Effect of transition zone on elastic stresses in concrete materials

Concrete or mortar has three phases, namely, aggregate, bulk paste, and the transition zone. The transition zone is the weakest link in the composite system; its presence may considerably affect the overall elastic moduli and the stress distributions in a concrete material. The transition zone has a relatively more porous structure compared with that of bulk paste, and it may not be, perfectly bonded to the aggregate. This paper proposes a four-phase composite model for investigating the elastic stress analysis of concretes materials. The analytical solutions of a four-phase composite model subjected to uniaxial compression are presented in two dimensions (2D) and three dimensions (3D). Modeling of imperfect shear interfacial bond in a four phase composite model is shown. The 3D and 2D uniaxial compression solutions are compared. The effect of an imperfect shear interfacial bond on the elastic moduli and stress solutions is illustrated. A parametric study is carried out to study the sensitivity of the stress distributions in the transition zone due to different aggregate types and due to changes in the elastic moduli of the transition zone. It is shown that the elastic moduli of the transition zone and its interfacial shear bond with the aggregate could considerably affect the overall elastic moduli and stress distributions in a cement composite.