Evaluation of corrosion inhibition and self healing capabilities of nanoclay and tung oil microencapsulated epoxy coatings on rebars in concrete

Corrosion of civil infrastructure is the biggest challenge faced by the construction industry worldwide and billions of dollars are spent for its repair and rehabilitation. One of the methods to mitigate the effects of corrosion is the use of Epoxy Coated Rebars (ECR) in concrete. But epoxy coatings are inherently brittle and susceptible to crack initiation and propagation. Thus, to further improve their efficiency in inhibiting corrosion, modifications in the epoxy coatings have to be done. In the present study, it is suggested to modify epoxy coatings by adding nano-clay and tung oil microcapsules. To measure the effectiveness of these coatings to corrosion inhibition, non-destructive monitoring has been done using electrochemical current measurements and ultrasonic guided wave propagation characteristics while the coated rebars are subjected to impressed current accelerated corrosion. The corrosion introduces non-uniform and localized pits in the rebars and disturbs the path of the propagating guided waves through it by mode conversions and scattering which results in drop in transmitted guided wave signal strengths. Nano dispersion of clay in epoxy not only increase of toughness, tensile and flexural properties of the epoxy but leads to torturing of the path for moisture progression. Lastly, the hydrophobic nature of modified clays will aid in reducing progression of water molecules. This was successfully illustrated by very small corrosion current values and small rate of drop in ultrasonic guided wave voltage signals as compared to plain epoxy coated rebars. On the other hand, tung oil microcapsules in Urea-formaldehyde (UF) shells prepared by in-situ polymerization improves the self-healing ability and adhesion strength of capsule embedded coatings and act as self-healing agents. Tung-oil micro-encapsulated coatings perform the best in terms to corrosion resistance as well as bonding with surrounding concrete. The drop in voltage amplitudes as well as the rate of voltage drop with increasing corrosion exposure is very nominal and insignificant. It points towards remarkable inhibition of corrosion offered by self-healing tung oil microcapsules to corrosion damage. (C) 2020 Elsevier Ltd. All rights reserved.