Graduation Year

2019

Document Type

Thesis

Degree

M.S.C.E.

Degree Name

MS in Civil Engineering (M.S.C.E.)

Degree Granting Department

Engineering

Major Professor

Alberto A. Sagüés, Ph.D.

Co-Major Professor

Christopher L. Alexander, Ph.D.

Committee Member

Rajan Sen, Ph.D.

Keywords

Corrosion Resistant Alloys, Durability, Electrochemistry, Propagation Stage, Reinforced Concrete

Abstract

Stainless steel (SS) has emerged as an alternative corrosion-resistant reinforcement in concrete instead of the commonly used carbon steel (CS). The biggest advantage of SS is that it takes more time for corrosion to initiate than for CS. An additional benefit from the use of SS in concrete may be derived from the period after the corrosion started until the concrete structure reaches a limit state. This period is called corrosion propagation stage (CPS) and it has been hardly studied in SS reinforced structures. The duration of this period could be related, among other factors, to the morphology of corrosion of stainless steel in concrete. In some instances, the corrosion detection methods for CS have been used on SS reinforced structures to estimate the corrosion condition. However, there is uncertainty if these methods can detect corrosion in SS reinforced structures properly. This investigation was organized in two parts: literature review and experimental work.

The literature review indicated among other findings that the duration of the CPS of SS’s embedded in concrete may be estimated to be in the order of several decades. High-grade SS’s would have a longer duration of the CPS. The review also indicated that even localized corrosion of SS reinforcement may induce concrete cracking. The literature also suggested that the corrosion detection on SS reinforced concrete may require a combination of conventional methods (half-cell potential) and advanced electrochemical techniques such as Electrochemical Impedance Spectroscopy, Electrochemical noise, etc.

The experimental work focused on further determining whether corrosion of SS in concrete can be detected by methods traditionally used for CS reinforcement, and to what extent localization of corrosion of SS compares with that of CS in concrete. The experiments consisted in accelerated corrosion testing of controlled anodic regions along concrete beams, for which tests were designed and initiated.

Martensitic UNS S41000 SS bars were partially embedded in chloride contaminated concrete (5.84% by weight of cement) to cause active corrosion. AISI 1018 CS was also used for comparison purposes. Traditional half-cell potential measurements on the reinforced concrete specimens were evaluated in comparison to that of advanced electrochemical impedance spectroscopy. Additional concrete resistivity monitoring gave an indication of the degree of the pore structure formation.

The traditional half-cell potential measurements on AISI 1018 CS reinforced concrete specimens appeared to be suitable to estimate the corrosion state of the reinforcement. However, there was uncertainty on the interpretation of the half-cell potential results and thus the corrosion state of UNS S41000 SS reinforced concrete specimens.

Low-dispersion corrosion rates values were found over large areas on SS and CS bars in concrete, but that SS embedded in concrete also seemed to develop instances of corrosion rate peaks. Among other findings, the duration of CPS of CS in concrete was estimated to be in the interval [6-59] years. Assuming that the CPS had been reached, SS specimens in concrete appeared to have a much longer duration of CPS than CS, with an interval [57-253] years. However, this assumption is likely not valid and more work is required to assess the CPS of SS reinforced concrete.

Download

Share

COinS