AC Impedance Characteristics Of Cemented Soil Contaminated By Sulfuric Acid And Sodium Sulfate

Taking cemented soil contaminated by sulfuric acid and sodium sulfate as the research object, based on pollution or not, different pollution components and content, the AC impedance and unconfined compressive strength have been measured through laboratory experiment. Considering age time effect, the quantitative relationship between AC impedance parameters and strength under different contaminative condition has been proposed. The main conclusions show as follows:(1) In Bode model figures, impedance values decrease with increasing current frequency; and the extent of the decreased impedance values are lesser at early-age, whereas the extent of that are greater at late-age. In other words, the percent frequency is smaller at early age than at late-age.(2) In Bode phase angle figures, phase angles first decrease and then increase with increasing current frequency, and that reach the minimum value when the current frequency is104Hz. At high frequencies, the phase angles increases with increasing age, but there is no rule at low frequencies. (3) In Nyquist figures, when the current frequency is higher, the image part Z"is large, the value of Z" first decreases, then increases, and finally decreases, along with a decrease in current frequency.(4) The unconfined compressive strength of the cemented soil increases with increasing logarithm of age. The strength gradually stabilize when the age time are longer than90days.(5) The unconfined compressive strength of the cemented soil first increases then decreases with increasing contaminant content, it reaches the maximum value when the content of sulfuric acid and sodium sulfate are10g/kg.(6) The impedance values increases with increasing logarithm of age time, the correlation are very good. The relationship between strength and age time follow the same rule. The results show that there is some correspondence between the compressive strengths and their resistance values.(7) The impedance values first decrease and then increases with increasing the sulfate content, and get the minimal values when the sulfuric acid content is10g/kg; Whereas the impedance values decrease with increasing content of sodium sulfate. There are different rule between the two different contaminants.(8) The unconfined compressive strength increase with linear increasing electrical resistivity. The predictor equation of unconfined compressive strength taking into account the current frequency is derived. The resistivity evaluation criterion of cemented soil contaminated by sulfuric acid and sodium sulfate is proposed. The variation trend of strength is been discussed.(9) The results show that, the AC impedance parameters are closely related to the pollution components, content, age time and unconfined compressive strength. The impedance method make up for the deficiency and limitations of the traditional method. This study will strongly promote the AC impedance method in the application of the geo-environmental engineering.