Each power with a capital gets to place 1 piece of Infrastruture on the board each turn FOR FREE.
Whether that is railroads/centers, sea mines, land mines, fortifications, or otherwise, it’s at each power’s discretion. (Maybe nothing more than 8IPC value?)
For every 20 IPC’s made after that (Not capture), Said power gets an additional piece to place each turn for FREE.
The reason it’s for free, is quite simply, that alot of these infrastructure pieces might not see regular integration, unless you’re just going to get them anyways. It represents some of the more civilian input into the war effort.
If you couple this, with a map overlay, of where infrastructure should already be historically, and with the Scars of War/Battle Damage package. This could make things incredibly interesting.
Perhaps you could also choose to REPAIR damaged infrastructe (Not factories) during the purchase phase, instead of placing one of your new ones.