Low carbon footprint road stabilisation layer material and method based on manufactured sand tailings recycled material

Abstract

This invention discloses a low-carbon footprint road stabilization layer material and method based on recycled sand production tailings, belonging to the fields of road construction materials, solid waste disposal, and carbon neutrality technology. This invention replaces all fine aggregates with recycled sand production tailings. Road stabilization layers prepared using this invention exhibit the following 7-day unconfined compressive strengths: base course ≥ 3.0 MPa, subbase course ≥ 2.0 MPa; 28-day base course ≥ 5.0 MPa, subbase course ≥ 3.0 MPa; 7-day water immersion strength loss ≤ 13%. The overall performance meets the industry standard JTG / T F20-2015 "Technical Specifications for Highway Pavement Base Course Construction," reducing costs by 18%~30% and carbon emissions by 30%~50%. It achieves resource utilization of sand production tailings, is compatible with existing construction equipment, and is suitable for base and subbase construction of Class I to IV highways and municipal roads, combining environmental friendliness and engineering economy.

Description

Technical Field

[0001] This invention belongs to the fields of road construction materials, solid waste disposal and carbon neutrality technology, and relates to the technology of resource utilization of sand making tailings solid waste. Specifically, it relates to a low-carbon footprint road stabilization layer material and method based on recycled sand making tailings. Background Technology

[0002] The typical mix proportions for conventional pavement stabilization layers are: 5%~10% cement, 40%~70% coarse aggregate, and 20%~30% fine aggregate. This mix proportion has been verified through long-term engineering projects and can ensure the load-bearing capacity and construction adaptability of the pavement stabilization layer. However, it relies on natural stone resources, which poses the problems of resource depletion and excessive carbon emissions.

[0003] In existing technologies, the use of cement and natural stone generates carbon emissions during production and processing, thus lacking environmental benefits. Furthermore, the tailings waste generated by the sand-making industry, due to its inherent physicochemical defects (high bound water content), presents unavoidable technical obstacles for direct use in road surface stabilization layer preparation. It fails to meet the core requirements of road surface stabilization layers for aggregate looseness, cementitious activity, and skeleton filling, resulting in low resource utilization rates and significant solid waste accumulation problems. Therefore, developing a technology that overcomes the inherent defects of sand-making tailings through modified compounding, effectively replaces some natural stone, reduces carbon footprint while meeting performance standards, and is compatible with existing construction processes can effectively reduce the material cost of road surface stabilization layers and simultaneously promote large-scale regeneration and resource conversion of sand-making tailings. Summary of the Invention

[0004] The purpose of this invention is to overcome the deficiencies in the prior art and provide a low-carbon footprint road stabilization layer material and method based on recycled sand production tailings. This invention specifically addresses the technical obstacles to the direct use of sand production tailings, reduces the amount of fine aggregate used, lowers carbon emissions, and is suitable for the construction of base and subbase layers for Class I to IV highways, municipal roads, industrial park roads, etc.

[0005] The specific technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a low-carbon footprint road stabilization layer material based on recycled sand-making tailings, comprising, by mass percentage, 20%~35% recycled sand-making tailings, 3%~15% cement, 45%~76% 5-40 mm coarse aggregate, and 0.1%~4.5% activating stabilizer, and the sum of the mass percentages of each component is 100%; The preparation method of the recycled tailings material is as follows: A water phase conversion agent is added to the sand making tailings, and the mixture is subjected to high-speed stirring, enhanced dispersing and physical aging treatment in sequence to convert the bound water originally contained in the sand making tailings into gravity water and capillary water, so as to obtain sand making tailings recycled material with a water content of <5%.

[0006] Preferably, the mass ratio of the sand-making tailings to the water phase conversion agent is (10-20):1, and the water phase conversion agent is at least one of fly ash, wood ash, and stone powder.

[0007] Furthermore, in the aqueous phase conversion agent, the mass ratio of fly ash to wood ash is 1:3, the mass ratio of fly ash to stone powder is 1:6, the mass ratio of wood ash to stone powder is 1:2, and the mass ratio of fly ash, wood ash, and stone powder is 1:3:6.

[0008] Furthermore, the fly ash is a solid waste generated from coal combustion in thermal power plants, with a particle size of 0.5~300 μm, conforming to the standard GB / T1596-2017 "Fly Ash for Cement and Concrete", and possessing high pozzolanic activity.

