6506-chemistry - ASPHALT CHEMISTRY MOLECULAR STRUCTURE...

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1 ASPHALT CHEMISTRY MOLECULAR STRUCTURE - Diverse molecular structures - Predominantly composed of carbon and hydrogen. - Most molecules contain one or more heteroatoms, such as sulfur, nitrogen and oxygen. - The type of molecular structure is more important than the total amount of each element present. TYPICAL ELEMENTAL ANALYSIS (Petroleum Asphalts) ELEMENT PERCENT Carbon 83 - 87 Hydrogen 10 -11 Sulfur 1 - 5 Nitrogen 0.3 - 1,1 Oxygen 0.2 - 0.8 Vanadium, ppm 4 - 1400 Nickel, ppm 0.4 - 110 ______________________________________
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2 FUNCTIONAL OR POLAR GROUPS - Heteroatoms (e.g. sulfur, nitrogen, oxygen) are attached to carbon atoms in asphalt molecules in different configurations and form different polar molecules or functional groups. - These molecules are polar because of imbalance of electrochemical forces which produces a dipole. - Molecular interactions among these polar molecules and other asphalt molecules strongly influence the physical properties and performance of the asphalt. - A small amount of polar molecules can have a great effect. - Resistance to stripping is thought to be affected by the adsorption of polar molecules by aggregate surface. CONCEPTUAL COMPOSITION OF ASPHALT ASPHALT N-Heptane Precipitate ASPHALTENE Soluble MALTENES OIL RESIN Liquid Propane Soluble Precipitate
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3 ASPHALTENES - Dark brown, friable solids - Highest polarity - Insoluble in nonpolar solvents (e.g. heptane, pentane) - Strong tendency to associate in conglomerates - Highest molecular weights - Carbon to hydrogen ratio greater than 0.8
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6506-chemistry - ASPHALT CHEMISTRY MOLECULAR STRUCTURE...

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