Concrete Drying Shrinkage

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Concrete Drying Shrinkage

• 17 November 2004
• Roads Pavement Forum
• Sebasti Badenhorst, Pr. Eng
• Holcim (South Africa) (Pty) Ltd

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Concrete drying shrinkage research ...
To look is one thing. To see what you look at
is another To understand what you see is
another. To learn from what you understand is
something else But to act on what you learn is
all that really matters Sir Winston Churchill
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Performance-based specifications for shrinkage

• To look is one thing.
• To see what you look at is another WC
• COLTO - Standard Specification for Road and
  Bridge Works for State Road Authorities 1998
• Shrinkage shall not exceed 0,04 , tested in
  accordance with SABS 1085

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Shrinkage tests...
SABS Method 10852001 - Initial drying and
wetting expansion of concrete Controversial
severe drying... 50 to 55 ?C,15 to 25 RH Cycles
of heating and cooling Small concrete
samples Poorly defined end point
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An investigation to review SABS 1085

• ...To understand what you see is another. WC
• Establish how the SABS 1085 shrinkage test result
  relate to other international shrinkage tests
  methods?
• International shrinkage test methods are based on
  natural (moderate) drying conditions
• Temperature between 22 to 25ºC
• Relative humidity between 50 to 70

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Laboratory investigation...

• 28 Concretes...different combinations
• aggregates
• cements
• Same size specimens
• SABS 1085
• natural drying test

...compared results...
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Results of investigationaggregate type
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Results of investigationcements
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Hilton Concrete Pavement trials
...To learn from what you understand is
something else WC
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Quartzite concrete
Dolerite concrete
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Shrinkage investigation at Hilton

• Seven pairs of crack measuring gauges installed
• Perpendicular and centred to crack inducing plate
• Non doweled joints
• Determine movement at joints with time

Crack inducing plate
Crack measuring gauges
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Environmental conditions day of casting
21,5C 37 RH
Dolerite concrete
13,3C 72 RH
Quartzite concrete
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Laboratory shrinkage testing
University of Witwatersrand 6 samples creep
and shrinkagequartzite and dolerite Cement
and Concrete Institute shrinkage tests... SABS
Method 1085
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Resultsnatural drying ...laboratory shrinkage

• Quartzite higher shrinkage potential
• Dolerite lower shrinkage potential

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Results SABS 1085 shrinkage

• Dolerite concrete, meets COLTO specification
• Quartzite concrete fails COLTO specification
• SABS 1085 does not account for variability

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Field results

• Quartzite cracked less, in spite of higher
  shrinkage potential

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Crack widthdolerite concrete
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Early concrete temperature changes
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Conclusions...

• Environmental condition at time of construction
  of greater significance in the formation of
  cracks than the shrinkage potential determined in
  the laboratory
• Changes in early temperature...significant effect
  on crack propagation
• Difference between... crack potentialshrinkage
  potential

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Further work...

• ...But to act on what you learn is all that
  really matters WC
• Draft of SANRAL specification, clause referring
  to SABS 1085 scraped
• CnCPave updated with revised shrinkage prediction
  model, no longer refer to SABS 1085
• Draft ISO test methodbased on natural drying
  tests... extrapolate the results from
  28-daysunder investigation