Asphalt Paving Materials
Bituminous Materials Bitumen—also known as asphalt or tar—is a black, oily, viscous form of petroleum, which is a naturally occurring organic byproduct of decomposed plants. Natural bitumen is the thickest form of petroleum there is, and is made up of 83% carbon, 10% hydrogen and lesser amounts of oxygen, nitrogen, sulfur, and other elements. CIVL 3137 2
Bituminous Materials Bituminous Materials Natural Tar & Petroleum Asphalts Pitch Asphalts (late 1800s) (late 1800s) (early 1900s) CIVL 3137 3
Natural Asphalt Rock Asphalt Asphalt Sand Native Asphalt CIVL 3137 4
Rock Asphalt Asphalt rock is formed when natural layers of petroleum harden in the pores of sedimentary rocks such as limestone or sandstone. Over time, the lighter components evaporate away leaving material that ranges in consistency from a thick liquid to a crumbly sand or stone. Only about 5% to 15% of the composition of asphalt rocks is asphalt. CIVL 3137 5
Rock Asphalt CIVL 3137 6
Rock Asphalt ROCK ASPHALT & OIL SHALE IN KENTUCKY CIVL 3137 7
Asphalt Sands Asphalt sands (also called oil or tar sands) are either loose sands or partially consolidated sandstone containing a mixture of sand, clay, water, and bitumen. It is increasingly used as a source for crude oil thanks to technological developments such as steam extraction. CIVL 3137 8
Asphalt Sands CIVL 3137 9
Asphalt Sands CIVL 3137 10
Asphalt Sands CIVL 3137 11
Native Asphalt Native asphalts are seepages of natural asphalt that rise to the surface from deeper oil-bearing rocks and collect in depressions on the ground surface. The lighter components evaporate to leave behind a viscous or semi-solid deposit. The asphalt is so viscous you can walk on the surface. But if you stand on the surface for too long, you will slowly sink into it! CIVL 3137 12
Native Asphalt CIVL 3137 13 Source: Geological Society of Trinidad and Tobago (www.gstt.org)
Native Asphalt CIVL 3137 14
La Brea “Tar” Pits Wilshire Blvd CIVL 3137 15
Pitch Lake, Trinidad CIVL 3137 16
Pitch Lake, Trinidad CIVL 3137 17 http://www.flickr.com/photos/striderv/4314238332/lightbox/
Pitch Lake, Trinidad CIVL 3137 18
Pitch Lake, Trinidad CIVL 3137 19
Pitch Lake, Trinidad CIVL 3137 20
Pitch Lake, Trinidad CIVL 3137 21
Pitch Lake, Trinidad CIVL 3137 22
Bituminous Materials Bituminous Materials Natural Tar & Petroleum Asphalts Pitch Asphalts (late 1800s) (late 1800s) (early 1900s) CIVL 3137 23
Tar / Pitch Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a variety of organic materials such as coal, wood, or peat. The material is heated without oxygen (so the source material doesn’t burn) until the tar liquefies and seeps out. CIVL 3137 24
Wood Tar Wood tar (primarily made from pine wood) has many uses as a disinfectant, a flavoring agent for candies and alcohol, a spice for meat, and a water repellant. It is also used in cosmetics and anti-dandruff shampoos. Turpentine and charcoal are the byproducts of wood tar distillation. CIVL 3137 25
Wood Tar Kiln, Sweden https://en.wikipedia.org/wiki/Tar CIVL 3137 26
Coal Tar Coal tar is produced by heating coal without oxygen to produce coke and oil gas. Coal tar was used to construct the first surfaced roads. This is where we get the term “tarmac” or “tar macadam”. Today it can still be found in some parking lot sealers though it’s being phased out due to environmental and health concerns. CIVL 3137 27
Dunlap, TN Coking Ovens CIVL 3137 28
Chickamauga Coking Ovens CIVL 3137 29
Pennsylvania Coking Ovens CIVL 3137 30
Bituminous Materials Bituminous Materials Natural Tar & Petroleum Asphalts Pitch Asphalts (late 1800s) (late 1800s) (early 1900s) CIVL 3137 31
Petroleum Asphalt Petroleum asphalt is produced as a byproduct of crude oil distillation. It is the fraction of the crude oil with the highest boiling point (greater than 500°C) so it represents the residual left over after everything else (gasoline, kerosene, diesel, etc.) has boiled off in the distillation process. CIVL 3137 32
Crude Oil Chemistry Oils (Hydrocarbons) Resin-coated asphaltenes CIVL 3137 33
Crude Oil Light Crude Heavy Crude “oils” “oils” “oils” “oils” Aromatic Saturated (oils) Hydrocarbons Hydrocarbons CIVL 3137 34
