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FHWA Condensed Superpave Asphalt Specifications Lecture Series SUPERPAVE.

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Presentation on theme: "FHWA Condensed Superpave Asphalt Specifications Lecture Series SUPERPAVE."— Presentation transcript:

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2 FHWA Condensed Superpave Asphalt Specifications Lecture Series SUPERPAVE

3 Aggregates Usually refers to a soil that has in some way been processed or sorted.

4 Aggregate Size Definitions Nominal Maximum Aggregate Size –one size larger than the first sieve to retain more than 10% Maximum Aggregate Size –one size larger than nominal maximum size

5 Percent Passing control point restricted zone max density line maxsizenommaxsize Sieve Size (mm) Raised to 0.45 Power

6 Superpave Aggregate Gradation Percent Passing Design Aggregate Structure Sieve Size (mm) Raised to 0.45 Power

7 Superpave Mix Size Designations Superpave Nom Max Size Max Size Designation (mm) (mm) 37.5 mm mm mm mm mm mm mm mm mm mm

8 Gradations * Considerations: - Max. size < 1/2 AC lift thickness - Larger max size + Increases strength + Improves skid resistance + Increases volume and surface area of agg which decreases required AC content + Improves rut resistance + Increases problem with segregation of particles - Smaller max size + Reduces segregation + Reduces road noise + Decreases tire wear

9 Percent Crushed Fragments in Gravels Quarried materials always 100% crushed Minimum values depended upon traffic level and layer (lift) Defined as % mass with one or more fractured faces

10 Percent Crushed Fragments in Gravels 0% Crushed 100% with 2 or More Crushed Faces

11 Coarse Aggregate Angularity Criteria TrafficDepth from Surface Millions of ESALs 100 mm < 0.3 < 1 < 3 < 10 < 30 < 100  /-- 65/-- 75/-- 85/80 95/90 100/100 --/-- 50/-- 60/-- 80/75 95/90 100/100 First number denotes % with one or more fractured faces Second number denotes % with two or more fractured faces

12 Asphalt Cements Background History of Specifications

13 Background Asphalt – Soluble in petroleum products – Generally a by-product of petroleum distillation process –Can be naturally occurring Tar –Resistant to petroleum products –Generally by-product of coke (from coal) production

14 Penetration Testing Sewing machine needle Specified load, time, temperature 100 g Initial Penetration in 0.1 mm After 5 seconds

15 Penetration Specification Five Grades

16 Ductility

17 Typical Penetration Specifications Penetration Flash Point, C Ductility, cm Solubility, % Retained Pen., % Ductility, cm NA 100+

18 Viscosity Graded Specifications

19 Types of Viscosity Tubes Asphalt Institute Tube Zietfuchs Cross-Arm Tube

20 Table 1 Example AC 2.5AC 40 AC 2.5AC 40 Visc, 60C , Visc, 135C Penetration Visc, 60C<1,250 <20,000 Ductility

21 Penetration Grades AC 40 AC 20 AC 10 AC 5 AC Viscosity, 60C (140F)

22 Asphalt Cements New Superpave Performance Graded Specification

23 PG Specifications Fundamental properties related to pavement performance Environmental factors In-service & construction temperatures Short and long term aging

24 High Temperature Behavior High in-service temperature –Desert climates –Summer temperatures Sustained loads –Slow moving trucks –Intersections Viscous Liquid

25 Pavement Behavior (Warm Temperatures) Permanent deformation (rutting) Mixture is plastic Depends on asphalt source, additives, and aggregate properties

26 Permanent Deformation Function of warm weather and traffic Courtesy of FHWA

27 Low Temperature Behavior Low Temperature –Cold climates –Winter Rapid Loads –Fast moving trucks Elastic Solid  E Hooke’s Law

28 Pavement Behavior (Low Temperatures) Thermal cracks –Stress generated by contraction due to drop in temperature –Crack forms when thermal stresses exceed ability of material to relieve stress through deformation Material is brittle Depends on source of asphalt and aggregate properties

29 Thermal Cracking Courtesy of FHWA

30 Superpave Asphalt Binder Specification The grading system is based on Climate PG Performance Grade Average 7-day max pavement temperature Min pavement temperature

31 Pavement Temperatures are Calculated Calculated by Superpave software High temperature –20 mm below the surface of mixture Low temperature –at surface of mixture Pave temp = f (air temp, depth, latitude)

32 u Concentric Cylinder Concentric Cylinder Rheometers  R   MiMi  R i 2 L   R R o - R i

33 Dynamic Shear Rheometer (DSR) Parallel Plate Shear flow varies with gap height and radius Non-homogeneous flow  R = R  h  R = 2 M  R 3

34 Short Term Binder Aging Rolling Thin Film Oven –Simulates aging from hot mixing and construction

35 Pressure Aging Vessel (Long Term Aging) Simulates aging of an asphalt binder for 7 to 10 years 50 gram sample is aged for 20 hours Pressure of 2,070 kPa (300 psi) At 90, 100 or 110 C

36 Bending Beam Rheometer Air Bearing Load Cell Deflection Transducer Fluid Bath Computer

37 Direct Tension Test  L e  L Load Stress =  = P / A Strain ff ff

38 Summary Fatigue Cracking Rutting RTFO Short Term Aging No aging Construction [RV] [DSR] Low Temp Cracking [BBR] [DTT] PAV Long Term Aging

