A multi-scale, multiphysics approach to corrosion-induced damage in concrete

Background

Concrete structures have high durability and are expected to last for several years. With time, constant exposure to moisture, formation of corrosion products, and loads deteriorate concrete's strength and durability through mechanisms of internal cracking. Reduced concrete strength and durability may shorten the structure's serviceability lifetime and jeopardize its structural integrity in severe cases. One of the crucial factors responsible for internal cracking in concrete is the corrosion of reinforcements. The ferrous ions released during corrosion initiation at the steel-concrete interface diffuse through the concrete's pores and undergo a plethora of chemical reactions, depending on the corrosive conditions. Over time, the products of the reactions (ferrous, ferric and chloride complexes) accumulate and grow within pores and exert pressure against the pore walls. As the stress-induced due to the pressure exceeds the material strength of concrete, internal cracking begins.

Contrary to surface cracks, cracks developed due to corrosion are internal and rarely show outward visual signs, making it hard to assess the damage caused through visual inspection. As a result, researchers have relied on numerical approaches rather than experimental ones to understand the conditions that lead to fracture. Although a significant understanding of corrosion-induced cracking has been established over the years, but knowledge gaps still exist regarding the interplay between various mechanisms and the effect of pores in concrete ranging from nanometers to micrometres.

Aims and objectives

The project aims to establish a better understanding of corrosion-driven damage in concrete. In particular, the role pores, ranging from nanometers to micrometres, play in the diffusion of ions, formation of corrosion products, and the time leading to the internal cracking. The goal of the project is thus to develop new physically and thermodynamically-consistent engineering tools capable of predicting corrosion-driven damage in concrete structures, which is crucial in service life design and life cycle cost analyses.

Methodology

We develop and employ multiscale, multiphysics numerical models to shed light on the role of different length scales, the interplay between other mechanisms, and the link between the micro-scale internal cracking and the structural behaviour. The digital pore structure with characteristics statistically equivalent to the actual pore structure is generated to simulate the corrosion mechanism at the microscale. The chemical reactions within pores are thermodynamically modelled and coupled with chemical species' ionic diffusion. Furthermore, we employ crystallization theory to predict the pressure within pores due to growing precipitate and couple it with crack initiation to capture the corrosion-driven fracture. The homogenization approach is employed to bridge the length scales and link the microscale activities to the structural deterioration at the macroscale.