The significance of the contact angle in characterising the pore size distribution of geotextiles

Abstract

The current test method for quantifying geotextile pore structure for filtration design is the AOS test ( ASTM D 4751 ). The AOS test quantifies structure using a single value, the O95 or 95% opening size. The bubblepoint test (ASTM D 6767) is a method for calculating the pore size distribution (PSD) of a geotextile. Information on a number of pore sizes more completely describes a geotextile, and may allow for better filtration design criteria. An important step of the bubblepoint test involves saturating a geotextile sample with a wetting fluid and then expelling the fluid using controlled airflow. The data reduction of ASTM D 6767 supposedly accounts for the effect of the wetting fluid, and several different wetting fluids are allowed. Accurate knowledge of the contact angle between the wetting fluid and the geotextile is essential to computing accurate pore size distributions. Even with accurate contact angle measurement, the use of different wetting fluids yields different pore size distributions. This suggests a need to re-examine the data reduction of ASTM D 6767.