[0009] Furthermore, the plant ash is solid waste generated from biomass power plant incineration, with a particle size ≤3 mm, loss on ignition ≤8%, and pH=12±0.5.

[0010] Furthermore, the stone powder is solid waste generated during the dry sand making process and obtained through collection and screening to remove impurities. Its moisture content is ≤2%, particle size is 0.075~2 mm, and pH is 8.5~8.7.

[0011] Preferably, the tailings sludge is solid waste generated during the wet sand making process and obtained by plate and frame filter press dewatering treatment, with a moisture content of 30%~50% and a pH of 8.5~8.7.

[0012] Preferably, the high-speed stirring treatment has a stirring rate of 50~100 r / min and a stirring time of 5~15 min; the enhanced dispersing treatment involves crushing the mud cake of sand-making tailings to a particle size ≤5 mm; and the physical aging treatment involves aging in a ventilated environment for 24~48 h.

[0013] In a second aspect, the present invention provides a method for preparing a low-carbon footprint road stabilization layer material based on recycled tailings as described in any of the first aspects, as follows: Mix 20%~35% recycled tailings from sand making, 3%~15% cement, 45%~76% 5-40 mm coarse aggregate, and 0.1%~4.5% activating stabilizer by mass percentage, and stir until uniform at a speed of 50~100 r / min; then add water to adjust the moisture content to 8%~12%, and continue stirring for 4~6 min until the mixture is uniform and free of lumps; wherein, the sum of the mass percentages of each component added is 100%.

[0014] Thirdly, the present invention provides an application of a low-carbon footprint road stabilization layer material based on recycled tailings as described in any of the first aspects in the construction of base or subbase layers of Class I to IV highways and municipal roads.

[0015] Compared with the prior art, the present invention has the following advantages: Compared with traditional pavement stabilization layer materials, this invention uses recycled sand production tailings to replace all fine aggregates. Road stabilization layers prepared using this invention exhibit the following 7-day unconfined compressive strengths: base course ≥ 3.0 MPa, subbase course ≥ 2.0 MPa; 28-day base course ≥ 5.0 MPa, subbase course ≥ 3.0 MPa; 7-day water immersion strength loss ≤ 13%. The overall performance meets the industry standard JTG / T F20-2015 "Technical Specifications for Construction of Highway Pavement Base Courses," reducing costs by 18%~30% and carbon emissions by 30%~50%. It achieves resource utilization of sand production tailings, is compatible with existing construction equipment, and is suitable for base and subbase construction of Class I to IV highways and municipal roads, combining environmental friendliness with engineering economics. Detailed Implementation

[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflict.

[0017] This invention provides a low-carbon footprint road stabilization layer material based on recycled sand production tailings, that is, using recycled sand production tailings to replace 20% to 35% of the fine aggregate in conventional road stabilization layer materials. By overcoming the technical obstacles of directly using sand production tailings through water phase conversion and modified compounding, the following objectives are achieved: 1) Replacing 20% ​​to 35% of the fine aggregate with recycled sand production tailings; 2) Reducing carbon emissions by 30% to 50%, balancing performance compliance and environmental benefits; 3) Adapting to existing construction equipment and processes, achieving efficient utilization of solid waste resources, and reducing engineering costs.

[0018] Specifically, the stabilized layer material strictly follows the conventional pavement stabilized layer mix design framework, with the mass percentage of each material precisely matching the actual needs of the project: it mainly includes 20%~35% recycled sand tailings, 3%~15% cement, 45%~76% 5-40 mm coarse aggregate, and 0.1%~4.5% activating stabilizer by mass percentage, and the sum of the mass percentages of each component is 100%.

[0019] Among them, recycled tailings from sand production can replace 20% to 35% of the fine aggregate in conventional pavement stabilization layers. It has fine particles, strong filling properties, and can precisely fill the voids in crushed stone, achieving the same skeletal filling effect as conventional sand. Furthermore, it is widely available and has low disposal costs. The specific preparation method is as follows: A water phase conversion agent is added to the sand making tailings, and the mixture is subjected to high-speed stirring, enhanced dispersing and physical aging treatment in sequence to convert the bound water originally contained in the sand making tailings into gravity water and capillary water, so as to obtain sand making tailings recycled material with a water content of <5%.

