Incidencia de la adición de cenizas volantes en la durabilidad de las estructuras de hormigón armado

Concrete fly ash adition and durability of structures

One of the main causes of the damage of concrete structures is the corrosion of its reinforcements, due to the loss of effectiveness of concrete protection. The main agents responsibles for reinforced corrosion are usually the chloride ions and/or the concrete carbonation caused by atmospheric CO₂. Both agents generally come from the outside. The use of flyashes as partial substitute for cement, added directly during the casting process is a practice which has increased a lot in recent years. The performance of this materials whithin the field of durability are not still well understood. This paper brings a study of the incidence of the addition of flyashes on the durability of reinforcements and concrete against the penetration of chloride ions in agressive surroundings, namely sea water. The studies have been carried out on specimens exposed both to the natural process and to laboratory conditions. The obtained results show a beneficial effect of the addition of flyashes against the penetration of chloride ions. A delay in corrosion initiation as well as lower corrosion rates were noticed. This phenomenon is explained by the lower contents of the soluble chloride ion in the pore water phase as a consequence forming the Friedel Salt. At the same time, this products gradually fill the pores, which results in : eventual lower rate of the penetration of the chloride ion in the concretes elaborated with flyashes; porosity refinement and as a consequence an increase of the material durability.