The colours of concrete as seen by X-rays and neutrons

Both x-ray tomography and neutron tomography give very detailed insight inthe microstructure of concrete. However, their different contrasts, due to dif-ferent compositional sensitivities, make one modality more relevant for somefeatures. The present study shows that both types of images acquired on thesame specimen may be registered onto each other, after the statistical joint dis-tribution of absorption coefficients has been learned. A Gaussian mixture modelhas been used to identify up to five different phases having different signatures.A staggered algorithm consisting in i) adjusting the joint histogram to fit phasesand their variances and ii) registering the two 3D images onto each other, withina multi-scale algorithm is presented in details. The analysed experimental dataillustrates the benefit of using jointly both modalities as compared to their par-allel usage.