The modifying of the rheological properties of pure bitumen to improve the performance of Asphalt mixtures has attracted many researchers in recent decades. The purpose of this study is to investigate the effect of Gilsonite on rheological properties of pure bitumen .For this purpose, different percentages of Gilsonite powder were used to modify the rheological properties of pure bitumen 60/70 .In the study of rheology of bitumen (modified and unmodified), viscosity test, softening point, penetration test and flash point were performed, in addition to, the thermal sensitivity of the bitumen was calculated. The results of this study indicate that the addition of Gilsonite to pure bitumen increases the viscosity and softening point and the penetration index of bitumen decreased. Also, Gilsonite improves the thermal sensitivity of pure bitumen, but this bitumen powder has no effect on the flash point. Gilsonite and bitumen used in this research are from the mine of Ilam province and the Pasargad oil refinery, respectively.
The lifetime of asphalt pavements is usually much less than its design period is also imposing heavy costs asphalt pavement maintenance is one of its main reasons the undesirable quality of bitumen, over time, It has been become a problem.
One of the ways that can improve the asphalt is improve the rheological properties of bitumen.
Gilsonite is one of the additive that can be used to correct bitumen features.
For this purpose, in this research studies the modified rheological properties of bitumen With Gilsonite during penetration tests, softening point, Viscosity and flash point.
Today Gilsonite is well known in the world and for Gilsonite sale in Iran Kardoost Company is the best Gilsonite sealer. Iran Gilsonite has very low ash, And that’s very high quality.
Gilsonite in Iran and especially in the West and Southwest of Iran is abundantly found that profile Physical and chemical are different. Degree of solubility In carbon disulfide or gasoline is an important factor in Gilsonite choice.
If Gilsonite’s solubility is lower in carbon disulfide or gasoline,Mixing Gilsonite with bitumen is better done.
Researchers have come to the conclusion that the use of Gilsonite as a modifier in addition to technical specifications Asphalt mixtures have a lot of economic benefits.
Preparation of materials
The Gilsonite used in this research is from ilam mine it has the physical and chemical properties of it in accordance with Table 1 and 2. Also, pure bitumen in this research from The Pasargad oil refinery has its physical properties Table 3 is shown.
Based on the proposal of the World Road Association (PIARC), the Gilsonite powder used to improve bitumen should be completely mixed from the 50th Sulfur Unit to 140 ° C for 150 minutes and 150 rpm. Then the mixture temperature rises to 180 ° C and continues for 30 minutes at 4500 rpm, until the homogeneous mixture of Gilsonite and bitumen is prepared.
To study the properties of modified bitumen and Unmodified, viscosity tests, softening point, degree of penetration and flash point is done. Also in this research thermal sensitivity modified and unmodified bitumen is also computed.
The comparison is shown in Table 4 and Figures 1-4.
As shown in Fig. 1, with increasing Gilsonite percentage of penetration rates reduced.
By adding Gilsonite to 15% bitumen, the degree of penetration of the unmodified sample has decreased by 25%. It is also shown in Fig. 2, with increasing Gilsonite percentage has also increased the softening point.
As the Gilsonite grows at a rate of 15% bitumen, 12% the softening point has increased than unmodified sample.
Fig. 3 also indicates the improvement of bitumen thermal sensitivity
So that by adding Gilsonite to a rate of 15% thermal sensitivity of bitumen increased by 24% compared to unmodified sample.
It is also seen in Fig. 4 as increasing Gilsonite percentage has increased bitumen viscosity.
But on Figure 5 it is seen that Gilsonite hasn’t effect on flash point.
Fig.2 shows changes in the softening point of the modified bitumen by increasing the Gilsonite percentage and indicates that the thermal sensitivity of the bitumen has been corrected.
The thermal sensitivity index shows with PI and calculated from this relationships:
PI= [1952 − 500 log (pen25) − 20SP]/ [50log (pen25) − SP − 120]
Pen25: penetration degree of bitumen at 25 ° C
SP: The softening point in degrees Celsius.
The PI value for road building tar is usually in the range is -2 and +2.
Fig.3 shows How to change PI with Gilsonite percentage increase. According to the process in this chart it can be concluded that Gilsonite improves the thermal shear sensitivity of pure bitumen.
Fig.4 shows how changes in viscosity with increase Gilsonite percentage.
According to tests conducted on pure bitumen 60/70 and Modified Bitumen with Different Percentages of Gilsonite It can be seen: