The mechanical properties of irradiated concrete aggregates: Insights from molecular dynamics simulations

Abstract

The concrete in nuclear power plant reactor buildings is exposed to neutron radiation, making it critical to evaluate and predict its deterioration under irradiation. The observed expansion of irradiated concrete is believed to be caused by the expansion of aggregate minerals, but the mechanisms behind this process are not well understood. This study uses molecular dynamics simulations to investigate the mechanical properties and mechanical fracture phenomena of a range of silicate minerals that are popular as concrete aggregates. Ten silicate minerals are targeted: $\alpha$-quartz, orthoclase, microcline, albite, oligoclase, andesine, labradorite, augite, diopside, and forsterite. The mechanical properties (Young's modulus, maximum stress, and Poisson's ratio) of the minerals are determined through neutron irradiation and tensile simulations. The irradiation simulations reveal a decrease in mineral density, an expansion process involving amorphousization, and a change from anisotropic to isotropic mechanical properties. The isotropic Young's modulus and maximum stress significantly decrease with irradiation, and this effect is reproduced well in experimental results. The origin and process of mechanical fracturing are estimated by finding atoms with large displacements in tensile simulations, and the behavior of the stress–strain curve on the atomic scale is explained. In irradiated minerals, local stress relaxation occurs due to local atomic displacement, and large-scale mechanical fractures are suppressed. The factors involved in the mechanical fracturing and local stress relaxation of Na-feldspar are identified and discussed in terms of chemical bonding theory.