Characterization of carbonation behavior of fly ash blended cement materials by the electrochemical impedance spectroscopy method

The carbonation behavior of fly ash blended cement materials is studied by the electrochemical impedance spectroscopy (EIS) method, and a novel equivalent circuit model Rs(Q1(Rct1W1)) (Q2(Rct2W2)) is proposed to investigate the influence of fly ash on the carbonation process in the cementitious materials. The experimental results demonstrate that the diameter of the impedance arc in high frequency region increases as carbonation progresses. Increasing the amount of fly ash incorporated in the cement paste is also found to enlarge the high frequency arc. The carbonation process can be quantified by the parameter Rct2 extracted from the equivalent circuit model Rs(Q1(Rct1W1)) (Q2(Rct2W2)). It is found that the Rct2 value increases with increase in fly ash content. A linear relationship between the Rct2 value and the carbonation time is also observed. As a consequence, prediction of the carbonation depth of fly ash bended cement materials can be achieved through knowledge of the Rct2 value.