Q. Can one scatter salt or sand on the snow during Shabbos to prevent people from falling?
A. Poskim permit scattering salt and even sand on snow or ice, since the salt melts and there is no intention for the sand to stay, but rather to be washed out with the later defrosting and rain. Therefore there is no prohibition of boneh or building. Mishna Berura (313: 55, 320: 14). Shemitas Shabbos K. (25: n.49).
In regards to placing it on the street to prevent accidents, where there is no eruv. Shemitas Shabbos K. (25: 9) permits if it is not a Biblical reshus horabim.
Horav Shlomo Miller’s Shlit’a opinion is similar.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a