Principle analysis and application of automatic leveling beam of asphalt concrete paver
flatness is an important parameter to evaluate the service quality of high-grade highway, so flatness control is also an important link in pavement construction control. The good flatness level comes from: ① the stability of the base and each structural layer, without abrupt and uneven settlement; ② Each structural layer has a continuous and balanced compactness and flatness level, with small variability; ③ In the construction process, the setting of datum level, the mixing, paving, rolling and joint treatment of asphalt concrete, as well as the fine operation of each link. Among them, how to provide an accurate flatness reference system for the paver during the pavement construction is one of the prerequisites to achieve a good flatness level(1) according to the technical code for construction of highway asphalt pavement (JTJ), "the asphalt concrete paver used to pave expressways and class I highways shall be equipped with an automatic or semi-automatic device to adjust the paving thickness and leveling...". "For automatic leveling of the paver, the middle and lower layers should adopt the elevation control mode guided by one side of the steel wire rope. The surface layer should adopt the sled paving thickness with the same height difference before and after the paving layer." 1. The BMW I3, whose body structure and frame are completely made of carbon fiber reinforced plastic, attracted many people to visit the control mode... ". Shenyang Dalian Expressway, Beijing Tianjin Tangshan Expressway and other expressways are also controlled according to this procedure.
(2) it is proposed in the pavement Manual of the American asphalt association that if the underlying layer is very close to the allowable error, the sledge can also provide a smooth surface layer. In the pavement construction practice of Shanghai Nanjing Expressway, through detailed investigation, analysis and comparison, it is considered that: in the construction of high-grade highway, 2. The plastic recycling granulator reprocesses the waste plastics from daily life to produce the plastic raw materials required by the enterprise and adopts imported paving machinery, the paving degree is easier to control; The elevation error has been relatively eliminated through the construction of subbase, base and lower layer. For the middle and upper layers, the flatness requirements become the main control factor, and the elevation requirements are relatively secondary; Moreover, the guidance of steel wire rope on one side is certainly not enough for imported paving machinery with relatively high sensitivity.
(3) therefore, it is suggested that each pavement construction unit: generally, for the paver with full width paving, the steel wire rope guidance control mode on both sides is only used for the paving of the upper and lower layers of the base course, while the equal thickness control mode of the suspended reference beam (i.e. sledge) can be used for the middle and upper layers. Such construction control methods not only come from practice, Moreover, based on the following analysis, "the world is difficult to deal with.
2 principle analysis
(1) The elevation control mode guided by steel wire rope shall be adopted. According to relevant regulations, the steel wire rope with a diameter of 2 ~ 2.5mm shall be used, 200m is a section, the spacing between upright poles is 10m, and the tension force shall be 800 ~ 1000N. Assuming that the tension of the steel wire rope is infinite and the elevation on the iron pole set by the measurement is absolutely accurate, the reference plane provided by the steel wire ropes on both sides of the route will be the absolute standard plane of the upper layer of the impact mechanical equipment. 1. However, in the actual construction process, the tension force on the steel wire rope cannot be infinite. Moreover, since the subbase and base course on the curbs on both sides have been hardened, it is difficult to set the tension support rod bearing the tension, and the specified tension of 800 ~ 1000N cannot be guaranteed; In addition, the workload of one day's pavement paving is 1 ~ 2km or more, and the task of measuring two steel wire ropes per day is quite arduous; In addition, it is difficult to eliminate the steel wire rope vibration caused by the walking process of the paver, and it is even more difficult to avoid human touch, touch and damage. Even the screed may scrape and squeeze the stay pile due to the deviation of the paver direction, which greatly compromises the accuracy of the elevation control method guided by the steel wire rope.
(2) the method of controlling the paving thickness by sledge is to use the following surface layer as the reference plane, and try to reduce the fluctuation and sudden change error transmitted to the upper surface layer during the running of the paver, so as to achieve the good flatness of the upper surface layer. Its principle is similar to the lever, that is, the fulcrum of the lever is placed on the new paving layer that is less affected by external factors, while many uneven factors at the next level are decomposed and reduced several times by the beam structure, so that the sensor can get a relatively stable or small fluctuation control signal. Compared with the previous method, under the premise of good flatness of the next level, the sledge method is obviously superior to the wire rope control method.
(3) all pavers made in foreign countries are equipped with an automatic leveling beam. However, due to its high price (about 350000 yuan, for example, the floating leveling device of American blowknox company, the price is 340000 yuan) and simple principle, most pavement construction units of Shanghai Nanjing Expressway use their own processing and production of automatic leveling beams.