Page 374 - Corrosion Engineering Principles and Practice

342 C h a p t e r 9 A t m o s p h e r i c C o r r o s i o n 343

loaded salt truck, spreading at the generally accepted rate of 140 kg per
two-lane km for general storm conditions, can treat a 36 km stretch of
roadway, traveling a total of 72 km. A sand truck requires seven loads,
must travel a total distance of 300 km to treat the same section of road
and that truck requires four times more fuel. In more ways than one,
salt used in snow and ice control contributes to energy savings.

The Bad and the Ugly Corrosion
The massive spreading of salt on roads and highways unfortunately
also has some serious negative effects. Besides environmental concerns,
one of the major criticisms of salt use for deicing is its contribution to
corrosion of metal in steel bridges (Fig. 9.13), road vehicles (Fig. 9.14),
reinforced concrete (Fig. 9.15) (bridge decks, parking garages), and
any other metallic objects in close proximity to roads and highways
(lampposts, statues, buildings, and so forth).
Although another effective but less corrosive deicing agent is
commercially available (calcium magnesium acetate or CMA), its
price seems to be too high for wide usage. One ton of CMA costs $300
to $600 as opposed to $20 to $70 for rock salt. The use of CMA has

FIGURE 9.13 Pack rust under a steel bridge.