Control of reinforcement corrosion by surface treatment of concrete

Abstract

It is known from laboratory studies that reinforcement corrosion in carbonated concrete can be controlled simply by ensuring that the concrete remains relatively dry. An apparently obvious and cost effective way of excluding external moisture from building components which are not exposed to effects of capillary suction from groundwater, etc. is by applying a waterproof coating to the surface of the concrete. A research programme was undertaken for six years, with the primary aim of assessing whether coatings with appropriate characteristics could maintain suitably dry conditions within concrete in real carbonated structures. A secondary aim was to determine whether a similar predicted extension of the service life could be achieved if corrosion of the reinforcement were induced by internal chlorides. It was recognized from the outset that trials on real structures should be planned so that critical questions that determine the feasibility of the protection technique might be answered. This paper gives an account of the procedures adopted to select appropriate reinforced concrete buildings and characterize repetitive components to allow adequate comparison between the treated materials and controls. It also deals with the selection of candidate surface treatments by specialist manufacturers, the application of these materials according to recommended procedures, the implementation of relevant in-situ monitoring techniques and the extraction of small specimens from the structures for parallel laboratory trials. Results showed that an appropriate elastomeric coating with good crack-bridging properties, fairly low adhesion and good resistance to weathering can maintain a coherent crack-free covering that excludes external moisture and controls the corrosion rate of the reinforcement in carbonated concrete at acceptable levels over a period of at least five years. When corrosion was caused by internal chlorides, however, the concrete could not be maintained in a sufficiently dry condition to provide adequate long term protection to the steel.