semi-rigid base layers, while increasing the water damage resistance of base material, which can greatly improve the service durability of roads and reduce maintenance costs. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The road structure provided in the following embodiments and comparative examples includes, from top to bottom, an anti-skid and wear-resistant layer, a high-strength load-bearing layer (upper base course), a stress transmission layer (lower base course), a stress dispersion layer (subbase course), and a subbase course. The thickness of the high-strength load-bearing layer (or upper base course), the stress transmission layer (or lower base course), and the stress dispersion layer (or subbase course) is 20 cm, the thickness of the anti-skid and wear-resistant layer is 4 cm, and the thickness of the drainage and absorption layer (or subbase course) is 10 cm.

[0037] For details on the paving method of the drainage stress-absorbing layer (or subbase), please refer to the "Technical Specifications for Highway Pavement Base Construction". For details on the paving method of the anti-skid and wear-resistant layer, please refer to the "Technical Specifications for Highway Asphalt Pavement Construction".

[0038] Unless otherwise specified, the road surface structures provided in the following examples and comparative examples are prepared and provided using the following raw materials in the following amounts and preparation methods:

[0039] (1) Among the raw materials used, ordinary Portland cement with PO 42.5 is selected for cement and polycarboxylate superplasticizer is selected for water reducing agent.

[0040] (2) The method for preparing modified phosphogypsum using raw materials is to crush the purchased phosphogypsum waste to a particle size ≤0.6mm, and then use a pH adjuster to adjust the pH value to 7-8, which is the modified phosphogypsum. The pH adjuster can be sodium hydroxide, or alkaline agents such as carbide slag and calcium hydroxide.

[0041] (3) The admixture used is a mixture of 60 parts blast furnace slag and 20 parts metakaolin, which are then ground to a specific surface area ≥ 400 m². 2 It is prepared after / kg.

[0042] (4) The self-toughening resin used is prepared by mixing cashew phenol (commercially available) and phenolic resin (commercially available foaming agent of phenol and formaldehyde) in a mass ratio of 2:1.

[0043] To facilitate testing of pavement structure performance, unless otherwise specified, the preparation method of the complexed water-resistant crosslinking agent is as follows: Take 350 parts by weight of water, 5.5 parts by weight of sodium hydroxide, and 2.5 parts by weight of sodium carbonate, stir until homogeneous, heat to 60°C, add 45 parts by weight of oleic acid, and stir until the oleic acid dissolves. Add 650 parts by weight of tap water at 25°C and continue stirring until homogeneous. After the mixture cools to ≤35°C, add 26 parts by weight of ammonia and 75 parts by weight of water glass, and stir until homogeneous to form the finished complexed water-resistant crosslinking agent. The ammonia concentration is 26-28%, the water glass modulus is 3.1-3.3, and the effective solid content is approximately 30%.

[0044] Optionally, in the preparation method of the complexed water-resistant crosslinking agent, hot water can be selected as 300-400 parts, sodium hydroxide as 5-6 parts, sodium carbonate as 3-4 parts, oleic acid as 42-52 parts, cold water as 600-700 parts, ammonia water as 24-30 parts, and water glass as 50-100 parts.

[0045] The pavement structures provided in the following examples and comparative examples were all maintained and tested in accordance with the methods of the "Highway Geotechnical Test Procedure" and the "Highway Engineering Asphalt and Asphalt Mixture Test Procedure".

[0046] Example 1

[0047] The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure provided in this embodiment is made by weighing each raw material according to the proportions described in Table 1 below.

[0048] Table 1. Road surface mix proportions for Example 1, kg / m² 3

[0049]

[0050] Example 2

[0051] The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure provided in this embodiment is made by weighing each raw material according to the proportions described in Table 2 below.

[0052] Table 2. Road surface mix proportions for Example 2, kg / m² 3

[0053]

[0054] Example 3

[0055] The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure provided in this embodiment is made by weighing each raw material according to the proportions described in Table 3 below.

[0056] Table 3. Road surface mix proportions for Example 3, kg / m³ 3

[0057]

[0058]

[0059] Comparative Example 1

[0060] The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure provided in this comparative example is prepared by weighing each raw material according to the proportions described in Table 4 below.

[0061] Table 4. Pavement structure mix proportions for Comparative Example 1, kg / m³ 3

[0062]

[0063] Experimental Examples: Performance Testing of Road Surface Structures in Examples and Comparative Cases

[0064] In the above embodiments and comparative examples of pavement structures, the mixing process of the materials used was carried out in an intermittent forced mixer. First, cement, crushed stone and manufactured sand were dry-mixed for 60-80 seconds, then water was added and wet-mixed for 60 seconds. Finally, the mixture was molded, vibrated, and shaped. The surface was covered with an impermeable film for film curing in accordance with the methods of the "Highway Geotechnical Test Procedure" and the "Highway Engineering Asphalt and Asphalt Mixture Test Procedure". After demolding, standard curing was carried out, and various performance tests were conducted at the corresponding age. The test results are shown in Table 5.

[0065] Table 5. Test results of pavement structure performance in the examples and comparative examples.

