Flagstaff I-40 Asphalt Rubber Overlay Project. Nine Years of Success. Paper Presented to Transportation Research Board 78th Annual Meeting

Transcription

1 Flagstaff I-40 Asphalt Rubber Overlay Project Nine Years of Success Paper Presented to Transportation Research Board 78th Annual Meeting by George B. Way, P.E. Arizona Department of Transportation 1221 N. 21st Ave. Phoenix, Arizona Phone: Fax: August 16,1999

2 Way 2 Flagstaff I-40 Asphalt Rubber Overlay Project Nine Years of Success George, B. Way, P.E. Arizona Department of Transportation 1221 N. 21st Ave. Phoenix, Arizona Phone: Fax: gway@dot.state.az.us August 16, 1999

3 Way 3 Flagstaff I-40 Asphalt Rubber Overlay Project Nine Years of Success Abstract: In 1990, the Arizona Department of Transportation designed and constructed a large scale Asphalt Rubber (AR) test project in Flagstaff, Arizona on the very heavily traffiked Interstate 40. The purpose of the test project was to determine whether a relatively thin overlay with AR could reduce reflective cracking. Asphalt Rubber is a mixture of 80% hot paving grade asphalt and 20% ground tire rubber. This mixture is also commonly referred to as the asphalt rubber wet process or McDonald process. The overlay project was built on top of a very badly cracked concrete pavement, which was in need of reconstruction. The asphalt rubber overlay has performed beyond the original expectation. After nine years of service the overlay is still virtually crack free, with good ride, virtually no rutting or maintenance and good skid resistance. The benefits of using asphalt rubber on this project represents about $18 million dollars in construction savings and four years less construction time. Strategic Highway Research Program SPS-6 test sections built in conjunction with the project further illustrate the very good performance of the asphalt rubber. Results of this project have led to widespread use of asphalt rubber hot mixes throughout Arizona. Based upon this work over 3,333km (2,000 miles) of successfully performing asphalt rubber pavements have built since 1990.

4 Way 4 KEY WORDS Asphalt rubber, overlay, pavement performance, success of asphalt rubber. INTRODUCTION The Arizona Department of Transportation (ADOT) maintains about 12,333km (7,400 centerline miles) of highways, of which approximately 500km (300 miles) are Portland Cement Concrete. A twenty year old, 16.7km (ten mile) section of concrete pavement on Interstate 40 near Flagstaff, Arizona suffered severe deterioration warranting reconstruction (Figure 1). Flagstaff is a mountainous area of 2134m (7,000 foot) elevation with an Alpine like climate. High temperatures in the summer are a pleasant 27 C (80 F) with winter time lows of -31 C (-23 F). Overall rainfall is 0.7m (28 inches) per year and winter snows average over 2,500mm (100 inches) per year. Interstate 40 cuts through this mountainous area and is built on soils and rock of generally poor engineering quality. The current traffic is over 20,000 vehicles per day. The traffic loading has rapidly increased over the years and is quite heavy, with presently over 35 percent large trucks.

5 Way 5 SELECTION OF REHABILITATION STRATEGY The Flagstaff Interstate 40 concrete pavement to be rehabilitated is located between the Flagstaff Interchange (Mile Post Marker 195) and the Walnut Canyon Interchange (Mile Post Marker 205). The concrete pavement originally built in 1969 (1) consisted of two 3.65m (twelve foot) eastbound and westbound lanes of 200mm (8 inch) thickness with 25mm (3 inch) thick hot mix asphalt (HMA) shoulders. The total width of the pavement surface is 11.6m (38 feet). The concrete pavement is non-reinforced except for reinforcing steel that tie the two concrete lanes together longitudinally. The concrete pavement had sawed and skewed joints that were randomly spaced 4.6m (15 feet) apart. Joints originally were not sealed. Underneath the concrete pavement is a 175mm (7 inches) cement treated base (CTB), built out of a frost susceptible limestone aggregate. Beneath the CTB is an unbound subbase, 175mm (7 inches) thick composed of the same limestone. Underlying the subbase is a clayey cinder material representative of the natural ground. The supporting base layers are the same under the shoulders except that 100mm (four inches) of cinder base was placed between the asphaltic concrete and the CTB. The concrete pavement began to fail in 1974, just five years after construction. The failure began as large corner cracks and progressed to transverse cracks and severe spalling at the transverse joints. Maintenance sealed the cracks and patched spalls as best as possible and in the process expended considerable funds averaging over $80,000 per year.

