AsphaltThe Bottom of the Barrel

Sponsored by: Minnesota LTAP Center

Presented by: Michael Marti, P.E.SRF Consulting Group, Inc.

Dan Wegman, P.E.SemMaterials

Crude Oil Distillation

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% Volume Boiled Off0 10 20 30 40 50 60 70 80 90 100

Butanes & Lighter

Gasoline

Naphtha

Kerosene/Jet Fuel/Diesel

Gas Oils

AtmosphericLight Vacuum

Heavy Vacuum

Resid

Asphalt Cement (AC)

• End product - crude oil distillation• Chemistry

– crude source– refining method

Chemistry Physical

Properties Performance

Primary use of ACHot Mix Asphalt (HMA)

Aggregate

AC

Mix Plant

Paving

AC Quality• Three major failure modes:

– Rutting (AC too soft at high temperatures; aggregate structure not strong enough)

– Thermal cracking (AC too hard/brittle at low temperatures)

– Fatigue cracking (AC ages and eventually “wears out”)

• Grade & Quality of AC determines resistance to failure

• Chemistry determines AC quality

Asphalt Cement - Penetration

• Asphalts originally “penetration graded”– Penetration at 25°C (77°F) “ambient temperature” – Softer (higher pen) - colder climates– Harder (lower pen) - hotter climates– 85/100, 120/150, 200/300

100 g100 g

penetration0 sec

5 sec

Asphalt Cement - Viscosity

• Later, “Viscosity graded” Viscosity = Resistance to flow

– Absolute Viscosity at 60°C (140°F) - Summer pavement temperature • AC-20 = 2000 ±20% (1600-2400) poise

• AC-10 = 800-1200 p• AC-5 = 400-600 p

– Softer (lower viscosity) - colder climates

vacuum

Performance Graded Asphalts

– Performance at high and low temperatures– SHRP Super Pave PG (Performance Grades)– PG Grading system based on:

• Climate (Temperatures in ºC)• Risk (Reliability Factor)• Traffic speed and load (Grade “Bumping”)

– PG 64-28 • 5-day High Pavement Temp, 64 °C = 147 °F

• Single day Coldest Air Temp, -28°C = -18 °F