Accuracy of SOBO 20 in the Measurement of Salt on Winter Pavements

Abstract

The use of chemicals is essential in snow and ice control operations. Sodium chloride (salt) is normally used, because it is efficient, widely available, and relatively inexpensive. However, it is harmful for the environment if large quantities are used, and currently there is much attention placed on the importance of reducing the usage of salt while road serviceability and safety are maintained. Optimizing the use of salt requires accurately knowing how much salt is already on a pavement surface. Unfortunately, there is currently no well-documented method available to determine this quantity. SOBO 20 is one of the most common instruments used by the winter maintenance community to calculate salt amounts, although the reliability of the instrument has not yet been shown. The present work aims to fill this gap by carrying out measurements on brine (dissolved salt), dry salt particles, and recrystallized salt. The presented results support the conclusion that SOBO 20 is an accurate and reliable instrument for measuring brine on asphalt pavements. However, the instrument largely underestimates the amount of dry or recrystallized salt, and more attention should be paid when SOBO 20 is used on dry pavements. Compliance with the manufacturer's recommendations regarding the proportion of acetone in the measuring fluid is also essential for accurate salt readings. These results on the instrument performance should lead to a better understanding of salt distribution and action time.