Most batching plants are installed outdoor, especially large stationary batching plants. Because it's more convenient to discharge concrete to mix truck. Large output batching plant need open space to store aggregate, moreover if there are two mixers to discharge so that the mix trucks can work at the same time.
However, if you think that batching plants can only be suitable for outdoor works, you are wrong. The fact is that more and more clients choose small size compact batching plant for their prefab products, you can them precast concrete plant, like the pics above, small and flexible.