A steel slag gradient thermally induced pavement structure based on carbon fiber lateral heat transfer

Abstract

A steel slag gradient thermally induced pavement structure based on carbon fiber lateral heat transfer belongs to the field of road construction technology. It includes an upper gradient heat-conducting structure and a lower lateral heat-dissipating structure. The upper gradient heat-conducting structure comprises at least two layers of asphalt mixture with different types of steel slag replacing coarse aggregate, with the thermal conductivity of the upper layer being lower than that of the lower layer. The lower lateral heat-dissipating structure is a composite structure layer of asphalt mixture with horizontally embedded carbon fibers. This invention can induce heat by forming a gradient structure of different steel slag pavement layers while ensuring pavement performance. The carbon fibers are laid laterally within the asphalt pavement structure, accelerating the downward and lateral release of heat accumulated within the pavement. This can alleviate the problem of high pavement temperature and asphalt pavement defects caused by heat accumulation within the asphalt pavement, and is of great significance for urban environmental protection and road construction.

Description

Technical Field

[0001] This invention relates to a steel slag gradient thermally induced pavement structure based on carbon fiber lateral heat transfer, belonging to the field of road construction technology. Background Technology

[0002] In hot urban areas during summer, asphalt pavement is the primary road surface. Its strong heat absorption capacity and low thermal conductivity result in poor heat conduction and dissipation, causing heat to easily accumulate within the pavement, with surface temperatures sometimes reaching 70-80°C. This has numerous adverse effects on the urban environment. For example, the urban thermal conductivity effect not only affects people's quality of life but also causes air pollution, light pollution, and acid rain. Furthermore, high road surface temperatures can damage the road structure itself. Under high temperatures, due to the viscoelastic properties of asphalt pavement, its resistance to shear deformation is greatly reduced, accelerating rutting under repeated vehicle traffic. The asphalt ages faster, reducing its adhesion and accelerating asphalt detachment and aggregate exposure, leading to potholes. High temperatures also cause asphalt to soften and bleed, affecting driving safety.

[0003] To alleviate the problem of high road surface temperatures in urban areas and thus reduce the urban heat island effect and road heat-related diseases, numerous technological studies on mitigating high road surface temperatures have been conducted both domestically and internationally. These mainly include: 1) altering the thermophysical parameters of road materials to change the road surface's ability to retain heat and reduce heat absorption; 2) heat reflection technology, which increases the road surface's ability to reflect solar radiation by applying heat-reflective coatings, thereby reducing heat absorption; 3) high-porosity asphalt pavement, which increases the porosity of the pavement to affect the continuity of heat transfer within the pavement and reduces its thermal conductivity, thus decreasing heat absorption; 4) heat-induced asphalt pavement technology, which incorporates materials with high / low thermal conductivity into the asphalt mixture to form a multi-layered gradient heat-induced asphalt pavement structure, inducing heat to be conducted downwards at an accelerated rate, reducing heat accumulation on the road surface; and 5) using functional pavements such as phase change heat pipe pavements, thermal energy collection pavements, thermal storage pavements, and thermal circuit pavements to convert and store heat within the pavement to reduce heat accumulation and lower road surface temperature.

[0004] The above studies have all helped alleviate the problem of high road surface temperature to some extent, but they also have some defects and shortcomings, such as: (1) By changing the thermophysical parameters of the material and the gradient thermal induction method, the change is not significant due to the limitations of the asphalt mixture gradation and road performance, and may affect the use of asphalt pavement; (2) Although heat reflection technology can reflect solar radiation, the reflected radiation may be absorbed and reflected by surrounding buildings, and its effect on the urban heat island effect cannot be estimated; (3) Due to its large pores, large-pore asphalt mixture pavement is easily invaded by water and small particles, which can damage the pavement structure and affect the service life of the pavement; (4) Other functional pavements that convert and store heat are affected by cost, construction, etc., and cannot be promoted and used on a large scale.

[0005] In summary, most existing technologies have shortcomings and limitations in alleviating the problem of high road surface temperatures. Therefore, it is necessary to design a road surface structure that induces heat transfer downwards while ensuring good road performance, and further induces heat from the road surface through other means. This not only facilitates heat dissipation, mitigating heat accumulation and secondary reflection after blockage, but also reduces the overall heat inside the road surface, alleviating the problem of heat release at night. This structure has a positive effect on mitigating high road surface temperatures and the urban heat island effect. Summary of the Invention

