C. Barros et al. 1 Improving Pavement Preservation Life Using Warm Mix Asphalt Cathrina B. Barros, PE (Corresponding author) Senior Transportation Engineer Materials Engineering and Testing Services California Department of Transportation 5900 Folsom Boulevard Sacramento, CA 95819 Phone: (916) 227-7162 [email protected]David Jones, PhD Project Scientist University of California Pavement Research Center Department of Civil and Environmental Engineering University of California, Davis One Shields Ave Davis, CA 95616 Phone: (530) 754-4421 [email protected]Joseph Peterson, PE Supervising Transportation Engineer Materials Engineering and Testing Services California Department of Transportation 5900 Folsom Boulevard Sacramento, CA 95819 Phone: (916) 227-7303 [email protected]Word count: 3,761 Date submitted: September 9, 2011
Transcript
C. Barros et al. 1
Improving Pavement Preservation Life Using Warm Mix Asphalt
Cathrina B. Barros, PE (Corresponding author) Senior Transportation Engineer Materials Engineering and Testing Services California Department of Transportation 5900 Folsom Boulevard Sacramento, CA 95819 Phone: (916) 227-7162 [email protected] David Jones, PhD
Project Scientist University of California Pavement Research Center Department of Civil and Environmental Engineering University of California, Davis One Shields Ave Davis, CA 95616 Phone: (530) 754-4421 [email protected] Joseph Peterson, PE
Supervising Transportation Engineer Materials Engineering and Testing Services California Department of Transportation 5900 Folsom Boulevard Sacramento, CA 95819 Phone: (916) 227-7303 [email protected] Word count: 3,761 Date submitted: September 9, 2011
At the California Department of Transportation (Caltrans), over 80 percent of preventative maintenance funding is spent on thin hot mix asphalt (HMA) overlays. Thin HMA overlays are defined by Caltrans as a layer less than 30 mm (1.2 in) and categorized into three types: dense-graded, open-graded and gap-graded. Typical binders used in thin overlays are performance grade (PG), polymer modified (PM) and rubberized binders.
The use of rubberized binders has greatly increased at Caltrans over the past decade. In 2005, Assembly Bill 338 (Levine) mandated the use of crumb rubber in asphalt paving materials in an effort to reduce scrap tire rubber waste in landfills. By 2013, Caltrans will use rubberized binder in 35% of its total HMA production statewide. California has many different climate zones resulting in challenges when properly placing thin overlays, specifically related to low ambient temperatures experienced in the coastal and mountainous areas and night paving on the busier urban and inter-urban routes. When rubberized binders are used, the challenges are exacerbated given the difficulty associated with placement of rubberized hot mix asphalt (RHMA).
Between 2006 and 2010, Caltrans placed over 80,000 tons in thin overlays using warm mix asphalt with the intent of quantifying the potential benefits to minimize these challenges. Warm mix additives have provided Caltrans with improved compaction at cooler temperatures, allowed longer haul distances to projects in remote areas, and lowered production temperatures. It has improved workability at the job site, which may ultimately lead to an extended pavement life.
In addition, Caltrans, in conjunction with the University of California Pavement Research Center (UCPRC), is in the process of conducting accelerated loading (Heavy Vehicle Simulator [HVS]), laboratory, and pilot field studies comparing the performance of RHMA with warm mix additives to conventional RHMA to further refine design and construction procedures for the state.
This paper details Caltrans’ experience using warm mix asphalt (WMA) for thin overlay applications in two case studies which includes project challenges and observations. It will also include key findings from the UCPRC HVS research and pilot project evaluations.
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INTRODUCTION
The California Department of Transportation (Caltrans) is responsible for maintaining over 50,000 lane miles of the State Highway System. With the baseline annual funding of $234 million, Caltrans has set a goal to repair 2,700 miles of roadway each year. (1)
Preventative maintenance is the most cost-effective means of protecting the State’s infrastructure investment. In Caltrans, common preventative maintenance treatments for flexible pavements include: chip seals, slurry seals, micro surfacing, crack sealing and thin hot mix asphalt (HMA) overlays. Of these strategies, Caltrans invests over 80 percent of its preventative maintenance funding in thin HMA overlays. In order for Caltrans to receive the highest return on its investment, extending the life of a thin asphalt overlay is a key component.
