Water Retention Characteristics of Various Sizes of Expanded Perlite Produced from Two Different Types of Rocks

This study presents the results of the water retention characteristics of six groups (0.25 mm to 8.35 mm) of expanded perlite (EP) produced from two crushed raw perlite rocks of Turkey (A) and China (B). The particle size proportions of EPs showed that the particle size less than 1.68 mm was higher in B than that of A and the particle size distribution curves (PSDC) of three samples of EP A and B were similar, while the percent finer value (D_N) of B was higher than that of A in all corresponding particle sizes. Volumetric water content (θ_v) for EPs of A and B were obtained at 11 levels of matric potentials between 0 to −50 kPa (sandbox with kaolin-plate) and −50 to −1500 kPa (pressure chamber), respectively, after fully saturating the uniformly packed EP in open-ended metal round rings. The results showed that the shapes of measured WRCs and particle size distribution curves of EP A and B were similar, while the percent values of PSDC were higher than those values of θ_v corresponding to each water potential greater than 0.1 kPa. The WRCs of respective EP showed that a substantial decline started at about −1 kPa and approached the residual water content (θ_r) observed at −500 kPa for all measurements. θ_v for all particle sizes of the EP A and B was not only decreased with the increasing matric potential but also distinctive with increasing particle size greater than 2.36 mm. θ_r was increased with decreasing particle size. For these results, we assumed that θ_v of the different particle sizes of EP A and B could be determined by actual pore volume excluding occluded pore volume depending on size and surface area in the EP particles.