6 Way 6 As the pavement deteriorated the cracking continued to increase. From 1980 to 1989 the percent cracking increased from one percent to nine percent (Figure 1). The ride quality also suffered, even though maintenance repaired the worst locations. In 1980 the ride was 1500mm/km (100 inches/mile) and by 1989 it had increased to 1980mm/km (132 inches/mile). A value of 2220mm/km (148 inches/mile) is considered objectionable. Twenty percent of the project miles exceeded the objectionable ride level before overlaying. In general the performance of the concrete pavement was very poor. In addition the traffic loadings over the course of time increased dramatically. In 1969 the annual 80kn (18 kip equivalent single axle loads (ESAL s)) was about 120,000. In 1990 it was 1,600,000 and by 1999 it is presently 2,500,000 which is about 21 times as great as Design began in 1988 and reconstruction was very strongly considered. The adjacent 6.7km (four mile) section of I-40 (MP ) had experienced the same type and degree of failure and had been reconstructed. The reconstruction (2) involved the building of detours and closing the interstate in one direction for one year. Thus two reconstruction projects were built over a two year period in the years of 1985 and The reconstructed sections were composed of mm (8-11 inches) of HMA on top of 150mm (6 inches) of permeable asphalt bound base and mm (5-7 inches) of drainable aggregate base. The pavement structural section was placed on top of a geotextile separation fabric to keep the wet clay from pumping into the aggregate base. A complete edge drain system with slotted pipe was also installed. The total

7 Way 7 cost of construction of the two projects was about $15 million. In order to reconstruct the Flagstaff I-40 (MP ) project it would have been necessary to build the project in four phases, since detours of more that 8.3km (five miles) were not allowed. In addition the construction would have taken four years to complete, however it was strongly questioned whether maintenance could maintain the pavement for that long, given its very poor condition (Figure 1). The overall cost of reconstruction was estimated to be at least $30 million. It was finally concluded that the project could not be reconstructed. In addition, due to money and time constraints the project would have to be overlaid within a tight budget and work completed in one construction season of about six months. Various overlay strategies were considered including many different overlay thicknesses, use of a fabric interlayer, asphalt rubber interlayer, various mixes, edge drains and cracking and seating. Each alternative was discussed and reviewed at both the central office and the district office. In addition the project was also selected (3) as a Strategic Highway Research Project (SHRP) Specific Pavement Studies (SPS-6) to test various overlay and rehabilitation strategies on concrete pavement. With an asphalt rubber binder the selected project design strategy represented a test of whether a relatively thin pavement overlay could control reflective cracking. Although the design was for ten years virtually everyone involved in the project considered this to be at best a six year design given the thin overlay design section and the very poor condition of the concrete. After much internal discussion and debate the final pavement design section included edge drains, crack and seat of

8 Way 8 the concrete pavement, a 125mm (five inch) overlay composed of a 75mm (3 inch) conventional dense hot mix asphalt (HMA) and 50mm (2 inch gap graded) asphalt rubber mix (AR-AC). An asphalt rubber open graded friction course (AR-OGFC) 12.5mm (one-half inch) thick was placed as the final wearing surface on the two travel lanes (Figure 2). The asphalt rubber used on the project was specified to be 80%, AC-10 asphalt binder, hot reacted with 20% ground tire rubber. No other additives or modifiers were used. The overlay thickness and layer placement was discussed right up to the final days before the bid advertisement. The discussion centered around whether the AR-AC or the HMA should be placed directly on top of the broken concrete. Previous experience with asphalt rubber interlayers indicated that the AR-AC should be placed on top of the cracked surface before overlay. The other position of placing the AC on top of the broken concrete seemed more in keeping with its role as a leveling and structural layer which would probably crack very soon after construction (first winter). The top overlay of AR-AC and AR-OGFC would then perform not only as the leveling and structural layer but also as the final flexible layer capable of resisting reflection cracking. The project was designed in this manner, however, a test section was built with the 50mm (two inch) AR-AC on top of the broken concrete pavement and a 50mm (two inch) HMA placed on top as the final overlay. The use of the AR-OGFC as the final wearing course had been previously tried on a concrete pavement in Tucson, Arizona. Its performance in Tucson on Interstate 19 has been very good and it was always considered as the most appropriate wearing course. Typically in 1990 OGFC s

