It is estimated that nearly 50 billion tonnes of sand are mined globally every year, equivalent to almost 18 kg per person per day. Such widespread use of sand has made it the second-most consumed natural resource on the planet, after freshwater. As a result, our planet is rapidly running out of sand and the emerging paradigm shift taking place is to replace sand with sustainable and alternative cost-effective geo-materials. Waste glass recycling to replace natural and quarried sand has therefore been trialled in recent years as a potential solution to the sand depletion problem in many engineering applications. This includes, for example, concrete production, road pavement construction (including asphalt), tile and brick manufacturing, water filtration, and sandblasting. The promising results obtained in the above applications strongly suggest that waste glass re-use can complement environmental sustainability and closed-loop recycling by decreasing the pressure on landfills, reducing the carbon footprint, and conserving natural and quarried sand.
Glass waste (also known as cullet) is theoretically 100% re-useable it does not degrade and can be recycled over and over again without any reduction in quality, it is predominantly composed of silica (SiO2), a key mineral found in natural sand, and it shares similar chemical composition to natural sand. However, it also has different thermal conductivity, abrasivity, permeability, and hydro-mechanical parameters to that of sand, and rock. Hence, it is expected that if used in asphalt production, its different mechanical parameters (particularly its higher thermal conductivity) could affect the cracking/fracturing behaviour, modulus, deformation resistance, fatigue, and ultimate fracture strength in asphalt pavements. This study aims to develop an experimentally and numerically validated understanding of the key processes controlling the thermo-mechanical coupling behaviour of crushed waste glass used in asphalt, from macro to granular scale.
The proposed project consists of the following overlapping stages:
- Mineralogical and image-based shape analyses, X-ray fluorescence spectroscopy, optical microscopy, and geotechnical testing (including sieve analysis, specific gravity, minimum & maximum dry density, permeability, abrasion loss, and direct shear strength testing) of natural aggregates commonly used in asphalt pavements as well as glass waste products available in the Australian and Indian markets;
- Experimental (physical modelling) of asphalt mixes with waste glass aggregates under similar thermo-mechanical coupling conditions (in 3D stress space) in practice using the world-class true triaxial testing facility at UQ Civil;
- Developing a broad understanding of the incidence, controls, and significance of thermo-mechanical coupling responses of asphalt mixes with crushed waste glass relating to its particle descriptors (i.e., sphericity, roundness, roughness, and grain interlocking), purity, size ranges, and gradations combined; and
- Publishing of the ideas and outcomes of the project in high-impact journals and conferences.