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With the advancement of world industry and the development of road construction, particularly the need for blacktop pavement installation, asphalt spreaders were introduced as early as the beginning of the last century. By the 1930s and 1940s, they had evolved into products with more sophisticated functions, with the self-propelled asphalt spreader being a representative model of this type. In China, asphalt spreaders have seen continuous technological innovation and improved performance over the years since the 1950s, as road construction has developed. To date, domestic asphalt spreaders have achieved a level of intelligence, with their technical specifications reaching international advanced standards. Looking back at the development of asphalt spreaders in our country, it can be broadly divided into two stages: the introduction and improvement period, and the innovation period. The introduction and improvement of asphalt spreaders: In the 1950s, China introduced the technology for self-propelled asphalt spreaders from the Soviet Union and began producing them. The main feature of this model is tubular heating for asphalt ； Volume-type asphalt pump spraying ； Change the spraying width by replacing or extending the spray bar ； As required by the project, the predetermined spreading rate (L/㎡) is achieved by adjusting the speed of the truck and the speed of the asphalt pump. Although the spreading quality of this equipment was not yet high enough and its operation was rather complicated, given the industrial standards of that time, it was still an advanced model. It played an important role in road construction, both by replacing manual labor and by increasing productivity. Due to the limitations in the level of industrial technology development, the structure and performance of these traditional asphalt spreaders remained largely unchanged in China until the end of the last century; such models are still being produced and used even in the past two years. With the reform and opening up of our country, as well as the rapid development of highway construction – particularly the building of expressways, the use of modified asphalt, and the need to decentralize highway maintenance – higher demands have been placed on the functions of asphalt spreaders. To this end, domestic experts, scholars, and relevant professionals have made unremitting efforts; many papers have been published to improve the structure and performance of asphalt spreaders. The main representative works include: 1. \"Discussion on Improving Certain Aspects of the Structure of Domestic Asphalt Spreaders\" ； 2. «Experimental Study on the Spraying Performance of Asphalt Spreader Nozzles» ； 3. “Power Balance and Design Calculations for Asphalt Spreading Trucks”, etc. Several patents were also applied for during the same period, and the main achievements include: 1. “Adoption of a five-wheel speed measurement system on the spreading vehicle”” ； 2. “The asphalt pump is driven by a hydraulic servo speed control system”” ； 3. “Regulate the speed of the asphalt pump using an asphalt flow meter and a speed detection device”” ； 4. “Using electronic monitoring devices for the pressure, temperature, and liquid level of the asphalt pump on the asphalt distributor truck”, etc. Thanks to the efforts of relevant professionals, the performance of domestic asphalt spreaders has seen some improvements; however, due to limitations in industrial capacity, these advancements have not really reached an industrial scale. Innovations in asphalt spreaders: Since the beginning of the 21st century, with further strengthening of international technological exchanges, as well as advancements and widespread use of electronic information technology, these factors have provided the technical and material support necessary for the improvement of asphalt spreading techniques in our country. Xi’an Dagang Highway Mechanical and Electrical Technology Co., Ltd. was the first in China to introduce the SX5190GLQ intelligent asphalt distributor, which features independent intellectual property rights. As a representative of innovations from that period, it drove technological progress in asphalt distributors in China. Compared with traditional asphalt spreaders, the main features of intelligent asphalt spreaders are: 1. An embedded heat transfer oil heating system that uses heat transfer oil as a medium to heat the asphalt, thereby eliminating the drawback of traditional fire-tube heating, which causes the asphalt to age more easily. Automatic ignition diesel burners are used; the temperature can be set manually as required, allowing for automatic heating of the asphalt. The heating speed is fast, which meets the requirement that the spraying temperature for modern modified asphalt be ≥175°C. By using heat transfer oil as the heat transfer medium, it is possible to heat and maintain the temperature of the entire asphalt pipeline system, including every nozzle, thereby replacing the traditional method of using a blowtorch to heat the nozzles before spraying, followed by rinsing them with diesel after spraying. 