Roadway Paving Operations Robert Rodden, P.E. www.robertrodden.com

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In Case You Arrived Late…. ALL OF TODAY’S PRESENTATIONS • Can be downloaded at any time at:

http://bit.ly/1PO7ixS

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Available in ACPA’s online bookstore: http://www.acpa.org/publications-for-purchase/

EB238

Primary Reference For This Presentation

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Producing Concrete Roadway Paving Operations

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The Loader Operator is KEY! • Manages stockpile � Prevents dirty or contaminated aggregates � Maintains uniform moisture content of aggregates – if

major variations exist, they MUST notify batch plant operator

�  Feeds hoppers � Checks supply

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FREE Aggregate Handling Training! •  Available  around  the  clock,  365  days  per  year.  

•  No  cost  to  par;cipants.  

•  Cer;ficates  of  comple;on  may  count  toward  a  total  of  11.0  professional  development  hours  (PDHs).    

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Mixing Concrete • A consistent concrete mixture is the primary objective

• Two primary mixing methods: � Central mixed (e.g.,

portable batch plant) � Truck mixed (e.g., ready-

mixed)

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Mixing Concrete • Mixing method impacts order of operations

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Truck Mixed

Hauling/Delivery • Uniform delivery rate is a key to smooth paving.

• This is not good:

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Methods of Transport

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End-Dump Truck

Side-Dump Truck

Agitating Truck

Ready-Mix Truck

Methods of Transport – Dump and Agitors • Generally have 30 mins to deliver and place concrete

• Agitator paddle in agitor can extend to 90 mins, as can the use of retarding admixtures

• Delivery time limit also depends on ambient temp

• HAVE ENOUGH TRUCKS to deliver concrete to match paving rate… see ACPA’s Rate of Delivery Calculator at apps.acpa.org

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Methods of Transport – Ready-Mix Trucks • Both for mixing and delivery

• Most commonly used for streets and roads

• Generally have 90 mins to deliver concrete

• Min 70 revolutions and max of 300 typical

•  Slump meter estimates slump within ½ in. (13 mm); for QC only!

• Contractor receives batch ticket upon delivery

• One addition of water may be permitted – requires 30 additional revolutions

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Placing Concrete Roadway Paving Operations

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Wetting the Grade • Application of water mitigates drying shrinkage from dry subgrade/subbase support; whitewash asphalt if hot

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Access •  If adequate space, deliver concrete from a haul road adjacent to paving operation

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Access • Example of truss to stringline over haul road

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Access •  If necessary, deliver in front of paver but ensure that subbase is capable of carrying delivery traffic

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Access • Must also work around pre-placed dowels

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Inappropriate Placement

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Fixed Form Paving Roadway Paving Operations

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Fixed Form Paving Machines •  Less complex equipment (e.g., vibratory screed and single

type finisher) good for complex areas

•  External (surface) vibration good to about 8 in. (200 mm)

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Fixed Form Paving Machines • Larger equipment (e.g., bridge deck finishers) can place and consolidate in one pass

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Fixed Form Paving Limitations • Fixed form paving can be used on widths upwards of 50 ft (15 m) but the owner and contractor must recognize limitations of fixed form paving machines

•  If placement is large enough, contractor might opt to use slipform; slipform also typically produces desirable consolidation and ride quality more efficiently than fixed form methods

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Fixed Form Paving – Spreading Mixture • Evenly deposit concrete on grade; pile too high and it is difficult to strike off

• Shovels are preferred hand moving tool; keep to min

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Fixed Form Paving – Consolidation • When necessary, supplemental spud vibration should precede placement screed; vertical plunge of spud roughly every 1 ft (0.3 m)… do not drag spud… mind the edges

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Dowel Bars and Tiebars

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Header Joints

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Fixed Form Paving – Thickness Verification • No brainer – forms set thickness

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Fixed Form Paving – Finishing • Can use roller screed, clary screed, laser screed, bridge deck finisher, etc.

