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

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

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.

Introduction Reconstruction – used less and less Cost Traffic disruption

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.

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).

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.

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

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

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

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

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

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

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

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.

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

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.

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

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.

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).

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

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

HCPR Generating RAP Example of normal milling operation generating RAP.

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.

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

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

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?

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 3-8.8.

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.

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.

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.

Key References Davis, B. 2000. “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. 2000. “Reclaimed Asphalt Pavement - User Guideline - Asphalt Concrete (Hot Recycling). Federal Highway Administration, Washington, DC. http://www.tfhrc.gov/hnr20/recycle/waste/rap132.htm

Key References Kandahl, P. S. and R. B. Mallick. 1997. Pavement Recycling Guidelines for State and Local Governments – Participant’s Reference Book. FHWA-SA-97. Available on CD dated March 1998. Federal Highway Administration, Washington, DC.

Key References McDaniel, R., and R. M. Anderson. 2000a. Recommended Use of Reclaimed Asphalt Pavement In Superpave Mix Design Method: Guidelines. NCHRP Project 9-12. NCHRP Research Results Digest Number 253. National Cooperative Highway Research Program, Transportation Research Board, Washington, DC.

Key References McDaniel, R., and R. M. Anderson. 2000b. Recommended Use of RAP in Superpave Mix Design: Technician’s Manual. NCHRP Project 9-12. NCHRP Report 452. National Cooperative Highway Research Program, Transportation Research Board, Washington, DC.

Key References CMI Communications. 2000. “The CMI Triple-Drum Hot Mix Asphalt Plant, The Ultimate Counter-Flow Plant Design for Productivity and Environmental Performance.” CMI Corporation, Oklahoma City, OK. http://www.cmicorp.com/frame/prod/denasph.html

Key References American Recycling and Reclaiming Association (ARRA). 2000. “ARRA Member Firms Recycle 34 Million Tons.” ARRA Newsletter Fall 2000. American Recycling and Reclaiming Association, Annapolis, MD.

Key References Kazmierowski, T., P. Marks, and S. Lee. 1999. “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. 1999. “Overview of Hot In-Place Recycling of Bituminous Pavements.” Transportation Research Record 1684. Transportation Research Board, Washington, DC.

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