Green long-life double-layer cement concrete pavement and construction method

Abstract

The application relates to a green long-life double-layer cement concrete pavement and a construction method, and belongs to the technical field of road engineering. The pavement comprises an upper layer and a lower layer, the upper layer is a cement concrete layer mixed with steel slag sand, the lower layer is a cement concrete layer mixed with short-cut basalt fibers, and the upper and lower layers are combined into an integral structure through wet-wet connection. During construction, the lower layer mixture is first paved, the upper layer mixture is paved before the initial setting of the lower layer, and the interval time is controlled according to the environmental temperature, then the double anti-skid structure is formed through roughening and grooving. The application improves the wear resistance and skid resistance through the upper layer steel slag sand, improves the crack resistance and fatigue resistance through the lower layer basalt fibers, and strictly controls the stability of the steel slag, realizes the organic combination of long-life pavement and green environmental protection, and is suitable for heavy-load traffic fields such as high-grade highways, urban roads and airport runways.

Description

Technical Field

[0001] This invention belongs to the field of road engineering technology, specifically relating to a green, long-life double-layer cement concrete pavement and its construction method. Background Technology

[0002] Cement concrete pavements are widely used in heavy-duty transportation sectors in my country, such as high-grade highways, urban roads, and airport runways, due to their advantages of high strength, good stability, high durability, and low maintenance costs. However, traditional single-layer cement concrete pavements have revealed the following prominent problems in actual use: First, there's the issue of surface wear and reduced skid resistance. Under repeated friction from vehicle tires, cement concrete pavement surfaces are prone to defects such as exposed aggregate, peeling, and abrasion, leading to a significant decrease in skid resistance and seriously affecting driving safety. Especially in wet environments, the braking distance of a worn-out pavement increases dramatically, significantly raising the risk of traffic accidents.

[0003] Secondly, there is the issue of fatigue cracking and service life. Under the coupled effects of heavy traffic and temperature stress, fatigue cracks are prone to occur on the bottom of cement concrete pavement slabs. These cracks gradually propagate, leading to slab fracture, which is the most significant form of structural damage to cement concrete pavements. Traditional concrete pavements are typically designed for a lifespan of 20-30 years, but structural damage often occurs prematurely in heavy traffic sections, making it difficult to meet the development requirements of "long-life pavements" (design lifespan of 40-50 years).

[0004] Secondly, there are issues of resource consumption and environmental pressure. The construction of cement concrete pavements requires a large amount of high-quality sand and gravel aggregates and cement, placing enormous pressure on natural resources. Simultaneously, my country's steel industry generates a large amount of steel slag annually, with a comprehensive utilization rate of less than 30%. Large quantities of steel slag are stockpiled, occupying land and causing environmental pollution. As a solid waste from the metallurgical industry, the resource utilization of steel slag is an important direction for green highway construction. Studies have shown that steel slag has good wear resistance and anti-skid properties when used as concrete aggregate; however, the presence of free calcium oxide (f-CaO) in steel slag leads to poor volume stability, potentially causing volume expansion or even cracking during long-term service, severely restricting its large-scale application in road engineering.

[0005] To address the aforementioned issues, double-layer cement concrete pavement technology has emerged. Existing technologies have introduced several solutions. For example, patent applications CN116434894B and CN116759025B respectively disclose mix design and manufacturing methods for concrete using steel slag to replace fine aggregate and coarse aggregate, achieving a certain degree of resource utilization of steel slag. However, these methods are limited to optimizing the mix proportion of a single-layer homogeneous concrete material and do not address the functionally graded double-layer structural design tailored to the specific stress and wear characteristics of the pavement. While patent application CN117263585B proposes using steel slag to replace all aggregates, its application is strictly limited to non-structural anti-buoyancy counterweight concrete, failing to meet the stringent mechanical requirements of high-grade road surface layers for load-bearing capacity, wear resistance, and skid resistance. Patent application CN104532711A discloses a cement concrete pavement and its double-layer paving method, proposing the concept of layered construction. However, its upper and lower layer materials often still use traditional homogeneous concrete, failing to fundamentally achieve innovative material combinations and functionally layered designs for heavy traffic. Patent application CN107010896A discloses a recycled concrete incorporating short-cut basalt fibers and recycled coarse aggregate. While utilizing the toughening and crack-resistant properties of basalt fibers, it is limited to a single-material-level mix design and does not address the macroscopic double-layer structure design of the pavement, nor does it solve the problem of reduced skid resistance and wear resistance of the pavement surface. Patent CN112195708A discloses a method for constructing a double-layer wet-wet transition gradient functional cement concrete pavement using a formwork system. This method focuses on the construction process and equipment coordination of the wet-wet transition. Although it mentions gradient functionality, it does not propose specific functional material combinations for long-life pavements (such as high wear resistance of steel slag aggregate in the upper layer and high fatigue resistance of fiber in the lower layer), nor does it propose clear and scientific control indicators for the core issue of applying bulk metallurgical solid waste in double-layer pavements—volume stability.

