A spiral rebar weldable metal rod with a constant or variable pitch of between 1 and 10 times a diameter of a cylinder into which the rod is inscribed; with a planar cross-section having at least two petals connected to the central section and separated from each other by gaps. The triangular petals are connected with the central section by their vertices; the petal edges distant from the central section are circular. The rebar has ribs; the ribs' height is between 0.5 mm and 1.0 mm and distances between the ribs are between 5 mm and 15 mm.