Investigation of Carbonation Profiles of a 60 Years Old Carbonated Concrete Specimens Subjected to Re-Alkalization
Investigation of carbonation profiles of a 60 years old carbonated concrete specimens subjected to re-alkalization
M.O. Mohsen1,*
1 College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar
Re-alkalization method is an electrochemical treatment which is commonly used to repair carbonated concrete elements. This method prevents further reinforcement corrosion by increasing the PH of the element which results in maintaining the reinforcement passivation. In this paper, the re-alkalization sacrificial anodes method is applied to 60 years old carbonated concrete specimens extracted from a demolished building in the state of Qatar which. The carbonation profiles in the specimens are studied by Thermogravimetric (TGA), phenolphthalein and Gammadensimetry analysis before and after re-alkalization. The thermogravimetric analysis (TGA) was supplemented with chemical analysis (CA) to proportion the sample cement content, the sand content and to correct the TGA results. These measurement methods provided a qualitative as well as a quantitative view of the carbonated portions. The results illustrated a significant change in the structure of the carbonation profiles after the re-alkalization process. However, repassivation of the steel rebars could not be demonstrated.
Keywords: Re-alkalization, Carbonation, pH INTRODUCTION Steel bars in reinforced concrete are protected from corrosion by the highly alkaline environment inside the concrete (pH≈13). If the pH decreases in the environment of the reinforcement, this protection ceases and the steel bars can corrode. Consequently, the rusting of the reinforcement usually leads to a severe reduction of the durability of the structure. One of the main processes facilitating the destruction of the protection by alkalinity is carbonation, i.e. the reaction of alkaline constituents of the concrete with atmospheric carbon dioxide to produce carbonates. The main carbonation reaction may be described by
CO2 + Ca(OH)2
M.O. Mohsen1,*
1 College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar
Re-alkalization method is an electrochemical treatment which is commonly used to repair carbonated concrete elements. This method prevents further reinforcement corrosion by increasing the PH of the element which results in maintaining the reinforcement passivation. In this paper, the re-alkalization sacrificial anodes method is applied to 60 years old carbonated concrete specimens extracted from a demolished building in the state of Qatar which. The carbonation profiles in the specimens are studied by Thermogravimetric (TGA), phenolphthalein and Gammadensimetry analysis before and after re-alkalization. The thermogravimetric analysis (TGA) was supplemented with chemical analysis (CA) to proportion the sample cement content, the sand content and to correct the TGA results. These measurement methods provided a qualitative as well as a quantitative view of the carbonated portions. The results illustrated a significant change in the structure of the carbonation profiles after the re-alkalization process. However, repassivation of the steel rebars could not be demonstrated.
Keywords: Re-alkalization, Carbonation, pH INTRODUCTION Steel bars in reinforced concrete are protected from corrosion by the highly alkaline environment inside the concrete (pH≈13). If the pH decreases in the environment of the reinforcement, this protection ceases and the steel bars can corrode. Consequently, the rusting of the reinforcement usually leads to a severe reduction of the durability of the structure. One of the main processes facilitating the destruction of the protection by alkalinity is carbonation, i.e. the reaction of alkaline constituents of the concrete with atmospheric carbon dioxide to produce carbonates. The main carbonation reaction may be described by
CO2 + Ca(OH)2
References: Tong Y, Bouteiller V, Marie-Victoire E, and Joiret S, 2012. Efficiency investigations of electrochemical realkalisation treatment applied to carbonated reinforced concrete — Part 1: Sacrificial anode process. Cement and Concrete Research, Volume 42, Issue1 Pages 84-94. Villain G, Thiery M, and Platret G 2007. Measurement methods of carbonation profiles in concrete: Thermogravimetry, chemical analysis and gammadensimetry Shear characteristics and design for high-strength self-consolidating concrete. Journal of Structural Engineering, ASCE, 136(8), pp 989-1000. Figure5. Hexagonal crystals at specimen