[0006] Technical Problem: To address the shortcomings of the aforementioned technologies, this invention provides a steel slag gradient thermally induced pavement structure based on the transverse heat transfer of carbon fibers. It utilizes a relatively mature steel slag asphalt pavement structure to form a vertically thermally induced upper structure with an increasing thermal conductivity gradient. Furthermore, it leverages the characteristic that the axial thermal conductivity of carbon fibers is greater than their radial thermal conductivity, by transversely embedding them into asphalt mixture specimens to form a transversely thermally induced lower structure. The upper structure uses steel slag to replace different proportions of coarse aggregate, creating layers of steel slag asphalt mixture with varying thermal conductivity. The lower structure is constructed by fixing long bundles of carbon fibers into carbon fiber bundles and transversely embedding them into ordinary asphalt mixture specimens. This structure utilizes the gradient structure of the steel slag asphalt mixture and the unique thermal conductivity of carbon fibers to induce heat both vertically and downward. The transverse carbon fibers then accelerate the lateral heat transfer and dispersion, simultaneously reducing pavement surface temperature and internal heat storage. This is of significant importance in mitigating the urban heat island effect and high pavement temperatures.

[0007] Technical solution: A steel slag gradient thermally induced pavement structure based on carbon fiber transverse heat transfer, comprising an upper gradient heat conduction structure and a lower transverse heat dissipation structure, wherein the upper gradient heat conduction structure comprises at least two layers of asphalt mixture with different steel slags replacing coarse aggregates, and the thermal conductivity of the upper layer is lower than that of the lower layer; the lower transverse heat dissipation structure is an asphalt mixture composite structure layer with transversely horizontally embedded carbon fibers.

[0008] Preferably, the thermal conductivity of the asphalt mixture with different steel slags replacing coarse aggregates is greater than that of ordinary asphalt mixtures.

[0009] Preferably, the upper gradient heat conduction structure comprises three layers of asphalt mixture with different types of steel slag replacing coarse aggregate, which are, from top to bottom, gradient heat conduction layer one, gradient heat conduction layer two, and gradient heat conduction layer three. In gradient heat conduction layer one, the amount of steel slag is 0% to 30% of the coarse aggregate; in gradient heat conduction layer two, the amount of steel slag is 30% to 40% of the coarse aggregate; and in gradient heat conduction layer three, the amount of steel slag is 40% to 50% of the coarse aggregate. The thickness of gradient heat conduction layer one, gradient heat conduction layer two, and gradient heat conduction layer three increases sequentially.

[0010] Preferably, the coarse aggregate has a particle size of 4.75 mm to 13.2 mm, and the steel slag has a particle size of 4.75 mm to 13.2 mm.

[0011] Preferably, the carbon fiber is a long bundle of carbon fiber with an axial thermal conductivity much greater than that of ordinary asphalt mixture, which is obtained by cutting the carbon fiber and the axial / radial thermal conductivity ratio of the carbon fiber is 10~15.

[0012] Preferably, the transversely embedded carbon fibers in the lower structure are located at the lateral center of the asphalt mixture composite structure layer, and the carbon fibers and asphalt mixture are fully bonded at the interface, with the overall thickness of the lower structure being 50 mm.

[0013] Beneficial effects: Compared with existing technologies, the present invention has the following features and advantages:

[0014] (1) This invention utilizes a relatively mature steel slag asphalt pavement structure with many practical cases as road support, which can better control the amount of steel slag and apply its thermal conductivity properties. This can ensure the reliability of the pavement structure and form a gradient thermal conductivity structure with a "smaller at the top and larger at the bottom", which induces heat to tend to be transferred to the lower part of the pavement. When the heat tends to be balanced, the heat also tends to be conducted downwards.

[0015] (2) The present invention uses an asphalt mixture layer with transversely embedded carbon fibers as the lower structure. It takes advantage of the fact that the axial thermal conductivity of carbon fibers is much greater than their radial thermal conductivity to induce the heat inside the road surface to be transferred to both sides of the road, thus broadening the ideas and directions for inducing heat inside the road surface. Moreover, the flexibility of the carbon fibers themselves has little impact on the structure of the asphalt mixture.

[0016] (3) The present invention combines the dual effects of vertical thermal induction of the gradient thermal conductivity structure of steel slag pavement and horizontal thermal induction of carbon fiber. The two promote each other. Vertical heat induction downward is conducive to strengthening the heat gathering and dissipation of carbon fiber; the horizontal dissipation of heat by carbon fiber reduces the heat inside the lower structure, prompting the upper structure to further transfer heat downward.

[0017] (4) The present invention uses steel slag material that meets the aggregate requirements to change the thermal conductivity of asphalt mixture, which can be well interlocked with the aggregate in asphalt mixture, avoiding the negative impacts such as performance reduction and structural damage that may occur to the pavement structure due to the addition of thermally conductive powder.

