A new method for corrosion assessment of reinforcing bars based on close-range photogrammetry: Experimental validation

In most developed countries, a significant portion of the nation's Gross Domestic Product (GDP) is spent on maintenance of reinforced concrete (RC) structures suffering from corrosion. Although extensive research has been devoted to this issue, little attention has been given to the study of accurate methods to quantify corrosion and its spatial variability. As a result, scattered data can be found in the literature, relating the rates of corrosion, its penetration depth, and the resulting structural deteriorating effects. In this paper, a new cost-effective and versatile method for corrosion assessment of RC structures based on close-range photogrammetry is proposed. This method was validated by applying it to an experimental research on an accelerated corrosion test of reinforcing bars (RBs). The tests performed show that the proposed method can provide accurate results independent of the RB diameter, length, and corrosion level (measured in terms of rebar's cross section loss percentage), as long as sufficient image overlapping is ensured along the axial and radial axes of the rebar. The results obtained also prove that the method is suitable to measure spatial variability of corrosion attack, providing much better results than those gained from existing geometrical models based on the maximum pit depth. More precise results can be achieved by using semi-professional Digital Single-Lens Reflex Cameras (DSLR) cameras having the additional advantage to be suitable for low levels of corrosion attack. However, the research performed shows that accurate results can also be obtained even when a less sophisticated or a smartphone camera is used.