PCC Overlay Design and C t ti Construction - American Concrete ...

PCC Overlay Design andConstructiontiTomorrow’s High Performance Concrete Pavements TodayWorkshop, Concord NC, February 28, 2012Michael E. Ayers, Ph.D., Global Pavement Consultants, Inc.yRepresenting - National Concrete Pavement Technology Center

Concrete Overlay Guide second editionContentst1. Overview of OverlayFamilies2. Overlay types and uses3. Evaluations & Selections4. Six Overlay Summaries(11”x17 “sheets)5. Design Section6. Miscellaneous DesignDetails7. Overlay Materials Section8. Work Zones under Traffic9. Key Points for OverlayConstruction10. Accelerated Construction11. SpecificationConsiderations12. Repairs of OverlaysSecond Edition September 2008

Design of Concrete Overlays UsingExisting Technologies• Listing and explanation of currentand recommended softwareprograms for specific overlays• Background of recommendedoverlay design techniques• Detailed examples of how to usethe existing design techniques• Learn by example – then apply toyour situation!ti

Types of Concrete OverlaysBondedUnbonded2” –5” 4” –11”

Concrete OverlaysService Life Expectations• Thickness of 2 to 6 in. – 15 to 25 years• Thickness > 6 in. – 20 to 30+ yearsOverlay service life is dependent upon :•Sound overlay structural design - compatiblewith expected traffic and site conditions, and•Good construction practices

Bonded and Unbonded

Pavement Evaluation to Determine ifExisting Pavement is a Candidate for aConcrete OverlayPoor Choice4” Bonded Overlayover 50 yr pavementPoor Choice4” Concrete Overlay over“D” cracked aggregate

Evaluations of Existing Pavementsfor Overlays• Evaluation is also used to determine:• Required repairs where needed• Establish the concrete overlay designthickness• When combined with an overlay can theexisting pavement help carry anticipatedi t traffic as:- an integrated part of the pavement(bonded)- or serve as a base or subbase

What are WeBuilding theOverlays On?

Concrete Overlay Quantities-REALITY CHECK-•Concrete is bid in sq.yards for placement,cu. yards for material•Profile is not perfectand needs corrected•Cross slope needscorrectionHoldMinimumThicknessPCC OVERLAYProfile needscorrectedEXISTING PAVEMENTSlope Varies

Engineering SurveyCost Comparison of Engineering/Surveying Pre Construction verses at Time of ConstructionTask DescriptionBase Cost Estimated 3 Line Profile and 10 Mile Project LegnthTask as Currently PerformedEstimatedHours3 LineProfile Rate TotalAdditional Profile CostFive LineProfileNine LineProfileProject scope development 25 $ 95.00 $ 2,375.00$ 2,375.00$ 2,375.00Project control establishment 65 $ 150.00 $ 9,750.00 $ 9,750.00 $ 9,750.00Topo survey 220 $ 150.00 $ 33,000.00 $ 41,250.00 $ 49,500.00Create existing road surface 13 $ 75.00 $ 975.00 $ 975.00 $ 975.00Design road profiles 100 $ 88.00 $ 8,800.00 $ 8,800.00 $ 8,800.00Construction ti survey 190 $ 150.0000$ 28,500.00$ 28,500.00$28,500.00Total $ 83,400.00 $ 91,650.00 $ 99,900.00Cost Per Mile $ 8,340.00 $ 9,165.00 $ 9,990.00*Note: The estimates show have been generated from six estimates for construction survey that were calculated. Wewere not the successful bidder meaning someone got the work for less money

Quantity Estimates• Estimating plan quantity• Overlay cubic yard pay item is to adjust the theoreticalvolume by an appropriate factor that accounts for thenon-uniformity of the existing surfaceConcreteOverlayThickness½” PlacementTolerance as a %of DesignThicknessAdditional %Adjustment forGross SurfaceIrregularities i in theExisting SurfaceTotal AdjustmentFactor to beApplied toTheoreticalVolume4” 12.5% 5% 17.5%6” 83% 8.3% 5% 13.3% 3%8” 6.3% 5% 11.3%10” 5.0% 5% 10.0%12” 4.2% 5% 9.2%

Paving with Outside & Inside Stringlines1 st Pass

Paving with Outside Edge Stringline &Ski Combination1 st PassUS 287US 69

Paving with Outside Stringline Only &Slope Control1 st Pass

Stringless Paving

Concrete Bonded Overlay ofConcrete2” – 5”

Uses and Advantages- BondedOverlay of Concrete2”–5” thickness• Use when existingpavement is in goodstructural t condition withsome surface distress.• Use to eliminate anysurface defects; increasestructural capacity; andimprove surface friction,noise, and rideability.• Typically used directly over concrete withoutadditional repairs except for spot-repairing ofseverely deteriorated areas.

