Concrete: I235 Experience

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ConcreteI-235 Experience

• John Hart P.E.
• District 1 Materials
• Iowa DOT

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Topics

• High performance concrete (HPC)
• Self consolidating concrete (SCC)
• Quality management concrete (QMC)

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HPC
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Developmental Specification

• HPC committee
• Released for spring 2002 projects on I-235
• Durability
• Revised 4 times
• Mix design
• Curing
• Testing
• Temperature

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Usage

• I-235/Metro
• 34 bridges
• Over 300 pours
• Over 30,000 yd3
• Substructure
• Footings
• Piers
• Pier caps
• Abutments
• Miscellaneous

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Usage

• Superstructure
• Deck

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Target Properties

• Substructure
• Basic w/c ratio 0.42
• Maximum w/c ratio 0.45
• 3i durability aggregate
• Maximum 4 inch slump
• Air content of 8.5 to 5.5
• Minimum average 28 day compressive strength of
  5000 psi
• Target permeability of 2500 coulombs
• 168 hours of curing
• 50 F minimum temperature

• Superstructure
• Basic w/c ratio 0.40
• Maximum w/c ratio 0.42
• 3i durability aggregate
• Maximum 4 inch slump
• Air content of 8.5 to 5.5
• Minimum average 28 day compressive strength of
  5000 psi
• Target permeability of 1500 coulombs
• 168 hours of curing
• 50 F minimum temperature

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Mix Design

• Substructure
• Preapproved mix
• C-4-C15-S35 with a water reducer
• Contractor mix design
• minimum 624lbs/yd3 of cement
• equivalent of 35 GGBFS
• trial batch

• Superstructure
• Preapproved mix
• 624lbs/yd3 of cement
• 3 aggregate (46/12/42)
• 15 class C fly ash
• 35 GGBFS
• Contractor mix design
• minimum 624lbs/yd3 of cement
• equivalent of 35 GGBFS
• trial batch

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Testing

• Contractor
• All pours
• six cylinders, 3 each for 28 and 56 day breaks
• cold weather temperature monitoring
• RCE
• All pours
• air and slump
• beams on flexural elements
• Materials
• Selected pours
• correlate air and monitor slump
• 3 cylinders for 28 day breaks
• 1 cylinder for permeability

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Performance

• Strength
• 28 and 56 days
• Average
• 1 data point 3 cylinder average
• Data points
• 250 substructure
• 70 superstructure

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Performance

• Permeability
• AASHTO T-277 (rapid cure)
• 1 data point 2 test average
• Data points
• 27 substructure
• 24 superstructure
• W/C ratio
• All water additions included
• 1 data point ticket of tested concrete
• Data points
• 20 substructure
• 21 superstructure

• Permeability Charge(coulombs)
• High gt 4000
• Moderate 2000-4000
• Low 1000-2000
• Very Low 100-1000
• Negligible lt 100

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Difficulties

• Producer capabilities
• Strength variation
• Cold weather issues

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Cold Weather Issues

• Difficulties
• Late season decks
• Gathering and analyzing temperature data
• Balancing retardation
• Maintaining temperature
• Maintaining curing
• Determining opening/buildup

• Solutions
• Reduced substructure curing
• Electronic temperature data
• Use of new reducer/retarder chart
• Heated concrete
• Protection and heating
• Different cementitious materials
• Modifying HPC mix
• Modified curing
• Field cured specimens

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SCC
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Usage

• Precast
• Field

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Precast

• Items fabricated
• MSE panels
• Intakes
• Noise walls
• Mixing
• Ready mix
• Pan mixer
• Dedicated person
• Dosage at plant
• Dosage at truck
• Placement
• Bucket
• Chute

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PRECAST
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Noise Wall
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Precast Advantages

• Crisp details
• Increased production
• Less labor
• Fewer repairs
• Higher earlier strengths
• Good durability

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Precast Challenges

• Forms
• Oil rings
• Tightness
• Trapped air
• Consistency
• Water
• Plant limitations

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Field

• Items fabricated
• Pedestals/wings
• Aesthetic pieces
• Mixing
• Ready mix
• Admixture technical representative
• Dosage at site
• Placement
• Bucket
• Pump

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SCC Field Application
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SCC Field Application
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Field Advantages

• Complex shapes, angles, slopes
• Limited access formwork
• Tight reinforcing
• Crisp details

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Field Challenges

• Formwork
• Tightness
• Strength
• Honeycombs
• Consistency
• Water
• Admixture dosage
• Air content
• Limited experience
• Field technical representative

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Mix Design

• Case by case approval
• HRWR and/or VMA
• Higher fines
• 725 lbs cementitious
• Aggregates
• Lower SPG better
• Coarse
• 1/4 to 3/8
• Texture and shape

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Testing

• Not formalized
• Air
• No rodding
• Standard limits
• Initial slump
• Spread
• 25 maximum limit without VMA
• No rodding
• Inverse used
• Average of 2 lengths

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QMC
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Strength Versus Gradation

• High strength mixes do not always ensure improved
  workability and long term durability

• Well graded mixes provide improved workability
  and long term durability, while maintaining or
  improving strength

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Gradation

• Gap graded
• segregate more easily
• difficult to place
• higher amount of fines
• require more cement
• greater water demand

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Gradation

• Well graded
• less prone to segregation
• easier to place
• lower amount of fines
• require less cement
• less water demand

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Shilstone Principles
Combined retained above 3/8 sieve Combined
retained above 8 sieve

• Coarseness factor
• indicates if a mix is gap or well graded
• Workability factor
• indicates if a mix is coarse or fine

Combined passing 8 sieve
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QMC Mix Design Constraints

• Minimum cementitious 560 lbs/yd3
• Coarse aggregate size gt 1inch
• Fly ash and GGBFS 2301.04 E, F
• W/C ratio 0.45 max.
• Target air content 6 /- 1.0
• 28 day flexural strength 640 psi

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Typical Aggregate Blends

• Coarser than traditional mixes
• Aggregate percentages (coarse)
• 58-62/42-38 coarse to fine
• 85-75/15-25 coarse to intermediate
• Aggregate percentages (total)
• 43-53 percent coarse
• 8-16 percent intermediate
• 38-42 percent fine

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Project Trends

• Improved workability
• reduced vibration
• higher after paver air content
• Gradation consistency
• consistent production
• improved stockpile management
• improved sampling techniques
• disincentive never applied
• Optimized mix
• cementitious
• strength
• durability