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
Conducting a Test Placement
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Remember:Silica-fume concrete is more cohesive and less
prone to segregation
To improve workability, increase slump by about
2 in. (50 mm)
Cohesive silica-fume concrete -- OK to increase
slump
Conducting a test placement
Transporting, Placing, and Consolidating
Silica-Fume Concrete
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Silica-fume concrete requires thorough consolidation
Finishing Silica-Fume Concrete Flatwork
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Click on the icon above to play a video on finishing silica-fume concrete
Video Clip
Under Finish Silica-Fume Concrete
Use the “One-Pass” Technique
One-Pass Finishing
Screed Float Texture
Cure
Protect,
Protect,
Protect!
One-pass finishing
Float and brooming tool
Broomed surface -- all that is required for a parking structure
Finishing Silica-Fume Concrete Bridge Decks
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Preventing Plastic Shrinkage Cracking
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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
Plastic shrinkage cracking
Silica fume concrete does not bleed and is more susceptible to
plastic shrinkage cracking
Evaporation retarders work well but are frequently misused
Curing Silica-Fume Concrete
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How Important is Curing Silica Fume Concrete?
“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
“It is recommended that a minimum of 7 days continuous moist curing be
specified.”
-- Whiting and Detwiler NCHRP Report 410
Applying curing compound while concrete is still fresh
Moist curing after concrete hardens
Don’t forget winter protection
End of Chapter 4
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