EPOXY-COATED REBARS IN CONRETE CONSTRUCTION

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EPOXY-COATED REBARS IN CONRETE CONSTRUCTION

• Ahmad S. Al-Gahtani
• Department of Civil Engineering
• King Fahd University of Petroleum Minerals

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Epoxy coating procedure
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Background

• Deterioration of bridge decks in the 1960s
• Research by U.S FHWA
• First bridge in 1973 in Philadelphia
• By 1977, 17 states adopted the use of FBECR
• Early studies showed FBECR is effective in
  reducing corrosion by many folds (11-41 times)
  compared to black steel(FHWA 1977-81)

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Florida Experience

• Florida long key bridges constructed in 1979
• In 1986 substructures showed signs of corrosions
  in major five bridges
• Corrosion was in tidal/splash zone (0.6-2.4 m
  above water mark)

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Florida Investigation

• Disbondment of coating
• Water blisters under the coating
• Corrosion initiated at damages/imperfections
• Corrosion aggravated by
• - Fabrication bending
• - Exposure to salt air in construction yard
• - Coating defects/damages
• In 1992 Florida D.O.T. discontinued
• use of FBECR.

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Performance of ECR in Pennsylvania (I)

• 11 bridges with ECR (ages 6 to 10 years) and 11
  bridges (comparable ages) with plain rebar
  subjected to deicing salt service. Initial
  stages of corrosion observed in the plain bar
  bridges but not in the ECR structures. Chloride
  0.7 Kg/m3. 1987

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Performance of ECR in Pennsylvania (II)

• Investigation of epoxy coated rebar and other
  protection systems of 21 bridge decks ( ages 10
  years) in deicing salt , Chloride 7 kg/m3 Both
  ECR rebar provided the most effective
  protection performance, some rebars being in
  excellent condition despite high chloride
  contents .

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Performance of ECR in Canada (C-SHRP)

• 19 ECR structures (3 to 16 years old) The ECR
  bars showed varying degrees of corrosion damage,
  with concrete damage and/or significant corrosion
  on bars at cracks and in low cover areas with
  high chloride. Many uncorroded after up to 16
  years service when no significant chloride had
  reached the bars. About 50 of bars showed
  reduced coating adhesion, (1992).

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Performance of ECR in Canada (Ontario)

• Ontario MOT, during 1989-1995, evaluated ECR in
  numerous structures in deicing salt service.
  Initially found little deterioration of ECR
  except for damage in a barrier wall ? 10 years
  old. By 1992 multiple instances of ECR corrosion
  were observed. Coating disbondment was observed.
  ECR was viewed as providing an improvement over
  plain steel, but the suitability for 75-year
  durability was questioned 16.

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Performance of ECR in New York Bridge Decks
(1992)

• DOT examined 14 of 7-12 year old "worst-case"
  bridges with deck surface distress ed in deicing
  salt service. Rebars from cores, 65 had
  negligible corrosion, 30 had corrosion at ribs
  only and 5 showed more pronounced corrosion. No
  undercoating was observed surrounding corroded
  areas. Chloride ?2 Kg/m3 the incidence of
  corrosion was not observed to be correlated with
  chloride level. Long-term corrosion performance
  could not be quantified yet.

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Performance of epoxy coated in Virginia (1993)

• Transportation Research Council investigated the
  condition of ECR in two test bridges built in
  1977 and in deicing salt service for 13 years.
  Chloride ?2 Kg/m3) . ECR bars were of early
  types, with many flaws and holidays. However,
  coating disbondment or signs of severe rusting
  were not observed. It was concluded that the
  combination of adequate depth of cover and ECR
  provided excellent protection.

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Performance of ECR in a Coastal Georgia Bridge
(1993)

• Georgia DOT examined ECR in the substructure of
  a 9-year old marine bridge (seawater tidal and
  splash service). Coating disbondment was
  observed at several of the ECR samples extracted.
  Severe corrosion of ECR was observed at an area
  of poor concrete consolidation. It was concluded
  that ECR provided questionable added corrosion
  protection, and recommended that epoxy coating
  not be used in continually wet marine
  substructure.

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Performance of ECR in West Virginia Bridges
(1994)

• DOT investigated 14 bridge decks (?13 years old)
  in deicing salt service using ECR and plain bar.
  ECR bridges exhibited little or no distress
  while plain bar bridges showed 2-17 deck
  delamination. Chloride ?1.5 to 3 Kg/m3. It was
  concluded that use of ECR resulted in dramatic
  reduction of delamination in bridge decks.

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Performance of ECR in Coastal North Carolina
Bridges (1993-1995)

• DOT examined the ECR in the substructure of
  three marine bridges (splash-tidal seawater
  service), ? 8 years old. Chloride 1-2 Kg/m.
  No significant corrosion of ECR or coating
  disbondment was observed. It was concluded that
  epoxy coating in the selected bridges was
  providing adequate corrosion protection at time
  of the survey.

