Study of Damage in Concrete Based on Microscopic Changes in Density

Abstract

Damage in concrete has been modeled using various approaches such as fracture mechanics, continuum damage mechanics and failure envelope theories. The current research proposes a new approach to model damage in concrete that addresses the limitations associated with the existing approaches. The proposed density driven damage mechanics (D3-M) approach defines damage in terms of changes in the density of the material at the microscopic level where such changes are induced by mechanical and chemical loading. The suggested approach is used to simulate the response of 2D concrete bodies to uni-axial tension and uni-axial compression. The simulation results indicate that the proposed model, by means of a single constitutive function, is able to correctly predict failure patterns and aptly capture the damage mechanisms under both uni-axial tension and uni-axial compression loadings using only the information related to the microstructure, the density field and the stiffness field. D3-M model, further, is used to model chemical and chemo-mechanical damages. It is based on the premise that low-density regions are created when concrete is subjected to a chemical attack or a coupled chemical-mechanical loading resulting in reduced stiffness and strength of the material. It is also highlighted that the response of the material to a scenario where chemical and mechanical loads are acting simultaneously cannot be considered equivalent to the response obtained by superposing the responses to mechanical and chemical loads acting separately. The D3-M modeling approach stands out among the past efforts to predict the response of concrete to mechanical and chemical loading scenarios due to its ability to effectively model the mechanical, chemical as well as the coupled mechanical-chemical responses of concrete using a single constitutive equation for both types of damage.