Behavior of ECC/Concrete Layer Repair System Under Drying Shrinkage Conditions

The lack of durability in concrete repairs induces repair failures in field and endless “repair of repairs”. Most often drying shrinkage of “new” repair material restrained by “old” concrete substrate causes cracking in the repair material, combined with interface delamination between the repair and the concrete substrate, which may also introduce chlorides, oxygen, moisture, alkali or sulphate into the repaired concrete structure and accelerate further deterioration. This paper suggests a material solution to the described drying shrinkage induced concrete repair failures. Engineered Cementitious Composites (ECC) is a material micromechanically designed with high ductility and toughness indicated by multiple micro-cracking behavior under uniaxial tension. Experimental study on a layered repair system verified that the high ductility of ECC can relieve shrinkage induced stresses in the ECC repair layer and at the ECC/concrete interface, thereby suppressing large surface cracks and interface delamination. The concept of translating ECC repair material ductility to the whole repair system durability can be widely applied to many concrete structures repair applications for developing cost-effective and durable concrete repairs.