Concrete Curing: Plastic Shrinkage Cracking, Bleeding, Evaporation, and Temperature

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Concrete Curing Plastic Shrinkage Cracking,
Bleeding, Evaporation, and Temperature

• Jennifer A. Distlehorst Cliff Hobson
• Dave Meggers John Wojakowski
• Kansas DOT

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Plastic Shrinkage CrackingAnalysis of the term

• Plastic - capable of continuous and permanent
  change in any direction without breaking apart
• Cracking - breaking apart or splitting

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Plastic Shrinkage Cracking
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Plastic Shrinkage Cracking Factors

• Evaporation Rate - Menzel, 1954 Lerch,1957
• Combination of 4 Factors - Concrete and Air
  Temperatures, Humidity and Wind Speed
• Critical Value from Lerch, 1957 0.2 lb/sq ft/hr
• Bleeding of the Concrete
• Are Todays Concretes Still the Same? Similar?
• New Value for regular, let alone high performance
  concrete?

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Bleed Test of Concrete ASTM C 232
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Bleeding of Concrete and Loss of Water at Various
Evaporation Rates
0.6
Laboratory Concrete, Air Entrained
0.5
0.4
0.3
Cumulative water bled or evaporated, lb/ft2
0.2
0.1
bleed water
0
043
126
209
252
time in hours
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I-635 Example - Hand Placement
0.6
0.5
Dump 1035 Consolidation 1040 Tining
1045 Curing Compound 1050
92-95 F, ADJACENT CURED CONCRETE 106 F
0.4
0.2
Cumulative water bled or evaporated, lb/ft2
0.3
0.2
0.1
Measured evaporation rate 0.07 lb/sq.ft/hr
0.1
bleed water
1030
1100
1130
1200
time of day
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I-70 Example -Slip Formed
0.6
0.5
0.2
0.4
Cumulative water bled or evaporated, lb/ft2
0.3
0.2
evaporation 0.12 lb/sq.ft/hr
0.1
0.1
bleed water
200
230
330
400
300
time of day
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Louisburg Example - Slip Formed
0.6
0.5
0.4
0.2
Cumulative water bled or evaporated, lb/ft2
0.3
0.13 lb/sq.ft/hr
0.2
0.1
0.1
bleed water
130
230
300
200
time of day
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I-635 Bridge Example
0.6
0.5
Consolidation 900
0.4
Grade 30, Field Concrete
0.2
Cumulative water bled or evaporated, lb/ft2
0.3
0.1
0.2
0.1
0.05 lb/sq.ft/hr
bleed water
900
1000
1030
930
time of day
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If the evaporation rate is greater than the
bleeding rate why isnt there a lot of plastic
shrinkage cracking in our concrete?

• Stiffer, cohesive concrete (used in slip form
  paving bridge decks) has some tensile strength
  to resist the force imposed by the surface
  tension of water
• Water reducers used in these mixtures reduce the
  surface tension of the water

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KDOT Bridge Deck Curing Specification
90M/R-91-R13

• Measure the evaporation rate on the bridge deck
  regularly
• Use monomolecular/precure immediately after the
  bridge deck finisher
• Fog immediately behind the tining float
• Produce a gloss to a semi-gloss sheen without
  water runoff

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KDOT Bridge Deck Curing Specification
90M/R-91-R13

• Apply curing compound to the damp wearing surface
• Cover with wet burlap for seven days
• Use soaker hoses
• Polyethylene sheeting is not allowed until the
  evening of the day following placement if the
  temperature is forecast to be above 50 F

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Temperatures of a Slab Bridge
15 F
PLASTIC PLACED
Air
N
N
N
N
N
N noon
N
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Evaporation retarder applied immediately
E. Holt, Concrete International , Sept 2000
(0.1 psf 0.02 in)
E. Holt, Concrete International , Sept 2000
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Water applied after 1 hour
E. Holt, Concrete International , Sept 2000
(0.2 psf 04 in)
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