Low-carbon cements: Potential for low-grade calcined clays to form supplementary cementitious materials

•Low-grade clays from geological formations with different mineralogy were calcined.•Mineralogical changes and amorphous content in calcined clays were measured.•Oxford and Ampthill clays produced superior pozzolanic activities at 850 °C.•Low-grade calcined clays are ideal for production of low-carbon cement. The use of low-carbon supplementary cementitious materials (SCM), such as calcined clays, to replace cement clinker has been recognized by the Cement Industry to achieve reductions in greenhouse gas emissions. This paper investigates eight low-grade clays, with