Thin Overlays in Caltrans
Thin HMA overlays are defined by Caltrans as a non-structural layer less than 30 mm (1.2 in). (2) Historically, there are three overlay types:
Dense graded Open Graded
o Open Graded Friction Course (OGFC) o Rubberized Hot Mix Asphalt Open Graded (RHMA-O) o Rubberized Hot Mix Asphalt Open Graded, High Binder (RHMA-O-HB)
Gap Graded Mixes o Rubberized Hot Mix Asphalt Gap Graded (RHMA-G)
A prevalent treatment used in Caltrans is the Open Graded Friction Course (OGFC and RHMA-O) overlay. It has shown to be highly effective in mitigating areas with skid problems and hydroplaning. In the coastal areas and the northern region of the state, it is a popular treatment due the amount of rainfall in the winter months. Rubberized Hot Mix Asphalt (RHMA) Usage
The State of California generates over 30 million waste tires annually. In an effort to be a good steward of the environment, Caltrans has established a variety of uses for recycled tire products. One of these uses is the placement of rubberized hot mix asphalt (RHMA). Over the past 14 years, Caltrans has placed over 12 million tons of RHMA. In 2005, Assembly Bill 338 went into effect and mandated Caltrans to use an increasing percentage of RHMA over the following 8 years. By 2013, the minimum RHMA usage will be 35% of the total HMA production in the state. RHMA presents challenges during construction placement. To obtain a workable mix, RHMA is generally produced at a temperature of 163ºC (325ºF), and requires a minimum atmospheric temperature of 13ºC (55ºF) and rising for placement. The combination of these high production temperatures and low ambient temperatures, results in the generation of smoke and odors that are considered a public nuisance.
OGFC and RHMA Overlay Construction Challenges
The state of California consists of nine diverse climatic regions, as shown in Figure 1.
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FIGURE 1 Map of California pavement climate regions.
These different climate zones present challenges in properly placing thin HMA overlays.
These challenges are primarily related to low ambient temperatures experienced in the coastal areas and during night paving on the busier urban routes. Low ambient temperatures during paving can quickly reduce the compaction time available for a thin HMA overlay and ultimately lead to premature raveling of the layer.
The current Caltrans specifications for the placement of OGFC with an unmodified binder and RHMA-O require an ambient air temperature 13ºC (55ºF) and rising. Using a polymer modified binder in OGFC drops the ambient air temperature requirement to 10ºC (50ºF). In the coastal and northern regions of the state, the summer months rarely see these ambient temperature requirements, while heavy fog is often prevalent during the day.
Paving in these conditions have lead to premature failure of thin overlays. The expected life of a thin overlay is estimated between 4 and 6 years. (2) In the northern coastal region of the state, the life expectancy of OGFC can be less than 18 months due to the challenging paving conditions. Using RHMA overlays in this area of the state is both a temperature and
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environmental challenge. In addition to sensitive placement temperatures, the production of RHMA has lead to public nuisance complaints due to the smoke and odors.
THE EVALUATION OF WARM MIX ASPHALT (WMA) BY CALTRANS
Caltrans initially approached the evaluation of WMA in the pavement preservation arena. There were historic problems with the placement of OGFC in coastal regions, and WMA was viewed as an innovative method of increasing the life of a pavement preservation strategy while being able to reduce asphalt production temperatures. Also, Caltrans needed to continue to use RHMA overlays as a pavement preservation strategy. Successful placement of RHMA overlays is highly dependent on higher production, placement and compaction temperatures, which made the use of WMA even more appealing to Caltrans.
Since 2008, Caltrans has placed 12 thin lift overlay projects using WMA. The location, mix type and tonnage are shown in Table 1. In general, all the installations are performing well, and are exhibiting comparable behavior to the control sections. Two of these projects are further detailed as case studies in this report.