Atmospheric Distillation Butane & Propane 1-4 Carbons Distillation Column Gasoline - 70°C 1-4 Carbons Naphtha - 120°C 5-10 Carbons Kerosene - 170°C 10-14 Carbons Crude Diesel Oil - 270°C 15-38 Carbons 400ºC Tube Heater Topped Crude 38-70 Carbons CIVL 3137 35
Vacuum Distillation Vacuum Light Gas OIl Medium Gas OIl Heavy Gas Oil Topped Crude Heat Bitumen Residuum (Asphalt Cement) Vaporizes the topped crude without using excessive heat (“cracking”) CIVL 3137 36
Crude Oil Gasoline Kerosene 6 21 Lt. Gas Oil 7 33 14 Hv. Gas Oil 26 10 20 28 16 Bitumen 58 Residuum 30 27 Nigeria Boscan Arabian Light Venezuela Heavy CIVL 3137 37
Petroleum Asphalt Petroleum asphalt at room temperature is very stiff. In order to mix it with aggregate to make asphalt concrete, it has to be liquefied. CIVL 3137 38
Liquefying Asphalt Cement Asphalt Cement (Bitumen Residuum) Heat Thin it with Suspend it solvents it in water Hot-Mix Cutback Emulsified Asphalt Asphalt Asphalt CIVL 3137 39
Temperature-Viscosity Peanut Butter Ketchup Chocolate Syrup Honey AASHTO T-245 MARSHALL COMPACTING TEMP. RANGE (280 +/- 30 cSt) Tomato Juice AASHTO T-245 MARSHALL MIXING TEMP. RANGE (170 +/- 20 cSt) Vegetable Oil CIVL 3137 40
Liquefying Asphalt Cement Asphalt Cement (Bitumen Residuum) Heat Thin it with Suspend it solvents it in water Hot-Mix Cutback Emulsified Asphalt Asphalt Asphalt CIVL 3137 41
Cutback Asphalt Cutback asphalt is asphalt cement that has been blended with a solvent in order to reduce its viscosity. After a cutback asphalt is applied the solvent evaporates leaving behind asphalt cement residue on the surface to which it was applied. A cutback asphalt is said to “cure” as the petroleum solvent evaporates away. CIVL 3137 42
Cutback Asphalt Cutback asphalt is classified according to the rate at which it cures (fast, medium, slow) and the viscosity of the liquid. The curing rate is a function of the boiling point of solvent used. The viscosity is based on how much solvent is used. CIVL 3137 43
Cutback Asphalt Grade 30 70 250 800 3000 Solvent Asphalt 30-60 70-140 250-500 800-1600 3000-6000 Kinematic Viscosity @ 140°F (in centistokes) CIVL 3137 45
Cutback Asphalt Rapid Curing (RC) Asphalt cement thinned with gasoline or naphtha Used for tack and seal coats (surface applications) Medium Curing (MC) Asphalt cement thinned with kerosene Used for prime coats, cold-laid pavement bases Slow Curing (SC) Asphalt cement thinned with diesel oil or gas oils Used for cold-laid pavement bases CIVL 3137 46
Liquefying Asphalt Cement Asphalt Cement (Bitumen Residuum) Heat Thin it with Suspend it solvents it in water Hot-Mix Cutback Emulsified Asphalt Asphalt Asphalt CIVL 3137 47
Emulsified Asphalt Emulsified asphalt is a suspension of very small asphalt cement droplet in water, which is assisted by an emulsifying agent (e.g., soap) that disrupts the surface tension of the water and imparts an electrical charge to the surface of the asphalt cement droplets so that they do not coalesce into larger droplets and fall out of suspension. CIVL 3137 48
Emulsified Asphalt hydrophilic group(s) Asphalt droplet hydrophobic component CIVL 3137 49
Emulsified Asphalt Asphalt Asphalt droplet droplet Repulsion between negative surface charges prevents coalescence CIVL 3137 50
Emulsified Asphalt CIVL 3137 52
Emulsified Asphalt Cationic Emulsifier Anionic Emulsifier LIMESTONE SILICA CIVL 3137 53
Emulsified Asphalt Emulsified asphalts appear as a thick brown liquid when first applied. When the asphalt droplets start to adhere to the aggregate the color changes to black and the emulsion is said to “break” (i.e., separate). As the water evaporates, the emulsion behaves more like pure asphalt cement. Once all the water has evaporated, the emulsion is said to have “set”. CIVL 3137 54
Emulsified Asphalt There are three main emulsion grades: rapid set, medium set and slow set. The terms relate to the amount of time it takes for the emulsion to set and the amount of mixing that can be performed before the emulsion breaks. Slow setting emulsions can stand up to more mixing than fast setting emulsions. CIVL 3137 55
Emulsified Asphalt Rapid Setting (RS or CRS) Used for surface coats, penetration macadam Medium Setting (MS or CMS) Used for open-graded asphalt-treated base Slow Setting (SS or CSS) Used for dense-graded asphalt-treated base CIVL 3137 56
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