1. HMA Pavement Recycling and Reconstruction
MODULE 3-8
HMA Pavement Recycling and Reconstruction

2. Learning Objectives
Identify options when pavement is near the end of its service life
Identify considerations associated with reconstruction

3. Introduction Recycling - A rehabilitation alternative
Essentially all 50 states use some form of recycling
73 million tons recycled annually
Recycling is not a new concept
Recycling was first recorded in 1915.
Most recycling has taken place since 1975.

4. Introduction Reconstruction – used less and less Cost
Traffic disruption

5. Recycling vs. Reconstruction
Condition of existing pavement
Traffic levels
Expected life after treatment
Costs and budget
Time required for construction
Many factors enter into the decision of whether to recycle or reconstruct.

6. Purpose and Application Recycling
Reduced cost
Preservation of existing pavement geometrics
Conservation of aggregates and binders
Preservation of the environment
Energy conservation
In 1999 industry estimated that a billion dollars had been saved in landfill tipping fees thru the use of recycling. An industry survey estimated 34 million tons of HMA were recycled and not placed into landfills (ARRA 2000).

7. Definitions Recycled asphalt pavement (RAP)
Reclaimed aggregate material (RAM)
Recycled hot-mix asphalt
Asphalt recycling agent
Asphalt modifier
RAP – removed and/or processed pavement materials containing asphalt binder and aggregate.
RAM – removed and/or processed pavement material containing no asphalt binder.
Recycled HMA – final mixture of RAP, new asphalt binder, recycling agent, & new aggregate if required.
Asphalt recycling agent – ASTM D4552, petroleum product with combination of chemical and physical properties designed to restore aged asphalt to a desired specification.
Asphalt modifier – any compound or material used as an admixture to alter/improve properties of asphalt binder or HMA mixture.

8. Types of HMA Pavement Recycling
Cold in-place recycling (CIPR)
Hot in-place recycling (HIPR)
Hot central plant recycling (HCPR)

9. Cold In-Place Recycling (CIPR)
Used by cities, counties, states and countries around the world for rehabilitation
Primarily used on lower volume roads
Substantial savings possible compared to hot recycling or reconstruction

10. CIPR Purpose and Application
Correcting asphalt pavement distress
No heat
In-place
Combined with
Stabilizing agent
Recycling agent
Aggregate

11. CIPR Equipment Train
Milling machine, small crusher, and pugmill for mixing along with tanks for liquid additives.

12. Hot In-place Recycling (HIPR)
Soften top 50 mm (2 in) of existing asphalt pavement with heat
Mechanically removing the pavement
Mixing with asphalt binder and/or new mixture
Replacing recycled pavement on surface

13. HIPR Purpose and Application
Corrects HMA surface distress
Rutting
Cracking
Raveling
Bleeding
Roughness

14. HIPR – Construction Methods and Equipment
Heater scarification
Repaving
Remixing
This may be performed in a single or multiple pass operation.

15. HIPR - What Are Potential Problems Here?
Heaters may kill the plants next to the curb. They also have the potential to melt traffic cones set to close to the heater.

16. HIPR Equipment Development Early Limitations
In-place air voids
Overheating
Air quality
Safety
Depth
Production / cost
Vegetation

17. HIPR - Needs Identified To Further Implementation
Higher mixture temperatures
Greater depths
Improved air quality
Variable widths
Reduced noise
Build slide – What would be some needs to further HIPR technology?
Outcome of 1994 workshop on HIPR outlining additional needs to be able to further the use of this technology.

18. HIPR - Needs Identified to Further Implementation
Larger amounts of new material
Climb steep grades
Better uniformity
QC/QA guidelines

19. HIPR Performance Improved penetration of asphalt cement Improved ride
Edge, transverse, and midlane cracking no improvement
Ontario recently conducted a follow-up review of 31 HIR projects they have completed since 1987 (Kazmierowski, Marks, and Lee 1999). This study found that the penetration of the asphalt binder was increased by an average of 18 penetration units. Projects constructed in latter years have been more successful in raising the penetration to acceptable levels comparable to that achieved from conventionally recycled HMA. This same study found that about half of the edge, transverse and midlane cracks reflected through in the first year. This would be comparable for thin overlays of the same pavement. One major difference was that longitudinal and centerline cracks have not reflected through. The author hypothesize that this may be due to hot joint construction during the paving process. Smoothness of the HIR pavements was comparable to new construction. Conclusions from this study include:
HIR is an acceptable rehabilitation technique for pavement exhibiting moderate surficial pavement distresses that are not associated with structural deficiencies.
Contractors can achieve, and are achieving, the recovered Pen values specified for the HIR process provided adequate attention is paid to the existing pavement and any changes in the material while determining the mix designs for use on the project.
Pavement with steel slag aggregates should not be HIR because of their porous and insulative properties.
Excessive quantities of temporary maintenance treatment materials (sand seals and cold mix) and rubberized asphalt sealant should be removed before HIR.

