Chapter 4. Working with Silica-Fume Concrete

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Chapter 4. Working with Silica-Fume Concrete

• Conducting a Test Placement
• Transporting, Placing, and Consolidating
• Finishing Flatwork
• Finishing Bridge Decks
• Preventing Plastic-Shrinkage Cracking
• Curing

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Conducting a Test Placement
Chapter Outline
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RememberSilica-fume concrete is more cohesive
and less prone to segregationTo improve
workability, increase slump by about 2 in. (50
mm)
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Cohesive silica-fume concrete -- OK to increase
slump
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Conducting a test placement
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Transporting, Placing, and Consolidating
Silica-Fume Concrete
Chapter Outline
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Silica-fume concrete requires thorough
consolidation
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Finishing Silica-Fume Concrete Flatwork
Chapter Outline
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Click on the icon above to play a video on
finishing silica-fume concrete
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Under Finish Silica-Fume ConcreteUse the
One-Pass Technique
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One-Pass Finishing

• Screed
• Float
• Texture
• Cure

Protect, Protect, Protect!
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One-pass finishing
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Float and brooming tool
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Broomed surface -- all that is required for a
parking structure
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Finishing Silica-Fume Concrete Bridge Decks
Chapter Outline
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Tined surface
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Preventing Plastic Shrinkage Cracking
Chapter Outline
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What is Plastic Shrinkage Cracking?

• Cracking that occurs in the surface of fresh
  concrete soon after it is placed and while it is
  still plastic.
• -- ACI
  116R

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Plastic shrinkage cracking
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Silica fume concrete does not bleed and is more
susceptible to plastic shrinkage cracking
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Good fogging
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Improper fogging
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Evaporation retarders work well but are
frequently misused
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Curing Silica-Fume Concrete
Chapter Outline
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How Important is Curing Silica Fume Concrete?
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If silica-fume concrete mixtures are given 7
days of continuous moist curing, then there is no
association between silica fume content and
cracking. -- Whiting and
Detwiler NCHRP Report
410
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It is recommended that a minimum of 7 days
continuous moist curing be specified. --
Whiting and Detwiler
NCHRP Report 410
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Applying curing compound while concrete is still
fresh
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Moist curing after concrete hardens
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Dont forget winter protection
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End of Chapter 4
Main Outline