Stabilising expansive soils with an un-calcinated kaolinite-based alkali-activated binder: from discovery to optimisation

Abstract

Expansive soils present significant geotechnical challenges, contributing directly and indirectly to significant economic losses through foundation damage, pavement deterioration, infrastructure instability, and higher maintenance costs as increasing repairs and rectifications become unavoidable. Conventional treatment approaches, mostly mechanical stabilisation and the use of calcium-based binders such as lime and Portland cement (PC), provide solutions that are deficient to varying degrees in different ways. There are many options for mechanical stabilisation including soil replacement, mechanical compaction and surcharging. Soil replacement is subject to sourcing of suitable local materials and disposal of the replaced soil, an undertaking that can be prohibitively expensive. Mechanical compaction is ineffectual except to stabilise expansive soils of minor swelling potential, while surcharging is unsuitable for light- loaded structures. Calcium-based binders are associated with high and direct carbon emissions, elevated production temperatures, and high calcium composition at risk of causing secondary phase swelling.

In response to traditional methods and deficiencies in stabilising expansive soil, more recent studies have developed a series of alkali-activated or geopolymer binders synthesised from high-temperature-processed or calcinated industrial by-products, such as ground granulated blast furnace slag (GGBS), fly ash (FA), metakaolin (MK), and an alkali activator. The results demonstrated that the binders exhibited superior durability, mechanical strength, and excellent capacity to control swelling in soils. Although the utilisation of the industrial by-products demonstrated a sustainable approach by valorising what are waste materials, competitive demand by the concrete and cement industries could limit their large-scale availability for soil stabilisation.

This thesis attempts to pivot towards the strategic goal of developing low-carbon, low-temperature and low-calcium alkali-activated stabilisation methods of expansive soil. Within the broader strategic goal, it seeks to develop treatment methods where the precursors used to synthesise the alkali-activated binders are maximally derived from un- calcinated clay minerals of clay-rich soils, more specifically kaolinite, with curing performed at ambient temperature during treatment. In saying this, low-carbon, low- temperature and low-calcium does not mean no carbon, no high temperature processing and no calcium as this would be unrealistic to achieve in the real world. Thus, this thesis further explores the trade-offs to optimise the treatment to achieve the requisite capacity to control swelling, achieve mechanical strength and on-site workability within the ambit of the strategic goal.

Date of Thesis submission	2026
Original language	English
Awarding Institution	Western Sydney University
Sponsors	Australian Government Research Training Program Scholarship
Supervisor	Chin Leo (Supervisor), Samanthika Liyanapathirana (Supervisor), Qinghua Zeng (Supervisor) & Pan Hu (Supervisor)