An exodermic deck is essentially a thin concrete deck poured on top of a steel grid deck. The two act compositely together. They tend to be lighter than traditional RC decks.
The advantage of the exodermic deck, and other grid deck systems, is that an existing bridge deck can be replaced on a daily basis during off-peak hours thereby eliminating long-term lane closures and detours. Another advantage of grid deck is its long service life, although with HP concrete that could change. Exodermic was used recently on the Tappan Zee Bridge [NYS Thruway, I-87] over the Hudson River. A few years ago, I was involved in a study that examined the use of grid deck for bridges on heavily travelled roads in NYC. It's about twice the cost of a traditional concrete deck.
