Concrete Pavement Rehabilitation

Concrete Pavement Rehabilitation Rehabilitating Concrete Pavements using CPR 3 Restoration Resurfacing Reconstruction By Tim Smith Director Transportation & Public Works Cement Association of Canada, April 10, 2001 Overview Rehabilitation Strategies Distress Classification Rehabilitation Selection Restoration Techniques Resurfacing Activities Reconstruction Activities 1

Concrete Pavement Rehabilitation Improves structural and/or functional condition of pavement Structural condition - the ability to carry traffic Functional condition - the ability to serve the user comfortably Concrete Pavement Rehabilitation Two things are required for rehabilitation to be cost effective & have desired performance: A feasible alternative Address the causes of existing deterioration Provide a reasonable improvement over existing pavement Applied at the appropriate time 2

Rehabilitation Strategies Three categories: Restoration Resurfacing Reconstruction Together, known as CPR 3 Which is used depends on existing condition Restoration (CPR) Used early when pavement has little deterioration Repairs isolated areas of distress Pavement Condition Restoration Min Acceptable Rating Age or Traffic 3

Resurfacing Used when pavement has medium to high levels of distress and restoration is no longer effective PCC over PCC Bonded Unbonded PCC over AC Whitetopping Ultra-thin Whitetopping Pavement Condition Resurfacing Min Acceptable Rating Age or Traffic Reconstruction Used when the pavement has high levels of distress Used after overlays are no longer effective or when standards have changed Pavement Condition Reconstruction Min Acceptable Rating Age or Traffic 4

Rehabilitation Timing Restoration Resurfacing Structural/Functional Condition Min Acceptable Rating Reconstruction Age or Traffic Rehabilitation Strategy Selection Determining correct strategy is complicated Determine the cause of distress Structural, Functional, Material, Drainage Look at more than one alternate Ride Quality, Traffic, Maintenance Requirements, Lane-Condition Uniformity, Future Performance, Cost Consider fast-track 5

Collect & Evaluate Information Project Information: Design Details Construction Traffic Environmental Distress/Condition Rehabilitation Strategy Selection Use a systematic approach to select the appropriate strategy Collect & Evaluate Project Information Define/Select Feasible Alternatives Restore, Resurface, Reconstruct Preliminary Design Alternatives Pavement costsnon-pavement costs Select Preferred Alternative 6

Distress Classification Distresses are either structural or functional Structural distresses affect the pavement s ability to carry traffic Cracking, spalling, durability Functional distresses affect the quality and safety of the pavement Roughness, noise, and surface polishing Distress Identification and Determination Site-condition survey Identify pavement distresses Type, severity, and quantity of each distress Determine why distress developed Design, load, water, temperature, materials, or construction Perform a once a year 7

Distress Identification and Determination Types of visual site-condition surveys Windshield Manual Automated Distress Identification and Determination Destructive and nondestructive testing Determines the structural condition and material properties below pavement surface Concrete Coring Falling Weight Deflectometer (FWD) Benkelman Beam 8

Distress Identification and Determination Two goals of the condition survey and destructive / non-destructive testing Determine the root cause of the distress Track the rate of deterioration Knowing the root cause and rate of pavement deterioration helps determine which rehabilitation techniques are appropriate Pavement Distress Types Transverse Cracking Loading Long joint spacing Shallow / late joint sawing Curling / warping Loss of support Settlement / heave Base / edge restraint 9

Pavement Distress Types Corner Cracking Loss of support Pumping of fines Long joint spacing Curling / warping Settlement / heave Pavement Distress Types Longitudinal Cracking Near Centerline Shallow / late joint sawing Long joint spacing Near Edge Loading Loss of support Settlement / heave 10

Pavement Distress Types Intersecting Cracks Loss of support Pavement Distress Types Joint / Crack Deterioration Incompressible in Joint / Crack Material Durability Problem Metal / plastic joint inserts Extreme cases can cause Blow-ups 11

Pavement Distress Types D-cracking D-shaped, hairline cracks near joints and cracks Poor quality aggregate Water in pavement Freezing temperatures Pavement Distress Types Alkali-Silica Reaction (ASR) Map-cracking pattern with cracks oriented parallel to slab-free edges A chemical reaction between alkalis in the concrete and certain siliceous aggregates Forms an alkali-silica gel that absorbs water, expands and cracks concrete 12

Pavement Distress Types Faulting The difference in elevation between slabs Poor Load Transfer Loss of Support Pumping of fines Distress Classification Concrete Pavement Distress Cracking Transverse Corner Longitudinal Intersecting crack Extends through the depth of a slab 13