9 Way 9 in Arizona were placed with conventional AC-20 (PG-64-16) at a six percent maximum binder content which is normally the maximum the rock can hold before an excess drains off. Asphalt rubber is over ten times more viscous than AC-20 (PG-64-16) at hot mixing temperatures of 177 C (350 F) and thus can be applied to an OGFC rock gradation at a rate of nine to ten percent by weight of the mix. This extra coating thickness increases durability and slows down aging. In addition the thick rubbery coating helps to retard reflection cracking. In addition to the material related design issues, constructability issues were addressed in the design by meeting with district construction personnel. It was agreed early on that the project construction phasing should be such that the project could be completed in one summer paving season. To do this the specifications required the contractor to begin with the edge drain. After sufficient edge drain was completed the crack and seat would start. Crack and seat operations had to be done at night to avoid interfering with the edge drain installation and to be in sync with the overlay operation. The crack and seat drop height and spacing was checked by deflection testing and cores to verify the quality of the work. In addition an incentive of $15,000 per day to finish paving the overlay ahead of schedule was included. The maximum incentive was set at $450,000 with a due date of October 1, With all the numerous design issues described in plans and special provision specifications the project was bid in April, 1990.

10 Way 10 CONSTRUCTION The project was awarded in May The low bid was $10,783,486 which was $190,000 (17%) lower than the state estimate. The quantity of asphalt rubber binder was 3.9Mkg (4,316 tons) the largest amount ever bid by ADOT in a single contract at that time. The unit cost of the asphalt rubber mix was $0.05/kg($45 per ton) and the HMA was $0.025/kg ($23 per ton). Construction began in June, 1990 with the installation of the edge drain and paving of some of the ramps and crossroads with HMA. In late June the crack and seat night operation began. Cracking of the pavement was accomplished with a guillotine hammer. Several drop heights from 0.6m (two feet ) to 1.2m (four feet) were tried. It originally appeared from cores that 1m (40 inch) drop height was adequate although ultimately a 1.2m (four feet) drop height was adopted to be certain that the slab was cracked full depth. A 0.6m (two feet) spacing was originally set and later reduced to 0.5m (18 inches). Seating was accomplished with a 45,359kg (50 ton) rubber tired roller. Generally one to two roller passes was adequate to seat the concrete. Paving of each nights crack and seat followed the next day. The 75mm (three inch) HMA overlay consisted of a dense graded HMA with 4.6 percent asphalt by weight of mix of an AC-20 grade (Table 1). No paving problems occurred, although later after traffic was applied about a dozen small areas failed. Each area was dug out and replaced with new HMA. During removal it was noted that the concrete had been previously in very poor condition. Apparently the crack and seat operation totally destroyed the concrete pavements structural load carrying capacity at these few spots.

11 Way 11 After the HMA overlay was placed and opened to traffic some minor roughness was noticed. This roughness appeared to be related to the seating process, since as more traffic was applied the pavement became noticeably smoother. Following the overlay the 50mm (two inch) AR-AC was placed. AR-AC was a slightly finer gap graded mix with the largest retained aggregate of 9.4mm (3/8 inch) (Table 1), whereas the AC overlay was 19mm (3/4 inch) mix. For the AR-AC mineral aggregate the minimum required sand equivalent was 55 percent and the crushed faces 70 percent. Both of these values are higher than typically required for AC mineral aggregate. The AR-AC contained 6.5 percent asphalt rubber by weight of mix. The asphalt rubber consisted of about 20 percent vulcanized ground rubber sized from 100 percent pass the 2.00mm (number 10 sieve), to no more than five percent passing the 75µm (200 sieve). The rubber was mixed and reacted with an AC-10 asphalt binder and kept at a 177 C (350 F) temperature for one hour, such that the mixture viscosity was between pascal seconds (1,500 to 4,000 centipoise). The resultant asphalt rubber was pumped into the drum mixer hot plant at about 177 C (350 F). The AR-AC mix in the field had to be at least 135 C (275 F) at time of compacting. Compaction was achieved with steel rollers. Rolling was not allowed after the mix cooled to 104 C (220 F). No placement problems occurred although at such elevated temperatures some smoke does occur. Asphalt rubber content was checked with a nuclear asphalt content gauge. After some cooling the pavement was opened to traffic. No bleeding or rutting occurred.

