So this is a good question. Depending on what exactly you are doing in the Cement business being strong could be important.
Sometimes when pouring concrete the forms are actually heavy and would require some strength. but if you are doing flat work like a large slab the forms are very small but may require more Brains to lay them out correctly.
Sometimes a concrete wall will have metal rebar in side, this can get heavy when you start tying it all together but manageable for most i would say.
Bottom line is I feel you need to be somewhat strong and in physical shape to do concrete work but also just as smart because laying out forms and making sure you calculate enough material can make a big difference.
Hope this helps answer your question.