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Corrosion assessment of reinforced concrete (RC) structures with fusion-bonded-epoxy (FBE)-coated steel rebars is a challenge because the common inspection methods and data cannot be applied or interpreted in the same way as that for the systems with uncoated rebars. If corrosion detection tools based on techniques such as half-cell potential (HCP), linear polarization resistance (LPR), or electrochemical impedance spectroscopy (EIS) are used for the assessment of systems with FBE-coated steel rebars without considering the difference in the electrochemical conditions between coated and uncoated systems, then the interpretation can result in the inability to detect ongoing corrosion. Therefore, the objective of this paper is to examine the suitability of these inspection methods and data to be applied to the RC systems with FBE-coated steel rebars. For this, the suitability of test methods on HCP, LPR, and EIS for assessing corrosion conditions of RC structures was assessed using laboratory specimens and field structures. Field investigation using HCP shows that the HCP could not detect corrosion of FBE-coated steel rebars unless the coating was severely disbonded due to corrosion of steel rebars. Also, the suitability of test methods on HCP, LPR, and EIS was assessed by additional laboratory specimens. Although complex, only the EIS technique could reliably detect the corrosion conditions of the FBE-coated steel rebars embedded in concrete. Therefore, a way forward to assess RC structures using the EIS technique is proposed.

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...

Currently, highway/railway bridges are designed for the service life of more than 100 y. In such reinforced concrete structures, fusion-bonded epoxy (FBE) coated steel rebars are being used in anticipation of delayed initiation of reinforcement corrosion. However, the FBE steel rebars get exposed to sunlight/ultraviolet rays during prolonged storage and delayed/staged construction. This paper presents microanalytical and electrochemical data (Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersion x-ray diffraction, and electrochemical impedance spectroscopy) and shows the adverse effects of sunlight/UV exposure on the corrosion resistance of FBE-coated steel reinforcement in concrete construction. Based on tests on steel-mortar specimens, the mechanisms of UV-induced chemical changes, shrinkage, and cracking of FBE coating, and the resulting steel corrosion mechanisms are proposed. Also, the adverse effects of sunlight/UV exposure on chloride threshold and reduction in the service life of FBE-coated steel in cementitious systems are presented. The paper recommends to minimize the exposure of FBE-coated steel rebars to sunlight/UV rays to less than one month.

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.

Currently, large infrastructures (bridges, highways, etc.) are designed for more than 100 years. To achieve long service life, coated rebars (mostly, cement polymer composite (CPC) coated rebars) are being used to enhance the corrosion resistance. However, inadequately coated rebars can lead to premature corrosion. This can also affect the bond between the rebar and the concrete. To assess the effect of CPC coating on bond strength, pull-out specimens of (150×150×100) mm with 12 mm diameter rebar with 100 mm embedded length were cast and tested. For this, three replica specimens with two types of reinforcement namely, i) Uncoated steel ii) CPC coated steel were cast. To induce corrosion, additional five specimens with CPC coated steel rebars were cast with premixed chloride and cured for 28 days. During the curing period, continuous monitoring of corrosion potential and rate was done and degree of corrosion was assessed. The effect of degree of corrosion on bond of steel-concrete-coating interface was quantified. The CPC coated rebars without corrosion exhibited 10% bond reduction. CPC coated rebars with corrosion exhibited 30-70% reduction in bond strength. Also, the corrosion is found to adversely influence the stiffness of the bond.