Strips of Lego could be sanded or scrapped on the edges and assembled to make a 'cast' master of a concrete bunker, thus giving it the proper look of wooden forms. Keeping it square is easy as the Lego will do that for you by design.
I once tried to cut apart clear Lego (red & green) for aircraft clearance lights. It was brittle and did not sand well, the only thing that would touch it was a high speed motor tool.