Non-Destructive Testing of Concrete Structure with Outer Steel Shell using Heat Transfer Principles

This article addresses the lack of proven non-destructive testing of the concrete quality in structures with an outer steel shell, such as concrete-filled steel tubes and structures with external steel plating or permanent formwork. Such methods as visual monitoring with cameras, have significant drawbacks, including subjectivity, technological limitations, and inability to inspect completed structures. Purpose: The aim of this work is the development and validation of non-destructive testing of concrete structure with outer steel shell using heat transfer principles. Methodology/approach: The proposed innovative methodology is based on thermal imaging of the outer steel surface. Its physical principle involves a thermal imager to detect temperature anomalies caused by the different thermal conductivity of solid concrete and defects (voids, inclusions). The method is applied in two modes. The passive mode utilizes exothermic heat releasing during the concrete curing, and the active mode involves the artificial heating or forced cooling of the structure to enhance thermal contrast. Research findings: The proposed methodology was successfully tested on two types of real structures: a high-rise concrete-filled steel tube column and a wall segment with the outer steel shell plating. Experiments involving artificially created defects demonstrate the reliable flaw detection directly against the steel sheet and at a 10 cm depth. The effectiveness of this method is confirmed both during the peak exothermic reaction and after 60 days of concreting. Research implication : This methodology can be used in industries as a reliable tool for monitoring the concrete integrity in complex composite structures.