A hot-mix asphalt concrete thin-layer paving construction process

Abstract

The present application relates to a kind of instant asphalt concrete thin layer paving construction process, by being hung instant heater on paver, thin layer paving asphalt mixture is heated again, while the contact area of new and old paving layer is heated instantaneously, on the one hand, the cooling rate of thin layer paving asphalt mixture is delayed, more compaction operation window time is sought;On the other hand, new and old paving layer forms thermal contact, generates more solid hot melt bonding, replaces the traditional interlayer poor cold-hot contact bonding mode.Compared with prior art, the present application has the advantages of reducing engineering cost, low heating energy consumption, good construction quality and easy to use, can further promote the popularization and application of hot mix asphalt mixture thin layer paving technology in road construction.

Description

Technical Field

[0001] This invention belongs to the field of road engineering technology, and in particular relates to a construction process for instant-heating asphalt concrete thin-layer paving. Background Technology

[0002] With increasing pressure from resource scarcity and environmental degradation, sustainable development faces severe challenges. To actively build a resource-saving and environmentally friendly society, the Ministry of Transport is vigorously promoting the construction of "green highways" nationwide, calling for a comprehensive improvement in highway construction standards by controlling resource consumption, reducing energy consumption, and lowering emissions. It also emphasizes a focus on life-cycle costs and a strong emphasis on both construction and maintenance. Given the large and continuously increasing mileage of newly built and maintained highways in my country, reducing engineering costs and the consumption of resources such as natural stone and petroleum asphalt has become a long-standing and urgent issue in the road engineering field. Reducing the thickness of asphalt pavement will become a future trend in the road industry.

[0003] Compared to the traditional 4cm thick asphalt anti-skid wear layer, thin-layer paving is only 1-2.5cm thick, saving 40%-70% in material costs and significantly reducing construction costs. Furthermore, because thin-layer paving can partially replace the function of the traditional asphalt anti-skid wear layer, it can restore the smoothness and driving comfort of the old road surface and extend its service life. Therefore, thin-layer paving technology is increasingly being used. It can be used for the surface layer construction of new roads, as well as for the repair of micro-cracks in various preventative maintenance projects. It is particularly suitable for major and medium-sized repairs of asphalt pavements, serving as a cost-effective and efficient means of restoring the appearance and smoothness of road surfaces.

[0004] However, due to the limited heat resistance of asphalt materials, asphalt concrete can only be mixed and heated to 160–180℃, with a heat capacity of approximately 837–921 J / (kg·℃). The thickness of a thin pavement layer is only 1–2.5 cm. Therefore, relative to ambient temperature, the heat reserve for thin pavement layer construction is only 20–50 kJ / m². 2Thin-layer pavement, with its small thickness and weak insulation, is subject to rapid heat loss in both directions—towards the air and the existing pavement—due to factors such as ambient temperature, wind, and heat conduction from the underlying layer. Its temperature drops much faster than that of thicker pavement. Furthermore, the rapid temperature drop of thin asphalt concrete layers causes the asphalt viscosity to increase rapidly with decreasing temperature, leading to a faster loss of fluidity and a shorter compaction window. This increases the demands on construction organization and compaction speed. In practice, current thin-layer pavement can only be carried out in the height of summer and under precise organizational conditions; otherwise, it is difficult to achieve compaction and ensure construction quality. Additionally, the temperature difference of over 100°C between the newly laid, hot layer and the cooler underlying layer means that even with continuous heat transfer from the new layer to the underlying layer, the temperature rise of the underlying layer is limited and insufficient to achieve heat fusion at the contact surface. Therefore, the problem of "cold" bonding between the new and old pavement layers has been a long-standing issue, resulting in lower strength. Compared to ordinary asphalt layers, hot-mix asphalt thin layers have a reduced thickness, less overall heat reserve, and faster cooling. The problem of "cold" bonding between new and old pavement layers is more prominent. The interlayer contact surface cannot form a good bond, which easily leads to structural layer separation. In practice, this manifests as pavement defects such as particle shedding and peeling.

[0005] In summary, asphalt concrete thin-layer pavement technology has the advantage of low cost and is gradually becoming a future trend in road construction and maintenance technology, and its use will increase. However, it also has technical difficulties such as rapid temperature drop, short compaction window time, and poor interlayer adhesion. In practice, serious defects such as particle shedding and peeling have occurred, limiting the widespread application of thin-layer pavement.

[0006] For the problems existing in the above-mentioned thin-layer paving of concrete, existing technologies have proposed corresponding solutions:

[0007] (1) Strengthen interlayer adhesion – prevent peeling

[0008] To address the adhesion problem between thin-layer asphalt concrete pavement and existing road surfaces, spraying an asphalt bonding layer is commonly used both domestically and internationally to prevent peeling of the overlay material. Current relatively mature technologies and standards provide recommended values ​​for the type and dosage of bonding layer materials. For example, AASHTO specifies the use of slow-setting emulsified asphalt as the bonding layer; France typically uses fast-setting cationic emulsified asphalt; Japan uses rubber-modified emulsified asphalt as the bonding layer for large-pore drainage pavements; and the most widely used thin-layer overlay technology, NovaChip, uses high-viscosity modified emulsified asphalt (NovaBond) to serve as both a seal and a bonding layer, with a typical application rate of 0.6–1.4 L / m². 2Furthermore, my country's research and published patents in this area focus more on developing stronger asphalt tack coats and determining the optimal application rate for different working conditions and new and old surface materials. However, a universal, scientific, and effective tack coat design method has not yet been formed. In various physical engineering projects, the specific dosage is usually determined by combining on-site paving test sections with relevant indoor and outdoor tests, and the selection of tack coat materials is generally limited to different types of modified emulsified asphalt.

