One of the most common methods of combating steel rebar corrosion in precast concrete applications is the use of fusion-bonded, epoxy-coated rebar in construction and repair
According to the Concrete Reinforcing Steel Institute (CRSI), epoxy-coated reinforcing steel was first used in a bridge application in Pennsylvania in 1973. Why 1973? Well, earlier in our infrastructure history there was less concern about vehicles sliding on icy roads or snow and ice removal during the winter. It wasn’t until the 1950s that deicing chemicals were used to clear bridges and highways, but the result of using these chemicals sent repair costs skyrocketing due to corrosion problems. The country needed a better solution to reduce the problem and, out of many protective-coating options tested, fusion-bonded epoxy coating of rebar was the best fit.1
When precast project specifications call for the use of epoxy-coated rebar, precast concrete manufacturers need to be armed with the appropriate ASTM standards in order to satisfy contract documents and owner demands. The most widely used ASTM standards covering epoxy-coated rebar are ASTM A775, “Standard Specification for Epoxy-Coated Steel Reinforcing Bars” and ASTM A934, “Standard Specification for Epoxy-Coated Prefabricated Steel Reinforcing Bars.” The difference between these two standards is one key word – prefabricated. ASTM A775 covers fusion-bonded epoxy coated bar lengths while ASTM A934 covers fusion-bonded, epoxy-coated bar that is cut and bent into specific required shapes, sizes and lengths such as stirrups and hooks. This occurs prior to cleaning and the powder-coating application.
Manufacturing epoxy-coated rebar
Epoxy-coated rebar is manufactured in CRSI certified plants under strict controls for cleaning, pre-heating, electro-powder coating and curing processes. Bars are cleaned by grit blasting to remove all mill scale and oxidation and then electro-induction heated to around 450 F. The bars and specialty shapes then go through an electrostatic powder-coating process. The heat of the bars and shapes causes the powder to melt on contact, forming the polymer coating. In the final stages of the process, bars are air and/or water cooled prior to removal from the manufacturing line. This cooling process allows the bars to be handled and stacked without damaging the epoxy coating. Danielle Kleinhans, Ph.D., P.E., certification program administrator and structural/transportation engineer at CRSI, said CRSI’s certification program for the application of epoxy coating on reinforcing steel has been in effect since 1991. The program outlines basic requirements for the quality control program to ensure a plant and its employees are trained, equipped and capable of producing epoxy-coated rebar. Today, 38 certified plants are part of the coating certification program, and they have recently established a certification program for fabricators of epoxy-coated reinforcement as well.
“Most epoxy-coated rebar produced in the country is coated by CRSI certified plants, so the chance a precast concrete producer is receiving domestic, non-certified product is slim,” she said. “We view that as a good thing.”
Handling and storage
When handling epoxy-coated rebar, plants must take special care not to damage the coating. Handling requirements are covered by ASTM D3963. Using nylon strapping and multiple lift points along the bar will help to ensure the coating is not marred or damaged by cables or chains and is not allowed to sag and rub during offloading. Epoxy-coated rebar needs to be stored separately from non-epoxy-coated rebar and proper protective measures such as storage on wooden racks or plastic or rubber-coated steel racks avoids the possibility of surface damage. Bars that have damaged coatings need to be repaired using an approved repair material and process prior to being placed in formwork. If stored outside, Epoxy-coated rebar needs to be protected from direct sunlight – ultra-violet light degrades the epoxy coating over time – by tarps and/or covered storage areas. CRSI recommends that bar be exposed to ultra-violet light no longer than 30 days unprotected, Kleinhans said.
Cage fabrication and formwork
When assembling reinforcing cages using epoxy-coated rebar, technicians should exercise care in assembly as to not damage the epoxy coating. Fabrication of cages should be accomplished using appropriate coated tie wire. Cages can be supported in the proper position in the formwork using plastic chairs and stand-offs and/or precast concrete spacer blocks as with conventional black bar applications.
Designers of structures using epoxy-coated rebar usually follow the standard recommended practices of ACI and AASHTO. However, plant personnel should be aware that laps and splices for epoxy-reinforcing steel need to have larger lap and development lengths due to the bond differences between conventional black bar and epoxy-coated bar.
Applications for epoxy-
The use of epoxy-coated rebar is commonplace today for precast concrete applications in bridges and roadways, marine applications, parking structures, concrete repair and structures challenged with corrosion from deicing chemicals, continuous moisture exposure and/or salts. Kleinhans said there are more than 65,000 reinforced concrete bridges with epoxy-coated rebar nationwide.
“Based on survey results, epoxy coating is second only to increased concrete cover as a method to prevent reinforcement corrosion,” she said.
References for precast producers
Precast concrete producers can obtain many valuable references and resource documents from CRSI in regard to the use of epoxy-coated rebar in precast products. The product guide titled, “Specialty & Corrosion-Resistant Steel Reinforcement” is an authoritative and comprehensive reference covering steel bars specified with improved corrosion resistance. The “Manual of Standard Practice” is another great resource for the precast industry, providing detailed information on steel reinforcement.
Phillip Cutler, P.E., is NPCA’s director of quality assurance programs.
1 For additional historical information, visit epoxyinterestgroup.org and crsi.org.
“Specialty & Corrosion-Resistant Steel Reinforcement” CRSI
“Manual of Standard Practice” CRSI
“Epoxy-Coated Reinforcing Steel Bars In Northern America” David McDonald, Managing Director, Epoxy Interest Group of CRSI
ASTM A775, “Standard Specification for Epoxy-Coated Steel Reinforcing Bars”
ASTM A934, “Standard Specification for Epoxy-Coated Prefabricated Steel Reinforcing Bars”