The KLMY90 # Asphalt and Its Mixture Performance Research for Gannan Area

Asphalt pavement is widely used at home and abroad because of its advantages of comfortable driving, convenient maintenance, short construction period, etc. Asphalt becomes brittle and is cracked  in winter. Gannan is located in the plateau, belonging to plateau climate, low year-round temperature, often wind and rain, day and night temperature difference, strong sunlight. Therefore, the asphalt was selected with high temperature stability and low temperature ductility. The KLMY90# asphalt and its mixture were studied for the technical properties. The results showed:  the content of saturates and aromatic components reduced at aging temperature; the saturated and aromatic content decreased at aging time; the saturated content decreased slowly than the content of aromatic content as the aging time decreasing; the dynamic stability increased with the asphalt-aggregate ratio; the asphalt mixture had superior performance , strong water resistance. The KLMY90# asphalt and its mixture were more suitable for paving roads for Gannan.


Introduction
Asphalt is a dark brown complex mixture composed of hydrocarbons of different molecular weights and their non-metal derivatives; it is soluble in carbon disulfide [1]. Asphalt pavement has many advantages such as comfortable driving, convenient maintenance, short construction period, easy maintenance, and no reflective driving at night [2][3][4][5][6]. There are many factors that affect the road performance of asphalt and asphalt mixtures, such as the nature of raw materials, climatic conditions, and composition of grading [2,3]. Gannan is located at the edge of the Qinghai-Tibet Plateau; the landforms are complex and diverse; the differences in elevation are obvious [7,8]. There is a great difference in the climate everywhere, and the asphalt is easy to crack. Therefore, the high-index asphalt is selected such as 90#, 110#; their softening point is lower, and the low-temperature ductility is good. The Shell Company makes a research on asphalt mixture with 100# asphalt. The penetration rate of bitumen is reduced to 70mm after experience mixing; the porosity is 3% to 12% after being laid on the road for 5 years [3]. The KLMY90# matrix asphalt and its mixture were studied to be suitable for the climate in Gannan region, and the reference basis put forward for the construction of asphalt pavement in this area.

Raw material test method and its technical performance indexes 2.1 KLMY90# asphalt technical indexes
The KLMY90 # asphalt's main technical indicators were tested according to the reference [9]. The results were shown in Table 1.

Aggregate and mineral powder
Coarse aggregates were available in 9.5 to 19mm, and 4.75 to 9.5mm; the technical specifications were shown in Table 2. Fine aggregates with an apparent density of 2.667g/cm 3 were selected. The technical specifications for ore powder and hydrated lime powder were shown in Table 3.

The Four-component
The chemical composition of KLMY90# asphalt was studied by changing rule of the four components of aged asphalt, which was tested by the method [9]. The design was as follows: (1) The asphalt four-component content was tested at the aging time for 5 hours under 153°C, 163°C, and 173°C respectively; the results were shown in Table 4; (2) the asphalt four-component content was tested at the aging time for 163°C at 5h, 10h and 15h respectively; the results were shown in Table 5   From Table 4: the content of asphaltenes and colloids increased with the increase of aging temperature at the aging time of 5h; the asphaltene content change is not obviously, but the colloids content changed greatly with the aging temperature. The content of saturates and aromatic components gradually reduced with the increase of aging temperature. The decrease of aromatic content was faster than that of saturated content.
From Table 5: the bitumen did not change at the aging temperature (163°C) ; the asphaltene content and the gum content increased with the aging time changing; and the increase degree for the colloid content was greater than that of the asphaltene content. The saturated content and aromatic content decreased with the increase of aging time; the content of saturated content decreased more slowly than the content of aromatic content as the aging time decreasing; the saturated components of asphalt and the content of aromatic components were oxidized in the aging process of asphalt; and the effects of ultraviolet rays were converted into asphaltenes and colloids, thereby reducing the performance of asphalt.

Mineral mix design
The design of the mineral composition was made according to the reference [10] for the AC-16. The composition of the gradation of the mineral materials was determined after adjustment (seen in Table 6).

Mixture composition design
The asphalt mixture Marshall test was carried out to determine the optimum oil consumption [9]. The results were shown in Table 7.   Table 7 showed: the relative density of the volume increased with the asphalt-aggregate ratio, but become smaller at 5.5. The ratio of voids and the change of voidage decreased; the gap rate of minerals decreased with the asphalt-aggregate ratio and unchanged at 5.5; the stability increased with the asphalt-aggregate ratio, but started to decrease at 5.0; the saturation and flow values increased with the asphalt-aggregate ratio. The optimum amount of asphalt was determined: OAC 1 =5.029%; OAC 2 =(4.997% ＋ 5.226%)/2=5.112%; OAC=(OAC 1 ＋ OAC 2 )/2=5.070%.

The road Performance
(1)High temperature stability: the experimental results were shown in Table 8. Table 8 showed: the rut depth increased. The material surface had good performance, flexibility, and durability. The dynamic stability increased with the asphalt-aggregate ratio. In addition, the experimental data also showed that the temperature had the greatest impact on the asphalt mixture, and the frequency and speed were both greater. (2) Water stability: the sability was 6.29kN at 30min of soaking; the sability was 6.12kN at 48h of soaking. The residual stability was 97.38%, which showed that the impact of water was relatively small, and the water resistance was relatively strong.

Conclusions
The content of saturates and aromatic components gradually reduced, the saturated and aromatic content decreased, and the saturated content decreased more slowly than the content of aromatic content as the aging time decreasing. The dynamic stability increased with the asphalt-aggregate ratio; the asphalt mixture was superior in performance and its ability to resist water intrusion was better; the water resistance was relatively strong. The KLMY90# asphalt and its mixture were more suitable for paving roads in cold regions of Gannan.