Corrosion Crack Pattern at Early Ages due to the Pressure Rust Layer in Reinforced Concrete

Abstract

Corrosion of a reinforcement bar leads to expansive pressure on the surrounding concrete that provokes internal cracking and, eventually, spalling and delamination. The aim of this paper is to study the mechanical effects of the rust layer in the surrounding concrete of the steel rebar at the initial stages of the corrosion. At the beginning of the corrosion the rust products penetrate the porous network of the concrete and the pressure is mitigated. The numerical and analytical modelling of the cover cracking due to corrosion of concrete usually assume that the pressure of the rust products of the rebar on concrete is delayed due to their penetration of the porous network. The assessment of this delayed time is based on empirical data. There is insufficient published research focused on the initial stage of the propagation of the rust products in the porous structure of the surrounding concrete. The aim of this work is to study thoroughly the penetration of the rust products in the porous network combined with the assessment of the strain and stresses of the concrete, near to the rebars, at the beginning of the corrosion process. A concrete with silica fume has been cast, which has a closer and narrower porous network in comparison with a conventional concrete. An accelerated corrosion test was carried out. The penetration of the rust layer in the concrete was observed and measured by means of scanning electron microscopy ( SEM) and energy-dispersive X-ray spectroscopy (EDS). In addition, the strain of the concrete due to the corrosion of the rebar was assessed by means of strain gauges. The increasing of the strain in the concrete is observed from the beginning of the test. A good relationship between the velocity of the penetration of the rust products in the porous network and the delaying of the cracking pressure in concrete has been observed.