• Depending on desired surface texture, subsequent finishing may or may not be necessary

•  If necessary, final finishing same as slipform paving, with a straightedge

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Fixed Form Paving – Form Removal • After texture, cure, etc., must remove forms from fixed form paving – remove before sawcutting if possible

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Slipform Paving Roadway Paving Operations

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Slipform Paving – Placer/Spreader Ahead of Slipform

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Can Otherwise Use Conveyor

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Slipform Paver Equipment Setup

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Slipform Paving – Auger • Large horizontal screw that spreads concrete sideways

• Keep concrete head not too big and not too small

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Slipform Paving – Plow • Sometimes a plow is used instead of an auger

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Slipform Paver Equipment Setup

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Slipform Paving – Sideform

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Slipform Paving – Vibrators • Consolidate and fluidize concrete inside form

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Slipform Paving – Vibrators • Equipment available to auto monitor frequency to prevent over/under vibration

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VIBRATOR TRAILS

from too much

vibrational energy

Slipform Paver Equipment Setup

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Slipform Paving – Dowel Bar Insertion (DBI)

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Slipform Paving – Dowel Bar Insertion (DBI)

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Slipform Paving – Dowel Bar Insertion (DBI) • Direct access in front of paver

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Slipform Paving – Slipform Mold or Pan • Applies confining pressure to fluidized concrete

• Pan builds cross slope and crown… note edge slump

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Slipform Paving – Tiebar Insertion

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We will see the “rocket launcher” in an upcoming video!

A Two-Lift Paving Train

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Avoid Stopping the Machine!!! • Delays in material supply, equipment breakdowns, or any other stoppage will increase pavement roughness

• We can now measure “real time” smoothness

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Slipform Paving – Thickness Verification • During construction: probe thickness; depending on subbase type, might require pre-placement of metal plates

• Post construction: coring or non-destructive testing (NDT) method

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Slipform Paving – Finishing •  Ideally, no finishing is necessary after slipforming

•  If necessary, use straightedge to close/smooth surface

• Overfinishing or adding water to surface during finishing leads to a weak surface and potential scaling; fogging of surface is acceptable to aid finishing

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Slipform Paving – Finishing

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Safety Edge

Texturing Methods Roadway Paving Operations

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Burlap Drag

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Broom Drag

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Astroturf Drag

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Transverse Tining

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Longitudinal Tining

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Exposed Aggregate

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Diamond Grooving

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Diamond Grinding

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Videos of US Practice Roadway Paving Operations

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Curing Roadway Paving Operations

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Definition of Curing • Maintenance of a satisfactory moisture content and temperature in concrete during some definite period immediately following placing and finishing so that the desired properties may develop.

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+

Curing Objectives • Prevent (or replenish) the loss of moisture…

• Maintain a favorable temperature…

…for a predefined period of time.

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Curing Methods and Materials •  Initial Cure � Evaporation Retarder � Misting or Fogging

• Final Cure � Wet Coverings �  Impervious Paper � Plastic Sheets �  Steam or Electrical Heating � Membrane-Forming Compounds �  Insulating Blankets �  Linseed oil cure/seals

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Common Common

Curing Compound: GOOD Practice

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Curing Compound: MARGINAL Practice

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Curing Compound: POOR Practice

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Blanket Insulation • Place after spraying curing compound

• Further reduces loss of hydration heat

• Lessen effects of: � Air temperature � Solar radiation

• Thermal Resistance (R) � 0.035 m2 oK/W � 0.5 hr ft2 oF/Btu

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When to Use Blankets

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Opening Time, Hr

8

Ambient Air Temperature

<10oC (<50oF)

10-18oC (50-65oF)

18-27oC (65-80oF)

>27oC (>80oF)

Yes

Yes

Yes

No

16 24 36 48

Yes

Yes

No

No

Yes

Yes

No

No

Yes

No

No

No

No

No

No

No

Blanket Curing GOOD Practice POOR Practice

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Jointing Roadway Paving Operations

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Dowel Location Identification

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Saw Cutting or Forming Joints

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Saw Blades • Most common are industrial diamond (require water cooling) or abrasive (carborundum)

• Must match the saw blade to the concrete; based primarily on aggregate hardness but also depends on power output of saw

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Order of Saw Cuts • Common practice to first cut transverse joints to alleviate internal stresses

• However, best practice to keep all sawing as close to the paving operation as possible

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Successful Crack Control + Location

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Check the Depth! • Too shallow = may not relieve stresses adequately; random cracking

• Too deep = additional effort and expense, unnecessary equipment wear, and reduce aggregate interlock

• As blade diameter decreases, the saw operator must adjust saw to ensure proper depth

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TRANSVERSE

LONGITUDINAL

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What about a concrete overlay on unmilled asphalt?

