Patching repair with ECC on cracked concrete surface

Performance requirements of the patch repair material are strength, size stability, shieldability, durability, bond property with the substrate concrete, ductility and so forth. Various kinds of patch repair materials with short fibers have been developed and used. Engineered Cementitious Composites (ECC) which provides multiple cracking and strain hardening behavior is also one of the attractive materials for a patching repair. It promotes the narrow crack width that gives resistance to penetration of substances such as chloride ions, water and so forth, and tensile capacity and anti-spalling performance to repaired structures. However, the conditions to obtain these advantages of the ECC should be clarified in its application. In order to apply the ECC to patching repair of concrete structures with cracks, this paper discusses the performance required for patch repair materials for concrete structures with existing cracks. Numerical and experimental studies on patching repair using the ECC or ductile repair materials are briefly introduced focusing on evaluation of zero-span elongation. It shows that existing cracks of substrate concrete induce a localized crack of patch repair material itself. On the other hand, it can be clarified that unbonded region around the existing cracks imparts crack distribution to the repaired specimens with the ECC. A trial application on patching repair of wall structure with existing cracks induced by ASR is conducted. In the observation at 12months after the repair, it is clarified that the applied repair material such as the ECC reduces the crack width on surface.