Subgrade Strength Performance Behavior of Alkali-Activated Binder and Cement Stabilized Expansive Soil: A Semifield Study

Abstract

Expansive subgrade soil possesses a dual nature of swelling and shrinkage, resulting in a premature failure on pavement surfaces. In the present investigation, an effort has been made to compare the field performance of expansive subgrade soil stabilized with cement and an alkali-activated binder (AAB). A 12-m-long semifield test section with cement, AAB treated, and untreated expansive soil as a subgrade was constructed to evaluate the strength properties. The AAB was produced by combining dry pozzolanic precursors (steel slag and fly ash) with an activator solution (sodium silicate and sodium hydroxide) in a 0.4 w/s ratio. The in situ subgrade strength behavior was evaluated by embedding a series of stress meters and strain gauges in the subgrade layer and applying a load through a dual wheel truck load (12-t rear axle load) on the test section. The influences of AAB, curing time, and steel slag/fly ash proportion in alkaline soil mixture on microstructural and geomechanical properties of soil were analyzed on samples collected from the field section. It is observed that the AAB treated subgrade layers achieved higher geomechanical strength than cement treated and untreated layers. The combined inclusion of slag-fly ash in the AAB mixture increases the subgrade strength by 23%–26% compared to cement treated soil. The recommendations for practical implementation of AAB stabilization for expansive soils as a subgrade are provided based on the semifield test section studies.