Patent ID: 7845123

Claim:
A pre-cast concrete block for constructing a staircase, comprising: a horizontal stepping surface; a rise surface perpendicular to the stepping surface; a rear surface which connects diagonally the stepping surface and the rise surface at respective edges thereof, the rear surface having a recess for reducing the weight of the block, the recess having a round part with a specified radius at an inner corner part of the recess between an underside of said horizontal stepping surface and a rear side of said rise surface; and a pair of side surfaces constituting outermost sides of said pre-cast concrete block, each of said pair of side surfaces having a displacement prevention groove formed on an exterior side thereof, wherein said round part forms a partially cylindrical recessed surface, wherein at least part of said pre-cast concrete block has a triangular shape in cross-section, wherein said displacement prevention grooves are formed in an L-shape with a horizontal part and a vertical part, and wherein said displacement prevention grooves have a triangular shape in cross-section.