This contribution introduces thermogravimetric analysis (TGA) for quantifying clay composition and highlights research findings on clay pozzolanic reactivity. By coupling with mass spectroscopy (MS), the analysis of mixed clay minerals is performed, addressing TGA quantification challenges through deconvolution methodology and MS coupling. The results are compared with quantitative-XRD (QXRD) analysis. Future research should focus on enhancing validation methods for TGA-MS quantitative phase analysis. Additionally, this paper outlines key findings and methodologies, including experimental and mathematical modeling, for correlating clay composition, calcined clay reactivity, and hydrate phase evolution. Progressing from simplified clay-portlandite systems to blended cementitious systems, future research should explore stoichiometric and kinetic modeling across diverse compositions, including carbonates, and establish the relationship between hydrate phase evolution and rheological properties in blended cementitious systems.