If you glue anything to the concrete, you will need to clean it first. Likely it has bond breaker still on the surface from the forms when it was poured. Even if it doesn't it will likely have some loose minerals that leached to the surface, making it chalky and hard to adhere to. You can clean it with vinegar, which is a weak acid. It won't hurt the bridge at all, but will clean off any contaminates and allow the glue to stick. Even better is muratic acid (like you get at the pool supply). It will etch slightly into the surface, making it slightly rougher and giving the adhesive something to "bite" into. If you use muratic acid, only apply it right on the spot you want the glue and be sure to rinse after it with water.
