NON-DESTRUCTIVE DETECTION OF CORROSION OF EPOXY COATED REBAR by BRIGITTE GOFFIN A DISSERTATION IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Civil Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) December 2017 ©Brigitte Goffin, 2017 Abstract Abstract Deteriorating infrastructure is an acute and dangerous problem, which is often caused by the corrosion of concrete reinforcement. Marine structures and bridge decks, where sea water and de- icing salts lead to chloride ion diffusion into the concrete are particularly at risk. Epoxy coated rebar (ECR) is a popular choice for the latter structures. However, corrosion of ECR, which occurs due to coating damage, poses a challenge to non-destructive corrosion detection. This study investigated the corrosion behaviour, accelerated corrosion and non-destructive corrosion detection of ECR. The electrochemical corrosion behaviour of ECR in simulated concrete pore solutions was studied and compared to uncoated rebar (UCR). The polarized area of ECR was related but not proportional to the sodium ion concentration of the test solution. Furthermore, ECR was more susceptible to corrosion than UCR, particularly in the presence of NaCl and in NaHCO3 solution. A test solution of Na2CO3 and NaHCO3 led to the formation of a very fragile passive layer, that grew slowly but continuously. However, the protective layer was sensitive to even small amounts of NaCl. Corrosion of ECR was accelerated in neutral and alkaline NaCl solutions as well as in concrete. Neutral and alkaline environments promoted coating holiday and undercoating corrosion, respectively. Part of the undercoating corrosion process was cathodic delamination, whose acceleration prior to corrosion acceleration slowed down the lateral corrosion expansion. Once corrosion had expanded across the entire surface, the subsequent corrosion rate was not affected by the initial cathodic disbondment. Successful ECR corrosion detection was limited with the linear polarization resistance and ground penetrating radar method. However, concrete properties such as maturity, moisture and chloride content had a significant effect on the measurements. Corroded bars affected the Hall effect (HE) voltage to a lesser extent than intact rebar. Furthermore, corrosion of ECR led to higher concrete surface and lower bar temperatures during active infrared thermography (IRT) tests. The thermal results of ECR opposed those of UCR. The HE and IRT tests showed that the effects of corrosion on the thermal and magnetic behaviour during induction thermography would complement and oppose each other for UCR and ECR respectively. ii Lay Summary Lay Summary Epoxy coated rebar (ECR) is often used in structures exposed to chloride-rich environments. The epoxy coating is a barrier between the concrete and steel and is designed to protect the steel from corrosion. However, damage in the coating often leads to delamination and subsequent corrosion expansion under the coating. Unfortunately, this damage becomes apparent only after significant corrosion has occurred. This study investigated the corrosion behaviour of ECR and compared it to that of uncoated rebar (UCR). ECR with coating damage was found to be more susceptible to corrosion in chloride rich environments than UCR. Furthermore, the suitability of conventional and new non- destructive testing methods for ECR corrosion detection were assessed. Conventional methods such as Ground Penetrating Radar (GPR) and Electrochemical Measurements (EM) showed limited success. Two other novel methods including Infrared Thermography and Hall Effect were relatively more successful. iii Preface Preface This dissertation is the original work by Brigitte Goffin and all experimental work was carried out at UBC. Financial support was provided by the British Columbia Ministry of Transportation and Infrastructure, by the Natural Sciences and Engineering Research Council of Canada (NSERC) through the Sustainable Building Science Program (SBSP) and by the India-Canada Centre for Innovative Multidisciplinary Partnerships to Accelerate Community Transformation and Sustainability (IC- IMPACTS). The research work presented in chapters 3.1 and 4.1 has led to the following journal paper submission: Brigitte Goffin, Nemkumar Banthia, “Corrosion behaviour of epoxy coated and uncoated rebar in simulated concrete pore solutions” The research work presented in chapter 3.3.2.1.2, 3.3.2.2.2 and 4.3.2.2 has led to the following journal paper submission: Brigitte Goffin, Nemkumar Banthia, Noboru Yonemitsu “Effect of corrosion on the thermal behaviour of epoxy coated and uncoated rebar embedded in concrete” The research work presented in chapter 3.3.2.1.1, 3.3.2.2.1 and 4.3.2.1 has led to the following journal paper submission: Brigitte Goffin, Nemkumar Banthia “Electromagnetic detection of corrosion of epoxy coated and uncoated rebar by means of a Hall effect sensor” iv Table of Contents Table of Contents Abstract .................................................................................................................................................. ii Lay Summary ......................................................................................................................................... iii Preface .................................................................................................................................................. iv Table of Contents ................................................................................................................................... v List of Tables ........................................................................................................................................ viii List of Figures ......................................................................................................................................... x List of Symbols ...................................................................................................................................... xix 1 Introduction ........................................................................................................................... 1 1.1 Motivation ...................................................................................................................... 1 1.2 Scope .............................................................................................................................. 4 2 Theoretical Background ......................................................................................................... 7 2.1 Corrosion ........................................................................................................................ 7 2.1.1 Thermodynamics ........................................................................................................ 8 2.1.2 Kinetics ..................................................................................................................... 16 2.2 Accelerated Corrosion .................................................................................................. 24 2.2.1 Potentiodynamic Polarization .................................................................................. 27 2.3 Corrosion in Concrete .................................................................................................. 30 2.3.1 Rebar ........................................................................................................................ 30 2.3.2 Corrosion Behaviour of Epoxy Coated Rebar ........................................................... 33 2.3.3 Effect of Chloride and Rebar Surface Conditions ..................................................... 35 2.4 Corrosion Detection of Epoxy Coated Rebar ............................................................... 36 2.4.1 Conventional Non-Destructive Testing .................................................................... 37 2.4.2 Induction Heating ..................................................................................................... 44 v Table of Contents 3 Experimental Procedure....................................................................................................... 53 3.1 Corrosion Behaviour ..................................................................................................... 53 3.1.1 Specimens ................................................................................................................ 53 3.1.2 Methodology ............................................................................................................ 54 3.2 Accelerated Corrosion .................................................................................................. 59 3.2.1 Concrete ................................................................................................................... 59 3.2.2 Uncoated Rebar........................................................................................................ 59 3.2.3 Epoxy Coated Rebar ................................................................................................. 60 3.3 Corrosion Detection ..................................................................................................... 65 3.3.1 Conventional Non-Destructive Testing .................................................................... 65 3.3.2 Hall-Effect and Thermography Specimens ..............................................................