This paper provides an evaluation of the upfront carbon footprint of a concrete mix containing 30% calcined clay designed for construction of up to 100 m3 of concrete for an Australian-first use in low risk non-structural road assets in metropolitan Melbourne. Clay used for the trial was produced at full scale in Victoria, utilising a clay residue from sand washing operations in an aggregate quarry. The evaluation was conducted using precise energy, fuel and material consumption data. Gaps in data were estimated using Australian Environmental Product Declarations (EPDs), databases or relevant and appropriate literature sources. A sensitivity analysis was also conducted on the data obtained in this study, demonstrating that efficiency of the pre and post-processing of the clay, distance from the quarry or source material, refinement of the concrete mix and substitution of the gas used for calcination are crucial in reducing the embodied carbon of calcined clay.
A carbon saving of more than 3 tonnes of CO2 equivalent (CO2e) was demonstrated for the trialled concrete quantity of 100 m3, with the carbon footprint of the calcined clay found to be 455 kgCO2e/t, 86% of which is attributed to the calcination process. The 30% calcined clay cement substitution results in an embodied carbon (A1-A3) of 257 kgCO2e/m3 of concrete, representing an 11% reduction in CO2 compared to an equivalent 100% cement based concrete mix used for this trial using low carbon GP cement (758 kgCO2e/t), or a 25% reduction compared to 100% cement based concrete using typical Australian GP cement (918 kgCO2e/t).
This demonstrates that calcined clay is a feasible alternative to traditional SCMs in Victoria which may be used to achieve low carbon concrete mixes. This project was a conservative introduction of calcined clay concrete in Australia, providing a pathway to continue to develop this technology across Australia through improved processing and mix design, driving further reductions in embodied carbon emissions of concrete.