[0020] As a preferred embodiment of the present invention, the sand-making tailings are solid waste generated during the wet sand-making process and obtained by plate and frame filter press dewatering treatment. Its moisture content is 30%~50%, pH is 8.5~8.7 and it is weakly alkaline. Other components are mainly (by mass percentage) SiO2 28%~35%, Al2O3 12%~18%, and CaO 5%~10%.

[0021] Since the aqueous phase in sand-making tailings is mainly bound water, it easily clumps and agglomerates after natural drying, making moisture removal difficult and thus becoming a bottleneck restricting the wet sand-making industry. This invention overcomes these problems by adding a water phase conversion agent to the sand-making tailings and then sequentially subjecting them to high-speed stirring, enhanced dispersal, and physical aging treatment. This invention utilizes the water phase conversion agent to disrupt the colloidal structure of the sand-making tailings, transforming the bound water in the tailings cake (40%~50% water content) that is difficult to evaporate naturally into freely migrating gravitational water and capillary water. Then, through mechanical stirring, dispersal, and aging treatment, moisture removal is accelerated, achieving efficient drying of the tailings. During the processing, over 90% of the moisture in the tailings cake is removed, ultimately yielding a uniform, loose, and non-clumping recycled tailings material (moisture content <5%), thus achieving commercial properties and replacing the fine aggregate used in traditional methods for road surface stabilization layers.

[0022] In a preferred embodiment of the present invention, the mass ratio of sand-making tailings to water phase conversion agent is (10~20):1, and the water phase conversion agent is at least one of fly ash, wood ash, and stone powder.

[0023] When the aqueous phase conversion agent is composed of fly ash and wood ash, the mass ratio of the two is 1:3; when the aqueous phase conversion agent is composed of fly ash and stone powder, the mass ratio of the two is 1:6; when the aqueous phase conversion agent is composed of wood ash and stone powder, the mass ratio of the two is 1:2; when the aqueous phase conversion agent is composed of fly ash, wood ash and stone powder, the mass ratio of the three is 1:3:6.

[0024] The fly ash used to prepare the aqueous phase conversion agent is a solid waste generated from the combustion of coal in thermal power plants. Its main components are SiO2 45%~55%, Al2O3 25%~35%, and CaO 5%~15%, with a particle size range of 0.5~300 μm, loss on ignition ≤6%, and water requirement ratio ≤95%. It meets the standard of GB / T1596-2017 "Fly Ash for Cement and Concrete" and has high pozzolanic activity.

[0025] The wood ash used to prepare the aqueous phase conversion agent is a solid waste generated from biomass power plant incineration. It has a particle size of ≤3 mm and its main components are K2O 10%~18%, CaO 20%~30%, and SiO2 15%~25%. Its loss on ignition is ≤8%, and its pH is about 12, which is strongly alkaline. It can create an alkaline environment for activation.

[0026] The stone powder used to prepare the water phase conversion agent is solid waste generated during the dry sand making process and obtained by collection and screening to remove impurities. It has a moisture content of ≤2%, a particle size of 0.075 mm to 2 mm, and its main components are SiO2 65% to 75%, Al2O3 8% to 12%, CaO 3% to 8%. It has a pH of 8.5 to 8.7, is weakly alkaline, and lacks gelling activity.

[0027] In a preferred embodiment of the present invention, the high-speed stirring treatment involves a stirring rate of 50-100 r / min and a stirring time of 5-15 min. The enhanced dispersing treatment involves crushing the tailings mud cake to a particle size ≤ 5 mm. The physical aging treatment involves aging in a ventilated environment for 24-48 h.

[0028] In a preferred embodiment of the present invention, the cement is commercially available conventional cement.

[0029] In a preferred embodiment of the present invention, the coarse aggregate is crushed stone or gravel used for gradation, which does not contain clay blocks or organic matter, and conforms to the standards of "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015 and "Construction Gravel and Crushed Stone" GB / T14685-2022.

[0030] In a preferred embodiment of the present invention, the activating stabilizer is prepared by compounding water glass, sodium sulfate, polycarboxylate superplasticizer, and metakaolin in a mass ratio of (45~60):(25~35):(5~10):(5~15), wherein the optimal mass ratio is water glass:sodium sulfate:polycarboxylate superplasticizer:metakaolin = 50:30:8:10. The activating stabilizer can enhance alkaline activation, improve the workability of the mixture, and optimize the structure of the gelation products.

