Visualization of mercury percolation in porous hardened cement paste by means of X-ray computed tomography

Mercury intrusion porosimetry (MIP) has been extensively used for the pore structure characterization of porous materials, but the percolation of mercury in porous cement-based materials during MIP has never been comprehensively investigated before. Here we visually probe the mercury percolation in a porous hardened cement paste (HCP) using X-ray computed tomography (X-CT). Novel double surface coatings on the HCP samples before and after MIP tests by an epoxy resin are specifically designed. The first coating enables the one-directional penetration of mercury in the HCP samples during MIP, while the second coating can partially seal the release of the entrapped mercury. MIP tests are operated under different maximum applied pressures (10,000 and 30,000 psi) and equilibrium time (5, 10, and 30 s). The high X-ray attenuation of mercury enables the visual trace of the intrusion mercury percolation pathways and the entrapped mercury clusters in the HCP samples by X-CT. The position-dependent entrapped mercury clusters in the pores account for the gray value changes and gradients in the HCP samples after MIP. The MIP characteristics, such as, total intrusion volume, volume size distribution and mercury entrapment, change with the maximum applied pressure and equilibrium time, but the percolation pore size shows the consistent values. The findings of this work deepen the understandings of MIP for the microstructure characterization of porous materials.