Damage and Fracture Mechanics

Interfaces between two different mixes or strengths of concrete appear in large concrete structures involving mass concreting such as dams, nuclear containment vessels, cooling towers etc., since joints between successive lifts are inevitable. These joints and interfaces are potential sites for crack formation, leading to weakening of mechanical strength and subsequent failure. Research involving concrete-concrete bi-material interface can provide very useful information in the field of repairs and rehabilitation of concrete structures. As concrete is a heterogeneous material, its fracture behavior is governed by the formation of a fracture process zone (FPZ) which forms ahead of the crack-tip. Due to the formation of FPZ, linear elastic fracture mechanics (LEFM) is not applicable to concrete, and hence the nonlinear fracture mechanics (NLFM) based study becomes essential. Further, in case of a bi-material interface the stress singularities are oscillatory in nature and the fracture behavior of a concrete-concrete bi-material interface is much more complicated. Advanced experimental techniques such as scanning electron microscopy, nano and micro indentation, acoustic emissions and digital image correlations are used for characterizing interfaces between different strengths of concrete with an aim of understanding the fracture processes and determination of the fracture parameters (Figures 4.16 and 4.17).