Prediction of the elastic modulus of concrete with inhomogeneous ITZ

An analytical method is presented for predicting the elastic modulus of concrete with the inhomogeneous interfacial transition zone (ITZ). Based on the characteristics of distribution of cement grains in the ITZ layer，the local water/cement ratio and porosity at any point in the ITZ layer were given. By dividing the inhomogeneous ITZ into a series of concentric spherical shell elements，the elastic moduli of each spherical shell element and the cement paste matrix were determined through the inverse method. The three-phase concrete was decomposed into a series of two-phase composite substructures. The elastic modulus of concrete was derived by applying the solution for a two-phase composite sphere model. The validity of the method presented in this paper was verified with two sets of experimental results reported in the literature. It demonstrates that，for a given aggregate volume fraction，the elastic modulus of concrete decreases with the increase of the maximum cement diameter and water/cement ratio，but increases with the increase of the maximum aggregate diameter. The aggregate gradation also has a certain influence on the elastic modulus of concrete.