Mesoscale modelling and simulation of irradiation-induced expansion in concrete

Abstract

The effects of irradiation on concrete is a topic of concern in nuclear applications, where for some specific members the material may be exposed at long-term to significant levels of neutron radiation. In this study, the effects of radiation-induced volumetric expansion (RIVE) of aggregates on concrete behavior are investigated numerically at the mesoscale. Cylindrical concrete specimens constituted of 3 phases, namely mortar matrix, polyhedral aggregates and interfaces between both of these phases, are generated in 3D. Besides RIVE of aggregates, temperature increase due to the energy deposited during the irradiation, drying and damage development are considered in the finite element simulations. A phase-field approach and a cohesive-zone model are applied to describe damage in the matrix and interfaces, respectively. The simulation results are compared to experimental data of concrete specimens exposed to significant neutron fluences exceeding 6 × 10-19 n/cm2, in terms of residual Young modulus, compressive strength, temperatures evolution and overall expansion of the specimens. Globally, with an adequate calibration of parameters and in particular those related to the damage evolution laws, the simulation results of residual mechanical properties are in relatively good agreement with the experimental data. In addition, specimen expansions are well reproduced, providing that RIVE effects are also considered for the mortar phase, which is justified by the significant volume fraction of embedded sand grains. Mortar RIVE is modelled with the same approach as aggregate RIVE by applying a proportionality parameter, whose effect is discussed. Finally, simulations predict an intense drying of the specimens due to temperature increase.