Volume Change Behaviors of Expansive Soils Stabilized with Recycled Ashes and Fibers

TLDR

The study evaluates class F fly ash, bottom ash, polypropylene fibers, and nylon fibers as potential stabilizers to improve the volume‑change behavior of sulfate‑rich expansive soils. The authors conducted a laboratory program on two Texas subgrade soils, testing four dosage levels of each stabilizer at two compaction moisture contents over a 14‑day cure, and measured free swell, shrinkage strain, and vertical swell pressure for isolated and combined ash‑fiber treatments, then discussed the mechanisms behind the observed improvements. Ash stabilizers reduced swelling, shrinkage, and plasticity by 20–80 %, while fibers produced variable improvements; the combination of class F fly ash and nylon fibers yielded the most effective results on Dallas and Arlington soils, achieving average‑to‑moderate property enhancements.

Abstract

In this paper, class F fly ash, bottom ash, polypropylene fibers, and nylon fibers were evaluated as potential stabilizers in enhancing volume change properties of sulfate rich expansive soils. As a part of the research evaluation, a comprehensive laboratory experimental program was designed and conducted on two different subgrade soils from two locations in Texas. Four dosage levels of each stabilizer, two compaction moisture content levels, and 14 days curing period were investigated. Volume change behavioral tests including volumetric free swell, volumetric shrinkage strain, and vertical swell pressure tests were conducted on both isolated stabilizer treated and combined ash-fiber stabilized soils. Ash stabilizers showed improvements in reducing swelling, shrinkage, and plasticity characteristics by 20–80% whereas fibers treatments resulted in varied improvements. In combined treatments, class F fly ash mixed with nylon fibers was the most effective treatment on both Dallas and Arlington soils, where the soil property enhancements were considered average-to-moderate. Possible mechanisms that resulted in the soil property improvements are discussed along with the recommended stabilizers and their dosages for expansive soil treatments.