Buy calcium chloride for the coldest days and rock salt for ordinary winter days. The Minnesota Pollution Control Agency puts the lowest practical melting pavement temperature at 15°F for rock salt and -20°F for calcium chloride, and PennDOT's Tech Sheet #129 says adding liquid calcium chloride to dry salt can extend its effectiveness to -20°. Penn State Extension adds that calcium chloride "costs about three times more than rock salt, but you only need to use approximately o
