Experimental Study on Chloride Binding of Slag-Blended Portland Cement with Different Slag Ratios

Abstract

This study examined the chloride binding properties of slag-blended cement at different replacement ratios with two water-to-binder (w/b) ratios and two curing temperatures. Hydrated samples were immersed in NaCl solutions, and bound chloride at equilibrium was determined, respectively. It is found that at each w/b and temperature, chemically and physically bound chloride increased with increasing slag ratio up to 50%, whereas a further increase of slag ratio to 70% tended to reduce chloride binding. Physically bound chloride accounted for a major portion in total binding. Moreover, Ca(OH)2 content and slag reaction degree were analyzed, indicating that slag reaction degree decreased with increasing slag ratio. According to the results, the influence of slag ratio on chloride binding is discussed. The relatively low chloride binding at 70% slag ratio is partially attributed to the low reaction degree of slag, resulting in a lower amount of C-S-H and AFm phase. It is also inferred that the decreased physical binding at 70% slag ratio is closely related to the changed surface electrical property of C-S-H.