[0066]

[0067]

[0068] As can be seen from Table 6 above, compared with the upper base layer, lower base layer, and lower base layer of Comparative Example 1:

[0069] 1. In the pavement structure of Example 1, the 90-day compressive strength of the high-strength load-bearing layer, stress transmission layer, and stress dispersion layer increased by 364.5%, 219.7%, and 126.3%, respectively; the water softening coefficient increased by 20.9%, 19.9%, and 17.6%; the 90-day flexural strength increased by 153.3%, 73.3%, and 26.7%; the elastic modulus increased by 61.3%, 30.2%, and 1.4%; and the 90-day shrinkage decreased by 132.2%, 128.2%, and 126.4%.

[0070] 2. In the pavement structure of Example 2, the 90-day compressive strength of the high-strength load-bearing layer, stress transmission layer, and stress dispersion layer increased by 317.1%, 188.2%, and 103.9%, respectively; the water softening coefficient increased by 19.2%, 18.2%, and 16.8%; the 90-day flexural strength increased by 126.7%, 46.7%, and 13.3%; the elastic modulus increased by 43.4%, 20.8%, and 4.2%; and the 90-day shrinkage decreased by 131.3%, 127.6%, and 126.1%.

[0071] 3. In the pavement structure of Example 3, the 90-day compressive strength of the high-strength load-bearing layer, stress transmission layer, and stress dispersion layer increased by 368.4%, 227.6%, and 130.3%, respectively; the water softening coefficient increased by 20.1%, 18.1%, and 17.3%; the 90-day flexural strength increased by 106.7%, 13.3%, and 6.7%; the elastic modulus increased by 60.8%, 30.2%, and 3.3%; and the 90-day shrinkage decreased by 137.9%, 132.2%, and 131.3%.

[0072] Analysis revealed that the expansion values ​​of Example 2 were reduced by 20.5%, 17.3%, and 18.5% compared to Example 1 due to the presence of the self-toughening resin.

[0073] 4. Using a layered continuous system model for stress field finite element analysis, compared with the upper base layer of Comparative Examples 1-3, the high-strength bearing layer of Examples 1-3 can transmit stress to the lower layer (the lower base layer in the comparative examples, and the stress transmission layer in Examples 1-3) by 30%; at the same time, compared with the comparative examples, the overall fatigue stress of the base layer of Examples 1-3 is reduced by 5-8%, and the fatigue life is increased by 50-90%.

[0074] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A stress gradient absorbing, self-toughening, high-load-bearing phosphogypsum pavement structure, characterized in that, From top to bottom, it includes a high-strength load-bearing layer, a stress-transferring layer, and a stress-dispersing layer; The raw materials of the high-strength load-bearing layer include, by weight, 1100-1300 parts of modified phosphogypsum, 120-150 parts of cement, 260-280 parts of admixture, 10-50 parts of complexing water-resistant crosslinking agent, 10-20 parts of water-reducing agent, 20-30 parts of self-toughening resin, and 190-230 parts of water. The raw materials of the stress transmission layer include, by weight, 1350-1450 parts of modified phosphogypsum, 75-95 parts of cement, 190-210 parts of admixture, 5-15 parts of complexing water-resistant crosslinking agent, 10-20 parts of water-reducing agent, 20-30 parts of self-toughening resin, and 150-190 parts of water. The raw materials of the stress dispersion layer include, by weight, 1100-1300 parts of modified phosphogypsum, 120-150 parts of cement, 155-175 parts of admixture, 5-15 parts of complexing water-resistant crosslinking agent, 10-20 parts of water-reducing agent, 20-30 parts of self-toughening resin, and 130-150 parts of water. The modified phosphogypsum is prepared by adjusting the pH value of phosphogypsum waste to 7-8; the admixture is blast furnace slag and / or metakaolin. The preparation method of the complexed water-resistant crosslinking agent includes: taking 300-400 parts of hot water at 60℃, 5-6 parts of sodium hydroxide and 3-5 parts of sodium carbonate by mass and stirring evenly; adding 42-52 parts of oleic acid and stirring evenly until the oleic acid dissolves; adding 600-700 parts of water and continuing to stir evenly; after the mixture is cooled to ≤35℃, adding 24-30 parts of ammonia water and 50-100 parts of water glass and stirring evenly to obtain the finished complexed water-resistant crosslinking agent.

2. The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure according to claim 1, characterized in that, The raw materials of the high-strength load-bearing layer include, by weight, 1182 parts modified phosphogypsum, 133 parts cement, 268 parts admixture, 12 parts complexed water-resistant crosslinking agent, 14.5 parts water-reducing agent, 24 parts self-toughening resin, and 208 parts water.

3. The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure according to claim 1 or 2, characterized in that, The self-toughening resin is prepared by mixing cashew phenol and phenolic resin in a mass ratio of 2:

1.

4. The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure according to claim 1, characterized in that, The thickness of the high-strength load-bearing layer is 18-20cm, the stress transmission layer is 18-20cm, and the stress dispersion layer is 18-20cm.

5. The stress gradient absorbing self-toughening high load-bearing phosphogypsum pavement structure according to claim 1, characterized in that, It also includes an anti-slip and wear-resistant layer and a drainage stress-absorbing layer, wherein the anti-slip and wear-resistant layer is located above the high-strength load-bearing layer and the drainage stress-absorbing layer is located below the stress dispersion layer.

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