Effect of hydrogel particle additives on water-accessible pore structure of sandy soils: A custom pressure plate apparatus and capillary bundle model

摘要

To probe the effects of hydrogel particle additives on the water-accessible pore structure of sandy soils, wenintroduce a custom pressure plate method in which the volume of water expelled from a wet granular packing isnmeasured as a function of applied pressure. Using a capillary bundle model, we show that the differential changenin retained water per pressure increment is directly related to the cumulative cross-sectional area distribution f (r)nof the water-accessible pores with radii less than r. This is validated by measurements of water expelled fromna model sandy soil composed of 2-mm-diameter glass beads. In particular, it is found that the expelled waternis dramatically dependent on sample height and that analysis using the capillary bundle model gives the samenpore size distribution for all samples. The distribution is found to be approximately log normal, and the totalncross-sectional area fraction of the accessible pore space is found to be f0 = 0.34.We then report on how the porendistribution and total water-accessible area fraction are affected by superabsorbent hydrogel particle additives,nuniformly mixed into a fixed-height sample at varying concentrations. Under both fixed volume and free swellingnconditions, the total area fraction of water-accessible pore space in a packing decreases exponentially as thengel concentration increases. The size distribution of the pores is significantly modified by the swollen hydrogelnparticles, such that large pores are clogged while small pores are formed.