In this paper, the asphalt pavement analyzer (APA) is used to carry out rutting tests on DA mixture and SMA mixture under standard working conditions and heavy traffic conditions. The rutting depth index is used to evaluate the rutting resistance of DA mixture and its sensitivity to loading grade, loading times and temperature. The influence of asphalt quality and mixture gradation type on the rutting resistance of DA mixture is analyzed, and the difference of rutting resistance between DA mixture and SMA mixture is analyzed, so as to judge the adaptability of DA mixture to heavy traffic road drainage asphalt pavement.
test material
Nine kinds of asphalt materials were used in this study. See table 1 for the zero shear viscosity (60℃), penetration and softening point of nine asphalt materials.
The aggregates used are 10~ 15mm diabase, 5~ 10mm diabase and 0~5mm limestone respectively, and the filler is ground limestone powder. The main technical indexes of aggregate and mineral powder of all grades meet the requirements of JTGF40-2004 Technical Specification for Highway Asphalt Pavement Construction.
test item
Asphalt Pavement Analyzer (APA) is used to analyze the rutting resistance of asphalt mixture. The sample size is 65438 050 mm in diameter and 75 mm in height. Asphalt mixture is formed by rotary compactor. According to NCAT design method, the compaction times of standard specimen are 50 times. In order to analyze the influence of molding times on the rutting resistance of DA mixture, 75 compaction times and 100 compaction times were also selected for comparison. The standard conditions of APA rutting test are: temperature 60℃; The load level of 445N was loaded 8000 times.
In addition, the loading level of 890N and the loading times of 24,000 times are selected to simulate the heavy traffic conditions. Rutting depth RD8000 is used as an evaluation index of rutting resistance of asphalt mixture.
When RD8000≤4mm, the rutting resistance of asphalt mixture meets the requirements of AASHTOTP63-03 standard.
Table 4 summarizes the test scheme of this paper. The APA rutting test was carried out with three parallel specimens at the same time, and the rutting depth test values of the three parallel specimens were obtained, and the average value was taken. If the deviation between the rut depth test value and the average value of the specimen exceeds 30%, the average value will be calculated after eliminating the test value. If the deviation between the rut depth test value and the average value of two specimens is more than 30%, the data set is invalid.
Test results and analysis.
Influence analysis of material composition When the temperature is 60℃, the loading level is 445N, and the loading times are 8000 times, the rutting depth test results of DA mixture with different materials are shown in Table 5.
Influence analysis of asphalt quality
From the data of scheme 1 in Table 5, it can be seen that even if SBS modified asphalt, high modulus asphalt and high viscosity asphalt-1~ high viscosity asphalt -4 are used, the rutting depth of DA mixture exceeds 4mm, which cannot meet the requirements of AASHTOTP63-03 standard. Figure 1 Based on the data of scheme 1 in Table 5 (8 groups) and the data of Table 1, the relationship between rutting depth of DA mixture and asphalt zero shear viscosity (60℃) is given.
As can be seen from Figure 1, the rutting depth of DA mixture is significantly related to the zero shear viscosity of asphalt. With the increase of zero shear viscosity of asphalt, the rutting depth of DA mixture decreases.
The cementation of asphalt is an important factor to ensure the stability of the void structure of DA mixture skeleton, so it is particularly important to use high viscosity asphalt in DA mixture. According to Figure 1, it is necessary to ensure that the rutting depth of DA mixture is less than 4mm, and the zero shear viscosity (60℃) of asphalt is not less than 70,000 Pa s. The influence of gradation composition is shown in Table 5, Scheme 2, and the relationship between the rutting depth of DA mixture and the qualified rate of 2.36mm mixture (see Table 2), and the results are shown in Figure 2. Draw the relationship between the void ratio of DA mixture composed of three gradations (see Table 3) and the qualified rate of 2.36mm mixture, and the result is shown in Figure 3.
As can be seen from Figure 2, the rutting depth of DA mixture decreases linearly with the increase of its passing rate of 2.36mm, which seems to be contrary to the view that increasing the proportion of coarse aggregate can improve the rutting resistance of asphalt mixture. Further analysis of Figure 3 shows that with the increase of 2.36mm passing rate and the decrease of coarse aggregate, the void ratio of DA mixture decreases significantly.
