Exploratory Study of Hot In-Place Recycling of Asphalt Pavements Volume 1
Hot in-place recycling (HIR) is a method for rehabilitation of asphalt pavements. Potential for cost savings and resource preservation are high because existing pavement materials are processed on-site, with only the addition of small amounts of recycling agent. ODOT constructed HIR projects in 1192 and 1993. In September 1992, ODOT contracted with Oregon State University (OSU) to evaluate the HIR projects, synthesize existing information on HIR, and develop guidelines for HIR use. This report summarizes the information developed during the study:
a) Construction equipment used on ODOT HIR projects is discussed.
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b) Field data from six HIR projects are presented.
c) Results of a limited laboratory investigation of HIR are presented.
d) Proper project selection was found to be extremely critical to HIR success.
A selection procedure is presented.
e) Based on information form the field studies and a limited laboratory testing
program, a recommended mix design procedure is presented. This report is in two volumes. Volume I includes the body of the report, Volume II includes the appendices.
Brugg Cable Mesh Rockfall Fence - Construction Report
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The Brugg Cable Mesh Rockfall Fence was installed in 1991 along I-84 from MP 52.1 to 52.7 to prevent large (.3 foot diameter) rocks from entering the travel lanes. This was one of the first major instillations of the Brugg Cable Mesh Rockfall Fence in the United States and it was a FHWA experimental features project. The fence is a patented proprietary item and consists of cable mesh attached to H-beam posts that incorporate a friction brake. The fence was installed in the Columbia Rive Gorge Scenic Area; to minimize its visual impact, it was painted a dark earth tone.
The bid price of installing the fence was $27.00 per square foot face. Even though this was the contractor’s first instillation, both the contractor and the Oregon Department of Transportation (ODOT) inspector considered the constructability very easy.
Woodburn Hot In-Plant Asphalt Pavement Recycling Project
In 1977, the Oregon Department of Transportation constructed a demonstration project using approximately 47,000 tons of stockpiled asphalt concrete (AC) material to overlay a section of pavement in Oregon. The stockpiled AC material was hot in-plant recycled and paved as a conventional hot AC mix. For twelve years of service, the hot in-plant recycled pavement performed well and carried traffic well in excess of the design loadings.
The construction details of this demonstration project were documented in an interim report published in 1977. This final report provides various information regarding the project, including the design, construction, and performance of the recycled AC pavement.
Based upon the design, construction, and performance of this project, the following conclusions were drawn:
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- Asphalt concrete material can be hot in-plant recycled and reused for surface paving. 2) The properties of slightly aged asphalt cement can be adequately modified through the addition of new "soft" asphalt cements without the incorporation of recycling additives.
- Emissions in recycling are a function of many factors, including mix temperature, grade of new asphalt being added, amount of new aggregate added, amount of water added, and plant production rate.
- Variability in the material properties may be expected. The additions of new asphalt and aggregate may further increase the variability.
- Cost savings and conservation of natural resources can be expected due to the use of the recycled AC materials.
- The new hot in-plant recycled pavement surface was rougher than average new AC pavements.
- The pavement performed well and carried traffic well in excess of the design loadings.
Fiber Reinforced Concrete Detention Pond
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This project involves the construction of two polypropylene fiber reinforced concrete lined detention ponds. The detention ponds are located on the north side of the 181st Avenue Interchange on the Columbia River Highway 0-84) approximately ten miles east of Portland in Multnomah County, Oregon. The project was completed in the autumn of 1991. The original design called for the detention ponds to be constructed with six inch thick, continuous, welded wire, fabric reinforced concrete over an impermeable geomembrane. An alternate to this design, replacing the welded wire fabric reinforced concrete with polypropylene fiber reinforced concrete, was proposed by the contractor through a no cost price agreement. The decision was made by Oregon Department of Transportation (ODOT) and Federal Highway Administration (FHWA) staff to accept the contractor's proposal and to evaluate the material as an experimental features project.
