This paper presents a mathematical model for the simulation of physical phenomena that appear in the hot dip galvanized rebars corrosion process, compared with the bare steel rebar in concrete, under the attack of chlorides and freeze-thaw cycles. The physical and corresponding mathematical model are presented and the system of governing equations along with initial and boundary conditions were established. The associated numerical model and the numerical methods of discretization and solving the differential equations system on which the mathematical model is based are also presented. The following parameters were considered: concrete humidity, chloride ions content and temperature variation. The time until corrosion initiation, rebar’s diameter reduction, the advance of the corrosion products front and corrosion current variation were determined, according to environment conditions, exposure time and type of rebar used.