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The National Academies

NCHRP IDEA 20-30/IDEA 240 [Active (IDEA)]

Stainless Steel Coated Rebar for Chloride Resistant Concrete Highways and Bridges

  Project Data
Funds: $138,750
Staff Responsibility: Inam Jawed
Research Agency: Allium Engineering, Inc., Peabody, Massachusetts
Principal Investigator: Samuel McAlpine
Fiscal Year: 2022

This project will develop low-cost, highly corrosion-resistant multilayer metallic composite steel rebars for concrete reinforcement. The work is being carried out in two stages. Work in Stage 1 primarily involves laboratory-scale testing of the stainless-clad steel rebars to determine optimal coating composition for corrosion resistance. The tolerance of the rebar to mechanical bending without damage to the corrosion-resistant coating will also be investigated. Prototype rebars with different coating grades will be produced. There are a variety of grades commercially available, including austenitic (FCC) steels and ferritic (BCC) steels. Cladded rebars with a minimum of four distinct coating grades, with and without molybdenum, will be produced. The produced prototype rebars will be tested for corrosion resistance and performance. Immersion testing in NaCl solution and salt spray testing will be conducted to investigate the coating performance in accelerated corrosion conditions. The rebars will also be subjected to various types of bend testing (90, 180 degree bends, bend/re-bend) to determine whether coating cracking during bending is a significant issue. If the issue is found to be significant, annealing experiments will be conducted to thermally repair the deformed microstructure of the coating and enhance ductility. Bend tests will then be performed on annealed samples to see if annealing resolves the issue. Bend tests will comply with industry standards established by the Concrete Reinforcing Steel Institute (CRSI). Work in Stage 2 will involve optimization of the rebar coating thickness. Tests to be conducted will include simulating coating damage to understand the impact of coating flaws/defects on performance as well as in-concrete mechanical pullout test. Since the production cost of the developed rebar will be related to the coating thickness, it is critical to determine the minimum thickness with the desired coating properties. After selecting a final coating grade from Stage 1 findings, prototypes will be produced with coating thicknesses of approximately 25, 50, 75, and 100 microns, and corrosion and bend tests will be conducted to determine the acceptable rebar thickness coating range. Abrasion, adhesion, and indentation tests also will be conducted on the coated rebars to assess their resistance to mechanical damage. Additionally, coating “holidays” will be created and defected rebars as well as bent rebars will be subjected to accelerated corrosion testing. Bonding between the coated rebar and concrete will be evaluated through rebar pullout testing. It is anticipated that the stainless-clad rebar will perform significantly better than epoxy-coated bar and will be comparable to uncoated rebar. The final report will provide all relevant data, methods, models, and conclusions along with guidance on how to implement the stainless-clad rebar in a pilot state DOT installation.

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