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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Tined surface

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

Good fogging

Improper fogging

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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