Using viscosity as an index for polymer loading of bentonite-polymer composite geosynthetic clay liners

Abstract

Bentonite-polymer composite (BPC) geosynthetic clay liners (GCLs) containing a mixture of air-dry granules of bentonite and polymer have been developed for containment of wastes that generate leachates that are too aggressive for conventional sodium bentonite GCLs. Sufficient polymer loading is essential for BPC GCLs to maintain low hydraulic conductivity, and expedient methods are needed for manufacturing quality control and construction quality control to confirm that BPC GCLs contain sufficient polymer. In this study, a methodology for developed to estimate the polymer loading based on viscosity testing of slurries prepared with the BPC. A simplified version of the method can be used to determine if polymer is present in a BPC. Factors influencing the viscosity measurement were evaluated systematically, including water-to-BPC ratio, tempering time, and mixing method. The method that was developed consists of (1) adding deionized water to dry BPCs to achieve a water-to-BPC ratio of 30, (2) blending the BPC-water mixture with an overhead stirrer at 5000 rpm for 30 min to create a homogeneous slurry, (3) tempering the slurry in a zip-top bag for 24 hr, and (4) measuring the viscosity of the slurry in a viscometer at 300 and 600 rpm. Linear relationships were developed between polymer loading and viscosity for two BPC GCLs. Independent validation confirmed that the polymer loading estimated with the method is ±0.25% of the actual polymer loading.