[0009] In practical use, emulsified asphalt requires a certain amount of time to demulsify. Excessive waiting time significantly reduces construction efficiency. To meet the requirements of construction speed and schedule, many existing projects use synchronous paving equipment (such as the Novapaver type) to immediately spread hot-mix asphalt mixture on the freshly spread bonding layer and compact it. This causes the water generated after the emulsified asphalt demulsifies to accumulate between layers and cannot be discharged in time or there is insufficient evaporation, which creates hidden dangers for interlayer bonding failure. As a result, early peeling still occurs after the project is opened to traffic.

[0010] (2) Use high-viscosity asphalt binder – to prevent particle loss

[0011] Asphalt concrete thin-layer pavement, as a surface wearing course, is most significantly affected by factors such as climate and vehicle load. Under the influence of various external forces such as solar radiation, rainwater erosion, and tire wear, the surface layer should possess excellent long-term properties such as skid resistance, rutting resistance, abrasion resistance, and noise reduction. Therefore, current overlay materials increasingly employ discontinuous gradation (such as SMA type) or open-graded large-pore asphalt mixtures (such as OGFC type), with a high proportion of coarse aggregate. This simultaneously meets the requirements of large pavement texture depth, strong surface drainage capacity, and easy evaporation of moisture from the emulsified asphalt binder. Furthermore, due to the limitations of pavement thickness, high-viscosity modified asphalt is widely used as a binder to enhance the coarse aggregate skeleton's adhesion and prevent structural separation and loosening. For example, the NovaChip ultra-thin wearing course technology, combined with NovaBinder modified asphalt, possesses exceptionally strong adhesion and anti-aging properties, meeting the binder performance requirements of AASHTO MP1, ASTM D6084, and SUPERPAVE, reducing the problem of early aggregate loss under various influences. In my country, most engineering projects use a combination of polymer additives or anti-stripping agents to prepare high-viscosity asphalt binders by adding various polymer additives or anti-stripping agents to road petroleum asphalt, ordinary rubber-modified asphalt, or SBS-modified asphalt.

[0012] The use of high-viscosity asphalt has alleviated the problem of particle shedding in thin-layer paving to some extent, but it has significantly increased the project cost. Furthermore, the rapid temperature drop of the thin-layer mixture has exacerbated the problem of high-viscosity asphalt mixture being difficult to compact.

[0013] (3) Other means

[0014] Preheating the road surface can extend the paving and compaction time of the thin layer to a certain extent. Existing technology has applied road surface heating to the construction of asphalt thin layer overlays. There is still a certain temperature difference between the heating temperature of the old road surface and the newly mixed asphalt. Moreover, the heating process and the paving process are carried out asynchronously. That is, according to the target heating temperature, the original road surface is first heated in one or more stages using road surface heating equipment, and then the paver spreads the bonding layer asphalt and lays the hot-mixed asphalt.

[0015] Currently, the main methods for heating asphalt pavement include hot air circulation heating, infrared radiation heating, and microwave heating. Considering the heating efficiency of the equipment and the potential for asphalt aging due to prolonged heating, multiple devices are needed to achieve multi-stage heating to reach the target temperature. This results in a working efficiency far lower than that of a paver. In actual construction operations, the heating equipment also needs to maintain a certain distance from the paver to allow sufficient space for material trucks to load materials. This leads to a significant loss of heat and waste of resources, and the modification of existing equipment is quite difficult.

[0016] Therefore, there is an urgent need to provide a construction process that can improve efficiency and provide instant heating for asphalt pavement. Summary of the Invention

[0017] The purpose of this invention is to overcome the shortcomings of the existing technology by providing an instant-heating asphalt concrete thin-layer pavement construction process. By heating the asphalt mixture and road surface of the thin-layer pavement, the cooling rate of the asphalt mixture is slowed down, allowing for more time for compaction. Furthermore, thermal contact is formed between the new and old pavement layers, resulting in a stronger heat-melt bond, replacing the traditional method of poor interlayer bonding due to cold-heat contact.

[0018] The objective of this invention can be achieved through the following technical solutions:

[0019] This invention provides a construction process for instant-heating asphalt concrete thin-layer paving, comprising the following steps:

[0020] S1: Construction Preparation

[0021] S1-1 Prepare asphalt mixture suitable for thin-layer paving construction;

[0022] S1-2 analyzes and evaluates the surface condition of the original pavement or underlying layer;

[0023] S1-3 Prepare construction equipment and attach an instant heater to the asphalt paver;

[0024] Based on the analysis and evaluation results in S1-2, and combined with the project requirements, site climate and environmental conditions, S1-4 proposes a preliminary construction plan, conducts test section paving according to the preliminary construction plan, and performs quality testing. Based on the test results, the preliminary construction plan is adjusted to determine the final construction plan.

[0025] S2: On-site construction:

[0026] S2-1 is based on the thin-layer pavement thickness designed in the final construction plan in S1, adjusting the proportions of aggregates, fillers and modified asphalt in the mixture, calibrating and adjusting the mixing plant, controlling the heating temperature of modified asphalt and aggregates, and the asphalt mixture's outlet temperature.

[0027] S2-2 uses dump trucks to transport the asphalt mixture and tests the temperature of the asphalt mixture at the factory and upon arrival at the site.

[0028] S2-3 uses a paver with an instant heater for paving operations, simultaneously heating the original road surface or underlying layer and secondary heating and paving of the thin-layer asphalt mixture;

[0029] S2-4 uses a road roller to compact the working surface after paving;

[0030] S2-5 conducts inspection and acceptance of the construction section based on the characteristics of thin-layer pavement and road performance, combined with the acceptance standards for asphalt concrete pavement.

[0031] After the final compaction of S2-6 is completed, traffic can be opened once the road surface has cooled to below 50°C.

[0032] Further, in S1-1, the asphalt mixture is a hot-mix asphalt mixture, and the raw materials of the asphalt mixture include coarse aggregate, fine aggregate, filler, asphalt or modified asphalt, and wood, mineral or polyester fiber; the mixing temperature of the asphalt mixture is 160-180℃; and the thickness of the thin-layer paving is 1.0-2.5cm.

