Hydration of a GCL with powdered bentonite

A series of laboratory experiments were conducted to study the isothermal and cyclic heating moisture uptake from silty sand subgrade soil by needle-punched and thermally-treated geosynthetic clay liners (GCLs) manufactured with powdered bentonite or fine-granular bentonite. The subgrade silty sand soil was compacted into PVC columns to dry density of 16.5 kN/m3 at water content (Wfdn) of 10, 16, or 21% and then covered by a GCL. The confining pressure on GCLs was 2 kPa. Test results indicated that under isothermal conditions, there was more rapid uptake of moisture and a higher steady-state GCL water content with increasing subgrade soil water content. The structure of the bentonite after 35 weeks of contact with soil examined looked well hydrated with no cracks over the range of Wfdn. Under similar conditions, GCLs with powered bentonite achieved a higher water content and degree of saturation than GCLs with fine-granular bentonite in the short-term. In the longer-term both GCLs can achieve a similar degree of saturation. However, under cyclic heating conditions, the GCL with powdered bentonite demonstrated greater moisture retention than the GCL with fine-granular bentonite for one case examined.