In recent years, several tests have been conducted with additives to road salt (such
as agricultural bi-products), with one of the purposes being reduction of the amount of salt used for winter maintenance. The Norwegian Public Roads Administration seeks to optimize salt usage in winter maintenance in order to minimize environmental impacts. In this respect there is a need for a better understanding of
how road salt additives can reduce usage of road salt. Focus is directed to the extension of the lifetime of salt on road surfaces.
This report describes the different mechanisms of salt removal from road surfaces and how salt additives possibly can affect these mechanisms. Following, it describes a case study performed in Norway to document the removal of salt with and without salt additives. Five tests have been performed where the change in salt amount is
described by over 1900 salt measurements.
An extended lifetime due to salt additives has not been found. In all tests, the lifetime
of salt with additive was about the same as the lifetime of salt without additives. On
wet road surfaces, where both the salt and the additive were dissolved, the salt loss
occurred by the same mechanisms; the spray of water from vehicles and possibly run-off. Under these conditions the additive had no possibilities to increase the
lifetime of salt.
On dry road surfaces, where the salt had crystallized due to evaporation of water,
salt remained on the road surface for a prolonged period of time, both with and
without the salt additive. In one case with favourable testing conditions, there were
no indications of salt loss after 30 hours, or 20 000 vehicle passages. This long lifetime quickly terminated when rain wetted the pavement.
In Norway, winter maintenance personnel appear to share a common opinion that “salt disappears when the road dries up”. This opinion, however, contradicts the measurements performed in this case study. There has been found clear indications that the instrument to measure salt (SOBO20) is unable to detect all salt that is
present in crystallized form. This underestimation of salt on dry surfaces may have
contributed to the opinion that “salt disappears when the road dries up”.
The similarity algorithm calculates how much two contents in the system are similar to one another. So far, similarity is calculated based on similarity of the project type, area of interest and user type. Generally, if two contents have more parameters in common they are more similar to each another. More information.
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