A system for reinforcing a concrete slab including: formwork including at least one elongate beam, the beam including: a channel for receiving concrete mix therein such that a rib is formed in the concrete slab; and at least one element protruding into the channel for engaging the concrete mix such that once the concrete mix hardens, the beam is anchored to the slab, wherein the beam is formed of two beam half parts (500,501) fastened together, each beam half part (500, 501) having a base wall connecting an inner side wall and an outer side wall, and wherein the beam half parts (500, 501) are fastened together such that inner side walls of each half part are aligned against one another, and the outer side walls and bases of the half parts respectively provide the side walls and base of the channel, the inner side walls of the half parts thereby providing a central stem within the channel, characterised in that each beam half part (500,501) has a top flange (504, 505) extending from the top of its inner side wall toward its outer side wall, and the beam half parts are fastened together with fastening means connecting the top flanges (504, 505), and wherein the top flanges (504, 505) of the beam half parts (500, 501) and central stem provide a substantially T-shaped cross section in the plane perpendicular to the elongate axis of the beam member. formwork including at least one elongate beam, the beam including: a channel for receiving concrete mix therein such that a rib is formed in the concrete slab; and at least one element protruding into the channel for engaging the concrete mix such that once the concrete mix hardens, the beam is anchored to the slab, wherein the beam is formed of two beam half parts (500,501) fastened together, each beam half part (500, 501) having a base wall connecting an inner side wall and an outer side wall, and wherein the beam half parts (500, 501) are fastened together such that inner side walls of each half part are aligned against one another, and the outer side walls and bases of the half parts respectively provide the side walls and base of the channel, the inner side walls of the half parts thereby providing a central stem within the channel, characterised in that each beam half part (500,501) has a top flange (504, 505) extending from the top of its inner side wall toward its outer side wall, and the beam half parts are fastened together with fastening means connecting the top flanges (504, 505), and wherein the top flanges (504, 505) of the beam half parts (500, 501) and central stem provide a substantially T-shaped cross section in the plane perpendicular to the elongate axis of the beam member. a channel for receiving concrete mix therein such that a rib is formed in the concrete slab; and at least one element protruding into the channel for engaging the concrete mix such that once the concrete mix hardens, the beam is anchored to the slab, wherein the beam is formed of two beam half parts (500,501) fastened together, each beam half part (500, 501) having a base wall connecting an inner side wall and an outer side wall, and wherein the beam half parts (500, 501) are fastened together such that inner side walls of each half part are aligned against one another, and the outer side walls and bases of the half parts respectively provide the side walls and base of the channel, the inner side walls of the half parts thereby providing a central stem within the channel, characterised in that each beam half part (500,501) has a top flange (504, 505) extending from the top of its inner side wall toward its outer side wall, and the beam half parts are fastened together with fastening means connecting the top flanges (504, 505), and wherein the top flanges (504, 505) of the beam half parts (500, 501) and central stem provide a substantially T-shaped cross section in the plane perpendicular to the elongate axis of the beam member.