39 Superpave Binder Purchase Specification

40 Superpave Asphalt Binder Specification The grading system is based on Climate PG Performance Grade Average 7-day max pavement temperature Min pavement temperature

41 PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82 (Rotational Viscosity) RV (110) 100 (110) 110 (110) (Flash Point) FP (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % (Direct Tension) DT (Bending Beam Rheometer) BBR Physical Hardening Avg 7-day Max, o C 1-day Min, o C (PRESSURE AGING VESSEL) PAV ORIGINAL > 1.00 kPa < 5000 kPa > 2.20 kPa S < 300 MPam > Report Value > 1.00 % 20 Hours, 2.07 MPa (Dynamic Shear Rheometer) DSR G* sin  ( Bending Beam Rheometer) BBR “S” Stiffness & “m” - value Performance Grades (Dynamic Shear Rheometer) DSR G*/sin  < 3 Pa. 135 o C > 230 o C CEC

42 PG 46 PG 52 PG 58 PG 64 PG 70 PG 76 PG 82 (Rotational Viscosity) RV (110) 100 (110) 110 (110) (Flash Point) FP (ROLLING THIN FILM OVEN) RTFO Mass Loss < 1.00 % (Direct Tension) DT (Bending Beam Rheometer) BBR Physical Hardening Avg 7-day Max, o C 1-day Min, o C (PRESSURE AGING VESSEL) PAV ORIGINAL < 5000 kPa > 2.20 kPa S < 300 MPam > Report Value > 1.00 % 20 Hours, 2.07 MPa (Dynamic Shear Rheometer) DSR G* sin  ( Bending Beam Rheometer) BBR “S” Stiffness & “m” - value How the PG Spec Works (Dynamic Shear Rheometer) DSR G*/sin  < 3 Pa. 135 o C > 230 o C CEC 5864 Test Temperature Changes Spec Requirement Remains Constant > 1.00 kPa

43 PG PG PG PG > Many agencies have established zones PG Binder Selection

44 Summary of How to Use PG Specification Determine –7-day max pavement temperatures –1-day minimum pavement temperature Use specification tables to select test temperatures Determine asphalt cement properties and compare to specification limits

45 Asphalt Concrete Mix Design History

46 Hot Mix Asphalt Concrete (HMA) Mix Designs Objective: –Develop an economical blend of aggregates and asphalt that meet design requirements Historical mix design methods –Marshall –Hveem New –Superpave gyratory

47 Requirements in Common Sufficient asphalt to ensure a durable pavement Sufficient stability under traffic loads Sufficient air voids –Upper limit to prevent excessive environmental damage –Lower limit to allow room for initial densification due to traffic Sufficient workability

48 MARSHALL MIX DESIGN

49 Marshall Mix Design Developed by Bruce Marshall for the Mississippi Highway Department in the late 30’s WES began to study it in 1943 for WWII –Evaluated compaction effort No. of blows, foot design, etc. Decided on 10 lb.. Hammer, 50 blows/side 4% voids after traffic Initial criteria were established and upgraded for increased tire pressures and loads

50 Marshall Mix Design Select and test aggregate Select and test asphalt cement –Establish mixing and compaction temperatures Develop trial blends –Heat and mix asphalt cement and aggregates –Compact specimen (100 mm diameter)

51 Marshall Design Criteria Light TrafficMedium Traffic Heavy Traffic ESAL 10 6 Compaction Stability N (lb.)3336 (750)5338 (1200) 8006 (1800) Flow, 0.25 mm (0.1 in) 8 to 18 8 to 16 8 to 14 Air Voids, % 3 to 5 3 to 5 3 to 5 Voids in Mineral Agg. (VMA)Varies with aggregate size

52 Asphalt Concrete Mix Design Superpave

53 Superpave Volumetric Mix Design Goals –Compaction method which simulates field –Accommodates large size aggregates –Measure of compactibility –Able to use in field labs –Address durability issues Film thickness Environmental

54 reaction frame rotating base loading ram control and data acquisition panel mold height measurement tilt bar Key Components of Gyratory Compactor Compaction

55 Gyratory compactor –Axial and shearing action –150 mm diameter molds Aggregate size up to 37.5 mm Height measurement during compaction –Allows densification during compaction to be evaluated 1.25 o Ram pressure 600 kPa

56 % G mm Log Gyrations N ini N des N max Three Points on SGC Curve

57 SGC Critical Point Comparison %G mm = G mb / G mm G mb = Bulk Mix Specific Gravity from compaction at N cycles G mm = Max. Theoretical Specific Gravity Compare to allowable values at: N INI : %G mm < 89% N DES : %G mm < 96% N MAX : %G mm < 98%

58 Design Compaction N des based on – average design high air temp – traffic level Log N max = 1.10 Log N des Log N ini = 0.45 Log N des % G mm Log Gyrations N ini N des N max

59 Superpave Testing Specimen heights Mixture volumetrics – Air voids – Voids in mineral aggregate (VMA) – Voids filled with asphalt (VFA) – Mixture density characteristics Dust proportion Moisture sensitivity

60 Superpave Mix Design Determine mix properties at N Design and compare to criteria –Air voids 4% (or 96% G mm ) –VMA See table –VFA See table –%G mm at N ini < 89% –%G mm at N max < 98% –Dust proportion 0.6 to 1.2

61 Superpave Mix Design Gyratory Compaction Criteria


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