On-Site Bridge Inspection by 950 keV/3.95 MeV Portable X-Band Linac X-Ray Sources

Abstract

Many bridges around the world face aging problems and degradation of structural strength. Visual and hammering sound inspections are under way, but the status of inner reinforced iron rods and prestressed concrete (PC) wires has not yet been confirmed. Establishing a diagnosis method for bridges based on X-ray visualization is required to evaluate the health of bridges accurately and to help with the rationalization of bridge maintenance. We developed 950 keV/3.95 MeV X-band electron linac-based X-ray sources for on-site bridge inspection and visualized the inner structure of a lower floor slab. The information regarding wire conditions by X-ray results was used for the structural analysis of a bridge to evaluate its residual strength and sustainability. For more precise inspection of wire conditions, we applied three-dimensional image reconstruction methods for bridge mock-up samples. Partial-angle computed tomography (CT) and tomosynthesis provided cross-sectional images of the samples at 1 mm resolutions. Image processing techniques such as the curvelet transform were applied to evaluate diameter of PC wires by suppressing noise. Technical guidelines of bridge maintenance using the 950 keV/3.95 MeV X-ray sources are proposed. We plan to offer our technique and guidelines for safer and more reliable maintenance of bridges around the world.

Quantitative Evaluation of Unfilled Grout in Tendons of Prestressed Concrete Girder Bridges by Portable 950 keV/3.95 MeV X-ray Sources

“…Magnetic testing can detect the disconnection of iron rods or wires up to 300 mm in thickness. With a 400 kV X-ray tube, transmitted images of the PC sheath, wires, rods, and grout can be obtained up to 400 mm in thickness, but it takes approximately 1 h. Compared with the above existing methods, we explain and emphasize the advantage of our method using 950 keV/3.95 MeV X-ray sources [14][15][16]. With them, clear detection and visualization with 1 mm resolution of PC iron structures and grout filling at a depth of 400-1000 mm are possible within minutes.…”

Highway PC Bridge Inspection by 3.95 MeV X-Ray/Neutron Source

“…We use X-band (9.3 GHz) linac based 3.95 MeV X-ray sources for the inspection of the actual bridge [1][2][3]. The systems are shown in Figure 4.…”

“…The Public Works Research Institute and the University of Tokyo are developing new technical guidelines for special inspections of bridges using 950 keV/3.95 MeV X-ray sources. An overview is provided in Figure 23 [4]. First, visual and hammer sound inspection screening should be performed based on regular inspection guidelines.…”

“…However, they are available for thinner concrete than 200 mm. On the other hand, 950 keV / 3.95 MeV X-ray sources can be used for transmission testing for thick concrete of 200-400 mm and 200-1,000 mm based on the calculation and our experience so far [1][2][3][4]. We think that only the 950 keV/3.95 MeV X-ray sources can enable transmission imaging of PC structures in 200-1,000 mm thick concrete within minutes.…”

“…But, practically it is difficult to evaluate PC in thicker concrete than 200 mm. We have developed portable 950 keV/3.95 MeV electron linac (linear accelerator)-based X-ray / neutron sources and applied them to inspection of PC concrete thicker than 200 mm within reasonable measuring time of seconds -minutes more than 10 times so far [1][2][3][4]. Major poor-construction and degradation of PC bridges to be detected by X-rays and neutrons are unfilled grout, rainwater intrusion, corrosion and thinning and disconnection of PC wires.…”