Construction segregation control of the hottest as

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Construction segregation control of high-power paver for asphalt concrete pavement construction segregation of asphalt concrete pavement makes the asphalt mixture deviate from the optimal design mix ratio, and its mechanical properties and service performance change greatly, so that the weak points of the pavement are damaged early, thus inducing large-scale damage to the pavement. The early damage of pavement is often caused by the segregation of pavement materials, such as road grooves, ruts, loose structure and oil flashing. Segregation is the most difficult phenomenon to control during construction, which is closely related to materials, construction technology, especially construction equipment. To solve the problem of pavement segregation is the common hope of many pavement engineers and mechanical engineers. It is necessary to carry out comprehensive and systematic research and analysis

theoretically, the high-power paver has the conditions to control segregation in terms of principle and performance, but it still lacks practical application experience in China, and has not been recognized by relevant specifications and quality supervision departments. In the current standard for quality inspection and evaluation of highway engineering, there is just a lack of quantitative indicators for segregation. The key assessment indicators for pavement construction quality are often judged by the naked eye, which is inevitable to be inaccurate

to further improve the high-power paver, optimize its performance and make it practical is the direction to solve the segregation problem. At the same time, it is necessary to establish a complete supporting control process through field application. In addition, the establishment of quantitative standards of pavement segregation degree and corresponding simple and applicable detection methods is also the work to be done to control pavement segregation

1 Classification and causes of asphalt concrete surface segregation

asphalt concrete segregation can be divided into strip segregation and block segregation according to appearance, including horizontal segregation, longitudinal segregation and vertical segregation, regular segregation and irregular segregation. There are many reasons for segregation, such as lax control of local materials, large variation, and unstable processing capacity of the quarry; The change of purchased materials is affected by the stacking method at the site and the excessive stacking. Improper construction process and operation mode will cause serious segregation, shutdown for material waiting, poor trapezoidal paving speed, improper overlapping width control, too fast bucket collection and not timely rolling are unreasonable processes. Irregular segregation is often caused by construction technology, while regular segregation is mostly determined by the performance of the paver

from the process of asphalt concrete pavement construction in recent years, the quality of mixing plant and paver is the main cause of asphalt concrete pavement segregation. At present, pavement segregation is the most difficult to control in pavement construction. Therefore, both at home and abroad are trying to start with the reconstruction of pavers. At present, foreign models mainly include super21002c (VOGLE), ingersoll2randabg525, and there are similar products in China. The correction method of Shaanxi torque tester after replacing the sensor. Western China University has developed dt1400 high-power paver, These improved equipment make it possible to solve the pavement segregation and improve the flatness

2 principle of controlled segregation of paving machinery

2.1 defects of paving machinery

according to the current principle of paver, the conveying and distribution of materials are composed of two links: scraper conveying and spiral distributor. The scraper is a translational layered feeding device, which will not produce a new mixing effect on the materials. Therefore, the physical properties of the materials produced in the previous processes can greatly improve the fatigue resistance of these metals, and the temperature segregation cannot be improved. For this reason, in recent years, the process of adding a material transfer vehicle in front of the paver has been tried to effectively improve the mixture temperature and physical segregation through its functions of heat preservation, heating and mixing. For the paver itself, the function of improving segregation and paving smoothness is mainly realized through the structure of the spiral distributor and the design of kinematic parameters

the internal friction force in the graded mixture (including foundation and surface course) and the external friction force between the material and the conveying screw affect the effect of the spiral conveying and secondary mixing (the mixer is a primary mixing). A reasonable paver spiral distributor should have a good ability to mix materials, effectively improve the material segregation generated in the previous process, and meet the amount of materials required for different parts of the paving width, Comprehensive function to ensure flatness. This is the final requirement for the design of the spiral distributor and a reasonable way to improve the performance of the paver

at present, the actual situation of most low-power pavers is that the internal and external friction of materials makes it easy for large particles to be sent to both sides of the spiral distributor, and the segregation will increase with the increase of paving width. The main reason is that if there is a defect in the working parameter setting of the unqualified feeder of the spiral separator, it is appropriate to emphasize that the material conveying height should be located at 2/3 of the blade diameter above the center of the spiral separator. Because the material level in the spiral separator is low, a higher working speed is required to meet the requirements of the material conveying volume (up to about 100r/min, or even higher). During the adjustment of throwing and fast moving, the materials with different particle sizes are separated again. The essence of this idea is to follow the traditional spiral design theory, that is, the main function of the spiral distributor is to evenly transport and distribute materials, but the secondary mixing function of the spiral distributor is not given to improve the physical and temperature segregation produced in the previous process

2.2 segregation control mechanism of high-power paver

the design theory of high-power paver (power above 160kW, maximum paving width of 16m, maximum paving thickness of 500mm) is to further extend the design of screw device with high production rate through anti segregation with secondary mixing to improve the comprehensive functions of segregation and uniform material conveying and distribution, supplemented by the high-power configuration of the whole machine and screw drive, to realize large width, large thickness Anti segregation one-time forming paving operation, improve segregation, and improve the segregation of the joint of dual machine parallel paving. Its main features are: increase the screw feeding capacity, reduce the screw driving speed, increase the screw secondary mixing function, reduce the impact and acceleration of the screw starting work, and make it start smoothly and slowly

(1) spiral work with materials fully buried

this is the key to increase the feeding capacity, reduce the screw speed, increase the secondary mixing effect, and avoid horizontal segregation. It is also a new concept. Improving the level control points of the scraper and screw level sensor is the external form to realize this concept. Its internal essence is to increase the driving torque of the screw and change the driver scheme. Change the transmission scheme of high-speed axial piston motor plus reducer for conventional paver, directly use low-speed radial piston high torque motor for driving, and increase the motor equivalent displacement of about 700ml/r to 1300ml/r for conventional paver. The torque and power are doubled compared with ABG-423. The full burying screw of materials reduces the rotating speed to 80 ~ 90r/min or below, effectively preventing the lateral segregation of large particle materials with the increase of conveying distance. At the same time, due to the screw burying at the bottom of materials, the secondary mixing effect is increased, and the temperature and physical segregation generated in the previous process are improved

the low-speed high torque motor can not only meet the requirements of larger driving torque for the fully buried screw of the material, but also avoid the impact starting phenomenon of the high-speed motor reducer under frequent intermittent working conditions due to its high starting efficiency, strong starting capacity with load and stable starting, thus reducing the impact, lifting and segregation of the material. Fully burying the spiral with materials, increasing the conveying capacity and driving capacity of the spiral also provides the possibility for large thickness one-time forming paving of foundation materials

(2) adopt variable diameter screw design

the spiral distributor of the paver is a semi open structure. Different from the general closed spiral conveyor, which transports all the materials, it transports the materials while unloading in the process of material distribution, and finally evenly distributes the materials on the whole width of the screed. Therefore, the screw at different positions should have different feeding capacity, which requires that the screw distributor should have different lifting angles or diameters to meet this performance requirement. The variable lift angle design has the defects of difficult manufacturing, poor interchangeability and uneven mixing. Dt1400 adopts the variable diameter screw design. The diameter of the screw gradually decreases from the inside to the outside. The overall section envelope is trapezoidal. Considering the convenience of manufacturing, it can be approximated as several discontinuous diameter structures. In this way, in the material distribution work, it can achieve the effect that all spiral materials are fully buried and the mixing intensity is consistent. In addition to effectively preventing horizontal segregation, it can also ensure that the compactness and flatness of the paved materials at different width positions are consistent

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