Tommy E' Nantung

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Bridge Decks and Rail Cracking Midwest Concrete
Consortium

• Tommy E. Nantung
• INDOT Research Division

St. Louis, MO April 18 20, 2006
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The Challenges
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The Challenges
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The Challenges
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The Challenges
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The Challenges
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The Challenges
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The Challenges
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The Challenges

• Do not read the specs
• Rely on somebody else to tell
• Bad specifications
• Lack of knowledge and expertise to keep up with
  the concrete technology
• Lack of resources for inspection
• Penalties are too light to penalize
• Owners most of the time ended up fixing and
  paying the mistakes
• Weather and fast track constructions

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Attempts to Reduce Cracks

• Materials and mixtures
• Strength maximum and minimum
• Water and cement contents (paste)
• Aggregate gradation (max size) and content
• Air content
• Coarser cement particles
• Slump low slump concrete
• Admixtures shrinkage reducing, superplasticizer
• Mineral admixtures fly ash, silica fume, GGBFS

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Attempts to Reduce Cracks

• Designs
• Bridge
• Cover thickness, both top (settlement cracking)
  and bottom (max size aggregate)
• Modified stay-in-place deck form placement
• Jointless bridge
• Pre-cast elements
• Shoring

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Attempts to Reduce Cracks

• Construction
• Environment temperature, relative humidity, wind
  speed, solar radiation
• Concrete pumping with less rich paste (bridge)
• Order of concrete placement (bridge)
• Monitoring concrete deck thickness (bridge)
• Concrete compaction
• Concrete finishing and tining/grooving
• Concrete curing type and time

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Balancing Acts
Cost, Constructability, and Knowledge
Material Properties and Methods
Location and Materials availability
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Key Opportunities for Codes

• All parameters that reduce cracks cannot all be
  incorporated in the spec
• Supplemental specs
• Special provisions
• Construction memo
• Design memo
• Characteristics
• Emphasize consistency of material properties,
  methods, etc. that ensure to decrease the
  tendency for cracking.
• Example smaller standard deviation for pay
  adjustment
• Move the responsibility more to the contractor
  side
• End results spec, performance related specs, etc.

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Key Opportunities for Research

• One size does not fit all
• Different state has different objectives
• Monitoring equipment and methods
• Performance of materials
• Performance of contractor (workmanship)
• Non-destructive evaluation
• Performance-prediction and maintenance-cost
  models for life-cycle-cost to determine
  incentives and penalties
• How do we measure quality?
• How do you reward quality work?
• Needs wholistic approach

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Questions???