1. Hot Mix Asphalt Production and Placement Gary L. Fitts, P.E. Sr. Field Engineer Asphalt Institute Texas A&M University, CVEN 342 Tuesday, July 14, 2015

2. ASPHALT INSTITUTE www.asphaltinstitute.org A SPHALT I NSTITUTE International association of petroleum asphalt producers, manufacturers, and affiliated businesses, established in 1919 Promotes the use, benefits and quality performance of petroleum asphalt through engineering, research and educational activities. HQ office-Lexington, KY

4. ASPHALT INSTITUTE www.asphaltinstitute.org References Asphalt Institute –www.asphaltinstitute.org –859-288-4960 Texas Asphalt Pavement Association –www.txhotmix.org –512-312-2099 National Asphalt Pavement Association –www.hotmix.org –888-468-6499 Asphalt Pavement Alliance –www.AsphaltAlliance.com

5. ASPHALT INSTITUTE www.asphaltinstitute.org HMA Plant Functions Aggregate and asphalt storage Aggregate drying Dust collection, air pollution control Aggregate and asphalt proportioning Mixing Mixture discharge/storage

6. ASPHALT INSTITUTE www.asphaltinstitute.org Topics Basic information on: –HMA Production –HMA Placement –HMA Compaction Considerations for developing HMA specifications

7. ASPHALT INSTITUTE www.asphaltinstitute.org Batch Plant

8. ASPHALT INSTITUTE www.asphaltinstitute.org Batch Plants-Features Aggregates dried, separated by size Aggregates recombined by weight in weigh hopper Aggregates introduced into pugmill, briefly mixed Asphalt introduced by weight, mixed with aggregates Completed HMA discharged or stored

9. ASPHALT INSTITUTE www.asphaltinstitute.org Batch Plant LayoutDryer BatchTower DustCollector Asphalt Cold Feed Bins Asphalt Trucking, Inc ColdElevator Hot Elevator Storage Silo (optional)

11. ASPHALT INSTITUTE www.asphaltinstitute.org Drum Plants Aggregates are dried, mixed with asphalt in a continuous operation Quality control entirely dependent on: –stockpile management –plant calibration Mixture must be stored in surge bin or silo

12. ASPHALT INSTITUTE www.asphaltinstitute.org Drum Plant Layout

13. ASPHALT INSTITUTE www.asphaltinstitute.org Multipav, S.A., El Salvador

14. ASPHALT INSTITUTE www.asphaltinstitute.org Drum Plant-Knippa, Texas

15. ASPHALT INSTITUTE www.asphaltinstitute.org Drum Plant Configurations Parallel flow Counter flow “Coater” (continuous dryer/pugmill) Drum in a drum –double –triple

16. ASPHALT INSTITUTE www.asphaltinstitute.org Weigh Bridge

17. ASPHALT INSTITUTE www.asphaltinstitute.org HMA Production Objective is to produce a mixture meeting the specified design requirements –Volumetric –Mechanical Samples are normally obtained from trucks at the plant, taken to the laboratory, and tested to confirm these qualities

18. ASPHALT INSTITUTE www.asphaltinstitute.org Surface Preparation Prime Coats Applied to unbound surface Moderate, uniform application (0.15-0.35 gal/sy) of low viscosity liquid asphalt Example materials –MC-30 –MC-70 –AEP

19. ASPHALT INSTITUTE www.asphaltinstitute.org Surface Preparation Tack Coats Applied to bound surface Light, uniform application of liquid asphalt (0.03-0.05 gal/sy residual) Example materials –Asphalt emulsions SS-1h, CSS-1h, MS-2 “Special Tack Emulsions” –Paving grade asphalt PG 64-22

20. ASPHALT INSTITUTE www.asphaltinstitute.org Tack Coat Application

21. ASPHALT INSTITUTE www.asphaltinstitute.org

22. ASPHALT INSTITUTE www.asphaltinstitute.org Paving Equipment Paving Machine Components Tractor unit Screed Electronic grade controls

24. ASPHALT INSTITUTE www.asphaltinstitute.org HMA Delivery Paver pulls up to meet the truck –DON’T BUMP THE PAVER! Break the load before opening tailgate Charge the hopper before it’s empty

