SEMINARIO INTERNACIONAL CONSTRUCCIÓN Y REHABILITACIÓN CON PAVIMENTOS DE HORMIGÓN

SANTIAGO  25  DE  MAYO  DE  2015  

Pre-Paving Considerations Robert Rodden, P.E. www.robertrodden.com

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Lafarge Research Center (LCR) www.lafarge.com @LafargeGroup

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

Infrastructure Solutions – Roads

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International Society for Concrete Pavements (ISCP) www.concretepavements.org @ConcPaveSociety

Executive Director 

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ISCP’s Mission

“The mission of ISCP is to facilitate the

advancement of knowledge and

technology related to concrete pavements

through education, technology transfer and

research at an international level.”

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ISCP is Online @ www.concretepavements.org

ALL OF TODAY’S PRESENTATIONS • Can be downloaded at any time at:

http://bit.ly/1PO7ixS

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Countries with the Largest Paved Roadway Networks

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7 Source: USA CIA’s World Factbook

Kil

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of P

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Roa

dway

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

EB237

Primary Reference For This Presentation

Joint Layout Pre-Paving Considerations

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Why Joint Concrete Pavement? • Historical Reason: control natural cracking

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40-80 ft

(12-24 m)

15-20 ft

(4.5-6 m)

Sawcut

@ 15 ft (4.5 m)

or less

Why Joint Concrete Pavement? • Other reasons we joint concrete pavements:

Divide pavement into construction lanes or increments. Accommodate slab movements. Provide load transfer via placed dowels. Provide uniform sealant reservoir. To leverage joint spacing in design!

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Why Joint Concrete Pavement? • Not for lane delineation!

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Types of Concrete Pavement Steel Reinforcing, Joint Spacing, and Crack Spacing Differentiate Between the JPCP, JRCP, and CRCP

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Jointed Plain

Concrete Pavement

(JPCP)

Steel 0%

Joints 12-20 ft

(3.6-6 m)

Cracks N/A

Jointed Reinforced Concrete Pavement

(JRCP)

Steel 0.06-0.25%

Joints

40-100 ft (12-30 m)

Cracks 15-20 ft

(4.5-6 m)

Continuously Reinforced Concrete Pavement

(CRCP)

Steel 0.6-0.85%

Joints N/A

Cracks 2-6 ft

(0.6-1.8 m)

Joint Layout • Critical to crack control

• Typically decided by engineer and included in project plans � No knowledge of contractor, equipment, processes � Hard to precisely place things like utilities

• Contractor may be allowed to develop plans but, even if not, field adjustments can and should be made

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The ACPA 10 Step Method of Joint Layout for Intersections

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Field Adjustments are Necessary • Adjust joints that are within 5 ft (1.5 m) of a utility!

• Must isolate utilities as shown on plans

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Contractor must also

consider impact of

moving joints!!!

Joint Layout Design…

References:

•  EB237 – Concrete Pavement Field Reference: Pre-Paving

•  IS006, Intersection Joint Layout

•  IS061 – Design and Construction of Joints for Concrete Streets

•  R&T Update 6.03 – Concrete Roundabouts

•  TB010 – Design and Construction of Joints for Concrete Highways

•  TB017 – Airfield Joints, Jointing Arrangements and Steel

•  TB019 – Concrete Intersections: A Guide for Design and Construction

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wikipave.org

is now live!

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Subgrade Construction Pre-Paving Considerations

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It Starts from the Ground Up • Roadbed (subgrade and subbase) design and construction are key to: �  Long-term performance �  Smoothness (initial and long-term)

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What is Good Support? • Roadbeds for a concrete pavement structure should: � Be free from abrupt changes in character of the materials

(should be uniform and constructed of a material that will provide requisite stability over the life of the pavement)

� Resist erosion � Be engineered to control subgrade soil expansion/frost

heave

• Above all other concerns, uniformity is of utmost importance

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Subgrades • Obtain uniform support by controlling: � Expansive soils �  Frost-susceptible soils (frost heave) � Pumping � Wet Soils

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Controlling Wet Soils • Enhancement

• Reinforcement/Separation

• Substitution

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Unstabilized Subgrades 1.  Grade to match roadway plans

2.  Cross haul to avoid abrupt changes

3.  Compact at optimum moisture content

4.  Identify soft spots and fix

5.  Protect from rain by “tight blading” and finishing with smooth drum roller

6.  Fine grade to plan elevations within tolerances

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Stabilized Subgrades 1.  Trim to match roadway plans but finish the

grade below the final grade elevation

2.  Spread stabilized agent as evenly as possible

3.  Mix, add water and compact

4.  Finish grade

5.  Cure the subgrade

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Step 3 for Cement-Treated Soils • Mix, add water, and compact (within 2 hours) in one continuous operation

• Moisture content within 2% of optimum

• Min of 60% passing #4 (4.75 mm) sieve

• Special attention to longitudinal overlap

• Strictly adhere to 2hr working period

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Step 3 for Lime-Stabilized Soils • Mix and add water simultaneously

