For what it's worth, I'm pretty sure that most/all of the concrete slab bridges you see on the Northeast Corridor east of New Haven were built in the late 1990s when the line was upgraded for high-speed service. In some cases it appears that they may have encased some of the old girders & beams in concrete instead of replacing them outright, but either way the bridges are generally modern structures.
Certainly, this bridge seems to support Ian's statement, since in my opinion it lacks the aspects of design and materials expected in a 1900 bridge.