When the proportion of coarse aggregate is too high, there are not enough bonding points between aggregates, the bonding effect of asphalt is weakened, and the structural integrity of DA mixture is not good, which leads to a serious decline in its rutting resistance.
From this point of view, the design void ratio of DA mixture should be about 20%, and in order to ensure the void ratio of DA mixture specimen, the qualified rate of 2.36mm in mineral aggregate gradation composition should not be less than 16%.
Influence analysis of test conditions
Under different test conditions, the rutting depth test results of DA mixture are shown in Table 6. As can be seen from Table 6:
(1) When the temperature is 60℃ and the loading times are 8000, when the loading level increases from 445N to 675N, the rutting depth of DA mixture (50 times of compaction) increases by about 1 times. When the temperature is 60℃ and the loading level is 445N, the rutting depth of DA mixture (75 times of compaction) increases by about 1 times when the loading times increase from 8000 to 24000 times.
(2) Under the same other conditions, when the temperature rises from 60℃ to 70℃, the rutting depth of DA mixture increases by about 65438 0 times.
(3) When the temperature is 60℃, the loading level is 445N, and the loading times are 8000, the void ratio of DA mixture decreases from 20.3% to 19.6%, then to 19.2%, and the rutting depth is from 3.
The results show that when the DA mixture reaches a certain dense state, increasing the compaction times has limited effect on reducing the void ratio and rutting depth of DA mixture. For DA mixture, it is reasonable to use 75 times of compaction during molding. Adaptability analysis and reasonable design of SMA mixture in heavy traffic are the first choice for asphalt overlay on heavy traffic roads at present. In this paper, SMA mixture is selected as the control material to judge the heavy-load traffic adaptability of DA mixture. The rutting depth of SMA mixture under different test conditions is shown in Table 7. Comparing the data in Table 6 and Table 7, we can see that:
(1) Under the same loading grade, loading times and temperature, the rutting depth of SMA mixture is less than that of DA mixture.
(2) Under the condition of 60℃ and 8000 times of loading, when the loading level increases from 445N to 890N, the rutting depth of SMA mixture increases by 10 1%, while that of DA mixture (compacted 75 times) only increases by 54%; Under the loading level of 60℃ and 445N, when the loading times increased from 8000 to 24000, the rutting depth of SMA mixture increased by 265438 08%, while that of DA mixture (compacted 75 times) increased by 65438 023%. When the temperature rises from 60℃ to 70℃, the rutting depth of SMA mixture increases by 65438 046% and that of DA mixture (compacted for 75 times) increases by 65438 007% under the condition of loading level of 445N and loading times of 8000 times.
The above analysis results show that the rutting resistance of DA mixture is less sensitive to loading level, loading times and temperature changes than that of SMA mixture under this test condition. Compared with SMA mixture, the contact points between aggregate particles in DA mixture are less, the locking effect is relatively weak, and the mixture structure is unstable at the initial stage of wheel loading because of the few compaction times of the specimen. For example, 8000 deformation of DA mixture accounts for 44.8% of 24000 deformation, while SMA mixture only accounts for 3 1.4%.
Under the continuous action of wheel load, the aggregate particle arrangement of DA mixture enters a stable state, the locking effect is enhanced, and the deformation resistance is correspondingly increased, so its sensitivity to load level and loading times is relatively small.
conclusion
(1) Because DA mixture has the characteristics of skeleton void structure, high viscosity asphalt, suitable gradation composition and sufficient compaction times must be adopted to ensure the rutting resistance of DA mixture. In order to meet the requirements of heavy traffic roads, the zero shear viscosity (60℃) of asphalt used in DA mixture should be greater than 70000 Pa·s, and the designed void ratio should be about 20%.
(2) Under the same loading grade, loading times and temperature, the rutting depth of DA mixture is slightly greater than that of SMA mixture; Compared with SMA mixture, the rutting resistance of DA mixture is less sensitive to loading level, loading times and temperature.
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