METALS AND MATERIALS International, Vol. 12, No. 4 (2006), pp. 323~329 Analysis of Corrosion Resistance Behavior of Inhibitors in Concrete using Electrochemical Techniques Ha-Won Song * and Velu Saraswathy School of Civil and Environmental Engineering, Yonsei University, 134, Sinchon-dong, Seodaemun-gu, Seoul 120-749, Korea Reinforced concrete is one of the most durable and cost effective construction materials. However, in high chloride environments, it can suffer from corrosion due to chloride induced breakdown of the normal passive layer protecting the reinforcing steel bars inside concrete. One means of protecting embedded steel rein- forcement from chloride induced corrosion is the addition of corrosion inhibiting admixtures. In the present investigation, various inhibitors such as sodium nitrite, zinc oxide, mono ethanol amine, diethanolamine, and triethanol amine have been used in concrete in different percentages. Their effectiveness was then studied using various electrochemical techniques such as rapid chloride ion penetration test, open circuit potential measurement, electrochemical impedance measurement, potentiodynamic polarization measurement, and gravi- metric weight loss measurement. The results thus obtained indicate that the addition of inhibitors enhances the corrosion resistance properties. Key words: inhibitors, concrete, chloride, diffusion, corrosion resistance 1. INTRODUCTION Corrosion of steel rebars in concrete is a serious problem from both economical and structural integrity standpoints. It is well known that steel in concrete is protected from corro- sion by a microscopically thin oxide layer that is formed in the highly alkaline condition of the concrete pore solution [1,2]. This insoluble and highly stable protective film sup- presses iron dissolution to negligibly low values. However, steel corrosion, even in well-constructed concrete, can be active when chlorides continuously accumulate at the depth of the steel. Once corrosion initiates, it propagates rapidly. Subsequent corrosion of steel produces rust products, which have a volume 3-8 times greater than that of the original metal [3]. This generates stress, causing cracking and spal- ling of the concrete cover, which further accelerates corro- sion. In order to minimize the corrosion processes a number of procedures can be employed. Among them, the use of a inhibitors is considered as a promising solution for corrosion control of rebars [4-7]. There are basically three groups of inhibitors: anodic, cathodic, and mixed inhibitors. Anodic inhibitors form an insoluble protective film on anodic surfaces to passivate the steel and cathodic inhibitors form an insoluble film as an oxygen-barrier or an insulator on the cathodic surface of the steel..Passivating inhibitors such as nitrites represent special types of anodic inhibitors and they are generally very effec- tive inhibitors if present in sufficient concentrations [8]. Mixed inhibitors influence both the anodic and cathodic reaction sites by forming an adsorptive film on the metal sur- face. These adsorption type inhibitors are typically organic compounds (e.g. amines and fatty acids). Research on corrosion inhibitors has increased substan- tially during the last 20 years and various chemicals have been investigated, including benzoates of amines and mor- pholine [9]. Amines and alkanolamines and salts thereof have been described and patented for different applications such as for the protection of steel in cementitious matrices [10,11]. Calcium nitrite-based corrosion inhibitors have been widely used since the mid-1970s. A prominent inhibiting effect has been reported in the majority of previous studies [12-16], showing an increase in the chloride threshold level and in the corrosion-free life of concrete structures. Notably, calcium nitrite is preferred over other corrosion inhibitors (sodium nitrite, sodium benzoate), because of its compatibil- ity with concrete properties. When added to concrete, sodium nitrite and sodium benzoate lower concrete strength [17], while the inhibition effect of stannous chloride is mar- ginal [18]. *Corresponding author: song@yonsei.ac.kr