[0033] Furthermore, in S1-2, specifically: the analysis and evaluation of the original pavement or underlying layer surface condition includes disease analysis, condition evaluation, and evaluation of the residual asphalt condition on the pavement surface;

[0034] The evaluation of the residual asphalt condition on the road surface includes the following steps:

[0035] S1-2-1 Selecting Sampling Points: Multiple random sampling points are taken for the construction section. The sampling frequency is selected according to the area of ​​the road section, with no less than 5 points per kilometer. The sampling point locations include the middle of the driving lane, the wheel track, the shoulder, and the intersection of adjacent lanes.

[0036] S1-2-2 Sampling: After simple cleaning of the original road surface, removing obvious debris and blowing away dust, take a picture of the clean and dry original road surface;

[0037] S1-2-3 Assessment: Using image analysis software, the surface condition of the original pavement is assessed, with the percentage of exposed aggregate area as the indicator. The assessment values ​​at various points on the original pavement are simply averaged to obtain the assessment value of the percentage of exposed aggregate area. Based on the assessment results, corresponding treatment methods for applying a tack coat to the original pavement are proposed. Furthermore, the specific treatment methods are as follows: a high percentage of exposed aggregate area indicates less residual asphalt, and more tack coat asphalt should be applied; a low percentage of exposed aggregate area indicates more residual asphalt, and less or no tack coat asphalt should be applied. Compared with traditional construction methods, this significantly saves material usage.

[0038] Furthermore, in S1-3, the instant heater is a splicable strip-shaped instant heater; even further, the length of a single instant heater is 1m or 2m, and it adopts an extendable splicing design. According to the actual paving operation width, when the instant heater is installed and hung, the corresponding number of instant heaters are installed to meet the road surface heating requirements of the corresponding width.

[0039] The instant heater is installed between the auger spreader and the rear wheel baffle of the track of the asphalt paver. The instant heater is equipped with a heating control system to heat the thin-layer asphalt mixture and the original road surface or underlying layer.

[0040] Furthermore, in S2-1, the heating temperature of the modified asphalt is 160-170℃, the heating temperature of the aggregate is 180-190℃, and the discharge temperature of the mixture is 165-175℃.

[0041] Furthermore, in S2-2, the dump truck is a clean dump truck with a metal floor, an insulation layer around the truck body, and a covering layer on the top of the truck body.

[0042] Temperature is monitored using a thermometer to ensure that the discharge temperature of the mixture meets the requirement of 165-175℃ and the arrival temperature is not lower than 150℃.

[0043] Furthermore, in S2-3, the screed and instant heater need to be preheated before paving, and the receiving hopper and screw feeder need to be coated with anti-sticking agent. The paving temperature is 160℃~170℃.

[0044] In S2-3, the heating of the original road surface or underlying layer specifically refers to: the instant heating temperature of the area where the original road surface or underlying layer and the thin-layer hot-mix asphalt mixture are about to come into contact reaches 120-180℃, so as to melt the residual or spread tack coat asphalt on the road surface and improve the interlayer bonding strength; to ensure the "welding" bond between the layers and prevent typical thin-layer pavement defects such as peeling; furthermore, the area about to come into contact is: since the instant heater is installed in front of the auger, when the paver moves forward, the instant heater first heats the currently passed original road surface (or underlying layer), and then the thin-layer hot-mix asphalt mixture slides down the slope of the instant heater through the auger and is spread on the just-heated original road surface area (or underlying layer); the original road surface heating area below the instant heater at any time during the paving operation is called the area about to come into contact; the instant heating temperature is: the heating temperature of the area about to come into contact by the instant heater is called the instant heating temperature;

[0045] In S2-3, the secondary heating of the thin-layer asphalt mixture is specifically as follows: the mixture is heated again to 160-180℃ during the process of sliding down the slope of the instant heater, which prolongs the compaction window time of the thin-layer pavement and effectively ensures the compaction density of the thin-layer pavement under the low temperature conditions of spring and autumn.

[0046] Furthermore, in S2-4, during compaction, the roller first compacts the new paved layer by 15cm, then gradually shifts diagonally to avoid the new paved layer and compacts it together with the newly paved mixture, and then switches to longitudinal compaction to make it smooth and compact.

[0047] The longitudinal joints are treated as vertical joints, and the uncompacted mixture at the joints is removed by milling. The transverse joints are treated as vertical flat joints, and the ends are cut off vertically along the road centerline.

[0048] Furthermore, in S2-5, the acceptance process needs to meet the following conditions:

[0049] The surface of S2-5-1 road is flat and uniform, with no oil seepage, looseness, cracks and obvious segregation.

[0050] S2-5-2 The longitudinal joints should be tight and smooth. If an emulsified asphalt bonding layer is set, the emulsified asphalt bonding layer should not be sprayed in an overlapping manner.

[0051] S2-5-3 thin-layer paving should be closely connected to the curb and other structures, and there should be no water accumulation or leakage.

[0052] The S2-5-4 measured quality control standards include: thickness, compaction, flatness, permeability coefficient, friction coefficient, and structural depth.

[0053] S2-5-5 Bond strength between new and old surface layers: Through core sampling, pull-out and shear tests are performed on the core samples. The pull-out strength should be greater than 0.7 MPa and the shear strength should be greater than 1.0 MPa.

[0054] Furthermore, the heating control system has two operating modes: manual control mode and automatic control mode, to adapt to different construction conditions, specifically:

[0055] In manual control mode, the operator can manually set the current power P of the instant heater on the control panel and make manual adjustments at any time; in manual control mode, the instant heater generates heat according to the set power.

[0056] The automatic control mode offers mode options suitable for various operation types. Operators can set the automatic operation mode according to construction needs, and can also set various operating parameters, including the system reference paving speed V, heating power P and various temperature feedback parameters, so as to perform real-time calculation and adjustment and realize the synchronous linkage between the instant heater and the thin-layer paving operation.

[0057] Compared with the prior art, the present invention has the following advantages:

[0058] 1. This invention slows down the cooling rate of thin-layer asphalt mixtures by subjecting them to secondary heating on-site, thereby allowing for more time for compaction.