Distress Classification Concrete Pavement Distress Joint / Crack Deterioration Spalling Breaking Cracking, or Chipping At slab edges within 50 mm of joints and cracks Distress Classification Concrete Pavement Distress Durability Distress Concrete material problems D-cracking Alkali-silica reactivity (ASR) Freeze-thaw damage Poor quality aggregate Poor air-void system Water in pavement 14

Determining Causes Freeze-thaw Damage Occurs in concrete with poor entrained-air system Entrained air - system of microscopic air bubbles that protects the concrete as it freezes Improper volume and spacing of air bubbles causes concrete matrix to deteriorates when it freezes Normal concretes should have 45% to 75% entrained air Load Transfer Load-transfer is a slab s ability to transfer part of its load to its neighboring slab Poor load transfer leads to: Corner Cracking Pumping of Fines Faulting L= x U= 0 Load Transfer = 0% (Poor) L= x U= x Load Transfer = 100% (Good) 15

Distress Classification Concrete Pavement Distress Surface polishing The wearing away of the surface texture to expose the concrete coarse aggregate Noise Typically described as a high-pitched whine Caused by the surface/tire interaction when the vehicle speed exceeds 55 km/h Surface defects Scaling, popouts, crazing, & plastic shrinkage cracking Do not affect the pavement structurally Select Feasible Alternatives Each strategy provides a different level of improvement Outside factors may make one strategy more appealing Pavement Condition Min Acceptable Rating Reconstruction Resurfacing Restoration Age or Traffic 16

Windows of Opportunities Defines when CPR techniques are feasible & appropriate Feasible - can correct a given distress Appropriate - applied at a time when effective Uses trigger & limit values Trigger values define when a technique starts being feasible and appropriate Limit values define when a technique is stops being feasible or appropriate In between, a technique is both feasible & appropriate Windows of Opportunities Structural Trigger and Limit Values for JPCP Traffic Volumes Low - High Severity Fatigue Cracking (% slabs) High ADT>10,000 Trigger / Limit Values Medium 3000<ADT<10,000 Low ADT<3000 15 / 50 20 / 100 25 / 150 Deteriorated Joints (% joints) 15 / 150 20 / 175 25 / 200 Corner Breaks (% joints) 10 / 80 15 / 100 20 / 120 Faulting (avg - mm) 20 / 120 20 / 150 20 / 180 D-Cracking (severity) Medium-High Joint Seal Damage (% joints) > 25 / --- Load Transfer (%) <50 / --- Skid Resistance Minimum Local Acceptable Level / --- 17

Windows of Opportunities Functional Trigger and Limit Values for JPCP Traffic Volumes High ADT>10,000 Trigger / Limit Values Medium 3000<ADT<10,000 Low ADT< 3000 IRI (m/km) 10 / 25 12 / 30 14 / 35 PSR 38 / 30 36 / 25 34 / 20 California Profilograph 12 / 60 15 / 80 18 / 100 Windows of Opportunities Structural Trigger and Limit Values for JPCP Traffic Volumes High ADT>10,000 Trigger / Limit Values Medium 3000<ADT<10,000 Low ADT<3000 Low - High Severity Fatigue Cracking (% slabs) 15 / 50 20 / 100 25 / 150 Deteriorated Joints (% joints) 15 / 150 20 / 175 25 / 200 Corner Breaks (% joints) 10 / 80 15 / 100 20 / 120 Faulting (avg - mm) 20 / 120 20 / 150 20 / 180 D-Cracking (severity) Medium-High Joint Seal Damage (% joints) > 25 / --- Load Transfer (%) <50 / --- Skid Resistance Minimum Local Acceptable Level / --- 18

Windows of Opportunities Functional Trigger and Limit Values for JPCP Traffic Volumes High ADT>10,000 Trigger / Limit Values Medium 3000<ADT<10,000 Low ADT< 3000 IRI (m/km) 10 / 25 12 / 30 14 / 35 PSR 38 / 30 36 / 25 34 / 20 California Profilograph 12 / 60 15 / 80 18 / 100 Rehabilitation Selection Choosing a Strategy: Life-cycle cost analysis Pavement elements Non-pavement elements Non-monetary factors 19

Rehabilitation Selection Pavement elements: Surface materials Base materials Drainage Paving operations Anticipated maintenance Future rehabilitation Rehabilitation Selection Non-pavement elements: Right-of-way High-accident locations Lighting requirements User-delay costs Overhead structures At-grade structures Interchanges Intersections Culvert extensions Sign adjustments Environmental concerns Noise barriers Geometrics Traffic control Median & fill slopes Utilities Median barriers Guard rail 20