The replacement of welded wire fabric reinforced concrete with polypropylene fiber reinforced concrete created no problems with respect to mixing, placement, workability, finish-ability, or visual appearance. The use of fiber reinforced concrete on this project resulted in a small cost reduction relative to the use of welded wire fabric reinforced concrete.
The fiber reinforced concrete should continue to be monitored to ensure that its functional performance is acceptable. If no problems with long-term functional performance are encountered, fiber reinforced concrete should be considered as an alternate to the welded wire fabric reinforced concrete for similar projects in the future.
Free Draining Base Materials Properties
The importance of providing a positive drainage system and removing free water from pavement structures has long been recognized. Inadequate drainage of the pavement structures has been identified as one of the primary causes of pavement distress.
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In the last few years, Oregon has started designing and constructing permeable bases in both flexible and rigid pavements. Two types of permeable bases have been used: one is asphalt treated permeable material (ATPM) base and the other is open-graded aggregate base. The desirable characteristics (permeability and resilient modulus) of both materials have not been determined. In addition, construction with the existing open-graded aggregate gradation revealed that the material was less stable and would ravel easily under construction traffic. Because of this raveling, compaction was poor, the grade was difficult to control, and the open graded aggregate materials did not provide a suitable surface for paving.
This project established the desirable materials properties (permeability and resilient modulus) for the two types of free-draining base materials and establishes a more stable gradation for the open-graded aggregate base. Appropriate layer and drainage coefficients for use in the AASHTO design of permeable base sections are also determined. For comparison, a dense-graded aggregate material is also investigated.
This project consisted primarily of a laboratory investigation. Pavement cores of the asphalt treated permeable base and samples of aggregate materials were tested in the laboratory for permeability and resilient modulus. The permeability was determined using both constant and falling head test procedures.
The laboratory study indicated that the current Oregon ATPM has a sufficient drainage capability and the resilient modulus of this material is typical of other states' findings. A modified open-graded aggregate gradation is proposed. The proposed aggregate gradation has a higher permeability and a higher resilient modulus than the existing gradation.
Recommendations for implementation include selection of layer and drainage coefficients for pavement structural design and use of the proposed open-graded aggregate gradation in pavement construction.
Asphalt-Rubber Concrete (ARC) and Rubber Modified Asphalt concrete (Metro Rumac) Evaluation - Construction Report
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This report covers the construction of two test pavements using asphalt concrete modified with tire rubber in September, 1991. The pavements are on an overlay of heavily traveled freeway in the Portland metropolitan area.
One test pavement uses an open-graded asphalt-rubber binder (ISI ARC). This binder was made by blending asphalt with shredded tire rubber. This test pavement is compared to a control pavement of an open-graded Oregon Department of Transportation (ODOT) mix. The other test pavement uses a dense-graded rubber modified asphalt concrete made by a process developed for the Metropolitan Services District of the Portland, Oregon urban area (METRO RUMAC). In this process, crumb rubber was added directly into the mix. This pavement is compared to a control pavement of a dense-graded ODOT mix.
Other than the blending of the asphalt-rubber, the construction of the ISI ARC and the control section were similar, and few problems were encountered.
When the METRO RUMAC was mixed, the system used to add the rubber to the drum was hard to control and monitor. As a result, the rubber content of the mix varied considerably from the desired proportion. This mix was hard to compact to the desired density, and this problem may be linked to variations in the mix’s rubber content and/or placement temperature.
After construction, both the ISI ARC and METRO RUMAC test sections had appearances, ride values, deflection reductions, and surface friction values typical of conventional asphalt concrete
Rubber Modified Asphalt Concrete (METRO RUMAC) Evaluation: Lakeview Junction - Matney Road Section
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This report covers the construction in 1991 of two test pavements using asphalt concrete modified with crumb rubber from scrap tires. The pavements are on arterial roadways in the Portland, Oregon metropolitan area. Both test pavements use a dense-graded rubber modified asphalt concrete (METRO RUMAC) developed for the Metropolitan Services District (METRO) of the Portland metropolitan area. In this process, crumb rubber made from recycled tires is mixed with aggregate before the asphalt is blended into the mix. Adjacent to the test pavements, control pavements were paved with conventional asphalt concrete. The test pavements are compared to these control pavements.
