section upon the sides and bottom the joint has keys that connect the joint to adjacent slabs the joint can also serve as formwork for concrete application_number US 76325907 A description the present art overcomes the prior art limitations by having a durable compressible joint secured between two slabs or a slab and a wall for the full depth of a slab with the slab resting upon a subgrade or lower foundation for ease of description fig1 shows the preferred embodiment of the collapsible expansion joint 1 emplaced between two slabs c the joint may be used where two other concrete sections abut following the same principles and description herein provided for abutting slabs c for sidewalks driveways abutting garages some runways and roads concrete is used as a durable pavement that resists the elements and turning vehicles and has a long life span and low maintenance costs fig1 shows two adjacent slabs as in a road the slabs c have a depth and an expansion spacing as specified in the construction documents the expansion spacing is occupied by the joint 1 the joint 1 is generally an elongated hollow member with a cross section that appears somewhat rectangular the joint can be made to any length by extrusion or other means the length of the joint matches the length of the expansion spacing between the slabs the expansion joint of the present invention has sufficient rigidity and stiffness to remain upright the expansion joint also can serve as formwork for the placement of plastic concrete or other pavement materials a straight edge for bull floating tools and other pavement finishing tools and can support tools personnel and light equipment for.