25. Tractor and Screed Units MS-22, Fig. 5.11 (Courtesy of Blaw-Knox)

26. ASPHALT INSTITUTE www.asphaltinstitute.org Forces Acting on Screed

27. ASPHALT INSTITUTE www.asphaltinstitute.org Automatic Screed Controls Electronic adjustment to screed height using sensing and reference system Sensor detects elevation changes, adjusts height of tow point Slope (transverse) controls

29. ASPHALT INSTITUTE www.asphaltinstitute.org Paving Operations Maintain uniform resistance to face of screed! –Keep uniform head of material at the face of the screed –Operate paver within a narrow range of forward speed Coordinate mixture delivery, paver speed and compaction operations

30. Uniform Head of Material

31. ASPHALT INSTITUTE www.asphaltinstitute.org

32. A SPHALT I NSTITUTE www.asphaltinstitute.org Compaction The process of compressing a material into a smaller volume while maintaining the same mass.

33. ASPHALT INSTITUTE www.asphaltinstitute.org Compaction Essential to good performance! Need to compact to desirable air voids level –Fine graded mixtures: 4-8% –Coarse or gap-graded mixtures: 3-6% Compaction can only achieved if: –Mixture is confined –Mixture is hot (workable)

34. ASPHALT INSTITUTE www.asphaltinstitute.org Factors Affecting Compaction Mixture properties Base/subgrade support (confinement) Ambient conditions Lift thickness

35. ASPHALT INSTITUTE www.asphaltinstitute.org Asphalt Binder Properties Binder grade –increase high temperature grade  stiffer binder –neat or modified? PG grades with 92C or more temp. difference are usually polymer modified Temperature –must complete compaction while mix temp exceeds: 85C (185F) for neat binders 115C (240F) for modified binders

36. ASPHALT INSTITUTE www.asphaltinstitute.org Compaction-Lift/Layer Thickness Coarse-graded mixtures, mixtures using modified asphalts –Minimum 4X nominal maximum size –½ in NMS – minimum 2” lift thickness Fine-graded mixtures –Minimum 3X nominal maximum size Thicker lifts also conserve heat, providing more time to complete compaction

37. ASPHALT INSTITUTE www.asphaltinstitute.org 100 0 Sieve Size, mm, raised to 0.45 power.075.3 2.36 12.5 19.0 Percent Passing control point restricted zone zone max density line maxsizenommaxsize Aggregate Gradation

38. ASPHALT INSTITUTE www.asphaltinstitute.org 100 0 Sieve Size, mm, raised to 0.45 power.075.3 2.36 12.5 19.0 Percent Passing maxsizenommaxsize Design Aggregate Structure Fine graded Coarse graded

39. 30 20 10 0 1234 Time avail. for Compaction, min Compacted Thickness, in 30F60F 90F 30 20 10 0 ~ 6 min Mix Temp. = 275F

40. ASPHALT INSTITUTE www.asphaltinstitute.org Rolling Phases Breakdown Intermediate Finish Different equipment and different techniques for each phase

41. ASPHALT INSTITUTE www.asphaltinstitute.org Compaction Equipment Screed unit –weight of screed –external force applied to screed –vibratory unit 35 Hz (2100 VPM) –tamper bar Rollers –vibratory steel-wheeled –pneumatic –static steel-wheeled –combination

42. ASPHALT INSTITUTE www.asphaltinstitute.org Vibratory Rollers Commonly used for initial (breakdown) rolling 8-18.5 tons, 57-84 in wide (“heavy” rollers) –50-200 lbs/linear inch (PLI) Frequency: 2700-4200 impacts/min. Amplitude: 0.016-0.032 in. –For thin overlays (≤ 2 in.) use low amplitude or static mode Operate to attain at least 10 impacts/ft –2-4 mph

43. ASPHALT INSTITUTE www.asphaltinstitute.org Amplitude & Frequency Amplitude Time between blows, t Frequency = 1/t

44. ASPHALT INSTITUTE www.asphaltinstitute.org Roller Eccentrics Low amplitude High amplitude Example from Dynapac CC 501

45. ASPHALT INSTITUTE www.asphaltinstitute.org Amplitude vs. Frequency High amplitude generates most force At same frequency, high amplitude does more work Is it logical to use high amplitude with high frequency?

