Study on Early Hydration Behavior and Mechanical Properties of Basic Magnesium Sulfate Cement Using Electrodeless Resistivity Measurements

The effect of early hydration behavior on the long-term performance of cement is profound, but its study is lacking. The early hydration behavior and mechanical properties of basic magnesium sulfate (BMS) cement were investigated by using electrodeless resistivity test combined with compressive strength measurement, XRD, SEM and Mercury intrusion porosimetry (MIP). As a result, the early hydration process of BMS cement can be clearly divided into three stages including induction period, acceleration period and deceleration period according to the resistivity variation curve. A linear correlation between the resistivity and setting time of BMS cement is established. Thus the initial setting time and final setting time of BMS cement can be estimated using feature point A (the time that the growth rate of resistivity starts rising) and feature point B (the time for the maximum growth rate of resistivity) on the differential curve of electrical resistivity, respectively. Moreover, a linear fitting equation between the resistivity (24 h) and compressive strength of BMS cement curing for 28 d is determined. The correlation coefficient is as high as 0.9979. Using the fitted linear equation, the long-term strength (28 d) of BMS cement can be precisely predicted by the measured resistivity (24 h). This study provides us a feasible, accurate and in situ method for understanding the early hydration behavior and quality monitoring of BMS cement.