Used maybe, but can they be used again? They sure don’t seem ready for the scrap heap. And why, if they’re good to go, why were they removed? Couldn’t find anyone around there to ask but they made a great piece of scenery for the layout.
Colours usually associated with earth tones and rust are Raw and Burnt Sienna as well as Raw and Burnt Umber. I go through huge quantities of these colours (Oils, Acrylics and chalks) on my layout. A mix of these would bring that dead concrete colour back to life. In the larger scales you can even detail the rail clamps.