Life quality, industrial productivity, and community safety can be assured by the reliability and the safety of infrastructure such as highways, bridges, and energy-supply systems. Reinforced concrete is the most-commonly used massive construction material in urban, road and industrial infrastructure because of its mechanical properties, durability, and mouldability. Concrete has acceptable compressive strength but relatively low tensile strength, so steel reinforcement rods (rebar) are usually added to concrete to enhance its tensile strength. However, steel rebar is subject to the serious and costly problem of corrosion, which eventually can significantly degrade the mechanical properties of concrete. Quantifying the corrosion condition of reinforcing steel can help manage associated risks arising from the unexpected function failure of reinforced concrete structures. In efforts to avoid such failures, engineers rely on quantitative time-history condition monitoring of reinforcing steel to help make decisions on rehabilitation, decommissioning, or replacement of concrete infrastructure.

The self-magnetic behaviour of ferromagnetic materials can be used for quantitative condition assessment. Inspection of reinforced concrete structures by a method based on this concept is under development. Improving the data recording, mathematical simulation and interpretation so as to obtain more-reliable outcomes from this novel NDT technology (Passive Magnetic Inspection (PMI)) is the main aim of this research project. This thesis, consisting of eight chapters, investigates various experiments and simulations, and delineates future work: Chapter 1 includes the introduction, theoretical background, and research objectives; Chapter 2 consists of numerical simulations and experimental results on the passive magnetic behavior of a rebar with pitting; Chapter 3 represents the simulations and experimental results of the investigations on rebars with local longitudinal defects; Chapter 4 investigates the self-magnetic behaviour of rebars with different sizes of crack; Chapter 5 covers numerical simulations and experimental results of passive magnetic behavior of an intact rebar and a rebar with general corrosion; Chapter 6 compares the magnetic flux density values generated from rebars with different degrees of general corrosion; Chapter 7 describes a successful fieldwork project; Chapter 8 outlines a general conclusion and future works that can help the further improvement of the inspection technology.