Graduation Year

2010

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Alberto A. Sagüés, Ph.D.

Keywords

Zinc, Impedance, Disbondment, Epoxy, Polarization

Abstract

This investigation is an examination of the behavior of dual coated reinforcing steel (DCR) with defects in the polymer coating exposing the only zinc layer in simulated concrete pore solution with and without chlorides. The intentional defects simulated the condition typically experienced by the rebar in service. Specimens were tested at open circuit potential, +100 mV, -500 mV, and -1000 mV for 30 to 100 days. The results were compared with that from previous DCR investigation with to-steel defects and epoxy-coated rebar (ECR). DCR with to-zinc defects had extensive corrosion damage when under strong anodic polarization and exposed to chlorides and was similar to that seen for DCR with to steel defects. The freely corroding (OCP) to-zinc DCR specimens in solutions both with and with no-chlorides experienced initially very active dissolution which ended after ~1 day. The zinc exposed at the coating breaks was not completely consumed even after 100 days and there was no visible corrosion product accumulation. This may be due to the formation of a calcium hydroxyzincate passive film and shows that the zinc passivates in alkaline solutions without the benefit of a crevice environment. The DCR with to-steel defects and the DCR with to-zinc defects had similar amounts of disbondment for all test conditions. Notable disbondment was seen only in highly anodic polarization regime with chlorides and was due to large amounts of solid corrosion product formation. These results suggest then that the overall process of zinc wastage in DCR in concrete pore water is not likely to be rapid, which would be beneficial to extending the period in which the barrier and galvanic properties of the zinc are maintained.

Share

COinS