Study on early hydration and properties of basic magnesium sulfate cement using electrodeless resistivity measurements

The effect of early hydration behaviour on the long-term performance of cement is profound, but such studies are lacking. The early hydration behaviour and mechanical properties of basic magnesium sulfate (BMS) cement were investigated using an electrodeless resistivity test combined with compressive strength measurement, X-ray diffraction analysis, scanning electron microscopy and mercury intrusion porosimetry. According to the resistivity variation curve, the early hydration process of BMS cement can be divided into three stages (induction period, acceleration period and deceleration period). A linear correlation between resistivity and setting time was established. The initial and final setting times of BMS cement could thus be estimated using two points on the differential resistivity curve - the time when the resistivity growth rate starts to increase and the time of maximum resistivity, respectively. A linear fitting equation between resistivity at 24h and compressive strength of the BMS cement after curing for 28days was determined. The correlation coefficient was high (0.9979). Using the equation, the long-term strength (28days) of BMS cement could be precisely predicted from the measured resistivity at 24h. This study provides a feasible, accurate and in situ method for understanding the early hydration behaviour and quality monitoring of BMS cement.