From Strib: Weather, age eroded 35E bridge
"The 6-foot-by-9-foot-by-1-inch patch that peeled off could be described as a veneer for the underside of the steel beams that span the length of the bridge and support it, Dorgan said. Those beams are structurally unaffected by the loss of concrete, he said."
If the aesthetics (i.e. veneer) distract from function (that is, it falls on cars), perhaps bridges should be strictly functional.