• Moisture content of optimum to +5% of optimum

•  Lightly compact and grade to drain excess water

•  Let soil sit idle for 24 to 72 hours

• Re-mix, adding water as necessary to target moisture content of optimum +3%; recompact

• Min of 60% passing #4 (4.75 mm)

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Subbase Construction Pre-Paving Considerations

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General Notes on Subbases •  Thick subbases (greater than 6 in. [150 mm]) are

typically not beneficial, and therefore are not recommended

•  The width of the subbase should accommodate the paving equipment by extending approximately 3 ft (1 m) beyond the width of the pavement on each side

•  Recommended minimum thickness: �  Unstabilized: 4 in. (100 mm) �  CTB or LCB: 4 in. (100 mm) �  ATB: 2 in. (50 mm)

•  Recycled materials are commonly used

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Unstabilized Subbases 1.  Mix a uniformly moist, homogeneous material

2.  Place using preferred method

3.  Compact to required density w/min effort

4.  Trim to plan elevation and tolerances

5.  Moisture content key during construction of subbase AND immediately before paving

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Cement-Treated Subbases (CTB) 1.  Central-mix and place material or road-mix

2.  Compact with rollers and trim to specified grade

a)  Must place and trim within 4 hrs of mixing!

3.  Cure the subbase

4.  If trimmed after curing, curing compound must be reapplied

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Lean Concrete Subbases (LCB) 1.  Central-mix the concrete

2.  Place to plan elevation and tolerances a)  No additional finishing b)  No texturing

3.  Cure (if necessary)

4.  Joint (If necessary)

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Asphalt-Treated Subbases (ATB) 1.  Mixed and placed with conventional asphalt

paving equipment

2.  Dense-graded mixtures require compaction

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Pre-Paving Setup Pre-Paving Considerations

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Safety • Ride quality is pointless if someone is hurt

• Plan out truck routes

• Use of highway patrol

• Daily safety meetings

• Employees get bold

• Teach employees to watch traffic

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Safety • Pay attention to broom handles, saws and protrusions in traffic

• Watch for backing trucks and make sure alarms are functional

• Be aware of surroundings

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FREE Safety 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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37 www.acpa.org/self-paced-online-courses/

Stringline

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Steering Control

Elevation Control

Stringline

Stringline Considerations • Can be wire, cable, woven nylon, polyethylene rope, or similar material

• Continuously check tension

• Clean and tight splices

• Stakes must be long enough

• Maximum stake spacing of 25 ft (7.6 m) •  See Staking Interval Calculator at

apps.acpa.org for recommendations on curves

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Stringline Considerations (con’t) • Place winches at ≤ 1,000 ft (305 m)

• Beneficial to have stringlines on both sides of paving

• Some situations require cantilever or trusses for sensors to reach stringline

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Setting the Stringline 1.  Set reference hubs at proper interval and

place a stringline support stake outside of each hub

2.  Set stake arm to the proper elevation

3.  Install stringline

4.  Tighten stringline

5.  Check installation

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Stringline Setup

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Benchmark

Control Points (Paving Hubs–Pins)

25 ft (7.6) typ.

Survey Reference Point

Stringline Setup

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Stringline Setup

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Notes on Setting Reference Hubs • Reference hubs are set using a variety of methods

• Contractor determines offset

• Grade info on identifier next to where hubs will be set

• Proper communication is KEY to a successful operation!!

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Once Set, the Paver Does the Rest Uniform Slope in a Superelevation into and though a Horizontal Curve

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Once Set, the Paver Does the Rest Rooftop Slope in a Straight Section to Encourage Drainage to Each Edge of Pavement

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Once Set, the Paver Does the Rest Transition from Rooftop Slope to Uniform Slope into a Horizontal Curve

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Communication in Key!!

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Maintain the Stringline!!!!!!!!!!!!!!!!!!

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…or Go Stringless!

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Setting Forms

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…or Just Slipform!

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Placing Embedded Steel Pre-Placed in Baskets •  Requires support system

•  Requires placement ahead of paving or at the same time as paving is occurring

•  Increased transport cost

•  Increased labor in placement

Placed with Insertion •  No support system needed

•  Dowels or tiebars are inserted after concrete is placed

•  Lower transport cost

•  Decreased labor in placement

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… both methods can place dowel bars and tiebars within typical specifications, though the concrete mixture characteristics are more important with insertion.

Placing Dowels

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55 BA BA

Placing & Staking Dowel Baskets

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Dowel Location Identification

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Placing Tiebars

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Slipform Paver Equipment Setup

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Like extrusion processes but we pull the form.

