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EPOXY-COATED REBARS IN CONRETE CONSTRUCTION

EPOXY-COATED REBARS IN CONRETE CONSTRUCTION. Ahmad S. Al-Gahtani Department of Civil Engineering King Fahd University of Petroleum & Minerals. Epoxy coating procedure. Background :. Deterioration of bridge decks in the 1960”s Research by U.S FHWA First bridge in 1973 in Philadelphia

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EPOXY-COATED REBARS IN CONRETE CONSTRUCTION

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  1. EPOXY-COATED REBARS IN CONRETE CONSTRUCTION Ahmad S. Al-Gahtani Department of Civil Engineering King Fahd University of Petroleum & Minerals

  2. Epoxy coating procedure

  3. Background : • Deterioration of bridge decks in the 1960”s • 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)

  4. 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)

  5. 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.

  6. 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

  7. 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 .

  8. 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).

  9. 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].

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Code Amendments; Upgrade in specification, -Min. thickness 130m175 m - Number of holidays 6/m3/m - Damages 2%1% - Improvement of adhesion, handling and storage procedures - Plant certification program

  20. Sales in USA:

  21. 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

  22. 90000 80000 70000 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 60000 50000 40000 30000 20000 10000 0 Sales in Saudi Arabia: Tones Time (Year)

  23. 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)

  24. Specimens at exposure site:

  25. Performance Criteria: • onset and propagation of cracks • weight loss in rebar • bar condition (rust and pitting)

  26. Results (after 7 years exposure): Black Steel FBECR Crack category 1 - No crack 4 - Wide 2 - Fine 5 - Heavy 3 - Medium 6 - Spalling

  27. Retrieved bars:

  28. 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)

  29. Results: • Coating disbondment • Corrosion at coating cracks • Corrosion started at deformation patterns • Corrosion proceeded underneath coating

  30. Corrosion underneath coating

  31. 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

  32. 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

  33. 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, )

  34. Cut and Bend at job sites

  35. Storage at sites

  36. Coating damages

  37. Mix of rebars

  38. Ineffective patching

  39. Sharp edge and seem in rebar:

  40. Gulf Environment Conditions: • Favorable Corrosion Conditions: - High temp. with salt laden humidity - High level of contamination of construction materials Temp. R.H.% Cl-

  41. 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 30°C).

  42. 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.

  43. 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.

  44. THANKS

  45. Initiation-Propagation Model: Initiation Propagation Black Steel FBECR In Poor Conc. FBECR In good Conc. Salt ingress Salt ingress Time Loss of adhesion Salt ingress Loss of adhesion

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