[0018] (5) The steel slag used in this invention is industrial waste, which is low in cost and widely available, promoting the secondary utilization of steel slag and saving resources.

[0019] (6) The present invention uses carbon fiber to transfer heat to both sides of the road surface, which alleviates the urban heat island effect at night that is aggravated by simply transferring heat downwards. It can effectively alleviate the urban heat island effect during both day and night. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the composite thermally induced pavement structure of the present invention;

[0021] Figure 2 This is a schematic diagram of the indoor simulated lighting experiment in Embodiment 2 of the present invention;

[0022] Figure 3 Figure 2 shows the temperature change over time during the irradiation experiment in Embodiment 2 of the present invention. Figure (a) shows the temperature change over time after heating at 0 cm for 4 hours; Figure (b) shows the temperature change over time after heating at 2 cm for 4 hours; Figure (c) shows the temperature change over time after heating at 5 cm for 4 hours; and Figure (d) shows the temperature change over time after heating at 10 cm for 4 hours.

[0023] In the figure: 1. Gradient thermal conduction layer one; 2. Gradient thermal conduction layer two; 3. Gradient thermal conduction layer three; 4. Carbon fiber bundle; 5. Ordinary asphalt; 6. Iodine tungsten lamp; 7. Support; 8. Insulation box; 9. Temperature monitoring instrument; 10. Specimen; I. Upper gradient thermal conduction structure; II. Lower transverse heat dissipation structure. Detailed Implementation

[0024] The method of the present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0025] The steel slag used in this embodiment is the original steel slag from Meishan Steel Slag Processing Co., Ltd., with a particle size of 4.75mm~13.2mm. The chemical composition of the steel slag is shown in Table 1 below:

[0026] Table 1 Chemical composition of steel slag

[0027]

[0028] The parameters of carbon fiber are shown in Table 2 below:

[0029] Table 2 Performance parameters of carbon fiber

[0030]

[0031] Ordinary asphalt mixture: basalt coarse and fine aggregates, mineral powder, and SBS modified asphalt. AC-13.

[0032] Example 1

[0033] A steel slag gradient thermally induced pavement structure based on carbon fiber lateral heat transfer, such as Figure 1 As shown, the pavement structure is divided into two parts: an upper gradient heat conduction structure I and a lower transverse heat dissipation structure II. The upper gradient heat conduction structure I consists of three steel slag asphalt mixture layers with different steel slag contents: gradient heat conduction layer 1, gradient heat conduction layer 2, and gradient heat conduction layer 3. The lower transverse heat dissipation structure II is a combination structure in which carbon fiber bundles are horizontally embedded in ordinary asphalt mixture. The three layers of the upper gradient heat conduction structure I—gradient heat conduction layer 1, gradient heat conduction layer 2, and gradient heat conduction layer 3—are made by replacing the coarse aggregate (4.75mm~13.2mm) in the ordinary asphalt mixture with steel slag in different proportions. Gradient heat conduction layer 1 is 1cm thick with a steel slag content of 20 wt%; gradient heat conduction layer 2 is 2cm thick with a steel slag content of 40 wt%; and gradient heat conduction layer 3 is 3cm thick with a steel slag content of 50 wt%. In the lower transverse heat dissipation structure II, the carbon fiber bundles are located at the center of the structure. The carbon fiber bundles have a diameter of 10mm and extend to the edge of the lower transverse heat dissipation structure II. The thickness of the lower transverse heat dissipation structure II is 50mm. The carbon fiber bundles are inserted into the lower transverse heat dissipation structure II by pre-reserving a 10mm hole in the center during the asphalt mixture paving. After the lower structure is formed, the gradient heat conduction layer 1, gradient heat conduction layer 2, and gradient heat conduction layer 3 of the upper gradient heat conduction structure I are laid in sequence.

[0034] Example 2

[0035] Similar to Example 1, the difference lies in that this example presents a steel slag gradient thermally induced pavement structure based on carbon fiber transverse heat transfer. The upper gradient heat conduction structure I consists of three layers: gradient heat conduction layer 1, gradient heat conduction layer 2, and gradient heat conduction layer 3. These layers are constructed by replacing a portion of the coarse aggregate (4.75mm~13.2mm) in the asphalt mixture with steel slag in different proportions. Gradient heat conduction layer 1 has a thickness of 2cm and a steel slag content of 0%; gradient heat conduction layer 2 has a thickness of 3cm and a steel slag content of 40%; and gradient heat conduction layer 3 has a thickness of 5cm and a steel slag content of 50%. In the lower transverse heat dissipation structure II, the carbon fiber bundle is located at the center of the structure, with a diameter of 15mm, and the thickness of the lower transverse heat dissipation structure II is 50mm. The lower transverse heat dissipation structure II is incorporating carbon fibers when the asphalt mixture is laid to half its thickness. After the other half is laid and compacted, the upper gradient heat conduction structure I is laid and compacted in sequence, consisting of gradient heat conduction layer 1, gradient heat conduction layer 2, and gradient heat conduction layer 3.