TABLE 1 Warm Mix Asphalt Thin Overlay Projects Completed as of May 30, 2011
Project Location
(County/Route/Post mile) Mix Type Binder Type WMA Tonnage
San Diego 94 PM 52.8/63.7 ½” RHMA -O PG 64-16 12,000 tons Total 88,720
The success of these projects has led to increased usage of WMA in Caltrans for the 2011 construction season. In 2011, an additional 1 million tons of WMA is planned in projects throughout the state. Case Study 1: State Route 1 PM 25.7/27.7: Morro Bay, CA
Introduction This project was the initial pilot project evaluation for WMA in California. It is located on California State Route 1 between San Luis Obispo and Morro Bay. The section consisted of 30 mm (1.2 in) OGFC with a PG 58-34 PM binder. The road has four-lanes and is divided, but only
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the northbound lanes have WMA test sections. One control and three WMA experimental sections, each 800 m long (0.5 mi), were constructed in both lanes. Advera® WMA, Evotherm™ and Sasobit® were tested. Average traffic details for the test section are provided in Table 2.
TABLE 2 Traffic Details for California SR-1
Total
AADT1
Truck
AADT
Percent
Trucks
Truck
2 Axle
Truck
3 Axle
Truck
4 Axle
Truck
5+ Axle
ESALs2/
Day
Traffic
Index (TI)
24,000 1,056 4.4 702 121 55 177 105 N/A3 1 Annual average daily traffic 2 Equivalent standard axle loads 3 Traffic index not applicable to open-graded friction course treatments
Mix Design
The mix design was performed by Caltrans following Caltrans CT-368 and ASTM-D-6390 methods. The mix design details are summarized in Table 3. The control mix and warm mixes were produced at the Union Asphalt Plant in Paso Robles.
TABLE 3 Mix Design Details for California SR-1
Parameter Wearing Course
Spec Target Actual
Control
Actual
Evotherm
Actual
Sasobit
Actual
Advera
Pavement Type 12.5 mm (0.5 in.) Max OGFC Grading: 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200
- 100
95-100 74-82 25-33 8-16 0-10
- -
0-3
- -
78 ± 4 29 ± 4 12 ± 4
- - - - -
100 98 79 28 11 7 4 2 1
0.5
100 98 79 28 11 7 4 2 1
0.5
100 98 79 28 11 7 4 2 1
0.5
100 98 79 28 11 7 4 2 1
0.5 Asphalt binder grade PG 58-34 PM Recommended bitumen content (% by mass of aggregate) Crushed particles (%) Los Angeles Abrasion at 100 repetitions (%) Los Angeles Abrasion at 500 repetitions (%)
- >90 ≤10 ≤40
6.7 100 8 35
6.8 100 8 35
6.5 100 8 35
6.7 100 8 35
6.5 100 8 35
Tons produced WMA Technology application rate (% by weight of binder) Production temperature (°C) Production temperature (°F) Moisture content before production Moisture content after production
675 -
160/127 320/260
N/A N/A
675 -
160 320 N/A N/A
675 5
127 260 N/A N/A
675 1.5
130 266 N/A N/A
675 0.3
127 260 N/A N/A
Control Section Construction
The control section was constructed on May 5, 2008 by R. Burke Corporation. The section took approximately 8 hours to construct. Weather conditions during construction of the section were foggy for most of the day with a little sun towards the end of the construction run. Temperatures ranged between 10°C (50°F) and 17°C (62°F). The control mix was produced at 160°C (320°F).
Standard OGFC paving procedures were followed, which involved the application of a tack coat (SS-1-H [diluted 50/50] at 0.32 L/m2 [0.07 gal/yd2]), windrowing the material ahead of
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the paver from bottom-dump trucks, pick-up with a shuttle-buggy, paving (CAT AP1000B paver), and then compaction (CAT CB634C roller).
The shoulder was paved first, followed by the Number 2 (outside) lane and then the Number 1 lane (inside). Haul distance from the plant to the site was 43 km (27 mi). Haul time was between 45 minutes and 60 minutes. Construction details are summarized in Table 4.
