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51318-11195-Criteria for Protective Film Growth on Carbon Steel Rebar in a Carbonation Process

This research was to determine if an iron carbonate (FeCO3) layer can be effective for prevention of CO2 corrosion of steel rebars, associated with production and use of carbonated calcium silicate cement-based concrete.

Product Number: 51318-11195-SG
Author: Yoon-Seok Choi / K. Channa R. De Silva / Xiang Yong / David Young / Srdjan Nesic
Publication Date: 2018
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The motivation behind this research was to determine if an iron carbonate (FeCO3) layer can be effective for prevention of CO2 corrosion of steel rebars, associated with production and use of carbonated calcium silicate cement-based concrete. Laboratory scale experiments were conducted on optimizing the conditions utilized to form a protective FeCO3 layer on reinforcement steel by controlling solution chemistry, temperature, and surface condition. Subsequently, the rebar with protective layers formed under different conditions was exposed to a 3.5 wt.% NaCl solution in air, representative of an extreme service condition. The corrosion rates were assessed electrochemically using the linear polarization technique. The surface morphologies of the steel and coating were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Iron carbonate formed on sandblasted rebar had the lowest corrosion rates (<0.2 mm/y) under the service condition, while the other surface conditions comprising of a mill scale had corrosion rates in excess of 0.3 mm/y. Future work will emphasize modifying the iron carbonate coating to counter its susceptibility to degradation in oxidizing environments.

Key words: Concrete, carbonation, steel rebar, CO2 corrosion, FeCO3 coating.

 

The motivation behind this research was to determine if an iron carbonate (FeCO3) layer can be effective for prevention of CO2 corrosion of steel rebars, associated with production and use of carbonated calcium silicate cement-based concrete. Laboratory scale experiments were conducted on optimizing the conditions utilized to form a protective FeCO3 layer on reinforcement steel by controlling solution chemistry, temperature, and surface condition. Subsequently, the rebar with protective layers formed under different conditions was exposed to a 3.5 wt.% NaCl solution in air, representative of an extreme service condition. The corrosion rates were assessed electrochemically using the linear polarization technique. The surface morphologies of the steel and coating were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Iron carbonate formed on sandblasted rebar had the lowest corrosion rates (<0.2 mm/y) under the service condition, while the other surface conditions comprising of a mill scale had corrosion rates in excess of 0.3 mm/y. Future work will emphasize modifying the iron carbonate coating to counter its susceptibility to degradation in oxidizing environments.

Key words: Concrete, carbonation, steel rebar, CO2 corrosion, FeCO3 coating.

 

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