[0036] To verify the effectiveness of the structure, an indoor irradiation experiment was conducted. Temperature changes of the pavement structure and ordinary pavement at depths of 0cm, 2cm, 5cm, and 10cm over 4 hours were measured and output. The indoor irradiation experiment setup is shown below. Figure 2 ,

[0037] The specific experimental steps are as follows:

[0038] (1) Assemble the test device: Place the experimental group and the control group specimens 10 into the heat-insulating box 8 with heat insulation board at the bottom (the sides are made of polystyrene foam board and the top is open to receive heat source) from left to right, and fix the thermocouples in the corresponding positions of the specimens.

[0039] (2) Determine the initial temperature: Adjust the vertical distance between the iodine tungsten lamp 6 and the surface of the two sets of specimens to 45cm (the iodine tungsten lamp 6 is fixed in position by the bracket 7) to ensure that the iodine tungsten lamp 6 illuminates the heat source receiving surface evenly. Use an infrared thermometer and a temperature monitoring instrument 9 to test the temperature of each point that needs to be tested. Test each group 4 times and take the average value as the average temperature of each point to control it at 25℃.

[0040] (3) Illumination experiment: Turn on the iodine tungsten lamp 6, output the temperature inside and bottom of the specimen every 15 minutes using the temperature monitoring instrument 9, and use an infrared thermometer to measure the temperature of the specimen surface at the corresponding time point.

[0041] The irradiation result curve is shown below. Figure 3It can be seen that this structure, compared to ordinary pavement, effectively induces a gradient of heat in the upper structure, accelerating heat transfer downwards and reducing the internal temperature of the pavement during the heat absorption period. The temperature decreased by 1.2℃, 1.3℃, 1.1℃, and 0.1℃ at positions of 0cm, 2cm, 5cm, and 10cm, respectively. Furthermore, the lower carbon fiber heat dissipation structure effectively dissipates heat from the pavement's interior to the outside, preventing a significant increase in temperature below.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. However, the present invention is not limited to the above examples, which are merely conventional structures selected based on these principles and should not be construed as patent protection guidelines. Any modifications and improvements made within the spirit and principles of the present invention should be within the scope of protection of the present invention.

Claims

1. A steel slag gradient thermally induced pavement structure based on carbon fiber transverse heat transfer, characterized in that, The system includes an upper gradient heat conduction structure and a lower transverse heat dissipation structure. The upper gradient heat conduction structure comprises three layers of asphalt mixture with different types of steel slag replacing coarse aggregate. The thermal conductivity of the asphalt mixture with different types of steel slag replacing coarse aggregate is higher than that of ordinary asphalt mixture. From top to bottom, these are gradient heat conduction layer one, gradient heat conduction layer two, and gradient heat conduction layer three. In gradient heat conduction layer one, the amount of steel slag is 0% to 30% of the coarse aggregate; in gradient heat conduction layer two, the amount of steel slag is 30% to 40% of the coarse aggregate. The steel slag content in the gradient thermal conductivity layer three is 40%~50% of the coarse aggregate. The thickness of the gradient thermal conductivity layer one, gradient thermal conductivity layer two, and gradient thermal conductivity layer three increases sequentially, with the thermal conductivity of the upper layer being less than that of the lower layer. Furthermore, the lower transverse heat dissipation structure is a composite structure layer of asphalt mixture with transversely embedded carbon fibers. The carbon fibers are long bundles of carbon fibers with a much higher axial thermal conductivity than ordinary asphalt mixtures, which are then cut to obtain carbon fiber bundles. The axial / radial thermal conductivity ratio of the carbon fibers is 10~15. The particle size of the coarse aggregate is 4.75~13.2 mm, and the particle size of the steel slag is 4.75~13.2 mm.

2. The steel slag gradient thermally induced pavement structure based on carbon fiber transverse heat transfer according to claim 1, characterized in that, The horizontally embedded carbon fiber in the lower transverse heat dissipation structure is located at the lateral center of the asphalt mixture composite structure layer, and the carbon fiber and asphalt mixture are fully bonded at the interface. The overall thickness of the lower structure is 50 mm.

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