Effects of chlorides on setting time, hydration heat and hydration products of fresh slurry of cemented paste backfill

Abstract

Mine water is rich in various chlorides, which will inevitably affect the performance of the cemented paste backfill (CPB). In this study, the TAM Air isothermal calorimeter was used, the effects of typical chlorides (NaCl, CaCl2 and MgCl2) in mine water on the hydration heat and hydration heat flow in the solidification stage of fresh CPB were studied, and the effects of chlorides on the setting time of fresh CPB were analyzed. The hydration products of CPB samples containing different chlorides were tested by the X-ray diffractometer and thermal gravimetric analyzer. The results show that NaCl and CaCl2 can promote the early hydration reaction of CPB; and the promoting effect of CaCl2 is more significant; while MgCl2 consumes OH- in the solution and reduce the pH of the solution, thus inhibiting the early hydration reaction of CPB. With the increase of chloride concentration, the promoting effect of NaCl on the early hydration of the CPB first increases and then decreases, the promoting effect of CaCl2 increases constantly, and the inhibitory effect of MgCl2 also increases continuously. Besides, CaCl2 can significantly shorten the hydration time of CPB in the induction stage and acceleration stage, and the higher the CaCl2 concentration, the higher the cumulative hydration heat and the hydration heat release rate of CPB in the same hydration stage. This study comprehensively evaluates the influence of typical chlorides in mine water on the early hydration process and setting time of the fresh CPB, providing a reference for the clean utilization of mine water, fly ash, gangue and other solid wastes.