Oklahoma State University Geothermal Smart Bridge Quarterly Progress Report:

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Oklahoma State University Geothermal Smart
BridgeQuarterly Progress Report

• Task 4.4.1-Corrsion Assessment PIs Knobbe
• Accomplishments
• US Navys corrosivity sensors with normal and
  extended service life
• were tested in concrete modules during the
  concrete curing stages and
• accelerated corrosion test (Figure 1)
• The data of all Cd/Au and Ni/Au corrosivity
  sensors was monitored
• for 500 hours during the curing test period
  (Figure 2(left).
• The specimen was subjected to a 15 sodium
  chloride electrolyte with
• a cycle of 3 days wet / 4 days dry (Figure 2.
  (right) to initiate corrosion of
• the rebar .
• The data show that all sensors normal Cd/Au
  and newly developed extended
• service life Ni/Au have response to
  electrolyte activity, i.e. Cl- concentration.
• The experiment incorporated was performed in
  cooperation with SPEC.

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Plans for Next Quater

• ? The experiment is set to correlate the real
  corrosion measurement
• with Cl- content in concrete and then with
  corrosivity sensors data
• ? Six 11 x 6 x 4.5 concrete blocks are formed
  in the Civil Engineering
• Department of OSU
• Three billet steel reinforcement bars are
  placed in the concrete of all blocks. (Fig. 3)
• Two concrete blocks are with uncoated billet
  steel rebars and 2 concrete
• blocks are with epoxy coated rebars. Two
  concrete blocks with uncoated rebars
• will be control samples and will not be
  subjected to corrosion test
• After curing period (28 days in moister room and
  14 days of drying) four
• concrete blocks will be exposed to a 3 salt
  exposure for a period of 90 days
• to initiate corrosion of the top steel
  reinforcement.
• This represents the test procedure in ASTM
  G109.
• The current between top and bottom rebars
  swill be registered
• as a function of time every week

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• After 90 days of exposure the solution shall be
  removed from the slabs
• and rebars will be weighed and examined for
  corrosion.

Sampling and testing for Cl- ion in concrete All
slabs will be tested for Cl- content every 30
days The core samples wcill be taken from 1, 2,
3 inches from the surface using the drill The
samples will be crushed and ground to a
powder The acid soluble chloride content will be
determined according AASHTO Standard Test T260
procedure
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• Calculation of the steel section loss and risk
  of cracking
• The measured electric current between top and
  bottom rebars is generated
• by the anodic reaction
• Fe Fe2 2e,
• And then converting the current flow to metal
  loss
• PIt/96500 M/2
• Where P the amount of steel that dissolved
• I is the current in amperes,
• t is the time in seconds,
• M56 (molecular weight for iron).
• This gives a conversion
• 1uA/cm2 11.6 um steel section loss per year

Corrosion of steel in concrete J.P. Broomfield,
1997 0.1 uA/cm2 1.1 um yr-1 steel section loss
3 um yr-1 rust growth 1 uA/cm2 11.5 um
yr-1 steel section loss 34 um yr-1 rust
growth 5 uA/cm2 57.5 um yr-1 steel section
loss 173 um yr-1 rust growth 10 uA/cm2 115
um yr-1 steel section loss 345 um yr-1 rust
growth
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Corrosion of steel in concrete J.P. Broomfield,
1997 No corrosion expected
Icorr lt 0.2 uA cm-2 Corrosion possible in 10-15
years Icorr 0.2 1 uA cm-2 Corrosion
possible in 2-10 years Icorr 1 10 uA
cm-2 Corrosion expected in 2 years or less
Icorr gt 10 uA cm-2 The Clear/Startfull
empirical calculation (for bridge) T(0.052d1.
22 t0.21) / Z0.24 P)0.83 where T-time to first
cracking (years) d-depth of cover
(millimeters) Z- surface or near surface chloride
concentration (per cent by weight of concrete) t-
the age at which Z was measured P- the water
cement ratio
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Conclusion
Correlation between corrosion current , chloride
ion concentration and corrosivity sensors data
will give the ability a) To convert corrosivity
sensors data to steel section loss per year b)To
predict the year of the possible
corrosion c)Using the empirical equation to
estimate the time to first cracking (years)
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ASTM G109-99 Standard Test Method 6 Test Modules
2 control without ponding with uncoated rebars ,
2 slabs with uncoated rebars subjected to
ponding, 2 slabs with epoxy coated rebar
subjected to ponding Class AA Portland Cement
Air Entraining Admixture 57 Coarse Aggregate 4
grade 60 A615 Rebar 14 lengths
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