Curling at floor joints is a common problem. However, field observations and experimental studies have shown that substantial reductions in curling can be achieved by using proprietary square steel dowels fitted with a clip-on device that puts the sides of the dowel in contact with a compressible material. This permits lateral movement due to concrete shrinkage or contraction and reduces the cracking caused by restraint of lateral movement, which is likely to occur with conventional round bars. The clip is made of a hard ABS plastic, with the compressible material affixed only to the clip's sides. Vertical load-transfer forces are transferred to the square dowel by the ABS plastic, which has compressibility similar to that of concrete.
Because the side material is compressible, the square bars can be misaligned in the horizontal plane without inducing tensile stresses in the slab when the joint opens. Instead, the side material compresses. In addition to reduced joint curling, benefits of using the square dowels include less corner cracking and less restraint stress that can cause cracking parallel to the joints.