The composition of the exposed weathering steel is presented in Table 1. The chemical composition of alloying elements was confirmed by inductively coupled plasma optical emission spectroscopy (ICP-OES). The specimen dimensions are 100 mm © 50 mm © 3 mm. The specimens were abraded with 800 # SiC paper, rinsed with water and acetone, dried, weighed and kept in a moisture free rust were carried out using a TA SDT Q600 thermal analyser at a heating rate of 5°C/min from room temperature to 1000°C in an air atmosphere. The specific surface area SA of the rust were determined using N2 adsorption/desorption studies with quanta chrome system at 77 K. Before the adsorption studies, the samples were degassed with N2 at 100°C for 12 hours. The SA and pore size distributions were calculated by using Brunauer-Emmet-Teller (BET) and Barret-Joyner-Halenda (BJH) methods, respectively.