Evaluation of characterization techniques for selecting kaolinitic clays as supplementary cementitious materials: An interlaboratory study

Calcined clays are a crucial asset to decarbonize the cement industry. Still, the natural variation of the composition of the clays means that each clay needs to be assessed for its suitability to be activated and used as a supplementary cementitious material (SCM). This paper analyzes a potential minimum characterization workflow to screen clays based on mineralogical and physical properties so as to predict their potential performance after activation in cements. We investigate and discuss various characterization techniques (x-ray fluorescence, thermogravimetric analysis, x-ray diffraction, and infrared spectroscopy) to assess the physical, chemical, and mineralogical properties of nine raw clay samples of industrial interest at four different laboratories. The results show that although XRF and TGA are important to obtain a first assessment of the clays, a mineralogy study is necessary to assess the order of crystallinity of the clays, the presence of 2:1 clay minerals, and other minerals that impact both the activation process and the performance of the activated clay as an SCM.