Unlocking the potential of UK clays for the production of low-carbon cements

This study evaluated the potential of different UK clays to be activated with the purpose of using them as supplementary cementitious materials (SCMs). A comprehensive field survey was carried out by the British Geological Survey, collecting more than 41 different clay samples from different locations. The clay samples were subjected to laboratory-based characterization, analysing their chemical and mineralogical composition through X-ray fluorescence spectroscopy (XRFS), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The majority of clays contained <40 wt.% kaolinite; the total clay content ranged widely from 10 – 82 wt.%, and carbonate minerals were frequently present, up to 20 wt.%. Clays were classified into four groups based on their mineralogical composition; from the two groups with mineralogical attributes deemed most suitable for calcination, 11 selected clays were then calcined at 800°C and their chemical reactivity was determined using the calorimetry method of the R3 test. Results revealed that after thermal activation, UK clays yielded R3 values ranging from 200 to 500 J/g SCM, classifying them as SCMs with moderate reactivity. Although clays with higher kaolinite content typically exhibited superior reactivity, the results indicated that additional factors, such as total clay content, need to be considered for predicting reactivity, particularly for mixed clays.