X. Ramon Novoa

Microstructural changes in a cementitious membrane due to the application of a DC electric field

The use of electromigration techniques to accelerate chloride ions motion is commonly employed to characterise the permeability of cementitious samples to chlorides, a relevant parameter in reinforced concrete corrosion. This paper is devoted to the study of microstructures changes occurring in mortar samples when submitted to natural diffusion and migration experiments. The application of an electric field reduces testing time in about one order of magnitude with respect to natural diffusion experiments. Nevertheless, the final samples microstructure differs in both tests. Impedance Spectroscopy is employed for real time monitoring of microstructural changes. During migration experiments the global impedance undergoes important increase in shorter period of time compared to natural diffusion tests. So, the forced motion of ions through the concrete membrane induces significant variations in the porous structure, as confirmed by Mercury Intrusion Porosimetry. After migration experiments, an important increase in the capillary pore size (10–100 nm) was detected. Conversely, no relevant variations are found after natural diffusion tests. Results presented in this work cast doubt on the significance of diffusion coefficient values obtained under accelerated conditions.

Impedance based method for non-contact determination of the corrosion rate in buried metallic structures

ABSTRACT The electrochemical impedance spectroscopy has been employed in the present investigation to assess the polarisation resistance of carbon steel rebars in different electrolytes. The measurements have been performed using the classical 3-electrode arrangement, where the element under test is the working electrode of the potentiostat, and a new 4-electrode arrangement where the element under test is floating from the electrical point of view (e.g. contact-less technique). The polarisation resistance values obtained using the contact-less technique are very close to those obtained using the traditional 3-electrode arrangement. The measurements, performed in a wide range of electrolyte resistivity values (including mortar) have thus demonstrated the applicability of this new technique for on-site corrosion rate assessment.

Electrochemical behaviour of Iron in chlorinated alkaline media: the effect of slurries from granite processing

Porrino is a well known zone of quarry and stone working of the SW of Galicia, Spain. In granites working processes 3 × 105 ton year-1 of granite powder are generated in this area, causing an important environmental problem. This dust has proved to be an efficient addition to high-strength concrete to improve mechanical properties. Nevertheless, no works have been published concerning the effect of this admixture in the passivation of steel reinforcements. The objective of the present work is to analyze the electrochemical behaviour of iron and carbon steel electrodes in alkaline solutions resulting from these slurries. The growth and evolution of the passive layers formed on the tested electrodes are studied by Cyclic Voltammetry and Electrochemical Impedance Spectroscopy. Scanning Electron Microscopy and X-ray powder Diffraction have been used for the morphological and chemical characterisation of the generated passive films. The effect of the presence of Cl- ions is also considered.

Characterization of Waterproofness in Ready-to-Wear Professional Garments

In the field of waterproof garments, there are commercial systems available that allow either fabrics or ready-to-wear garments to be tested, complying with existing testing standards. These standards and systems, however, do not account for some important effects, as for instance proper test ergonomics or the diagnosis of wrong sealing of seams, which are in fact very significant to the final quality of the product. In a previous work, the authors have presented the high-level design and development of a testing system that covers all aspects of waterproof garment testing. It is divided in a mechanical subsystem, consisting of a rain conditions emulator and a manikin that wears the clothes under test, and an electronic subsystem, consisting of sensors, an artificial vision environment and the associated elements in charge of all data acquisition, control and supervisory tasks. In this paper, the practical aspects of waterproofness testing are presented and discussed, with emphasis on the issues related to the set-up and integration of the electronic subsystem and, in particular, the humidity and water presence sensors