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• Infrared thermal imaging can effectively detect corrosion of rebar in concrete. • Corrosion of uncoated rebar increased thermal insulation of the reinforcement. • Corrosion of epoxy coated rebar decreased thermal insulation of the reinforcement. • Cracks in the epoxy coating decreased thermal insulation of the reinforcement. Infrared thermal imaging is a novel corrosion detection technique that is influenced by the thermal properties of the object under investigation. This study investigated the effect of corrosion of epoxy coated and uncoated rebar on the thermal behaviour of reinforced concrete without electromagnetic influences. A heating element was inserted into the rebar embedded in concrete. The heating element heated the rebar from the inside and the thermal response on the concrete surface was monitored with an infrared camera. The thermal measurements showed that corrosion thermally insulated uncoated rebar. However, corrosion of epoxy coated rebar led to cracking of the coating and thereby reduced the thermal insulation of the rebar. [ABSTRACT FROM AUTHOR]