Honeycomb hexagons

Honeycombs are actively built by bees, the bees could make just about any shape but over a long period of natural selection their behavior evolved to make shapes that minimize the area of wax needed and still be structurally functional for their needs. Perhaps the same structural principles could be used when trying to improve concrete casting and reducing the amount of material needed to make a variety of concrete shapes.

Image source: https://www.quora.com/Why-does-nature-prefer-hexagonal-shapes