The METRO RUMAC was successfully blended in both a batch and a drum mixing plant. In both cases, the plant's exhaust gas opacity was an acceptable level. The rubberized mixes were placed and compacted by conventional equipment.
Experience on these projects showed that caution is needed in determining the mix properties by solvent extraction and in measuring pavement density by a nuclear gauge. Testing showed that two solvents commonly used in vacuum extractions dissolve finer particles of the crumb rubber. Using mathematical modeling, it was found that solvent dissolving rubber during the extraction had these effects on test results: it did not significantly affect the test results for the overall gradation of the mix, it had a significant effect on the asphalt content test results, and it invalidated rubber gradation and rubber content test results. To get accurate nuclear density test results, special care was needed when the gauge was seated on the surface of the METRO RUMAC.
After construction, both the METRO RUMAC test sections had appearances, ride values, deflection reductions, and surface friction values similar to their respective control pavements and typical ODOT dense-graded overlays.
The METRO RUMAC mixes cost about 1½ times more than their conventional counterparts. Most of this increase was due to the cost of the rubber and the expense of adding the rubber. At this time, it is not certain that the greater initial cost of these rubberized mixes will be offset by a commensurate increase in the pavement's service life.
Evaluation of a Keystone/Tensar Geogrid Retaining Wall System
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The KeyStone/Tensar Geogrid retaining wall system is an alternative to conventional reinforced concrete retaining wall structures. Keystone concrete wall units, Tensar geogrid, and compacted soils are combined to form a reinforced soil mass that together act as a gravity wall structure to resist lateral earth pressures and surcharge loads.
The objective of this experimental features project is to evaluate the construction and performance of the KeyStone/Tensar retaining wall system. The benefits, as stated by the manufacturer, of this wall system include: design flexibility, easy installation, cost efficient, beauty, and wall face drainage properties.
The features of this wall system that were evaluated include: construction (including installation times and labor costs), quality and availability of pre-cast elements, wall costs, aesthetics, wall stability and performance, and appropriateness of design details and parameters.
Two walls located in Portland, Oregon were evaluated as part of this research. Wall 1 is approximately 183 feet long, facing Southwest Taylors Ferry Road. The wall has multiple footing steps to accommodate the roadway grade and ranges in height from approximately 2.5 feet to 16 feet. Wall 2 is approximately 190 feet long, fronting on Southwest Bertha Boulevard. The wall has one footing step to accommodate roadway grade and ranges in height from 2.5 feet to 6.5 feet.
The KeyStone/Tensar geogrid retaining walls evaluated as a part of this project have performed well for two years. Although problems were encountered with block placement during construction of the walls, these problems can be avoided in future projects by designing footing and block placement with consideration of horizontal growth, batter due to block setback and thickness of geogrid.
Even though costs were not substantially lower than the estimate for conventional reinforced concrete retaining wall structures, the aesthetic qualities, performance, and construction time make this type of wall an acceptable alternative. Therefore, it is recommended that the KeyStone/Tensar Geogrid retaining wall system be considered as an acceptable alternative to conventional retaining walls for similar installations. Full acceptance of this retaining wall system for use on State projects will require completion of the OSHD Bridge Section's "Wall Acceptance Procedures;" these acceptance procedures are currently being developed.
Table-1 and Table-2 Asphalt
Comparison of Oregon State Highway Division Table-1 and Table-2 Asphalt
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The objective of this study was to compare the effect of using the Oregon State Highway Division (OSHD) modified Table-1 asphalts and the OSHD modified Table-2 asphalts in asphalt concrete; the primary factors for comparison were reflected and thermal cracking. Crack information obtained prior to paving was compared to crack information obtained two years after paving.
