Clay activation through CO2-derived oxalic acid for advancing its reactivity and strength of limestone calcined clay cement (LC3)

The widespread deployment of limestone calcined clay cement (LC 3 ) is constrained by its dependence on high-grade kaolinitic clays. Abundant, low-grade clays often exhibit poor pozzolanic reactivity and require tailored activation strategies. This study proposes a novel clay activation approach using oxalic acid, an organic acid producible through electrochemical CO 2 reduction utilizing a waste carbon stream, for the development of LC 3 . Three activation regimes were examined: thermal activation (TH), thermal followed by oxalic acid immersion (TI), and co-calcination with oxalic acid (CT). Comprehensive characterization (XRF, QXRD, R 3 ) reveals that the CT method uniquely enhances reactivity by promoting selective leaching of Fe 2 O 3 and enriching Al 2 O 3 content, while also inducing mineralogical transitions from quartz to more reactive phases like cristobalite. The R 3 test confirmed CT’s superiority, showing the highest bound water content (14.4 %) and showed a significant correlation with strength at all ages (correlation co-efficient ranging from 0.89 to 0.94). In LC 3 binders, CT-activated clay yielded a more balanced hydration phase assemblage, accelerating early-age hydration. This translated directly to superior mechanical performance; LC 3 -CT blends nearly met the ASTM strength criterion (i.e., 42.5 MPa) benchmark at 28 days (within 1 % deviation), significantly outperforming LC 3 -TH blends (10 % deficit). Despite the added acid, the LC 3 -CT system maintains a compelling environmental advantage, achieving 21–23 % reductions in CO 2 emissions compared to OPC, alongside cost savings of 8–11 %. Results establish CT activation as a technically superior and environmentally sustainable pathway for valorizing low-grade clays. By simultaneously enhancing reactivity and leveraging CO 2 utilization, this approach strengthens the foundation for next-generation, low-carbon cement technologies.