Pore space analysis of cement-based materials by combined Nitrogen sorption – Wood’s metal impregnation and multi-cycle mercury intrusion

The analysis of pore space is crucial for a profound understanding of transport and mechanical properties of porous materials. Cement-based materials have a broad pore size distribution ranging from micro- to macro-pores. The analysis of this kind of pore space therefore becomes difficult. Because the resolution of image based methods is limited, indirect analysis methods like Nitrogen sorption or mercury intrusion porosimetry (MIP) are often applied. The standard MIP results in an underestimation of large pores because of its intrinsic limitation due to ink-bottle type pores (i.e., pores that are connected to the surface by smaller neck entrances only). The adsorption of Nitrogen seems to be less influenced by such connectivity effects, but the analysis of pores larger than about 100 nm is not possible. To overcome these limitations, in this study pores were selectively filled with Wood’s metal. The liquid metal (at elevated temperature) is intruded into the samples by applying different pressure regimes and then re-solidified in place. The partial impregnation with this metal allowed the analysis of non-ink-bottle type pore space in a subsequent Nitrogen sorption experiment and its comparison with an empty pore system. Furthermore, Mercury intrusion experiments with an additional pressurization–depressurization cycles (multi-cycle-MIP) were performed. The pore size distributions and pore volumes as calculated from Nitrogen sorption data are then compared with MIP and multi-cycle MIP data.