Approximately $10 Billion is spent annually to directly remediate corrosion problems with our nation’s bridges, and indirect costs push that annual expenditure up by a factor of ten. Epoxy coatings have been widely used for corrosion protection of steel rebar in reinforced concrete (RC) structures. However, epoxy coatings reduce the concrete-steel bond strengths, thus requiring longer development lengths for epoxy-coated rebar and causing extensive rebar congestions in the joint areas of structures.
In this study, enamel coating is introduced to enhance both corrosion resistance and bond strength of reinforcing steel. The overall goal of this study was to optimize this technology for the construction of RC structures in bridge applications, with the objective of reducing construction and maintenance costs and improving structural performance.
The technical scope of work includes:
1) Characterize the bond strength between deformed steel rebar and concrete;
2) Characterize the corrosion resistant properties of coated rebar in alkaline environments, including reinforced concrete; and
3) Study the behavior of beam-column concrete structures reinforced with enamel-coated rebar, develop and validate new design equations for the tension development lengthsof coated steel rebar in RC members.
This report summarizes the findings and recommendations on the use of various enamel coatings in RC structures. Pseudostatic tests with pullout, beam and column specimens were performed to establish the development lengthequations of enamel-coated steel rebar in lap splice and anchorage areas.
The splice length equation was validated by testing large-scale columns under cyclic loading. Salt spray, accelerated corrosion, ponding, potentiodynamic and electrochemical impedance spectroscopy (EIS) tests were conducted to evaluate the corrosion resistance and performance of enamel-coated steel rebar.
Significant Findings Steel-mortar cylinders failed in different modes from ductile steel pullouts to brittle concrete splitting and their bond strengths increased as the calciumsilicate component of a reactive enamel coating was increased. For example, the steel rods coated with pure enamel were consistently pulled out of the mortar whereasthe rods coated with 50/50 enamel coating consistently failed in splitting the mortar cylinder.As the mortar strength increased over time, the failure mode became less ductileand the slip before the steel-mortar bond stress reached at its maximum increased for specimens that failed in concrete splitting.