Performance-normalized life cycle assessment of calcined and mechanochemically activated clays in Australia as cement substitutes

Abstract

In response to the decreasing availability of high-grade kaolinitic clays, there is a growing shift toward using natural waste clays as supplementary cementitious materials. The performance of these waste clays is generally evaluated based on either strength or environmental impact, but the combination of both is rarely considered. This study undertakes a strength-normalized life cycle assessment to understand the interaction between these two parameters and utilizes the output to identify the most suitable activation process. The study used five Australian natural waste clays activated by calcination (600–900 °C) and high-shear mechanical grinding, replacing 30% of the general-purpose cement by mass with the activated clay. The environmental impacts were normalized to MPa using the Australian life cycle impact assessment framework. Results revealed that calcined binders achieved up to 18.6% lower global warming potential than general-purpose cement. However, burden shifting can be observed, with mechanochemically activated clays exhibiting up to 255% higher abiotic depletion potential, primarily due to increased electricity consumption and the use of steel grinding media. Sensitivity analysis showed that reducing transport distance by 100 km decreased resource depletion by 3.0%, human health impacts by 0.7%, and ecosystem damage by 0.5%. Using projected renewable energy sources and alternative fuel sources for activation reduced environmental impacts by up to 18%. These results underscore that the suitability of activated natural waste clays depends not only on the percentage of cement replacement but also on clay type, activation method, energy source, and transport logistics.