In 1989, an overlay project was constructed in Southern Oregon. The project consisted of one control section and one test section. Witco AC-15 asphalt cement, representing Table-1, was used in the control section. Chevron AC-20 and Idaho AC-20 asphalt cements, representing Table-2, were used in the test section. After two years of service. The control section showed significantly more reflective cracking than the test section. This indicates the Table-2 asphalt was more effective than Table-1 asphalt in reducing reflective cracking. However, the effect of cold temperatures on the development of cracking in both the control and test sections was not clear. It may be expected that Table-2 asphalts would have better thermal resistance than Table-1 asphalt because Table-2 asphalts are less temperature susceptible than Table-1 asphalts. The study conclusions were based on limited information. Further verification, if necessary, should be conducted in a wider scale.
Concrete Mix Design Study
This study investigates several aspects of concrete mix design. The variability of compressive strength, slump and air content from batch to batch is examined. The effect of increasing the sand content per cubic yard of concrete on the compressive strength is studied with another series of laboratory batches. Finally, the effect of the maximum coarse aggregate size on compressive strength is evaluated with a third set of laboratory batches.
The difference between the mean compressive strength of batches were evaluated using the Student 1 statistic. Some of the findings were:
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- Variability in average 28-day compressive strength between laboratory batches of the same design is very low.
- The average 28-day compressive strength of concrete made with a 10% increase in the sand content is higher than that of concrete made with standard mix proportions. The workability of the former as measured by the slump is lower.
- The average 28-day compressive strength of concrete made with ¾” maximum size aggregate is significantly higher then concrete made with 1 ½” maximum size aggregate.
Evaluation of Grit-Impregnated, Epoxy Coated Prestressing Strand on South Slough (Charleston) Bridge
Construction of the South Slough (Charleston) Bridge was completed in March of 1991. The structure was constructed with pre-stressed concrete beams using grit-impregnated, epoxy coated pre-stressing strands. While epoxy coated reinforcing steel has been used successfully to combat corrosion for several years, epoxy coating for pre-stressing strands is a relatively new application. The use of epoxy coated strands did not cause any significant construction problems. The strands and concrete mix were bonded well. The bonding characteristics of the grit-impregnated epoxy pre-stressed strands to the concrete will be monitored for two years, until March 1993, to detect any loss in bonding.
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Evaluation of the Baladi Indirect Tensile Test Apparatus
Dr. Gilbert Baladi, of Michigan State University, has designed an indirect tensile test device to measure certain characteristics of asphalt concrete. The Oregon Department of Transportation currently uses the Retsina Mark VI device to measure the modulus of resiliency of A/C, and is participating in a study that compares the MŘ test results of the two devices. This report gives a brief description of the two systems, the test procedure, the results obtained by each and a statistical analysis of those results.
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Eleven calibration specimens and over thirty asphalt briquette specimens were tested with varying degrees of success and failure. Representative results are presented in tables one through three, which also show the variance from the mean MŘ, prints depicting the horizontal deformation of some specimens (recorded with the ATS Scope Program) are included (figures 1-16). These show the uneven horizontal deformation experienced in Dr. Baladi’s device. Tables A-D present the statistical analysis.
In conclusion, the Retsina Mark VI System is the easier to operate of the two; but the Baladi device (run by the ATS Software) is superior in data collection, storage and retrieval. The Baladi device operated erratically and needs improvement before further comparison can be done.
Polymer Modified Chip Seal Test: Oregon Route 22
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This report describes the construction and performance of ten pavement chip seals applied on June 17 - 18, 1987 using nine different emulsified asphalt binders. Seven of these asphalts were modified with different polymers, and the remaining two were conventional. The polymers used in the emulsions were Styrene Butadiene, Styrene Butadiene Synthetic Rubber, Styrene Butadiene Styrene Block Co-Polymer, Styrene Malam, Neoprene Latex Synthetic Rubber Co-Polymer, Ethylene Vinyl Acetate or Rubber Styrene Butadiene Styrene.
