Stabilisation of high and low reactive clays utilising glass waste and polymer for application in road pavement subgrade
Creators: name: Perera, Salpadoru Tholkamudalige
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400502
subject: Civil geotechnical engineering
classificationCode: 400505
subject: Construction materials

description: Reactive clays, also known as expansive soils, are problematic clays that are commonly encountered across the globe and have the potential to undergo significant variations in volume as the amount of moisture present changes. These clays present an increase in their volume (swelling) following wetting, while presenting a decrease in volume (shrinkage) upon drying. In addition to this, reactive clays also have several other troublesome characteristics, including desiccation cracks, inferior strength and high compressibility. Such clays have long been identified to cause significant damage to residential dwellings and transport infrastructure. It is estimated that the cost incurred due to the damage caused to structures amounts in excess of 15 billion annually in China as well as the US. Thus, it is vital that necessary steps are taken to mitigate the adverse impacts of reactive clays prior to any construction taking place on or within them.

The accumulation of non-biodegradable waste in landfill sites has been identified as another major issue throughout the world, posing hazardous conditions to natural flora &amp; fauna in addition to consuming vast amounts of land. In excess of 130 million tonnes of glass waste is generated around the world, and only a meagre 21% of this glass waste is recycled while the majority of it is dumped into landfill sites. The main factor standing against achieving high recycling rates is the breakage of glass during its collection and transportation to the recycling facility, making it a near-impossible task to sort the broken glass into the respective colours for recycling. Although the aforementioned breaking of glass limits the degree of glass recycling via traditional means (remelting), this has little impact on the use of glass waste in engineering applications, including its use as a supplementary pavement aggregate. In the past, waste glass has been utilised in contrasting civil engineering tasks, including asphalt mixes, as a supplementary material in road aggregates and replacement of sand in concrete.
Furthermore, the past decades have led to remarkable advancement of polymers, resulting in an increased interest in their use as a sustainable, environmentally friendly and effective alternative to traditional construction materials. Thus, polymers are now available in various forms and contain many different additives that induce unique properties, leading to a more diversified range of applications. Among the many game-changing polymers developed in the recent past, is a polymer group referred to as vinyl acetate-ethylene (VAE) polymers. VAE polymers have incorporated ethylene as an additive in the polymer development, inducing deformability of a specimen prior to failure as well as bringing about hydrophobic properties. These polymers have the potential to stabilise the swelling-shrinkage behaviour of reactive clay, by providing a continuous hydrophobic film around the clay particles, thereby reducing its interaction with moisture. A reduction in the interaction with water has a direct effect on reducing the swelling-shrinkage potential. Furthermore, the relative deformability offered by VAE polymers leads to improved shock absorption, which is especially important when considering the impulse loading imposed by vehicular traffic on a given point in a road.
The initial phase of the research project involved evaluating basic geotechnical properties of the two clays: one highly reactive clay and the other a low/slightly reactive clay. Next, the same properties of crushed waste glass were assessed for purposes of providing classifications as well as obtaining an understanding of the material’s physical attributes. The second stage of the research gauged the effect of the glass content on the geotechnical parameters of the low and highly reactive clay by conducting standard compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), resilient modulus test and swelling-shrinkage tests. This stage was performed by introducing different glass contents of 0, 5, 10, 15 and 20% into the two clay types. From the results of these tests, an optimum glass content that best enhanced the geotechnical performance was determined for each clay. The third (penultimate) stage of the research included evaluating the impact of polymer content for each clay, where polymer contents of 1, 1.5 and 2 % were introduced to both the low and high reactive clay. These mixtures were then subjected to standard compaction, UCS, CBR, resilient modulus and swell-shrink testing to obtain critical geotechnical parameters. The optimum glass contents for each clay, together with varied polymer contents of 1, 1.5 and 2%, were then considered for the fourth (final) stage of the research in order to assess the impact that the polymer content along with the respective optimum glass content have on the two different clay types. 

With respect to the results contained within the thesis, it was deemed that the introduction of glass into the clay improved the mechanical strength. The comparison of results obtained through the experimental testing conducted in the second stage of the research led to the determination of the optimum glass content for each type of clay. Thus, the optimum glass contents which best improved the overall strength of the samples were determined to be 10 and 15% for the highly reactive clay and slightly reactive clay, respectively. The optimum polymer content to be utilised for clay (no glass) was decided following the testing scheme from the third stage, where polymer contents of 2 and 1% were decided as the optimum amounts for the high and low reactive clays, orderly. According to the results from the final stage, it is evident that an optimum inclusion of 1.5% polymer yields the best strength results for both the highly reactive clay containing an optimum inclusion of 10% glass as well as the low reactive clay with an optimum glass content of 15%.

This research focused on the stabilisation of reactive clays employing waste glass and VAE polymer, where the findings led to several benefits. These include reducing the impact of the undesirable swelling-shrinkage behaviour of the reactive clays, providing a solution to the accumulation of waste glass in landfills and allowing for a more sustainable approach to achieving chemical stabilisation of reactive clays while deviating from traditional soil stabilisers that form large amounts of greenhouse gases during their manufacture.