Assessing Cement Matrix Permeability by Neutron Dark Field Imaging

The permeability of hardened cement plays a crucial role in determining the durability of cement-based materials. In this contribution, we explore a novel approach to the study of small-scale porosity in cement pastes, and how its modification can affect the overall permeability. Experiments based on neutron dark-field imaging (BOA beamline - Paul Scherrer Institut) were designed with the aim of achieving a detailed and quantitative description of the pore structure in cement pastes. Paste and mortar samples were prepared with a water-to-cement ratio of 0.45. After curing in wet conditions, all samples were cut in slices of different thickness (2, 4, 6, 8 and 10 mm) to evaluate optimal neutron transmission conditions. Correlation length plots obtained from the dark field imaging signals are aimed to provide quantitative information on the pore network topology, which in turn controls the permeability of cement-based materials. This technique was preliminary implemented to the characterization of changes occurring within the pore network, in the presence of admixtures based on Cu-doped C-S-H nanocomposites, which were shown to induce a modification in the mechanism of C-S-H nucleation, promoting both an acceleration of early hydration kinetics and a reduction in permeability.