[0006] In summary, existing patents concerning the application of steel slag in road engineering mostly focus on single-layer material proportions, non-structural component applications, or flexible asphalt pavements, lacking customized designs for the functional differences between the upper and lower layers of cement concrete pavements. How to organically combine the resource utilization of steel slag, fiber reinforcement technology, and double-layer paving processes to create a double-layer cement concrete pavement that combines long service life, environmental friendliness, and excellent road performance is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a green, long-life double-layer cement concrete pavement and its construction method, aiming to solve the problems of poor wear resistance and skid resistance of existing cement concrete pavement surfaces, insufficient fatigue cracking resistance of structural layers, and difficulty in controlling volume stability in the utilization of steel slag resources, thereby achieving an organic combination of long pavement life and green environmental protection.

[0008] On the one hand, the present invention provides a green, long-life double-layer cement concrete pavement, which adopts the following technical solution: A green, long-life double-layer cement concrete pavement, comprising: The upper layer is a cement concrete layer mixed with steel slag sand; The lower layer is a cement concrete layer mixed with short-cut basalt fibers; The upper layer and the lower layer are combined into an integral structure through a wet-wet connection.

[0009] Preferably, the upper layer comprises fine aggregate and coarse aggregate; The fineness modulus of the first fine aggregate is 2.4-3.2; the first fine aggregate includes steel slag sand with a particle size of 0.15-4.75 mm, and also includes any one of manufactured sand or natural sand with a particle size of 0-5 mm; the steel slag sand accounts for 30-50% of the volume of the first fine aggregate. The coarse aggregate includes crushed stone with a particle size of 5-20 mm.

[0010] Preferably, the stability of the steel slag sand meets the following requirements: free calcium oxide content ≤2%, autoclaving pulverization rate ≤2%; and the autoclaving expansion rate of the cement concrete layer prepared from the steel slag sand is ≤0.04%.

[0011] Preferably, the volume fraction of the short-cut basalt fibers in the lower layer is 0.15-0.35%, the length is 12-30 mm, and the diameter of the single filament is 10-20 μm; The lower layer also includes fine aggregate II and coarse aggregate II; The fine aggregate 2 includes manufactured sand with a particle size of 0-5mm; The coarse aggregate 2 includes crushed stone with a particle size of 5-26.5 mm.

[0012] Preferably, the total thickness of the green, long-life double-layer cement concrete pavement is 24-32 cm; The upper layer is 40-50mm wider on each side than the lower layer; The thickness of the upper layer is 6-10cm, and the thickness of the lower layer is 18-22cm.

[0013] On the one hand, the present invention also provides a construction method for preparing the above-mentioned green long-life double-layer cement concrete pavement, which adopts the following technical solution: A construction method for a green, long-life double-layer cement concrete pavement includes the following steps: 1) Prepare basalt fiber-reinforced cement concrete as the lower layer mixture, and control the slump to be 20-40mm; 2) Prepare steel slag sand cement concrete as the upper layer mixture, and control the slump to 40-70mm; 3) The lower layer mixture is laid to form the lower layer; 4) Before the lower layer initially sets, the upper layer mixture is spread on top of the lower layer to form the upper layer; 5) Apply an anti-slip surface treatment to the upper layer.

[0014] Preferably, in step 4), the paving interval between the lower and upper layers of the mixture is controlled according to the ambient temperature. When the ambient temperature is 10-20℃, the interval is 60-90 minutes; When the ambient temperature is 20-30℃, the interval is 30-60 minutes; When the ambient temperature is above 30℃, the interval should be 30-40 minutes, and shading and cooling measures should be taken.

[0015] Preferably, in step 5), the surface anti-slip structure treatment includes: roughening the wet upper layer to form a fine texture, and grooving the upper layer after it has hardened to form a macro texture.

