Another example of a concrete mine (with a somewhat different purpose).
German Stock-Mine 43 consists of a small hollow concrete cylinder, made of weak cement mortar composition containing a shrapnel filling. An explosive charge of about 3.5oz was contained by the concrete cylinder, and the mine was mounted on a stake that was set in the ground. <https://www.iwm.org.uk/collections/item/object/30019953#:~:text=mine the German Stock-Mine,was set in the ground.>