[0031] The pavement stabilization layer material obtained according to the method of this invention has the following properties: base course 7-day unconfined compressive strength ≥ 3.0 MPa, subbase course 28-day unconfined compressive strength ≥ 3.0 MPa, 28-day splitting tensile strength ≥ 0.5 MPa, and drying shrinkage coefficient ≤ 3.5 × 10⁻⁶. -6 / ℃, compaction degree ≥97%, meeting the requirements of "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015.

[0032] The preparation method of the low-carbon footprint road stabilization layer material based on recycled sand tailings provided by the present invention is as follows: Mix 20%~35% recycled tailings from sand making, 3%~15% cement, 45%~76% 5-40 mm coarse aggregate, and 0.1%~4.5% activating stabilizer by mass percentage, and stir until uniform at a speed of ≥30 r / min; then add water to adjust the moisture content to 8%~12%, and continue stirring for 4~6 min until the mixture is uniform and free of lumps; wherein, the sum of the mass percentages of each component added is 100%.

[0033] In actual use, the water added during the preparation process can be clean tap water with a pH of 6-8.

[0034] The low-carbon footprint road stabilization layer material based on recycled sand-making tailings provided by this invention can be applied in the construction of base or subbase layers of Class I to IV highways and municipal roads. Specific application scenarios include highway subgrade reinforcement, subbase layers of urban secondary arterial roads, base layers of branch roads, and subgrade treatment after backfilling municipal pipelines. This material fundamentally overcomes the technical obstacles of directly using sand-making tailings in the preparation of road surface stabilization layers, achieving efficient utilization of solid waste resources.

[0035] Specifically, the construction method using the pavement stabilization layer material of the present invention is as follows: For paving and compaction, use a paver at a speed of 0.8~1.5 m / min, with a loose paving thickness of 20~25 cm and a loose paving coefficient of 1.2~1.3. Then, compact according to the sequence of "static pressure-weak vibration-strong vibration-static pressure," achieving a base course compaction degree of 96%~98% and a subbase course compaction degree of ≥95%. After compaction, cover with geotextile fabric, keep moist, and allow a curing period of ≥7 days (≥14 days for high-grade highways). Traffic will be closed during the curing period.

[0036] The principles of this invention will be explained below.

[0037] Sand making tailings are mainly produced by wet sand making. Due to inherent defects in their composition and physicochemical properties, direct use in the preparation of road surface stabilization layer materials faces unavoidable technical obstacles, failing to meet the core requirements of road surface stabilization layers for aggregate looseness, cementitious activity, and skeleton filling. This invention, through the targeted development of an aqueous phase conversion agent, supplemented by high-speed stirring, enhanced dispersing, and physical aging treatment, and combined with components such as activating stabilizers, prepares a stabilization layer material. This fundamentally overcomes the aforementioned obstacles, achieving the resource-efficient utilization of sand making tailings, rather than simply using them directly. Details are as follows: 1) Core technological obstacles to directly preparing road surface stabilization layer materials from sand-making tailings Sand making tailings are the product of wet sand making solid waste dewatered by plate and frame filter press. With a pH of 8.5-8.7, they are weakly alkaline. Their composition and physical properties determine that direct use presents a core problem: Mud cake contains a large amount of bound water. Under natural conditions, only the surface is dry, and its moisture content remains between 30% and 50%. It is prone to hardening and clumping, and is likely to collapse after being filled. Direct use will cause uneven mixing of the pavement stabilization layer mixture, resulting in problems such as excessive porosity, loose structure, and pavement collapse after paving and compaction. It cannot meet the requirements for the looseness and stability of the pavement stabilization layer aggregate.

[0038] 2) Specific solutions for overcoming technical obstacles by specifically adding activation stabilizers in this invention This invention does not directly use sand-making tailings. Instead, it precisely adds a water phase conversion agent to address the inherent defects of sand-making tailings, such as easy caking and the presence of a large amount of bound water. It is supplemented with high-speed stirring, enhanced dispersing and physical aging treatment, and combined with components such as activating stabilizers. This addresses the technical obstacles from four dimensions: looseness, gelling activity, alkaline environment and particle size distribution.