[0016] Preferably, it also includes: setting joints according to the design, with the joint depth being 1 / 3 of the total pavement thickness; and using sprayed curing agent and covering with geotextile for moisture retention maintenance, with a maintenance time of not less than 14 days.

[0017] Preferably, when the total road surface thickness is ≤26cm, no dowel bars and / or tie bars are installed; when the total road surface thickness is >26cm, dowel bars and / or tie bars are installed. When it is necessary to install dowel bars and / or tie bars, the dowel bars and / or tie bars shall be installed in the lower layer of concrete at a depth of 1 / 2 of the total thickness of the pavement.

[0018] In summary, the present invention has the following beneficial technical effects: 1. This invention divides the road surface into a wear-resistant and skid-resistant upper functional layer and a crack-resistant and fatigue-resistant lower main layer. The upper layer uses steel slag sand concrete, utilizing the rough microstructure and high wear resistance of steel slag to improve surface durability. The lower layer uses basalt fiber reinforced concrete to inhibit crack propagation and improve fatigue life, achieving a road surface design life of 40-50 years. Simultaneously, steel slag sand partially replaces natural fine aggregate (30-50%), solving the problem of metallurgical solid waste accumulation and aligning with the circular economy strategy.

[0019] 2. This invention addresses the core issue of steel slag application, namely volume stability, and creatively proposes a triple control index: free calcium oxide content in steel slag ≤2%, autoclaving pulverization rate ≤2%, and autoclaving expansion rate of steel slag concrete ≤0.04%. This index system comprehensively ensures the long-term stability of steel slag in the upper layer of concrete from source to result, avoiding the risk of pavement cracking caused by steel slag expansion.

[0020] 3. This invention employs a wet-wet bonding construction process, completing the bonding of upper and lower concrete layers before the initial setting of the cement, resulting in a combination of chemical adhesion and mechanical interlocking between the layers. By precisely controlling the construction interval (30-90 minutes) for different ambient temperatures, the interlayer shear strength can reach 2.5-3.5 MPa, significantly exceeding the standard requirement of 1.5-2.0 MPa for the shear strength of two layers of concrete materials with traditional "wet-dry" bonding, effectively avoiding interlayer delamination.

[0021] 4. This invention involves sequentially roughening and grooving the surface of the upper layer to create fine and macroscopic textures, significantly improving the anti-skid performance of the pavement at different service stages. Simultaneously, it provides a complete construction technology solution from mixture preparation, paving sequence control, joint setting to maintenance, offering strong operability. The total life-cycle cost is significantly lower than traditional pavements, resulting in substantial economic and social benefits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the green, long-life double-layer cement concrete pavement of the present invention; Figure 2 Photograph of a core sample of a double-layer cement concrete pavement; Figure 3 Comparison of the microstructures of steel slag sand and manufactured sand; Figure 4 This is a schematic diagram of the construction process of the green, long-life double-layer cement concrete pavement of the present invention.

[0023] Explanation of reference numerals in the attached diagram: 1. Base layer; 2. Lower layer; 3. Upper layer. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description of a green, long-life, double-layer cement concrete pavement and its construction method, in conjunction with specific embodiments, is provided. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0025] Example Example 1 Reference Figure 1 and Figure 2 A green, long-life double-layer cement concrete pavement includes a base layer 1, a lower layer 2, and an upper layer 3 distributed from bottom to top. The pavement adopts a functional gradient integrated double-layer design, which is composed of the upper layer 3 and the lower layer 2 stacked on top of each other. The two layers are tightly bonded together as an integral load-bearing structure through a wet-wet connection process, which can work together to bear load and realize functional stratification.

[0026] Reference Figure 1and Figure 2 The upper layer 3 is a cement concrete functional layer with steel slag sand admixture, with a thickness of 6-10cm. This layer uses steel slag sand as part of the fine aggregate; its core function is to utilize the high hardness and rough microstructure of steel slag sand to improve the wear resistance and micro-skid resistance of the road surface. The surface is roughened and grooved to form a double anti-skid structure, ensuring driving safety.

[0027] Reference Figure 1 The lower layer 2 is a cement concrete structural bearing layer with short-cut basalt fiber. This layer contains short-cut basalt fiber. Its core function is to improve the crack resistance and fatigue resistance of the pavement through the toughening and crack-resistant effect of basalt fiber, to withstand the coupling effect of heavy traffic load and temperature stress, and to avoid fatigue cracking of the pavement slab bottom.

