Experimental and probabilistic studies on mode ii fracture of cementitious materials

Abstract

Fracture in engineering structures is a common problem that society has faced ever since the development of engineering techniques to structures. The mechanical behavior of civil engineering structures made with cement concrete are greatly influenced by its constituent materials, since the bleeding or segregation of fresh concrete will induce cracks at the interface between the matrix and the aggregate when the concrete is hardened. Also hardening of fresh concrete is accompanied by loss of moisture in the cement paste, causes shrinkage of the concrete. This shrinkage happens only within the cement paste. The shrinkage strain is usually not uniform in a concrete structure because the loss of moisture is different for the surface area and for the interior part of the concrete. The shrinkage in the paste is usually restrained by the aggregates and boundary conditions of the concrete during casting. Both the non uniform distribution of the shrinkage strain and the restraints from the aggregates and the boundary conditions can develop a certain value of tensile stress in some parts of the concrete, which may induce shrinkage crack before the application of loads. As the properties of concrete are influenced by its chemical constituents and micro and macrostructures, which are characterized by amounts and distribution of internal pores and micro cracks, these existing flaws and micro cracks grow stably under external loading and coalesce with existing or newly formed micro cracks until large fracture are formed. Therefore, fracture processes in concrete may primarily depend on stability of these interfacial cracks. The mechanical behavior of concrete subjected to different loading conditions is governed by the initiation and propagation of these internal cracks and flaws during loading. The severity of the problem varies with the type of structure and importance of the structure.