BondedConcreteOverlay overConcrete• Where any of the above distress are present, their severity and extentshould be considered to determine if a bonded overlay is appropriate.p• Working cracks to be repaired or sawed since they will reflect through.

Coefficient of Thermal Expansion(CTE)• Overlay CTE should be similar to underliningpavement• If not near the same at least overlay CTE should belower than existing pavementShearTensile stressOerla OverlayShearExistingPavement

Poor Bonding: Delamination ofConcrete Overlay over Concrete

Maintaining Bond• Replaced Asphalt Patch with Concrete Patch

Spot Repairs for BondedOverlays of ConcreteJointPatchingFull Depth Patches

Bonded Overlay of Concrete- FullDepth Cut & Width of Cut

Bonded on ConcreteKeys to Success• Bond is important• Concrete aggregate used in overlay should have thermalproperties similar to that of existing pavement•Matching gjoints with underlying gpavement allows structure tomove monolithically.• Existing joints must be in fair condition or be repaired• Timing of joint sawing is important.• Cut transverse joints full depth +1/2” and longitudinal joints atT/2.• Width of transverse joint of overlay to be equal to or greaterthan underlying crack width of the existing pavement.• Curing should be timely and adequate,.

Concrete Bonded Overlay ofAsphalt or Composite

Bonded Overlay of Asphalt orComposite Pavements2”–5” thicknessExisting pavement conditionFair or better structural condition withsurface distressApplications•To eliminate surface defects such asrutting and shoving•Improve surface characteristics likefriction, noise, and rideability•To increase structural capacity wheretraffic loads have or will increased

Feasibility• HMA pavements with some structural integrity- Limited structural (fatigue) cracking- No stripping/raveling in HMA layers- HMA thickness after milling > 3 in to 4 in. minimum• Rutting in HMA layers ok• Non-load associated cracking ok

Typical Uses of Concrete Overlay ofExisting Asphalt PavementMichigan Intersection•300 trucks per day•160,000 lbs loading

Typical Uses of Concrete Overlayover AsphaltBefore –Asphalt lasted 3 to 6 monthsAfter- 9 years service of concreteoverlay in wheel lines still performing

BondedConcreteResurfacingofCompositePavements• Asphalt is a good reflector of underlining concrete pavement condition.• A review of the existing profile grade line should be conducted and areas ofsignificant ifi deviation investigated t through h analysis of core samples in thelaboratory.CONCRETE RESURFACING OF ASPHALT PAVEMENTS

Purpose of Asphalt Milling forConcrete Bonded Overlay•Remove distortions 2” or more•Reduce high spots to insure minimumoverlay depth•Match adjacent lanes•Help insure good bond•Meet M t vertical elevation requirements•Restore Profile

Cautions on Milling• Milling should beminimized to retain structuralsupport of pavement•Preferable to mill to depththat will minimize thepotential for delaminationbetween lifts•Grade G d corrections shouldbe made in the thickness ofthe concrete overlayExcessive milling of existing asphaltbeyond asphalt lifts (tack line)

Over Milling Can Result in StructuralFailure of Concrete Bonded Overlayover HMA

Joint Design• Max.spacingof3to8ftft- Limit 1.0 to 1.5 times thicknessin feet.- Some agencies include tie barsat longitudinal joints > 5 in- No dowels (aggregateinterlock relied upon)

Longitudinal Joint Layout2 ft x 2 ft 4 ft x 4 ftOuterShould derOuterShould der3 ft x 3 ft12 ftTraffic6 ft x 6 ft12 ft

PCC Joint SawingCRITICAL•Effective curing•Timely joint sawing

Bonded over Asphalt/CompositeKeys to Success•Bonding is critical•Small square panels reduce curling,warping, & shear stresses in bond (1.5times thickness).•Mill to remove surface distresses, orimprove bonding.•Be sure to leave 3” to 4” of HMA aftermilling.•HMA surface temperature below 120 Fbefore paving.•Joints in the overlay should not beplaced in wheel paths, if possible•Application of curing compound is critical

Concrete Unbonded Overlay ofConcrete

Uses and Advantages - UnbondedOverlay of Concrete Pavements4” - 11” thickness• Use when existing gpavement isin poor condition, includingwith material-related distresssuch as D-cracking, whenunderlying pavement andsubbase are stable anduniform except for isolatedareas that can be repaired.• Use to restore structural t capacity of the existingpavement and increase pavement life equivalent to fulldepthpavement..