The chip seals were applied in a single pass using conventional construction techniques. Other than the addition of a modifier in each emulsified asphalt, no special procedures were required or used.
The chip seals were rated for overall performance based on both initial chip retention and their condition after two years of service. Three sections containing conventional asphalt and one section with polymerized asphalt were rated in a poor condition after two years. The low ratings may be related to conditions during construction as well as materials properties.
The Rockfall Hazard Rating System
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The development and dissemination of the Rockfall Hazard Rating System (RHRS) is complete. RHRS is intended to be a proactive tool that will allow transportation agencies to address rationally their rockfall hazards instead of simply reacting to rockfall accidents. The RHRS provides a defensible, standardized way to spend the limited construction funds available by numerically differentiating the apparent risk at rockfall sites.
Much of the RHRS's rating is subjective. Proper training in its application is necessary to ensure the consistency of ratings between different raters. The responsibility for slope evaluations and design concepts should rest with experienced individuals.
The Oregon Department of Transportation (ODOT) began developing the RHRS in 1984. Funding from a Federal Highway Administration (FHWA) sponsored pooled-fund, Highway Planning and Research (HPR) Grant allowed ODOT to complete development of the system, test it at over 3,000 sites, prepare an RHRS Implementation Manual, and conduct five multi-state training workshops around the country. The workshops gave participants an introduction to the RHRS and guidance on how to implement the system.
Microsilica Modified Concrete for Bridge Deck Overlays (First-Year)
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The study objective is to see if microsilica concrete (MC) is a viable alternative to the latex modified concrete (LMC) usually used on bridge deck overlays in Oregon. The study addresses MC overlays placed in 1989 on seven Portland cement concrete (PCC) bridge decks. This report covers the performance of the overlays during the first year of use.
After one year, the only distresses on these overlays were cracking and delamination. There was cracking on all of the overlays. In most cases, the cracking was hairline and random. In heavily cracked areas, the cracks connected to form a map pattern. This cracking may be due to drying shrinkage. Similar problems are seen on Oregon State Highway Division (OSHD) LMC overlays.
In addition, there were delaminations on five of the seven overlays. This distress was not extensive, as the worst deck had only 2.5% of its surface delaminated. In most cases, the delaminations were small, scattered throughout the deck, and covered by uncracked MC. The exceptions were two large delaminations that were under sections of the overlay with severe map cracking, and numerous delaminations adjacent to construction and expansion joints. The delaminations that were repaired were almost always between the overlay and the old deck. The cause of these delaminations is not known. Similar distress is often seen on OSHD LMC overlays.
The wheel-to-pavement friction numbers of these overlays were similar to typical state highway pavements and LMC bridge decks in Oregon.
The only maintenance and repair cost to the OSHD was the sealing of cracks on one deck with methacrylate and sand, at a cost of $4,000. This sealant was effective.
The overlays met two of their three design objectives after one year's use. They were still adding strength to the deck and providing a smooth and durable wearing surface. However, as they were cracked, it is surmised that they were no longer sealing the underlying deck from the intrusion of chlorides.
A successful MC overlay was recently placed for the OSHD in Portland. This overlay contrasted to most of the overlays in this study, as the concrete supplier was experienced with MC, the batching to pouring durations were short, and the weather was cool and/or humid with small daily temperature swings.
Continued use of MC is recommended in areas where capable MC suppliers are close to the jobsite and the overlay is to be poured in favorable weather. Further experimentation is recommended to find ways to successfully pour MC in other conditions.
Preformed, Patterned Striping Material
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In 1989, two pavement striping tape materials were placed on two new asphalt pavements. A two-year performance evaluation of the materials has been completed by the Oregon State Highway Division's Materials & Research Section.
