The vibrating beam and screed vibrator are the two most important mechanisms that affect the initial compaction of asphalt mixture when the paver is working. Reasonably set the vibration parameters of the vibrating beam and screed to increase the initial compaction of asphalt mixture. Not only can reduce the number of subsequent compaction passes, but also effectively improve the smoothness of the asphalt pavement while ensuring the compactness of the pavement.
The setting of vibration parameters has an important influence on the compaction effect of asphalt mixture. The resonance theory believes that the best compaction effect is obtained within the natural frequency of the machine and material composition system. When the vibration frequency is close to the natural frequency of the material, the particle amplitude increases The internal friction resistance between the particles is greatly reduced, and the vibration compaction has the highest efficiency at this time, and the best compaction effect can be obtained. At present, the highest adjustable frequency of the vibrating beam of the commonly used paver is about 25 ~ 30Hz, the highest adjustable frequency of the screed vibrator is about 50 ~ 60Hz, and the own frequency of the asphalt mixture is about 40Hz.
Theoretically, the larger the corresponding vibration frequency is, the closer it is to the vibration frequency of the asphalt mixture itself, and the more beneficial it is to improve the initial compaction degree. However, in the actual construction process, as the vibration frequency of the mechanism increases, the paver's own jitter significantly increases, and the possibility of inducing mechanical failures also increases accordingly, which may increase the later maintenance cost of the paver. Therefore, it is of positive practical significance to study the relationship between the vibrating beam of the paver, the frequency of the vibrator, the speed of the paving and the initial compaction of the asphalt mixture, and to set economical and reasonable parameters of the paver.
Effect of vibration frequency on initial compaction
Using the Troxler2701-B coreless density meter to detect the initial compaction during the paving process of the AC-20C in the mid-surface layer, 5 points were detected on each cross section of the pile, and 2 cross sections of each pile were tested at each frequency, and the average value was taken. analysis. During the test, the paving speed is 2.5m / min, the change frequency of the vibration beam is 5, 10, 15, 20 Hz, and the change frequency of the screed vibrator is 10, 15, 20, 25, 30 Hz. The test results are shown in Table 1. ,figure 1.
Table 1 Initial compaction degree of asphalt mixture under different vibration parameters
Fig.1 The initial compaction degree of asphalt mixture under different vibration parameters
From the analysis results of Table 1 and Figure 1, it can be seen that: under the condition that the vibration beams are at the same frequency, as the frequency of the paver screed vibrator increases, the initial compaction of the asphalt mixture gradually increases; the vibrator The initial compaction rate increases faster at the beginning of the frequency increase, and the growth rate tends to slow down after exceeding 25 Hz.
Under the condition that the vibrator is at the same frequency, the initial compactness of the asphalt mixture gradually increases with the frequency of the vibrating beam. However, from the perspective of on-site construction, when the frequency of the vibrating beam exceeds 20 Hz and continues to increase, the paver vibrates more and is not suitable for continuous long-term paving operations. Therefore, during normal construction, the frequency of the paver vibration beam and screed vibrator should be set to 15 ~ 20Hz and 25 ~ 30Hz respectively, which can not only ensure a high initial compaction of the asphalt mixture, but also ensure the paver. Continuous and reliable operation.
Effect of paving speed on initial compaction
Normally, the asphalt mixture paver is equipped with two vibrating beams, the width of a single vibrating beam is about 20 ~ 40mm, and the width of the vibrator is about 400 ~ 500mm. The vibrating beam plays an important role in strengthening the compaction and embedding of coarse aggregates, while the vibrator plays a key role in the distribution and compaction effect of fine aggregates. Because the width of the vibrating beam is small and the vibration frequency is low, too fast paving speed will reduce the number of times of the vibrating beam, and at the same time shorten the action time of the screed vibrator and the mixture, so that the mixture cannot be effectively compacted . Set the frequency of the vibrating beam and screed vibrator of the paver to 20 and 25 Hz, adjust the paving speed to 1.5, 2.5, 3.5 and 4.5 m / min, and use a non-nuclear density meter to detect the initial compaction of the paving process. The effect of speed on the initial compaction degree is studied. The test results are shown in Figure 2.
Figure 2 The effect of paving speed on initial compaction
It can be seen from the data analysis results in Figure 2 that under the condition of fixed paver vibration parameters, the initial compaction degree of asphalt mixture decreases rapidly with the acceleration of the paving speed; and the greater the paving speed, the initial compaction degree The greater the decrease, indicating that the vibrating beam and screed of the paver can no longer effectively compact the asphalt mixture; the compaction of the pavement can only be improved by the subsequent roller compaction, but the smoothness of the pavement must be affected influences. Therefore, combined with test detection analysis and engineering experience, the pavement paving speed should be controlled between 2.5 ~ 3.5m / min.
