Reconstructing Pavements Using Full- Depth Reclamation. Matthew Singel

Transcription

1 Reconstructing Pavements Using Full- Depth Reclamation Matthew Singel

2 Introduction Applications Benefits Construction Performance

3 Introduction

4 Definition of Full-Depth Reclamation Method of flexible pavement reconstruction that utilizes the existing asphalt, base, and subgrade material to produce a new stabilized base course for a chip seal, asphalt, or concrete wearing surface.

5 Inside a Reclaimer

6 Applications

7 Surfaced Roadways in the United States (2,495,000 total centerline miles) Rigid 6.5% Composite 11.3% Flexible 82.2%

8 Texas Pavements Miles (x 1000) ' Federal 1.0 State 79.0 County City/Local 79.0 Composite Rigid 6.5% 5.3% 88.2% Flexible Centerline Miles of Road By Jurisdiction (296,000 Miles) Type of Pavement

9 Reclamation: A Logical Choice Aging road systems Most highway systems now in place Emphasis shifting to maintenance/rehabilitation Most roads are local, low-volume, unpaved or flexible pavements Possible strategies: Thick structural overlays Removal and replacement Reclamation with cement & thin overlay

10 Challenges Facing Our Roadways Continuing growth Rising expectations from users A heavily used, aging system Environmental compatibility Changes in the workforce Funding limitations Combined with large increases in traffic volumes and/or allowable loads often leads to serious roadway base failures!

11 How do you know if you have a base problem and not just a surface deficiency?

12 Examples of Pavement Distress Alligator cracking Rutting Excessive patching Base failures Potholes Soil stains on surface

13 Benefits

14 Advantages of the FDR Process Use of in-place materials Little or no material hauled off and dumped Maintains or improves existing grade Conserves virgin material Saves cost by using in-place investment Saves energy by reducing mining and hauls Very sustainable process

15 Benefits of FDR with Cement Increased rigidity spreads loads Eliminates rutting below surface Reduced moisture susceptibility Reduced fatigue cracking in asphalt surfacing Allows for thinner pavement section

16 Sustainable Element of FDR Process Trucks (trips) Material (tons) 300 4,500 New Disposal (cu yd) 0 2,700 Reclaim Diesel (gal) 500 3,000 1 mile of 24-foot wide, 2-lane road, with a 6-inch base

17 Design

18 Pavement Thickness Design Procedures 1993 AASHTO Pavement Design Guide Structural Numbers Layer Coefficients Proposed New AASHTO Design Guide Mechanistic-Empirical Design Evaluates effects of pavement materials, traffic loading conditions, environmental factors, design features, and construction practices

19 Pavement Materials Tests Sieve Analysis (ASTM C136) Atterberg Limits (ASTM D4318) Moisture-Density (ASTM D558) Durability Tests Wet-Dry (ASTM D559) Freeze-Thaw (ASTM D560) Soluble Sulfates (ASTM C1580) Compressive Strength (ASTM D1633)

20 Laboratory Mix Design Obtain representative samples of roadway material Usually about 100 pounds of material is required Determine the maximum dry density and optimum moisture content at various cement percentages (ASTM D558) Typical designs vary between 2 and 8 percent cement by weight of dry material Prepare samples Cure samples

21 Strength Determination Unconfined Compressive Strength Testing ASTM D1633 Used by most governing agencies Simple and quick procedure 7-day strengths ranging from 300 to 400 psi are generally recommended Proven strength (support) under extremely heavy traffic conditions Proven performance (durability) in wet-dry and freeze-thaw environments

22 Please keep in mind that strength and performance are NOT the same thing! The purpose of the mix design procedure is to select the correct amount of stabilizer that most closely balances both strength AND performance for the roadway materials!

23 Construction

24 FDR Construction Process Pulverize, Shape, Add Cement, Mix In Place, Compact, and Surface Bituminous Surfacing Granular Base Pulverized Pulverized Stabilized New Surfacing Stabilized Subgrade Subgrade Subgrade Subgrade Subgrade Existing road Pulverization to desired depth Removal of excess material (if necessary) and shaping Addition of cement, mixing, reshaping, and compaction Final surface application

25 Pulverization Pulverize mat to appropriate gradation Usually, only one pass is required!

26 Cement Spreading Cement is spread on top of the pulverized material in a measured amount in either a dry or slurry form

27 Blending of Materials and Cement is blended into pulverized, reclaimed material and, with the addition of water, is brought to optimum moisture Moisture Addition

28 Compaction and Grading Material is compacted to 96 to 98 percent minimum standard proctor density and then graded to appropriate lines, grades, and crosssections

29 Curing Bituminous Compounds (cutbacks or emulsions) Water (kept continuously moist)

30 Field Testing

31 Testing Requirements Gradation/Uniformity Density Moisture A common gradation requirement is for 100 percent to pass a 3-inch sieve, a minimum of 95 percent to pass a 2-inch sieve, and a minimum of 55 percent to pass a No. 4 sieve (ASTM C136). A common density requirement is to be between 96 and 98 percent of the established laboratory standard Proctor density (ASTM D558). A common moisture requirement is to be within 2 percent of the laboratory established optimum moisture content (ASTM D558).

