Development of an integrated methodology for monitoring corrosion in reinforced concrete

In the context of degradation prevention and maintenance of civil infrastructure, there is a strong demand for non-destructive testing aimed at monitoring the condition of reinforced concrete systems, particularly regarding the corrosion of reinforcement bars. Rebar corrosion is one of the main causes of deterioration of engineering reinforced structures and this degradation phenomena reduces their service life and durability. Non-destructive testing and evaluation of the rebar corrosion by electrochemical tests is a major issue for predicting the service life of reinforced concrete structures. The research group of the University of Ferrara is gaining experience on this topic combining structural engineering and electrochemical techniques with NDT geophysical methods. The new regulatory provisions require the monitoring of "strategic" reinforced and prestressed concrete structures from the construction phase, conducting periodic investigations into reinforcement corrosion and maintaining a record of the data. Many non-destructive electrochemical techniques are useful for this purpose, such as measuring the open circuit potential (OCP) and linear polarization resistance (LPR), surface potential (SP) measurement, and measuring the resistivity of concrete. However, these methodologies are not so effective in the case of a structure where the degradation state is being assessed for the first time, because the electrochemical techniques allow for determining whether the corrosion process has initiated and estimate the corrosion rate at that time, but they are not able to assess the extent of degradation. Recently, Ground Penetrating Radar (GPR) has been applied to monitor the evolution of the corrosion process affecting reinforcement bars, also using new methods for processing GPR data, highlighting a strong correlation between the corrosive phenomenon and the electromagnetic response of the acquired signals. This project is proposing to develop an integrated methodology that enables the creation of a predictive model capable of estimating the overall degradation state of reinforced concrete and providing a quantitative assessment of its structural stability.

Over the past few years, numerous experiments have been conducted using various NDT methods, each capable of illustrating signal variations during the corrosion phenomena. These results emphasize the sensitivity of NDT methods in detecting rebar corrosion. The use of multi-sensor tools serves as the starting point for integrated observation, facilitating the transition from qualitative assessments to monitoring the evolving corrosion phenomenon on reinforced steel rebars. This approach aims to establish a quantitative analysis of the observed phenomena. For these aims, several reinforced concrete samples were produced using cement (Type II), suitable for structural applications, in which carbon steel rebars were embedded. The rebars were protected with an epoxy paint, leaving an exposed area of about 13 cm2. The samples were immersed in chloride-containing solutions and the rebars polarized for increasing periods of time. This aimed at inducing accelerated corrosion and achieving increased weight mass loss values of the exposed portion of the steel reinforcement. At the end of the polarization, the samples were opened for a degradation assessment and for actual mass loss evaluation. Finally the obtained weight loss values were correlated with the electromagnetic signals detected by GPR measurements.