UR2: Ultra-rapid reactivity test for real-time, low-cost quality control of calcined clays

Abstract

To reduce cement's carbon footprint, there is growing interest in commercial adoption of sustainable SCMs such as calcined clays. However, the existing ASTM standard (R3 test, C1897) to test the reactivity of such clays takes up to 7 days and cannot be used for real-time quality control in an industrial setting. We address this issue by introducing a 5-min Ultra-Rapid Reactivity (UR2) test. By dissolving 47 clay specimens in 4 M NaOH solutions at 90 °C, we report that a dissolution index of 1.54Al + Si correlates strongly to the 7-day R3 heat (R2 = 0.92, RMSE = 94.1 J/g). This dissolution index also correlates to the 28-day compressive strength for 14 clay mixtures (R2 = 0.94, RMSE = 1.7 MPa). This UR2 test relies on colorimetry and can be conducted via off-the-shelf, low-cost cameras. Overall, our new UR2 test opens a pathway for real-time, low-cost quality control of calcined clays.