Geopolymer is one of the innovative binders used over traditional binders such as cement and lime in order to stabilise soil by improving the strength and durability of soils. This research will utilise geopolymer consisting of fly-ash and slag in order to evaluate its impact on stabilising different clays for deep soil mixing (DSM) application. This research evaluates the stress-strain behaviour of clays treated with varying geopolymer contents (10%, 20%, 30%) for DSM application. This paper looks to establish a relationship between the soil plasticity and mechanical strength (i.e., stress-strain behaviour) of soil. Three soils: kaolin clay, bentonite clay and pure sand were utilised to produce a spectrum of soil types with varying soil plasticity from 0% to 100%. Due to the lack of literature present on the investigation of different clays for geopolymer treatment it was necessary to understand the impact of soil type on the geo-mechanical behaviour. The geo-mechanical properties such as the stress-strain behaviour, peak stress and stiffness behaviour was obtained through conducting unconfined compression strength (UCS) tests. The soil alkalinity post geopolymer treatment was assessed and compared to understand the impact of soil type with cure time using pH testing. Microstructural analysis using scanning electron microscopy (SEM) test was performed to understand and compare the bonding of the soil-geopolymer matrix for varying soil types. Collectively the pH testing and SEM analysis explained the enhanced soil strength due to the formation of cementitious products due to geopolymer addition. Overall, this research recommends geopolymer treatment for plasticity index less than 30% in order to satisfy the minimum design requirement of 1MPa for deep mixing applications. As an outcome of this study a graph/ equation has been produced to determine the minimum geopolymer quantity required to achieve a design UCS at 28 days for a given soil plasticity. This is a predicted amount that can be utilised during the initial laboratory testing stage to avoid a trial-and-error approach which allows engineers to figure out the geopolymer quantity to use on field to treat in-situ soils.

Bio-cementation is a process of strengthening soil by treating the soil with a cementation solution (consisting of usually urea and calcium chloride) in the presence of a urease enzyme catalyst to produce calcium carbonate crystals that bond the soil particles. Bio-blocks produced using bio-cementation have been researched over the last decade to reduce the large carbon footprint resulting from the production of conventional bricks and blocks. Enzyme Induced Calcite Precipitation is a type of bio-cementation technique with limited research in the preparation of bio bricks and blocks. This research investigates whether EICP using soybean sourced urease enzyme can be used to produce bio-blocks that satisfy the unconfined compressive strength and salt attack resistance requirements set out in the standard AS/NZS 4455.3 – Segmental Retaining Wall Units. This paper reports the results obtained from different methods of EICP treatment (submergence, percolation, and mix and compact with xanthan gum bio-polymer) in the preparation of bio-blocks. The research also includes the properties of bio-blocks prepared using Enzyme Induced Magnesium Carbonate Precipitation (EIMP), which is similar to EICP except the substitution of Calcium Chloride with Magnesium Oxide in the cementation solution. The highest mean UCS was displayed by the bio-block prepared through EICP and xanthan gum bio polymer (4.314 MPa), followed by the bio-block prepared using EIMP (4.055 MPa). EICP with 4 cycles of percolation displayed a very low UCS of 547 kPa in comparison. Although the bio-block prepared using EICP and biopolymer showed the highest strength, it displayed very low durability when in contact with water. While the mean UCS of the prepared bio-blocks did not meet the AS 4455.3 strength threshold of 5 MPa, the obtained values are very close to meeting the requirements. Considering the promising results obtained from this research, further optimisation of the Magnesium Oxide in the EIMP technique may result in a stronger bio-block that meets the AS 4455.3 requirements.

Our ecosystem is degrading at an alarming rate with rapidly growing carbon emission levels and limited natural resources to serve the human needs of our population. Spent coffee ground (SCG) is one of many food wastes that commonly end up in landfill releasing methane and carbon dioxide but has massively underestimated value as a carbon sequestration material. This study proposes a review of the physical and chemical properties of SCG biochar produced under different pyrolysis temperatures and residence time, as well as the feasibility of SCG derived biochar as a sustainable material in products such as pavement and concrete. Pyrolysis of SCG samples were carried out at 300°C, 400°C, and 500°C at various residence time to obtain nine SCG biochar samples. Particle size distribution, Scanning Electron Microscope (SEM) imaging, and elemental analysis using Energy Dispersive Spectroscopy (EDS) were undertaken to investigate the carbon content, microstructure, particle sizes, and biochar yield of each SCG biochar samples. The results showed that even though solid yield at the highest temperature of 500°C is the lowest, the carbon content and porosity of the biochar are much higher than biochar produced at lower temperatures. In addition, there were no major distinctions in the properties between the biochar samples produced at the same temperature at different residence times. Therefore, SCG biochar produced at 500°C at the lowest residence time of 10 minutes demonstrated the highest carbon sequestration potential and is recommended for further investigation into its potential engineering application.

Our ecosystem is degrading at an alarming rate with rapidly growing carbon emission levels and limited natural resources to serve the human needs of our population. Spent coffee ground (SCG) is one of many food wastes that commonly end up in landfill releasing methane and carbon dioxide but has massively underestimated value as a carbon sequestration material. This study proposes a review of the physical and chemical properties of SCG biochar produced under different pyrolysis temperatures and residence time, as well as the feasibility of SCG derived biochar as a sustainable material in products such as pavement and concrete. Pyrolysis of SCG samples were carried out at 300°C, 400°C, and 500°C at various residence time to obtain nine SCG biochar samples. Particle size distribution, Scanning Electron Microscope (SEM) imaging, and elemental analysis using Energy Dispersive Spectroscopy (EDS) were undertaken to investigate the carbon content, microstructure, particle sizes, and biochar yield of each SCG biochar samples. The results showed that even though solid yield at the highest temperature of 500°C is the lowest, the carbon content and porosity of the biochar are much higher than biochar produced at lower temperatures. In addition, there were no major distinctions in the properties between the biochar samples produced at the same temperature at different residence times. Therefore, SCG biochar produced at 500°C at the lowest residence time of 10 minutes demonstrated the highest carbon sequestration potential and is recommended for further investigation into its potential engineering application.