On the first project, a 3M Stamark Pliant Polymer Pavement Marking Tape - Series 5730, was placed on an Oregon dense-graded Class "B" asphalt concrete pavement. Only the skip line was marked with the pavement marking tape. Paint was used to mark the fog line and crosswalk. This area has a high volume of cross traffic, much of which is truck traffic. Over the two year period, the material proved to be durable in that it provided a full service skip line, whereas the painted lines had to be repainted several times. The marking tape material reflectance was below the OSHD standards.
On the second project, 3M Stamark Pliant Polymer Marking Tape - Series A350 (white) and Series 351 (yellow) were placed on an Oregon open-graded C1ass"F" asphalt concrete pavement. This area is in a snow zone with a significant amount of studded tire usage during the winter months. Over the two-year period, the marking tape did well in retaining its reflectance, but had bonding problems. Some of the material came up after the first snowfall and had to be replaced.
The recommendations of this study are:
The Series 5730 pavement marking tape is not recommended for use on Oregon's highways.
The Series A350 pavement marking tape is not recommended for open-graded pavements on Oregon's highways unless the durability problems can be resolved.
The Series A350 pavement marking tape should be examined on a dense-graded pavement.
Asphalt Content of Hot Bituminous Mixes Using Nuclear Asphalt Content Gauges
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The Oregon State Highway Division (OSHD) currently uses the Vacuum Extraction procedure for acceptance testing for asphalt content of asphaltic concrete. Because of the concern with Chlorinated solvent, i.e. safety, disposal, and expense, OSHD has investigated the potential of Nuclear Asphalt content Gauges.
In June 1988, OSHD published a report titled “Precision and Accuracy of Nuclear Asphalt content Gauges in Determining Asphalt content in Asphaltic concrete Pavement.” This report concluded a proper calibration is essential, moisture correction is necessary, and the Nuclear Gauges are cost effective. This study is to validate previous findings, evaluate field performance, and develop necessary calibration and operation procedures.
A total of thirteen OSHD projects were included in this study. Asphalt content comparisons were evaluated between Extraction, Nuclear Gauge, Tank Stick, and Plant Meter. The latest model nuclear Gauges, Troxler 3241-C and CPN AC-2, were used. Gradation comparisons were evaluated between extracted and cold feed grading.
This study concluded the asphalt gauge to be a precise and accurate instrument, but the reading must be corrected for moisture content. The Microwave moisture correction is not acceptable, therefore, a detailed procedure was written for moisture correction using a conventional oven. Also, a new nuclear gauge procedure entailed the use of calibration transfers for field operation.
Oregon is proceeding with outfitting each OSHD Region with asphalt nuclear gauges and is immediately reducing solvent usage by replacing vacuum extraction testing of open graded and plant mix bituminous base mixtures with a Tank Stick/Meter asphalt content determination method.
Pay Adjustment System for AC Pavements
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This study first presents the historical background and an overview of the technical basis for Oregon's current method of statistical quality control. It then evaluates the benefits that the State of Oregon receives by paying out bonuses to contractors on asphalt concrete paving jobs and makes recommendations for improving quality, control methods. This problem was approached with the realization that an accurate accounting of costs and benefits was not possible. However, by combining two approaches: statistical analysis of test data; and a questionnaire to field personnel, it became clear from both viewpoints that there are both tangible and intangible benefits that outweigh the costs.
The questionnaire revealed that project managers who work regularly with contractors under this system generally believe that it improves the atmosphere of cooperation between the state and contractors and also is effective in improving pavement quality. The statistical analysis demonstrates that relative compaction has increased by at least 1.1% since the system was initiated. This improvement in compaction alone is estimated to increase pavement fatigue life by an average of approximately 16% while the average bonus is only 1.7% of the original bid price.
An analysis is also made of recent paving projects showing signs of early distress. This information and suggestions from field personnel are combined to form recommendations for improving the pay adjustment system.