Correlation of microstructure, electrical properties and electrochemical phenomena in reinforced mortar. Breakdown to multi-phase interface structures. Part I: Microstructural observations and electrical properties D.A. Koleva a, ⁎ , K. van Breugel a , J.H.W. de Wit b , E. van Westing c , O. Copuroglu a , L. Veleva d , A.L.A. Fraaij a a Delft University of Technology, Faculty of Civil Engineering and Geosciences, Section Material Science, Stevinweg 1, 2628 CN Delft, The Netherlands b Delft University of Technology, Faculty 3mE, Department of Materials Science and Engineering, Mekelweg 2, 2628 CD Delft, The Netherlands c Netherlands Institute for Metal Research, Mekelweg 2, 2628 CD Delft, The Netherlands d CINVESTAV-Merida, Applied Physics Department, Carr. Ant. A Progreso Km.6, C.P. 97310, Merida, Yuc., Mexico ARTICLE DATA ABSTRACT Article history: Received 8 December 2006 Accepted 22 January 2007 Reinforced mortar and concrete are multi-phase composite materials at different levels of aggregation. In the framework of an extensive experimental study on cathodic protection (CP) efficiencies, the authors have investigated the electrochemical phenomena of steel reinforcement corrosion in aggressive environments by means of Electrochemical Impedance Spectroscopy (EIS). Microscopic and image analysis techniques render possible quantitative characterization of the composite microstructure at various interfaces, including structural morphology of steel corrosion and cement hydration products, pore structure, as well as the interfacial transition zones between cement paste and aggregate or bulk cementitious matrix and steel. This work aims to explore the microstructure alterations of the bulk mortar matrix and the steel/cement paste interface in reinforced mortar, relevant to corrosion and cathodic protection and compare to reference (non-corroding) conditions. Further, the morphological aspects, chemical composition and distribution of corrosion and hydration products are discussed in terms of modifying the material characteristics as consequence of the conditioning regimes. Both chloride-induced corrosion and CP are found to exert influence on the bulk material and the relevant interfaces, thus affecting the electrical properties and electrochemical characteristics, derived by EIS measurements. The correlation between EIS measurements and microstructure investigations allows breaking down the electrical properties of reinforced mortar during the corrosion process to the micro-level. © 2007 Elsevier Inc. All rights reserved. Keywords: Corrosion EIS Multi-phase interfaces Pore structure Reinforced concrete 1. Introduction Corrosion of embedded steel in concrete is of significant importance as far as durability and safe operation of reinforced concrete structures are concerned. Both corrosion process and protection techniques based on electrochemical methods (realkalization, desalination, cathodic protection) are influencing the material structure on macro- and micro-level. MATERIALS CHARACTERIZATION 59 (2008) 290 – 300 ⁎ Corresponding author. Tel.: +31 15 278 7451; fax: +31 15 278 8162. E-mail address: D.A.Koleva@TUDelft.nl (D.A. Koleva). 1044-5803/$ – see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.matchar.2007.01.015