[0028] Reference Figure 1 and Figure 2 The interlayer connection and overall structure: The upper layer 3 and the lower layer 2 adopt a wet-wet connection to form an integral structure. The interlayers are bonded by chemical bonding generated by cement hydration, combined with the mechanical interlocking of aggregates, to achieve high-strength interlayer bonding and effectively prevent interlayer delamination. The total thickness of the pavement is 24-32cm, the upper layer 3 is 6-10cm thick, and the lower layer 2 is 18-22cm thick.

[0029] This structure achieves a comprehensive performance improvement in road surface characteristics, including long service life, high wear resistance, high skid resistance, fatigue resistance, and environmental friendliness, through a differentiated design that integrates upper functional layers and lower load-bearing layers, combined with the resource utilization of steel slag solid waste and basalt fiber reinforcement technology.

[0030] Example 2 A main road in a city, designed for a 40-year service life, with six lanes in both directions, classified as heavy traffic, a design axle load of 100kN, and a cumulative number of applications of the standard axle load per lane of design lanes of 5×10 7 Second-rate.

[0031] Reference Figure 3 and Figure 4 The construction process is as follows: I. Road surface structure design This embodiment uses a green, long-life, double-layer cement concrete pavement with a total thickness of 26cm, of which the upper layer is 8cm thick and the lower layer is 18cm thick. The upper layer uses steel slag sand C35 cement concrete, and the lower layer uses basalt fiber C30 cement concrete. The upper and lower layers are bonded together as a whole structure through a wet-wet connection.

[0032] II. Material Composition and Mix Proportion ① Top layer of steel slag sand C35 concrete Cement: P·O42.5 ordinary Portland cement, dosage 380 kg / m³ 3 .

[0033] Fine aggregate 1: Fineness modulus of 3.1, including steel slag sand and manufactured sand. Steel slag sand has a particle size of 0.15-4.75mm and a density of 3200kg / m³. 3 After 6 months of aging, the free calcium oxide content was 1.2%, and the autoclaving pulverization rate was 1.9%; steel slag sand accounted for 47% of the fine aggregate by volume, with a dosage of 406 kg / m³. 3 The manufactured sand is limestone manufactured sand, with a particle size of 0-5mm and a density of 2700 kg / m³. 3 Dosage: 380 kg / m 3 .

[0034] Coarse aggregate 1: Limestone crushed stone with a particle size of 5-20mm, dosage 1100kg / m³ 3 .

[0035] Water: 152 kg / m³ 3 The water-to-binder ratio is 0.40.

[0036] Admixtures: Polycarboxylate superplasticizer, dosage is 0.15% of the cementitious material dosage; air-entraining agent dosage is 0.01%, with an air content of 4.5%.

[0037] The steel slag sand concrete prepared according to the above mix proportion was tested using 75mm×75mm×275mm specimens in accordance with the "Technical Specification for Application of Steel Slag Aggregate in Hydraulic Concrete" (DL / T5877-2024). The autoclave expansion rate was 0.035%, which meets the requirement of ≤0.04%.

[0038] Workability: slump 45mm, initial setting time 185min, final setting time 245min.

[0039] Mechanical properties: 28-day compressive strength is 38.5 MPa, and flexural strength is 5.2 MPa.

[0040] ② Lower layer basalt fiber C30 concrete Cement: P·O42.5 ordinary Portland cement, dosage 331 kg / m³ 3 .

[0041] Mineral admixture: Grade I fly ash, at a dosage of 20% of the cement mass, at a rate of 66 kg / m³. 3 .

[0042] Fine aggregate 2: Manufactured limestone sand, particle size 0-5mm, fineness modulus 3.1, dosage 698kg / m³ 3 .

[0043] Coarse aggregate 2: Limestone crushed stone with a particle size of 5-26.5mm, dosage 1189kg / m³ 3 .

[0044] Short-cut basalt fiber: 12mm in length, 17μm in diameter per filament, 0.15% volume fraction, and 3.975kg / m² dosage. 3 .

[0045] Water: Drinking water, usage 163 kg / m³ 3 The water-to-binder ratio is 0.41.

[0046] Admixture: Polycarboxylate superplasticizer, dosage is 0.15% of the cementitious material.

[0047] Workability: Slump is 30mm, workability is good, and the fibers are evenly dispersed without clumping.

[0048] Mechanical properties: 28-day compressive strength is 34.2 MPa, and flexural strength is 4.8 MPa.