Interviews with the paving crew after construction indicated that the Control mix was typical of mixes of this type. Common problems included chunking of the mix during transport and in the windrow (removed manually), webbing, adherence of the mix to equipment, difficulty with raking, pick-up by the roller and odors. Advera® WMA Mix Production and Section Construction The Advera® WMA section was constructed on May 6, 2008 by R. Burke Corporation. Weather conditions during construction of the section were foggy for most of the day with a little sun towards the end of the construction run. Temperatures ranged between 10°C (50°F) and 17°C (62°F). The mix was produced at 127°C (260°F). At the HMA plant, Advera® WMA was blended into the binder using calibrated, customized equipment. The blended material was then introduced into the plant via the binder line. The Advera® WMA section was constructed using standard OGFC paving procedures, with the same equipment as used in the control section. The haul distances were the same as in the control section. Problems were similar to those in the control mix, although there was reportedly less adherence of the mix to the equipment and improved raking. The crew also reported the Advera® WMA mix was initially more “stringy” and that some strings were picked up by the roller and deposited back on top of the mat. The problem was less apparent later in the day when the mix temperatures were lower. The crew generally believed that hotter mixes were more workable. Sasobit® Mix Production and Section Construction The Sasobit® section was constructed on May 7, 2008 by R. Burke Corporation. The section took approximately 8 hours to construct. Weather conditions during construction of both sections were foggy for most of the day with a little sun towards the end of the construction run. Temperatures ranged between 10°C (50°F) and 17°C (62°F).
At the HMA plant, Sasobit® was blown into the binder line using calibrated, custom equipment. The mix was produced at 130°C (266°F).
The section was constructed using standard OGFC paving procedures, with the same equipment as used in the control section. The haul distances were the same as in the control section. Problems were similar to those in the control mix, although there was reportedly less adherence of the mix to the equipment and improved workability. The crew also reported that the workability of the Sasobit® mix reduced when the temperatures dropped below 125°C (260°F). At the lower temperatures, the mix was also more “stringy” and that some strings were picked up by the roller and deposited back on top of the mat. These problems were not experienced when the mix temperatures were above 125°C (260°F) and were less apparent later in the day when the ambient temperatures had increased. The crew generally believed that hotter mixes were more workable.
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Evotherm™ Mix Production and Section Construction
The Evotherm™ section was constructed on May 8, 2008 and took approximately 8 hours to construct. Weather conditions during construction of both sections were foggy for most of the day with a little sun towards the end of the construction run. Temperatures ranged between 10°C (50°F) and 17°C (62°F).
At the HMA plant, Evotherm™ was pumped into the binder line using calibrated, customized equipment. The mix was produced at 127°C (260°F).
The section was constructed using standard OGFC paving procedures, with the same equipment as used in the control section. The haul distances were the same as in the control section. Problems were similar to those in the control section, although there was reportedly less adherence of the mix to equipment, and improved workability. The crew also reported that the Evotherm™ mix was initially more “stringy” and that some strings were picked up by the roller and deposited back on top of the mat. The problem was less apparent later in the day when the mix temperatures were lower. The crew generally believed that hotter mixes were more workable.
Post Construction Observations While the overall temperature range remained constant during project construction, the weather did vary in terms of the amount of fog or wind on a daily basis. Since this was an initial pilot project, all the WMA manufactures were instructed to keep their production temperatures at approximately 127°C (260°F). Given the current level of experience Caltrans has with warm mix applications, in retrospect these production temperatures should have been changed based on the weather conditions encountered a particular paving day. This may have minimized the amount of construction difficulties encountered on the project.
TABLE 4 Construction Details for California SR-1
Parameter Target Actual
Control
Actual
Advera
Actual
Sasobit
Actual
Evotherm
Tons produced Loads delivered Period stored in silo Average temperature at load out
675 - - -
675 26
Not recorded 158°C (316°F)
675 26
Not recorded 132ºC (269ºF)
750 29
Not recorded 132°C (270°F)
675 26
Not recorded 132°C (269°C)
OGFC thickness Paving date Paving start time Paving end time Temperature behind paver at start Temperature behind paver at end Temperature after rolling at start Temperature after rolling at end
The experiment was monitored by the University of California Pavement Research Center (UCPRC). Only visual assessments were undertaken. The first assessment was done immediately after construction to obtain baseline measurements, and thereafter at approximately
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six month intervals. A summary of the observations from each visit is provided in Tables 5 and 6. May 2008
The control and the three test sections section were very similar in appearance and were all given an overall rating of good (Figure 2). Some areas of compacted binder strings were evident on all sections (Figure 3). Track marks were observed on all sections in the Number 2 lane (Figures 4 and 5). Some stone loss was noted in the track marks (Figures 6 and 7) in all sections. The marks were attributed to asphalt delivery trucks tracking tack coat from the Number 1 lane. No other problems were noted.
