Magnetic resonance imaging studies of spontaneous capillary water imbibition in aerated gypsum

Abstract

In this paper we investigate both capillary water imbibition and the sorptivity of aerated gypsum plaster, and how these sorption characteristics are related to the pore structure of the material. These characteristics are examined by monitoring mass change using the conventional gravimetric method and by obtaining water content profiles using non-destructive magnetic resonance imaging (MRI) techniques during capillary imbibition of water. Here, three different gypsum samples are investigated: one non-aerated reference gypsum sample and two aerated gypsum samples produced with different volumetric air fractions. The capillary water absorption into the reference sample follows t 1/2 kinetics (Fickian diffusion), where t is the time of ingress. However, in the aerated gypsum samples there are deviations from t 1/2 kinetics. The MRI results show unambiguously that two wetting fronts advance through the aerated structure; an observation that cannot be made from the gravimetric data alone. The water content profiles of the aerated gypsum samples are therefore analysed by treating them as the sum of two separate absorption processes using sharp front analysis. The capillary water absorption properties of this material are well described as a parallel combination of fast absorption into fine matrix pores and slow absorption into a modified structure of matrix pores inter-connected to air voids introduced into the slurry by aeration.

NMR 1D-Imaging of Water Infiltration into Porous Bitumen-Salt Matrices: The Effect of Salt Solubility

“…In this case, one typically records the NMR signal on the proton ( 1 H) or possibly on the deuterium ( 2 H) if D 2 O is used as a solvent. Applications include building materials, − soil science, , drug delivery systems, , or the study of catalytic phenomena. , …”

NMR observation of water transfer between a cement paste and a porous medium

“…Alternatively in 1 H MRI (Magnetic Resonance Imaging of Hydrogen), a 3D magnetic field gradient induces a specific distribution of spin precession frequencies at different locations in the sample; this information can then be analysed to extract local characteristics of the liquid phase, as many common fluids contain hydrogen in their chemical composition. This makes it particularly useful for directly measuring the evolution of water distribution along specific directions during absorption in, or drying of, porous materials [15][16][17][18][19][20]. On the other hand 1 H NMR (Nuclear Magnetic Resonance) relaxometry provides the distribution of (NMR) relaxation times of hydrogen-bearing fluid molecules embedded in a sample volume that are known to depend on pore size, surface chemistry and saturation state.…”

Synthesis and Characterization of Novel Ion‐Conducting Membranes Based on Poly(ether sulfone) and Protic Ionic Liquid

“…Time‐domain nuclear magnetic resonance (TD‐NMR) is an important technique in the evaluation of physical and chemical properties in a variety of porous materials, such as plaster slurry or cement and carbonate rocks . Recently, it is being employed in spin diffusion (self‐diffusion) and spin‐lattice relaxation by fast field cycling for viscosity and molecular dynamics in ionic liquids or yet in the observation of molecular arrangements and rotational correlation time calculations from longitudinal relaxation …”

“…For systems comprising 50 and 60 wt.% ionic liquid, this value was 400 µs, as the ionic liquid features a spin‐spin relaxation value much greater than the polymer matrix. The obtained signal decay was submitted to an Inverse Laplace Transform (ILT) via WinDXP ® software and only the even echoes were used for data processing . Samples were kept under the analysis temperature for 20 min, so that total thermal stabilization could be reached, before signal acquisition.…”