Slipform Mold (Pan) Setup • Preliminary leveling of paving machine’s frame and then slipform mold

• Check joints in the pan

• Adjust center to account for cross slope

• Check alignment

• Adjust edges for edge slump

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Vibrator Setup

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Vibrator Setup

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Slipform Paver Setup

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Slipform Paver Setup

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Final Grade and Cross Slope Check

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Concrete Mixture Analysis and Approval Pre-Paving Considerations

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Concrete Mix Proportioner App apps.acpa.org

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Which Tests To Use

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Which Tests To Use

Cement • The “glue” that hold concrete together

•  Increase cement content = increase strength, but: � Need more air entraining admixture for desired air � Need more water, resulting in more drying shrinkage �  Increased risk of segregation with more paste � More bleed water, increasing permeability � Earlier sawing required �  Stiffer mixture �  Less fatigue capacity

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Cementitious Materials Content • Use least amount of cementitious materials necessary to meet strength and workability �  Typical minimum is about 500 lb/yd3 (300 kg/m3) for slipform

• Dosage typically reported as cement replacement:

•  SCMs may retard strength gain

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Water-Cementitious Mataerial Ratio • Lower w/cm = higher strength �  Slipform paving - maximum: 0.45; typical = 0.40 �  Fixed-form paving/hand pours - max: 0.50; typ = 0.45

• For w/cm below about 0.40, autogenous shrinkage becomes a concern

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Aggregates • 60-75% of mixture

• Provide volume stability!

• Coarse to fine ≈ 60/40

•  Selection in critical � All aggregate should be prequalified for durability to freeze-

thaw, ASR, alkali-carbonate, D-cracking

• Coarse agg is major driver in concrete CTE

• Agg hardness impacts sawing operations

• Cleanliness and surface moisture important

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Aggregate Gradation • CONTROLS workability!!

• Well-graded combined aggregate gradation will: � Reduce water demand �  Lower drying shrinkage �  Increase workability �  Improve strength

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Gradation Analyzer App apps.acpa.org

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Gradation Analyzer App apps.acpa.org

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Testing – Temperature • ASTM C1064

• EASY, just place thermometer in concrete

• Results help verify conformance to requirements

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Testing – Slump • ASTM C143 / AASHTO T119

• Measures consistency; NOT QUALITY!

• Typical values: �  Slipform: 0.5-1.5 in. (13-38 mm) �  Fixed form: 3-4 in. (75-100 mm)

• Slump is dependent on mixture and also on time of testing

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Testing – Density (Unit Weight) • ASTM C138 / AASHTO T121

• Measures known volume

•  Typically 130 to 150 lb/ft3 (2,000 – 2,400 kg/m3)

•  Indicates batch-to-batch variability

• Reduction in density may indicate: �  Higher air content, higher water content, lower cement content,

change in proportions of ingredients, or change in aggregate specific gravity or moisture

• One of the most valuable tests for process control

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Testing – Air Content • ASTM C231 / AASHTO T152

• Target air depends on agg size

• Testing at plant or in front of paver doesn’t account for air loss of up to 2% in paver

• Quality critical to durability

• AVA and petrography are other means to measure

• Super Air Meter latest tool!

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Max Agg Size Target Air

3/8 in. (9.5 mm) 7 ½%

½ in. (13 mm) 7%

¾ in. (19 mm) 6%

1 in. (25 mm) 6%

1 ½ in. (38 mm) 5 ½%

Testing – Air Content (continued) • Affected in the field by: � Cement �  SCMs � Chemical admixtures � Gradation of aggregates � w/cm ratio �  Temperature � Delays � Placement/consolidation

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Testing – Compressive & Flexural Strength • ASTM C39 / AASHTO T22 for cylinders

• ASTM C78 / AASHTO T97 for beams

• Typical strength requirements (low / avg / high) � Compressive: 3,000 psi (20 MPa) / 3,500 (24) / 4,000 (28) �  Flexural 550 psi (3.8 MPa) / 600 (4.1) / 650 (4.5)

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Testing – Maturity to Estimate Strength

• ASTM C1074 / AASHTO T325

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Testing – Maturity to Estimate Strength

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Testing – Maturity

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Maturity Calculator apps.acpa.org

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COMPASS www.pccmix.com

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Specifications Pre-Paving Considerations

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Specifications • Address concrete materials durability and what needs to be measured to control critical elements of construction and design

• All specifications act to assign risk. � Method specifications assign risk to the owner. � End result specifications assign risk to the contractor.

• Alternative types of specifications and contracting methods are being used on an ever increasing number of projects: � Performance based specifications, design/build,

warranties and others

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Quality Control Pre-Paving Considerations

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Quality Control (QC) versus Quality Assurance (QA) • QA is responsibility of owner – ensure the end product is of proper quality and motivates QC

• QC is responsibility of contractor – makes the product of proper quality and motivated by QA and acceptance

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Which Tests To Use

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Which Tests To Use

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Which Tests To Use

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Which Tests To Use

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Coordination • QC plan must be discussed at pre-paving meeting

• Communication between owner, project engineer, inspector, plant manager, etc. is crucial to project success!

• Hot/cold weather contingencies

• Who conducts QA tests?

• Communicate necessary mix adjustments based on QC results!!!!!

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Test Specimens • Hardened tests (e.g., strength, hardened air, etc.) are more susceptible to ambient conditions and handling than fresh tests (e.g., air content, unit weight, etc.)

• Cylinders typically preferred over beams � Less sensitive to handling and curing of specimen � Smaller and easier to transport

• Portable containers available to control both moisture and temp in transport

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

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