2. The maximum spreading width is 6m, with a total of 48 nozzles installed; each nozzle can be controlled independently. The advantages include a rapid start-up and complete shutdown during the spraying process, as well as the ability to set the spreading width arbitrarily within a maximum width of 6m (with increments equal to the distance between adjacent nozzles). The unique nozzle design ensures that the spraying angle α of a single nozzle meets the requirement of triple overlapping spraying, namely: (1) In the formula: α—nozzle spraying angle ； B—Nozzle spacing, mm ； H—Nozzle height above the ground, mm ； The angle between the centerline of the β-nozzle opening and the axis of the spraying rod. 3. The application of micro-industrial computers enables the realization of the functions that asphalt spreaders have long desired, namely: 1) spreading parameters such as spreading width W, spreading density D, and asphalt specific gravity G, which can be set manually based on the requirements of road construction; these values are entered via keyboard. In addition to operating according to these set parameters, the computer also provides the driver with a reference speed V, as well as information regarding the gear that should be used in the transmission. The reference speed V provided from a design perspective is the result of optimization; it ensures that the machinery can operate the engine, asphalt pump, and other components under optimal conditions across a wide range of spreading parameters. It is actually difficult to drive the vehicle strictly at the reference speed V; this system allows for significant deviations in speed without affecting the accuracy of the application rate per square meter. 2) Timely control: When the vehicle speed changes, the asphalt spreading system can ensure that the asphalt flow rate matches the vehicle speed, so as to maintain a constant amount of asphalt applied per square meter. That is: In equation (2), D represents the set spreading density, in kg/㎡ ； QL – Asphalt pump flow rate, kg/min ； V – Dynamic vehicle speed, m/min ； W – Spreading width, in meters. To maintain a constant spreading density D, the automatic control system ensures that the flow rate QL of the asphalt pump is adjusted proportionally in response to changes in vehicle speed V, which is not difficult to achieve in the era of modern hydraulic transmission and computers. 3) The adoption of the industrial computer combined with independent control for individual nozzles enables trapezoidal surface spraying at the work site; that is, during the spraying process, the number of nozzles can be increased or decreased one by one, thereby adjusting the spraying width to meet the requirements of specific work surfaces. During the change in spreading width, the spreading density remains constant. 4) The LCD display can show dynamic parameters in real time, such as vehicle speed V, the rotation speed of the asphalt pump nL, the spreading distance L, as well as the asphalt temperature and liquid level. 4. Compressed air is introduced into the operating system; it is used not only as power to control the asphalt valves and nozzles via solenoid valves, but also for purging the asphalt pipelines. That is, after the spraying operation is completed, the remaining asphalt in the pipes can be pumped back into the storage tank, and all nozzles can be cleaned thoroughly to facilitate use next time. As can be seen from the above, modern asphalt spreaders generally have four fluid systems, namely the hydraulic transmission system, the heat transfer oil heating system, the asphalt spreading system, and the compressed air system. Correspondingly, higher requirements are placed on mechanical design, especially for foldable spraying pipelines; both asphalt and heat transfer oil need to be transmitted through rotary joints, which makes the structure more complex. The SX5190GLQ intelligent asphalt distributor was the first to use double-layer insulated metal hoses, as well as a coaxial rotating dual-media transmission sealing structure and devices using Hall elements to measure vehicle speed; these features effectively addressed the functional issues associated with this equipment, resulting in the acquisition of a **patent**. Overall in the domestic market, the level of asphalt spreading technology is improving rapidly, with traditional products being upgraded or replaced by new technologies ； Driven by the market, some new and established domestic enterprises are producing mid- to low-end products that meet various market demands; at the same time, they have started from a high technical baseline and have developed intelligent asphalt spreaders that are at the advanced level in China. The prospects for asphalt spreaders: The rapid development of road construction in our country, particularly the adoption of new technologies and materials as well as the demand for improved construction quality, have opened up broad prospects for the use of asphalt spreaders. High-quality asphalt spraying is required for the \"primer layer,\" \"underseal layer,\" and \"adhesive layer\" of newly built highways ； The \"layered paving method\" used in low-grade roads and numerous rural roads requires high-quality asphalt for spraying ； A large number