[0059] 2. This invention heats the contact area between the new and old paving layers in real time, so that the new and old paving layers form a thermal contact and generate a stronger hot melt bond, which replaces the traditional bonding method with poor interlayer cold and hot contact.

[0060] 3. This invention has the advantages of reducing engineering costs, low heating energy consumption, good construction quality, and convenient use, which can further promote the application of hot-mix asphalt thin-layer paving technology in road construction. Attached Figure Description

[0061] Figure 1 This is a schematic diagram showing the movement direction of the thin-layer asphalt mixture in Example 1;

[0062] Figure 2 This is a schematic diagram showing the movement direction of the thin-layer asphalt mixture in Example 1 (i.e., a local view of the heat exchanger);

[0063] Figure 3 This is a schematic diagram of the temperature distribution at the contact tip between the thin-layer paving and the underlying layer in Example 1;

[0064] Figure 4 This is a schematic diagram of the appearance of the smooth arc-shaped instantaneous heater in Example 1;

[0065] Figure 5This is a schematic diagram of the appearance of the arc-shaped pleated instantaneous heater in Example 1;

[0066] Figure 6 This is a schematic diagram of the appearance of the sloping smooth instantaneous heater in Example 1;

[0067] Figure 7 This is a schematic diagram of the appearance of the inclined pleated instantaneous heater in Example 1;

[0068] Figure 8 This is a schematic diagram of the instant heater control logic and control panel in Example 1;

[0069] Figure 9 A flowchart of a construction process for instant-heating asphalt concrete thin-layer paving.

[0070] Figure 10 This is a schematic diagram showing that the original road surface aggregate exposed area is estimated to be 50% in Example 1;

[0071] Figure 11 This is a schematic diagram showing that the original road surface aggregate exposed area is evaluated as 0% in Example 1.

[0072] Figure 1 Explanation of Chinese markings:

[0073] 1-Cab, 2-Hopper, 3-Crawler, 4-Spiral transverse spreader, 5-Screw, 6-Thin-layer asphalt mixture, 7-Old pavement layer or underlying layer, 8-Instant heater, 9-Secondary heating surface of thin-layer asphalt mixture, 10-Thin-layer loose pavement layer to be compacted;

[0074] Figure 2 Explanation of Chinese markings:

[0075] 9-Secondary heating surface of thin-layer asphalt mixture; 11-Heating surface of old pavement layer or underlying layer;

[0076] Figure 3 Explanation of Chinese markings:

[0077] 6. Thin-layer asphalt mixture for paving; 7. Old paving layer or underlying layer;

[0078] Figure 4 Explanation of Chinese markings:

[0079] 12-Suspension fixing point, 13-Cavity, 14-Heat source, 15-Spring rod, 16-Smooth curved sidewall;

[0080] Figure 5 Explanation of Chinese markings:

[0081] 17-Arc-shaped pleated sidewall;

[0082] Figure 6 Explanation of Chinese markings:

[0083] 18-Sloping smooth sidewall;

[0084] Figure 7 Explanation of Chinese markings:

[0085] 19- Sloping pleated sidewall. Detailed Implementation

[0086] The following examples illustrate specific implementations of the present invention. These examples are carried out based on the solution described in the present invention, and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following examples.

[0087] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0088] Example 1

[0089] The principles of the construction process of this invention are mainly in the following aspects:

[0090] (1) Principle of secondary heating. The mixing temperature of hot-mix asphalt mixture for thin-layer paving is about 160-180℃. During the transportation of vehicles to the construction site, some heat is lost, and further heat is lost after paving. The temperature at the beginning of the compaction operation is about 120-140℃. Because the thickness of the thin layer is only 1-2.5cm, the heat storage is less, the heat preservation is poor and the temperature drops quickly. Therefore, the temperature of the loose layer drops even faster, which can easily lead to construction quality problems such as insufficient compaction.

[0091] This invention involves attaching an instant heating device to a paver to reheat the hot-mix asphalt mixture for thin-layer paving, raising its temperature from 120-140°C back to 160-180°C, restoring it to the appropriate viscosity required for compaction, and simultaneously restoring its heat storage capacity to minimize its rate of temperature loss.

[0092] (2) Thermal bonding principle. For example... Figure 1 As shown, the paver includes a cab 1, a hopper 2, tracks 3, a auger transverse spreader 4, and a screed 5. The hopper 2 is filled with a thin-layer asphalt mixture 6. This invention adds an instant heater 8 to the paver. While heating the thin-layer asphalt mixture 9, the instant heater 8 simultaneously heats the surface of the old pavement layer or underlying layer 11, causing a new loose thin-layer pavement layer 10 to be compacted to be laid on top of the old pavement layer or underlying layer 7. As the paver moves forward, the heated adjacent interfaces rapidly contact and bond at high temperatures, such as... Figure 2 As shown, the new and old pavement layers form a stronger hot-melt bond, thereby improving the adhesion between the new and old asphalt pavement layers and preventing defects such as delamination during the service life of the road surface.

[0093] (3) Instant heating principle. The instant heating heater is installed in a special position on the asphalt paver, at the contact tip of two adjacent layers during construction. It heats both layers simultaneously. The heating power and temperature can be manually or automatically controlled to adapt to different paver speeds, preventing overheating when the paving speed is too slow or when the paver is stopped, and also preventing insufficient heating when the paving speed is too fast. Therefore, this heating method exhibits instant heating characteristics. As the paver moves forward, the two interfaces that have just been heated and rapidly heated quickly come into contact and bond, achieving convenient, flexible, efficient and inexpensive "instant heating and paving" operation.

[0094] (4) Low-energy and green principle. The instant heating equipment only heats the contact tips of two adjacent layers during the construction process. The heating range is small and the area is narrow, which greatly reduces energy consumption compared with traditional large-area road heating operations. Since the instant heater is surrounded by the upper and lower layers, the heating energy is absorbed by the two layers to the maximum extent when heating the two layers, and the heat loss is minimal, thus achieving a more effective heating effect.

