CEEN 3144 Construction Materials. Asphalts. Francisco Aguíñiga Assistant Professor Civil Engineering Program Texas A&M University Kingsville

Transcription

1 CEEN 3144 Construction Materials Asphalts Francisco Aguíñiga Assistant Professor Civil Engineering Program Texas A&M University Kingsville Page 1 History of asphalts One of the oldest materials Used in 3000 B.C. Originally used from natural pools La Brea Pitch Lake, Trinidad and Tobago Page 2 1

2 Classification of bituminous materials Page 3 Distillation of crude petroleum Page 4 2

3 Solid road asphalts Asphalt cement Cannot be used without heating (highly viscous at normal temperatures) high molecular weight Most common binder in pavements better quality than liquid asphalts Page 5 Liquid road asphalts Asphalt cutback Made by dissolving asphalt cement in a light molecular weight hydrocarbon solvent When used to make roads the solvent evaporates, leaving the cutback as the binder Not used because has three disadvantages Solvents are too expensive Hazardous because of the volatile solvents Application releases environmentally unacceptable hydrocarbons into the atmosphere Page 6 3

4 Liquid road asphalts Asphalt emulsion Micron size globules 60 to 70% asphalt residue, 30 to 40% water, fraction of a percent of soap Almost same specific gravity as water so asphalt does not float nor sink When emulsion is mixed with aggregates and the water evaporates the asphalt acts as a binder Evaporation of water is called breaking or setting Aggregates that bear positive surface charges (limestone) tend to be compatible with anionic emulsions Aggregates that bear negative surface charges (siliceous aggregate) tend to be compatible with cationic emulsions Advantage Do not require hazardous and costly solvents Page 7 Uses of asphalt Main uses pavement construction and maintenance Also used in sealing and waterproofing Asphalt cements Hot-mix asphalt concrete asphalt pavements Liquid asphalts Pavement maintenance: fogs, seals, chip seals, slurry seals, and microsurfacing Sealing cracks Mixed with aggregates to make cold asphalt Page 8 4

5 Asphalt applications Page 9 Asphalt applications Page 10 5

6 Paving applications of asphalt Page 11 Temperature susceptibility of asphalt Low temperatures brittle High temperatures soft Viscosity decreases with temperature Page 12 6

7 Temperature susceptibility of asphalt Adjust asphalt grade to climate Soft grade cold climate Hard grade hot climate Page 13 Chemical composition Asphalt contains mainly Hydrocarbons (hydrogen and carbon atoms) with a small amounts of sulfur, nitrogen, and oxygen Asphalt consists of asphaltenes and maltenes Asphaltenes Dark brown friable solids responsible for viscosity and adhesive properties of asphalt Maltenes Consist of resins and oils Resins are dark with a viscosity dependent on temp. Resins act as agents to disperse aspahltenes in the oils Oils are clear or white liquids Page 14 7

8 Superpave Strategic Highway Research Program Superior Performing Asphalt Pavements Mix design method Performance grading methods for asphalt binders Performance based specifications for asphalt binders and mixtures to control Rutting Fatigue cracking Thermal cracking Page 15 Characterization of asphalt Mainly characterize asphalt cement Conduct test at a given temperature Performance grade characterization Test properties at lower, middle, and upper operating temperatures Previous tests perform test at fixed temperature, then vary requirements for different grades of asphalt New tests perform test at critical temperature and fix criteria for all grades of asphalt Page 16 8

9 New tests of asphalts Perform tests at three temperatures Maximum temperature Highest successive 7-day average maximum pavement temperature Minimum temperature Minimum expected temperature for the pavement over its service life Intermediate temperature Average of maximum and minimum plus 4 C Temperatures used to evaluate Rutting potential - maximum Fatigue potential - intermediate Thermal-cracking minimum plus 10 C Page 17 Performance grade binder characterization Rolling thin-film oven Pressure-aging vessel Flash point Rotational viscometer test Dynamic shear rheometer test Bending beam rheometer test Direct tension test Page 18 9

10 Rolling thin-film oven Used to simulate short-term aging that occurs in asphalt during the production of asphalt concrete Asphalt binder poured into special bottles, the placed in a rack, the rack rotates vertically in an oven at 163 C for 75 min. Aged binder is used in dynamic shear rheometer and pressure aging vessel Page 19 Pressure-aging vessel Designed to simulate oxyidative aging that occurs during pavement service Asphalt is aged under specified temperature for 20 h at 305 psi Residue from the test can be used to estimate physical or chemical properties at 5 or 10 years of service Page 20 10

11 Flash point Cleveland open cup Safety test measures temperature at which asphalt flashes Fire temperature cause vapors to ignite Flash temperature sustain burning > 5 sec Page 21 Rotational viscometer test Used to measure the viscosity of asphalt Test performed on unaged binders Place sample in chamber at 135 C, then placed in a thermocell, then spindle is placed in asphalt and rotated Viscosity determined by amount of torque required to rotate spindle Page 22 11

12 Dynamic shear rheometer test Used to evaluate rutting and fatigue potential Consists of two parallel metal plates, an environmental chamber, a loading device and a data acquisition system Rutting potential evaluated at upper temperature (about 60 C) Sample 25 mm diameter and 1 mm thick Sample preconditioned in rolling thin-film oven Fatigue potential evaluated at intermediate temperature (about 25 C) Sample 8 mm diameter and 2 mm thick Sample preconditioned in rolling thin-film oven followed by pressure-aging vessel Page 23 Bending beam rheometer test Used to evaluate thermal cracking Measures midpoint deflection of an asphalt binder beam under constant load Loading frame, controlled bath, and data acquisition Specimen tested at 10 C above the lower temperature Sample preconditioned in rolling thin-film oven and pressure-aging vessel Deflection measured at 8, 15, 30, 60, 120, and 240 sec Page 24 12

13 Direct tension test Displacement controlled tensile loading machine in a temperature controlled chamber Specimen preconditioned in rolling thin-film and pressureaging vessel Pulled at 1mm/min Test temperature is low temperature plus 10 C Report failure load, stress, and strain Failure strain is a measure of elongation without cracking Page 25 Traditional asphalt characterization tests Penetration Measures asphalt cement consistency Asphalt prepared at 25 C Place 100 g needle on asphalt surface Measure penetration in 5 sec Absolute and kinematic viscosity tests Measures asphalt consistency Heat asphalt, put it in a water or oil bath at 60 C Viscosity measured as flow of asphalt in a U-tube Page 26 13

14 Characterization of emulsion and Cutback Distillation of cutback and emulsion Cutback Measures amount of volatile constituents Determine percentage by volume constituents at specified temperature Emulsion Determines percent of residue and oil distillates by weight Saybolt viscosity of emulsion When applied in a spray must be thin enough to be uniformly applied through the spray bar of the distribution truck Emulsion tested at 25 or 50 C and allowed to flow through the orifice Test result = time in seconds required to fill a flask Page 27 Classification of asphalt Asphalt binders are graded by 4 methods Performance Penetration Viscosity Viscosity of aged residue Page 28 14

15 Performance grading of asphalts Page 29 Penetration grading ASTM D946 Page 30 15

16 Viscosity grading ASTM D3381 Page 31 16