of road maintenance tasks, which employ the \"single surface treatment\" or \"double surface treatment\" methods, also require high-quality asphalt spraying. The emergence of modified asphalts, particularly rubberized asphalts, has increased the operating temperature of asphalt to above 190°C, resulting in a significant increase in its dynamic viscosity (reaching over 3 Pa·s at 190°C), which poses considerable difficulties in the application of asphalt. Therefore, in the future, our country will need to increase the number of asphalt spreaders not only in terms of quantity, but also to further improve their performance. Internationally, industrially developed countries **such as the United States, France, Germany, etc. have introduced advanced models, some of which have already entered China. However, due to differences in national conditions, the range of mechanical applications, and designers’ approaches, there are still significant variations in the performance of asphalt spreaders across different countries. Its main development trends are: 1. Microcomputerization of control, where the driver can carry out all settings and operations using a dedicated micro industrial computer in the cab. The application rate is controlled proportionally via a radar speed measurement system, ensuring even distribution with a precision of up to 1% ； The display screen can show the necessary dynamic parameters such as vehicle speed, asphalt pump flow rate and rotation speed, asphalt temperature, liquid level, etc., so that the driver can stay informed about the equipment’s operation at any time. 2. The tank capacity is standardized, ranging generally from 1000L to 15000L, or even more. For small-scale maintenance work, where little asphalt is required, a sprayer with a small capacity is sufficient ； For large-scale highway construction, large-capacity asphalt spreaders are required to reduce the number of trips the spreaders need to make back to the depot during construction and thereby improve work efficiency. 3. The spreading width is available in various ranges; generally, it ranges from 2.4 to 6 meters, or even wider. Independent or grouped control of nozzles is an essential feature of modern asphalt spreaders, allowing the actual spreading width to be set on-site at any time within the maximum spreading width range. 4. The spreading density extends toward the poles. The paving density is determined based on engineering design. As recommended by the **Asphalt Technology Center at Auburn University in the United States**, for the surface treatment of HMA road maintenance using chip seal, the amount of asphalt to be used varies depending on the size of the aggregates, ranging from 0.15 to 0.5 gallons per square yard (1.05 to 3.5 L/m²). For some modified asphalts containing rubber particles, the application rate can sometimes require up to 5 L/m², whereas for those using emulsified asphalt as a prime coat, the required application rate is less than 0.3 L/m². 5. Improving the heating efficiency of asphalt and reducing heat loss is a new concept in the design of modern asphalt spreaders. It requires rapidly heating the lower-temperature asphalt in the asphalt distributor to reach the spraying temperature. To this end, the temperature of the asphalt should increase at a rate of over 10°C per hour, while its average temperature drop should be less than 1°C per hour. 6. For modified asphalt mixtures that tend to separate easily, or those that require time to react in a tank, the asphalt tank should be equipped with an agitator. 7. Improving the quality of initial spreading is one of the important performance goals for asphalt spreaders. The starting spraying quality includes the distance from start to the initial spray point, as well as the accuracy of the spraying volume in the initial spraying stage (0–3 m). Achieving a zero spray distance is very difficult, but reducing the initial spray distance facilitates the continuity of spraying operations. Modern asphalt spreaders should minimize the starting spray distance, ensuring a uniform start to the spraying in a straight line across the width. The SX5190GLQ intelligent asphalt distributor produced by Xi’an Dagang Company is capable of spraying accurately at a distance of 0.7 meters from the starting point, in a straight line horizontally. The application rate and accuracy at the initial spraying stage are related to the initial spraying distance; generally, the shorter the initial spraying distance, the more difficult it is to control the application rate, and the lower the accuracy of application. Furthermore, improving the operability, comfort, and reliability of asphalt spreaders, as well as reducing production costs, are also goals pursued in the technological advancement of modern asphalt spreaders. The development of road construction has provided a broad platform for construction machinery. It is believed that, through the efforts of those working in this field, China’s asphalt spreading technology will, along with other types of construction machinery, quickly reach international advanced levels, enabling the production of high-quality products to meet the needs of China’s road construction projects.