A metal joint for concrete slabs including means of separating the slabs and means allowing the horizontal movement of slabs relative to each other while avoiding vertical movement between the edges of the slabs, the metal joint comprising a first part incorporated in a first slab, comprising a vertical web with an upper edge and provided with a series of tenons which extend horizontally towards the exterior of the slab and a second part incorporated in a second slab comprising in its upper section a web with an upper edge and a series of mortise elements which extend towards the interior of the slab and are arranged opposite the tenons so that they can engage with each other, wherein the upper edges of the webs terminate at the top by an upper sharp edge strengthened by a cold-rolled fold so as to form a right angle on the outer side of the slab and a sharp edge with an acute angle in contact with the concrete of the slab thus forming a smooth upper surface and a sharp edge of the joint of the adjacent slabs.