12 Way 12 Following the AR-AC placement, an AR-OGFC was applied as the final wearing course on the two travel lanes. The aggregate grading for the AR-OGFC (Table 1) is very similar to the standard OGFC with 100 percent passing the 9.4mm (3/8 inch) sieve and no more than 9 percent passing the 2.36mm (number 8) sieve (Table 1). A maximum of only 2.5 percent could pass the 75µm (200 sieve). The aggregate properties had to conform to the same quality criteria as the AR-AC. The asphalt rubber was the same as for the AR-AC. The percent asphalt rubber was 9.0 percent by weight of the mix, typically an OGFC has only 6.0 percent binder. The AR-OGFC was mixed, placed and compacted in the same manner as the AR-AC except compaction effort ceased at 93 C (200 F) instead of 104 C (220 F). After cooling the AR-OGFC was opened to traffic with no problems. Virtually all the paving was completed by the end of September. By working Saturday and Sunday as well as 10 and 12 hour shifts the contractor was able to finish early enough to receive an incentive payment of well over $400,000. In general the construction was rushed and hectic, however, the final product appeared to be of very good quality. In addition to the routine project work, 4.6km (2.76 miles) of SHRP experimental sections and a weight-in-motion site were constructed on Interstate 40 (4). In addition a one-mile concrete section of Interstate 17 was overlayed with 37.5m (1.5 inches) of AR-AC. PERFORMANCE Since paving was completed in October 1990 nine years of very good service have occurred, far more than expected. Each year data for each mile was recorded by the ADOT Pavement Management Section (PMS). In addition this section also retrieves the traffic loading data and

13 Way 13 the pavement surface maintenance data from other computer files. Table 2 shows the average yearly summary of pavement performance data for the 33.3km (20 miles) of pavement. In addition the data is also shown representative of the pavement condition before overlay. As can be seen virtually no reflective cracking has occurred since construction. The ride is expressed in inches per mile units and is indicative of a very smooth riding surface. The rut depth is virtually not existent. Skid resistance as measured by the Mu meter is good. Maintenance costs have been low throughout the life of the overlay. For comparative purposes the adjoining section of Interstate 40 referred to as the Riordan project (milepost marker 191 to 195) was reconstructed in 1985 and 1986 under two separate construction projects. The old very badly cracked concrete pavement was removed and crushed for aggregate base. The existing cement treated base had turned to a mushy poor quality material and was wasted. The wet clay subgrade was regraded and an edge drain system constructed. A geotextile separation layer was placed followed by mm (four to seven inches) of aggregate base. The aggregate base was then covered with 150mm (six inches) of a asphalt permeable base. The final HMA was mm (eight to eleven inches) in thickness (Figure 3). All of the HMA was built with an AC-20 binder. The two construction projects required detours and two years of construction. The total cost for about four miles of new pavement was $14 million. For comparative purposes Table 3 shows the distress history of these two Riordan reconstruction projects as measured by the ADOT PMS. Cracking of the mm (eight to eleven inch) pavements began in the second year and proceeded to a degree requiring

14 Way 14 rehabilitation by the tenth year. Other pavement performance measures indicated that the pavement was performing very poorly. Another comparison of how well the ADOT AR section have performed can be seen from reviewing Strategic Highway Research Project test sections built as part of the Flagstaff overlay project. The Flagstaff project was selected as an SPS-6 concrete rehabilitation test project. Table 4 shows the layout of the test sections. ADOT decided to build several of its own test section to be included in the study. The test section are all located in the east bound direction of Interstate 40 from mile post marker to SHRP test section is a 200mm (eight inch) overlay of the concrete pavement. Test section , and are all 100mm (four inch) overlays of the concrete pavement. The 200mm & 100mm (eight and four inch) overlay test sections were all built using the ADOT HMA base mix with 4.6% asphalt with AC-20 binder. Test section was an ADOT test section composed of a two inch overlay of ADOT HMA base mix followed by a 50mm (two inch) overlay with the AR gap graded mix with 6.5% binder. Table 4 shows the cracking by year in lineal feet of cracking (5). These crack measurements were estimated from the LTPP file and from the crack maps and/or ADOT photos and field reviews. Again this table shows how well the AR sections are performing compared to the other conventional overlays. Figure 4 shows a photo taken from 19.8m (65 feet) above the test section by using an ADOT cherry picker (high boom) truck. It clearly shows the degree of cracking in the 100mm (four inch) overlay and the lack of cracking in the AR test section.