[0095] This invention proposes adding an instant heater to a traditional asphalt paver to achieve reheating of thin-layer asphalt mixtures and instant heating of old pavement layers or underlying layers. The instant heater meets the following technical standards and has the following characteristics:

[0096] (1) Overview of instant heater. The instant heater is a high-power asphalt mixture and road surface heating device. It can be attached to engineering equipment such as asphalt pavers, road rollers, and graders to simultaneously heat various materials, road surfaces, or other structures on site, and assist in completing various construction projects such as low-temperature construction, road surface recycling, thin-layer paving, and maintenance.

[0097] The instant heater can be equipped with various heat sources, such as PTC electric heaters, natural gas or gasoline / diesel burners, laser heaters, and far-infrared heaters, with a heating power of 0.1 to 100 kW per meter, achieving a rapid heating effect.

[0098] The instant heaters are strip-shaped and adjustable, with individual heaters being 1m or 2m in length. They feature an extendable splicing design, allowing for the installation of an appropriate number of heaters based on the actual paving width to meet the heating needs of the corresponding road surface. For example... Figure 4 As shown, the instant heater includes a suspension fixing point 12, a cavity 13, a heat source 14, a spring rod 15, and side walls. The overall cross-section of the instant heater is trapezoidal, narrower at the top and wider at the bottom, with an open bottom surface, which facilitates heat conduction, convection, and radiation to the road surface or underlying layers. The top surface of the instant heater is equipped with a suspension fixing point for easy hanging or fixing on various construction machinery.

[0099] The trapezoidal cross-section has metal sidewalls with good thermal conductivity, such as steel, aluminum, or alloys. One side contacts the thin layer of asphalt mixture to complete heat conduction and heating, while the other side is left empty for later use.

[0100] (2) Installation location and size requirements of the instant heater. In this invention, the instant heater is installed in the gap between the auger spreader and the rear wheel baffle of the asphalt paver. The width of this gap is generally 1m and the height is about 50 to 80cm. Therefore, the cross-section of the instant heater does not exceed this size range.

[0101] Since the maximum width of asphalt paving operations can reach 12m, the instant heater adopts an extendable splicing design, with 1m or 2m as the unit length of the instant heater, which can be spliced ​​to extend or shorten the use according to actual needs.

[0102] (3) Heating method, heat source, and power. The instant heater cavity can be equipped with or switch between multiple heat sources, such as PTC electric heaters, natural gas or gasoline / diesel burners, laser heaters, and far-infrared heaters. The heating power varies from approximately 0.1 to 100 kW per linear meter, achieving a rapid heating effect. The instant heater obtains energy from a mobile power source, generator, or fuel tank to generate heat, which is then transferred in two directions: to the thin-layer asphalt mixture and the road surface. Figure 3 As shown. The sidewall of the instant heater is in direct contact with the thin layer of asphalt mixture, and heating mainly relies on contact heat conduction. To improve heating efficiency, increasing the contact area is the most effective method. Therefore, the side of the instant heater is designed with a slope or arc surface, and pleats parallel to the downward direction are added to further increase the contact area, such as... Figures 4-7 The image shows various appearance forms of instant heaters, specifically: Figure 4 It is a 16-inch instant heater with a smooth, curved sidewall. Figure 5 The instant heater has a curved, pleated sidewall. Figure 6 The instant heater has a sloping, smooth sidewall. Figure 7 The instantaneous heater has a sloping, pleated sidewall.

[0103] To improve the flexibility and adaptability of the instant heater in the construction site, its two sides adopt the same symmetrical design. In case of emergency such as breakage, deformation, or excessive wear on one side, the other side can be used to continue construction.

[0104] (4) Heating control. The instant heater is equipped with a heating control system, which can control the operation of the instant heater manually or automatically.

[0105] ① Operational status monitoring

[0106] Through various sensors installed inside the instantaneous heater and on the paver, the instantaneous heater operation status monitoring system mainly monitors and displays the following data in real time, so that technicians can understand the current construction status and make appropriate adjustments in a timely manner:

[0107] A. The forward speed V of the paver;

[0108] B. Current power P of the instantaneous heater;

[0109] C. Instantaneous heater temperature T heater ;

[0110] D. Temperature T of thin-layer asphalt mixture HMA ;

[0111] E. Instantaneous heater sidewall heating temperature T wall ;

[0112] F. Road surface (underlying layer) temperature T road ;

[0113] ② Heating control mode

[0114] The instant heater has both manual and automatic heating control modes to adapt to different construction conditions:

[0115] In manual mode, operators can manually set the instant heater's current power P on the control panel and make manual adjustments at any time. In this mode, the instant heater generates heat according to the set power, and operators must closely monitor all operating parameters.

[0116] The automatic mode offers mode options suitable for various operation types. Operators can set the automatic operation mode according to construction needs, or set various specific operating parameters. The system refers to the paving speed V, heating power P and various temperature feedback parameters to perform real-time calculations and adjustments, so as to realize the synchronous linkage between the instant heater and the thin-layer paving operation.

[0117] A corresponding control system was designed for the instant heater heating control mode, and its control logic and control panel are as follows: Figure 8 As shown.

[0118] This embodiment provides a construction process for instant-heating asphalt concrete thin-layer paving, such as... Figure 9 As shown, it includes the following steps:

[0119] S1: Construction Preparation

[0120] S1-1 Preparation of thin-layer asphalt mixture. The thin-layer paving material is a hot-mix asphalt mixture, and the raw materials include coarse aggregate, fine aggregate, filler, asphalt or modified asphalt, and wood, mineral, or polyester fibers. In order to ensure the integrity of the thin-layer paving during its service life and prevent pavement distresses such as particle shedding, loosening, and peeling, high-viscosity asphalt is used to increase the cohesion of the mixture.

[0121] To accommodate the construction needs of thin-layer paving, the gradation of the asphalt mixture can be appropriately adjusted. The thickness of the thin-layer paving layer should not be less than 2.5 to 3 times the maximum aggregate size, in order to avoid problems such as segregation during the paving process and insufficient compaction during the compaction process.

