A free movement, arris protection, construction joint for dividing the concrete during pouring of slabs on opposite sides of the joint, the joint having a top-to-bottom depth in its use orientation, giving this depth to the slabs, the joint comprising: • a pair of elongate fabrications one for each side of the joint and means for frangibly connecting the formations together, the fabrications including: • means for anchoring them in the respective concrete slabs on opposite sides of the joint, • arris protection members (2,3) for the respective concrete slabs at each side of the joint, • the arris protection members (2,3) being complementarily formed along the length of the joint with a regular wave shape, with each member extending regularly across a mid-plane of the joint from one side to the other and back again at successive positions along the joint at least whilst the fabrications remain frangibly connected, • at least one of them: • having width transverse the length of the joint giving the joint its top-to-bottom depth, and • being configured to act as a divider for dividing the concrete slabs and • the regular wave shape extending throughout the depth of the arris protection members (2,3) including the or each dividing one, whereby on pouring, the slabs are formed with interdigitated concrete fingers edged at their arrises by the arris protection members and extending through the depth of the slabs, and • welded-in-place dowels extending plainly outwards of the mid-plane on one side of the joint and having sleeves in their extent on the other side of the joint for transferring vertical load between the slabs on opposite sides of the joint. • a pair of elongate fabrications one for each side of the joint and means for frangibly connecting the formations together, the fabrications including: • means for anchoring them in the respective concrete slabs on opposite sides of the joint, • arris protection members (2,3) for the respective concrete slabs at each side of the joint, • the arris protection members (2,3) being complementarily formed along the length of the joint with a regular wave shape, with each member extending regularly across a mid-plane of the joint from one side to the other and back again at successive positions along the joint at least whilst the fabrications remain frangibly connected, • at least one of them: • having width transverse the length of the joint giving the joint its top-to-bottom depth, and • being configured to act as a divider for dividing the concrete slabs and • the regular wave shape extending throughout the depth of the arris protection members (2,3) including the or each dividing one, whereby on pouring, the slabs are formed with interdigitated concrete fingers edged at their arrises by the arris protection members and extending through the depth of the slabs, and • welded-in-place dowels extending plainly outwards of the mid-plane on one side of the joint and having sleeves in their extent on the other side of the joint for transferring vertical load between the slabs on opposite sides of the joint. • means for anchoring them in the respective concrete slabs on opposite sides of the joint, • arris protection members (2,3) for the respective concrete slabs at each side of the joint, • the arris protection members (2,3) being complementarily formed along the length of the joint with a regular wave shape, with each member extending regularly across a mid-plane of the joint from one side to the other and back again at successive positions along the joint at least whilst the fabrications remain frangibly connected, • at least one of them: • having width transverse the length of the joint giving the joint its top-to-bottom depth, and • being configured to act as a divider for dividing the concrete slabs and • the regular wave shape extending throughout the depth of the arris protection members (2,3) including the or each dividing one, whereby on pouring, the slabs are formed with interdigitated concrete fingers edged at their arrises by the arris protection members and extending through the depth of the slabs, and • welded-in-place dowels extending plainly outwards of the mid-plane on one side of the joint and having sleeves in their extent on the other side of the joint for transferring vertical load between the slabs on opposite sides of the joint. • the arris protection members (2,3) being complementarily formed along the length of the joint with a regular wave shape, with each member extending regularly across a mid-plane of the joint from one side to the other and back again at successive positions along the joint at least whilst the fabrications remain frangibly connected, • at least one of them: • having width transverse the length of the joint giving the joint its top-to-bottom depth, and • being configured to act as a divider for dividing the concrete slabs and • having width transverse the length of the joint giving the joint its top-to-bottom depth, and • being configured to act as a divider for dividing the concrete slabs and • the regular wave shape extending throughout the depth of the arris protection members (2,3) including the or each dividing one, whereby on pouring, the slabs are formed with interdigitated concrete fingers edged at their arrises by the arris protection members and extending through the depth of the slabs, and • welded-in-place dowels extending plainly outwards of the mid-plane on one side of the joint and having sleeves in their extent on the other side of the joint for transferring vertical load between the slabs on opposite sides of the joint.