Study of Alternating Current Impedance of Basic Magnesium Sulfate Cement

Alternating current impedance has been used to study effects of hydration stages and molar ratio on the pore structure and hydration characters of basic magnesium sulfate cement. The alternating current impedance spectra of at early hydration almost appears as a straight line because none crystal hydration phases form. And it appears high frequency semicircle at late hydration stage because of decreasing of porosity and amount of 5Mg (OH) 2 ·MgSO 4 ·7H 2 O gradually form with ages. Besides, alternating current impedance spectra differences among basic magnesium sulfate, magnesium oxysulfate and magnesium oxychloride cement have been studied. These differences indicate that additives such as citric acid may change the structure and charge characteristics of MgO hydration layer which make tends to form more 5Mg (OH) 2 ·MgSO 4 ·7H 2 O phase in basic magnesium sulfate cement than that in magnesium oxysulfate cement. The higher pore solution resistance of BMS cement is the main factor of better steel-protection.