[0122] To meet the skid resistance and safety requirements of thin-layer pavement, continuous dense mix, semi-open or open gradation, and discontinuous gradation are adopted to ensure the depth of surface texture of the pavement layer. The specific adjustment scheme is determined based on the on-site test results after the test section is paved.

[0123] The mixing temperature of hot-mix asphalt mixtures for thin-layer paving should be at least 160-180℃. In spring and autumn when the temperature is low, the mixing temperature can be appropriately increased to ensure that the appropriate temperature is maintained during the on-site paving and compaction process.

[0124] Other construction preparations can be found in the "Technical Specification for Construction of Asphalt Pavement on Highways" JTJ F40.

[0125] S1-2 Evaluation of the original road surface or underlying layer. First, the original road surface or underlying layer is treated, removing larger debris, mud, oil stains from repairs, etc., and sweeping other garbage away from the curb. Then, a wind-powered fire extinguisher is used to blow away surface dust, resulting in a clean and dry original road surface or underlying layer. Before thin-layer paving, the original road surface or underlying layer is analyzed and evaluated as follows:

[0126] Thin-layer overlay maintenance on the existing pavement. For this maintenance project, in addition to analyzing and evaluating the condition of the original pavement, the residual asphalt condition on the surface should be evaluated to determine whether it is necessary to apply a tack coat to enhance interlayer adhesion during hot-applied construction. The evaluation method is briefly described below:

[0127] S1-2-1 Selecting Sampling Points. Multiple random sampling points shall be used for the construction section. The sampling frequency shall be selected according to the area of ​​the road section, with no less than 5 points per kilometer. The sampling point locations include, but are not limited to, the middle of the driving lane, the wheel track, the shoulder, and the intersection of adjacent lanes.

[0128] S1-2-2 Sampling. After simple cleaning of the original road surface, removing obvious debris and blowing away dust, take photos of the clean and dry original road surface or make a subjective evaluation by direct visual inspection.

[0129] S1-2-3 Assessment. The surface condition of the original pavement is assessed using subjective evaluation methods or image analysis software, expressed as the percentage of exposed aggregate area (%). Figure 10 , Figure 11 As shown, specifically:

[0130] The evaluation values ​​at various points on the original road surface are simply averaged, as shown in the following formula, which represents the percentage of exposed aggregate area on the original road surface. Comparing this with Table 1, a recommendation can be made regarding whether the original road surface needs a tack coat.

[0131]

[0132] In the formula, S avg This is the percentage of exposed aggregate area on the original road surface;

[0133] S i These are the evaluation values ​​for each sampling point.

[0134] Table 1 Reference Table for Original Road Surface Treatment

[0135]

[0136] For newly constructed thin-layer pavements, the underlying layer is usually a freshly laid asphalt intermediate layer. Since traffic is not fully open and only a small number of construction and transport vehicles pass through, the surface aggregate is still completely covered by asphalt, meaning the underlying layer has approximately 100% residual asphalt. In special circumstances, such as long-term project suspension, temporary traffic opening, or natural disasters, the road surface needs to be assessed to determine the percentage of exposed underlying aggregate area, and measures should be taken according to the reference opinions in Table 1.

[0137] S1-3 Construction equipment and instant heaters are added. Construction equipment includes intermittent asphalt mixing plants, dump trucks, asphalt pavers, and road rollers, which can be referenced in the "Technical Specification for Construction of Highway Asphalt Pavement" JTJ F40.

[0138] Instantaneous heating thin-layer paving construction requires the asphalt paver to be equipped with an instant heater, connected to a mobile power supply and control circuit, to ensure the normal operation of the heating control system.

[0139] S1-4 Trial Paving and Final Construction Scheme. Based on project requirements, site climate and environmental conditions, and the evaluation results of the original pavement surface, a preliminary construction scheme was drafted. The preliminary construction scheme included the production, transportation organization, paving, compaction combination, and quality inspection of the thin-layer hot-mix asphalt concrete. According to the requirements of the "Technical Specification for Construction of Highway Asphalt Pavement" JTJ F40, an instant heater was added to the paver according to the preliminary construction scheme and installed and fixed, ensuring the normal operation of the relevant control system. A test section was paved and quality inspection was conducted. In addition to the testing items required by the specification, a field pull-out test was added to determine the bonding condition between the thin-layer pavement and the original pavement or underlying layer. Based on the field test results, the optimal parameters for thin-layer pavement paving construction were determined, including heating method, heating control mode, instant heater power, heating temperature of the original pavement (or underlying layer), paver forward speed, type and amount of emulsified asphalt, and loose paving coefficient. The preliminary construction scheme was adjusted to determine the final construction scheme.

[0140] S2: On-site construction:

[0141] The construction method for instant-heating thin-layer paving with a thickness of 1.0–2.5 cm includes the following steps:

[0142] S2-1 Mixture Mixing: First, based on the design thickness of the thin-layer pavement, determine the proportions of aggregates, fillers, and modified asphalt in the mixture, calibrate and adjust the mixing plant, and strictly control the heating temperatures of asphalt and aggregates as well as the discharge temperature of the asphalt mixture. The heating temperature of modified asphalt is 160-170℃, the aggregate temperature is 180-190℃, and the discharge temperature of the mixture is 165-175℃. If it exceeds 195℃, it should be discarded.

[0143] S2-2 Mixed Material Transportation: Clean dump trucks with metal bottoms and insulation layers around the cargo box shall be used to transport the mixed material. The top of the cargo box must be covered. The temperature of the mixed material leaving the site and arriving at the site shall be checked for each truck using a thermometer. The thermometer should be inserted to a depth of more than 150mm to ensure that the temperature of the mixed material leaving the site is between 165 and 175℃, which can be determined according to the air temperature and wind force on the construction day. The temperature arriving at the site shall not be lower than 150℃.