Unbounded OverlaysCan be Placed overBadly DistressedConcrete Pavements

Unbonded onConcreteExisting concrete and its subbbase must providea uniform strength platform……if it doesn’t, what actions are necessary to achieve uniformity?

Separator Layer• Required for good performance- Isolate overlay from existing distress• Prevent reflection cracking• Prevent bonding/mechanicali interlocking- Provide level surface for overlayconstruction• Recommended interlayer material:- 1-2 in HMA- Geotextile (Missouri Demo – Sept2008)

Need for Adequate Interlayer"KEY"OVERLAYOLD PAVEMENTTHICKERINTERLAYER (1”)SMOOTHER SLIP PLANE

Geotextile Separation Layer(Interlayer)No turnsNo wrinkles

Michigan's Porous HMA SeparationLayer

Asphalt Stripping

Cross Section or Grade Correctionswith Interlayer• Tendency to utilize the asphalt separation layer as themedium for correcting cross slope & profile• Results in variable asphalt thickness and can lead tovery thin asphalt sections (less than 1”)• When compacted creates variable roll down• Varying thickness for fastening dowel bars• Use constant t thickness (typically 1”) as a separationlayer• Make cross slope and smoothness adjustments in the• Make cross-slope and smoothness adjustments in theconcrete overlay

Jointing-Load Transfer• JPCP joint spacing-1.5 times slab thickness in feet < 6 in.-2 times slab thickness > 6 in. ( up to 15’)• Transverse joints offset from those in existing• Transverse joints offset from those in existingslab (when possible)

Dowel Bars in Wheel PathFasteners to Existing Pavement Important

Direct Concrete Placement in Frontof PaverRemove Unnecessary Dowels

Unbonded Overlay of Concrete PavementsKeys to Success• Full-depth repairs -only wherestructural integrity is lost at isolatedspots.• Separator layer (normally 1”asphalt or geotextile fabric)• Use to restore structural capacity of the existing pavement andincrease pavement life equivalent to full-depth pavement.• Faulting of 3/8 in. or less in the existing concrete pavement• Shorter joint spacing helps minimize curling and warpingstresses.• To not match joints with those of the underlying concretepavement. p

Concrete Unbonded Overlay of HMA orComposites- Trouble Shooting

Unbonded Concrete Overlay of Asphalt orComposite Pavements4” - 11” thicknessExisting pavement conditionDeteriorated (severe rutting, potholes,alligator cracking, shoving, and pumping)but stable and uniformApplications•To restore or enhance pavement’sstructural capacity•To increase pavement life equivalent tofull-depth pavement•To eliminate deterioration problems•To reduce urban heat island effect byincreasing i pavement surface albedo

Semi- Uniform PlatformRemaining i HMA severelydamaged from truckshauling away millingsRemoved 6 in of existing 9-inHMA Pavement

Iowa 175 Longitudinal Crack

Unbonded Over Asphalt/CompositeKeys to Success• Milling to eliminate surface distortionsof 2 in. or more• Complete repairs at isolated spotswhere structural integrity needsrestoring• Concrete patches in the existingpavement should be separated fromthe overlay• Surface temperature of existing asphaltpavement should be maintained below120ºF (48.9ºC) when placing overlay• Partial bonding between the overlayand the existing asphalt pavement isacceptable and may even improveload-carrying capacity

SpringConditionsOverlayExisting pavement (HMA,PCC, HMA on PCC, etc.)• Cool base; cool nights- Slows set throughout depth of overlay (not just the bottom up)• Base movement is the controlling factor- Cool ground + warming during day = movement- Cooling of base at night (cold above & cold below)Countermeasure: Place concrete overlay during base expansion, notbase contraction- Start early; consider covering with plastic sheeting- Avoid afternoon & evening pours- Increase and monitor concrete placement temperature- Use minimum amount of required SCM’s

FallConditionsOverlayExisting Pavement(HMA, PCC)• Warm base; cool nights- Concrete sets from the bottom up• Base movement generally not a problem• May get some random cracks- Too green on top to allow for saw cutting, yet stresses building upfrom bottom of slabCountermeasures:- Place early in day; Use heat of day & sunlight to help surface gainstrength to allow saw cutting- Increase and monitor concrete placement temperature; warmer isbetter- Cover the slab with plastic sheeting

THANK YOU!Michael E. AyersGlobal Pavement Consultants, Inc.Representing the National ConcretePavement Technology Centermayers@globalpavements.com217-621-3438