• Schutter, Geert De
• Belie, Nele De
• Alava, Hugo Eguez
• Tsangouri, Eleni

Abstract

Penetration of chloride ions into concrete is a complex topic. These ions together with other dissolved chemical species can penetrate into cementitious materials by convection through capillary pores or cracks. Prolonged periods of drying followed by re-wetting can provoke a similar transport mechanism. Saturated cement based materials experience diffusion of water dissolved ions. Ions in the diffusing solution experience chemical interaction with a hydrated cement paste. Some ions are physically adsorbed, others react chemically and part remain free in the solution. This turns the transport into a reactive form of diffusion. The nano-pores which are part of the cement gel, act as sinks for the intruding aggressive chlorides. When concrete is subjected to splitting tensile stresses and a critical stress ratio is surpassed the presence of micro-cracks modifies the transport of chlorides within this material. It was noticed that the chloride content of concrete decreased in zones close to the surface specially where the main pattern of micro-cracks follows the loading plane. It was also observed a secondary micro-crack system which develops perpendicularly to the main splitting-crack system and is connected to it. It was found that this secondary system was also responsible of lowering the level of the chloride content in regions close to the surface even at unexpected distances located far away from the direct influence of the splitting plane. The presence of an inner peak of chloride was also observed, which represents the extent of the damaged or altered zone. This region will be called in this paper as the convection zone. It is believed that the form of the obtained chloride profiles are influenced by the type and amount of binder utilized. Thus, some similarities were found in all the studied concretes such as the formation of a convection zone. On the other hand the level of chloride content and the shape of the profile seem to vary depending on BFS replacement of OPC or when high sulfate resistant cement (HSR) is used as a single binder.

Topics

• impedance spectroscopy
• pore
• surface
• crack
• cement
• drying
• chloride content