  Inspection of ageing, reinforced concrete structures is a world-wide
challenge. Existing non-destructive evaluation techniques in civil and
structural engineering have limited penetration depth and don't allow to
precisely ascertain the configuration of reinforcement within large concrete
objects. The big challenge for critical infrastructure (bridges, dams, dry
docks, nuclear bioshields etc.) is understanding the internal condition of the
concrete and steel, not just the location of the reinforcement. In most new
constructions the location should be known and recorded in the as-built
drawings, where these might not exist due to poor record keeping for older
structures. Muon scattering tomography is a non-destructive and non-invasive
technique which shows great promise for high-depth 3D concrete imaging.
Previously, we have demonstrated that individual bars with a diameter of 33.7
+- 7.3 mm at 50 cm depth can be located using muon scattering tomography. Here
we present an improved method that exploits the periodicity of bar structures.
With this new method, reinforcement with bars down to 6 mm thickness can be
detected and imaged.
