Damage characterization of concrete panels due to impact loading by motionless X-ray laminography

Abstract

Concrete structures are often subjected to extreme dynamic loading conditions due to direct impact. Typical examples of these loading conditions include transportation structures subjected to vehicle crash impact, marine and offshore structures exposed to ice impact, protective structures subjected to projectile or aircraft impact and structures sustaining shock and impact loads during explosions or earthquakes. The assessment and extent of damage to the structure associated with these transient dynamic loading conditions is of paramount importance. Often there are external visual signs of damage after dynamic loading events, however, the extent of damage inside the structure and the determination of its integrity remains obscure. Therefore, one needs to resort to non-destructive evaluation (NDE) techniques not only to detect damage but also to assess the severity of damage. Unfortunately, high-resolution NDE methods to characterize damage in structural materials have been less successful when applied to concrete, partly due to its inhomogeneous microand macrostructure associated with heterogeneities at various length scales that create interferences, such as scattering, attenuation, reflection and diffraction. This paper illustrates the feasibility of using motionless X-ray laminography to detect and characterize damage caused by dynamic loading events. Plain and fabric reinforced concrete panels are subjected to impact loading by a steel projectile of certain initial velocity. The fabric reinforced concrete panels consist of polypropylene fabric attached to the front and back panel. Whereas in plain concrete panels, the damage due to impact loading is clearly visible, in fabric reinforced concrete panels the damage is obscured by the presence of the fabric. Hence, motionless laminography based on reverse geometry X-ray radiography is applied to these fabric reinforced concrete panels to obtain information on the damage evolution through the thickness of the concrete panel. The motionless X-ray laminography concept and its advantage over conventional laminography are briefly described, followed by discussions on the effect of impact loading on plain and fabric reinforced concrete panels.