Rehabilitation Selection Non-monetary factors: Experience Time constraints Availability of materials Availability of contractors Impact to local business Network programming Restoration Techniques Concrete Pavements Full-depth repair Partial-depth repair Diamond grinding Joint & crack resealing Slab stabilization Retrofitting dowels Retrofitting concrete shoulders Cross-stitching long cracks/joints 21

Full Depth Repairs Repairs distresses greater than 1/3 the slab depth Consists of removing and replacing at least a portion of the existing slab to the bottom of the concrete Completed Patch Patch under Construction Full Depth Repairs Joint Deterioration Spalling (also below surface) Cracking 22

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Standard technology for mix design Important to understand it is also sequencing methodology Fast Track Partial Depth Repairs Repairs deterioration in the top 1/3 of the slab Generally located at joints, but can be placed anywhere surface defects occur 24

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Carbide-Milling Longitudinal Milling Transverse or Longitudinal Joint/Crack Near vertical edges Transverse Milling (Half-moon) Transverse or Longitudinal Joint/Crack Carbide-Milling Transverse Milling (Half-moon) 1984 1998 27

Improves ride by removing: Faulting at joints Slab warping Surface deformations caused by studded tires Reestablishes skid resistance Corrects cross-slope Diamond Grinding 28

Joint and Crack Resealing Minimizes water & incompressibles into pavement system Reduces: Subgrade softening Pumping Erosion of fines Spalling Sealant Nozzle Reservoir Backer Rod 29

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Dowel Bar Retrofitting Load Transfer Restoration Reestablishes loadtransfer at undoweled joints or cracks Used to limit future faulting L= x Poor Load Transfer U= 0 L= x Good Load Transfer U= x 31

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Slab Stabilization Fills voids (3 mm or less) underneath the pavement Reestablishes uniform support Reduces stresses and deflections Grout Fill Void - not Raise Slab 33

Longitudinal Crack Repair Retrofit Concrete Shoulders Longitudinal Crack Repair Adds reinforcement to non-working cracks by inserting tie bars Retrofit Concrete Shoulders Adds a concrete shoulders to an existing pavement Reduces critical stresses and deflections Restoration Performance Provides 10 or more years of service Preliminary engineering & timing are critical Overall effectiveness is highly dependent on design adequacy, construction quality, and other restoration activities 34

Resurfacing Activities Concrete overlays for concrete pavements: Bonded Concrete Overlays Unbonded Concrete Overlays Concrete overlays for asphalt pavements: Conventional Whitetopping Ultra-Thin Whitetopping Bonded Overlays Consists of a thin concrete layer (100 mm or less) on top of an existing concrete surface Specific steps are taken to bond the new concrete overlay to the existing concrete 35

Bonded Overlays Bonded Overlays Surface Preparation Cleanliness is key to long-term performance Surface preparation procedures: Shotblasting Milling 36

Bonded Overlays Shotblasting Bonded Overlays Surface Cleaning 37

Performance Good when: Bonded Overlays Placed correctly and at the right time Poor when: Placed on deteriorated pavements Loss of bond does not necessarily constitute failure Unbonded Overlay Consists of thick concrete layer (125 mm or greater) on top of an existing concrete Uses a separation interlayer to separate new overlay and existing concrete 38

Unbonded Overlays Separation Interlayer: Allows layers to act independently Prevents distresses from reflecting into overlay Materials that work: Asphalt concrete Some surface treatments Materials that do not: Polyethylene Roofing paper Curing compound Unbonded Overlays Separation Interlayer: Key Overlay Old Pavement Smooth Slip Plane Overlay Old Pavement Thick Interlayer (> 50 mm) 39

Unbonded Overlays Whitewash Prevent heat build-up by reflecting heat/energy Temperature reduction as much as 11ºC (20ºF) Typically lime slurry or curing compound Heat/Energy is Absorbed into Black Leveling Surface Heat/Energy is Reflected by Whitewashed Surface -20 F 40

Performance Unbonded Overlays Very Good Can be expected to perform for 20+ years Most failures are due to the use of inadequate separation layers Conventional Whitetopping Consists of thick concrete layer (100 mm or greater) on top of an existing asphalt pavement Behaves as a new pavement on a strong base 41

Whitetopping - Advantages Construction Can place on pavement in bad condition Little or no pre-overlay repair needed Avoid reconstruction problems Minimal rain delays Maintain traffic on existing surface Structural Whitetopping - Advantages Improved structural capacity Maintains high level of serviceability Reacts structurally as if on strong base course Concrete slabs bridge problems asphalt cannot Reduced potential for pumping, faulting and loss of support 42

