How to consider the Interfacial Transition Zones in the finite element modelling of concrete?

Because the ITZs' thickness in concrete surrounding aggregates is tiny, it is difficult to take them into account explicitly in the modelling of concrete. A methodology is suggested to consider the effect of the ITZs on the mechanical behaviour of concrete at the mesoscopic scale. For that, the mechanical ITZ properties have been calculated according to the hydration of cement at various distances of the aggregate boundary. Then, we have defined an effective mixed interphase (EMI) around each aggregate which is formed by the ITZ and a volume fraction of the bulk cement paste. Simulations have been performed to show the influence of this EMI on the tensile failure of concrete. Results have shown that the maximum strength of the specimens depends on the local tensile strength of the ITZs. Stresses were more diffused for the cases without the ITZs and with the ITZs having a lower tensile strength.