INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 8, ISSUE 12, DECEMBER 2019 ISSN 2277-8616 400 IJSTR©2019 www.ijstr.org Micro-Characterization Of Pure Mg And AZ91D Used As Sacrificial Anodes In Reinforced Cement Concrete Yogesh Iyer Murthy * , Sumit Gandhi , Abhishek Kumar, Abstract: Off-shore reinforced cement concrete structures are exposed to severe chloride atmosphere and are hence prone to corrosion. Prevention of corrosion of such structures by cathodic protection technique has evolved as a major method. Magnesium and its alloys are very commonly used as sacrificial anodes in this regard. The current paper investigates the micro-characterization of pure Magnesium (Mg) and AZ91D anodes used for cathodic protection of structural steel reinforcement in concrete slabs using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) after 270 days of embedment in concrete. The presence of inter-mettalics was found to decrease the rate of corrosion in AZ91D compared to pure Mg. Bare steel reinforcements with and without anodes were also tested in severe Chloride atmosphere for weight loss and tensile strength on different days and compared for 80 days. The tensile strengths and weight loss of bare steel reinforcements with anodes were found to be much less affected in chloride atmosphere, as against those without anode, indicating the effectiveness of the latter, although similar values of stresses were found for both Mg and AZ91D. The results of micro characterization, tensile strength and rate of corrosion can be used for optimal selection of anodes for different exposure conditions. Keywords: AZ91D, micro-characterization, cathodic protection, mechanical properties, steel, corrosion. ——————————  —————————— 1 INTRODUCTION The prevention of corrosion of steel in RCC structures is a herculean task, especially in marine atmosphere. Corrosion mitigation techniques include use of corrosion resistant steel re-bars [1], stainless steel and galvanized steel, thermosetting polymers [2], laminates and reinforced plastics [3], thermoplastics, non-metals like elastomers, use of inhibitors[4], paints[5,6], epoxy coatings[7], powder coating [8] and cathodic protection, each having inherent advantages and disadvantages. The selection of a suitable method largely depends on the degree of exposure of structure, economics and the discretion of the designer. Among the above mentioned methods of corrosion prevention, cathodic protection (CP) technique is unique as most of the other methods (except application of corrosion resistant steel re- bars and stainless steel and galvanized steel) involve coating of suitable material over the steel and subsequent embedment of steel in concrete. The peeling off such coatings while pouring of concrete is a common phenomenon resulting in the ingress of corrosion. On the other hand, CP involves the installation of suitable electrochemically active electrode as anode as an exterior member, designed for a suitable time period. The application of such anodes as exterior member aids in visual inspection and upon the completion of design period, or otherwise, the anodes can be conveniently replaced. Thus, precise monitoring of reinforcement is enabled. The commonly used anodes for CP of steel in concrete are Aluminum, Magnesium and Zinc anodes, in either pure form or as alloys in varying proportion [9]. The primary objective of the current investigation is thus to experimentally investigate the mechanical properties of steel which is electro-chemically in contact with Mg and AZ91D anodes in high chloride atmosphere, the rate of corrosion of the two anodes and to understand the micro structural features of the corroded anodes after significant days of embedment in concrete containing free chloride ions. The outcome of such experimental investigations is expected to aid in judicious selection of right anodes for excess chloride exposure condition. 2. EXPERIMENTAL SET-UP The current work is carried out in two stages. A set of experiment is carried out with bare steel reinforcements, while another set of experiments with reinforcements embedded in concrete containing free chloride ions. The experimental set up for both the cases is discussed below. 2.1 Experimental set up for bare steel in chloride atmosphere: In order to investigate the performance of pure Mg and AZ91D anodes on corrosion prevention of bare steel reinforcements three set of six steel reinforcements were tied together intact with centrally placed anode to complete the electrochemical cell as shown in Fig.1. All the samples were dipped in high chloride atmosphere of 7.5% NaCl in tap water with specifications shown in Table 1. Sample set one did not contain any anode; sample set two consisted of AZ91D anode while sample set three contained pure Mg anode. These samples were tested for weight loss, tensile strength and microstructure. ______________________________  Jaypee University of Engineering and Technology, Guna (India)  Motilal Nehru National Institute of Technology Allahabad (India)  Corresponding Author: yogesh.murthy@juet.ac.in