Michael L. Koenigstein

Corrosion Behavior of Enamel Coated Steel Rebar by EIS

In this study, the corrosion process of enamel-coated deformed rebar completely immersed in 3.5 wt.% NaCl solution was evaluated over a period of 84 days by EIS testing. Three types of enamel coating were investigated: pure enamel, 50/50 enamel coating, and double enamel. Surface condition of the enamel coatings that were intentionally damaged prior to corrosion tests was visually examined at different immersion times. After 84 days of testing, the damaged coating areas were characterized by SEM, and the corrosion products on and adjacent to the damaged areas were collected and analyzed by XRD. Corrosion initiated at the damaged locations with no undercutting of the coating observed. The 50/50 enamel coating had the least corrosion resistance, due to its interconnected pore structure, and prior damage drastically reduced the corrosion resistance of pure and double enamel coated rebar.

Blast Test of Full-Size Wall Barriers Reinforced with Enamel-Coated Steel Rebar

A type of enamel coating that contain hydraulically reactive calcium silicates have been developed to improve the performance and service life of steel used as reinforcement in concrete structures. To demonstrate the effect of enamel coating on the mechanical performance of concrete structures subject to blast loading, two wall barriers with identical dimensions, which were often used to keep the terrorism attack (such as car bomb attack) away from critical buildings, were fabricated and tested in a military base. One of the wall barriers was reinforced with coated rebar and the other with regular rebar. Four equivalent TNT weights, 4 lbs, 10 lbs, 30 lbs and 45 lbs explosive were applied to observe the deformation, cracking and failure mode of the two barrier walls. Generally, the test results indicate that the barrier wall reinforced with enamel coated rebar has much better integrity than that with regular rebar: fewer cracks on the front and back faces of the wall, more stress transferred to the steel rebar, and mitigated catastrophic failure of the wall. The new coating can be of great value in increasing the performance and the service life of defense-critical infrastructure.

Corrosion Resistance of a Sand Particle-Modified Enamel Coating Applied to Smooth Steel Bars

The protective performance of a sand particle-modified enamel coating on reinforcing steel bars was evaluated in 3.5 wt% NaCl solution by electrochemical impedance spectroscopy (EIS). Seven percentages of sand particles by weight were investigated: 0%, 5%, 10%, 20%, 30%, 50% and 70%. The phase composition of the enamel coating and sand particles were determined with the X-ray diffraction (XRD) technique. The surface and cross-sectional morphologies of the sand particle-modified enamel coating were characterized using scanning electron microscopy (SEM). XRD tests revealed three phases of sand particles: SiO2, CaCO3 and MgCO3. SEM images demonstrated that the enamel coating wetted well with the sand particles. However, a weak enamel coating zone was formed around the sand particles due to concentrated air bubbles, leading to micro-cracks as hydrogen gas pressure builds up and exceeds the tensile strength of the weak zone. As a result, the addition of sand particles into the enamel coating reduced both the coating and corrosion resistances.

Corrosion Performance of Reactive-Enamel Coated Reinforcing Steel

ACI Materials Journal, V. 109, No. 4, July-August 2012. MS No. M-2011-132 received May 16, 2011, and reviewed under Institute publication policies. Copyright

Deterioration of Enamel and Epoxy Coated Steel Rebar in 3.5 wt.% NaCl Solution

Reinforcing steel bars coated with pure enamel and fusion-bonded epoxy (FBE) were immersed in 3.5 wt.% NaCl solution for a period of 84 days. Predetermined damage of the coatings was created with a standard impact tester to study the coating resistance to potential damage caused during transportation and construction. Open-circuit potential and electrochemical impedance spectroscopy (EIS) tests were used to investigate deterioration processes of the two coating systems. An equivalent electrical circuit model was established to extract corrosion-indicative dielectric properties of enamel and FBE coatings from the EIS data. The change of coating capacitance over time was represented by a diffusion-controlled process. In comparison with the FBE coating with the same extent of damage, the enamel coating corroded sooner due to its thinner layer and porous microstructure, but deteriorated more slowly due to its robust bond with the steel substrate.