Predictive model for Carbonation Corrosion Phenomena in Reinforced Concrete Elements

Abstract

Reinforced concrete is the most common used material for construction worldwide. However, environmental effects such as freeze-thaw cycles, steel corrosion, sulfate attacks, chloride and carbon dioxide intake severely affect concrete durability. It became evident with time that more in depth investigations were required to better understand the different deterioration phenomena that affect reinforced concrete elements. To this extent, in recent years the health monitoring of existing buildings with non destructive techniques allowed to collect important data describing the environmental effects on reinforced concrete structures. Eventually, the data collected from the monitoring systems can be employed to develop forecasting models which can be utilized to organize a more effective long-term maintenance schedule for reinforced concrete structures.

With this purpose in mind, a numerical model which describes the rupture of the concrete cover due to the corrosion of the rebar has been developed. The model starts by considering the carbon dioxide diffusion-reaction process and couples it with the transport of water within the concrete pores, as it heavily affects the diffusive behaviour of gasses into concrete. As a result of the carbon dioxide intake, the pH of the pore water drops to neutral values, and once the carbonation front reaches the steel rebar the corrosion process begins. Using the electrochemical kinetics equations the amount of rust produced on the metal surface due to the corrosion process is evaluated. Moreover, oxygen diffusion through the concrete cover and through the rust layer is also considered as it greatly affects the corrosion rate. Eventually, as the rust deposits grow in volume, overpressures are generated on the concrete surrounding the steel rebar. Once the tensile resistance of the concrete is reached, cracking and spalling of the cover is observed and modelled via the phase field approach for brittle fracture.