Exploring the mechanics of corrosion induced cracking

Peter Grassl
James Watt School of Engineering
University of Glasgow
Glasgow, UK

Summary:

Corrosion-induced cracking is the most widely encountered and studied long-term deterioration process in reinforced concrete. Naturally occurring corrosion rates are so low that rust accumulates often over tens of years near the surface of the reinforcement bars before sufficient pressure in the surrounding concrete is generated to induce cracking in the concrete cover. To speed up the process in laboratory tests, corrosion setups with impressed currents have been developed in which the corrosion rate is controlled to be so high that cracking of the concrete cover occurs within a few days. Extrapolating the results of the accelerated tests to those of naturally occurring corrosion requires an understanding of the long-term mechanics of corrosion induced cracking which involves, among others, cracking of concrete in tension and compression, penetration of corrosion products in voids and micro-cracks, creep and changes of maturity of concrete.

In this talk, I will present recent results on the use of an axis-symmetric thick-walled cylinder model for exploring independently the importance of various processes of corrosion induced cracking. The thick-walled cylinder approach is capable to model cracking in tension and compression, penetration of corrosion products in voids and cracks, as well as the effect of basic creep and change of maturity of concrete. In the model, the cracking process due to corrosion is driven by a prescribed radial displacement rate at the inner boundary of the thick-walled cylinder. The governing nonlinear ordinary differential equation is solved using MATLAB with the boundary value solver bvp4c. Basic creep is predicted in all three approaches by means of the B3 model developed by Bažant and co-workers. Time dependence of strength of concrete is modelled using fib Model Code expressions. The work highlights the relative importance of processes involved in predicting the time to cracking due to corrosion.

Speaker Biography:

Peter Grassl is a Senior Lecturer at the James Watt School of Engineering at the University of Glasgow. He studied Civil Engineering at the RWTH Aachen in Germany, Structural Engineering at Chalmers University of Technology in Göteborg, Sweden and was awarded a PhD in Structural Engineering at the same university. He also worked as researcher at EPFL in Lausanne, Switzerland and at Northwestern University in Evanston, USA.

The aim of Peter Grassl’s research at the James Watt School of Engineering at the University of Glasgow is to understand, predict and improve the response of concrete and concrete structures. His group’s work is focused on deterioration processes, development of new materials, optimisation of material use, repair and strengthening techniques, and response of structures subjected to accidental loading. The group’s methodologies comprise meso/micro scale, constitutive and structural modelling. Peter contributes to the development of the open source finite element program OOFEM.