[0039] 3) Technical effects after compounding This invention processes sand-making tailings (20%~35%, pH 8.5~8.7) and a water phase conversion agent (<5%) into recycled tailings material through a specific ratio. By employing high-speed mixing, enhanced dispersing, and physical aging treatment, it overcomes the technical obstacles to directly using sand-making tailings. (1) The material is loose and uniform, without caking, and has good workability after being mixed with crushed stone aggregate. It is compatible with the paving and compaction requirements of existing construction equipment and does not require the addition of special construction equipment. (2) The gelling activity is significantly improved, and the core indicators such as 7 d / 28 d unconfined compressive strength, water immersion strength loss rate, and drying shrinkage coefficient all meet the standards of JTG / T F20-2015 "Technical Specifications for Construction of Highway Pavement Base". (3) Each cubic meter of material can consume 529~736 kg of recycled tailings from sand production, realizing the resource utilization of solid waste while reducing carbon emissions by 40%~65% and engineering costs by 12%~18%, combining environmental protection, engineering economy and construction adaptability.

[0040] 4) Core technological advantages (1) The proportion is in line with the norm: following the conventional framework of 40%~80% coarse aggregate, only the fine aggregate is replaced by the recycled tailings material, which specifically solves the inherent technical obstacles of tailings, without the need to adjust the construction parameters, and has strong engineering adaptability; (2) The amount of recycled sand and tailings material disposed of per cubic meter of material is 529~736 kg, and the loose bulk density of the road stabilization layer material is taken as 2300 kg / m³. 3 Based on a recycled material ratio of 23% to 32%, the calculated value is within the conventional range of bulk density for inorganic binder stabilized materials, and the recycled material utilization rate reaches 20% to 35%, achieving efficient resource utilization of solid waste. (3) Stable and compliant performance: All performance parameters meet the industry standard JTG / T F20-2015 "Technical Specifications for Construction of Highway Pavement Base Layer", and are close to the performance of traditional pavement stabilization layers, with no risk in engineering applications; (4) Significant cost advantage: The cost is reduced by 18% to 30% compared with traditional materials, and no new special equipment is required, making it easy to scale up and promote. (5) Low carbon footprint: Carbon emissions are significantly reduced by using recycled materials and processes; the formula for calculating the low carbon footprint is based on the "Building Carbon Emission Calculation Standard" GB / T51366-2019.

[0041] The following examples will illustrate the method of the present invention and the properties of the resulting materials.

[0042] Example 1 This embodiment presents a low-carbon footprint road stabilization layer material based on recycled sand tailings, suitable for base course construction, as detailed below: 1) Raw materials Cement: Ordinary Portland cement, in accordance with GB175-2023 "General Portland Cement", with a 3-day compressive strength ≥23.0 MPa (actually measured 25.6 MPa) and a 28-day compressive strength ≥42.5 MPa (actually measured 48.3 MPa), meeting the requirements for inorganic binder stabilized materials.

[0043] Coarse aggregate: Crushed stone used for gradation, free of clay lumps or organic matter, and conforming to the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015 and the "Construction Gravel and Crushed Stone" GB / T14685-2022 standards.

[0044] Activating stabilizer: According to the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015, it is a compound of water glass: sodium sulfate: polycarboxylate high-efficiency water-reducing agent: metakaolin = 52.5:30:7.5:10, which can enhance alkaline activation, improve workability, and optimize cementitious structure.

[0045] Water: Clean tap water with pH=6~8, in accordance with the revised version of "Code for Construction and Quality Acceptance of Urban Road Engineering" CJJ1-2008, which meets the standard requirements for concrete water.

[0046] Sand making tailings: solid waste generated from wet sand making.

[0047] Aqueous phase conversion agent: includes fly ash, wood ash and stone powder, with a mass ratio of 1:3:6.

[0048] 2) Composition ratio (mass percentage) Tailings recycled material: 25%, including 23% sand making tailings and 2% water phase conversion agent; cement: 8%; coarse aggregate: 66.5%; activator and stabilizer: 0.5%.

[0049] 3) Preparation process S1, Preparation of recycled sand-making tailings: The sand-making tailings and water phase conversion agent are put into a forced mixer and stirred at 60 r / min for 4 min until uniform. Then, the mixture is aged for 24 h to obtain loose and non-caking recycled sand-making tailings.

[0050] S2, Preparation of pavement stabilization layer material: Mix recycled material, coarse aggregate, cement and activating stabilizer in proportion and stir at 60 r / min for 5 min; add water to the moisture content (8%) and stir at 60 r / min for 5 min until the mixture is uniform and free of lumps to obtain pavement stabilization layer material.

