The domes are where they keep the raw materials before sending it through the kiln. The kiln is the big, l-o-n-g tube set at about a 40-degree angle. The componets are fed in to the top of the heated tube and are converted into cement as they get dehydrated as they flow down the tube.

Here's a great book that describes all the different industrial things that make up our civilized world:
Infrastructure: A Field Guide to the Industrial Landscape
Even my DW read found this book interesting, though mainly to answer all the DDs' questions.
-Blast