The electrochemical frequency modulation technique is an electrochemical technique used to determine the corrosion rate in steel embedded in concrete made with mixtures of fly ash and steel slag alkali activated and exposed to accelerated carbonation. This technique uses two signals input AC voltage; and has the quality of each signal has a different frequency, these signals are applied to reinforced concrete. As the current is a nonlinear function of the potential, the system responds in a nonlinear manner to the excitation potential is obtained as a measurement of response current in this response sum components they are jointly involved difference and multiples of the input frequency. This technique uses causality factors, which can verify experimental data, finds the exact values of the corrosion current density, the corrosion current and obtaining the cathodic and anodic slopes. The characterization of cementitious materials, was performed by X-ray diffraction. It was determined that mixtures containing steel slag generate low corrosion rate values.