[0049] III. Construction Method S1. Construction preparation and paving of the lower layer The underlying layer is a cement-stabilized crushed stone base course. The top surface is cleaned, moistened with water, and free of standing water. Steel formwork is erected, with a height of 26cm, and fixed using triangular supports. The elevation of the top surface of the formwork is controlled according to the designed road surface elevation.

[0050] The lower layer mix (basalt fiber-reinforced cement concrete) is centrally mixed at the batching plant, with the mixing time extended by 30 seconds compared to ordinary concrete to ensure uniform fiber dispersion. Dump trucks transport the concrete to the site, controlling the unloading height to within 1.5m to prevent segregation. Excavators, in conjunction with manual labor, are used for transverse placement of the concrete, with a loose paving coefficient of 1.15. A tamping machine is used to compact the concrete until the surface is covered with slurry. Then, a three-roller vibrator (168mm shaft diameter, 50Hz vibration frequency) is used for vibration, leveling, and slurry lifting to form the lower layer. The flatness of the top surface of the lower layer is controlled; a 3m straightedge is used to check that the maximum gap is ≤5mm.

[0051] S2, Wet-to-wet connection paving of the top layer After the lower layer is vibrated and leveled, the ambient temperature is 25℃. The construction interval is controlled according to the ambient temperature, which is 45 minutes (30-60 minutes when the ambient temperature is 20-30℃). At this time, the surface of the lower layer concrete can withstand light footsteps (a person weighing 65-80kg can leave a footprint about 3mm deep), and there is a small amount of water film on the surface, which is in the pre-setting state.

[0052] The upper layer mix (steel slag sand cement concrete) is centrally mixed at the mixing plant and transported to the site. Excavators are used for horizontal spreading, ensuring uniform height and avoiding accumulation. Construction workers wear flat-soled rubber shoes to assist in spreading the lower layer surface; heavy machinery is strictly prohibited from compacting it. A vibrating beam is used for vibration, leveling, and slurry raising, with a vibration frequency of 45Hz and a travel speed of 2.5m / min. An aluminum alloy scraper is used for fine leveling, controlling the elevation of the top surface of the upper layer to ensure a total thickness of 26cm. The upper layer is paved 40-50mm wider on each side than the lower layer to prevent edge deformation.

[0053] S3, Roughening process creates fine texture Combination Figure 1 After the paving is completed, a roughening treatment is applied to the moist top layer, with a texture depth of 3mm and a spacing of 20mm.

[0054] S4. Joint Treatment and Maintenance When the top layer of concrete reaches a level suitable for pedestrian use, joints should be cut to a depth of 1 / 3 of the total pavement thickness (i.e., 8.7 cm). After the top layer of concrete has initially set, a curing agent should be sprayed and the surface covered with geotextile. Water should be sprinkled to maintain moisture and cure for at least 14 days.

[0055] S5, Grooving process to create macroscopic textures Combination Figure 1 After the top layer has hardened (when the concrete compressive strength reaches 40%, approximately the 4th day), a grooving machine is used to create macroscopic textures.

[0056] In this embodiment, the total thickness of the road surface is 26cm (≤26cm), so no transverse force transmission bar is set. The longitudinal tie bar is inserted into the reserved hole in the side template and vibrated to compact and adhere firmly.

[0057] Example 3 A certain heavy-load section of a highway has a design service life of 50 years, a design axle load of 120kN, and a design lane standard axle load cumulative action number of 1×10⁻¹⁰. 8 The construction process is as follows: I. Road surface structure design This embodiment uses a green, long-life, double-layer cement concrete pavement with a total thickness of 28cm, of which the upper layer is 8cm thick and the lower layer is 20cm thick. The upper layer uses steel slag sand C40 cement concrete, and the lower layer uses basalt fiber C35 cement concrete. The upper and lower layers are bonded together as a whole structure through a wet-wet connection.

[0058] II. Material Composition and Mix Proportion ① Top layer of steel slag sand C40 concrete Cement: P·II52.5 Portland cement, dosage 400 kg / m³ 3 .

[0059] Fine aggregate 1: includes steel slag sand and manufactured sand. The steel slag sand has a particle size of 0.15-4.75mm, is aged for 6 months and carbonized, has a free calcium oxide content of 0.9%, and a pressure pulverization rate of 1.7%. Steel slag sand accounts for 50% of the volume of fine aggregate 1, with a dosage of 407kg / m³. 3 The manufactured sand is limestone manufactured sand, with a particle size of 0-5mm, and a dosage of 369kg / m³. 3 .

