Rapid assessment of calcined clay reactivity for strength prediction in LC3 systems

Understanding the reactivity of calcined clays is critical for their application as supplementary cementitious materials (SCMs) in low-carbon cements. Despite recent advancements in reactivity testing, existing methods are constrained by long evaluation times, limiting their industrial use. This study develops an integrated test framework that combines complementary reactivity tests to predict the 28-day compressive strength of cementitious composites produced with limestone calcined-clay cement (LC3). To quantify these reactivity contributions, the intrinsic dissolution potential of the calcined clays was assessed using the UR2 test, which quantifies dissolved Al and Si concentrations in 5-15 minutes. Aluminate-sulfate interactions were evaluated in a clinker-free model system by determining sulfate depletion time from isothermal calorimetry, and early pozzolanic reactivity was measured using the 24-hour cumulative heat release from the R3 test. These methods were applied to four natural clays calcined at 600 and 800 °C. For the studied clays, all results were obtained within a 24-hour experimental period and incorporated into a multi-variable regression model fit for 28-day strength prediction. Altogether, the proposed integrated test framework enables rapid assessment of calcined clay reactivity and prediction of 28-day strength from data obtained within 24 hours, supporting faster material screening and quality control in industrial settings.