[en] A new corrosion testcell concept to study macroelement activity on concrete covered steel rebars is presented. This test cell makes it possible for the first time to divide an active corroding central area from its passive surrounding with definite variable area proportions. With help of this testcell practical and theoretical aspects of steel rebar corrosion in concrete were examined in a more detailed way: a) The possibility and limitations of concrete-building inspection-service with frequency response analysis (FRA) b) Macroelement impedance data and resulting physical models should be brought in a reasonable connection with the existing theory. Those under laboratory conditions performed FRA showed a strong dependence upon the area proportion between the corroding area and its passive surrounding within the corrosion macroelement (CME). This area-ratio is throughout presented as an unknown quantity in the practice of concrete-building inspection-service. Impedance spectra of such different active/passive area-ratios generally showed at the first view 2 time constants. These two time constants cannot necessarily be directly assigned to the basic electrochemical reaction such as the metal dissolution reaction and the oxygen reduction reaction. This has been discussed for the dynamical system analysis of an appropriate electrical simulation-circuit, mainly consisting of two parallel RC-circuits. (author) 20 refs., 9 figs