No Speeding! • Sawing speed controls cut depth; hard aggregate might require a slower speed

• Speed typically controlled by saw’s self-propelling mechanism

• Saw operators that attempt to speed up cutting may tend to push a saw too fast, causing the blade to ride up out of its full cut… not cutting to proper depth = risk for cracking!

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Starting and Stopping a Cut • Cut start and stop requires special attention

• Early-entry saws may require the saw cut stop about ½ in. (13 mm) short of the pavement edge to prevent “blow out”

•  In windy conditions, best to orient direction of sawing with wind; the slab face exposed to the wind will dry quicker

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Down-Cut Saw

Up-Cut Saw

Make Certain the Joint is Clean! • All sealed joints must be cleaned immediately behind saw cutting or joint widening and immediately prior to sealing operations � Removes saw-cut slurry, soil, sand, etc.

• Cleanliness of both joint faces is extremely important to concrete/sealant bond

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It’s not Hard to Check… •  If wiping a finger along the face picks up dirt or dust, recleaning should be done before sealing!

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… and is not Expensive to Fix!

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Backer Rod (if used) • Minimizes excess stress on sealant material from improper shape factor

• Provides support for the tooling of the surface

• Prevents self-leveling mat’l from filling entire joint

• Prevents three-sided adhesion

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Sealing the Joint • Only apply when temps are above min recommended by manufacturer

•  Ensure joint faces clean and dry before sealing

•  Fill joint from the bottom up to prevent air from becoming trapped under the sealant

•  Fill from beginning to end in one smooth operation

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Transverse Construction Joints (Headers) • Built at the end of a section of pavement � Must be constructed at the end of a day’s run � Constructed due to significant paving delays

• Either formed or sawed

• No way to account for in layout planning

•  If next to previously placed pavement, best to match header with existing transverse joint

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Formed Header • Either two-part form with dowels or tiebars protruding through form or false-dowels attached to form face and dowels inserted upon form removal; consolidate concrete well at form

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Formed Header

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Sawed Header • Paving continued through of header, pavement sawed back, dowel/tiebar holes drilled, and dowels/tiebars installed

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Opening to Traffic Requirements Roadway Paving Operations

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Strength Requirements • Required flexural strength for construction equipment:

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Strength Requirements • Required flexural strength for public traffic:

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Determining Strength • Flexural versus compressive �  Flex is a sensitive test, especially at early ages �  In most cases, comp is correlated to flex for mixture

• Strength assessment methods � Opening strength cylinders

�  Field-cured

� Maturity method �  Estimate in-place strength via TTF

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Concrete Mixture Considerations •  If opening strength cannot be met with conventional mixture, can use high-early strength mixture �  Type III or HE high-early-strength cement � High cement content (675 - 850 lb/yd3 [400 - 500 kg/m3]) �  Lower w/cm to as low as 0.37 � Use higher concrete mixing temp with heated water or

agg � Use accelerating admixtures � Use insulating curing practices � Etc….

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Paving in Inclement Weather Roadway Paving Operations

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Cold Weather Paving • Potential problems:

� Cement hydration slows, slowing strength development

�  Surface cools faster, causing differential stresses

• Mitigation: � Don’t pave on frozen subgrade � Don’t use frozen aggregate lumps �  Use higher cement content �  Use accelerating admixture �  Use blanket curing to contain heat of

hydration �  Heat materials to raise temp of mixture

(see Concrete Temp app)

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Hot Weather Paving • Potential problems: � Moisture loss during hauling and placing � Aggregate stockpiles dry out, affecting batch consistency �  Subbase dries out and absorbs moisture from slab � Dark subbase heats bottom, causing differential stresses � Rapid evaporation = plastic shrinkage cracks � Difficult to entrain air at higher temps � Concrete sets more quickly, making finishing difficult �  Sawing operations must proceed more rapidly

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Hot Weather Paving • Mitigation: � Begin curing ASAP � Don’t pave on hot day, if possible � Maintain uniform stockpiles � Use retarding admixtures � Use SCMs to lower cement content � Whiteswash dark colored subbases � Pave in morning, evening or night when cooler �  Increase dosage of air-entraining admixture � Keep subbase, forms, equipment cool and damp � Use temporary sunshades and/or windbreakers…

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Rained on Pavements •  Irony: rainy cold front is conducive to concrete curing

•  If rain occurs before final set, can leave imprints on surface or wash away paste at surface