FIGURE 2 Control - general view (05/2008).
FIGURE 3 Control - string pick-up by roller
(05/2008).
FIGURE 4 Control - Track marks from
construction vehicles (05/2008).
FIGURE 5 WMA Section - Track marks from
construction vehicles (05/2008).
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FIGURE 6 Control - Close up of track marks
and stone loss record (05/2008).
FIGURE 7 WMA Section - Close up of track
marks and stone loss record (05/2008).
October 2008
No deterioration was noted on any sections. The track marks observed in the May 2008 assessment were carefully scrutinized and compared to photographs taken during the May 2008 assessment. No further deterioration or stone loss was noted (Figures 8 and 9).
FIGURE 8 Control - Track mark assessment
(09/2008).
FIGURE 9 WMA Section - Track mark
assessment (09/2008).
May 2009
No deterioration was noted on any sections. The track marks observed in the May 2008 and October 2008 assessments were carefully scrutinized and compared to photographs taken during the May 2008 assessment. No further deterioration or stone loss was noted. October 2009 No deterioration was noted on any section. The track marks observed in the May 2008 assessment were carefully scrutinized and compared to photographs taken during the May 2008 assessment. No further deterioration or stone loss was noted (Figures 10 and 11).
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FIGURE 10 Control - Track mark assessment
(09/2009).
FIGURE 11 WMA Section -Track mark
assessment (09/2009).
TABLE 5 Summary of Monitoring Observations for California SR-1
Parameter Control Evotherm
May 08 Oct 08 May 09 Oct 09 May 08 Oct 08 May 09 Oct 09
Overall performance Good Good Good Good Good Good Good Good Texture Void clogging
Good No
Good No
Good No
Good No
Good No
Good No
Good No
Good No
Mechanical damage Other damage
Yes No
Same No
Same No
Same No
Same No
Same No
Same No
Same No
Bleeding/flushing Surface cracks Binder condition Aggregate loss
Riding quality Skid resistance Surface drainage Side drainage
Good Good Good Good
Good Good Good Good
Good Good Good Good
Good Good Good Good
Good Good Good Good
Good Good Good Good
Good Good Good Good
Good Good Good Good
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Case Study 2: Interstate 5 PM R20.0/28.8: Orland, CA
Introduction This project was constructed in May 2009 and consisted of placing a warm mix treated RHMA-O at a thickness of 30 mm (1.2 in) on Interstate 5 near Orland, CA. In October 2007, a similar project was placed using RHMA-O without WMA just south of Orland on I-5. Due to cooler paving temperatures, the 2007 project mix failed prematurely and the failure mechanism was raveling. The decision was made by Caltrans to incorporate WMA into the 2009 project for further evaluation of performance under truck traffic and in early season paving conditions. Traffic data for this location is given in Table 7. The total WMA tonnage was approximately 15,000 tons with a separate 3,000 ton control section.
TABLE 7 Traffic Details for California Interstate 5
Total
AADT1
Truck
AADT
Percent
Trucks
Truck
2 Axle
Truck
3 Axle
Truck
4 Axle
Truck
5+ Axle
ESALs2/
Day
Traffic
Index (TI)
26,000 6,586 25.33 413 324 169 5680 2029 N/A3 1 Annual average daily traffic 2 Equivalent standard axle loads 3 Traffic index not applicable to open-graded friction course treatments
Mix Design The mix design was performed by Caltrans following Caltrans CT-368 and ASTM-D-6390 methods. The mix design details are summarized in Table 8.
