The efficient selection of clay deposits is critical for the widespread use of calcined clays as suitable supplementary cementitious material (SCM). The current initial assessment relies on chemical composition determined by X-ray fluorescence. However, the assumed direct correlation between elemental composition and mineral phase does not always hold true, especially for complex materials like clays. And, this approach often excludes promising non-kaolinite clays. Therefore, a simple minerology-based test is essential to improve the accuracy of initial screening for a large number of samples. This study proposes the use of the methylene blue (MB) test as a rapid and low-cost alternative for the initial assessment of clays. In this study, 38 natural samples were collected and characterised for chemical and mineralogical composition. The results demonstrate a good correlation between the MB test and X-ray diffraction analysis. The MB test effectively distinguishes clay from non-clay materials and also differentiates between clay mineral types. The simplicity, rapidity and low cost make this test a highly practical tool for preliminary screening of a large number of samples and enhances the efficiency of SCM selection.
Dhar et al. (2026) studied this question.