From raw clay to ceramics: Evaluating the suitability of raw materials through compositional analysis

Raw clay has been an essential material for thousands of years, valued for its distinctive properties and versatility, particularly in ceramic production. Thus, this study seeks to systematically classify raw clays based on their suitability for manufacturing ceramic building materials. Key indicators such as 0.063 mm sieve residue and chemical composition were evaluated to enable a preliminary and rapid assessment. The 50 raw clays from Serbia were grouped using Principal Components Analysis (PCA) according to compositional similarities, and these classifications were subsequently compared against industrial samples. Further analysis through mineralogical composition and behavior during heating within these groups provided a comprehensive understanding of their physical behavior. The results demonstrate that PCA effectively distinguishes raw clays based on their chemical composition, paving the way for a reliable classification for ceramic production. This system enables manufacturers to optimize materials for diverse applications, including common bricks and blocks, roof tiles and clay ceilings, ceramic tiles, and refractory products. Key findings reveal that raw clays containing 15–20% Al₂O₃, 3–9% Fe₂O₃, and at least 2% fluxing oxides are well-suited for heavy clay products. For ceramic tile production, optimal clay batches should contain no more than 1.5% Fe₂O₃, 1.0% TiO₂, and less than 0.2% organic carbon. Meanwhile, refractory clays must exhibit a minimum of 15–20% and up to over 42% Al₂O₃, with constraints on SiO₂ (below 76%), Fe₂O₃ (3.7%), Na₂O and K₂O (3.7%), and CaO (1.0%) after firing. Through this classification framework, manufacturers can more effectively select and refine raw clays to meet the stringent demands of ceramic production, ensuring both efficiency and performance in industrial applications.