Methods of Asphalt Characterization for Understanding the link between Chemistry and Material Failure FHWA Project Review January 26, 2012 Ryan B. Boysen John F. Schabron Eric W. Kalberer Joseph F. Rovani Jr. Mark Pooler Mike Farrar
Goals What Problems are we addressing? A need for Improved characterization of materials Moisture damage Forensics (small sample size) Rapid highway core materials evaluation Thin film aging (aging and durability) What kind of products are we delivering? New characterization methods Quantification of Water in Asphalt Miniaturizing and automating older methods
Why quantify Water? What questions are we addressing? How does lower mixing temperature and/or the use of WMA technologies affect the moisture content of the binder? How do these same variables affect the moisture content of the mix? How does the remaining moisture in the mix affect both the short and long term pavement durability?
FTIR Van de Voort method for lubricating oils Methods Extraction of moisture with dried acetonitrile (3676 cm -1 Absorption) O H H C N N C GC Ca C C + O H H H C C H + Ca OH OH DSC Detects difference between free and bound water Karl Fischer Titration Gold Standard, but problems due to interference of by sulfur functional groups
Utilizes I 2 (I - )as a titrant for water. Karl Fischer for Moisture in Binder Known as the gold standard for water measurement. 1 mole I 2 reacts with 1 mole of H 2 O. Coulometric - Provides the sensitivity needed and is versatile enough for use with asphalt. Detection limit ~ 10ppm Interference from functional groups such as thiols sulfides and ketones These interferences may be overcome with innovative approaches Hydranal as solvent Drying asphalt to quantify interference Quantifying interference with model compound doping studies and FTIR
Products Automated/miniaturized SARA Major improvement in asphalt separation Higher throughput for large sample sets (2 hrs compared to 2 days for gravimetric method) Couple with Asphaltene Determinator (obtain additional information such as Aging Index)
Polarity / Aromatic Continuum SARA SEPARATION FRACTIONS The particular methods used define the fraction cut points and chemistry Maltenes / Petrolenes Subfractions Asphaltenes Pre-coke Mesophase Saturates, Saturates Naphthenes Aromatics Polars / Resins, Pericondensed Structures with Side Chains Asphaltenes: Pericondensed Aromatic Structures Adsorption Chromatography Fractions Precipitation / Solubility
Gravimetric Asphaltene and Maltenes Separation Mix asphalt with hydrocarbon solvent Filter asphaltenes Remove solvent from maltenes Perform column chromatography on maltenes (SARA) Takes 2 days There are a variety of different asphaltene precipitation methods and SARA methods in use, each providing different results
4-10 pericondensed aromatic ring systems 4-6 alkyl carbon chains 20-40 aliphatic carbons 60-90 hydrogens Average H/C atomic ratio 1.2 Number average molecular weights near 700 g/mol Heteroatoms Sulfur: aromatic thiophene, aliphatic sulfide Nitrogen: aromatic pyrrole or pyridine, and metal (Ni, V) chelating structures Oxygen: naphthenic (carboxylic) acids Component molecules self-associate Petroleum Asphaltene Component Molecules
Typical Polar/Resin Molecule Highly aromatic Contains heteroatoms Polar molecules (either acidic, basic, or amphoteric) Molecules associate with asphaltenes and each other. Asphaltene Like Less polar and lower surface energy S