[0051] S3. To verify the performance of the pavement stabilization layer material prepared in this embodiment, pavement construction was carried out, as follows: The paving speed was 1.2 m / min, the loose paving thickness was 22 cm, and the loose paving coefficient was 1.25. According to the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-15, the compaction was carried out according to the following procedures: static pressure (1~2 passes, speed 1.5~2.0 km / h), weak vibration (1~2 passes, speed 2.0~2.5 km / h), strong vibration (2~3 passes, speed 2.0~3.0 km / h), and static pressure (1~2 passes, speed 2.0~3.0 km / h), with a compaction degree of 97.5%. The surface was covered with geotextile and cured for 14 days.

[0052] 4) Performance tests were conducted according to the methods specified in the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015. The specific results are as follows: The 7-day unconfined compressive strength is 3.2 MPa, the 28-day unconfined compressive strength is 5.5 MPa, the strength loss after 7 days of immersion in water is 10%, and the drying shrinkage coefficient is 3.2 × 10⁻⁶. -6 / ℃, with a compaction degree of 97.5%, the cost is reduced by 22% compared to traditional materials, and carbon emissions are reduced by 38% compared to traditional materials.

[0053] Example 2 This embodiment presents a low-carbon footprint road stabilization layer material based on recycled sand tailings, suitable for subbase construction, as detailed below: 1) Raw materials Same as Example 1.

[0054] 2) Composition ratio (mass percentage) Tailings recycled material: 30%, including 28% sand making tailings and 2% water phase conversion agent; cement: 5%; coarse aggregate: 64.8%; activator and stabilizer: 0.2%.

[0055] 3) Preparation process S1, Preparation of recycled sand-making tailings: The sand-making tailings and water phase conversion agent are put into a forced mixer and stirred at 60 r / min for 5 min until uniform. Then, the mixture is aged for 24 h to obtain loose and non-caking recycled sand-making tailings.

[0056] S2, Preparation of pavement stabilization layer material: Mix recycled material, coarse aggregate, cement and activating stabilizer in proportion and stir at 60 r / min for 5 min; add water to the moisture content (10%) and stir at 60 r / min for 5 min until the mixture is uniform and free of lumps to obtain pavement stabilization layer material.

[0057] S3. To verify the performance of the pavement stabilization layer material prepared in this embodiment, pavement construction was carried out, as follows: The paving speed was 1.0 m / min, the loose paving thickness was 24 cm, and the loose paving coefficient was 1.22. According to the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-15, the compaction was carried out according to the following procedures: static pressure (1~2 passes, speed 1.5~2.0 km / h), weak vibration (1~2 passes, speed 2.0~2.5 km / h), strong vibration (2~3 passes, speed 2.0~3.0 km / h), and static pressure (1~2 passes, speed 2.0~3.0 km / h), with a compaction degree of 95.5%. The surface was covered with geotextile for curing for 7 days.

[0058] 4) Performance tests were conducted according to the methods specified in the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015. The specific results are as follows: The 7-day unconfined compressive strength is 2.2 MPa, the 28-day unconfined compressive strength is 3.3 MPa, the strength loss rate after 7 days of immersion in water is 12%, and the drying shrinkage coefficient is 3.4 × 10⁻⁶. -6 / ℃, with a compaction degree of 95.5%, the cost is reduced by 25% compared to traditional materials, and carbon emissions are reduced by 42% compared to traditional materials.

[0059] Example 3 This embodiment prepares a low-carbon footprint road stabilization layer material based on sand-making tailings recycled material, using a high-content tailings recycled material, as detailed below: 1) Raw materials Same as Example 1.

[0060] 2) Composition ratio (mass percentage) Tailings recycled material: 35%, including 32% sand making tailings and 3% water phase conversion agent; cement: 3%; coarse aggregate: 61.7%; activator and stabilizer: 0.3%.

[0061] 3) Preparation process S1, Preparation of recycled sand-making tailings: The sand-making tailings and water phase conversion agent are put into a forced mixer and stirred at 60 r / min for 5 min until uniform. Then, the mixture is aged for 48 h to obtain loose and non-caking recycled sand-making tailings.

