Engineering Geopolymer Soil Material Using Fine Dredged Material (FDM) and Alkali-Activated Fly Ash Cement (AAFA)

Abstract

Hydraulic conductivity is a vital input parameter when designing foundations, embankments, retaining walls, or roadways. Much research has been done on methods of improving hydraulic conductivity through soil improvement techniques available today. This work investigates an engineered solution to the waste materials piling up in a disposal facility in northern Minnesota. A sample of fine dredged material (FDM) from the Erie Pier facility in Duluth, MN, was classified as sand lean clay (CL) with a hydraulic conductivity of 6.06 x 10-6 cm/s. To increase the hydraulic conductivity, Class C fly ash, an industrial by-product from the local power plant in Duluth, MN, was activated with a combination of alkaline activator solutions, sodium hydroxide (NaOH) and sodium silicate (Na2SiO3), to generate alkali-activated fly ash cement (AAFA). The AAFA cement caused FDM soil particles to flocculate, which led to an increase in particle diameters. This new product, engineered geopolymer soil (EGS), was classified as poorly graded sand (SP) with a hydraulic conductivity at least two orders of magnitude higher than that of the original FDM. This technique improved the hydraulic conductivity of fine-dredged material and could contribute to the efforts of increasing reuse of waste by-products for engineered fill applications.