TABLE 8 Mix Design Details for California Interstate 5
Asphalt binder grade PG 64-28 PM Recommended bitumen content (% by mass of aggregate) OBC w/ 1.3 multiplier Crushed particles (%) Los Angeles Abrasion at 100 repetitions (%) Los Angeles Abrasion at 500 repetitions (%)
-
> 90 ≤ 10 ≤ 40
5.5 7.2 92 6 23
Tons produced WMA Technology application rate (% of OBC) Production temperature (°C) Production temperature (°F) Moisture content before production Moisture content after production
15000 5
140-148 285-300
N/A -
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Construction The project was constructed between May 11 and May 20, 2009 by Knife River Construction. Ambient air temperature ranged from 16ºC (60ºF) and 21ºF (70ºF). Average daily production was 2400 tons.
The mix was produced by Knife River at their Orland plant. Evotherm™ was metered into the binder. The control mix was produced at 160ºC (320ºF). The WMA mix was produced in the range of 140ºC (285ºF) to 149ºC (300ºF). It was noted by the contractor that while operating at higher temperatures, plant production was limited by the baghouse temperature and slat conveyor amperage. With the addition of the warm mix additive, the plant was able to increase production between 25 and 50 tons per hour.
The paving operation consisted of material delivered by belly dump trucks; the material was then picked up by with a windrow elevator. No more than three trucks were allowed to dump in front of the paver at any time. Caltrans construction staff observed that no blue smoke was evident during WMA usage. Smoke is normally evident during normal RHMA-O production. The mix was placed with no noticeable changes in the quality of the mat. The mix appeared to be more workable, even down to a temperature of 110ºC (230º F). Finish rolling was completed at an average temperature of 97ºC (206ºF). The pavement was open to traffic at 58ºC (135ºF).
Performance Visual assessment was performed by Caltrans staff. May 2009 The warm mix section appeared darker in color than the hot mix control section. After 48 hours of traffic loading, there was no visible rutting in the mat. July 2009 No visual deterioration was observed in the mat (Figure 12).
FIGURE 12 General view (7/25/2009).
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May 2011 Slight rutting was observed visible in the Number 2 lane. The overall pavement condition was good. The WMA section showed a more uniform mat compared to the control section (Figures 13 and 14).
FIGURE 13 Slight rutting in No. 2 lane
(05/2011).
FIGURE 14 Comparison between control
section (left) and WMA section (right) (05/2011).
Conclusion
When the initial project RHMA-O project without warm mix was constructed in October 2007, severe raveling was observed within one year of initial placement. In May 2009, a similar section of RHMA-O was placed with warm mix. In addition to reducing production temperatures, the WMA section has exhibited a longer service life. Based on this and similar experiences with WMA, the District Materials Engineer has made the decision to specify warm mix additive for all RHMA-O projects in the district. Heavy Vehicle Simulator (HVS) Testing of Rubberized Warm Mix Asphalt Sections
In 2007, Caltrans began a comprehensive study into the use of WMA in conjunction with the University of California Pavement Research Center (UCPRC). The study work plan consisted of test site identification, the design and construction of a test track, an accelerated loading test using the Heavy Vehicle Simulator (HVS) to assess rutting behavior, and a series of laboratory tests on specimens sampled from the test track.
The objective of the study was to determine whether the use of WMA to reduce the production and construction temperatures of hot mix asphalt influences the performance of the mix. The study compared the performance of a control mix with three warm mixes, produced and compacted at approximately 35ºC (50ºF) lower than the control. The additives tested included Advera ®WMA, Evotherm™ and Sasobit®.
Phases 1 and 2 of the study consisted of HVS testing and a series of laboratory tests which included: rutting, cracking, durability, moisture sensitivity and fatigue. These phases were completed in June 2009, and from this testing UCPRC recommended to Caltrans continued use of warm mix technologies in full-scale pilot studies on in-service pavements. (3)
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Phase 3 HVS Study Caltrans had the opportunity to continue the HVS evaluation of warm mix additives in rubberized hot mix asphalt in 2010. Since the number of producers of warm mix additives had grown since the initial study in 2007, the number of participants in the latest study also increased.