[0062] S2, Preparation of pavement stabilization layer material: Mix recycled material, coarse aggregate, cement and activating stabilizer in proportion and stir at 60 r / min for 3 min; add water to the moisture content (11%) and stir at 60 r / min for 6 min until the mixture is uniform and free of lumps to obtain pavement stabilization layer material.

[0063] S3. To verify the performance of the pavement stabilization layer material prepared in this embodiment, pavement construction was carried out, as follows: The paving speed is 0.8 m / min, the loose paving thickness is 25 cm, and the loose paving coefficient is 1.3. The compaction is carried out according to the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-15, using the following procedures: static pressure (1~2 passes, speed 1.5~2.0 km / h), weak vibration (1~2 passes, speed 2.0~2.5 km / h), strong vibration (2~3 passes, speed 2.0~3.0 km / h), and static pressure (1~2 passes, speed 2.0~3.0 km / h), with a compaction degree of 96%. The surface is covered with geotextile for curing for 14 days.

[0064] 4) Performance tests were conducted according to the methods specified in the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015. The specific results are as follows: The 7-day unconfined compressive strength was 2.8 MPa, the 28-day unconfined compressive strength was 4.8 MPa, the strength loss after 7 days of immersion in water was 11%, and the drying shrinkage coefficient was 3.3 × 10⁻⁶. -6 / ℃, with a compaction degree of 96%, the cost is reduced by 30% compared to traditional materials, and carbon emissions are reduced by 50% compared to traditional materials.

[0065] Comparative Example This comparative example shows a road surface stabilization layer material prepared using conventional methods, as detailed below: 1) Raw materials The same cement, coarse aggregate, and water were used as in Example 1, but sand-making tailings, water phase conversion agent, and activating stabilizer were not used.

[0066] In addition, it also includes natural fine aggregate: 0-5mm (compliant with the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015 standard).

[0067] 2) Composition ratio (mass percentage) Cement: 8%; Coarse aggregate: 65%; Natural fine aggregate: 27%.

[0068] 3) Preparation process S1, Preparation of pavement stabilization layer material: Coarse aggregate and natural fine aggregate are put into a mixer and stirred at 60 r / min for 3 min; cement is added and stirred at 60 r / min for 2 min; tap water is added in batches until the moisture content is 6% and stirred at 60 r / min for 5 min until the mixture is uniform and free of lumps, thus obtaining the pavement stabilization layer material.

[0069] S2. To verify the performance of the pavement stabilization layer material prepared in this comparative example, pavement construction was carried out, as follows: The paving speed was 1.2 m / min, the loose paving thickness was 22 cm, and the loose paving coefficient was 1.25. The compaction was carried out according to the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-15, using the following procedures: static pressure (1-2 passes, speed 1.5-2.0 km / h), weak vibration (1-2 passes, speed 2.0-2.5 km / h), strong vibration (2-3 passes, speed 2.0-3.0 km / h), and static pressure (1-2 passes, speed 2.0-3.0 km / h), with a compaction degree of 97%. The surface was covered with geotextile and cured for 14 days.

[0070] 4) Performance tests were conducted according to the methods specified in the "Technical Specifications for Construction of Highway Pavement Base Course" JTG / T F20-2015. The specific results are as follows: The 7-day unconfined compressive strength is 3.1 MPa, the 28-day unconfined compressive strength is 5.2 MPa, the strength loss rate after 7 days of immersion in water is 8%, and the drying shrinkage coefficient is 3.0 × 10⁻⁶. -6 / ℃, compaction degree of 97%, cost as a benchmark, carbon emissions as a benchmark.

[0071] The results of the above embodiments and comparative examples were analyzed, and the results are as follows: 1) Performance comparison: The core performance indicators of the embodiments all meet the standard of "Technical Specifications for Construction of Highway Pavement Base Course" JTG / TF20-2015, and are close to the performance of the comparative example, meeting the requirements for engineering use; among them, the 28-day strength of Embodiment 1 is slightly higher than that of the comparative example, and the strength of Embodiment 3 is slightly lower than that of the comparative example, but both are within the allowable range of the standard.

[0072] 2) Cost comparison: The cost of each embodiment is reduced by 18% to 30% compared with the comparative example. The cost reduction of embodiment 3 is the largest, mainly due to the replacement of natural fine aggregate with high-volume sand-making tailings recycled material, which reduces the procurement cost of natural materials.

