The behavior of Fe500-3 iron was studied in the interstitial solution of mortar concrete, formulated from sand, cement, water, admixtures and in the presence of a clay (attapulgite) added as corrosion inhibitor. Indeed, in most cases in Senegal, mixing water and sand used in concrete formulations for buildings are subject to no treatment. The study solution was synthesized from these concretes at the 3rd, 7th and 28th day of wet cure. Fe500-3 iron corrosion tests in the interstitial concrete solution were carried out by monitoring the free corrosion potential, Tafel polarization curves and electrochemical impedance spectroscopy measurement. The protective power of attapulgite was also evaluated by electrochemical methods with different levels of inhibitor (0 to 20%). The measurements reveal a probable attack of Fe500-3 iron at the 3rd and 7th day of cure in the absence of inhibitor and the protective effect of the interstitial solution of the concretes without inhibitor at the 28th day of cure by the formation of a protective layer on the iron surface. The results also showed the corrosion inhibition effect of the clay on the 3rd and 7th day of cure by the formation of a protective film on the surface of the metal. The layer thickness increases with the content of the clay. A maximum average inhibitory efficiency of about 87.8% was obtained at the 7th day of cure at the 20% clay content.