•  If rain occurs after final set, can lead to rapid cooling of the surface and differential stresses

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Rained on Pavements • Mitigation: �  For slipform operations,

advantageous to install forms where severe erosion of edges occurs

�  If it starts to rain during placing, cover the fresh concrete with plastic or burlap – as soon as the surface sets, texture and apply curing

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Rained on Pavements • Protect surface with plastic sheeting if possible

• Expect some marring of the surface from the sheet

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Rained on Pavements • Finish rain into the surface = higher w/cm at surface = a non-durable layer = crazing, scaling, dusting

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Rained on Pavements • Petrographic examination is usually not necessary but can be useful in determining the extend of damage

• Repair: �  If surface is damaged or rain is finished into surface to

increase w/cm, recommended repair is diamond grinding �  If pavement edges are compromised, make cut a

minimum of 2 ft (0.6 m) from pavement edge, remove, and replace w/tiebars

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Night Paving • Might consider to mitigate hot weather; minimize traffic; maximize production rates; etc.

• Observe precautions such as safety meetings; traffic control; ample lighting; subscription to weather service; maint. of haul roads during day; sawcut timing

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FREE Smooth Construction Training! •  Available  around  the  clock,  365  days  per  year.  

•  No  cost  to  par;cipants.  

•  Cer;ficates  of  comple;on  may  count  toward  a  total  of  11.0  professional  development  hours  (PDHs).    

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Troubleshooting

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Concrete Overlays Roadway Paving Operations

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What is a Concrete Overlay? • Part of the resurfacing family and are defined as a new or fresh surface on a existing pavement

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Urban arterial Rural primary/interstate

Urban freeway/interstate Intersections Rural secondary roads

THE Overlay Guide � Overlay types and uses � Evaluation & selection � Design guidance � Miscellaneous design details � Overlay materials selection � Work zones under traffic � Key points for overlay construction � Accelerated construction �  Specification considerations � Repairs of overlays

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Types of Concrete Overlays

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BONDED -versus-

UNBONDED

Increasing Common in the US!

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overlays.acpa.org

Bonded on Asphalt => No Longer Research-Grade… Full Implementation • KS I-70

• Approx 1.25 mil m2

• 15cmx1.8mx1.8m slabs

• 48km 4-lane w/shoulders

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KS I-70 in 2011 – Bonded on Asphalt

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Wright County, Iowa � 6  bidders  

› 5  concrete  (5”  [125mm])  › 2  asphalt  (4”  [100mm]  on  3”  CIP  [75mm])  

� Concrete  13%  below  the  low  asphalt  bid  � Cost  

› $189,874  per  mile  

� Prepara;on  › No  milling  › Plans  assumed  10%  overrun  › Actual  overrun  was  11%  

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Concrete Pavement Preservation (Rehabilitation) Roadway Paving Operations

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Steps Towards Proper Preservation

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Partial-Depth Repair • Purpose: � Repair surface distresses � Reestablish joint reservoir

• Used for: � Midslab surface spalling �  Joint spalling �  Severe scaling

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Remove and Replace Deteriorated Surface Concrete

Partial-Depth Repair

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Full-Depth Repair • Purpose � Restore structure � Restore ride

• Used for �  Joint/crack deterioration

�  Spalling (also below surface) �  Cracking

� Broken slabs � Corner breaks

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Remove and Replace Concrete

Full-Depth Repair

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Full-Depth Repair

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Dowel Bar Retrofit • Purpose � Reestablish load transfer �  Limit future faulting

• Used for: �  Faulted trans. joints �  Faulted trans. cracks

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Dowel Bar Retrofit

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Cross-Stitching • Purpose � Reestablish load transfer �  Limit future faulting

• Used for: � Mitigating tiebar omission �  Tying faulting long. joints �  Tying shoulders that are causing maintenance problems

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Cross-Stitching

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Diamond Grinding • Purpose �  Smooth the surface � Reestablish skid resistance � Correct cross-slope

• Used for: �  Faulted joints � Wheel track wear � Drainage slope improvements � Polished pavement

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Diamond Grinding

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Joint and Crack Resealing • Purpose � Protect rehabilitated pavement � Prevent infiltration of water and incompressibles

•  Used for: � Replace ineffective sealant � Minimize moisture infiltration � Minimize incompressible infiltration

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Joint and Crack Resealing

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Questions? Robert Rodden, P.E. www.robertrodden.com

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