Estimation of Critical Microcrack Length in Concrete by Considering Interfacial Properties

Abstract

Concrete is considered as a homogeneous material from a design perspective. However, on a close examination, it is observed that concrete is heterogeneous, which consist of coarse aggregate and fine aggregate embedded in cement paste. Further, there exists an interfacial region, which bonds the aggregate with the cement paste. The strength of this interfacial transition zone (ITZ) depends on its microstructural characteristics. This interfacial region neither possesses the properties of aggregate nor of the cement paste. Interface being the weakest zone, the microcracks are likely to initiate here when the local major principal stress exceeds the initial tensile strength of the interface. When these microcracks reach certain critical length, it propagates and coalesces with the existing macrocrack to form a major crack resulting in the failure of the bond. The microstructural character of the interfacial zone governs the mode I crack propagation in conventional concrete . The material behavior of concrete is influenced by the geometry, the spatial distribution, and the material property of the individual constituents and their interactions. This study aims at estimating the critical microcrack length using the principles of linear elastic fracture mechanics (LEFM) by analyzing the crack opening displacement at different scales. Also, a procedure to determine the material properties such as the elastic modulus and fracture toughness at the interface by knowing the concrete mix proportion is explained.