Sodium Chloride Dihydrate - A Potential Cause of Slippery Accidents

From a thermodynamic point of view, it can be expected that sodium chloride dihydrate (hydrohalite, NaCl2H2O) will form on winter roads under certain conditions at temperatures below 0.1¢®C. In order to elucidate whether or not the formation of hydrohalite on the pavement can explain the phenomenon of ice appearing to be resistant to road salt, a comparative study has been made on a number of different surfaces measuring the friction index.

The friction measurements were performed with a Portable Skid-Resistance Tester. Discontinuous surfaces consisting of small islands of hydrohalite was classified as potentially slippery surfaces. It is therefore possible that the formation of hydrohalite contributes to accidents on slippery roads.