[0060] Coarse aggregate 1: Limestone crushed stone with a particle size of 5-20mm, dosage 1154kg / m³ 3 .

[0061] Water: 160 kg / m³ 3 The water-to-binder ratio is 0.40.

[0062] Admixture: Polycarboxylate superplasticizer, at a dosage of 0.18% of the cementitious material.

[0063] The steel slag sand concrete prepared according to the above mix proportion was tested using 75mm×75mm×275mm specimens in accordance with the "Technical Specification for Application of Steel Slag Aggregate in Hydraulic Concrete" (DL / T5877-2024). The autoclave expansion rate was 0.028%, which meets the requirement of ≤0.04%.

[0064] Performance characteristics: slump of 40mm.

[0065] Mechanical properties: 28-day compressive strength is 45.2 MPa, and flexural strength is 6.1 MPa.

[0066] ② Lower layer basalt fiber C35 concrete Cement: P·O42.5 ordinary Portland cement, dosage 345 kg / m³ 3 .

[0067] Mineral admixture: S95 grade mineral powder, with a dosage of 15% of the cement mass, at a rate of 52 kg / m³. 3 .

[0068] Fine aggregate 2: Manufactured sand, particle size 0-5mm, dosage 698kg / m³ 3 .

[0069] Coarse aggregate 2: Limestone crushed stone with a particle size of 5-26.5mm, dosage 1189kg / m³ 3 .

[0070] Short-cut basalt fiber: 12mm in length, 0.35% in volume fraction, and 9.275kg / m³ in dosage. 3 .

[0071] Water: Drinking water, usage 167 kg / m³ 3The water-to-binder ratio is 0.42.

[0072] Admixture: Polycarboxylate superplasticizer, at a dosage of 0.16% of the cementitious material.

[0073] Performance characteristics: slump of 25mm.

[0074] Mechanical properties: 28-day compressive strength is 42.6 MPa, and flexural strength is 5.8 MPa.

[0075] III. Construction Method This embodiment uses two slipform pavers for double-layer continuous paving.

[0076] S1. Construction Preparation Treatment of the underlying layer, measurement and layout.

[0077] S2, Preparation of lower layer mixture Prepare basalt fiber-reinforced cement concrete according to the above mix proportions, and control the slump to 20-40mm.

[0078] S3, Lower layer paving The lower layer was paved using a slipform paver, with a thickness of 20cm. The paving speed was 1m / min, and the vibration frequency was 150Hz.

[0079] S4. Preparation of the upper layer mixture Prepare steel slag sand cement concrete according to the above mix proportions, and control the slump to 40-70mm.

[0080] S5, Wet-to-wet connection paving of the top layer One hour after the lower layer is laid (at an ambient temperature of 25℃, with intervals controlled within the range of 30-60 minutes, at which point the lower layer has not yet initially set), a second slipform paver is used to lay the upper layer, with a thickness of 8cm and a vibration frequency of 150Hz. The upper layer is paved 40-50mm wider on each side than the lower layer to prevent edge deformation. After paving, the surface is roughened to create a fine texture.

[0081] S6, Surface anti-slip treatment After the top layer has hardened (when the concrete compressive strength reaches 40%, approximately the 4th day), a grooving machine is used to create macroscopic textures.

[0082] S7. Joint Treatment and Maintenance: When the top layer of concrete reaches a level suitable for pedestrian use, joints should be cut to a depth of 1 / 3 (approximately 9cm) of the total pavement thickness. Cover with geotextile and water for moisture retention and maintenance, with a maintenance period of no less than 14 days.

[0083] In this embodiment, the total road surface thickness is 28cm (>26cm), therefore transverse dowel bars are installed. For slipform paving, an automatic dowel bar insertion device (DBI) is used to install the dowel bars, which are placed in the lower layer of concrete at a depth of 1 / 2 of the total road surface thickness (i.e., 14cm). Longitudinal tie bars are inserted manually, also placed in the lower layer of concrete at a depth of 1 / 2 of the total road surface thickness.

[0084] Comparative Example Comparative Example 1 This comparative example uses a traditional single-layer cement concrete pavement with a total thickness of 30cm and a strength grade of C35. It does not distinguish between upper and lower layers, does not add short-cut basalt fibers, and does not use steel slag aggregate. Other construction conditions are the same as in Example 1.

