Strength and Shrink/Swell Behavior of Highly Plastic Clay Treated with Geopolymer

Abstract

This paper presents findings from an experimental study in which a novel, non-energy intensive, environmentally-friendly stabilizer known as geopolymer was used for stabilization of a highly plastic clay. Two forms of the stabilizer were synthesized, one using metakaolin (MK) and the other using fly ash (FA) as the alumino-silicate precursor. The paper describes the process of geopolymer synthesis as well as quality control tests conducted during geopolymer synthesis. Synthesized geopolymers were analyzed using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX). The paper also presents results obtained from a comprehensive laboratory test program that examined the effectiveness of the stabilizer in improving strength and controlling moisture induced swelling of a highly plastic clay soil. The geopolymer content of the soil ranged from 3% to 15% by weight ratio. SEM-EDX and XRD were performed to investigate the treated specimen for uniformity and stabilization mechanism. The data obtained from unconfined compressive strength tests conducted after seven days of curing showed three- to four-fold improvement in strength for geopolymer stabilized soils with MK geopolymer consistently providing better performance than FA geopolymer. The results from one-dimensional swell tests indicated significant reduction of swell behavior in FA geopolymer treated specimens while no improvement in swell behavior was observed in MK treated soil. This study demonstrates that, while geopolymers can overcome many limitations that exist in traditional stabilizers, the strength and swell performance of geopolymer stabilized clay soil can vary significantly depending on the source of alumino-silicate used in the production of the geopolymer.

The Role of Clay Swelling and Mineral Neoformation in the Stabilization of High Plasticity Soils Treated with the Fly Ash- and Metakaolin-Based Geopolymers

“…The study will further examine the possibility of the formation of newly formed minerals or cementitious phases that might put constraints on the total soil swelling. Finally, the mineralogical inquiry undertaken herein is expected to provide meaningful answers to the contrasting swelling test results provided by Khadka et al [20] where MKG-treated soils showed an aggressive swelling behavior compared to the moderate expansion shown by FAG-treated soils.…”

“…The dry soil sample was mixed with water to reach the optimum moisture content (OMC) of 30.8%. The OMC was determined in a series of geomechanical experiments performed on the same set of samples [20]. Then, the soil was sealed in a container for at least 16 h to equilibrate.…”

“…Each sample was confined from the side using a metallic ring to force the soil to absorb water from the bottom via the porous stone. Khadka et al [20] described in detail the soil preparation and methods used to perform mechanical swelling measurements and unconfined compressive tests. The results of the swelling test obtained from Khadka et al [20] for clay samples stabilized with different percentages of MKG and FAG along with an untreated soil sample are presented in Figure 1.…”

“…Khadka et al [20] described in detail the soil preparation and methods used to perform mechanical swelling measurements and unconfined compressive tests. The results of the swelling test obtained from Khadka et al [20] for clay samples stabilized with different percentages of MKG and FAG along with an untreated soil sample are presented in Figure 1. Swelling data provided in Figure 1 represent an average of two measurements performed on two replicates with the standard deviation values of 1.85 (untreated soil), 0.15 (6% MK-treated soil), 1.39 (9% MK-treated soil), 15.04 (12% MK-treated soil), 0.83 (6% FA-treated soil), 1.99 (9% FA-treated soil), and 0.91 (12% FA-treated soil) [20].…”

“…The soil expansion test results of untreated soil in comparison to the soils stabilized with different contents of the FAG and MKG stabilizer. Data after Khadka et al[20].…”