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Fusion-bonded-epoxy (FBE)-coated steel rebars have been used in many concrete structures in anticipation of better corrosion resistance. However, due to premature corrosion observed, FBE-coated reb...

This paper presents a market study indicating that Patch Repair without galvanic anodes (PR strategy) can lead to continued corrosion (due to the halo effect and residual chloride effect) and another major repair in about five years. Repeated patch repairs can lead to continued corrosion and eventual replacement of structures and huge life cycle cost (LCC). On the other hand, the strategy of cathodic protection using galvanic anodes (CP strategy) can enhance the service life and reduce LCC. The data on long-term depolarized potential of steel, output current from the anodes and/or visual observations indicated that the galvanic anodes were successful in controlling the chloride-induced corrosion for up to 14 and 10 years, in a jetty and industrial building, respectively. It was also found that the additional cost of galvanic anodes is only about 4% of the repair cost for the jetty structure – breaking the myth of high capital cost of CP strategy. Then, a framework to estimate the LCC of PR and CP repair strategies is developed and it is found that CP and cathodic prevention (CPrev) strategies are highly economical than the PR strategy. Also, the LCC of 30 repair projects confirmed that the use of CP strategy can lead to LCC saving of up to about 90% in about 30 years after the first repair. More importantly, the CP and CPrev strategies can enhance the service life to as long as needed by the replacement of anodes at regular intervals and at minimal cost. Also, a way forward to promote CP strategy in concrete repair industry is provided.

Corrosion is one of the major deterioration mechanisms of reinforced concrete structures . The conventional patch repair without addressing the root cause of the corrosion can lead to repeated repairs. Therefore, a form of cathodic protection (CP) using galvanic anodes is a viable electrochemical technique to mitigate corrosion. However, practitioners hesitate to adopt CP for repair due to the lack of evidence and limited knowledge on the long-term performance of galvanic anodes in concrete systems. For this, two reinforced concrete panels with and without discrete galvanic anodes were cast with admixed chlorides and exposed to a natural environment for 12 years. Electrochemical measurements, such as depolarized corrosion potentials and corrosion rate of the rebars, and output protection current density of the galvanic anodes were measured. In addition, physico-chemical characteristics such as elemental composition , residual lithium content, pH, pore volume, and pore size distribution in the encapsulating mortar were determined on a 12-year in-service galvanic anode. This paper indicates that the alkali-activated galvanic anodes can protect the steel rebars from corrosion for at least 12 years. Analysis after 12 years showed that the pores in encapsulating mortar were partially filled with zinc corrosion products , resulting in substantial pore blockage surrounding the zinc metal. This led to a reduction in the pH buffer in the vicinity of the zinc metal. Also, characteristics of tie wire-zinc metal interface may affect the long-term performance of galvanic anodes. Based on this study, specifications are proposed to help manufacturers to design durable galvanic anode systems.

This paper evaluates the suitability of various techniques such as half-cell potential, macrocell corrosion, linear polarization resistance, and electrochemical impedance spectroscopy (EIS) to detect corrosion initiation of fusion-bonded-epoxy (FBE) coated steel rebars in concrete. It was found that EIS is the best technique for this purpose. Then, a new test method (named as “cs-ACT” test) using EIS is developed to detect the initiation of corrosion and determine chloride threshold at the coating-steel interface, which was not a practice in the literature. Also, the reduction in the resistance of the FBE coating was monitored and a a 4-stage degradation process and corrosion initiation process are identified and discussed using SEM, EDAX, and statistical analysis of the change in the polarization resistance of steel (from repeated EIS tests - Nyquist/Bode plots). Then, a new method that uses the properties of epoxy coating, steel-coating interface, and concrete cover to estimate the service life of reinforced concrete systems with FBE coated rebars is demonstrated. Modifications to the existing specifications to achieve target service life are also proposed.

The urge to reduce the carbon footprints from cement production warrants the development of more sustainable approaches in the construction industry. Towards this, the long term corrosion resistance of the embedded steel rebar in a novel ternary-blended reinforced concrete system with 56 wt% Ordinary Portland cement (OPC), 40 wt% fly ash, 2 wt% nanomodifiers, and 2 wt% corrosion inhibitor (referred to as CFNI) was studied by chemical and electrochemical tests in a simulated chloride environment for 180 days. The performance was compared with three other concrete systems (CC (100% OPC), CF (60 wt% OPC and 40 wt% fly ash) and CFN (58 wt% OPC, 40 wt% fly ash and 2 wt% nanomodifiers). The electrochemical results indicated a significant enhancement in the corrosion resistance of steel in the CFNI concrete as compared to other systems. A five times higher value of polarization resistance (Rp) is obtained in CFNI, as compared to the control concrete, indicate the better resistance of CFNI. Further, in CFNI specimen, the chloride ingress rate was significantly lower and the Field Emission Scanning Electron Microscopy (FESEM) images showed no microcracks or pores at the corroded concrete-steel interface of CFNI specimens. The apparent diffusion coefficient (Dcl) of the concrete system was determined using the bulk diffusion test and chloride profiling. The value of Dcl for CFNI concrete was found to be one order less in magnitude than other concrete specimens, indicating the enhanced resistance against chloride attack. These results show that CFNI concrete is a promising ternary-blended concrete mix to achieve long corrosion-free service life for the structures in aggressive chloride environments.

Nowadays, Cement-Polymer-Composites are widely used to coat steel rebars to delay the initiation of corrosion in reinforced concrete (RC) structures. However, Cement-Polymer-Composite (CPC) coating is sometimes inadequately applied on rusted steel and can lead to premature under film/crevice corrosion. This paper investigates the effect of such inadequate applications of CPC coating and premature corrosion on the service life of RC structures. For this, maximum surface chloride concentrations, diffusion coefficients, and chloride thresholds were determined by a one-year-long laboratory study on the specimens obtained from a 6-year-old bridge and prepared in the laboratory. Studies found that the chloride threshold of inadequately coated steel rebar (i.e., coating on ‘as received’ surface) is significantly lower than that of the adequately coated steel rebars (i.e., coating on ‘sandblasted’ surface). Also, the corrosion initiation time for systems with inadequately coated steel rebar was about 50% less than that of the systems with adequately coated steel rebars. The corrosion mechanisms were justified with micrographs. It is recommended not to use CPC coated steel rebars if adequate surface preparation (say, cleaning/sandblasting) is not implemented.