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Performance of ECR in California (1995)

• 4 bridges, 7 to 10 years old in deicing salt
  service. Preliminary findings revealed ECR
  corrosion in 8 of 32 cores examined chloride ?10
  Kg/m3. Some bars were showing no corrosion with
  6 Kg/m3 chloride. Coating disbondment was
  observed at some of the bars. The concrete was
  often dry for extended time periods. The bridges
  examined were not showing severe distress.

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Performance of ECR in Indiana (1995)

• Investigations by Purdue University of 5 bridges
  in deicing salt service. Preliminary findings
  showed no corrosion or disbondment ,Chloride ?2.5
  Kgm3 . Corrosion of ECR was seen at one bridge
  at bends in the bar and chloride ?3 Kg/m3.

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Performance of ECR in Kansas (1995)

• DOT investigated Bridges in deicing salt
  service made in 1995 24 . Preliminary findings
  show chloride levels at rebar depth less than 0.5
  Kg/3 and good ECR condition.

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Performance of ECR in Minnesota (1995)

• DOT in 1994 investigated 10 bridges in deicing
  salt service. Cores taken from cracked
  concrete showed only one core with ECR
  corrosion. Satisfaction with ECR performance was
  reported, indicating that bridge overlays and
  good concreting were also factors in the observed
  performance.

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Code Amendments

• Upgrade in specification,
• -Min. thickness 130m 175 m
• - Number of holidays 6/m 3/m
• - Damages 2 1
• - Improvement of adhesion, handling
• and storage procedures
• - Plant certification program

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Sales in USA
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Use of FBECR in the Gulf

• Early 1980s used in some projects in U.A.E.
• By mid 1980s set up of coating plants in U.A.E.
  (now 5 plants)
• Early 1990s 3 plants established in Eastern
  Province of S.A.
• 1996/97 New plant in State of Qatar.
• Total 9 plants

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Sales in Saudi Arabia
Tones
Time (Year)
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Research Experience

• CE-KFUPM
• Specimens prisms 120 X 120 X 305 mm four
  bars with 25mm cover
• Reinforcements Mild steel, galvanized steel,
  FBECR and stainless steel
• Contamination 2.4, 4.8 and 19.2 kg/m3 of
  chloride
• Exposure Natural exposure site, Dhahran
  (above ground)

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Specimens at exposure site
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Performance Criteria

• onset and propagation of cracks
• weight loss in rebar
• bar condition (rust and pitting)

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Results (after 7 years exposure)
Black Steel
FBECR
Crack category 1 - No crack 4 - Wide 2 - Fine 5
- Heavy 3 - Medium 6 - Spalling
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Retrieved bars
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RI-KFUPM Study

• Specimens prisms 62.5 X 100 X 305 mm
• 62.5 X 202 X 305 mm
• with 25 mm cover
• Reinforcements FBECR straight bars
• J-bend bars
• Exposure 5 sodium chloride solution,
• in room temp.
• (Accelerated lab. testing)

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Results

• Coating disbondment
• Corrosion at coating cracks
• Corrosion started at deformation patterns
• Corrosion proceeded underneath coating

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Corrosion underneath coating
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U.A.E. Study

• Dubai Municipality, 1991
• Specimens 150 X 150 X 360 mm with
  10 mm and 30 mm cover
• Reinforcements FBECR and black steel
• Exposure -Below ground
• -Tidal zone
• -Above ground

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Results after 3 years

• FBECR generally in good conditions
• Some adhesion loss of coating for below and tidal
  specimens
• Specimens collected from construction sites were
  far from satisfactory w.r.t. ASTM standards

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Local Construction Practices

• Improper Cut and Bend at job sites
• Improper storage at sites
• No repair for damages
• Mix of coated and uncoated rebars
• Unskilled laborers (damages, scratches bending,
  cutting, )

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Cut and Bend at job sites
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Storage at sites
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Coating damages
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Mix of rebars
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Ineffective patching
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Sharp edge and seem in rebar
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Gulf Environment Conditions

• Favorable Corrosion Conditions
• - High temp. with salt laden humidity
• - High level of contamination of
• construction materials

Temp.
R.H.
Cl-
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CONCLUDING REMARKS

• Good quality FBECR would provide satisfactory
  protection if constructed with good quality
  concrete.
• Moisture and temperature of the exposure
  conditions are key factors for the disbondment of
  coating.
• Epoxy-coating powders shall be handled without
  exposure to high temperature (above 30C).

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CONCLUDING REMARKS

• Long storage time for reinforcement and time
  between cleaning and coating should be minimized.
• Storage time at the construction site should be
  limited.
• Repair of damaged coating by touch-up should be
  done immediately.
• Plant fabrication is highly preferable.

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CONCLUDING REMARKS

• Bending at site should be carried by proper
  equipment and tools.
• Mix of uncoated and coated reinforcement should
  be avoided.
• Construction interruption should be minimized.
• Manufacturers of rebars should produce more
  suitable product for coating.

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THANKS
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Initiation-Propagation Model