Reconstructing Pavements Using Full- Depth Reclamation Matthew Singel
Introduction Applications Benefits Construction Performance
Introduction
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.
Inside a Reclaimer
Applications
Surfaced Roadways in the United States (2,495,000 total centerline miles) Rigid 6.5% Composite 11.3% Flexible 82.2%
Texas Pavements 150 138.0 Miles (x 1000) ' 100 50 0 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
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
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!
How do you know if you have a base problem and not just a surface deficiency?
Examples of Pavement Distress Alligator cracking Rutting Excessive patching Base failures Potholes Soil stains on surface
Benefits
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
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
Sustainable Element of FDR Process Trucks (trips) 12 180 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
Design
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
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)
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
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
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!
Construction
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
Pulverization Pulverize mat to appropriate gradation Usually, only one pass is required!
Cement Spreading Cement is spread on top of the pulverized material in a measured amount in either a dry or slurry form
Blending of Materials and Cement is blended into pulverized, reclaimed material and, with the addition of water, is brought to optimum moisture Moisture Addition
Compaction and Grading Material is compacted to 96 to 98 percent minimum standard proctor density and then graded to appropriate lines, grades, and crosssections
Curing Bituminous Compounds (cutbacks or emulsions) Water (kept continuously moist)
Field Testing
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).
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
Full-Depth Reclamation in Tarrant County The Benefits of Microcracking Neal Welch-Precinct Supervisor Tarrant County Precinct 3
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
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
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
Ottinger Road Keller, TX Reclaimed in Spring 2007 1+ mile road FDR with 4% cement Middle section microcracked after 24 hours End sections reclaimed but not microcracked [control sections]
Ottinger Road Keller/Roanoke Area
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
Ottinger Road Non-Microcracked Section
Ottinger Road Non-Microcracked Section
Ottinger Road Microcracked Section
Ottinger Road Microcracked Section
Going Forward Very pleased with microcracking results Cost is insignificant Currently microcracking all cementstabilized bases going forward.
Neil said, feel free to call with questions or for more information on his experience Richard Schiller Current Precinct Supervisor Tarrant County Precinct 3 817-514-5000 rschiller@tarrantcounty.com
Projects
Welcome to Navasota, TX Population 6,296
$22,410 per mile 20 Days 8-hour days City Crews City Equipment Rented CMI Chip seal Delaying overlay is working well
City of Fort Worth
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
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
Tarrant County Reclaiming with cement since 2001. 4.5% cement six to eight inches deep. Two-inches of asphalt or a two-course surface treatment tops the roadways. Material costs = $1.25 - $1.50 per sq. yd.
Texas DOT Bryan District On rural FM system Increased oil field and farm traffic District recycled 10 inches of base creating a layer 300-400 psi, 4% Roads were opened to traffic daily TTI Pavement evaluations of treated layers include Stiffness, Cracking, Moisture Susceptibility and performance
Hailey, Idaho 2006 FDR with cement was only design alternate of 4 to guarantee reopening in 30 days
Hailey, Idaho
2006 FDR used to reconstruct old soil cement and asphalt runway Runway crossed a second runway presenting grade issues Waycross, Georgia
Removed 2 asphalt Added sand-clay material to modify gradation Place 4 asphalt Waycross, Georgia
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
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
Performance
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
Performance Evaluation
79 Projects Studied Average = 9 years
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
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
Thank You! Matthew Singel msingel@cementx.org www.cementx.org 817-709-4313