Non-destructive tomographic energy-dispersive diffraction imaging of the interior of bulk concrete

A new tomographic technique, termed TEDDI (tomographic energy-dispersive diffraction imaging) has recently been invented by Hall et al. [C. Hall, P.Barnes, J.K. Cockcroft, S.L. Colston, D. Hausermann, S.D.M. Jacques, A.C. Jupe, M. Kunz, Synchrotron radiation energy-dispersive diffraction tomography, Nucl Instrum Methods Res, Sect B 140 (1998) 253–257; C. Hall, P. Barnes, J.K. Cockcroft, S.D.M. Jacques, A.C. Jupe, X. Turrillas, M. Hanfland, D. Hausermann, Rapid whole-rock mineral analysis and composition mapping by synchrotron X-ray diffraction, Anal Commun 33 (1996) 245–248] and applied to cementitious systems. TEDDI has notable unique features in that: • it exploits diffraction, rather than spectroscopic sensing, and therefore directly yields compositional/structural information about the sample; • the diffracting region can be made small or large depending on application, the ultimate spatial resolution being in the micron range; • with the use of energetic (20–125 keV) synchrotron beams, bulk objects such as concrete blocks can be penetrated so that the technique becomes non-destructive. We report on early tests of this technique as a means to non-destructively examine the interior of concrete prism specimens. Concrete, by definition, is a heterogeneous material because it contains coarse aggregates on a length scale of ∼1 cm. This is orders of magnitude larger than the effective penetration depth of conventional X-ray diffraction systems (typically <100 μm at 1.54 A) which, therefore, cannot probe the interior of intact concrete specimens. It is possible to pulverize concrete, sift out the aggregates, and analyze the remaining fraction but the degree of representation of such powders is questioned since certain phases may be lost or enriched during this process; furthermore, the spatial distribution of the analyzed phases within the concrete will be lost and, with it, important information such as whether the phase in question forms in the cement paste matrix or at the aggregate interface. Even after these limitations, conventional diffraction/microscopy analysis is at best a “one shot” process in time. The TEDDI technique has the promise to avoid all these problems by enabling the examination of intact concrete specimens on the length scale of several centimeters.