Whitetopping Construction Pre-overlay Preparation Distress Repair Performed Other Factors Rutting (< 50 mm) Rutting (> 50 mm) Shoving Raveling Trans Cracking Block Cracking Alligator Cracking Long Cracking Bleeding None Milling or Leveling Milling? None None None None None None Joint Sawing Depth Cost Comparison Drainage Sweep Surface Bond Breaker? Whitetopping Overlays Performance Most projects are too new to provide data 20 Years or less Those that are old enough are providing excellent performance Oldest in-service project built 1956 (Columbus AFB, Miss) 43

Recent Whitetopping Projects Intersection at Windsor, Ontario Weigh scales at Truro, NS Intersection at Toronto, Ontario ( bonded concrete overlay) Ultra-Thin Whitetopping Consists of thin concrete layer (50-100 mm) on top of an existing asphalt pavement Specific steps are taken to bond the new concrete to the existing asphalt and to saw short joint spacing 44

Ultrathin Whitetopping Design Considerations of UTW Bond is critical - milled surface is best Slab size (Jointing) is important Underlying asphalt thickness is important (min 75mm required) Attention to concrete mix design is important for high early strength, and early opening for traffic Placement considerations 45

Bonding Effects Bonding Effects on Edge Stress Concrete NA Concrete NA Comp Comp Tension Asphalt Tension Asphalt Unbonded 849 MPa Bonded 290 MPa 75 mm Concrete, 100 mm AC, K=81 Mpa/m, Ec = 27,580 Mpa, Eac = 2,758 MPa 46

Effects of AC Thickness Concrete Tension NA Asphalt 50 mm 100 mm Concrete Tension NA Asphalt Concrete Stress AC Strain Deflection 50 mm AC 100 mm AC 573 MPa 60 x 10-4 2743 mm 368 MPa 51 x 10-4 2082 mm Corner Stress:75 mm Concrete, K=81 MPa/m, Ec = 27,580 MPa, Eac = 2,758 MPa Ultra-Thin Whitetopping 06m 06m 06m 18m Short joint spacing allows the slabs to deflect instead of bend This reduces slab stresses to reasonable values 47

Thickened edge for Ultra-thin Whitetopping Saw cut face AC SURFACE T AC BASE T+75 mm L L = Standard length between joints L Construction Steps UTW Core existing surface for asphalt depth Mill and clean the surface Place, finish, and cure Early saw Open to traffic 48

UTW Projects Intersections / Roadway Mississauga Brampton Hamilton Bus stop Vancouver Ottawa Roller Compacted Concrete Zero-slump concrete mixture that is placed and roller compacted with the same equipment used for asphalt pavement construction Durable Low cost 49

Portland cement Materials for RCC Supplementary cementing materials Fine and coarse aggregate water admixtures Typical Construction Equipment Continuous flow pugmill mixer or central mix plant Dump trucks Asphalt paver or ABG paver Rollers (vibratory and pneumatic tire) Water truck 50

RCC Highway and Street Projects Intersections Edmonton and Calgary, Alberta Climbing lane Fort McMurray, Alberta Subdivision street in Edmonton, Alberta Downhill lane Horsefly Road, B C City street Montreal, Quebec Reconstruction Activities Final stage of rehabilitation Involves removing and replacing existing pavement with a new pavement Complete removal & replacement Partial removal & replacement (Inlay) Can correct: Subgrade / subbase deficiencies, Roadway geometrics, Roadside safety features, Drainage 51

Reconstruction Activities Controls the final elevation Minimizes roadside appurtenances adjustments Can recycle the old pavement Recycling Techniques Concrete Pavements Coarse aggregate Base course aggregate Shoulders Median Barriers Non-pavement applications 52

Summary CPR 3 repairs structural / functional deficiencies Improves pavement condition to an acceptable level Appropriate activity depends on the existing pavement condition As condition declines, the optimum activity changes Applying correct activity at correct time is essential Summary Restoration Repairs isolated areas of deterioration Resurfacing Repairs a pavement with medium to high severity levels of distress Reconstruction Used at the end of the pavement s life, when it has very high severity levels of distress 53

Why Use Concrete Pavements Economical Environmental Improved Road Characteristics User Cost Economical Lower maintenance cost Increased life of the network Lowest life cycle cost Reduced truck fuel costs Economic spin-off 54

Environmental Improved truck fuel efficiency Greenhouse gas reduction Smog reduction Uses less aggregate than asphalt structure Recyclable Energy savings due to reduced lighting requirements Use of Supplementary Cementing Materials in concrete (fly ash, silica fume, blast furnace slag) Improved Road Characteristics Does not rut or washboard Non rutting surface reduces potential for hydroplaning Good skid resistance Decreased stopping distance Minimal pothole damage Eliminates Spring Weight Restrictions 55

User Cost Minimized construction delays Fuel savings Accidents Discomfort THANK YOU QUESTIONS 56