[0085] Comparative Example 2 The materials used in this comparative example are basically the same as those in Example 1. A full-scale double-layer road slab measuring 3m × 1m was fabricated and placed outdoors to withstand natural rainfall. The only difference from Example 1 is that the stability of the steel slag sand used does not meet the requirements of this invention, specifically, the free calcium oxide content is 3.5% and the autoclaving pulverization rate is 4.0%. Apart from the stability index of the steel slag sand, the other materials and construction methods are the same as in Example 1.

[0086] Test case Performance tests were conducted on Examples 2, 3, Comparative Example 1, and Comparative Example 2 according to the test items. The test methods and results are as follows.

[0087] Test Example 1 Abrasion resistance test The abrasion resistance of concrete materials was tested according to the "Test Procedures for Cement and Cement Concrete in Highway Engineering" (JTG3420-2020), with the abrasion loss after 240 revolutions (kg / m²) as the metric. 2 The evaluation index is . The test results are shown in Table 1.

[0088] Table 1 Wear tests of Examples 2-3 and Comparative Example 1

[0089] As shown in Table 1, the wear resistance of the embodiments of the present invention is significantly better than that of traditional single-layer pavement.

[0090] Test Example 2 Anti-slip performance test The pendulum friction coefficient (BPN) value of the road surface was determined according to the "Verification Procedure for Pendulum Friction Coefficient Tester" (JJG (Traffic) 053-2017). Test results: The BPN value of Example 2 was 67, the BPN value of Example 3 was 70, the BPN value of Comparative Example 1 was 54, and the BPN value of Comparative Example 2 was 65. The results indicate that the anti-skid performance of the embodiments of the present invention is significantly better than that of traditional single-layer pavement.

[0091] Test Example 3 Crack resistance test Early crack resistance tests were conducted according to Appendix E of the "Technical Specifications for Construction of Cement Concrete Pavement of Highways" (JTG / TF30-2014), and the number of cracks was observed. Test results: No cracks were found in Examples 2 and 3; 3 cracks appeared in Comparative Example 1; and no cracks were found in Comparative Example 2. The results indicate that the lower layer with added short-cut basalt fibers effectively inhibited the formation of early cracks.

[0092] Test Example 4 Fatigue performance test Fatigue tests were conducted according to the "Test Procedure for Fatigue Performance of Railway Concrete" (T / CECS1499-2023). The specimen size was 100mm×100mm×400mm, the stress level was 0.6, the loading frequency was 10Hz, and an MTS testing machine was used. The test results are shown in Table 2 below.

[0093] Table 2. Fatigue life tests of Examples 2-3 and Comparative Example 1

[0094] As shown in Table 2, the addition of short-cut basalt fibers significantly improves the fatigue resistance of concrete.

[0095] Test Example 5 Volume stability test The surface cracking of the full-scale test slab of Comparative Example 2 was observed after one year of outdoor placement. The results showed that Comparative Example 2 exhibited multiple bulges, flaky cracks, and pitted cracks on its surface, while Examples 2 and 3 showed no expansion cracking caused by steel slag. The results indicate that the triple control index for steel slag stability proposed in this invention (free calcium oxide content ≤2%, autoclaving pulverization rate ≤2%, and concrete autoclaving expansion rate ≤0.04%) can effectively ensure the long-term volume stability of the pavement.

[0096] In summary, Examples 2 and 3 of this invention exhibit superior wear resistance and skid resistance compared to traditional single-layer cement concrete pavement (Comparative Example 1) due to the use of steel slag sand in the upper layer; significantly improved crack resistance and fatigue life due to the addition of short-cut basalt fibers in the lower layer; and good long-term volume stability due to strict control of steel slag stability indicators. While Comparative Example 2 has the same structure and fiber content as Example 2, its steel slag stability does not meet the requirements of this invention, leading to volume expansion in the later stages and resulting in surface bulging, flaky, and pitted cracking.

[0097] Therefore, the present invention provides a green long-life double-layer cement concrete pavement and its construction method, which achieves an organic combination of long pavement life and green environmental protection through functional layer design, steel slag resource utilization, strict control of stability indicators, wet-wet connection process and double anti-skid structure, and has significant social and economic benefits and promotion and application value.

