What should be paid attention to in asphalt pavement construction in winter?

1. Strength formation mechanism of asphalt mixture and strength mechanism of asphalt mixture in construction temperature field: The strength of asphalt mixture consists of two parts: first, the embedding force and internal friction between minerals depend on the size uniformity, particle shape and surface roughness of minerals, and the mixture composed of cubic, uniform, angular and rough minerals has large internal friction; On the contrary, the viscosity of asphalt has little effect on the internal friction of mixture. Second, the cohesive force between mixtures is influenced by the properties of asphalt and mineral aggregate, the specific surface area of asphalt and mineral aggregate and the compactness of mixture. However, low-temperature construction is easy to cause insufficient density and low cohesive force of the mixture, which affects the strength of the asphalt mixture, showing rutting in the early stage of opening to traffic. Moreover, due to the large void ratio, the mixture is easy to form looseness and pit damage after being soaked in rain. Influence of construction temperature field of asphalt commercial concrete pavement: Experimental research shows that the heat of hot-mix asphalt mixture is transferred to the air and under the pavement during paving. Upward, the air temperature at the heights of 5cm, 15cm and 30cm on the surface of the mixture slowly rises within 0 ~ 9 min, and starts to decrease after 1~9min, while the air temperature at the heights of 50cm and 80cm does not change much before and after paving, which plays a role in forming a higher temperature shielding zone in the air near the surface of the mixture and protecting the hot mix from more heat loss. The downward transfer of heat makes the temperature of asphalt mixture drop sharply within 15min, while the temperature of the lower bearing layer rises sharply. After 15min, the temperature of each layer tends to be flat, and after 1 h, it tends to be equal. Although the asphalt mixture loses some heat, it heats the lower pavement to some extent, which is helpful for the connection between the upper and lower floors. Through observation, it is found that the temperature distribution of asphalt mixture and its surroundings is related to the initial temperature of asphalt mixture, weather, wind and other factors. Second, the main problems in winter construction 1. The temperature of asphalt mixture drops rapidly, resulting in a large proportion of waste. Due to the low temperature in winter, the temperature difference between hot-mixed asphalt mixture and ambient temperature is large, which easily leads to the rapid temperature drop of asphalt mixture, which can be rolled in a short time, and the mixture temperature easily fails to meet the construction requirements, which is easy to produce waste. 2. It is difficult to ensure compactness and quality control. As the temperature drops rapidly, the viscosity of asphalt increases and the workability of asphalt mixture becomes worse. At this time, the required compaction work will increase, the pavement compactness will be difficult to achieve, and the quality will be difficult to guarantee. Three. In view of the low temperature construction in winter, the following measures have been taken. In view of the particularity of this project, the following measures have been taken to ensure the final quality of the pavement. (1) Construction technology control 1, construction preparation (1) The importance of improving the quality of winter construction, and fully implementing the quality management responsibility system at all levels. (2) Check in strict accordance with the design and relevant national construction and acceptance specifications, and strengthen organization and coordination. (3) Strengthen the contact between the site and the asphalt mixing station, assign personnel to conduct unified command and dispatch, and organize the supply in a quantitative, regular and planned way, and provide materials in time. (4) All kinds of machinery and equipment on site are complete, and there must be spare equipment. (5) Before the surface course construction, check the base course to ensure that it meets the quality requirements. Before paving, cover the lower bearing course with heat preservation and moisture-proof, so that its surface is dry and free from cold. 2, the construction time control (1) pay close attention to the weather, grasp the construction time, strong winds, rain and snow weather, hot mix asphalt pavement construction is not allowed. (2) When paving, choose sunny days with wind power not exceeding Grade 4, and it is forbidden to construct at night. The paving time is arranged from 9: 00 a.m. to 4: 00 p.m., so as to achieve quick unloading, quick paving and quick rolling. 3. Temperature control (1) Designate a person to be responsible for the temperature detection of asphalt mixture. (2) Appropriately raise the ex-factory temperature of asphalt mixture, and the temperature of mixture mixing, transportation, paving and rolling shall be appropriately raised by 5℃ ~ 10℃. (3) Although increasing the construction temperature can improve the compactness of the mixture to a certain extent, it has the following shortcomings: (a) The asphalt aging phenomenon is obvious when the asphalt heating temperature or the mixture mixing temperature is too high, which affects the quality of asphalt and asphalt mixture; (2) The temperature is not easy to control. Relevant data show that the higher the temperature of the mixture, the faster the temperature drops. 4. Appropriately increase the number of mechanical equipment and rolling equipment, and determine the number of rollers according to the output of the mixing station and the paving speed of the paver. On this basis, two more road rollers are added to keep continuous paving operation as far as possible, and it is emphasized to "follow closely" the paver for rolling. Select the appropriate amplitude and vibration frequency of paver rammer to make the initial compaction degree reach more than 85%. Steel roller should be laid with pressure, and reduce the amount of water spray. Rubber roller shall not stop rolling, and local areas such as road edges after rolling by steel roller shall be compacted by vibration rammer. The edge area of the inspection well shall be tamped with vibrating rammer. 5. Properly increase the asphalt-aggregate ratio, increase the mixing time and the optimum asphalt dosage (about 0. 1%). In addition, pay attention to heat preservation during transportation, and double-layer cotton felt covering measures must be taken for the material delivery vehicle; Try to use large transport vehicles; Before the paver starts to work, the screed should be preheated to no less than1.0h in advance.