Correlation of microstructure, electrical properties and electrochemical phenomena in reinforced mortar. Breakdown to multi-phase interface structures. Part I: Microstructural observations and electrical properties

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.