32 Traffic and Surfacing Completed FDR base can be opened immediately to lowspeed local traffic and to construction equipment Subsequent pavement layers can be placed at any time

33 Full-Depth Reclamation in Tarrant County The Benefits of Microcracking Neal Welch-Precinct Supervisor Tarrant County Precinct 3

34 Tarrant County, Pct 3 Background Maintain most county roads internally Maintain many city streets through inter-local agreements Have significant equipment inventory Includes 2 CMI reclaimers Asphalt paving equipment Dedicated crews for each operation

35 Tarrant County, Pct 3 Reclamation Procedure Pulverize 6 to 8 depth Typically apply 4% cement Water, Grade & Roll Cure with asphalt emulsion prime coat Apply sand to avoid tracking of prime coat Open to traffic overnight in most cases

36 Microcracking Procedure 10 to 12 ton vibratory roller 24 to 48 hours after placement Creep speed High amplitude Typically 3 passes Waive stiffness reduction testing Satisfied with results No need to document

37 Ottinger Road Keller, TX Reclaimed in Spring mile road FDR with 4% cement Middle section microcracked after 24 hours End sections reclaimed but not microcracked [control sections]

38 Ottinger Road Keller/Roanoke Area

39 Unusual Weather 2006 Extremely Wet in DFW area 2007 Unusually Dry in DFW This combination caused premature cracking on many roads in isolated areas of DFW independent of construction method Was obvious on newly constructed/maintained roads Cracks originated in subgrade soils below pavement section

40 Ottinger Road Non-Microcracked Section

41 Ottinger Road Non-Microcracked Section

42 Ottinger Road Microcracked Section

43 Ottinger Road Microcracked Section

44 Going Forward Very pleased with microcracking results Cost is insignificant Currently microcracking all cementstabilized bases going forward.

45 Neil said, feel free to call with questions or for more information on his experience Richard Schiller Current Precinct Supervisor Tarrant County Precinct rschiller@tarrantcounty.com

46 Projects

47 Welcome to Navasota, TX Population 6,296

48 $22,410 per mile 20 Days 8-hour days City Crews City Equipment Rented CMI Chip seal Delaying overlay is working well

49 City of Fort Worth

50 Since 1996: 296 lanemiles or 2.26 million SY Spending 60% of $10- million budget on reclamation Average material cost: $1.95 to $2.45 SY City of Fort Worth FDR

51 Replace vs Recycle Full reconstruction = $278,500 per lane mile replacing curbs, gutters, sidewalks & driveway approaches. FDR = $200,000, a $78,500 costsavings. BUT city keeps 40% to 90% of concrete, cutting cost to $83,050 per lane mile. Final Cost Savings = $116,950/ lane mile

52 Tarrant County Reclaiming with cement since % cement six to eight inches deep. Two-inches of asphalt or a two-course surface treatment tops the roadways. Material costs = $ $1.50 per sq. yd.

53 Texas DOT Bryan District On rural FM system Increased oil field and farm traffic District recycled 10 inches of base creating a layer psi, 4% Roads were opened to traffic daily TTI Pavement evaluations of treated layers include Stiffness, Cracking, Moisture Susceptibility and performance

54 Hailey, Idaho 2006 FDR with cement was only design alternate of 4 to guarantee reopening in 30 days

55 Hailey, Idaho

56 2006 FDR used to reconstruct old soil cement and asphalt runway Runway crossed a second runway presenting grade issues Waycross, Georgia

57 Removed 2 asphalt Added sand-clay material to modify gradation Place 4 asphalt Waycross, Georgia

58 Milestones TXDOT Corpus Christi; FDR a key Annual Maintenance Program NCTCOG Cement Stabilization Specification adopted; 100 cities in 16 counties TXDOT-Tyler District - US 69 CMS (15 lane miles) TXDOT Bryan Dist. - Over 500 miles roads TXDOT San Antonio Dist. - I-37 S. TX - 18 miles of recycling

59 Who Is Using It In Texas? (Partial List) Goliad County Bell County Bexar County Grand Prairie City of Ft Worth Tarrant County Goliad County Town of Navasota Lubbock District Corpus Christi District Bryan District San Antonio District Fort Worth District

60 Performance

61 PCA Funded Project Study conducted in 2005 Identified candidate project sites in concert with PCA State (DOT), County, City Agencies, Private Interaction with select officials Visual Pavement Condition Index (PCI) survey Extracted roadway cores for UCS measurements

62 Performance Evaluation

63 79 Projects Studied Average = 9 years

64 LTP Study Conclusions Overall, excellent LTP Average Pav t Condition Index of 89 UCS of cores 260 to over 1,000 psi Cement contents 2 to 12 percent with average being 5 percent Most surface distress was in the asphalt layer No major failures attributed to the cementstabilized base Owners are happy with performance and plan to do more in the future

65 Concluding Comments Use of in-place materials Very sustainable process Fast operation Constructed under traffic Structurally better than granular base Can apply local traffic almost immediately 30 to 60 percent less expensive than removal and replacement

66 Thank You! Matthew Singel