[0073] 3) Carbon emission comparison: The carbon emissions of each embodiment are reduced by 30% to 50% compared with the comparative embodiment. This is mainly due to the reduction in the mining and transportation of natural fine aggregates and the reduction in cement usage. At the same time, the solid waste of sand making tailings is disposed of, avoiding carbon emissions from solid waste stockpiling.

[0074] 4) Solid waste utilization comparison: In the example, each cubic meter of material can consume 529~736 kg of recycled sand-making tailings, realizing the efficient resource utilization of sand-making tailings and solving the environmental protection problem of sand-making tailings storage.

[0075] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A low-carbon footprint road stabilization layer material based on recycled sand-making tailings, characterized in that, It includes, by mass percentage, 20%–35% recycled tailings from sand making, 3%–15% cement, 45%–76% 5–40 mm coarse aggregate, and 0.1%–4.5% activating stabilizer, and the sum of the mass percentages of all components is 100%. The preparation method of the recycled tailings material is as follows: A water phase conversion agent is added to the sand making tailings, and the mixture is subjected to high-speed stirring, enhanced dispersing and physical aging treatment in sequence to convert the bound water originally contained in the sand making tailings into gravity water and capillary water, so as to obtain sand making tailings recycled material with a water content of <5%.

2. The low-carbon footprint road stabilization layer material based on recycled sand-making tailings as described in claim 1, characterized in that, The mass ratio of the sand-making tailings to the water phase conversion agent is (10-20):1, and the water phase conversion agent is at least one of fly ash, wood ash, and stone powder.

3. The low-carbon footprint road stabilization layer material based on recycled sand-making tailings as described in claim 2, characterized in that, In the aqueous phase conversion agent, the mass ratio of fly ash to wood ash is 1:3, the mass ratio of fly ash to stone powder is 1:6, the mass ratio of wood ash to stone powder is 1:2, and the mass ratio of fly ash, wood ash, and stone powder is 1:3:

6.

4. The low-carbon footprint road stabilization layer material based on recycled sand-making tailings as described in claim 2, characterized in that, The fly ash is a solid waste generated from the combustion of coal in thermal power plants. It has a particle size of 0.5~300 μm, conforms to the standard GB / T1596-2017 "Fly Ash for Cement and Concrete", and has high pozzolanic activity.

5. The low-carbon footprint road stabilization layer material based on recycled sand-making tailings as described in claim 2, characterized in that, The plant ash is solid waste generated from biomass power plant incineration, with a particle size ≤3 mm, loss on ignition ≤8%, and pH=12±0.

5.

6. The low-carbon footprint road stabilization layer material based on recycled sand-making tailings as described in claim 2, characterized in that, The stone powder is solid waste generated during the dry sand making process and is obtained through collection, screening and impurity removal. Its moisture content is ≤2%, particle size is 0.075~2 mm, and pH is 8.5~8.

7.

7. The low-carbon footprint road stabilization layer material based on recycled sand-making tailings as described in claim 1, characterized in that, The tailings sludge is solid waste generated during the wet sand making process and obtained by plate and frame filter press dewatering treatment. Its moisture content is 30%~50% and its pH is 8.5~8.

7.

8. The low-carbon footprint road stabilization layer material based on recycled sand-making tailings as described in claim 1, characterized in that, The high-speed mixing treatment has a mixing rate of 50~100 r / min and a mixing time of 5~15 min; the enhanced dispersing treatment involves crushing the mud cake of sand-making tailings to a particle size ≤5 mm; the physical aging treatment involves aging in a ventilated environment for 24~48 h.

9. A method for preparing a low-carbon footprint road stabilization layer material based on recycled tailings as described in any one of claims 1 to 8, characterized in that, Specifically as follows: Mix 20%~35% recycled tailings from sand making, 3%~15% cement, 45%~76% 5-40 mm coarse aggregate, and 0.1%~4.5% activating stabilizer by mass percentage, and stir until uniform at a speed of ≥30 r / min; then add water to adjust the moisture content to 8%~12%, and continue stirring for 4~6 min until the mixture is uniform and free of lumps; wherein, the sum of the mass percentages of each component added is 100%.

10. The application of a low-carbon footprint road stabilization layer material based on recycled sand tailings as described in any one of claims 1 to 8 in the construction of base or subbase layers of Class I to IV highways and municipal roads.