THE EFFECT OF ITZ AREA BETWEEN THE AGGREGATE AND MORTAR TO THE LOAD-DISPLACEMENT BEHAVIOR IN CONVENTIONAL CONCRETE AND ITS INFLUENCE ON STRUCTURES

Abstract

An integrated research method on the Interfacial Transition Zone (ITZ) between aggregates and mortar, involving specific experiments in combination with a Finite Element Model (FEM) incorporating this ITZ, has been conducted. Whiles the laboratory tested specimens provided the basic input data for the FEM, another set was prepared to validate the correctness and the sensitivity of the model. The research outcome demonstrated that the FEM-ITZ model is a powerful tool in predicting the stress-strain behavior of concrete as a three phase material, including the ITZ. The FEM is built as a four-node isoparametric quadratic quadrilateral element having two-by-two Gauss points, while the ITZ is represented by a doublespring linkage element. The resulting curves established that the presence of the ITZ substantially influences the stiffness and ultimate load carrying capacity of the concrete specimen. Further research was expanded to study the effect of the ITZ area to the overall behavior of the concrete specimen. The ITZ area variation was obtained by superimposing a range of aggregate diameters for the cylindrical inclusions, while maintaining a constant specimen dimension. The FEM and experimental results showed that the ultimate compression capacity fluctuates as a function of ITZ area increase. A simulation of the ITZ' influence to a rigid pavement slab, is presented at the end. This simulation will bring a realistic touch how the micro scale of concrete can impact the macro scale of a structural element.