Relative Effects of Sodium Chloride and Magnesium Chloride on Reinforced Concrete: State of the Art

Magnesium chloride (MgCl₂) use for snow and ice control is becoming a well-established practice but has been limited to the past 10 years. Impacts associated with sodium chloride (NaCl) use are well documented, but concerns have been raised regarding the potential effects of MgCl₂ use on concrete and steel reinforcement. The British Columbia Ministry of Transportation intended to establish guidelines for MgCl₂ use by highway maintenance contractors. Information was gathered from available literature and interviews with academia and industry. Generally, few studies directly and comprehensively address the topic, and although significant research efforts are currently under way, results are not expected for several years. Past laboratory studies suggest that MgCl₂ reacts with cement paste to reduce concrete strength and degrade concrete. Studies also suggest that chloride ions associated with MgCl₂ have higher diffusion coefficients than those associated with NaCl. Field studies are limited, but laboratory coefficients for chloride ion diffusion correlate with results of a field study conducted in Montana. Higher chloride diffusion coefficients can reduce the initiation time for chloride-induced corrosion of reinforcing steel. No evidence to date directly links the increased deterioration of a structure to MgCl₂ use; however, the history of use is short, and caution is recommended until additional studies can establish more evidence.