[0144] S2-3 Instantaneous Asphalt Mixture Paving: Paving operations are carried out using pavers equipped with instantaneous heaters. According to the final construction plan, the original road surface or underlying layer is heated simultaneously, and the thin-layer asphalt mixture is heated and paved in accordance with the corresponding heating temperature, power and heating control mode.

[0145] The instant heating temperature of the area where the original pavement or underlying layer and the thin-layer hot-mix asphalt mixture will come into contact should reach 120-180℃ to melt the residual or spread tack coat asphalt on the road surface, improve the interlayer bond strength, ensure a "welded" bond between layers, and prevent typical thin-layer pavement defects such as peeling. The area about to come into contact is defined as follows: Since the instant heater is installed in front of the auger transverse distributor, when the paver moves forward, the instant heater first heats the currently passing original pavement (or underlying layer), and then the thin-layer hot-mix asphalt mixture slides down the slope of the instant heater via the auger transverse distributor and is spread onto the newly heated original pavement area (or underlying layer). The area of ​​the original pavement heated below the instant heater at any given moment during paving is called the area about to come into contact; the instant heating temperature is the temperature at which the instant heater heats the area about to come into contact.

[0146] Preheat the screed and instant heater before paving. Apply anti-sticking agent to the hopper and screw feeder. The paving temperature is 160℃~170℃. Manually or automatically control the construction process based on the real-time temperature data displayed on the control panel by the temperature sensor to ensure that the paving temperature is greater than 140℃.

[0147] During paving, the material transport vehicle should stop 30-50cm in front of the paver, and must not collide with the paver. During unloading, the material transport vehicle should be in neutral and pushed forward by the paver. After unloading, the vehicle should leave quickly without lingering, and wait for the unloading vehicle to quickly retreat in front of the paver to unload, ensuring that there is always material in the paver's hopper during the paving process.

[0148] S2-4 Compaction: Compaction begins as soon as the mixture has a certain working surface after paving. When the road surface temperature is 130-165℃, use a steel-drum roller for 3-6 static passes; when the road surface temperature is 80-90℃, use a rubber-tired roller for 1-2 passes; final compaction is done by using a steel-drum roller for 1-2 static passes to finish the surface. The roller tire overlap width is 20cm, and the compaction speed is controlled at 2-3km / h. In addition, to avoid damage to the curb stones, a small double-drum vibratory roller is used for repeated compaction along the edge to ensure that compaction is completed within the corresponding road surface temperature range. If the temperature drops rapidly due to cold weather, and the road surface temperature is low, an instant heater can be attached to the front of the roller's steel drum for simultaneous heating and compaction.

[0149] During compaction, the longitudinal joints are treated as vertical joints, and the uncompacted mixture at the joints is removed by milling to ensure that the joints are flat, dense and firm. During paving, the joints are preheated with hot material, and after manual leveling, the roller is used for longitudinal compaction. In addition, the roller first compacts the new paved layer for 15cm, then gradually moves diagonally to miss the new paved layer and compacts it together with the newly paved mixture, and then switches to longitudinal compaction to make it smooth and dense.

[0150] The transverse joints are vertical flat joints, and the ends are cut off vertically with the road centerline. The joints are preheated with an instant heater during paving. After manual leveling, a small steel wheel roller is used for transverse compaction. During compaction, the roller first compacts the new paved layer for 15cm, then gradually moves diagonally to miss the new paved layer and compacts it together with the newly paved mixture. Then it is changed to longitudinal compaction to make it smooth and compact.

[0151] S2-5 Post-Construction Inspection: Based on the characteristics of thin-layer paving and road performance, and in accordance with my country's national acceptance standards for asphalt concrete pavements, the following acceptance standards are recommended:

[0152] The S2-5-1 surface should be smooth and uniform, free from oil seepage, looseness, cracks, and obvious segregation. For expressways and Class I highways, the sum of the areas with the above defects (for single cracks, the area should be calculated by multiplying the actual length by 0.2m width) should not exceed 0.03% of the inspected area; for other highway grades, it should not exceed 0.05%. Reflective cracks in semi-rigid base layers are not considered construction defects, but should be promptly grouted.

[0153] S2-5-2 The longitudinal joints should be tight and smooth. If an emulsified asphalt bonding layer is set, the emulsified asphalt bonding layer should not be sprayed in an overlapping manner.

[0154] S2-5-3 Thin-layer paving should be closely connected to curbs and other structures, and there should be no water accumulation or leakage.

[0155] The S2-5-4 measured quality control standards include: thickness, compaction, flatness, permeability coefficient, friction coefficient, and structural depth.

[0156] S2-5-5 Bond strength between new and old surface layers: Through core sampling, pull-out and shear tests are performed on the core samples. The pull-out strength should be greater than 0.7 MPa and the shear strength should be greater than 1.0 MPa.

[0157] S2-6: Open to traffic. After final compaction, traffic can be opened once the road surface has cooled to below 50°C.