46. ASPHALT INSTITUTE www.asphaltinstitute.org Vibratory Frequency Frequency is drum impacts per minute Working speed must match frequency Best results when impact spacing is 10-14 per foot

47. ASPHALT INSTITUTE www.asphaltinstitute.org Frequency Impacts/ft = 1/Impact Spacing

48. ASPHALT INSTITUTE www.asphaltinstitute.org Impacts per Foot of Travel Vibratory Rollers VPM2 mph2.5 mph3 mph3.5 mph4 mph 200011.4--- 250014.211.4--- 300017.013.611.4--- 350019.915.913.311.410.0 400022.718.215.213.011.4 Reed Tachometer-used to check frequency of vibratory rollers

49. ASPHALT INSTITUTE www.asphaltinstitute.org Static Steel-Wheeled Rollers 10-14 ton rollers normally used for HMA compaction –Commonly use vibratory rollers operated in static mode Lighter rollers used for finish rolling Drums must be smooth and clean For initial compaction, drive wheel must face paver AI MS-22, Figure 6.05

50. ASPHALT INSTITUTE www.asphaltinstitute.org Static Steel-Wheeled Rollers

51. ASPHALT INSTITUTE www.asphaltinstitute.org Pneumatic Tire Manipulation Overlap manipulates mat under and between tire Tight finish resists moisture penetration Manipulation increased by lowering tire pressure Static force increased by high tire pressure

52. ASPHALT INSTITUTE www.asphaltinstitute.org Rolling Pattern Speed & lap pattern for each roller No. of passes for each roller Min. temperature by which each roller must complete pattern IMPORTANT: Paver speed must not exceed that of the compaction operation!!!

53. ASPHALT INSTITUTE www.asphaltinstitute.org Typical Pattern, 2 inch Overlay 2-4 passes, tandem vibratory roller –Mix temperature above 250F –Lowest amplitude setting, highest frequency –Vibration on one or both drums –Travel speed to obtain 10 impacts/ft (~3 mph) 2-4 passes, pneumatic roller –Mix temperature 180-230F –Roller speed ~ 3 mph 2-4 passes, static rolling –Mix temperature 140-180F –As necessary to remove blemishes

54. ASPHALT INSTITUTE www.asphaltinstitute.org HMA Specifications General types of project specifications: –Method –Statistically-based acceptance “QC/QA” –End result –Warranty Short-term (workmanship related) Long-term (design-build) No one type is appropriate for all conditions

55. ASPHALT INSTITUTE www.asphaltinstitute.org Method Specifications Contractor is required to follow specific instructions during all phases of construction –Owner provides mixture design –Mixture is accepted on the basis of owner’s (or contractor’s) quality monitoring tests –Delivery, placement, and compaction accepted based on inspection by owner/owner’s agent Examples of method spec: –TxDOT, Item 340 (all Standards Spec’s through 1982) –2004 Standard Specifications to include method-type Item 340

56. ASPHALT INSTITUTE www.asphaltinstitute.org Statistically-Based QC/QA Requires a minimum established level of contractor quality monitoring tests –Contractor usually furnishes the mixture design Defines lots and sublots for production and placement, requires stratified random sampling of materials Acceptance/payment performed on a lot-to-lot basis –Usually includes penalty/bonus provisions on key materials qualities –Many agencies applying percent-within-limits (PWL) criteria, whereby upper and/or lower limits of key criterion are defined Most commonly applied specification type for highways and airports 1993 TxDOT Standard Specifications, all 2004 HMA items (except 340) Most common PWL specification: FAA P-401

57. ASPHALT INSTITUTE www.asphaltinstitute.org Short-Term Warranty Acceptance based on observed performance under limited term Performance defined through measurement of: –Roughness/ride quality –Cracking (non-wheelpath) –Rutting –Surface friction Contractor controls materials selection, mixture design, and all construction requirements Term may vary from 1 to 7 years, becoming more popular for use on highway projects –Indiana, Wisconsin, Michigan, other states

58. ASPHALT INSTITUTE www.asphaltinstitute.org Long-Term Warranties Contractor is required to deliver a pavement with performance characteristics at defined levels at the end of an extended period (15-30 years) Contractor responsible for pavement structural design and construction Most often used outside USA (design/build/operate/concessions projects in Central and South America, Europe) Best US example, NM 44 project

59. ASPHALT INSTITUTE www.asphaltinstitute.org Comparison of Different Types of Specifications Relative Risk TypeOwnerCntrctrComment Method++- Requires diligent inspection QC/QA++ Best applicable to large- scale projects S-T Warranty -+ Project selection is crucial L-T Warranty --++ Bonding a concern, full control must be given to contractor

60. Thanks for your attention!