GILSONITE, AN ASPHALT MODIFIER

Experimental Investigation of the Effect of Gilsonite on Performance of Hot-Mix Asphalt

Over the last several years asphalt pavements have experienced early deterioration and premature pavement failures. Permanent deformation or rutting and fatigue cracking are two major distress types in asphalt concrete pavements.

In the past two decades, many different additives like polymer and rubber powder have been proposed in order to improve rutting and fatigue resistance of asphalt mixtures.

In order to modify the bitumen performance and asphalt, several countries namely Australia, Singapore, Indonesia, Japan, France and Germany have used Gilsonite for roads with high traffic load and this action lead to  successful results.

Here, the effect of Iranian Gilsonite on the rutting and fatigue resistance of hot-mix asphalt (HMA) has been investigated. Results of the tests conducted on the modified bitumen with Gilsonite, as well as HMA containing Gilsonite, show that Gilsonite can improve the high and intermediate performance temperature of bitumen and improve the rutting and fatigue resistance of modified HMA.

Gilsonite, is a naturally occurring solid hydrocarbon that has been evaluated and used in various industrial applications and is currently being marketed as an asphalt modifier. Addition of Gilsonite to bitumen increases its viscosity and reduces its penetration

While at low temperatures it causes brittleness of the bitumen and provides a suitable condition for low temperature cracking in the pavement, Investigations of Iranian Gilsonite show that addition of Gilsonite to bitumen causes improvement in performance of bitumen at high temperatures

Gilsonite in iran from mines in Kermanshah province was selected. Table 1shows the physical properties and elemental analysis of the Gilsonite. Previous research shows that addition of 12% Gilsonite to natural bitumen will result in better performance at intermediate and high temperatures. Table 2 shows the physical properties the bitumen used in this experiment.

Table 1.  Physical properties and basic analysis of Kermanshah Gilsonite

 

 

Parameter measured Test

 

Test  method

 

Test Results

Specific gravity@25°C (gr/cm3) ASTM D3289 1.158
Solubility in CS2 (%) ASTM D4 94.12
Solubility in TCE (%) ASTM D2042 92.87
Penetration@25°C(0.1mm) ASTM D5 0
Ash content (%) ASTM D3174 3.62
Moisture content (%) ASTM D3173 1.3
Carbon content (%) ASTM D5291 78.7
Hydrogen content (%) ASTM D5291 8.0
Nitrogen content (%) ASTM D5291 1.0
Oxygen content (%) ASTM

D5291

 

1.7
Sulfur content (%) UOP 864 7.24 7.24

Table 2. Physical properties of bitumen

 

 

Parameter measured

 

Test method

 

Test Results

Specific gravity@25°C (gr/cm3) ASTM D70 1.013
Penetration@25°C (0.1mm) ASTM D5 60
Flash point (°C) ASTM D92 311
Softening point  (R & B,

°C)

ASTM D36 48
Viscosity@160°C(c.stokes) ASTM D2170 139

On this basis, the gilsonite powder was passed through sieve No.50 (0.2 mm), up to an amount of 12% of the weight of the bitumen. This was then added to the base bitumen, which was heated up to 140oC and blended for 150 minutes at the speed of 150 rounds per minute in the mixer. Then, the blending temperature was raised to 180oC and the process was repeated for another 30 minutes at the speed of 4500 rounds per minute to ensure that a homogenous blend of gilsonite and the basebitumen is produced.

Tables 3 and 4 show the aggregate properties that were used in this research. The aggregate gradation was selected in accordance with type IV of Iran highway asphalt paving code.

Table 3. Physical properties of aggregate

 

 

Parameter measured

 

Test method

 

Test Results

Los Angeles

Abrasion (%)

 

 

ASTM

C131

23
Soundness  of aggregate by use of sodium sulfate ASTM

C88

Fine aggregate:2.7 Coarse aggregate: 0.3
Fractured particles in

coarse aggregate

(larger Than

4.75mm) (%)

ASTM D5821 One fractured face: 99.8

Two fractured faces: 97.2

Elongation  index BS812 9
Flakiness index BS812 22

 

Table 4. Specific gravity and water absorption of aggregate

 

Aggregate type Bulk Specific gravity (gr/cm3) Apparen specific gravity (gr/cm3) Water absorption (%)
Coarse 2.584 2.668
Fine 2.730 2.600 1.5
Filler 2.600 1.8
 

Conclusions:

All in all By Addition of Gilsonite to asphalt the following conclusions are deduced:

  • Increasing the rigidity and strength of the burden of traffic
  • Modified bitumen with Gilsonite improves resilient.
  • Modified bitumen with Gilsonite improves high performance temperature of bitumen and rutting resistance of HMA
  • Reducing the effect of tires on pavement
  • Reducing cracking at low temperatures
  • Gilsonite has effects on rutting and fatigue resistance and prevents deformation in hot weather and also the effects of humidity.

 

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