20. HIPR Limitations Structurally sound existing pavement
HIR limited to 50 mm (2 in) depth
Prefer dry and warm weather
Manholes and utility vaults
Surface treatments
Air quality
Economics may constrain on short sections
HIR like all rehabilitative methods has its limitations. Button, Estakhri, and Little (1999) summarized the limitations as:
Existing pavement needs to have adequate load carrying capacity.
Pavements with obvious base failures, irregular and frequent patching and needing major drainage improvements are not candidates for HIR.
HIR should be limited to the top 50 mm (2 in) although projects have been completed which used a depth of 75 mm (3 in).
Existing pavements should be at least 75 mm (3 in) thick.
Narrow roads are not good candidates for HIR unless traffic can be rerouted due to the width of the heating and milling equipment.
Streets with numerous metal appurtenances such as manholes and utility access covers are not good candidates for HIR.
Preferred weather is hot, calm days with no moisture in or on the existing pavement. Less than ideal weather conditions will slow the operation due to increased heating time.
Surface treatments of the existing pavement negatively affect the ability of the equipment to heat the pavement. It may be advisable to remove surface treatments (especially multiple chip seals) before HIR is employed.
Surface courses with aggregate larger than 25 mm (1 in) in diameter may be unsuitable for current HIR practices.
The pavement must be heated to the desired temperature without creating air quality concerns or burning the asphalt cement.
Many of the operations of a HIR operation are not visible to observers. Quality control best becomes the responsibility of the contractor and not the owner. Specifications should be end-result or performance related.
Limited ability to affect large changes in grades. Rutting may be corrected but the user will not be able to correct large undulations due to swelling or heaving soils.
Mobilization of equipment may not be cost effective to perform work on short sections that require the equipment to be transported in and out. Most cost effective on long runs (I.e., several city blocks in urban area).

21. Hot Central Plant Recycling (HCPR)
RAP use
Tens of millions of tons used
Everyday occurrence
Over 40 million tons generated/year
80 percent of all HMA removed is recycled into HMA
Severe limitations in some areas

22. HCPR – Construction Methods and Equipment
Construction sequence
Pavement removal
Crushing and stockpiling
Mixing in central plant
Laydown and compactions

23. HCPR Generating RAP
Example of normal milling operation generating RAP.

24. HCPR Milled RAP Little additional processing required
Uniform properties in layer
Gradation
Asphalt content
Asphalt properties
Usually stored in separate stockpile
Some states have requirement on maximum particle size for RAP.
Additional processing after milling may be necessary.

25. HCPR RAP Performance FHWA survey of 17 states
RAP mixes comparable to virgin mixes
Proper design
Process control
Louisiana study
No significant differences in RAP mix and control

26. HCPR Quality Control Similar tests used for virgin asphalt cement
Additional tests required
More frequent testing
Greater variation in test results

27. HCPR - Recycled Mix Design & Performance
Uniformity
Depth of HMA
Presence of chip seals
Asphalt content (bleeding)
Aggregate gradation
Asphalt properties
Traffic
Types of pavement distress
Build slide.
What are some key elements to proper design and performance of a recycled mixture?