15 Way 15 CONCLUSION Based upon the outstanding performance of this project as well as many others, ADOT routinely uses AR gap graded and open graded mixes throughout the state. Over 3,333km (2,000 miles) of AR projects have been built since Figure 5 is a map showing those ADOT system miles paved with AR. In addition the performance of all AR projects has been tracked through the ADOT PMS, Figure 6 shows the percent cracking for those overlay projects built with and without AR since 1988 (6). As shown the percent cracking is much less over time than for conventional overlays without AR. In addition Figure 7 shows less routine maintenance for AR projects than for conventional overlays. It should also be noted that the average thickness of the AR projects is 42.5mm (1.7 inches) and for conventional mixes it is 137.5mm (5.5 inches). Thus even though AR mixes cost about twice as much per ton, they are generally placed half as thick and crack at a rate less than one fourth than that of conventional mix. The overall AR performance seems to be in agreement with findings in 1977 (7) that AR in cold weather can withstand about five times the strain before rupture than can asphalt. The Arizona Department of Transportation in cooperation with The Federal Highway Administration and the Strategic Highway Research Program have designed and constructed an extremely valuable research project. Field performance in nine years of service is providing experience indicating the effectiveness of a thin flexible overlay and wearing course composed of asphalt rubber. Results of this work are being incorporated into paving projects, throughout the

16 Way 16 state. Continued field performance measurements provide the data necessary to develop rational cost effective designs. ACKNOWLEDGMENT The author is indebted to the good work of Jackie Hostetler in typing the paper. Also, Ali Zareh and Doug Carlson were of immense help in preparing the figures. REFERENCES 1. Way, George Flagstaff I-40 Overlay Project, De., 11-13, R Conference & Road Show, Cincinnati, Ohio. 2. Lawson, John Subsurface Drainage System in Flagstaff, Arizona, 13th Southwest Geotechnical Engineers Conference, April 25-29, 1988 Oklahoma City. 3. SHRP, Strategic Highway Research Program. Specific Pavement Studies Experimental Design and Research Plan for experiment SPS-6: Rehabilitation of Jointed Portland Cement Concrete Pavements, Washing, D.C., 1989.

17 Way Austin Research Engineers, SPS-6: Rehabilitation of Jointed Portland Cement Concrete Pavements; Construction Report, Nov., 1992, ADOT Report Number FHWA-AZ ATRC Research Notes, Concrete Pavement Rehabilitation Update, ADOT, Dec., 1994, SPS-6 Note. 6. Way, George Asphalt Rubber - The Arizona Experience, Feb., 3, 1999 Asphalt Rubber 1999: A Global Summary of Practices, Rubber Pavements Association International Symposium, Tempe, Arizona. 7. Green, E. L., Tolonen, William J., The Chemical and Physical Properties of Asphalt Rubber Mixtures, July 1977, ADOT Report ADOT-RS-14(162).

18 Way 18 LIST OF FIGURES FIGURE 1. Pictures of concrete pavement before overlay. FIGURE 2. Flagstaff I-40 pavement overlay cross section FIGURE 3. Riordan I-40 pavement reconstruction cross section. FIGURE 4. Overhead cherry picker view of overlay with and without asphalt rubber. FIGURE 5. Arizona State Highway Map showing asphalt rubber overlays built since FIGURE 6. Percent cracking over a ten year period with and without asphalt rubber. FIGURE 7. Maintenance costs with and without asphalt rubber. LIST OF TABLES TABLE mix design, HMA, AR gap graded and AR open graded. TABLE 2. Flagstaff I-40 pavement performance. TABLE 3. Riordan I-40 pavement performance. TABLE 4. LTPP test section pavement performance.