The WMA technologies that are being assessed include: Advera® WMA Astec Double Barrel Green® Cecabase RT® Evotherm DAT™ Gencor Ultrafoam GX™ Rediset™ WMX Sasobit®
The HVS testing and laboratory testing protocol mirror the testing protocol followed in
the Phase 1 and Phase 2 studies. Test Site and Track Construction In April 2010, two HVS test tracks were constructed by Teichert Construction using mix produced by Granite Construction (Gencor plant) and George Reed (Astec plant) at the University of California Pavement Research Center’s Advanced Transportation Infrastructure Research Center (ATIRC) at UC Davis. Each test track includes a hot mix control section.
Ambient temperatures on the day of construction averaged 10°C (50°F). The haul time from the Granite Construction plant was about 60 minutes, and 120 minutes from the George Reed plant. Smoke and odors were notably less on the warm-mix sections and the paving crew commented that the warm mixes were much more workable than the control mixes. Chunking was noted on the two control sections, but not on the warm mix sections.
Each track is being considered as a separate project to account for the different mix designs, aggregate, base binder, and plant used.
The pavement section consists of: 400 mm (16 in) of aggregate base, 60 mm (2 in) of conventional hot mix asphalt concrete and 60 mm (2 in) of rubberized hot mix asphalt. A PG 64-16 binder was used as the base binder. Phase 3 HVS and Laboratory Testing
HVS testing began on Project 1 in June 2010 and in July 2010 on Project 2, after an initial cure period. As of December 2010, HVS testing had been completed on all four of the Project 1 sections and four of the five Project 2 sections.
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Initial observations indicate that the Project 2 mix has a higher rut resistance than the Project 1 mix despite having higher binder and rubber contents. Overall, the warm mix sections are performing comparably to the control sections for both projects (Figures 15 and 16).
.
0
2
4
6
8
10
12
14
16
0 50 100 150 200 250 300 350 400
Number of Load Repetitions (x 1,000)
Avera
ge M
axim
um
Ru
t D
ep
th (
mm
)
Control
Cecabase
Evotherm
Gencor
40kN 60kN 80kN
FIGURE 15 Plot of Phase 3 rutting performance for Project 1 sections.
0
2
4
6
8
10
12
14
16
0 50 100 150 200 250 300 350 400
Number of Load Repetitions (x 1,000)
Avera
ge M
axim
um
Ru
t D
ep
th (
mm
)
ControlAdveraAstec DBGRedisetSasobit
40kN 60kN 80kN
FIGURE 16 Plot of Phase 3 rutting performance for Project 2 sections.
Specimens for laboratory testing have been cut from the test track and prepared for testing. Shear, fatigue, and moisture sensitivity testing on these samples are currently underway.
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Initial Phase 3 Findings
To date, HVS testing is complete and laboratory testing is on-going. Initial findings include:
During construction, WMA mixes had significantly less smoke and were notably more workable
From rutting testing, WMA has equal or better performance on 4 out of 7 sections
After completion of laboratory testing and forensic investigations, the Phase 3 report will be issued with the final conclusions. THE FUTURE OF WMA IN CALTRANS
Total WMA tonnage in the 2011 construction year is estimated at over 1 million tons. A majority of this tonnage will be in thin overlay applications. Caltrans districts that have gained a high comfort level in the use of WMA continue to specify WMA in thin overlay applications due to the improved workability of the mix, the reduced emissions at the job site and the increased service life of the pavement. Beyond 2011, it is Caltrans goal to have a WMA project in every one of its twelve districts. HVS research and evaluation of pilot projects are aiding in the implementation of this goal by educating district materials engineering, maintenance and construction staff in the benefits of WMA. With an estimated total annual HMA production of 3 million tons, Caltrans is well on its way in becoming a leading advocate in the use WMA, and continuing in its mission of being a good steward of resources and the environment. REFERENCES
1. 2011 Five –Year Maintenance Plan, California Department of Transportation, January
31, 2011. 2. Maintenance Technical Advisory Guide, Chapter 10, California Department of
Transportation, November 2007. 3. Jones, D., Wu, R., Tsai, B.W., Lu, Q. and Harvey, J.T., Warm-Mix Asphalt Study: Test
Track Construction and First-Level Analysis of Phase 1 HVS and Laboratory Testing. Davis and Berkley, CA: University of California Pavement Research Center (RR-2008-11, pp. v-viii)
