Abstract: A resilient, deformable, adhesive-free sealing strip for expansion joints in concrete comprises an elongated central core with a reinforcing web embedded therein. First, second and third pairs of fins extend from opposite sides of the central core, the first pair being shorter than the second and third pairs, the first pair disposed at the top of the strip and the second and third pairs being disposed at spaced intervals down the elongated core. Each pair of fins has a combined width greater than the width of the joint to be sealed. Upon insertion of the strip, the second and third pairs of fins are substantially deformed in the direction opposite insertion, exerting pressure against the concrete void walls, and through the central core, against one another, firmly locking the strip in place. The first pair of fins are only moderately so deformed, sealing the open top of the joint.