19 Way 19 FIGURE 1. Pictures of concrete pavement before overlay.

20 Way 20 FIGURE 2. Flagstaff I-40 pavement overlay cross section. Typical Section I-40 Flagstaff project 38' Fog Coat* 25' Fog Coat* Shldr. Build-Up 6" Lt. travel Rt. travel lane lane 6" Shldr. Build-Up Edge Drain 1/2" AR-OGFC 2" AR-AC Tack Coats 3" AC(3/4) Tack Coats Existing PCCP (Crack & seat) Existing HMA Shoulder I-40 EB MP * The fog coat shall overlap the new AR-OGFC 6

21 Way 21 FIGURE 3. Riordan I-40 pavement reconstruction cross section. Typical Section I- 40 RIORDAN Project 38' 20' 16' 22' 2.5' WB Centerline 2.5' Slope Under Drain Tack Coats 2" AC(1/2") 3" AC(3/4") 3" AC(3/4") 3" AC(3/4") 6" BTB Prime Coat Engineering Fabric 4" AB Subgrade

22 Way 22 FIGURE 4. Overhead cherry picker view of overlay with and without asphalt rubber. I-40 SHRP test sections 4 conventional AC (left) and 2 Asphalt-Rubber Hot Mix placed in Photos taken in 1998

23 Way 23 FIGURE 5. Arizona State Highway Map showing asphalt rubber overlays built since 1988.

24 Way 24 FIGURE 6. Percent cracking over a ten year period with and without asphalt rubber. Arizona DOT, Materials Group, Overlay Performance Years Overlays/Inlays Neat Asphalt Asphalt-Rubber

25 Way 25 FIGURE 7. Maintenance costs with and without asphalt rubber Arizona DOT, Materials Group, Maintenance Cost, Dollars Per Lane Mile Years Overlays/Inlays Neat Asphalt AR-ACFC

26 Way 26 TABLE MIX DESIGN Basalt Aggregate Flagstaff I-40 Asphalt Asphalt Base Mix Rubber Rubber HMA Gap Open AC-20 Graded Graded Sieve % Pass % Pass % Pass / / / / # # # # # # # # # % Asphalt % Lime Bulk Density VMA % Effective Air Voids % Maximum Theo. Density Marshall Stability (Lb) Flow Agg. Combined Sp. Grav Agg. Water Abs. % Agg. Asphalt Abs. % Sand Equivalent Crushed Faces % Immersion Comp. Wet Strength 542 % Retained Wet Strength 86

27 Way 27 TABLE 2. FLAGSTAFF I-40 PAVEMENT PERFORMANCE Flagstaff I-40 Mile Post Marker Before Overlay Percent Cracking Ride IRI inch/mile Rut inches Skid Mu Meter Number Maintenance Dollars Per Mile Traffic 18 Kip ESAL s per year PCCP NA ,500,000 After Overlay ,600, ,700, ,800, ,900,000, ,000, ,100, ,300, ,400, ,500,000 TABLE 3. RIORDAN I-40 PAVEMENT PERFORMANCE PCCP Before Reconstruction Riordan HMA Mile Post Percent Ride Rut Skid Cracking IRI Depth Inch Mu Meter Maintenance Dollars Per Mile Traffic 18 Kip ESAL s per year Inch/Mile Number NA ,200,000 After Reconstruction ,300, ,400, ,500, ,600, ,700, ,800, ,900, ,000, ,100, ,300, Rehab.

28 Way 28 TABLE 4. LTPP TEST SECTION PAVEMENT PERFORMANCE I-40 SHRP LTPP SPS-6 Test Section Begin Mile End Mile Test Section Linear Feet Cracking Test Section Description # Post Post Type * STATE HMA Overlay, Rubberized Concrete STATE 10 PCC Overlay, 2 HMA Overlay, C&S * SHRP HMA Overlay, Crack & Seat (C&S) * SHRP HMA Overlay, C&S * SHRP HMA Overlay, Max., Restoration PCC * STATE HMA Overlay, Fabric, 2 HMA, C&S * STATE ARAC Surface, 2 HMA, C&S * SHRP HMA Overlay with Saw & Seal * STATE HMA Surface, 2 ARAC, C&S * SHRP HMA, Minimum Restoration PCC SHRP Out of Service PCC Section SHRP Out of Service PCC Section SHRP Out of Service PCC Section * A 0.50 open graded (ACFC) surface placed after overlay to improve skid resistance. An AC-20 binder was used, as the binder. Note some sections have a dual number. TS # was , TS # was , TS # was and TS # was