Concrete Structures Exposed to Cyclic Wetting and Drying in Aba Metropolis, Nigeria

Abstract

An inspection study of concrete structures located within the Aba metropolis reveals that concrete exposed to cyclic rainfall deteriorates relatively faster, compared to those shielded by the cover of shelter, in corrosion.  This suggests that ions of chloride alongside dissolved ions of Carbon and Sulphur dioxide are prevalent in rainfall. This is because these dissolved substances penetrate exposed concrete to attack the concrete cover by a de-alkalizing process, or by destruction of the protective barrier to induce corrosion in embedded steel reinforcement. However, attempts to predict the service life of exposed concrete components using existing models of deterioration led to serious difficulties. This is primarily due to a lack of a sufficiently simple functional description of the cyclic attack of rain-borne ions, especially of chlorides. For a simple and accurate description of deteriorations in reinforced concrete exposed to cyclic wetting and drying, this study focuses on developing an empirical algorithm capable of simulating chloride penetration in concrete, considering the effect of concrete mix-design on sorptivity when sorption coupled with diffusion is the mode of transport.  For verification, a comparison is made between values calculated using an advanced model and values obtained from experimental simulations on samples of concrete of water/binder ratios 0.3, 0.4, 0.5 and 0.6, prepared from CEM 11/A-L 42.5R and granite aggregates of size 19mm. Very good agreement exists between values calculated using the advanced model and values obtained from experimental simulations.