Macro-cell and Micro-cell Corrosion of Steel in Concrete with Different Interfacial Transition Zones (ITZ) and Variations of Seawater Concentrations

Abstract

A comprehensive research examination was conducted to evaluate the chloride entrance in concrete by measuring the macro-cell and micro-cell corrosion of steel bars with varying interfacial transition zones and seawater concentrations. The interfacial transition zones were made by applying cement coating around the steel bars having different water-cement ratios and distinctive chloride concentrations. The study included ten scenarios and utilized cylindrical and prism examples, including a controlled case with uncoated steel rebar. The prism specimens comprised of three segmented steel bars and one continuous bar that were electrically connected to the outside of the specimens. This arrangement encouraged the steady observing of macro-cell corrosion current for 60 days utilizing a data logger. Taking after the measurement of macro-cell corrosion, the samples went through Limited wetting in a highly humid environment (99%), even with temperature variations (20°C to 40°C), resulted in minimal steel corrosion. However, submersion in seawater at 40°C caused rapid microcell corrosion, emphasizing the crucial role of electrolytes in accelerating the process. During these cycles, various parameters were measured, including half-cell potential along the steel bar, concrete resistance, macro-cell and micro-cell corrosion, and chloride concentration. A portable corro-map device was used to examine the micro-cell corrosion of the steel bars at 10- day intervals. After all examinations, the specimens were carefully cracked, and the steel bars were collected to assess the corroded area. Also, deposits were analyzed utilizing a Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX). Regardless of the specific case studied, macro-cell corrosion exhibited a consistent trend of decrease. Conversely, micro cell corrosion displayed a tendency to increase with time. Coating steel bars initially showed promise in reducing corrosion, acting as a barrier against chloride ions. However, increased seawater content within the coating led to higher corrosion. This suggests coating degradation, possibly from chloride damage or pathways created by imperfections. The outcomes have implications for the durability of reinforced concrete. SEM revealed more voids and EDX confirmed rust at the steel-coating interface with higher water-cement ratio, however deposition of potentially ettringite, calcium hydride, and calcium monohydrate may reduce macro-cell corrosion.