Abstract: A joint stabilizing apparatus having an expandable cylindrical housing is inserted into a circular hole drilled at a “loose joint” of a concrete slab that is to be stabilized against relative vertical displacement between adjacent slab sections. The hole is drilled downward into the concrete, centered on the plane of a lateral opening/joint in the concrete slab. The expandable housing comprises two rigid semi-circular housing halves, and the assembly is oriented inside of the circular hole such that the two housing halves are on opposite sides of the centerline of the lateral opening/joint. The housing halves are pushed apart by turning of a threaded bolt inside of the housing. Turning of the bolt causes two bi-laterally symmetric wedge blocks to draw towards each other, and pressing the bearing surfaces of the wedge blocks against inclined surfaces inside of the respective housing halves.