Corrosion of reinforcing steel presents a major durability issue worldwide and is the focus of much research activity. The long time periods involved in replicating reinforcement corrosion within laboratories has resulted in a number of accelerated test methods being developed. The basis of the research presented in this paper was to examine the impressed current technique often used to induce reinforcement corrosion. The suitability of the technique to model chloride-induced corrosion was investigated by examining the electrochemical nature of the test method. Corrosion was induced in prisms of differing characteristic strengths and cover thicknesses by applying a current between 3 days and 17 days. The acoustic emission (AE) technique detected the onset of corrosion. The gravimetrical and theoretical mass losses are compared and a modified expression based on Faraday's law relating the electrical current to the mass loss is also proposed, which accounts for the localized nature of chloride-induced corrosion. This improved method is dependent upon a reliable method of detecting the onset of corrosion, which can be achieved by AE. On balance, the impressed current technique appears suitable to simulate reinforcement corrosion.

The deterioration of reinforced concrete is a serviceability problem world-wide. The cover zone plays an important role in the durability and serviceability of concrete and provides the initial barrier to aggressive species. The research presented investigates the potential of acoustic emission (AE) as a means of identifying corrosion at an early stage, before any significant cover damage has occurred. The purpose of part of the study was to identify the influential cover zone factors that affect the magnitude of the acoustic emission measurements per gram of steel loss. Prisms with various combinations of strength, cover thickness, aggregate and rebar diameters were studied to ascertain the important variables likely to be encountered on reinforced structures.The experimental results confirmed that early corrosion, verified by internal visual inspection and mass loss, can be detected by AE and before any external signs of cracking. They also show that the most influential parameter affecting the AE measurement is concrete strength, being exponentially related to the AE Energy.Material properties such as cover thickness had a negligible effect on AE Energy during the initial stages of reinforcement corrosion, whereas from this initial work, the rebar diameter indicated a promising relationship with AE Energy per gram of steel loss.

Chloride rich reinforced concrete prisms were coupled to chloride free prisms and exposed to diurnal and seasonal temperature cycles typical of those found in the UK.Acoustic Emissions (AE) and galvanic currents were continuously monitored and correlated with ambient temperature. AE and galvanic currents were found to emulate the evolution of temperature in the diurnal cycles, although no specific relationship between AE and galvanic current could be obtained. The influence of seasonal variations in galvanic current had no obvious influence on AE Energy per second over the range of corrosion rates studied. The findings suggest that AE is more sensitive to short term (diurnal) changes in corrosion rates than the longer (seasonal) effects. It was hypothesised that this is due to transitory changes in the internal microclimate of the concrete.