[0158] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A construction process for instant-heating asphalt concrete thin-layer paving, characterized in that, Includes the following steps: S1: Construction Preparation S1-1 Prepare asphalt mixture suitable for thin-layer paving construction; the asphalt mixture is a hot-mix asphalt mixture, and the raw materials of the asphalt mixture include coarse aggregate, fine aggregate, filler, asphalt or modified asphalt, and wood or mineral or polyester fiber; the mixing temperature of the asphalt mixture is 160~180℃; the thickness of the thin-layer paving is 1.0~2.5cm. S1-2 analyzes and evaluates the surface condition of the original pavement or underlying layer; S1-3 Prepare construction equipment and attach an instant heater to the asphalt paver; the instant heater is a connectable strip-shaped instant heater; The instant heater is installed between the auger spreader and the rear wheel baffle of the track of the asphalt paver. The instant heater is equipped with a heating control system to heat the thin-layer asphalt mixture and the original road surface or underlying layer. Each instant heater is 1m or 2m long and features an extendable splicing design. Depending on the actual paving operation width, the corresponding number of instant heaters can be installed during installation to meet the road surface heating requirements of the corresponding width. Based on the analysis and evaluation results in S1-2, and combined with the project requirements, site climate and environmental conditions, S1-4 proposes a preliminary construction plan, conducts test section paving according to the preliminary construction plan, and performs quality testing. Based on the test results, the preliminary construction plan is adjusted to determine the final construction plan. S2: On-site construction: S2-1 is based on the thin-layer pavement thickness designed in the final construction plan in S1, adjusting the proportions of aggregates, fillers and modified asphalt in the mixture, calibrating and adjusting the mixing plant, controlling the heating temperature of modified asphalt and aggregates, and the asphalt mixture's outlet temperature. S2-2 uses dump trucks to transport the asphalt mixture and tests the temperature of the asphalt mixture at the factory and upon arrival at the site. S2-3 uses a paver with an instant heater for paving operations, simultaneously heating the original road surface or underlying layer and secondary heating and paving of the thin-layer asphalt mixture; Before paving, the screed and instant heater need to be preheated, and the receiving hopper and screw feeder should be coated with anti-sticking agent. The paving temperature is 160℃~170℃. The document sets indicators and standards for the heating temperature of the original pavement or underlying layer. Specifically, the immediate heating temperature of the area where the original pavement or underlying layer and the thin-layer hot-mix asphalt mixture are about to come into contact should reach 120~180℃ in order to melt the residual or spread tack coat asphalt on the road surface and improve the interlayer bonding strength. The secondary heating temperature of thin-layer asphalt mixture is specified and standardized. Specifically, the mixture should be heated to 160-180℃ during the process of sliding down the slope of the instant heater to extend the compaction window time of the thin-layer pavement. Under the low temperature conditions of spring and autumn, this effectively ensures the compaction density of the thin-layer pavement. S2-4 uses a road roller to compact the working surface after paving; S2-5 conducts inspection and acceptance of the construction section based on the characteristics of thin-layer pavement and road performance, combined with the acceptance standards for asphalt concrete pavement. After the final compaction of S2-6 is completed, traffic can be opened once the road surface has cooled to below 50°C.

2. The instantaneous heating asphalt concrete thin-layer paving construction process according to claim 1, characterized in that, Specifically, S1-2 includes the analysis and evaluation of the original pavement or underlying layer surface condition, including defect analysis, condition evaluation, and evaluation of residual asphalt condition on the pavement surface. The evaluation of the residual asphalt condition on the road surface includes the following steps: S1-2-1 Selecting Sampling Points: Multiple random sampling points are taken for the construction section. The sampling frequency is selected according to the area of ​​the road section, with no less than 5 points per kilometer. The sampling point locations include the middle of the driving lane, the wheel track, the shoulder, and the intersection of adjacent lanes. S1-2-2 Sampling: After simple cleaning of the original road surface, removing obvious debris and blowing away dust, take a picture of the clean and dry original road surface; S1-2-3 Assessment: Using image analysis software, the surface condition of the original pavement is assessed, with the percentage of exposed aggregate area as the indicator. The assessment values ​​of each point on the original pavement are simply averaged to obtain the assessment value of the percentage of exposed aggregate area. Based on the assessment results, a corresponding treatment method for spreading a tack coat on the original pavement is proposed.

3. The instantaneous heating asphalt concrete thin-layer paving construction process according to claim 1, characterized in that, In S2-1, the heating temperature of the modified asphalt is 160~170℃, the heating temperature of the aggregate is 180~190℃, and the discharge temperature of the mixture is 165~175℃.

4. The instantaneous heating asphalt concrete thin-layer paving construction process according to claim 1, characterized in that, In S2-2, the dump truck is a clean dump truck with a metal floor, an insulation layer around the truck body and a covering layer on the top of the truck body. Temperature is monitored using a thermometer to ensure that the temperature of the mixture leaving the factory is 165~175℃ and the temperature arriving at the factory is not lower than 150℃.

5. The instantaneous heating asphalt concrete thin-layer paving construction process according to claim 1, characterized in that, In S2-4, during compaction, the roller first compacts the new paved layer by 15cm, then gradually shifts diagonally to avoid the new paved layer and compacts it together with the newly paved mixture, and then switches to longitudinal compaction to make it smooth and compact. The longitudinal joints are treated as vertical joints, and the uncompacted mixture at the joints is removed by milling. The transverse joints are treated as vertical flat joints, and the ends are cut off vertically along the road centerline.

6. The instantaneous heating asphalt concrete thin-layer paving construction process according to claim 1, characterized in that, In S2-5, the acceptance process needs to meet the following conditions: The surface of S2-5-1 road is flat and uniform, with no oil seepage, looseness, cracks and obvious segregation. S2-5-2 The longitudinal joints should be tight and smooth. If an emulsified asphalt bonding layer is set, the emulsified asphalt bonding layer should not be sprayed in an overlapping manner. S2-5-3 thin-layer paving should be closely connected to the curb and other structures, and there should be no water accumulation or leakage. The S2-5-4 measured quality control standards include: thickness, compaction, flatness, permeability coefficient, friction coefficient, and structural depth. S2-5-5 Bond strength between new and old surface layers: Through core sampling, pull-out and shear tests are performed on the core samples. The pull-out strength should be greater than 0.7 MPa, and the shear strength should be greater than 1.0 MPa.

7. The instantaneous heating asphalt concrete thin-layer paving construction process according to claim 1, characterized in that, The heating control system has two operating modes: manual control mode and automatic control mode, to adapt to different construction conditions. Specifically: In manual control mode, the operator can manually set the current power P of the instant heater on the control panel and make manual adjustments at any time; in manual control mode, the instant heater generates heat according to the set power. The automatic control mode offers mode options suitable for various operation types. Operators can set the automatic operation mode according to construction needs, and can also set various operating parameters, including the system reference paving speed V, heating power P and various temperature feedback parameters, so as to perform real-time calculation and adjustment and realize the synchronous linkage between the instant heater and the thin-layer paving operation.

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