28. HCPR Superpave and Recycling
Research completed NCHRP 9-12
Table 2 - MP2
Refer to table 3-8.8
NCHRP 9-12
One recurring question concerning Superpave and RAP is whether RAP acts like “black rock.” If RAP acts like a black rock, the aged binder will not combine, to any appreciable extent, with the virgin binder and will not change the binder properties. If this is the case, then the premise behind blending charts, which combine the properties of the new and old binders, is void. This question was addressed through National Cooperative Highway Research (NCHRP) Project 9-12, “Incorporation of Reclaimed Asphalt in the Superpave System.” The objectives of this research were to investigate the effects of RAP on binder grade and mixture properties and to develop guidelines for incorporating RAP in the Superpave system on a scientific basis.
The findings of this research largely confirmed current practice (NCHRP 2000). The concept behind the current blending charts was supported, as was the use of a tiered approach. The advantage of this approach is that for relatively low levels of RAP extensive testing of the RAP binder is not required. If higher RAP contents are used, conventional Superpave binder tests can be used to determine how much RAP can be added and the proper virgin binder to blend with. A possible binder selection guide is shown in table

29. HCPR Limitations Stockpile variability Gaseous emissions
Surface treatments and rubberized materials
Structural evaluation of recycled materials
Build slide.
What are some of the major issues facing bituminous recycling in the future.
Variability of stockpiles is still a big issue, especially when contractors mix materials from different sources into one stockpile.
Emissions from hot-mix plants and HIPR is a continuing issue. The limits of percent recycled may be controlled by this issue.
The ability to take surface treatments, rubberized materials, special polymers and to be able to recycle them is still in the working stage.
How to value recycled materials in a structural analysis. Are they better or worse than all virgin material or are they the same.

30. Reconstruction Issues
Condition of subgrade
Traffic control
Utilities
Geometrics
Safety
Project budget
Build slide – question for participants.
Condition of subgrade
Will extensive subcuts be required?
Traffic control
Detour, length of construction.
Utilities
Relocation, cost - Relocation cost for utilities for I-235 reconstruction in Des Moines, IA were estimated to cost up to $100 million on a project with construction costs of $450 million.
Geometrics – inadequate geometrics can be corrected.
Safety – full reconstruction can result in a much safer road.
Project budget – what do you have the money to do? Much higher cost to reconstruct.

31. Review
What are some rehabilitation options when a pavement is near the end of its service life?
What are the major issues concerned with reconstruction?
What are some rehabilitation options when a pavement is near the end of its service life?
Reconstruction.
Recycling.
Cold in-place recycling (CIPR).
Hot in-place recycling (HIPR).
Hot central plant recycling (HCPR).
What are the major issues concerned with reconstruction?
Condition of subgrade.
Traffic control.
Utilities.
Geometrics.
Safety.
Project budget.

32. Key References
Davis, B “Survey Shows Public Ignorant of Industry Progress – Asphalt Pavement Recycling Leader.” California Asphalt May/June 2000, Asphalt Pavement Association, Laguna Hills, CA
Federal Highway Administration “Reclaimed Asphalt Pavement - User Guideline - Asphalt Concrete (Hot Recycling). Federal Highway Administration, Washington, DC.

33. Key References
Kandahl, P. S. and R. B. Mallick Pavement Recycling Guidelines for State and Local Governments – Participant’s Reference Book. FHWA-SA-97. Available on CD dated March Federal Highway Administration, Washington, DC.

34. Key References
McDaniel, R., and R. M. Anderson a. Recommended Use of Reclaimed Asphalt Pavement In Superpave Mix Design Method: Guidelines. NCHRP Project NCHRP Research Results Digest Number National Cooperative Highway Research Program, Transportation Research Board, Washington, DC.

35. Key References
McDaniel, R., and R. M. Anderson b. Recommended Use of RAP in Superpave Mix Design: Technician’s Manual. NCHRP Project NCHRP Report National Cooperative Highway Research Program, Transportation Research Board, Washington, DC.

36. Key References
CMI Communications “The CMI Triple-Drum Hot Mix Asphalt Plant, The Ultimate Counter-Flow Plant Design for Productivity and Environmental Performance.” CMI Corporation, Oklahoma City, OK.

37. Key References
American Recycling and Reclaiming Association (ARRA) “ARRA Member Firms Recycle 34 Million Tons.” ARRA Newsletter Fall American Recycling and Reclaiming Association, Annapolis, MD.

38. Key References
Kazmierowski, T., P. Marks, and S. Lee “Ten-Year Performance Review of In Situ Hot-Mix Recycling in Ontario.” Transportation Research Record. Transportation Research Board, Washington, DC.
Button, J. W., C. K. Estakhri, and D. N. Little “Overview of Hot In-Place Recycling of Bituminous Pavements.” Transportation Research Record Transportation Research Board, Washington, DC.

39. Standards
ASTM D4552 – Standard Practice for Classifying Hot-Mix Recycling Agents.