Effect of specimen preparation on the swell index of bentonite-polymer GCLs

Abstract

Experiments were conducted to investigate how specimen preparation (crushing and sieving) affects the swell index (SI) of bentonite-polymer (B–P) composites and the relationship between SI and hydraulic conductivity of B–P GCLs. Seven B–P and one Na–B GCLs were used in this study. Tests were conducted using DI water and synthetic municipal solid waste incineration ash leachates. Specimens were prepared using the ASTM D5890 and two alternative methods prior to SI testing. For both Na–B and B–P composites, <100% of the specimen passed through the #100 sieve regardless of the amount of crushing performed using a mortar and pestle. SIs and loss on ignitions (LOI) of the portion of the B–P composites passing #100 sieve were comparable to the Na–B, whereas the B–P specimen retained on #100 sieve had very high SIs and LOIs. These observations indicate that crushing and sieving of the B–P composites lead to segregation of polymer. A stronger correlation (R2 = 0.90) was observed between SI and hydraulic conductivity, only when SI tests were conducted with B–P without any crushing and sieving, suggesting that SI tests should conduct with B–P composites retrieved from the GCLs without sieving to provide a better prediction of hydraulic compatibility.