Typical Aromatics fraction Unsaturated Carbon Bonds Contains few heteroatoms Nonpolar Typically 500-800 Daltons
Typical Saturates molecule Completely saturated Contains no heteroatoms Nonpolar Typically 500-800 Daltons C H 3 CH3
WRI Asphaltene Determinator SOLUBILITY BASED SEPARATION NOT CHROMATOGRAPHY Separation of Asphaltene Solubility Subfractions Solubility of Individual Components PTFE-Packed Column Signal Output Column Packing Detector Waste Solvent Precipitation Solvent Re-dissolution Solvent Column Solvent Selection Valve Injector Pump Sample Solution
Heptane Maltenes Varnish Following filtration of asphaltenes through 10 micron and 0.45 micron filters, soluble material in the heptane maltenes strongly adsorbs to glass This material irreversibly adsorbs to aminopropyl and silica stationary phases, but it can be rinsed off glass. By using a glass bead packed column, this material will not reach the aminopropyl or activated silica columns. NOVEL AUTOMATED SARA METHOD CONDITIONS
Combined AD / SAR Separation Rapid Evaluation of Asphalts and Heavy Oils Evaluate Materials and Changes with Aging and Processing Whole asphalt injected :2 mg Repeat injections possible Four columns Ground PTFE: Separates maltenes and asphaltenes Glass beads: Reversibly adsorbs maltenes varnish Aminopropyl Bonded Silica: Adsorbs polars/resins Activated Silica: Separates saturates and aromatics
Integrated AD / Normal Phase SARA Separation Flow Diagram
Integrated AD / Normal Phase SARA Separation Flow Diagram
Automated AD / SARA Separation Profile for a Vacuum Residuum 200 ELSD Scatter Units 160 120 80 40 0 ELSD Saturates Asphaltenes Toluene Cyclohexane CH 2 Cl 2 :MeOH Aromatics Resins nm Absorbance at 500 500 nm Asphaltenes Toluene Aromatics Cyclohexane CH 2 Cl 2 :MeOH Resins 0 10 20 30 40 50 60 70 Elution Time, min 80 90
Repeat Injections Possible Without Changing Columns Evaporative Light Scattering Detector Area Percent Normal-Phase Separation of Maltenes Solubility Separation of Asphaltenes Saturates Aromatics Resins Cyclohexane Touene CH 2 Cl 2 :MeOH Total 19.0 36.1 33.7 4.2 6.8 0.1 11.2 19.4 36.7 33.1 4.0 6.7 0.1 10.8 20.1 35.7 32.9 4.3 6.9 0.1 11.3 19.0 38.1 32.3 3.9 6.6 0.1 10.6 19.2 38.3 32.0 3.9 6.5 0.1 10.5 18.8 38.6 32.1 3.9 6.6 0.1 10.5 19.4 38.3 31.7 3.9 6.7 0.1 10.7 19.3 38.7 31.5 4.0 6.5 0.1 10.6 19.9 36.4 32.4 4.3 7.0 0.1 11.4 18.8 38.7 32.0 3.8 6.6 0.1 10.5 mean 19.3 37.6 32.4 4.0 6.7 0.1 10.8 s 0.44 1.18 0.69 0.19 0.15 0.01 0.33 %rsd 2.3 3.1 2.1 4.8 2.3 11.9 3.1
Model Compound Elution Saturates Aromatics C H 3 Cholestane CH3 Benzo(a)pyrene Microcrystalline Wax Squalene
Comparison of Automated and Gravimetric SARA Methods Total Automated SARA Values (ELSD Area %) Saturates Aromatics Resins Asphaltenes AAA 19.4 38.3 31.7 10.7 AAB 19.5 29.9 39.3 11.3 AAC 32.1 21.7 39.6 6.7 AAD 13.9 33.4 37.8 14.9 AAE 20.5 22.3 37.0 20.2 AAF 19.8 27.9 45.2 7.1 AAG 21.0 22.2 54.0 2.7 AAK 11.7 36.8 38.3 13.2 AAM 22.6 24.6 50.4 2.4 Gravimetric SARA Values (%) Saturates Aromatics Resins Asphaltenes AAA 22.9 43 16 17.3 AAD 20.7 41.4 16.0 22.0 AAG 23.2 51.9 21.1 5.7 AAK 18.6 42.1 16.7 20.7 Automated SARA data (2 hours) are comparable with laboratory scale data (2 + days) Method optimization experiments underway