Repair and prevention of damage due to transverse shrinkage cracks in bridge decks

Transverse shrinkage cracking of bridge decks occurs during and shortly after construction. It allows cracks to form and later allows water and other elements to enter the concrete matrix of the deck and most importantly to fall onto the supporting structure below. This leads to significant structural damage of that support structure. This paper describes a field application of the design for an in-situ means of controlling and repairing transverse shrinkage cracking, by utilizing brittle tubes with sealants in the concrete deck. Repair adhesives in chemically inert tubes, fibers or beads are cast within concrete. At the onset of cracking, the walls of the encapsulator are fractured or pulled apart by the forces of shrinkage, allowing adhesive to exit and penetrate the developing crack. This application can be applied to bridge decks specifically to control the location of transverse shrinkage cracks by creating control joints on the surface as a transverse row of sealant-filled tubes. These tubes, which are weaker than the concrete in tension because they are scored, break due to shrinkage strain, thereby focusing the transverse cracks along this line. A sealant adhesive is then released from the tube and seals the cracks in concrete. The repair sealant (which is also an adhesive) has a low modulus of elasticity, thereby allowing future movement to resist stresses. Four full-scale bridge decks have been fabricated, and results in the first two decks after one month of monitoring showed that repair tubes embedded just under the deck's top indeed ruptured and created repair control joints as designed. Full-scale testing of this design is being done at ATREL Lab of the University of Illinois under sponsorship from NCHRP - IDEA program of the Transportation Research Board, National Academy of Sciences.