[0098] The embodiments shown in this specification are only used to illustrate the technical solutions of the present invention and are intended to help those skilled in the art understand the principles and advantages of the present invention. They do not constitute a limitation on the scope of protection of the present invention. Although the present invention has been specifically described, those skilled in the art can still make any modifications, equivalent substitutions or other reasonable variations to the implementation methods without departing from the spirit and scope of the present invention. All equivalent technical solutions resulting therefrom should be considered within the scope of protection of this patent.

Claims

1. A green, long-life double-layer cement concrete pavement, characterized in that, include: The upper layer (3) is a cement concrete layer mixed with steel slag sand; The lower layer (2) is a cement concrete layer with short-cut basalt fibers added; The upper layer (3) and the lower layer (2) are combined into an integral structure through a wet-wet connection.

2. The green, long-life double-layer cement concrete pavement according to claim 1, characterized in that, The upper layer (3) includes fine aggregate 1 and coarse aggregate 1; The fineness modulus of the first fine aggregate is 2.4-3.2; the first fine aggregate includes steel slag sand with a particle size of 0.15-4.75 mm, and also includes any one of manufactured sand or natural sand with a particle size of 0-5 mm; the steel slag sand accounts for 30-50% of the volume of the first fine aggregate. The coarse aggregate includes crushed stone with a particle size of 5-20 mm.

3. A green, long-life double-layer cement concrete pavement according to claim 1 or 2, characterized in that, The stability of the steel slag sand meets the following requirements: free calcium oxide content ≤2%, autoclaving pulverization rate ≤2%; and the autoclaving expansion rate of the cement concrete layer prepared from the steel slag sand ≤0.04%.

4. The green, long-life double-layer cement concrete pavement according to claim 1, characterized in that, The volume fraction of the short-cut basalt fibers in the lower layer (2) is 0.15-0.35%, the length is 12-30 mm, and the diameter of the single filament is 10-20 μm; The lower layer (2) also includes fine aggregate II and coarse aggregate II; The fine aggregate 2 includes manufactured sand with a particle size of 0-5mm; The coarse aggregate 2 includes crushed stone with a particle size of 5-26.5 mm.

5. The green, long-life double-layer cement concrete pavement according to claim 1, characterized in that, The total thickness of the green, long-life double-layer cement concrete pavement is 24-32cm. The paving width of the upper layer (3) is 40-50mm wider on each side than that of the lower layer (2); The thickness of the upper layer (3) is 6-10cm, and the thickness of the lower layer (2) is 18-22cm.

6. A construction method for preparing a green, long-life double-layer cement concrete pavement as described in any one of claims 1-5, characterized in that, Includes the following steps: 1) Prepare basalt fiber-reinforced cement concrete as the lower layer mixture, and control the slump to be 20-40mm; 2) Prepare steel slag sand cement concrete as the upper layer mixture, and control the slump to 40-70mm; 3) The lower layer mixture is spread to form the lower layer (2); 4) Before the lower layer (2) has initially set, the upper layer mixture is spread on the lower layer (2) to form the upper layer (3). 5) Perform surface anti-slip construction treatment on the upper layer (3).

7. The construction method for green, long-life double-layer cement concrete pavement according to claim 6, characterized in that, In step 4), the paving interval between the lower and upper layers of the mixture is controlled according to the ambient temperature. When the ambient temperature is 10-20℃, the interval is 60-90 minutes; When the ambient temperature is 20-30℃, the interval is 30-60 minutes; When the ambient temperature is above 30℃, the interval should be 30-40 minutes, and shading and cooling measures should be taken.

8. The construction method for green, long-life double-layer cement concrete pavement according to claim 6, characterized in that, In step 5), the surface anti-slip structure treatment includes: roughening the wet upper layer (3) to form a fine texture, and grooving the upper layer (3) after it has hardened to form a macro texture.

9. The construction method for green, long-life double-layer cement concrete pavement according to claim 6, characterized in that, Also includes: Joints should be set according to the design, and the joint depth should be 1 / 3 of the total pavement thickness; In addition, spraying a curing agent and covering with geotextile for moisture retention should be carried out for a period of no less than 14 days.

10. The construction method for green, long-life double-layer cement concrete pavement according to claim 6, characterized in that, When the total road surface thickness is ≤26cm, no dowel bars and / or tie bars are installed; when the total road surface thickness is >26cm, dowel bars and / or tie bars are installed. When it is necessary to install dowel bars and / or tie bars, the dowel bars and / or tie bars shall be installed in the lower layer of concrete at a depth of 1 / 2 of the total thickness of the pavement.

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